| Author | Tokens | Token Proportion | Commits | Commit Proportion |
|---|---|---|---|---|
| Paolo Valente | 11343 | 71.73% | 45 | 59.21% |
| Arianna Avanzini | 3918 | 24.78% | 4 | 5.26% |
| Jens Axboe | 289 | 1.83% | 5 | 6.58% |
| Bart Van Assche | 59 | 0.37% | 4 | 5.26% |
| Christoph Hellwig | 50 | 0.32% | 3 | 3.95% |
| Federico Motta | 43 | 0.27% | 1 | 1.32% |
| Luca Miccio | 41 | 0.26% | 2 | 2.63% |
| weiping zhang | 14 | 0.09% | 2 | 2.63% |
| Davide Sapienza | 13 | 0.08% | 2 | 2.63% |
| Angelo Ruocco | 13 | 0.08% | 2 | 2.63% |
| Hou Tao | 12 | 0.08% | 1 | 1.32% |
| Colin Ian King | 7 | 0.04% | 1 | 1.32% |
| Ben Hutchings | 5 | 0.03% | 1 | 1.32% |
| Omar Sandoval | 4 | 0.03% | 1 | 1.32% |
| Dennis Zhou | 1 | 0.01% | 1 | 1.32% |
| Filippo Muzzini | 1 | 0.01% | 1 | 1.32% |
| Total | 15813 | 76 |
/* * Budget Fair Queueing (BFQ) I/O scheduler. * * Based on ideas and code from CFQ: * Copyright (C) 2003 Jens Axboe <axboe@kernel.dk> * * Copyright (C) 2008 Fabio Checconi <fabio@gandalf.sssup.it> * Paolo Valente <paolo.valente@unimore.it> * * Copyright (C) 2010 Paolo Valente <paolo.valente@unimore.it> * Arianna Avanzini <avanzini@google.com> * * Copyright (C) 2017 Paolo Valente <paolo.valente@linaro.org> * * This program is free software; you can redistribute it and/or * modify it under the terms of the GNU General Public License as * published by the Free Software Foundation; either version 2 of the * License, or (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU * General Public License for more details. * * BFQ is a proportional-share I/O scheduler, with some extra * low-latency capabilities. BFQ also supports full hierarchical * scheduling through cgroups. Next paragraphs provide an introduction * on BFQ inner workings. Details on BFQ benefits, usage and * limitations can be found in Documentation/block/bfq-iosched.txt. * * BFQ is a proportional-share storage-I/O scheduling algorithm based * on the slice-by-slice service scheme of CFQ. But BFQ assigns * budgets, measured in number of sectors, to processes instead of * time slices. The device is not granted to the in-service process * for a given time slice, but until it has exhausted its assigned * budget. This change from the time to the service domain enables BFQ * to distribute the device throughput among processes as desired, * without any distortion due to throughput fluctuations, or to device * internal queueing. BFQ uses an ad hoc internal scheduler, called * B-WF2Q+, to schedule processes according to their budgets. More * precisely, BFQ schedules queues associated with processes. Each * process/queue is assigned a user-configurable weight, and B-WF2Q+ * guarantees that each queue receives a fraction of the throughput * proportional to its weight. Thanks to the accurate policy of * B-WF2Q+, BFQ can afford to assign high budgets to I/O-bound * processes issuing sequential requests (to boost the throughput), * and yet guarantee a low latency to interactive and soft real-time * applications. * * In particular, to provide these low-latency guarantees, BFQ * explicitly privileges the I/O of two classes of time-sensitive * applications: interactive and soft real-time. In more detail, BFQ * behaves this way if the low_latency parameter is set (default * configuration). This feature enables BFQ to provide applications in * these classes with a very low latency. * * To implement this feature, BFQ constantly tries to detect whether * the I/O requests in a bfq_queue come from an interactive or a soft * real-time application. For brevity, in these cases, the queue is * said to be interactive or soft real-time. In both cases, BFQ * privileges the service of the queue, over that of non-interactive * and non-soft-real-time queues. This privileging is performed, * mainly, by raising the weight of the queue. So, for brevity, we * call just weight-raising periods the time periods during which a * queue is privileged, because deemed interactive or soft real-time. * * The detection of soft real-time queues/applications is described in * detail in the comments on the function * bfq_bfqq_softrt_next_start. On the other hand, the detection of an * interactive queue works as follows: a queue is deemed interactive * if it is constantly non empty only for a limited time interval, * after which it does become empty. The queue may be deemed * interactive again (for a limited time), if it restarts being * constantly non empty, provided that this happens only after the * queue has remained empty for a given minimum idle time. * * By default, BFQ computes automatically the above maximum time * interval, i.e., the time interval after which a constantly * non-empty queue stops being deemed interactive. Since a queue is * weight-raised while it is deemed interactive, this maximum time * interval happens to coincide with the (maximum) duration of the * weight-raising for interactive queues. * * Finally, BFQ also features additional heuristics for * preserving both a low latency and a high throughput on NCQ-capable, * rotational or flash-based devices, and to get the job done quickly * for applications consisting in many I/O-bound processes. * * NOTE: if the main or only goal, with a given device, is to achieve * the maximum-possible throughput at all times, then do switch off * all low-latency heuristics for that device, by setting low_latency * to 0. * * BFQ is described in [1], where also a reference to the initial, * more theoretical paper on BFQ can be found. The interested reader * can find in the latter paper full details on the main algorithm, as * well as formulas of the guarantees and formal proofs of all the * properties. With respect to the version of BFQ presented in these * papers, this implementation adds a few more heuristics, such as the * ones that guarantee a low latency to interactive and soft real-time * applications, and a hierarchical extension based on H-WF2Q+. * * B-WF2Q+ is based on WF2Q+, which is described in [2], together with * H-WF2Q+, while the augmented tree used here to implement B-WF2Q+ * with O(log N) complexity derives from the one introduced with EEVDF * in [3]. * * [1] P. Valente, A. Avanzini, "Evolution of the BFQ Storage I/O * Scheduler", Proceedings of the First Workshop on Mobile System * Technologies (MST-2015), May 2015. * http://algogroup.unimore.it/people/paolo/disk_sched/mst-2015.pdf * * [2] Jon C.R. Bennett and H. Zhang, "Hierarchical Packet Fair Queueing * Algorithms", IEEE/ACM Transactions on Networking, 5(5):675-689, * Oct 1997. * * http://www.cs.cmu.edu/~hzhang/papers/TON-97-Oct.ps.gz * * [3] I. Stoica and H. Abdel-Wahab, "Earliest Eligible Virtual Deadline * First: A Flexible and Accurate Mechanism for Proportional Share * Resource Allocation", technical report. * * http://www.cs.berkeley.edu/~istoica/papers/eevdf-tr-95.pdf */ #include <linux/module.h> #include <linux/slab.h> #include <linux/blkdev.h> #include <linux/cgroup.h> #include <linux/elevator.h> #include <linux/ktime.h> #include <linux/rbtree.h> #include <linux/ioprio.h> #include <linux/sbitmap.h> #include <linux/delay.h> #include "blk.h" #include "blk-mq.h" #include "blk-mq-tag.h" #include "blk-mq-sched.h" #include "bfq-iosched.h" #include "blk-wbt.h" #define BFQ_BFQQ_FNS(name) \ void bfq_mark_bfqq_##name(struct bfq_queue *bfqq) \ { \ __set_bit(BFQQF_##name, &(bfqq)->flags); \ } \ void bfq_clear_bfqq_##name(struct bfq_queue *bfqq) \ { \ __clear_bit(BFQQF_##name, &(bfqq)->flags); \ } \ int bfq_bfqq_##name(const struct bfq_queue *bfqq) \ { \ return test_bit(BFQQF_##name, &(bfqq)->flags); \ } BFQ_BFQQ_FNS(just_created); BFQ_BFQQ_FNS(busy); BFQ_BFQQ_FNS(wait_request); BFQ_BFQQ_FNS(non_blocking_wait_rq); BFQ_BFQQ_FNS(fifo_expire); BFQ_BFQQ_FNS(has_short_ttime); BFQ_BFQQ_FNS(sync); BFQ_BFQQ_FNS(IO_bound); BFQ_BFQQ_FNS(in_large_burst); BFQ_BFQQ_FNS(coop); BFQ_BFQQ_FNS(split_coop); BFQ_BFQQ_FNS(softrt_update); #undef BFQ_BFQQ_FNS \ /* Expiration time of sync (0) and async (1) requests, in ns. */ static const u64 bfq_fifo_expire[2] = { NSEC_PER_SEC / 4, NSEC_PER_SEC / 8 }; /* Maximum backwards seek (magic number lifted from CFQ), in KiB. */ static const int bfq_back_max = 16 * 1024; /* Penalty of a backwards seek, in number of sectors. */ static const int bfq_back_penalty = 2; /* Idling period duration, in ns. */ static u64 bfq_slice_idle = NSEC_PER_SEC / 125; /* Minimum number of assigned budgets for which stats are safe to compute. */ static const int bfq_stats_min_budgets = 194; /* Default maximum budget values, in sectors and number of requests. */ static const int bfq_default_max_budget = 16 * 1024; /* * When a sync request is dispatched, the queue that contains that * request, and all the ancestor entities of that queue, are charged * with the number of sectors of the request. In constrast, if the * request is async, then the queue and its ancestor entities are * charged with the number of sectors of the request, multiplied by * the factor below. This throttles the bandwidth for async I/O, * w.r.t. to sync I/O, and it is done to counter the tendency of async * writes to steal I/O throughput to reads. * * The current value of this parameter is the result of a tuning with * several hardware and software configurations. We tried to find the * lowest value for which writes do not cause noticeable problems to * reads. In fact, the lower this parameter, the stabler I/O control, * in the following respect. The lower this parameter is, the less * the bandwidth enjoyed by a group decreases * - when the group does writes, w.r.t. to when it does reads; * - when other groups do reads, w.r.t. to when they do writes. */ static const int bfq_async_charge_factor = 3; /* Default timeout values, in jiffies, approximating CFQ defaults. */ const int bfq_timeout = HZ / 8; /* * Time limit for merging (see comments in bfq_setup_cooperator). Set * to the slowest value that, in our tests, proved to be effective in * removing false positives, while not causing true positives to miss * queue merging. * * As can be deduced from the low time limit below, queue merging, if * successful, happens at the very beggining of the I/O of the involved * cooperating processes, as a consequence of the arrival of the very * first requests from each cooperator. After that, there is very * little chance to find cooperators. */ static const unsigned long bfq_merge_time_limit = HZ/10; static struct kmem_cache *bfq_pool; /* Below this threshold (in ns), we consider thinktime immediate. */ #define BFQ_MIN_TT (2 * NSEC_PER_MSEC) /* hw_tag detection: parallel requests threshold and min samples needed. */ #define BFQ_HW_QUEUE_THRESHOLD 4 #define BFQ_HW_QUEUE_SAMPLES 32 #define BFQQ_SEEK_THR (sector_t)(8 * 100) #define BFQQ_SECT_THR_NONROT (sector_t)(2 * 32) #define BFQQ_CLOSE_THR (sector_t)(8 * 1024) #define BFQQ_SEEKY(bfqq) (hweight32(bfqq->seek_history) > 19) /* Min number of samples required to perform peak-rate update */ #define BFQ_RATE_MIN_SAMPLES 32 /* Min observation time interval required to perform a peak-rate update (ns) */ #define BFQ_RATE_MIN_INTERVAL (300*NSEC_PER_MSEC) /* Target observation time interval for a peak-rate update (ns) */ #define BFQ_RATE_REF_INTERVAL NSEC_PER_SEC /* * Shift used for peak-rate fixed precision calculations. * With * - the current shift: 16 positions * - the current type used to store rate: u32 * - the current unit of measure for rate: [sectors/usec], or, more precisely, * [(sectors/usec) / 2^BFQ_RATE_SHIFT] to take into account the shift, * the range of rates that can be stored is * [1 / 2^BFQ_RATE_SHIFT, 2^(32 - BFQ_RATE_SHIFT)] sectors/usec = * [1 / 2^16, 2^16] sectors/usec = [15e-6, 65536] sectors/usec = * [15, 65G] sectors/sec * Which, assuming a sector size of 512B, corresponds to a range of * [7.5K, 33T] B/sec */ #define BFQ_RATE_SHIFT 16 /* * When configured for computing the duration of the weight-raising * for interactive queues automatically (see the comments at the * beginning of this file), BFQ does it using the following formula: * duration = (ref_rate / r) * ref_wr_duration, * where r is the peak rate of the device, and ref_rate and * ref_wr_duration are two reference parameters. In particular, * ref_rate is the peak rate of the reference storage device (see * below), and ref_wr_duration is about the maximum time needed, with * BFQ and while reading two files in parallel, to load typical large * applications on the reference device (see the comments on * max_service_from_wr below, for more details on how ref_wr_duration * is obtained). In practice, the slower/faster the device at hand * is, the more/less it takes to load applications with respect to the * reference device. Accordingly, the longer/shorter BFQ grants * weight raising to interactive applications. * * BFQ uses two different reference pairs (ref_rate, ref_wr_duration), * depending on whether the device is rotational or non-rotational. * * In the following definitions, ref_rate[0] and ref_wr_duration[0] * are the reference values for a rotational device, whereas * ref_rate[1] and ref_wr_duration[1] are the reference values for a * non-rotational device. The reference rates are not the actual peak * rates of the devices used as a reference, but slightly lower * values. The reason for using slightly lower values is that the * peak-rate estimator tends to yield slightly lower values than the * actual peak rate (it can yield the actual peak rate only if there * is only one process doing I/O, and the process does sequential * I/O). * * The reference peak rates are measured in sectors/usec, left-shifted * by BFQ_RATE_SHIFT. */ static int ref_rate[2] = {14000, 33000}; /* * To improve readability, a conversion function is used to initialize * the following array, which entails that the array can be * initialized only in a function. */ static int ref_wr_duration[2]; /* * BFQ uses the above-detailed, time-based weight-raising mechanism to * privilege interactive tasks. This mechanism is vulnerable to the * following false positives: I/O-bound applications that will go on * doing I/O for much longer than the duration of weight * raising. These applications have basically no benefit from being * weight-raised at the beginning of their I/O. On the opposite end, * while being weight-raised, these applications * a) unjustly steal throughput to applications that may actually need * low latency; * b) make BFQ uselessly perform device idling; device idling results * in loss of device throughput with most flash-based storage, and may * increase latencies when used purposelessly. * * BFQ tries to reduce these problems, by adopting the following * countermeasure. To introduce this countermeasure, we need first to * finish explaining how the duration of weight-raising for * interactive tasks is computed. * * For a bfq_queue deemed as interactive, the duration of weight * raising is dynamically adjusted, as a function of the estimated * peak rate of the device, so as to be equal to the time needed to * execute the 'largest' interactive task we benchmarked so far. By * largest task, we mean the task for which each involved process has * to do more I/O than for any of the other tasks we benchmarked. This * reference interactive task is the start-up of LibreOffice Writer, * and in this task each process/bfq_queue needs to have at most ~110K * sectors transferred. * * This last piece of information enables BFQ to reduce the actual * duration of weight-raising for at least one class of I/O-bound * applications: those doing sequential or quasi-sequential I/O. An * example is file copy. In fact, once started, the main I/O-bound * processes of these applications usually consume the above 110K * sectors in much less time than the processes of an application that * is starting, because these I/O-bound processes will greedily devote * almost all their CPU cycles only to their target, * throughput-friendly I/O operations. This is even more true if BFQ * happens to be underestimating the device peak rate, and thus * overestimating the duration of weight raising. But, according to * our measurements, once transferred 110K sectors, these processes * have no right to be weight-raised any longer. * * Basing on the last consideration, BFQ ends weight-raising for a * bfq_queue if the latter happens to have received an amount of * service at least equal to the following constant. The constant is * set to slightly more than 110K, to have a minimum safety margin. * * This early ending of weight-raising reduces the amount of time * during which interactive false positives cause the two problems * described at the beginning of these comments. */ static const unsigned long max_service_from_wr = 120000; #define RQ_BIC(rq) icq_to_bic((rq)->elv.priv[0]) #define RQ_BFQQ(rq) ((rq)->elv.priv[1]) struct bfq_queue *bic_to_bfqq(struct bfq_io_cq *bic, bool is_sync) { return bic->bfqq[is_sync]; } void bic_set_bfqq(struct bfq_io_cq *bic, struct bfq_queue *bfqq, bool is_sync) { bic->bfqq[is_sync] = bfqq; } struct bfq_data *bic_to_bfqd(struct bfq_io_cq *bic) { return bic->icq.q->elevator->elevator_data; } /** * icq_to_bic - convert iocontext queue structure to bfq_io_cq. * @icq: the iocontext queue. */ static struct bfq_io_cq *icq_to_bic(struct io_cq *icq) { /* bic->icq is the first member, %NULL will convert to %NULL */ return container_of(icq, struct bfq_io_cq, icq); } /** * bfq_bic_lookup - search into @ioc a bic associated to @bfqd. * @bfqd: the lookup key. * @ioc: the io_context of the process doing I/O. * @q: the request queue. */ static struct bfq_io_cq *bfq_bic_lookup(struct bfq_data *bfqd, struct io_context *ioc, struct request_queue *q) { if (ioc) { unsigned long flags; struct bfq_io_cq *icq; spin_lock_irqsave(q->queue_lock, flags); icq = icq_to_bic(ioc_lookup_icq(ioc, q)); spin_unlock_irqrestore(q->queue_lock, flags); return icq; } return NULL; } /* * Scheduler run of queue, if there are requests pending and no one in the * driver that will restart queueing. */ void bfq_schedule_dispatch(struct bfq_data *bfqd) { if (bfqd->queued != 0) { bfq_log(bfqd, "schedule dispatch"); blk_mq_run_hw_queues(bfqd->queue, true); } } #define bfq_class_idle(bfqq) ((bfqq)->ioprio_class == IOPRIO_CLASS_IDLE) #define bfq_class_rt(bfqq) ((bfqq)->ioprio_class == IOPRIO_CLASS_RT) #define bfq_sample_valid(samples) ((samples) > 80) /* * Lifted from AS - choose which of rq1 and rq2 that is best served now. * We choose the request that is closesr to the head right now. Distance * behind the head is penalized and only allowed to a certain extent. */ static struct request *bfq_choose_req(struct bfq_data *bfqd, struct request *rq1, struct request *rq2, sector_t last) { sector_t s1, s2, d1 = 0, d2 = 0; unsigned long back_max; #define BFQ_RQ1_WRAP 0x01 /* request 1 wraps */ #define BFQ_RQ2_WRAP 0x02 /* request 2 wraps */ unsigned int wrap = 0; /* bit mask: requests behind the disk head? */ if (!rq1 || rq1 == rq2) return rq2; if (!rq2) return rq1; if (rq_is_sync(rq1) && !rq_is_sync(rq2)) return rq1; else if (rq_is_sync(rq2) && !rq_is_sync(rq1)) return rq2; if ((rq1->cmd_flags & REQ_META) && !(rq2->cmd_flags & REQ_META)) return rq1; else if ((rq2->cmd_flags & REQ_META) && !(rq1->cmd_flags & REQ_META)) return rq2; s1 = blk_rq_pos(rq1); s2 = blk_rq_pos(rq2); /* * By definition, 1KiB is 2 sectors. */ back_max = bfqd->bfq_back_max * 2; /* * Strict one way elevator _except_ in the case where we allow * short backward seeks which are biased as twice the cost of a * similar forward seek. */ if (s1 >= last) d1 = s1 - last; else if (s1 + back_max >= last) d1 = (last - s1) * bfqd->bfq_back_penalty; else wrap |= BFQ_RQ1_WRAP; if (s2 >= last) d2 = s2 - last; else if (s2 + back_max >= last) d2 = (last - s2) * bfqd->bfq_back_penalty; else wrap |= BFQ_RQ2_WRAP; /* Found required data */ /* * By doing switch() on the bit mask "wrap" we avoid having to * check two variables for all permutations: --> faster! */ switch (wrap) { case 0: /* common case for CFQ: rq1 and rq2 not wrapped */ if (d1 < d2) return rq1; else if (d2 < d1) return rq2; if (s1 >= s2) return rq1; else return rq2; case BFQ_RQ2_WRAP: return rq1; case BFQ_RQ1_WRAP: return rq2; case BFQ_RQ1_WRAP|BFQ_RQ2_WRAP: /* both rqs wrapped */ default: /* * Since both rqs are wrapped, * start with the one that's further behind head * (--> only *one* back seek required), * since back seek takes more time than forward. */ if (s1 <= s2) return rq1; else return rq2; } } /* * Async I/O can easily starve sync I/O (both sync reads and sync * writes), by consuming all tags. Similarly, storms of sync writes, * such as those that sync(2) may trigger, can starve sync reads. * Limit depths of async I/O and sync writes so as to counter both * problems. */ static void bfq_limit_depth(unsigned int op, struct blk_mq_alloc_data *data) { struct bfq_data *bfqd = data->q->elevator->elevator_data; if (op_is_sync(op) && !op_is_write(op)) return; data->shallow_depth = bfqd->word_depths[!!bfqd->wr_busy_queues][op_is_sync(op)]; bfq_log(bfqd, "[%s] wr_busy %d sync %d depth %u", __func__, bfqd->wr_busy_queues, op_is_sync(op), data->shallow_depth); } static struct bfq_queue * bfq_rq_pos_tree_lookup(struct bfq_data *bfqd, struct rb_root *root, sector_t sector, struct rb_node **ret_parent, struct rb_node ***rb_link) { struct rb_node **p, *parent; struct bfq_queue *bfqq = NULL; parent = NULL; p = &root->rb_node; while (*p) { struct rb_node **n; parent = *p; bfqq = rb_entry(parent, struct bfq_queue, pos_node); /* * Sort strictly based on sector. Smallest to the left, * largest to the right. */ if (sector > blk_rq_pos(bfqq->next_rq)) n = &(*p)->rb_right; else if (sector < blk_rq_pos(bfqq->next_rq)) n = &(*p)->rb_left; else break; p = n; bfqq = NULL; } *ret_parent = parent; if (rb_link) *rb_link = p; bfq_log(bfqd, "rq_pos_tree_lookup %llu: returning %d", (unsigned long long)sector, bfqq ? bfqq->pid : 0); return bfqq; } static bool bfq_too_late_for_merging(struct bfq_queue *bfqq) { return bfqq->service_from_backlogged > 0 && time_is_before_jiffies(bfqq->first_IO_time + bfq_merge_time_limit); } void bfq_pos_tree_add_move(struct bfq_data *bfqd, struct bfq_queue *bfqq) { struct rb_node **p, *parent; struct bfq_queue *__bfqq; if (bfqq->pos_root) { rb_erase(&bfqq->pos_node, bfqq->pos_root); bfqq->pos_root = NULL; } /* * bfqq cannot be merged any longer (see comments in * bfq_setup_cooperator): no point in adding bfqq into the * position tree. */ if (bfq_too_late_for_merging(bfqq)) return; if (bfq_class_idle(bfqq)) return; if (!bfqq->next_rq) return; bfqq->pos_root = &bfq_bfqq_to_bfqg(bfqq)->rq_pos_tree; __bfqq = bfq_rq_pos_tree_lookup(bfqd, bfqq->pos_root, blk_rq_pos(bfqq->next_rq), &parent, &p); if (!__bfqq) { rb_link_node(&bfqq->pos_node, parent, p); rb_insert_color(&bfqq->pos_node, bfqq->pos_root); } else bfqq->pos_root = NULL; } /* * Tell whether there are active queues with different weights or * active groups. */ static bool bfq_varied_queue_weights_or_active_groups(struct bfq_data *bfqd) { /* * For queue weights to differ, queue_weights_tree must contain * at least two nodes. */ return (!RB_EMPTY_ROOT(&bfqd->queue_weights_tree) && (bfqd->queue_weights_tree.rb_node->rb_left || bfqd->queue_weights_tree.rb_node->rb_right) #ifdef CONFIG_BFQ_GROUP_IOSCHED ) || (bfqd->num_groups_with_pending_reqs > 0 #endif ); } /* * The following function returns true if every queue must receive the * same share of the throughput (this condition is used when deciding * whether idling may be disabled, see the comments in the function * bfq_better_to_idle()). * * Such a scenario occurs when: * 1) all active queues have the same weight, * 2) all active groups at the same level in the groups tree have the same * weight, * 3) all active groups at the same level in the groups tree have the same * number of children. * * Unfortunately, keeping the necessary state for evaluating exactly * the last two symmetry sub-conditions above would be quite complex * and time consuming. Therefore this function evaluates, instead, * only the following stronger two sub-conditions, for which it is * much easier to maintain the needed state: * 1) all active queues have the same weight, * 2) there are no active groups. * In particular, the last condition is always true if hierarchical * support or the cgroups interface are not enabled, thus no state * needs to be maintained in this case. */ static bool bfq_symmetric_scenario(struct bfq_data *bfqd) { return !bfq_varied_queue_weights_or_active_groups(bfqd); } /* * If the weight-counter tree passed as input contains no counter for * the weight of the input queue, then add that counter; otherwise just * increment the existing counter. * * Note that weight-counter trees contain few nodes in mostly symmetric * scenarios. For example, if all queues have the same weight, then the * weight-counter tree for the queues may contain at most one node. * This holds even if low_latency is on, because weight-raised queues * are not inserted in the tree. * In most scenarios, the rate at which nodes are created/destroyed * should be low too. */ void bfq_weights_tree_add(struct bfq_data *bfqd, struct bfq_queue *bfqq, struct rb_root *root) { struct bfq_entity *entity = &bfqq->entity; struct rb_node **new = &(root->rb_node), *parent = NULL; /* * Do not insert if the queue is already associated with a * counter, which happens if: * 1) a request arrival has caused the queue to become both * non-weight-raised, and hence change its weight, and * backlogged; in this respect, each of the two events * causes an invocation of this function, * 2) this is the invocation of this function caused by the * second event. This second invocation is actually useless, * and we handle this fact by exiting immediately. More * efficient or clearer solutions might possibly be adopted. */ if (bfqq->weight_counter) return; while (*new) { struct bfq_weight_counter *__counter = container_of(*new, struct bfq_weight_counter, weights_node); parent = *new; if (entity->weight == __counter->weight) { bfqq->weight_counter = __counter; goto inc_counter; } if (entity->weight < __counter->weight) new = &((*new)->rb_left); else new = &((*new)->rb_right); } bfqq->weight_counter = kzalloc(sizeof(struct bfq_weight_counter), GFP_ATOMIC); /* * In the unlucky event of an allocation failure, we just * exit. This will cause the weight of queue to not be * considered in bfq_varied_queue_weights_or_active_groups, * which, in its turn, causes the scenario to be deemed * wrongly symmetric in case bfqq's weight would have been * the only weight making the scenario asymmetric. On the * bright side, no unbalance will however occur when bfqq * becomes inactive again (the invocation of this function * is triggered by an activation of queue). In fact, * bfq_weights_tree_remove does nothing if * !bfqq->weight_counter. */ if (unlikely(!bfqq->weight_counter)) return; bfqq->weight_counter->weight = entity->weight; rb_link_node(&bfqq->weight_counter->weights_node, parent, new); rb_insert_color(&bfqq->weight_counter->weights_node, root); inc_counter: bfqq->weight_counter->num_active++; } /* * Decrement the weight counter associated with the queue, and, if the * counter reaches 0, remove the counter from the tree. * See the comments to the function bfq_weights_tree_add() for considerations * about overhead. */ void __bfq_weights_tree_remove(struct bfq_data *bfqd, struct bfq_queue *bfqq, struct rb_root *root) { if (!bfqq->weight_counter) return; bfqq->weight_counter->num_active--; if (bfqq->weight_counter->num_active > 0) goto reset_entity_pointer; rb_erase(&bfqq->weight_counter->weights_node, root); kfree(bfqq->weight_counter); reset_entity_pointer: bfqq->weight_counter = NULL; } /* * Invoke __bfq_weights_tree_remove on bfqq and decrement the number * of active groups for each queue's inactive parent entity. */ void bfq_weights_tree_remove(struct bfq_data *bfqd, struct bfq_queue *bfqq) { struct bfq_entity *entity = bfqq->entity.parent; __bfq_weights_tree_remove(bfqd, bfqq, &bfqd->queue_weights_tree); for_each_entity(entity) { struct bfq_sched_data *sd = entity->my_sched_data; if (sd->next_in_service || sd->in_service_entity) { /* * entity is still active, because either * next_in_service or in_service_entity is not * NULL (see the comments on the definition of * next_in_service for details on why * in_service_entity must be checked too). * * As a consequence, its parent entities are * active as well, and thus this loop must * stop here. */ break; } /* * The decrement of num_groups_with_pending_reqs is * not performed immediately upon the deactivation of * entity, but it is delayed to when it also happens * that the first leaf descendant bfqq of entity gets * all its pending requests completed. The following * instructions perform this delayed decrement, if * needed. See the comments on * num_groups_with_pending_reqs for details. */ if (entity->in_groups_with_pending_reqs) { entity->in_groups_with_pending_reqs = false; bfqd->num_groups_with_pending_reqs--; } } } /* * Return expired entry, or NULL to just start from scratch in rbtree. */ static struct request *bfq_check_fifo(struct bfq_queue *bfqq, struct request *last) { struct request *rq; if (bfq_bfqq_fifo_expire(bfqq)) return NULL; bfq_mark_bfqq_fifo_expire(bfqq); rq = rq_entry_fifo(bfqq->fifo.next); if (rq == last || ktime_get_ns() < rq->fifo_time) return NULL; bfq_log_bfqq(bfqq->bfqd, bfqq, "check_fifo: returned %p", rq); return rq; } static struct request *bfq_find_next_rq(struct bfq_data *bfqd, struct bfq_queue *bfqq, struct request *last) { struct rb_node *rbnext = rb_next(&last->rb_node); struct rb_node *rbprev = rb_prev(&last->rb_node); struct request *next, *prev = NULL; /* Follow expired path, else get first next available. */ next = bfq_check_fifo(bfqq, last); if (next) return next; if (rbprev) prev = rb_entry_rq(rbprev); if (rbnext) next = rb_entry_rq(rbnext); else { rbnext = rb_first(&bfqq->sort_list); if (rbnext && rbnext != &last->rb_node) next = rb_entry_rq(rbnext); } return bfq_choose_req(bfqd, next, prev, blk_rq_pos(last)); } /* see the definition of bfq_async_charge_factor for details */ static unsigned long bfq_serv_to_charge(struct request *rq, struct bfq_queue *bfqq) { if (bfq_bfqq_sync(bfqq) || bfqq->wr_coeff > 1) return blk_rq_sectors(rq); return blk_rq_sectors(rq) * bfq_async_charge_factor; } /** * bfq_updated_next_req - update the queue after a new next_rq selection. * @bfqd: the device data the queue belongs to. * @bfqq: the queue to update. * * If the first request of a queue changes we make sure that the queue * has enough budget to serve at least its first request (if the * request has grown). We do this because if the queue has not enough * budget for its first request, it has to go through two dispatch * rounds to actually get it dispatched. */ static void bfq_updated_next_req(struct bfq_data *bfqd, struct bfq_queue *bfqq) { struct bfq_entity *entity = &bfqq->entity; struct request *next_rq = bfqq->next_rq; unsigned long new_budget; if (!next_rq) return; if (bfqq == bfqd->in_service_queue) /* * In order not to break guarantees, budgets cannot be * changed after an entity has been selected. */ return; new_budget = max_t(unsigned long, bfqq->max_budget, bfq_serv_to_charge(next_rq, bfqq)); if (entity->budget != new_budget) { entity->budget = new_budget; bfq_log_bfqq(bfqd, bfqq, "updated next rq: new budget %lu", new_budget); bfq_requeue_bfqq(bfqd, bfqq, false); } } static unsigned int bfq_wr_duration(struct bfq_data *bfqd) { u64 dur; if (bfqd->bfq_wr_max_time > 0) return bfqd->bfq_wr_max_time; dur = bfqd->rate_dur_prod; do_div(dur, bfqd->peak_rate); /* * Limit duration between 3 and 25 seconds. The upper limit * has been conservatively set after the following worst case: * on a QEMU/KVM virtual machine * - running in a slow PC * - with a virtual disk stacked on a slow low-end 5400rpm HDD * - serving a heavy I/O workload, such as the sequential reading * of several files * mplayer took 23 seconds to start, if constantly weight-raised. * * As for higher values than that accomodating the above bad * scenario, tests show that higher values would often yield * the opposite of the desired result, i.e., would worsen * responsiveness by allowing non-interactive applications to * preserve weight raising for too long. * * On the other end, lower values than 3 seconds make it * difficult for most interactive tasks to complete their jobs * before weight-raising finishes. */ return clamp_val(dur, msecs_to_jiffies(3000), msecs_to_jiffies(25000)); } /* switch back from soft real-time to interactive weight raising */ static void switch_back_to_interactive_wr(struct bfq_queue *bfqq, struct bfq_data *bfqd) { bfqq->wr_coeff = bfqd->bfq_wr_coeff; bfqq->wr_cur_max_time = bfq_wr_duration(bfqd); bfqq->last_wr_start_finish = bfqq->wr_start_at_switch_to_srt; } static void bfq_bfqq_resume_state(struct bfq_queue *bfqq, struct bfq_data *bfqd, struct bfq_io_cq *bic, bool bfq_already_existing) { unsigned int old_wr_coeff = bfqq->wr_coeff; bool busy = bfq_already_existing && bfq_bfqq_busy(bfqq); if (bic->saved_has_short_ttime) bfq_mark_bfqq_has_short_ttime(bfqq); else bfq_clear_bfqq_has_short_ttime(bfqq); if (bic->saved_IO_bound) bfq_mark_bfqq_IO_bound(bfqq); else bfq_clear_bfqq_IO_bound(bfqq); bfqq->ttime = bic->saved_ttime; bfqq->wr_coeff = bic->saved_wr_coeff; bfqq->wr_start_at_switch_to_srt = bic->saved_wr_start_at_switch_to_srt; bfqq->last_wr_start_finish = bic->saved_last_wr_start_finish; bfqq->wr_cur_max_time = bic->saved_wr_cur_max_time; if (bfqq->wr_coeff > 1 && (bfq_bfqq_in_large_burst(bfqq) || time_is_before_jiffies(bfqq->last_wr_start_finish + bfqq->wr_cur_max_time))) { if (bfqq->wr_cur_max_time == bfqd->bfq_wr_rt_max_time && !bfq_bfqq_in_large_burst(bfqq) && time_is_after_eq_jiffies(bfqq->wr_start_at_switch_to_srt + bfq_wr_duration(bfqd))) { switch_back_to_interactive_wr(bfqq, bfqd); } else { bfqq->wr_coeff = 1; bfq_log_bfqq(bfqq->bfqd, bfqq, "resume state: switching off wr"); } } /* make sure weight will be updated, however we got here */ bfqq->entity.prio_changed = 1; if (likely(!busy)) return; if (old_wr_coeff == 1 && bfqq->wr_coeff > 1) bfqd->wr_busy_queues++; else if (old_wr_coeff > 1 && bfqq->wr_coeff == 1) bfqd->wr_busy_queues--; } static int bfqq_process_refs(struct bfq_queue *bfqq) { return bfqq->ref - bfqq->allocated - bfqq->entity.on_st; } /* Empty burst list and add just bfqq (see comments on bfq_handle_burst) */ static void bfq_reset_burst_list(struct bfq_data *bfqd, struct bfq_queue *bfqq) { struct bfq_queue *item; struct hlist_node *n; hlist_for_each_entry_safe(item, n, &bfqd->burst_list, burst_list_node) hlist_del_init(&item->burst_list_node); hlist_add_head(&bfqq->burst_list_node, &bfqd->burst_list); bfqd->burst_size = 1; bfqd->burst_parent_entity = bfqq->entity.parent; } /* Add bfqq to the list of queues in current burst (see bfq_handle_burst) */ static void bfq_add_to_burst(struct bfq_data *bfqd, struct bfq_queue *bfqq) { /* Increment burst size to take into account also bfqq */ bfqd->burst_size++; if (bfqd->burst_size == bfqd->bfq_large_burst_thresh) { struct bfq_queue *pos, *bfqq_item; struct hlist_node *n; /* * Enough queues have been activated shortly after each * other to consider this burst as large. */ bfqd->large_burst = true; /* * We can now mark all queues in the burst list as * belonging to a large burst. */ hlist_for_each_entry(bfqq_item, &bfqd->burst_list, burst_list_node) bfq_mark_bfqq_in_large_burst(bfqq_item); bfq_mark_bfqq_in_large_burst(bfqq); /* * From now on, and until the current burst finishes, any * new queue being activated shortly after the last queue * was inserted in the burst can be immediately marked as * belonging to a large burst. So the burst list is not * needed any more. Remove it. */ hlist_for_each_entry_safe(pos, n, &bfqd->burst_list, burst_list_node) hlist_del_init(&pos->burst_list_node); } else /* * Burst not yet large: add bfqq to the burst list. Do * not increment the ref counter for bfqq, because bfqq * is removed from the burst list before freeing bfqq * in put_queue. */ hlist_add_head(&bfqq->burst_list_node, &bfqd->burst_list); } /* * If many queues belonging to the same group happen to be created * shortly after each other, then the processes associated with these * queues have typically a common goal. In particular, bursts of queue * creations are usually caused by services or applications that spawn * many parallel threads/processes. Examples are systemd during boot, * or git grep. To help these processes get their job done as soon as * possible, it is usually better to not grant either weight-raising * or device idling to their queues. * * In this comment we describe, firstly, the reasons why this fact * holds, and, secondly, the next function, which implements the main * steps needed to properly mark these queues so that they can then be * treated in a different way. * * The above services or applications benefit mostly from a high * throughput: the quicker the requests of the activated queues are * cumulatively served, the sooner the target job of these queues gets * completed. As a consequence, weight-raising any of these queues, * which also implies idling the device for it, is almost always * counterproductive. In most cases it just lowers throughput. * * On the other hand, a burst of queue creations may be caused also by * the start of an application that does not consist of a lot of * parallel I/O-bound threads. In fact, with a complex application, * several short processes may need to be executed to start-up the * application. In this respect, to start an application as quickly as * possible, the best thing to do is in any case to privilege the I/O * related to the application with respect to all other * I/O. Therefore, the best strategy to start as quickly as possible * an application that causes a burst of queue creations is to * weight-raise all the queues created during the burst. This is the * exact opposite of the best strategy for the other type of bursts. * * In the end, to take the best action for each of the two cases, the * two types of bursts need to be distinguished. Fortunately, this * seems relatively easy, by looking at the sizes of the bursts. In * particular, we found a threshold such that only bursts with a * larger size than that threshold are apparently caused by * services or commands such as systemd or git grep. For brevity, * hereafter we call just 'large' these bursts. BFQ *does not* * weight-raise queues whose creation occurs in a large burst. In * addition, for each of these queues BFQ performs or does not perform * idling depending on which choice boosts the throughput more. The * exact choice depends on the device and request pattern at * hand. * * Unfortunately, false positives may occur while an interactive task * is starting (e.g., an application is being started). The * consequence is that the queues associated with the task do not * enjoy weight raising as expected. Fortunately these false positives * are very rare. They typically occur if some service happens to * start doing I/O exactly when the interactive task starts. * * Turning back to the next function, it implements all the steps * needed to detect the occurrence of a large burst and to properly * mark all the queues belonging to it (so that they can then be * treated in a different way). This goal is achieved by maintaining a * "burst list" that holds, temporarily, the queues that belong to the * burst in progress. The list is then used to mark these queues as * belonging to a large burst if the burst does become large. The main * steps are the following. * * . when the very first queue is created, the queue is inserted into the * list (as it could be the first queue in a possible burst) * * . if the current burst has not yet become large, and a queue Q that does * not yet belong to the burst is activated shortly after the last time * at which a new queue entered the burst list, then the function appends * Q to the burst list * * . if, as a consequence of the previous step, the burst size reaches * the large-burst threshold, then * * . all the queues in the burst list are marked as belonging to a * large burst * * . the burst list is deleted; in fact, the burst list already served * its purpose (keeping temporarily track of the queues in a burst, * so as to be able to mark them as belonging to a large burst in the * previous sub-step), and now is not needed any more * * . the device enters a large-burst mode * * . if a queue Q that does not belong to the burst is created while * the device is in large-burst mode and shortly after the last time * at which a queue either entered the burst list or was marked as * belonging to the current large burst, then Q is immediately marked * as belonging to a large burst. * * . if a queue Q that does not belong to the burst is created a while * later, i.e., not shortly after, than the last time at which a queue * either entered the burst list or was marked as belonging to the * current large burst, then the current burst is deemed as finished and: * * . the large-burst mode is reset if set * * . the burst list is emptied * * . Q is inserted in the burst list, as Q may be the first queue * in a possible new burst (then the burst list contains just Q * after this step). */ static void bfq_handle_burst(struct bfq_data *bfqd, struct bfq_queue *bfqq) { /* * If bfqq is already in the burst list or is part of a large * burst, or finally has just been split, then there is * nothing else to do. */ if (!hlist_unhashed(&bfqq->burst_list_node) || bfq_bfqq_in_large_burst(bfqq) || time_is_after_eq_jiffies(bfqq->split_time + msecs_to_jiffies(10))) return; /* * If bfqq's creation happens late enough, or bfqq belongs to * a different group than the burst group, then the current * burst is finished, and related data structures must be * reset. * * In this respect, consider the special case where bfqq is * the very first queue created after BFQ is selected for this * device. In this case, last_ins_in_burst and * burst_parent_entity are not yet significant when we get * here. But it is easy to verify that, whether or not the * following condition is true, bfqq will end up being * inserted into the burst list. In particular the list will * happen to contain only bfqq. And this is exactly what has * to happen, as bfqq may be the first queue of the first * burst. */ if (time_is_before_jiffies(bfqd->last_ins_in_burst + bfqd->bfq_burst_interval) || bfqq->entity.parent != bfqd->burst_parent_entity) { bfqd->large_burst = false; bfq_reset_burst_list(bfqd, bfqq); goto end; } /* * If we get here, then bfqq is being activated shortly after the * last queue. So, if the current burst is also large, we can mark * bfqq as belonging to this large burst immediately. */ if (bfqd->large_burst) { bfq_mark_bfqq_in_large_burst(bfqq); goto end; } /* * If we get here, then a large-burst state has not yet been * reached, but bfqq is being activated shortly after the last * queue. Then we add bfqq to the burst. */ bfq_add_to_burst(bfqd, bfqq); end: /* * At this point, bfqq either has been added to the current * burst or has caused the current burst to terminate and a * possible new burst to start. In particular, in the second * case, bfqq has become the first queue in the possible new * burst. In both cases last_ins_in_burst needs to be moved * forward. */ bfqd->last_ins_in_burst = jiffies; } static int bfq_bfqq_budget_left(struct bfq_queue *bfqq) { struct bfq_entity *entity = &bfqq->entity; return entity->budget - entity->service; } /* * If enough samples have been computed, return the current max budget * stored in bfqd, which is dynamically updated according to the * estimated disk peak rate; otherwise return the default max budget */ static int bfq_max_budget(struct bfq_data *bfqd) { if (bfqd->budgets_assigned < bfq_stats_min_budgets) return bfq_default_max_budget; else return bfqd->bfq_max_budget; } /* * Return min budget, which is a fraction of the current or default * max budget (trying with 1/32) */ static int bfq_min_budget(struct bfq_data *bfqd) { if (bfqd->budgets_assigned < bfq_stats_min_budgets) return bfq_default_max_budget / 32; else return bfqd->bfq_max_budget / 32; } /* * The next function, invoked after the input queue bfqq switches from * idle to busy, updates the budget of bfqq. The function also tells * whether the in-service queue should be expired, by returning * true. The purpose of expiring the in-service queue is to give bfqq * the chance to possibly preempt the in-service queue, and the reason * for preempting the in-service queue is to achieve one of the two * goals below. * * 1. Guarantee to bfqq its reserved bandwidth even if bfqq has * expired because it has remained idle. In particular, bfqq may have * expired for one of the following two reasons: * * - BFQQE_NO_MORE_REQUESTS bfqq did not enjoy any device idling * and did not make it to issue a new request before its last * request was served; * * - BFQQE_TOO_IDLE bfqq did enjoy device idling, but did not issue * a new request before the expiration of the idling-time. * * Even if bfqq has expired for one of the above reasons, the process * associated with the queue may be however issuing requests greedily, * and thus be sensitive to the bandwidth it receives (bfqq may have * remained idle for other reasons: CPU high load, bfqq not enjoying * idling, I/O throttling somewhere in the path from the process to * the I/O scheduler, ...). But if, after every expiration for one of * the above two reasons, bfqq has to wait for the service of at least * one full budget of another queue before being served again, then * bfqq is likely to get a much lower bandwidth or resource time than * its reserved ones. To address this issue, two countermeasures need * to be taken. * * First, the budget and the timestamps of bfqq need to be updated in * a special way on bfqq reactivation: they need to be updated as if * bfqq did not remain idle and did not expire. In fact, if they are * computed as if bfqq expired and remained idle until reactivation, * then the process associated with bfqq is treated as if, instead of * being greedy, it stopped issuing requests when bfqq remained idle, * and restarts issuing requests only on this reactivation. In other * words, the scheduler does not help the process recover the "service * hole" between bfqq expiration and reactivation. As a consequence, * the process receives a lower bandwidth than its reserved one. In * contrast, to recover this hole, the budget must be updated as if * bfqq was not expired at all before this reactivation, i.e., it must * be set to the value of the remaining budget when bfqq was * expired. Along the same line, timestamps need to be assigned the * value they had the last time bfqq was selected for service, i.e., * before last expiration. Thus timestamps need to be back-shifted * with respect to their normal computation (see [1] for more details * on this tricky aspect). * * Secondly, to allow the process to recover the hole, the in-service * queue must be expired too, to give bfqq the chance to preempt it * immediately. In fact, if bfqq has to wait for a full budget of the * in-service queue to be completed, then it may become impossible to * let the process recover the hole, even if the back-shifted * timestamps of bfqq are lower than those of the in-service queue. If * this happens for most or all of the holes, then the process may not * receive its reserved bandwidth. In this respect, it is worth noting * that, being the service of outstanding requests unpreemptible, a * little fraction of the holes may however be unrecoverable, thereby * causing a little loss of bandwidth. * * The last important point is detecting whether bfqq does need this * bandwidth recovery. In this respect, the next function deems the * process associated with bfqq greedy, and thus allows it to recover * the hole, if: 1) the process is waiting for the arrival of a new * request (which implies that bfqq expired for one of the above two * reasons), and 2) such a request has arrived soon. The first * condition is controlled through the flag non_blocking_wait_rq, * while the second through the flag arrived_in_time. If both * conditions hold, then the function computes the budget in the * above-described special way, and signals that the in-service queue * should be expired. Timestamp back-shifting is done later in * __bfq_activate_entity. * * 2. Reduce latency. Even if timestamps are not backshifted to let * the process associated with bfqq recover a service hole, bfqq may * however happen to have, after being (re)activated, a lower finish * timestamp than the in-service queue. That is, the next budget of * bfqq may have to be completed before the one of the in-service * queue. If this is the case, then preempting the in-service queue * allows this goal to be achieved, apart from the unpreemptible, * outstanding requests mentioned above. * * Unfortunately, regardless of which of the above two goals one wants * to achieve, service trees need first to be updated to know whether * the in-service queue must be preempted. To have service trees * correctly updated, the in-service queue must be expired and * rescheduled, and bfqq must be scheduled too. This is one of the * most costly operations (in future versions, the scheduling * mechanism may be re-designed in such a way to make it possible to * know whether preemption is needed without needing to update service * trees). In addition, queue preemptions almost always cause random * I/O, and thus loss of throughput. Because of these facts, the next * function adopts the following simple scheme to avoid both costly * operations and too frequent preemptions: it requests the expiration * of the in-service queue (unconditionally) only for queues that need * to recover a hole, or that either are weight-raised or deserve to * be weight-raised. */ static bool bfq_bfqq_update_budg_for_activation(struct bfq_data *bfqd, struct bfq_queue *bfqq, bool arrived_in_time, bool wr_or_deserves_wr) { struct bfq_entity *entity = &bfqq->entity; if (bfq_bfqq_non_blocking_wait_rq(bfqq) && arrived_in_time) { /* * We do not clear the flag non_blocking_wait_rq here, as * the latter is used in bfq_activate_bfqq to signal * that timestamps need to be back-shifted (and is * cleared right after). */ /* * In next assignment we rely on that either * entity->service or entity->budget are not updated * on expiration if bfqq is empty (see * __bfq_bfqq_recalc_budget). Thus both quantities * remain unchanged after such an expiration, and the * following statement therefore assigns to * entity->budget the remaining budget on such an * expiration. */ entity->budget = min_t(unsigned long, bfq_bfqq_budget_left(bfqq), bfqq->max_budget); /* * At this point, we have used entity->service to get * the budget left (needed for updating * entity->budget). Thus we finally can, and have to, * reset entity->service. The latter must be reset * because bfqq would otherwise be charged again for * the service it has received during its previous * service slot(s). */ entity->service = 0; return true; } /* * We can finally complete expiration, by setting service to 0. */ entity->service = 0; entity->budget = max_t(unsigned long, bfqq->max_budget, bfq_serv_to_charge(bfqq->next_rq, bfqq)); bfq_clear_bfqq_non_blocking_wait_rq(bfqq); return wr_or_deserves_wr; } /* * Return the farthest past time instant according to jiffies * macros. */ static unsigned long bfq_smallest_from_now(void) { return jiffies - MAX_JIFFY_OFFSET; } static void bfq_update_bfqq_wr_on_rq_arrival(struct bfq_data *bfqd, struct bfq_queue *bfqq, unsigned int old_wr_coeff, bool wr_or_deserves_wr, bool interactive, bool in_burst, bool soft_rt) { if (old_wr_coeff == 1 && wr_or_deserves_wr) { /* start a weight-raising period */ if (interactive) { bfqq->service_from_wr = 0; bfqq->wr_coeff = bfqd->bfq_wr_coeff; bfqq->wr_cur_max_time = bfq_wr_duration(bfqd); } else { /* * No interactive weight raising in progress * here: assign minus infinity to * wr_start_at_switch_to_srt, to make sure * that, at the end of the soft-real-time * weight raising periods that is starting * now, no interactive weight-raising period * may be wrongly considered as still in * progress (and thus actually started by * mistake). */ bfqq->wr_start_at_switch_to_srt = bfq_smallest_from_now(); bfqq->wr_coeff = bfqd->bfq_wr_coeff * BFQ_SOFTRT_WEIGHT_FACTOR; bfqq->wr_cur_max_time = bfqd->bfq_wr_rt_max_time; } /* * If needed, further reduce budget to make sure it is * close to bfqq's backlog, so as to reduce the * scheduling-error component due to a too large * budget. Do not care about throughput consequences, * but only about latency. Finally, do not assign a * too small budget either, to avoid increasing * latency by causing too frequent expirations. */ bfqq->entity.budget = min_t(unsigned long, bfqq->entity.budget, 2 * bfq_min_budget(bfqd)); } else if (old_wr_coeff > 1) { if (interactive) { /* update wr coeff and duration */ bfqq->wr_coeff = bfqd->bfq_wr_coeff; bfqq->wr_cur_max_time = bfq_wr_duration(bfqd); } else if (in_burst) bfqq->wr_coeff = 1; else if (soft_rt) { /* * The application is now or still meeting the * requirements for being deemed soft rt. We * can then correctly and safely (re)charge * the weight-raising duration for the * application with the weight-raising * duration for soft rt applications. * * In particular, doing this recharge now, i.e., * before the weight-raising period for the * application finishes, reduces the probability * of the following negative scenario: * 1) the weight of a soft rt application is * raised at startup (as for any newly * created application), * 2) since the application is not interactive, * at a certain time weight-raising is * stopped for the application, * 3) at that time the application happens to * still have pending requests, and hence * is destined to not have a chance to be * deemed soft rt before these requests are * completed (see the comments to the * function bfq_bfqq_softrt_next_start() * for details on soft rt detection), * 4) these pending requests experience a high * latency because the application is not * weight-raised while they are pending. */ if (bfqq->wr_cur_max_time != bfqd->bfq_wr_rt_max_time) { bfqq->wr_start_at_switch_to_srt = bfqq->last_wr_start_finish; bfqq->wr_cur_max_time = bfqd->bfq_wr_rt_max_time; bfqq->wr_coeff = bfqd->bfq_wr_coeff * BFQ_SOFTRT_WEIGHT_FACTOR; } bfqq->last_wr_start_finish = jiffies; } } } static bool bfq_bfqq_idle_for_long_time(struct bfq_data *bfqd, struct bfq_queue *bfqq) { return bfqq->dispatched == 0 && time_is_before_jiffies( bfqq->budget_timeout + bfqd->bfq_wr_min_idle_time); } static void bfq_bfqq_handle_idle_busy_switch(struct bfq_data *bfqd, struct bfq_queue *bfqq, int old_wr_coeff, struct request *rq, bool *interactive) { bool soft_rt, in_burst, wr_or_deserves_wr, bfqq_wants_to_preempt, idle_for_long_time = bfq_bfqq_idle_for_long_time(bfqd, bfqq), /* * See the comments on * bfq_bfqq_update_budg_for_activation for * details on the usage of the next variable. */ arrived_in_time = ktime_get_ns() <= bfqq->ttime.last_end_request + bfqd->bfq_slice_idle * 3; /* * bfqq deserves to be weight-raised if: * - it is sync, * - it does not belong to a large burst, * - it has been idle for enough time or is soft real-time, * - is linked to a bfq_io_cq (it is not shared in any sense). */ in_burst = bfq_bfqq_in_large_burst(bfqq); soft_rt = bfqd->bfq_wr_max_softrt_rate > 0 && !in_burst && time_is_before_jiffies(bfqq->soft_rt_next_start) && bfqq->dispatched == 0; *interactive = !in_burst && idle_for_long_time; wr_or_deserves_wr = bfqd->low_latency && (bfqq->wr_coeff > 1 || (bfq_bfqq_sync(bfqq) && bfqq->bic && (*interactive || soft_rt))); /* * Using the last flag, update budget and check whether bfqq * may want to preempt the in-service queue. */ bfqq_wants_to_preempt = bfq_bfqq_update_budg_for_activation(bfqd, bfqq, arrived_in_time, wr_or_deserves_wr); /* * If bfqq happened to be activated in a burst, but has been * idle for much more than an interactive queue, then we * assume that, in the overall I/O initiated in the burst, the * I/O associated with bfqq is finished. So bfqq does not need * to be treated as a queue belonging to a burst * anymore. Accordingly, we reset bfqq's in_large_burst flag * if set, and remove bfqq from the burst list if it's * there. We do not decrement burst_size, because the fact * that bfqq does not need to belong to the burst list any * more does not invalidate the fact that bfqq was created in * a burst. */ if (likely(!bfq_bfqq_just_created(bfqq)) && idle_for_long_time && time_is_before_jiffies( bfqq->budget_timeout + msecs_to_jiffies(10000))) { hlist_del_init(&bfqq->burst_list_node); bfq_clear_bfqq_in_large_burst(bfqq); } bfq_clear_bfqq_just_created(bfqq); if (!bfq_bfqq_IO_bound(bfqq)) { if (arrived_in_time) { bfqq->requests_within_timer++; if (bfqq->requests_within_timer >= bfqd->bfq_requests_within_timer) bfq_mark_bfqq_IO_bound(bfqq); } else bfqq->requests_within_timer = 0; } if (bfqd->low_latency) { if (unlikely(time_is_after_jiffies(bfqq->split_time))) /* wraparound */ bfqq->split_time = jiffies - bfqd->bfq_wr_min_idle_time - 1; if (time_is_before_jiffies(bfqq->split_time + bfqd->bfq_wr_min_idle_time)) { bfq_update_bfqq_wr_on_rq_arrival(bfqd, bfqq, old_wr_coeff, wr_or_deserves_wr, *interactive, in_burst, soft_rt); if (old_wr_coeff != bfqq->wr_coeff) bfqq->entity.prio_changed = 1; } } bfqq->last_idle_bklogged = jiffies; bfqq->service_from_backlogged = 0; bfq_clear_bfqq_softrt_update(bfqq); bfq_add_bfqq_busy(bfqd, bfqq); /* * Expire in-service queue only if preemption may be needed * for guarantees. In this respect, the function * next_queue_may_preempt just checks a simple, necessary * condition, and not a sufficient condition based on * timestamps. In fact, for the latter condition to be * evaluated, timestamps would need first to be updated, and * this operation is quite costly (see the comments on the * function bfq_bfqq_update_budg_for_activation). */ if (bfqd->in_service_queue && bfqq_wants_to_preempt && bfqd->in_service_queue->wr_coeff < bfqq->wr_coeff && next_queue_may_preempt(bfqd)) bfq_bfqq_expire(bfqd, bfqd->in_service_queue, false, BFQQE_PREEMPTED); } static void bfq_add_request(struct request *rq) { struct bfq_queue *bfqq = RQ_BFQQ(rq); struct bfq_data *bfqd = bfqq->bfqd; struct request *next_rq, *prev; unsigned int old_wr_coeff = bfqq->wr_coeff; bool interactive = false; bfq_log_bfqq(bfqd, bfqq, "add_request %d", rq_is_sync(rq)); bfqq->queued[rq_is_sync(rq)]++; bfqd->queued++; elv_rb_add(&bfqq->sort_list, rq); /* * Check if this request is a better next-serve candidate. */ prev = bfqq->next_rq; next_rq = bfq_choose_req(bfqd, bfqq->next_rq, rq, bfqd->last_position); bfqq->next_rq = next_rq; /* * Adjust priority tree position, if next_rq changes. */ if (prev != bfqq->next_rq) bfq_pos_tree_add_move(bfqd, bfqq); if (!bfq_bfqq_busy(bfqq)) /* switching to busy ... */ bfq_bfqq_handle_idle_busy_switch(bfqd, bfqq, old_wr_coeff, rq, &interactive); else { if (bfqd->low_latency && old_wr_coeff == 1 && !rq_is_sync(rq) && time_is_before_jiffies( bfqq->last_wr_start_finish + bfqd->bfq_wr_min_inter_arr_async)) { bfqq->wr_coeff = bfqd->bfq_wr_coeff; bfqq->wr_cur_max_time = bfq_wr_duration(bfqd); bfqd->wr_busy_queues++; bfqq->entity.prio_changed = 1; } if (prev != bfqq->next_rq) bfq_updated_next_req(bfqd, bfqq); } /* * Assign jiffies to last_wr_start_finish in the following * cases: * * . if bfqq is not going to be weight-raised, because, for * non weight-raised queues, last_wr_start_finish stores the * arrival time of the last request; as of now, this piece * of information is used only for deciding whether to * weight-raise async queues * * . if bfqq is not weight-raised, because, if bfqq is now * switching to weight-raised, then last_wr_start_finish * stores the time when weight-raising starts * * . if bfqq is interactive, because, regardless of whether * bfqq is currently weight-raised, the weight-raising * period must start or restart (this case is considered * separately because it is not detected by the above * conditions, if bfqq is already weight-raised) * * last_wr_start_finish has to be updated also if bfqq is soft * real-time, because the weight-raising period is constantly * restarted on idle-to-busy transitions for these queues, but * this is already done in bfq_bfqq_handle_idle_busy_switch if * needed. */ if (bfqd->low_latency && (old_wr_coeff == 1 || bfqq->wr_coeff == 1 || interactive)) bfqq->last_wr_start_finish = jiffies; } static struct request *bfq_find_rq_fmerge(struct bfq_data *bfqd, struct bio *bio, struct request_queue *q) { struct bfq_queue *bfqq = bfqd->bio_bfqq; if (bfqq) return elv_rb_find(&bfqq->sort_list, bio_end_sector(bio)); return NULL; } static sector_t get_sdist(sector_t last_pos, struct request *rq) { if (last_pos) return abs(blk_rq_pos(rq) - last_pos); return 0; } #if 0 /* Still not clear if we can do without next two functions */ static void bfq_activate_request(struct request_queue *q, struct request *rq) { struct bfq_data *bfqd = q->elevator->elevator_data; bfqd->rq_in_driver++; } static void bfq_deactivate_request(struct request_queue *q, struct request *rq) { struct bfq_data *bfqd = q->elevator->elevator_data; bfqd->rq_in_driver--; } #endif static void bfq_remove_request(struct request_queue *q, struct request *rq) { struct bfq_queue *bfqq = RQ_BFQQ(rq); struct bfq_data *bfqd = bfqq->bfqd; const int sync = rq_is_sync(rq); if (bfqq->next_rq == rq) { bfqq->next_rq = bfq_find_next_rq(bfqd, bfqq, rq); bfq_updated_next_req(bfqd, bfqq); } if (rq->queuelist.prev != &rq->queuelist) list_del_init(&rq->queuelist); bfqq->queued[sync]--; bfqd->queued--; elv_rb_del(&bfqq->sort_list, rq); elv_rqhash_del(q, rq); if (q->last_merge == rq) q->last_merge = NULL; if (RB_EMPTY_ROOT(&bfqq->sort_list)) { bfqq->next_rq = NULL; if (bfq_bfqq_busy(bfqq) && bfqq != bfqd->in_service_queue) { bfq_del_bfqq_busy(bfqd, bfqq, false); /* * bfqq emptied. In normal operation, when * bfqq is empty, bfqq->entity.service and * bfqq->entity.budget must contain, * respectively, the service received and the * budget used last time bfqq emptied. These * facts do not hold in this case, as at least * this last removal occurred while bfqq is * not in service. To avoid inconsistencies, * reset both bfqq->entity.service and * bfqq->entity.budget, if bfqq has still a * process that may issue I/O requests to it. */ bfqq->entity.budget = bfqq->entity.service = 0; } /* * Remove queue from request-position tree as it is empty. */ if (bfqq->pos_root) { rb_erase(&bfqq->pos_node, bfqq->pos_root); bfqq->pos_root = NULL; } } else { bfq_pos_tree_add_move(bfqd, bfqq); } if (rq->cmd_flags & REQ_META) bfqq->meta_pending--; } static bool bfq_bio_merge(struct blk_mq_hw_ctx *hctx, struct bio *bio) { struct request_queue *q = hctx->queue; struct bfq_data *bfqd = q->elevator->elevator_data; struct request *free = NULL; /* * bfq_bic_lookup grabs the queue_lock: invoke it now and * store its return value for later use, to avoid nesting * queue_lock inside the bfqd->lock. We assume that the bic * returned by bfq_bic_lookup does not go away before * bfqd->lock is taken. */ struct bfq_io_cq *bic = bfq_bic_lookup(bfqd, current->io_context, q); bool ret; spin_lock_irq(&bfqd->lock); if (bic) bfqd->bio_bfqq = bic_to_bfqq(bic, op_is_sync(bio->bi_opf)); else bfqd->bio_bfqq = NULL; bfqd->bio_bic = bic; ret = blk_mq_sched_try_merge(q, bio, &free); if (free) blk_mq_free_request(free); spin_unlock_irq(&bfqd->lock); return ret; } static int bfq_request_merge(struct request_queue *q, struct request **req, struct bio *bio) { struct bfq_data *bfqd = q->elevator->elevator_data; struct request *__rq; __rq = bfq_find_rq_fmerge(bfqd, bio, q); if (__rq && elv_bio_merge_ok(__rq, bio)) { *req = __rq; return ELEVATOR_FRONT_MERGE; } return ELEVATOR_NO_MERGE; } static struct bfq_queue *bfq_init_rq(struct request *rq); static void bfq_request_merged(struct request_queue *q, struct request *req, enum elv_merge type) { if (type == ELEVATOR_FRONT_MERGE && rb_prev(&req->rb_node) && blk_rq_pos(req) < blk_rq_pos(container_of(rb_prev(&req->rb_node), struct request, rb_node))) { struct bfq_queue *bfqq = bfq_init_rq(req); struct bfq_data *bfqd = bfqq->bfqd; struct request *prev, *next_rq; /* Reposition request in its sort_list */ elv_rb_del(&bfqq->sort_list, req); elv_rb_add(&bfqq->sort_list, req); /* Choose next request to be served for bfqq */ prev = bfqq->next_rq; next_rq = bfq_choose_req(bfqd, bfqq->next_rq, req, bfqd->last_position); bfqq->next_rq = next_rq; /* * If next_rq changes, update both the queue's budget to * fit the new request and the queue's position in its * rq_pos_tree. */ if (prev != bfqq->next_rq) { bfq_updated_next_req(bfqd, bfqq); bfq_pos_tree_add_move(bfqd, bfqq); } } } /* * This function is called to notify the scheduler that the requests * rq and 'next' have been merged, with 'next' going away. BFQ * exploits this hook to address the following issue: if 'next' has a * fifo_time lower that rq, then the fifo_time of rq must be set to * the value of 'next', to not forget the greater age of 'next'. * * NOTE: in this function we assume that rq is in a bfq_queue, basing * on that rq is picked from the hash table q->elevator->hash, which, * in its turn, is filled only with I/O requests present in * bfq_queues, while BFQ is in use for the request queue q. In fact, * the function that fills this hash table (elv_rqhash_add) is called * only by bfq_insert_request. */ static void bfq_requests_merged(struct request_queue *q, struct request *rq, struct request *next) { struct bfq_queue *bfqq = bfq_init_rq(rq), *next_bfqq = bfq_init_rq(next); /* * If next and rq belong to the same bfq_queue and next is older * than rq, then reposition rq in the fifo (by substituting next * with rq). Otherwise, if next and rq belong to different * bfq_queues, never reposition rq: in fact, we would have to * reposition it with respect to next's position in its own fifo, * which would most certainly be too expensive with respect to * the benefits. */ if (bfqq == next_bfqq && !list_empty(&rq->queuelist) && !list_empty(&next->queuelist) && next->fifo_time < rq->fifo_time) { list_del_init(&rq->queuelist); list_replace_init(&next->queuelist, &rq->queuelist); rq->fifo_time = next->fifo_time; } if (bfqq->next_rq == next) bfqq->next_rq = rq; bfqg_stats_update_io_merged(bfqq_group(bfqq), next->cmd_flags); } /* Must be called with bfqq != NULL */ static void bfq_bfqq_end_wr(struct bfq_queue *bfqq) { if (bfq_bfqq_busy(bfqq)) bfqq->bfqd->wr_busy_queues--; bfqq->wr_coeff = 1; bfqq->wr_cur_max_time = 0; bfqq->last_wr_start_finish = jiffies; /* * Trigger a weight change on the next invocation of * __bfq_entity_update_weight_prio. */ bfqq->entity.prio_changed = 1; } void bfq_end_wr_async_queues(struct bfq_data *bfqd, struct bfq_group *bfqg) { int i, j; for (i = 0; i < 2; i++) for (j = 0; j < IOPRIO_BE_NR; j++) if (bfqg->async_bfqq[i][j]) bfq_bfqq_end_wr(bfqg->async_bfqq[i][j]); if (bfqg->async_idle_bfqq) bfq_bfqq_end_wr(bfqg->async_idle_bfqq); } static void bfq_end_wr(struct bfq_data *bfqd) { struct bfq_queue *bfqq; spin_lock_irq(&bfqd->lock); list_for_each_entry(bfqq, &bfqd->active_list, bfqq_list) bfq_bfqq_end_wr(bfqq); list_for_each_entry(bfqq, &bfqd->idle_list, bfqq_list) bfq_bfqq_end_wr(bfqq); bfq_end_wr_async(bfqd); spin_unlock_irq(&bfqd->lock); } static sector_t bfq_io_struct_pos(void *io_struct, bool request) { if (request) return blk_rq_pos(io_struct); else return ((struct bio *)io_struct)->bi_iter.bi_sector; } static int bfq_rq_close_to_sector(void *io_struct, bool request, sector_t sector) { return abs(bfq_io_struct_pos(io_struct, request) - sector) <= BFQQ_CLOSE_THR; } static struct bfq_queue *bfqq_find_close(struct bfq_data *bfqd, struct bfq_queue *bfqq, sector_t sector) { struct rb_root *root = &bfq_bfqq_to_bfqg(bfqq)->rq_pos_tree; struct rb_node *parent, *node; struct bfq_queue *__bfqq; if (RB_EMPTY_ROOT(root)) return NULL; /* * First, if we find a request starting at the end of the last * request, choose it. */ __bfqq = bfq_rq_pos_tree_lookup(bfqd, root, sector, &parent, NULL); if (__bfqq) return __bfqq; /* * If the exact sector wasn't found, the parent of the NULL leaf * will contain the closest sector (rq_pos_tree sorted by * next_request position). */ __bfqq = rb_entry(parent, struct bfq_queue, pos_node); if (bfq_rq_close_to_sector(__bfqq->next_rq, true, sector)) return __bfqq; if (blk_rq_pos(__bfqq->next_rq) < sector) node = rb_next(&__bfqq->pos_node); else node = rb_prev(&__bfqq->pos_node); if (!node) return NULL; __bfqq = rb_entry(node, struct bfq_queue, pos_node); if (bfq_rq_close_to_sector(__bfqq->next_rq, true, sector)) return __bfqq; return NULL; } static struct bfq_queue *bfq_find_close_cooperator(struct bfq_data *bfqd, struct bfq_queue *cur_bfqq, sector_t sector) { struct bfq_queue *bfqq; /* * We shall notice if some of the queues are cooperating, * e.g., working closely on the same area of the device. In * that case, we can group them together and: 1) don't waste * time idling, and 2) serve the union of their requests in * the best possible order for throughput. */ bfqq = bfqq_find_close(bfqd, cur_bfqq, sector); if (!bfqq || bfqq == cur_bfqq) return NULL; return bfqq; } static struct bfq_queue * bfq_setup_merge(struct bfq_queue *bfqq, struct bfq_queue *new_bfqq) { int process_refs, new_process_refs; struct bfq_queue *__bfqq; /* * If there are no process references on the new_bfqq, then it is * unsafe to follow the ->new_bfqq chain as other bfqq's in the chain * may have dropped their last reference (not just their last process * reference). */ if (!bfqq_process_refs(new_bfqq)) return NULL; /* Avoid a circular list and skip interim queue merges. */ while ((__bfqq = new_bfqq->new_bfqq)) { if (__bfqq == bfqq) return NULL; new_bfqq = __bfqq; } process_refs = bfqq_process_refs(bfqq); new_process_refs = bfqq_process_refs(new_bfqq); /* * If the process for the bfqq has gone away, there is no * sense in merging the queues. */ if (process_refs == 0 || new_process_refs == 0) return NULL; bfq_log_bfqq(bfqq->bfqd, bfqq, "scheduling merge with queue %d", new_bfqq->pid); /* * Merging is just a redirection: the requests of the process * owning one of the two queues are redirected to the other queue. * The latter queue, in its turn, is set as shared if this is the * first time that the requests of some process are redirected to * it. * * We redirect bfqq to new_bfqq and not the opposite, because * we are in the context of the process owning bfqq, thus we * have the io_cq of this process. So we can immediately * configure this io_cq to redirect the requests of the * process to new_bfqq. In contrast, the io_cq of new_bfqq is * not available any more (new_bfqq->bic == NULL). * * Anyway, even in case new_bfqq coincides with the in-service * queue, redirecting requests the in-service queue is the * best option, as we feed the in-service queue with new * requests close to the last request served and, by doing so, * are likely to increase the throughput. */ bfqq->new_bfqq = new_bfqq; new_bfqq->ref += process_refs; return new_bfqq; } static bool bfq_may_be_close_cooperator(struct bfq_queue *bfqq, struct bfq_queue *new_bfqq) { if (bfq_too_late_for_merging(new_bfqq)) return false; if (bfq_class_idle(bfqq) || bfq_class_idle(new_bfqq) || (bfqq->ioprio_class != new_bfqq->ioprio_class)) return false; /* * If either of the queues has already been detected as seeky, * then merging it with the other queue is unlikely to lead to * sequential I/O. */ if (BFQQ_SEEKY(bfqq) || BFQQ_SEEKY(new_bfqq)) return false; /* * Interleaved I/O is known to be done by (some) applications * only for reads, so it does not make sense to merge async * queues. */ if (!bfq_bfqq_sync(bfqq) || !bfq_bfqq_sync(new_bfqq)) return false; return true; } /* * Attempt to schedule a merge of bfqq with the currently in-service * queue or with a close queue among the scheduled queues. Return * NULL if no merge was scheduled, a pointer to the shared bfq_queue * structure otherwise. * * The OOM queue is not allowed to participate to cooperation: in fact, since * the requests temporarily redirected to the OOM queue could be redirected * again to dedicated queues at any time, the state needed to correctly * handle merging with the OOM queue would be quite complex and expensive * to maintain. Besides, in such a critical condition as an out of memory, * the benefits of queue merging may be little relevant, or even negligible. * * WARNING: queue merging may impair fairness among non-weight raised * queues, for at least two reasons: 1) the original weight of a * merged queue may change during the merged state, 2) even being the * weight the same, a merged queue may be bloated with many more * requests than the ones produced by its originally-associated * process. */ static struct bfq_queue * bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq, void *io_struct, bool request) { struct bfq_queue *in_service_bfqq, *new_bfqq; /* * Prevent bfqq from being merged if it has been created too * long ago. The idea is that true cooperating processes, and * thus their associated bfq_queues, are supposed to be * created shortly after each other. This is the case, e.g., * for KVM/QEMU and dump I/O threads. Basing on this * assumption, the following filtering greatly reduces the * probability that two non-cooperating processes, which just * happen to do close I/O for some short time interval, have * their queues merged by mistake. */ if (bfq_too_late_for_merging(bfqq)) return NULL; if (bfqq->new_bfqq) return bfqq->new_bfqq; if (!io_struct || unlikely(bfqq == &bfqd->oom_bfqq)) return NULL; /* If there is only one backlogged queue, don't search. */ if (bfqd->busy_queues == 1) return NULL; in_service_bfqq = bfqd->in_service_queue; if (in_service_bfqq && in_service_bfqq != bfqq && likely(in_service_bfqq != &bfqd->oom_bfqq) && bfq_rq_close_to_sector(io_struct, request, bfqd->last_position) && bfqq->entity.parent == in_service_bfqq->entity.parent && bfq_may_be_close_cooperator(bfqq, in_service_bfqq)) { new_bfqq = bfq_setup_merge(bfqq, in_service_bfqq); if (new_bfqq) return new_bfqq; } /* * Check whether there is a cooperator among currently scheduled * queues. The only thing we need is that the bio/request is not * NULL, as we need it to establish whether a cooperator exists. */ new_bfqq = bfq_find_close_cooperator(bfqd, bfqq, bfq_io_struct_pos(io_struct, request)); if (new_bfqq && likely(new_bfqq != &bfqd->oom_bfqq) && bfq_may_be_close_cooperator(bfqq, new_bfqq)) return bfq_setup_merge(bfqq, new_bfqq); return NULL; } static void bfq_bfqq_save_state(struct bfq_queue *bfqq) { struct bfq_io_cq *bic = bfqq->bic; /* * If !bfqq->bic, the queue is already shared or its requests * have already been redirected to a shared queue; both idle window * and weight raising state have already been saved. Do nothing. */ if (!bic) return; bic->saved_ttime = bfqq->ttime; bic->saved_has_short_ttime = bfq_bfqq_has_short_ttime(bfqq); bic->saved_IO_bound = bfq_bfqq_IO_bound(bfqq); bic->saved_in_large_burst = bfq_bfqq_in_large_burst(bfqq); bic->was_in_burst_list = !hlist_unhashed(&bfqq->burst_list_node); if (unlikely(bfq_bfqq_just_created(bfqq) && !bfq_bfqq_in_large_burst(bfqq) && bfqq->bfqd->low_latency)) { /* * bfqq being merged right after being created: bfqq * would have deserved interactive weight raising, but * did not make it to be set in a weight-raised state, * because of this early merge. Store directly the * weight-raising state that would have been assigned * to bfqq, so that to avoid that bfqq unjustly fails * to enjoy weight raising if split soon. */ bic->saved_wr_coeff = bfqq->bfqd->bfq_wr_coeff; bic->saved_wr_cur_max_time = bfq_wr_duration(bfqq->bfqd); bic->saved_last_wr_start_finish = jiffies; } else { bic->saved_wr_coeff = bfqq->wr_coeff; bic->saved_wr_start_at_switch_to_srt = bfqq->wr_start_at_switch_to_srt; bic->saved_last_wr_start_finish = bfqq->last_wr_start_finish; bic->saved_wr_cur_max_time = bfqq->wr_cur_max_time; } } static void bfq_merge_bfqqs(struct bfq_data *bfqd, struct bfq_io_cq *bic, struct bfq_queue *bfqq, struct bfq_queue *new_bfqq) { bfq_log_bfqq(bfqd, bfqq, "merging with queue %lu", (unsigned long)new_bfqq->pid); /* Save weight raising and idle window of the merged queues */ bfq_bfqq_save_state(bfqq); bfq_bfqq_save_state(new_bfqq); if (bfq_bfqq_IO_bound(bfqq)) bfq_mark_bfqq_IO_bound(new_bfqq); bfq_clear_bfqq_IO_bound(bfqq); /* * If bfqq is weight-raised, then let new_bfqq inherit * weight-raising. To reduce false positives, neglect the case * where bfqq has just been created, but has not yet made it * to be weight-raised (which may happen because EQM may merge * bfqq even before bfq_add_request is executed for the first * time for bfqq). Handling this case would however be very * easy, thanks to the flag just_created. */ if (new_bfqq->wr_coeff == 1 && bfqq->wr_coeff > 1) { new_bfqq->wr_coeff = bfqq->wr_coeff; new_bfqq->wr_cur_max_time = bfqq->wr_cur_max_time; new_bfqq->last_wr_start_finish = bfqq->last_wr_start_finish; new_bfqq->wr_start_at_switch_to_srt = bfqq->wr_start_at_switch_to_srt; if (bfq_bfqq_busy(new_bfqq)) bfqd->wr_busy_queues++; new_bfqq->entity.prio_changed = 1; } if (bfqq->wr_coeff > 1) { /* bfqq has given its wr to new_bfqq */ bfqq->wr_coeff = 1; bfqq->entity.prio_changed = 1; if (bfq_bfqq_busy(bfqq)) bfqd->wr_busy_queues--; } bfq_log_bfqq(bfqd, new_bfqq, "merge_bfqqs: wr_busy %d", bfqd->wr_busy_queues); /* * Merge queues (that is, let bic redirect its requests to new_bfqq) */ bic_set_bfqq(bic, new_bfqq, 1); bfq_mark_bfqq_coop(new_bfqq); /* * new_bfqq now belongs to at least two bics (it is a shared queue): * set new_bfqq->bic to NULL. bfqq either: * - does not belong to any bic any more, and hence bfqq->bic must * be set to NULL, or * - is a queue whose owning bics have already been redirected to a * different queue, hence the queue is destined to not belong to * any bic soon and bfqq->bic is already NULL (therefore the next * assignment causes no harm). */ new_bfqq->bic = NULL; bfqq->bic = NULL; /* release process reference to bfqq */ bfq_put_queue(bfqq); } static bool bfq_allow_bio_merge(struct request_queue *q, struct request *rq, struct bio *bio) { struct bfq_data *bfqd = q->elevator->elevator_data; bool is_sync = op_is_sync(bio->bi_opf); struct bfq_queue *bfqq = bfqd->bio_bfqq, *new_bfqq; /* * Disallow merge of a sync bio into an async request. */ if (is_sync && !rq_is_sync(rq)) return false; /* * Lookup the bfqq that this bio will be queued with. Allow * merge only if rq is queued there. */ if (!bfqq) return false; /* * We take advantage of this function to perform an early merge * of the queues of possible cooperating processes. */ new_bfqq = bfq_setup_cooperator(bfqd, bfqq, bio, false); if (new_bfqq) { /* * bic still points to bfqq, then it has not yet been * redirected to some other bfq_queue, and a queue * merge beween bfqq and new_bfqq can be safely * fulfillled, i.e., bic can be redirected to new_bfqq * and bfqq can be put. */ bfq_merge_bfqqs(bfqd, bfqd->bio_bic, bfqq, new_bfqq); /* * If we get here, bio will be queued into new_queue, * so use new_bfqq to decide whether bio and rq can be * merged. */ bfqq = new_bfqq; /* * Change also bqfd->bio_bfqq, as * bfqd->bio_bic now points to new_bfqq, and * this function may be invoked again (and then may * use again bqfd->bio_bfqq). */ bfqd->bio_bfqq = bfqq; } return bfqq == RQ_BFQQ(rq); } /* * Set the maximum time for the in-service queue to consume its * budget. This prevents seeky processes from lowering the throughput. * In practice, a time-slice service scheme is used with seeky * processes. */ static void bfq_set_budget_timeout(struct bfq_data *bfqd, struct bfq_queue *bfqq) { unsigned int timeout_coeff; if (bfqq->wr_cur_max_time == bfqd->bfq_wr_rt_max_time) timeout_coeff = 1; else timeout_coeff = bfqq->entity.weight / bfqq->entity.orig_weight; bfqd->last_budget_start = ktime_get(); bfqq->budget_timeout = jiffies + bfqd->bfq_timeout * timeout_coeff; } static void __bfq_set_in_service_queue(struct bfq_data *bfqd, struct bfq_queue *bfqq) { if (bfqq) { bfq_clear_bfqq_fifo_expire(bfqq); bfqd->budgets_assigned = (bfqd->budgets_assigned * 7 + 256) / 8; if (time_is_before_jiffies(bfqq->last_wr_start_finish) && bfqq->wr_coeff > 1 && bfqq->wr_cur_max_time == bfqd->bfq_wr_rt_max_time && time_is_before_jiffies(bfqq->budget_timeout)) { /* * For soft real-time queues, move the start * of the weight-raising period forward by the * time the queue has not received any * service. Otherwise, a relatively long * service delay is likely to cause the * weight-raising period of the queue to end, * because of the short duration of the * weight-raising period of a soft real-time * queue. It is worth noting that this move * is not so dangerous for the other queues, * because soft real-time queues are not * greedy. * * To not add a further variable, we use the * overloaded field budget_timeout to * determine for how long the queue has not * received service, i.e., how much time has * elapsed since the queue expired. However, * this is a little imprecise, because * budget_timeout is set to jiffies if bfqq * not only expires, but also remains with no * request. */ if (time_after(bfqq->budget_timeout, bfqq->last_wr_start_finish)) bfqq->last_wr_start_finish += jiffies - bfqq->budget_timeout; else bfqq->last_wr_start_finish = jiffies; } bfq_set_budget_timeout(bfqd, bfqq); bfq_log_bfqq(bfqd, bfqq, "set_in_service_queue, cur-budget = %d", bfqq->entity.budget); } bfqd->in_service_queue = bfqq; } /* * Get and set a new queue for service. */ static struct bfq_queue *bfq_set_in_service_queue(struct bfq_data *bfqd) { struct bfq_queue *bfqq = bfq_get_next_queue(bfqd); __bfq_set_in_service_queue(bfqd, bfqq); return bfqq; } static void bfq_arm_slice_timer(struct bfq_data *bfqd) { struct bfq_queue *bfqq = bfqd->in_service_queue; u32 sl; bfq_mark_bfqq_wait_request(bfqq); /* * We don't want to idle for seeks, but we do want to allow * fair distribution of slice time for a process doing back-to-back * seeks. So allow a little bit of time for him to submit a new rq. */ sl = bfqd->bfq_slice_idle; /* * Unless the queue is being weight-raised or the scenario is * asymmetric, grant only minimum idle time if the queue * is seeky. A long idling is preserved for a weight-raised * queue, or, more in general, in an asymmetric scenario, * because a long idling is needed for guaranteeing to a queue * its reserved share of the throughput (in particular, it is * needed if the queue has a higher weight than some other * queue). */ if (BFQQ_SEEKY(bfqq) && bfqq->wr_coeff == 1 && bfq_symmetric_scenario(bfqd)) sl = min_t(u64, sl, BFQ_MIN_TT); bfqd->last_idling_start = ktime_get(); hrtimer_start(&bfqd->idle_slice_timer, ns_to_ktime(sl), HRTIMER_MODE_REL); bfqg_stats_set_start_idle_time(bfqq_group(bfqq)); } /* * In autotuning mode, max_budget is dynamically recomputed as the * amount of sectors transferred in timeout at the estimated peak * rate. This enables BFQ to utilize a full timeslice with a full * budget, even if the in-service queue is served at peak rate. And * this maximises throughput with sequential workloads. */ static unsigned long bfq_calc_max_budget(struct bfq_data *bfqd) { return (u64)bfqd->peak_rate * USEC_PER_MSEC * jiffies_to_msecs(bfqd->bfq_timeout)>>BFQ_RATE_SHIFT; } /* * Update parameters related to throughput and responsiveness, as a * function of the estimated peak rate. See comments on * bfq_calc_max_budget(), and on the ref_wr_duration array. */ static void update_thr_responsiveness_params(struct bfq_data *bfqd) { if (bfqd->bfq_user_max_budget == 0) { bfqd->bfq_max_budget = bfq_calc_max_budget(bfqd); bfq_log(bfqd, "new max_budget = %d", bfqd->bfq_max_budget); } } static void bfq_reset_rate_computation(struct bfq_data *bfqd, struct request *rq) { if (rq != NULL) { /* new rq dispatch now, reset accordingly */ bfqd->last_dispatch = bfqd->first_dispatch = ktime_get_ns(); bfqd->peak_rate_samples = 1; bfqd->sequential_samples = 0; bfqd->tot_sectors_dispatched = bfqd->last_rq_max_size = blk_rq_sectors(rq); } else /* no new rq dispatched, just reset the number of samples */ bfqd->peak_rate_samples = 0; /* full re-init on next disp. */ bfq_log(bfqd, "reset_rate_computation at end, sample %u/%u tot_sects %llu", bfqd->peak_rate_samples, bfqd->sequential_samples, bfqd->tot_sectors_dispatched); } static void bfq_update_rate_reset(struct bfq_data *bfqd, struct request *rq) { u32 rate, weight, divisor; /* * For the convergence property to hold (see comments on * bfq_update_peak_rate()) and for the assessment to be * reliable, a minimum number of samples must be present, and * a minimum amount of time must have elapsed. If not so, do * not compute new rate. Just reset parameters, to get ready * for a new evaluation attempt. */ if (bfqd->peak_rate_samples < BFQ_RATE_MIN_SAMPLES || bfqd->delta_from_first < BFQ_RATE_MIN_INTERVAL) goto reset_computation; /* * If a new request completion has occurred after last * dispatch, then, to approximate the rate at which requests * have been served by the device, it is more precise to * extend the observation interval to the last completion. */ bfqd->delta_from_first = max_t(u64, bfqd->delta_from_first, bfqd->last_completion - bfqd->first_dispatch); /* * Rate computed in sects/usec, and not sects/nsec, for * precision issues. */ rate = div64_ul(bfqd->tot_sectors_dispatched<<BFQ_RATE_SHIFT, div_u64(bfqd->delta_from_first, NSEC_PER_USEC)); /* * Peak rate not updated if: * - the percentage of sequential dispatches is below 3/4 of the * total, and rate is below the current estimated peak rate * - rate is unreasonably high (> 20M sectors/sec) */ if ((bfqd->sequential_samples < (3 * bfqd->peak_rate_samples)>>2 && rate <= bfqd->peak_rate) || rate > 20<<BFQ_RATE_SHIFT) goto reset_computation; /* * We have to update the peak rate, at last! To this purpose, * we use a low-pass filter. We compute the smoothing constant * of the filter as a function of the 'weight' of the new * measured rate. * * As can be seen in next formulas, we define this weight as a * quantity proportional to how sequential the workload is, * and to how long the observation time interval is. * * The weight runs from 0 to 8. The maximum value of the * weight, 8, yields the minimum value for the smoothing * constant. At this minimum value for the smoothing constant, * the measured rate contributes for half of the next value of * the estimated peak rate. * * So, the first step is to compute the weight as a function * of how sequential the workload is. Note that the weight * cannot reach 9, because bfqd->sequential_samples cannot * become equal to bfqd->peak_rate_samples, which, in its * turn, holds true because bfqd->sequential_samples is not * incremented for the first sample. */ weight = (9 * bfqd->sequential_samples) / bfqd->peak_rate_samples; /* * Second step: further refine the weight as a function of the * duration of the observation interval. */ weight = min_t(u32, 8, div_u64(weight * bfqd->delta_from_first, BFQ_RATE_REF_INTERVAL)); /* * Divisor ranging from 10, for minimum weight, to 2, for * maximum weight. */ divisor = 10 - weight; /* * Finally, update peak rate: * * peak_rate = peak_rate * (divisor-1) / divisor + rate / divisor */ bfqd->peak_rate *= divisor-1; bfqd->peak_rate /= divisor; rate /= divisor; /* smoothing constant alpha = 1/divisor */ bfqd->peak_rate += rate; /* * For a very slow device, bfqd->peak_rate can reach 0 (see * the minimum representable values reported in the comments * on BFQ_RATE_SHIFT). Push to 1 if this happens, to avoid * divisions by zero where bfqd->peak_rate is used as a * divisor. */ bfqd->peak_rate = max_t(u32, 1, bfqd->peak_rate); update_thr_responsiveness_params(bfqd); reset_computation: bfq_reset_rate_computation(bfqd, rq); } /* * Update the read/write peak rate (the main quantity used for * auto-tuning, see update_thr_responsiveness_params()). * * It is not trivial to estimate the peak rate (correctly): because of * the presence of sw and hw queues between the scheduler and the * device components that finally serve I/O requests, it is hard to * say exactly when a given dispatched request is served inside the * device, and for how long. As a consequence, it is hard to know * precisely at what rate a given set of requests is actually served * by the device. * * On the opposite end, the dispatch time of any request is trivially * available, and, from this piece of information, the "dispatch rate" * of requests can be immediately computed. So, the idea in the next * function is to use what is known, namely request dispatch times * (plus, when useful, request completion times), to estimate what is * unknown, namely in-device request service rate. * * The main issue is that, because of the above facts, the rate at * which a certain set of requests is dispatched over a certain time * interval can vary greatly with respect to the rate at which the * same requests are then served. But, since the size of any * intermediate queue is limited, and the service scheme is lossless * (no request is silently dropped), the following obvious convergence * property holds: the number of requests dispatched MUST become * closer and closer to the number of requests completed as the * observation interval grows. This is the key property used in * the next function to estimate the peak service rate as a function * of the observed dispatch rate. The function assumes to be invoked * on every request dispatch. */ static void bfq_update_peak_rate(struct bfq_data *bfqd, struct request *rq) { u64 now_ns = ktime_get_ns(); if (bfqd->peak_rate_samples == 0) { /* first dispatch */ bfq_log(bfqd, "update_peak_rate: goto reset, samples %d", bfqd->peak_rate_samples); bfq_reset_rate_computation(bfqd, rq); goto update_last_values; /* will add one sample */ } /* * Device idle for very long: the observation interval lasting * up to this dispatch cannot be a valid observation interval * for computing a new peak rate (similarly to the late- * completion event in bfq_completed_request()). Go to * update_rate_and_reset to have the following three steps * taken: * - close the observation interval at the last (previous) * request dispatch or completion * - compute rate, if possible, for that observation interval * - start a new observation interval with this dispatch */ if (now_ns - bfqd->last_dispatch > 100*NSEC_PER_MSEC && bfqd->rq_in_driver == 0) goto update_rate_and_reset; /* Update sampling information */ bfqd->peak_rate_samples++; if ((bfqd->rq_in_driver > 0 || now_ns - bfqd->last_completion < BFQ_MIN_TT) && get_sdist(bfqd->last_position, rq) < BFQQ_SEEK_THR) bfqd->sequential_samples++; bfqd->tot_sectors_dispatched += blk_rq_sectors(rq); /* Reset max observed rq size every 32 dispatches */ if (likely(bfqd->peak_rate_samples % 32)) bfqd->last_rq_max_size = max_t(u32, blk_rq_sectors(rq), bfqd->last_rq_max_size); else bfqd->last_rq_max_size = blk_rq_sectors(rq); bfqd->delta_from_first = now_ns - bfqd->first_dispatch; /* Target observation interval not yet reached, go on sampling */ if (bfqd->delta_from_first < BFQ_RATE_REF_INTERVAL) goto update_last_values; update_rate_and_reset: bfq_update_rate_reset(bfqd, rq); update_last_values: bfqd->last_position = blk_rq_pos(rq) + blk_rq_sectors(rq); bfqd->last_dispatch = now_ns; } /* * Remove request from internal lists. */ static void bfq_dispatch_remove(struct request_queue *q, struct request *rq) { struct bfq_queue *bfqq = RQ_BFQQ(rq); /* * For consistency, the next instruction should have been * executed after removing the request from the queue and * dispatching it. We execute instead this instruction before * bfq_remove_request() (and hence introduce a temporary * inconsistency), for efficiency. In fact, should this * dispatch occur for a non in-service bfqq, this anticipated * increment prevents two counters related to bfqq->dispatched * from risking to be, first, uselessly decremented, and then * incremented again when the (new) value of bfqq->dispatched * happens to be taken into account. */ bfqq->dispatched++; bfq_update_peak_rate(q->elevator->elevator_data, rq); bfq_remove_request(q, rq); } static void __bfq_bfqq_expire(struct bfq_data *bfqd, struct bfq_queue *bfqq) { /* * If this bfqq is shared between multiple processes, check * to make sure that those processes are still issuing I/Os * within the mean seek distance. If not, it may be time to * break the queues apart again. */ if (bfq_bfqq_coop(bfqq) && BFQQ_SEEKY(bfqq)) bfq_mark_bfqq_split_coop(bfqq); if (RB_EMPTY_ROOT(&bfqq->sort_list)) { if (bfqq->dispatched == 0) /* * Overloading budget_timeout field to store * the time at which the queue remains with no * backlog and no outstanding request; used by * the weight-raising mechanism. */ bfqq->budget_timeout = jiffies; bfq_del_bfqq_busy(bfqd, bfqq, true); } else { bfq_requeue_bfqq(bfqd, bfqq, true); /* * Resort priority tree of potential close cooperators. */ bfq_pos_tree_add_move(bfqd, bfqq); } /* * All in-service entities must have been properly deactivated * or requeued before executing the next function, which * resets all in-service entites as no more in service. */ __bfq_bfqd_reset_in_service(bfqd); } /** * __bfq_bfqq_recalc_budget - try to adapt the budget to the @bfqq behavior. * @bfqd: device data. * @bfqq: queue to update. * @reason: reason for expiration. * * Handle the feedback on @bfqq budget at queue expiration. * See the body for detailed comments. */ static void __bfq_bfqq_recalc_budget(struct bfq_data *bfqd, struct bfq_queue *bfqq, enum bfqq_expiration reason) { struct request *next_rq; int budget, min_budget; min_budget = bfq_min_budget(bfqd); if (bfqq->wr_coeff == 1) budget = bfqq->max_budget; else /* * Use a constant, low budget for weight-raised queues, * to help achieve a low latency. Keep it slightly higher * than the minimum possible budget, to cause a little * bit fewer expirations. */ budget = 2 * min_budget; bfq_log_bfqq(bfqd, bfqq, "recalc_budg: last budg %d, budg left %d", bfqq->entity.budget, bfq_bfqq_budget_left(bfqq)); bfq_log_bfqq(bfqd, bfqq, "recalc_budg: last max_budg %d, min budg %d", budget, bfq_min_budget(bfqd)); bfq_log_bfqq(bfqd, bfqq, "recalc_budg: sync %d, seeky %d", bfq_bfqq_sync(bfqq), BFQQ_SEEKY(bfqd->in_service_queue)); if (bfq_bfqq_sync(bfqq) && bfqq->wr_coeff == 1) { switch (reason) { /* * Caveat: in all the following cases we trade latency * for throughput. */ case BFQQE_TOO_IDLE: /* * This is the only case where we may reduce * the budget: if there is no request of the * process still waiting for completion, then * we assume (tentatively) that the timer has * expired because the batch of requests of * the process could have been served with a * smaller budget. Hence, betting that * process will behave in the same way when it * becomes backlogged again, we reduce its * next budget. As long as we guess right, * this budget cut reduces the latency * experienced by the process. * * However, if there are still outstanding * requests, then the process may have not yet * issued its next request just because it is * still waiting for the completion of some of * the still outstanding ones. So in this * subcase we do not reduce its budget, on the * contrary we increase it to possibly boost * the throughput, as discussed in the * comments to the BUDGET_TIMEOUT case. */ if (bfqq->dispatched > 0) /* still outstanding reqs */ budget = min(budget * 2, bfqd->bfq_max_budget); else { if (budget > 5 * min_budget) budget -= 4 * min_budget; else budget = min_budget; } break; case BFQQE_BUDGET_TIMEOUT: /* * We double the budget here because it gives * the chance to boost the throughput if this * is not a seeky process (and has bumped into * this timeout because of, e.g., ZBR). */ budget = min(budget * 2, bfqd->bfq_max_budget); break; case BFQQE_BUDGET_EXHAUSTED: /* * The process still has backlog, and did not * let either the budget timeout or the disk * idling timeout expire. Hence it is not * seeky, has a short thinktime and may be * happy with a higher budget too. So * definitely increase the budget of this good * candidate to boost the disk throughput. */ budget = min(budget * 4, bfqd->bfq_max_budget); break; case BFQQE_NO_MORE_REQUESTS: /* * For queues that expire for this reason, it * is particularly important to keep the * budget close to the actual service they * need. Doing so reduces the timestamp * misalignment problem described in the * comments in the body of * __bfq_activate_entity. In fact, suppose * that a queue systematically expires for * BFQQE_NO_MORE_REQUESTS and presents a * new request in time to enjoy timestamp * back-shifting. The larger the budget of the * queue is with respect to the service the * queue actually requests in each service * slot, the more times the queue can be * reactivated with the same virtual finish * time. It follows that, even if this finish * time is pushed to the system virtual time * to reduce the consequent timestamp * misalignment, the queue unjustly enjoys for * many re-activations a lower finish time * than all newly activated queues. * * The service needed by bfqq is measured * quite precisely by bfqq->entity.service. * Since bfqq does not enjoy device idling, * bfqq->entity.service is equal to the number * of sectors that the process associated with * bfqq requested to read/write before waiting * for request completions, or blocking for * other reasons. */ budget = max_t(int, bfqq->entity.service, min_budget); break; default: return; } } else if (!bfq_bfqq_sync(bfqq)) { /* * Async queues get always the maximum possible * budget, as for them we do not care about latency * (in addition, their ability to dispatch is limited * by the charging factor). */ budget = bfqd->bfq_max_budget; } bfqq->max_budget = budget; if (bfqd->budgets_assigned >= bfq_stats_min_budgets && !bfqd->bfq_user_max_budget) bfqq->max_budget = min(bfqq->max_budget, bfqd->bfq_max_budget); /* * If there is still backlog, then assign a new budget, making * sure that it is large enough for the next request. Since * the finish time of bfqq must be kept in sync with the * budget, be sure to call __bfq_bfqq_expire() *after* this * update. * * If there is no backlog, then no need to update the budget; * it will be updated on the arrival of a new request. */ next_rq = bfqq->next_rq; if (next_rq) bfqq->entity.budget = max_t(unsigned long, bfqq->max_budget, bfq_serv_to_charge(next_rq, bfqq)); bfq_log_bfqq(bfqd, bfqq, "head sect: %u, new budget %d", next_rq ? blk_rq_sectors(next_rq) : 0, bfqq->entity.budget); } /* * Return true if the process associated with bfqq is "slow". The slow * flag is used, in addition to the budget timeout, to reduce the * amount of service provided to seeky processes, and thus reduce * their chances to lower the throughput. More details in the comments * on the function bfq_bfqq_expire(). * * An important observation is in order: as discussed in the comments * on the function bfq_update_peak_rate(), with devices with internal * queues, it is hard if ever possible to know when and for how long * an I/O request is processed by the device (apart from the trivial * I/O pattern where a new request is dispatched only after the * previous one has been completed). This makes it hard to evaluate * the real rate at which the I/O requests of each bfq_queue are * served. In fact, for an I/O scheduler like BFQ, serving a * bfq_queue means just dispatching its requests during its service * slot (i.e., until the budget of the queue is exhausted, or the * queue remains idle, or, finally, a timeout fires). But, during the * service slot of a bfq_queue, around 100 ms at most, the device may * be even still processing requests of bfq_queues served in previous * service slots. On the opposite end, the requests of the in-service * bfq_queue may be completed after the service slot of the queue * finishes. * * Anyway, unless more sophisticated solutions are used * (where possible), the sum of the sizes of the requests dispatched * during the service slot of a bfq_queue is probably the only * approximation available for the service received by the bfq_queue * during its service slot. And this sum is the quantity used in this * function to evaluate the I/O speed of a process. */ static bool bfq_bfqq_is_slow(struct bfq_data *bfqd, struct bfq_queue *bfqq, bool compensate, enum bfqq_expiration reason, unsigned long *delta_ms) { ktime_t delta_ktime; u32 delta_usecs; bool slow = BFQQ_SEEKY(bfqq); /* if delta too short, use seekyness */ if (!bfq_bfqq_sync(bfqq)) return false; if (compensate) delta_ktime = bfqd->last_idling_start; else delta_ktime = ktime_get(); delta_ktime = ktime_sub(delta_ktime, bfqd->last_budget_start); delta_usecs = ktime_to_us(delta_ktime); /* don't use too short time intervals */ if (delta_usecs < 1000) { if (blk_queue_nonrot(bfqd->queue)) /* * give same worst-case guarantees as idling * for seeky */ *delta_ms = BFQ_MIN_TT / NSEC_PER_MSEC; else /* charge at least one seek */ *delta_ms = bfq_slice_idle / NSEC_PER_MSEC; return slow; } *delta_ms = delta_usecs / USEC_PER_MSEC; /* * Use only long (> 20ms) intervals to filter out excessive * spikes in service rate estimation. */ if (delta_usecs > 20000) { /* * Caveat for rotational devices: processes doing I/O * in the slower disk zones tend to be slow(er) even * if not seeky. In this respect, the estimated peak * rate is likely to be an average over the disk * surface. Accordingly, to not be too harsh with * unlucky processes, a process is deemed slow only if * its rate has been lower than half of the estimated * peak rate. */ slow = bfqq->entity.service < bfqd->bfq_max_budget / 2; } bfq_log_bfqq(bfqd, bfqq, "bfq_bfqq_is_slow: slow %d", slow); return slow; } /* * To be deemed as soft real-time, an application must meet two * requirements. First, the application must not require an average * bandwidth higher than the approximate bandwidth required to playback or * record a compressed high-definition video. * The next function is invoked on the completion of the last request of a * batch, to compute the next-start time instant, soft_rt_next_start, such * that, if the next request of the application does not arrive before * soft_rt_next_start, then the above requirement on the bandwidth is met. * * The second requirement is that the request pattern of the application is * isochronous, i.e., that, after issuing a request or a batch of requests, * the application stops issuing new requests until all its pending requests * have been completed. After that, the application may issue a new batch, * and so on. * For this reason the next function is invoked to compute * soft_rt_next_start only for applications that meet this requirement, * whereas soft_rt_next_start is set to infinity for applications that do * not. * * Unfortunately, even a greedy (i.e., I/O-bound) application may * happen to meet, occasionally or systematically, both the above * bandwidth and isochrony requirements. This may happen at least in * the following circumstances. First, if the CPU load is high. The * application may stop issuing requests while the CPUs are busy * serving other processes, then restart, then stop again for a while, * and so on. The other circumstances are related to the storage * device: the storage device is highly loaded or reaches a low-enough * throughput with the I/O of the application (e.g., because the I/O * is random and/or the device is slow). In all these cases, the * I/O of the application may be simply slowed down enough to meet * the bandwidth and isochrony requirements. To reduce the probability * that greedy applications are deemed as soft real-time in these * corner cases, a further rule is used in the computation of * soft_rt_next_start: the return value of this function is forced to * be higher than the maximum between the following two quantities. * * (a) Current time plus: (1) the maximum time for which the arrival * of a request is waited for when a sync queue becomes idle, * namely bfqd->bfq_slice_idle, and (2) a few extra jiffies. We * postpone for a moment the reason for adding a few extra * jiffies; we get back to it after next item (b). Lower-bounding * the return value of this function with the current time plus * bfqd->bfq_slice_idle tends to filter out greedy applications, * because the latter issue their next request as soon as possible * after the last one has been completed. In contrast, a soft * real-time application spends some time processing data, after a * batch of its requests has been completed. * * (b) Current value of bfqq->soft_rt_next_start. As pointed out * above, greedy applications may happen to meet both the * bandwidth and isochrony requirements under heavy CPU or * storage-device load. In more detail, in these scenarios, these * applications happen, only for limited time periods, to do I/O * slowly enough to meet all the requirements described so far, * including the filtering in above item (a). These slow-speed * time intervals are usually interspersed between other time * intervals during which these applications do I/O at a very high * speed. Fortunately, exactly because of the high speed of the * I/O in the high-speed intervals, the values returned by this * function happen to be so high, near the end of any such * high-speed interval, to be likely to fall *after* the end of * the low-speed time interval that follows. These high values are * stored in bfqq->soft_rt_next_start after each invocation of * this function. As a consequence, if the last value of * bfqq->soft_rt_next_start is constantly used to lower-bound the * next value that this function may return, then, from the very * beginning of a low-speed interval, bfqq->soft_rt_next_start is * likely to be constantly kept so high that any I/O request * issued during the low-speed interval is considered as arriving * to soon for the application to be deemed as soft * real-time. Then, in the high-speed interval that follows, the * application will not be deemed as soft real-time, just because * it will do I/O at a high speed. And so on. * * Getting back to the filtering in item (a), in the following two * cases this filtering might be easily passed by a greedy * application, if the reference quantity was just * bfqd->bfq_slice_idle: * 1) HZ is so low that the duration of a jiffy is comparable to or * higher than bfqd->bfq_slice_idle. This happens, e.g., on slow * devices with HZ=100. The time granularity may be so coarse * that the approximation, in jiffies, of bfqd->bfq_slice_idle * is rather lower than the exact value. * 2) jiffies, instead of increasing at a constant rate, may stop increasing * for a while, then suddenly 'jump' by several units to recover the lost * increments. This seems to happen, e.g., inside virtual machines. * To address this issue, in the filtering in (a) we do not use as a * reference time interval just bfqd->bfq_slice_idle, but * bfqd->bfq_slice_idle plus a few jiffies. In particular, we add the * minimum number of jiffies for which the filter seems to be quite * precise also in embedded systems and KVM/QEMU virtual machines. */ static unsigned long bfq_bfqq_softrt_next_start(struct bfq_data *bfqd, struct bfq_queue *bfqq) { return max3(bfqq->soft_rt_next_start, bfqq->last_idle_bklogged + HZ * bfqq->service_from_backlogged / bfqd->bfq_wr_max_softrt_rate, jiffies + nsecs_to_jiffies(bfqq->bfqd->bfq_slice_idle) + 4); } static bool bfq_bfqq_injectable(struct bfq_queue *bfqq) { return BFQQ_SEEKY(bfqq) && bfqq->wr_coeff == 1 && blk_queue_nonrot(bfqq->bfqd->queue) && bfqq->bfqd->hw_tag; } /** * bfq_bfqq_expire - expire a queue. * @bfqd: device owning the queue. * @bfqq: the queue to expire. * @compensate: if true, compensate for the time spent idling. * @reason: the reason causing the expiration. * * If the process associated with bfqq does slow I/O (e.g., because it * issues random requests), we charge bfqq with the time it has been * in service instead of the service it has received (see * bfq_bfqq_charge_time for details on how this goal is achieved). As * a consequence, bfqq will typically get higher timestamps upon * reactivation, and hence it will be rescheduled as if it had * received more service than what it has actually received. In the * end, bfqq receives less service in proportion to how slowly its * associated process consumes its budgets (and hence how seriously it * tends to lower the throughput). In addition, this time-charging * strategy guarantees time fairness among slow processes. In * contrast, if the process associated with bfqq is not slow, we * charge bfqq exactly with the service it has received. * * Charging time to the first type of queues and the exact service to * the other has the effect of using the WF2Q+ policy to schedule the * former on a timeslice basis, without violating service domain * guarantees among the latter. */ void bfq_bfqq_expire(struct bfq_data *bfqd, struct bfq_queue *bfqq, bool compensate, enum bfqq_expiration reason) { bool slow; unsigned long delta = 0; struct bfq_entity *entity = &bfqq->entity; int ref; /* * Check whether the process is slow (see bfq_bfqq_is_slow). */ slow = bfq_bfqq_is_slow(bfqd, bfqq, compensate, reason, &delta); /* * As above explained, charge slow (typically seeky) and * timed-out queues with the time and not the service * received, to favor sequential workloads. * * Processes doing I/O in the slower disk zones will tend to * be slow(er) even if not seeky. Therefore, since the * estimated peak rate is actually an average over the disk * surface, these processes may timeout just for bad luck. To * avoid punishing them, do not charge time to processes that * succeeded in consuming at least 2/3 of their budget. This * allows BFQ to preserve enough elasticity to still perform * bandwidth, and not time, distribution with little unlucky * or quasi-sequential processes. */ if (bfqq->wr_coeff == 1 && (slow || (reason == BFQQE_BUDGET_TIMEOUT && bfq_bfqq_budget_left(bfqq) >= entity->budget / 3))) bfq_bfqq_charge_time(bfqd, bfqq, delta); if (reason == BFQQE_TOO_IDLE && entity->service <= 2 * entity->budget / 10) bfq_clear_bfqq_IO_bound(bfqq); if (bfqd->low_latency && bfqq->wr_coeff == 1) bfqq->last_wr_start_finish = jiffies; if (bfqd->low_latency && bfqd->bfq_wr_max_softrt_rate > 0 && RB_EMPTY_ROOT(&bfqq->sort_list)) { /* * If we get here, and there are no outstanding * requests, then the request pattern is isochronous * (see the comments on the function * bfq_bfqq_softrt_next_start()). Thus we can compute * soft_rt_next_start. If, instead, the queue still * has outstanding requests, then we have to wait for * the completion of all the outstanding requests to * discover whether the request pattern is actually * isochronous. */ if (bfqq->dispatched == 0) bfqq->soft_rt_next_start = bfq_bfqq_softrt_next_start(bfqd, bfqq); else { /* * Schedule an update of soft_rt_next_start to when * the task may be discovered to be isochronous. */ bfq_mark_bfqq_softrt_update(bfqq); } } bfq_log_bfqq(bfqd, bfqq, "expire (%d, slow %d, num_disp %d, short_ttime %d)", reason, slow, bfqq->dispatched, bfq_bfqq_has_short_ttime(bfqq)); /* * Increase, decrease or leave budget unchanged according to * reason. */ __bfq_bfqq_recalc_budget(bfqd, bfqq, reason); ref = bfqq->ref; __bfq_bfqq_expire(bfqd, bfqq); if (ref == 1) /* bfqq is gone, no more actions on it */ return; bfqq->injected_service = 0; /* mark bfqq as waiting a request only if a bic still points to it */ if (!bfq_bfqq_busy(bfqq) && reason != BFQQE_BUDGET_TIMEOUT && reason != BFQQE_BUDGET_EXHAUSTED) { bfq_mark_bfqq_non_blocking_wait_rq(bfqq); /* * Not setting service to 0, because, if the next rq * arrives in time, the queue will go on receiving * service with this same budget (as if it never expired) */ } else entity->service = 0; /* * Reset the received-service counter for every parent entity. * Differently from what happens with bfqq->entity.service, * the resetting of this counter never needs to be postponed * for parent entities. In fact, in case bfqq may have a * chance to go on being served using the last, partially * consumed budget, bfqq->entity.service needs to be kept, * because if bfqq then actually goes on being served using * the same budget, the last value of bfqq->entity.service is * needed to properly decrement bfqq->entity.budget by the * portion already consumed. In contrast, it is not necessary * to keep entity->service for parent entities too, because * the bubble up of the new value of bfqq->entity.budget will * make sure that the budgets of parent entities are correct, * even in case bfqq and thus parent entities go on receiving * service with the same budget. */ entity = entity->parent; for_each_entity(entity) entity->service = 0; } /* * Budget timeout is not implemented through a dedicated timer, but * just checked on request arrivals and completions, as well as on * idle timer expirations. */ static bool bfq_bfqq_budget_timeout(struct bfq_queue *bfqq) { return time_is_before_eq_jiffies(bfqq->budget_timeout); } /* * If we expire a queue that is actively waiting (i.e., with the * device idled) for the arrival of a new request, then we may incur * the timestamp misalignment problem described in the body of the * function __bfq_activate_entity. Hence we return true only if this * condition does not hold, or if the queue is slow enough to deserve * only to be kicked off for preserving a high throughput. */ static bool bfq_may_expire_for_budg_timeout(struct bfq_queue *bfqq) { bfq_log_bfqq(bfqq->bfqd, bfqq, "may_budget_timeout: wait_request %d left %d timeout %d", bfq_bfqq_wait_request(bfqq), bfq_bfqq_budget_left(bfqq) >= bfqq->entity.budget / 3, bfq_bfqq_budget_timeout(bfqq)); return (!bfq_bfqq_wait_request(bfqq) || bfq_bfqq_budget_left(bfqq) >= bfqq->entity.budget / 3) && bfq_bfqq_budget_timeout(bfqq); } /* * For a queue that becomes empty, device idling is allowed only if * this function returns true for the queue. As a consequence, since * device idling plays a critical role in both throughput boosting and * service guarantees, the return value of this function plays a * critical role in both these aspects as well. * * In a nutshell, this function returns true only if idling is * beneficial for throughput or, even if detrimental for throughput, * idling is however necessary to preserve service guarantees (low * latency, desired throughput distribution, ...). In particular, on * NCQ-capable devices, this function tries to return false, so as to * help keep the drives' internal queues full, whenever this helps the * device boost the throughput without causing any service-guarantee * issue. * * In more detail, the return value of this function is obtained by, * first, computing a number of boolean variables that take into * account throughput and service-guarantee issues, and, then, * combining these variables in a logical expression. Most of the * issues taken into account are not trivial. We discuss these issues * individually while introducing the variables. */ static bool bfq_better_to_idle(struct bfq_queue *bfqq) { struct bfq_data *bfqd = bfqq->bfqd; bool rot_without_queueing = !blk_queue_nonrot(bfqd->queue) && !bfqd->hw_tag, bfqq_sequential_and_IO_bound, idling_boosts_thr, idling_boosts_thr_without_issues, idling_needed_for_service_guarantees, asymmetric_scenario; if (bfqd->strict_guarantees) return true; /* * Idling is performed only if slice_idle > 0. In addition, we * do not idle if * (a) bfqq is async * (b) bfqq is in the idle io prio class: in this case we do * not idle because we want to minimize the bandwidth that * queues in this class can steal to higher-priority queues */ if (bfqd->bfq_slice_idle == 0 || !bfq_bfqq_sync(bfqq) || bfq_class_idle(bfqq)) return false; bfqq_sequential_and_IO_bound = !BFQQ_SEEKY(bfqq) && bfq_bfqq_IO_bound(bfqq) && bfq_bfqq_has_short_ttime(bfqq); /* * The next variable takes into account the cases where idling * boosts the throughput. * * The value of the variable is computed considering, first, that * idling is virtually always beneficial for the throughput if: * (a) the device is not NCQ-capable and rotational, or * (b) regardless of the presence of NCQ, the device is rotational and * the request pattern for bfqq is I/O-bound and sequential, or * (c) regardless of whether it is rotational, the device is * not NCQ-capable and the request pattern for bfqq is * I/O-bound and sequential. * * Secondly, and in contrast to the above item (b), idling an * NCQ-capable flash-based device would not boost the * throughput even with sequential I/O; rather it would lower * the throughput in proportion to how fast the device * is. Accordingly, the next variable is true if any of the * above conditions (a), (b) or (c) is true, and, in * particular, happens to be false if bfqd is an NCQ-capable * flash-based device. */ idling_boosts_thr = rot_without_queueing || ((!blk_queue_nonrot(bfqd->queue) || !bfqd->hw_tag) && bfqq_sequential_and_IO_bound); /* * The value of the next variable, * idling_boosts_thr_without_issues, is equal to that of * idling_boosts_thr, unless a special case holds. In this * special case, described below, idling may cause problems to * weight-raised queues. * * When the request pool is saturated (e.g., in the presence * of write hogs), if the processes associated with * non-weight-raised queues ask for requests at a lower rate, * then processes associated with weight-raised queues have a * higher probability to get a request from the pool * immediately (or at least soon) when they need one. Thus * they have a higher probability to actually get a fraction * of the device throughput proportional to their high * weight. This is especially true with NCQ-capable drives, * which enqueue several requests in advance, and further * reorder internally-queued requests. * * For this reason, we force to false the value of * idling_boosts_thr_without_issues if there are weight-raised * busy queues. In this case, and if bfqq is not weight-raised, * this guarantees that the device is not idled for bfqq (if, * instead, bfqq is weight-raised, then idling will be * guaranteed by another variable, see below). Combined with * the timestamping rules of BFQ (see [1] for details), this * behavior causes bfqq, and hence any sync non-weight-raised * queue, to get a lower number of requests served, and thus * to ask for a lower number of requests from the request * pool, before the busy weight-raised queues get served * again. This often mitigates starvation problems in the * presence of heavy write workloads and NCQ, thereby * guaranteeing a higher application and system responsiveness * in these hostile scenarios. */ idling_boosts_thr_without_issues = idling_boosts_thr && bfqd->wr_busy_queues == 0; /* * There is then a case where idling must be performed not * for throughput concerns, but to preserve service * guarantees. * * To introduce this case, we can note that allowing the drive * to enqueue more than one request at a time, and hence * delegating de facto final scheduling decisions to the * drive's internal scheduler, entails loss of control on the * actual request service order. In particular, the critical * situation is when requests from different processes happen * to be present, at the same time, in the internal queue(s) * of the drive. In such a situation, the drive, by deciding * the service order of the internally-queued requests, does * determine also the actual throughput distribution among * these processes. But the drive typically has no notion or * concern about per-process throughput distribution, and * makes its decisions only on a per-request basis. Therefore, * the service distribution enforced by the drive's internal * scheduler is likely to coincide with the desired * device-throughput distribution only in a completely * symmetric scenario where: * (i) each of these processes must get the same throughput as * the others; * (ii) the I/O of each process has the same properties, in * terms of locality (sequential or random), direction * (reads or writes), request sizes, greediness * (from I/O-bound to sporadic), and so on. * In fact, in such a scenario, the drive tends to treat * the requests of each of these processes in about the same * way as the requests of the others, and thus to provide * each of these processes with about the same throughput * (which is exactly the desired throughput distribution). In * contrast, in any asymmetric scenario, device idling is * certainly needed to guarantee that bfqq receives its * assigned fraction of the device throughput (see [1] for * details). * The problem is that idling may significantly reduce * throughput with certain combinations of types of I/O and * devices. An important example is sync random I/O, on flash * storage with command queueing. So, unless bfqq falls in the * above cases where idling also boosts throughput, it would * be important to check conditions (i) and (ii) accurately, * so as to avoid idling when not strictly needed for service * guarantees. * * Unfortunately, it is extremely difficult to thoroughly * check condition (ii). And, in case there are active groups, * it becomes very difficult to check condition (i) too. In * fact, if there are active groups, then, for condition (i) * to become false, it is enough that an active group contains * more active processes or sub-groups than some other active * group. More precisely, for condition (i) to hold because of * such a group, it is not even necessary that the group is * (still) active: it is sufficient that, even if the group * has become inactive, some of its descendant processes still * have some request already dispatched but still waiting for * completion. In fact, requests have still to be guaranteed * their share of the throughput even after being * dispatched. In this respect, it is easy to show that, if a * group frequently becomes inactive while still having * in-flight requests, and if, when this happens, the group is * not considered in the calculation of whether the scenario * is asymmetric, then the group may fail to be guaranteed its * fair share of the throughput (basically because idling may * not be performed for the descendant processes of the group, * but it had to be). We address this issue with the * following bi-modal behavior, implemented in the function * bfq_symmetric_scenario(). * * If there are groups with requests waiting for completion * (as commented above, some of these groups may even be * already inactive), then the scenario is tagged as * asymmetric, conservatively, without checking any of the * conditions (i) and (ii). So the device is idled for bfqq. * This behavior matches also the fact that groups are created * exactly if controlling I/O is a primary concern (to * preserve bandwidth and latency guarantees). * * On the opposite end, if there are no groups with requests * waiting for completion, then only condition (i) is actually * controlled, i.e., provided that condition (i) holds, idling * is not performed, regardless of whether condition (ii) * holds. In other words, only if condition (i) does not hold, * then idling is allowed, and the device tends to be * prevented from queueing many requests, possibly of several * processes. Since there are no groups with requests waiting * for completion, then, to control condition (i) it is enough * to check just whether all the queues with requests waiting * for completion also have the same weight. * * Not checking condition (ii) evidently exposes bfqq to the * risk of getting less throughput than its fair share. * However, for queues with the same weight, a further * mechanism, preemption, mitigates or even eliminates this * problem. And it does so without consequences on overall * throughput. This mechanism and its benefits are explained * in the next three paragraphs. * * Even if a queue, say Q, is expired when it remains idle, Q * can still preempt the new in-service queue if the next * request of Q arrives soon (see the comments on * bfq_bfqq_update_budg_for_activation). If all queues and * groups have the same weight, this form of preemption, * combined with the hole-recovery heuristic described in the * comments on function bfq_bfqq_update_budg_for_activation, * are enough to preserve a correct bandwidth distribution in * the mid term, even without idling. In fact, even if not * idling allows the internal queues of the device to contain * many requests, and thus to reorder requests, we can rather * safely assume that the internal scheduler still preserves a * minimum of mid-term fairness. * * More precisely, this preemption-based, idleless approach * provides fairness in terms of IOPS, and not sectors per * second. This can be seen with a simple example. Suppose * that there are two queues with the same weight, but that * the first queue receives requests of 8 sectors, while the * second queue receives requests of 1024 sectors. In * addition, suppose that each of the two queues contains at * most one request at a time, which implies that each queue * always remains idle after it is served. Finally, after * remaining idle, each queue receives very quickly a new * request. It follows that the two queues are served * alternatively, preempting each other if needed. This * implies that, although both queues have the same weight, * the queue with large requests receives a service that is * 1024/8 times as high as the service received by the other * queue. * * The motivation for using preemption instead of idling (for * queues with the same weight) is that, by not idling, * service guarantees are preserved (completely or at least in * part) without minimally sacrificing throughput. And, if * there is no active group, then the primary expectation for * this device is probably a high throughput. * * We are now left only with explaining the additional * compound condition that is checked below for deciding * whether the scenario is asymmetric. To explain this * compound condition, we need to add that the function * bfq_symmetric_scenario checks the weights of only * non-weight-raised queues, for efficiency reasons (see * comments on bfq_weights_tree_add()). Then the fact that * bfqq is weight-raised is checked explicitly here. More * precisely, the compound condition below takes into account * also the fact that, even if bfqq is being weight-raised, * the scenario is still symmetric if all queues with requests * waiting for completion happen to be * weight-raised. Actually, we should be even more precise * here, and differentiate between interactive weight raising * and soft real-time weight raising. * * As a side note, it is worth considering that the above * device-idling countermeasures may however fail in the * following unlucky scenario: if idling is (correctly) * disabled in a time period during which all symmetry * sub-conditions hold, and hence the device is allowed to * enqueue many requests, but at some later point in time some * sub-condition stops to hold, then it may become impossible * to let requests be served in the desired order until all * the requests already queued in the device have been served. */ asymmetric_scenario = (bfqq->wr_coeff > 1 && bfqd->wr_busy_queues < bfqd->busy_queues) || !bfq_symmetric_scenario(bfqd); /* * Finally, there is a case where maximizing throughput is the * best choice even if it may cause unfairness toward * bfqq. Such a case is when bfqq became active in a burst of * queue activations. Queues that became active during a large * burst benefit only from throughput, as discussed in the * comments on bfq_handle_burst. Thus, if bfqq became active * in a burst and not idling the device maximizes throughput, * then the device must no be idled, because not idling the * device provides bfqq and all other queues in the burst with * maximum benefit. Combining this and the above case, we can * now establish when idling is actually needed to preserve * service guarantees. */ idling_needed_for_service_guarantees = asymmetric_scenario && !bfq_bfqq_in_large_burst(bfqq); /* * We have now all the components we need to compute the * return value of the function, which is true only if idling * either boosts the throughput (without issues), or is * necessary to preserve service guarantees. */ return idling_boosts_thr_without_issues || idling_needed_for_service_guarantees; } /* * If the in-service queue is empty but the function bfq_better_to_idle * returns true, then: * 1) the queue must remain in service and cannot be expired, and * 2) the device must be idled to wait for the possible arrival of a new * request for the queue. * See the comments on the function bfq_better_to_idle for the reasons * why performing device idling is the best choice to boost the throughput * and preserve service guarantees when bfq_better_to_idle itself * returns true. */ static bool bfq_bfqq_must_idle(struct bfq_queue *bfqq) { return RB_EMPTY_ROOT(&bfqq->sort_list) && bfq_better_to_idle(bfqq); } static struct bfq_queue *bfq_choose_bfqq_for_injection(struct bfq_data *bfqd) { struct bfq_queue *bfqq; /* * A linear search; but, with a high probability, very few * steps are needed to find a candidate queue, i.e., a queue * with enough budget left for its next request. In fact: * - BFQ dynamically updates the budget of every queue so as * to accommodate the expected backlog of the queue; * - if a queue gets all its requests dispatched as injected * service, then the queue is removed from the active list * (and re-added only if it gets new requests, but with * enough budget for its new backlog). */ list_for_each_entry(bfqq, &bfqd->active_list, bfqq_list) if (!RB_EMPTY_ROOT(&bfqq->sort_list) && bfq_serv_to_charge(bfqq->next_rq, bfqq) <= bfq_bfqq_budget_left(bfqq)) return bfqq; return NULL; } /* * Select a queue for service. If we have a current queue in service, * check whether to continue servicing it, or retrieve and set a new one. */ static struct bfq_queue *bfq_select_queue(struct bfq_data *bfqd) { struct bfq_queue *bfqq; struct request *next_rq; enum bfqq_expiration reason = BFQQE_BUDGET_TIMEOUT; bfqq = bfqd->in_service_queue; if (!bfqq) goto new_queue; bfq_log_bfqq(bfqd, bfqq, "select_queue: already in-service queue"); /* * Do not expire bfqq for budget timeout if bfqq may be about * to enjoy device idling. The reason why, in this case, we * prevent bfqq from expiring is the same as in the comments * on the case where bfq_bfqq_must_idle() returns true, in * bfq_completed_request(). */ if (bfq_may_expire_for_budg_timeout(bfqq) && !bfq_bfqq_must_idle(bfqq)) goto expire; check_queue: /* * This loop is rarely executed more than once. Even when it * happens, it is much more convenient to re-execute this loop * than to return NULL and trigger a new dispatch to get a * request served. */ next_rq = bfqq->next_rq; /* * If bfqq has requests queued and it has enough budget left to * serve them, keep the queue, otherwise expire it. */ if (next_rq) { if (bfq_serv_to_charge(next_rq, bfqq) > bfq_bfqq_budget_left(bfqq)) { /* * Expire the queue for budget exhaustion, * which makes sure that the next budget is * enough to serve the next request, even if * it comes from the fifo expired path. */ reason = BFQQE_BUDGET_EXHAUSTED; goto expire; } else { /* * The idle timer may be pending because we may * not disable disk idling even when a new request * arrives. */ if (bfq_bfqq_wait_request(bfqq)) { /* * If we get here: 1) at least a new request * has arrived but we have not disabled the * timer because the request was too small, * 2) then the block layer has unplugged * the device, causing the dispatch to be * invoked. * * Since the device is unplugged, now the * requests are probably large enough to * provide a reasonable throughput. * So we disable idling. */ bfq_clear_bfqq_wait_request(bfqq); hrtimer_try_to_cancel(&bfqd->idle_slice_timer); } goto keep_queue; } } /* * No requests pending. However, if the in-service queue is idling * for a new request, or has requests waiting for a completion and * may idle after their completion, then keep it anyway. * * Yet, to boost throughput, inject service from other queues if * possible. */ if (bfq_bfqq_wait_request(bfqq) || (bfqq->dispatched != 0 && bfq_better_to_idle(bfqq))) { if (bfq_bfqq_injectable(bfqq) && bfqq->injected_service * bfqq->inject_coeff < bfqq->entity.service * 10) bfqq = bfq_choose_bfqq_for_injection(bfqd); else bfqq = NULL; goto keep_queue; } reason = BFQQE_NO_MORE_REQUESTS; expire: bfq_bfqq_expire(bfqd, bfqq, false, reason); new_queue: bfqq = bfq_set_in_service_queue(bfqd); if (bfqq) { bfq_log_bfqq(bfqd, bfqq, "select_queue: checking new queue"); goto check_queue; } keep_queue: if (bfqq) bfq_log_bfqq(bfqd, bfqq, "select_queue: returned this queue"); else bfq_log(bfqd, "select_queue: no queue returned"); return bfqq; } static void bfq_update_wr_data(struct bfq_data *bfqd, struct bfq_queue *bfqq) { struct bfq_entity *entity = &bfqq->entity; if (bfqq->wr_coeff > 1) { /* queue is being weight-raised */ bfq_log_bfqq(bfqd, bfqq, "raising period dur %u/%u msec, old coeff %u, w %d(%d)", jiffies_to_msecs(jiffies - bfqq->last_wr_start_finish), jiffies_to_msecs(bfqq->wr_cur_max_time), bfqq->wr_coeff, bfqq->entity.weight, bfqq->entity.orig_weight); if (entity->prio_changed) bfq_log_bfqq(bfqd, bfqq, "WARN: pending prio change"); /* * If the queue was activated in a burst, or too much * time has elapsed from the beginning of this * weight-raising period, then end weight raising. */ if (bfq_bfqq_in_large_burst(bfqq)) bfq_bfqq_end_wr(bfqq); else if (time_is_before_jiffies(bfqq->last_wr_start_finish + bfqq->wr_cur_max_time)) { if (bfqq->wr_cur_max_time != bfqd->bfq_wr_rt_max_time || time_is_before_jiffies(bfqq->wr_start_at_switch_to_srt + bfq_wr_duration(bfqd))) bfq_bfqq_end_wr(bfqq); else { switch_back_to_interactive_wr(bfqq, bfqd); bfqq->entity.prio_changed = 1; } } if (bfqq->wr_coeff > 1 && bfqq->wr_cur_max_time != bfqd->bfq_wr_rt_max_time && bfqq->service_from_wr > max_service_from_wr) { /* see comments on max_service_from_wr */ bfq_bfqq_end_wr(bfqq); } } /* * To improve latency (for this or other queues), immediately * update weight both if it must be raised and if it must be * lowered. Since, entity may be on some active tree here, and * might have a pending change of its ioprio class, invoke * next function with the last parameter unset (see the * comments on the function). */ if ((entity->weight > entity->orig_weight) != (bfqq->wr_coeff > 1)) __bfq_entity_update_weight_prio(bfq_entity_service_tree(entity), entity, false); } /* * Dispatch next request from bfqq. */ static struct request *bfq_dispatch_rq_from_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq) { struct request *rq = bfqq->next_rq; unsigned long service_to_charge; service_to_charge = bfq_serv_to_charge(rq, bfqq); bfq_bfqq_served(bfqq, service_to_charge); bfq_dispatch_remove(bfqd->queue, rq); if (bfqq != bfqd->in_service_queue) { if (likely(bfqd->in_service_queue)) bfqd->in_service_queue->injected_service += bfq_serv_to_charge(rq, bfqq); goto return_rq; } /* * If weight raising has to terminate for bfqq, then next * function causes an immediate update of bfqq's weight, * without waiting for next activation. As a consequence, on * expiration, bfqq will be timestamped as if has never been * weight-raised during this service slot, even if it has * received part or even most of the service as a * weight-raised queue. This inflates bfqq's timestamps, which * is beneficial, as bfqq is then more willing to leave the * device immediately to possible other weight-raised queues. */ bfq_update_wr_data(bfqd, bfqq); /* * Expire bfqq, pretending that its budget expired, if bfqq * belongs to CLASS_IDLE and other queues are waiting for * service. */ if (!(bfqd->busy_queues > 1 && bfq_class_idle(bfqq))) goto return_rq; bfq_bfqq_expire(bfqd, bfqq, false, BFQQE_BUDGET_EXHAUSTED); return_rq: return rq; } static bool bfq_has_work(struct blk_mq_hw_ctx *hctx) { struct bfq_data *bfqd = hctx->queue->elevator->elevator_data; /* * Avoiding lock: a race on bfqd->busy_queues should cause at * most a call to dispatch for nothing */ return !list_empty_careful(&bfqd->dispatch) || bfqd->busy_queues > 0; } static struct request *__bfq_dispatch_request(struct blk_mq_hw_ctx *hctx) { struct bfq_data *bfqd = hctx->queue->elevator->elevator_data; struct request *rq = NULL; struct bfq_queue *bfqq = NULL; if (!list_empty(&bfqd->dispatch)) { rq = list_first_entry(&bfqd->dispatch, struct request, queuelist); list_del_init(&rq->queuelist); bfqq = RQ_BFQQ(rq); if (bfqq) { /* * Increment counters here, because this * dispatch does not follow the standard * dispatch flow (where counters are * incremented) */ bfqq->dispatched++; goto inc_in_driver_start_rq; } /* * We exploit the bfq_finish_requeue_request hook to * decrement rq_in_driver, but * bfq_finish_requeue_request will not be invoked on * this request. So, to avoid unbalance, just start * this request, without incrementing rq_in_driver. As * a negative consequence, rq_in_driver is deceptively * lower than it should be while this request is in * service. This may cause bfq_schedule_dispatch to be * invoked uselessly. * * As for implementing an exact solution, the * bfq_finish_requeue_request hook, if defined, is * probably invoked also on this request. So, by * exploiting this hook, we could 1) increment * rq_in_driver here, and 2) decrement it in * bfq_finish_requeue_request. Such a solution would * let the value of the counter be always accurate, * but it would entail using an extra interface * function. This cost seems higher than the benefit, * being the frequency of non-elevator-private * requests very low. */ goto start_rq; } bfq_log(bfqd, "dispatch requests: %d busy queues", bfqd->busy_queues); if (bfqd->busy_queues == 0) goto exit; /* * Force device to serve one request at a time if * strict_guarantees is true. Forcing this service scheme is * currently the ONLY way to guarantee that the request * service order enforced by the scheduler is respected by a * queueing device. Otherwise the device is free even to make * some unlucky request wait for as long as the device * wishes. * * Of course, serving one request at at time may cause loss of * throughput. */ if (bfqd->strict_guarantees && bfqd->rq_in_driver > 0) goto exit; bfqq = bfq_select_queue(bfqd); if (!bfqq) goto exit; rq = bfq_dispatch_rq_from_bfqq(bfqd, bfqq); if (rq) { inc_in_driver_start_rq: bfqd->rq_in_driver++; start_rq: rq->rq_flags |= RQF_STARTED; } exit: return rq; } #if defined(CONFIG_BFQ_GROUP_IOSCHED) && defined(CONFIG_DEBUG_BLK_CGROUP) static void bfq_update_dispatch_stats(struct request_queue *q, struct request *rq, struct bfq_queue *in_serv_queue, bool idle_timer_disabled) { struct bfq_queue *bfqq = rq ? RQ_BFQQ(rq) : NULL; if (!idle_timer_disabled && !bfqq) return; /* * rq and bfqq are guaranteed to exist until this function * ends, for the following reasons. First, rq can be * dispatched to the device, and then can be completed and * freed, only after this function ends. Second, rq cannot be * merged (and thus freed because of a merge) any longer, * because it has already started. Thus rq cannot be freed * before this function ends, and, since rq has a reference to * bfqq, the same guarantee holds for bfqq too. * * In addition, the following queue lock guarantees that * bfqq_group(bfqq) exists as well. */ spin_lock_irq(q->queue_lock); if (idle_timer_disabled) /* * Since the idle timer has been disabled, * in_serv_queue contained some request when * __bfq_dispatch_request was invoked above, which * implies that rq was picked exactly from * in_serv_queue. Thus in_serv_queue == bfqq, and is * therefore guaranteed to exist because of the above * arguments. */ bfqg_stats_update_idle_time(bfqq_group(in_serv_queue)); if (bfqq) { struct bfq_group *bfqg = bfqq_group(bfqq); bfqg_stats_update_avg_queue_size(bfqg); bfqg_stats_set_start_empty_time(bfqg); bfqg_stats_update_io_remove(bfqg, rq->cmd_flags); } spin_unlock_irq(q->queue_lock); } #else static inline void bfq_update_dispatch_stats(struct request_queue *q, struct request *rq, struct bfq_queue *in_serv_queue, bool idle_timer_disabled) {} #endif static struct request *bfq_dispatch_request(struct blk_mq_hw_ctx *hctx) { struct bfq_data *bfqd = hctx->queue->elevator->elevator_data; struct request *rq; struct bfq_queue *in_serv_queue; bool waiting_rq, idle_timer_disabled; spin_lock_irq(&bfqd->lock); in_serv_queue = bfqd->in_service_queue; waiting_rq = in_serv_queue && bfq_bfqq_wait_request(in_serv_queue); rq = __bfq_dispatch_request(hctx); idle_timer_disabled = waiting_rq && !bfq_bfqq_wait_request(in_serv_queue); spin_unlock_irq(&bfqd->lock); bfq_update_dispatch_stats(hctx->queue, rq, in_serv_queue, idle_timer_disabled); return rq; } /* * Task holds one reference to the queue, dropped when task exits. Each rq * in-flight on this queue also holds a reference, dropped when rq is freed. * * Scheduler lock must be held here. Recall not to use bfqq after calling * this function on it. */ void bfq_put_queue(struct bfq_queue *bfqq) { #ifdef CONFIG_BFQ_GROUP_IOSCHED struct bfq_group *bfqg = bfqq_group(bfqq); #endif if (bfqq->bfqd) bfq_log_bfqq(bfqq->bfqd, bfqq, "put_queue: %p %d", bfqq, bfqq->ref); bfqq->ref--; if (bfqq->ref) return; if (!hlist_unhashed(&bfqq->burst_list_node)) { hlist_del_init(&bfqq->burst_list_node); /* * Decrement also burst size after the removal, if the * process associated with bfqq is exiting, and thus * does not contribute to the burst any longer. This * decrement helps filter out false positives of large * bursts, when some short-lived process (often due to * the execution of commands by some service) happens * to start and exit while a complex application is * starting, and thus spawning several processes that * do I/O (and that *must not* be treated as a large * burst, see comments on bfq_handle_burst). * * In particular, the decrement is performed only if: * 1) bfqq is not a merged queue, because, if it is, * then this free of bfqq is not triggered by the exit * of the process bfqq is associated with, but exactly * by the fact that bfqq has just been merged. * 2) burst_size is greater than 0, to handle * unbalanced decrements. Unbalanced decrements may * happen in te following case: bfqq is inserted into * the current burst list--without incrementing * bust_size--because of a split, but the current * burst list is not the burst list bfqq belonged to * (see comments on the case of a split in * bfq_set_request). */ if (bfqq->bic && bfqq->bfqd->burst_size > 0) bfqq->bfqd->burst_size--; } kmem_cache_free(bfq_pool, bfqq); #ifdef CONFIG_BFQ_GROUP_IOSCHED bfqg_and_blkg_put(bfqg); #endif } static void bfq_put_cooperator(struct bfq_queue *bfqq) { struct bfq_queue *__bfqq, *next; /* * If this queue was scheduled to merge with another queue, be * sure to drop the reference taken on that queue (and others in * the merge chain). See bfq_setup_merge and bfq_merge_bfqqs. */ __bfqq = bfqq->new_bfqq; while (__bfqq) { if (__bfqq == bfqq) break; next = __bfqq->new_bfqq; bfq_put_queue(__bfqq); __bfqq = next; } } static void bfq_exit_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq) { if (bfqq == bfqd->in_service_queue) { __bfq_bfqq_expire(bfqd, bfqq); bfq_schedule_dispatch(bfqd); } bfq_log_bfqq(bfqd, bfqq, "exit_bfqq: %p, %d", bfqq, bfqq->ref); bfq_put_cooperator(bfqq); bfq_put_queue(bfqq); /* release process reference */ } static void bfq_exit_icq_bfqq(struct bfq_io_cq *bic, bool is_sync) { struct bfq_queue *bfqq = bic_to_bfqq(bic, is_sync); struct bfq_data *bfqd; if (bfqq) bfqd = bfqq->bfqd; /* NULL if scheduler already exited */ if (bfqq && bfqd) { unsigned long flags; spin_lock_irqsave(&bfqd->lock, flags); bfq_exit_bfqq(bfqd, bfqq); bic_set_bfqq(bic, NULL, is_sync); spin_unlock_irqrestore(&bfqd->lock, flags); } } static void bfq_exit_icq(struct io_cq *icq) { struct bfq_io_cq *bic = icq_to_bic(icq); bfq_exit_icq_bfqq(bic, true); bfq_exit_icq_bfqq(bic, false); } /* * Update the entity prio values; note that the new values will not * be used until the next (re)activation. */ static void bfq_set_next_ioprio_data(struct bfq_queue *bfqq, struct bfq_io_cq *bic) { struct task_struct *tsk = current; int ioprio_class; struct bfq_data *bfqd = bfqq->bfqd; if (!bfqd) return; ioprio_class = IOPRIO_PRIO_CLASS(bic->ioprio); switch (ioprio_class) { default: dev_err(bfqq->bfqd->queue->backing_dev_info->dev, "bfq: bad prio class %d\n", ioprio_class); /* fall through */ case IOPRIO_CLASS_NONE: /* * No prio set, inherit CPU scheduling settings. */ bfqq->new_ioprio = task_nice_ioprio(tsk); bfqq->new_ioprio_class = task_nice_ioclass(tsk); break; case IOPRIO_CLASS_RT: bfqq->new_ioprio = IOPRIO_PRIO_DATA(bic->ioprio); bfqq->new_ioprio_class = IOPRIO_CLASS_RT; break; case IOPRIO_CLASS_BE: bfqq->new_ioprio = IOPRIO_PRIO_DATA(bic->ioprio); bfqq->new_ioprio_class = IOPRIO_CLASS_BE; break; case IOPRIO_CLASS_IDLE: bfqq->new_ioprio_class = IOPRIO_CLASS_IDLE; bfqq->new_ioprio = 7; break; } if (bfqq->new_ioprio >= IOPRIO_BE_NR) { pr_crit("bfq_set_next_ioprio_data: new_ioprio %d\n", bfqq->new_ioprio); bfqq->new_ioprio = IOPRIO_BE_NR; } bfqq->entity.new_weight = bfq_ioprio_to_weight(bfqq->new_ioprio); bfqq->entity.prio_changed = 1; } static struct bfq_queue *bfq_get_queue(struct bfq_data *bfqd, struct bio *bio, bool is_sync, struct bfq_io_cq *bic); static void bfq_check_ioprio_change(struct bfq_io_cq *bic, struct bio *bio) { struct bfq_data *bfqd = bic_to_bfqd(bic); struct bfq_queue *bfqq; int ioprio = bic->icq.ioc->ioprio; /* * This condition may trigger on a newly created bic, be sure to * drop the lock before returning. */ if (unlikely(!bfqd) || likely(bic->ioprio == ioprio)) return; bic->ioprio = ioprio; bfqq = bic_to_bfqq(bic, false); if (bfqq) { /* release process reference on this queue */ bfq_put_queue(bfqq); bfqq = bfq_get_queue(bfqd, bio, BLK_RW_ASYNC, bic); bic_set_bfqq(bic, bfqq, false); } bfqq = bic_to_bfqq(bic, true); if (bfqq) bfq_set_next_ioprio_data(bfqq, bic); } static void bfq_init_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq, struct bfq_io_cq *bic, pid_t pid, int is_sync) { RB_CLEAR_NODE(&bfqq->entity.rb_node); INIT_LIST_HEAD(&bfqq->fifo); INIT_HLIST_NODE(&bfqq->burst_list_node); bfqq->ref = 0; bfqq->bfqd = bfqd; if (bic) bfq_set_next_ioprio_data(bfqq, bic); if (is_sync) { /* * No need to mark as has_short_ttime if in * idle_class, because no device idling is performed * for queues in idle class */ if (!bfq_class_idle(bfqq)) /* tentatively mark as has_short_ttime */ bfq_mark_bfqq_has_short_ttime(bfqq); bfq_mark_bfqq_sync(bfqq); bfq_mark_bfqq_just_created(bfqq); /* * Aggressively inject a lot of service: up to 90%. * This coefficient remains constant during bfqq life, * but this behavior might be changed, after enough * testing and tuning. */ bfqq->inject_coeff = 1; } else bfq_clear_bfqq_sync(bfqq); /* set end request to minus infinity from now */ bfqq->ttime.last_end_request = ktime_get_ns() + 1; bfq_mark_bfqq_IO_bound(bfqq); bfqq->pid = pid; /* Tentative initial value to trade off between thr and lat */ bfqq->max_budget = (2 * bfq_max_budget(bfqd)) / 3; bfqq->budget_timeout = bfq_smallest_from_now(); bfqq->wr_coeff = 1; bfqq->last_wr_start_finish = jiffies; bfqq->wr_start_at_switch_to_srt = bfq_smallest_from_now(); bfqq->split_time = bfq_smallest_from_now(); /* * To not forget the possibly high bandwidth consumed by a * process/queue in the recent past, * bfq_bfqq_softrt_next_start() returns a value at least equal * to the current value of bfqq->soft_rt_next_start (see * comments on bfq_bfqq_softrt_next_start). Set * soft_rt_next_start to now, to mean that bfqq has consumed * no bandwidth so far. */ bfqq->soft_rt_next_start = jiffies; /* first request is almost certainly seeky */ bfqq->seek_history = 1; } static struct bfq_queue **bfq_async_queue_prio(struct bfq_data *bfqd, struct bfq_group *bfqg, int ioprio_class, int ioprio) { switch (ioprio_class) { case IOPRIO_CLASS_RT: return &bfqg->async_bfqq[0][ioprio]; case IOPRIO_CLASS_NONE: ioprio = IOPRIO_NORM; /* fall through */ case IOPRIO_CLASS_BE: return &bfqg->async_bfqq[1][ioprio]; case IOPRIO_CLASS_IDLE: return &bfqg->async_idle_bfqq; default: return NULL; } } static struct bfq_queue *bfq_get_queue(struct bfq_data *bfqd, struct bio *bio, bool is_sync, struct bfq_io_cq *bic) { const int ioprio = IOPRIO_PRIO_DATA(bic->ioprio); const int ioprio_class = IOPRIO_PRIO_CLASS(bic->ioprio); struct bfq_queue **async_bfqq = NULL; struct bfq_queue *bfqq; struct bfq_group *bfqg; rcu_read_lock(); bfqg = bfq_find_set_group(bfqd, bio_blkcg(bio)); if (!bfqg) { bfqq = &bfqd->oom_bfqq; goto out; } if (!is_sync) { async_bfqq = bfq_async_queue_prio(bfqd, bfqg, ioprio_class, ioprio); bfqq = *async_bfqq; if (bfqq) goto out; } bfqq = kmem_cache_alloc_node(bfq_pool, GFP_NOWAIT | __GFP_ZERO | __GFP_NOWARN, bfqd->queue->node); if (bfqq) { bfq_init_bfqq(bfqd, bfqq, bic, current->pid, is_sync); bfq_init_entity(&bfqq->entity, bfqg); bfq_log_bfqq(bfqd, bfqq, "allocated"); } else { bfqq = &bfqd->oom_bfqq; bfq_log_bfqq(bfqd, bfqq, "using oom bfqq"); goto out; } /* * Pin the queue now that it's allocated, scheduler exit will * prune it. */ if (async_bfqq) { bfqq->ref++; /* * Extra group reference, w.r.t. sync * queue. This extra reference is removed * only if bfqq->bfqg disappears, to * guarantee that this queue is not freed * until its group goes away. */ bfq_log_bfqq(bfqd, bfqq, "get_queue, bfqq not in async: %p, %d", bfqq, bfqq->ref); *async_bfqq = bfqq; } out: bfqq->ref++; /* get a process reference to this queue */ bfq_log_bfqq(bfqd, bfqq, "get_queue, at end: %p, %d", bfqq, bfqq->ref); rcu_read_unlock(); return bfqq; } static void bfq_update_io_thinktime(struct bfq_data *bfqd, struct bfq_queue *bfqq) { struct bfq_ttime *ttime = &bfqq->ttime; u64 elapsed = ktime_get_ns() - bfqq->ttime.last_end_request; elapsed = min_t(u64, elapsed, 2ULL * bfqd->bfq_slice_idle); ttime->ttime_samples = (7*bfqq->ttime.ttime_samples + 256) / 8; ttime->ttime_total = div_u64(7*ttime->ttime_total + 256*elapsed, 8); ttime->ttime_mean = div64_ul(ttime->ttime_total + 128, ttime->ttime_samples); } static void bfq_update_io_seektime(struct bfq_data *bfqd, struct bfq_queue *bfqq, struct request *rq) { bfqq->seek_history <<= 1; bfqq->seek_history |= get_sdist(bfqq->last_request_pos, rq) > BFQQ_SEEK_THR && (!blk_queue_nonrot(bfqd->queue) || blk_rq_sectors(rq) < BFQQ_SECT_THR_NONROT); } static void bfq_update_has_short_ttime(struct bfq_data *bfqd, struct bfq_queue *bfqq, struct bfq_io_cq *bic) { bool has_short_ttime = true; /* * No need to update has_short_ttime if bfqq is async or in * idle io prio class, or if bfq_slice_idle is zero, because * no device idling is performed for bfqq in this case. */ if (!bfq_bfqq_sync(bfqq) || bfq_class_idle(bfqq) || bfqd->bfq_slice_idle == 0) return; /* Idle window just restored, statistics are meaningless. */ if (time_is_after_eq_jiffies(bfqq->split_time + bfqd->bfq_wr_min_idle_time)) return; /* Think time is infinite if no process is linked to * bfqq. Otherwise check average think time to * decide whether to mark as has_short_ttime */ if (atomic_read(&bic->icq.ioc->active_ref) == 0 || (bfq_sample_valid(bfqq->ttime.ttime_samples) && bfqq->ttime.ttime_mean > bfqd->bfq_slice_idle)) has_short_ttime = false; bfq_log_bfqq(bfqd, bfqq, "update_has_short_ttime: has_short_ttime %d", has_short_ttime); if (has_short_ttime) bfq_mark_bfqq_has_short_ttime(bfqq); else bfq_clear_bfqq_has_short_ttime(bfqq); } /* * Called when a new fs request (rq) is added to bfqq. Check if there's * something we should do about it. */ static void bfq_rq_enqueued(struct bfq_data *bfqd, struct bfq_queue *bfqq, struct request *rq) { struct bfq_io_cq *bic = RQ_BIC(rq); if (rq->cmd_flags & REQ_META) bfqq->meta_pending++; bfq_update_io_thinktime(bfqd, bfqq); bfq_update_has_short_ttime(bfqd, bfqq, bic); bfq_update_io_seektime(bfqd, bfqq, rq); bfq_log_bfqq(bfqd, bfqq, "rq_enqueued: has_short_ttime=%d (seeky %d)", bfq_bfqq_has_short_ttime(bfqq), BFQQ_SEEKY(bfqq)); bfqq->last_request_pos = blk_rq_pos(rq) + blk_rq_sectors(rq); if (bfqq == bfqd->in_service_queue && bfq_bfqq_wait_request(bfqq)) { bool small_req = bfqq->queued[rq_is_sync(rq)] == 1 && blk_rq_sectors(rq) < 32; bool budget_timeout = bfq_bfqq_budget_timeout(bfqq); /* * There is just this request queued: if the request * is small and the queue is not to be expired, then * just exit. * * In this way, if the device is being idled to wait * for a new request from the in-service queue, we * avoid unplugging the device and committing the * device to serve just a small request. On the * contrary, we wait for the block layer to decide * when to unplug the device: hopefully, new requests * will be merged to this one quickly, then the device * will be unplugged and larger requests will be * dispatched. */ if (small_req && !budget_timeout) return; /* * A large enough request arrived, or the queue is to * be expired: in both cases disk idling is to be * stopped, so clear wait_request flag and reset * timer. */ bfq_clear_bfqq_wait_request(bfqq); hrtimer_try_to_cancel(&bfqd->idle_slice_timer); /* * The queue is not empty, because a new request just * arrived. Hence we can safely expire the queue, in * case of budget timeout, without risking that the * timestamps of the queue are not updated correctly. * See [1] for more details. */ if (budget_timeout) bfq_bfqq_expire(bfqd, bfqq, false, BFQQE_BUDGET_TIMEOUT); } } /* returns true if it causes the idle timer to be disabled */ static bool __bfq_insert_request(struct bfq_data *bfqd, struct request *rq) { struct bfq_queue *bfqq = RQ_BFQQ(rq), *new_bfqq = bfq_setup_cooperator(bfqd, bfqq, rq, true); bool waiting, idle_timer_disabled = false; if (new_bfqq) { if (bic_to_bfqq(RQ_BIC(rq), 1) != bfqq) new_bfqq = bic_to_bfqq(RQ_BIC(rq), 1); /* * Release the request's reference to the old bfqq * and make sure one is taken to the shared queue. */ new_bfqq->allocated++; bfqq->allocated--; new_bfqq->ref++; /* * If the bic associated with the process * issuing this request still points to bfqq * (and thus has not been already redirected * to new_bfqq or even some other bfq_queue), * then complete the merge and redirect it to * new_bfqq. */ if (bic_to_bfqq(RQ_BIC(rq), 1) == bfqq) bfq_merge_bfqqs(bfqd, RQ_BIC(rq), bfqq, new_bfqq); bfq_clear_bfqq_just_created(bfqq); /* * rq is about to be enqueued into new_bfqq, * release rq reference on bfqq */ bfq_put_queue(bfqq); rq->elv.priv[1] = new_bfqq; bfqq = new_bfqq; } waiting = bfqq && bfq_bfqq_wait_request(bfqq); bfq_add_request(rq); idle_timer_disabled = waiting && !bfq_bfqq_wait_request(bfqq); rq->fifo_time = ktime_get_ns() + bfqd->bfq_fifo_expire[rq_is_sync(rq)]; list_add_tail(&rq->queuelist, &bfqq->fifo); bfq_rq_enqueued(bfqd, bfqq, rq); return idle_timer_disabled; } #if defined(CONFIG_BFQ_GROUP_IOSCHED) && defined(CONFIG_DEBUG_BLK_CGROUP) static void bfq_update_insert_stats(struct request_queue *q, struct bfq_queue *bfqq, bool idle_timer_disabled, unsigned int cmd_flags) { if (!bfqq) return; /* * bfqq still exists, because it can disappear only after * either it is merged with another queue, or the process it * is associated with exits. But both actions must be taken by * the same process currently executing this flow of * instructions. * * In addition, the following queue lock guarantees that * bfqq_group(bfqq) exists as well. */ spin_lock_irq(q->queue_lock); bfqg_stats_update_io_add(bfqq_group(bfqq), bfqq, cmd_flags); if (idle_timer_disabled) bfqg_stats_update_idle_time(bfqq_group(bfqq)); spin_unlock_irq(q->queue_lock); } #else static inline void bfq_update_insert_stats(struct request_queue *q, struct bfq_queue *bfqq, bool idle_timer_disabled, unsigned int cmd_flags) {} #endif static void bfq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq, bool at_head) { struct request_queue *q = hctx->queue; struct bfq_data *bfqd = q->elevator->elevator_data; struct bfq_queue *bfqq; bool idle_timer_disabled = false; unsigned int cmd_flags; spin_lock_irq(&bfqd->lock); if (blk_mq_sched_try_insert_merge(q, rq)) { spin_unlock_irq(&bfqd->lock); return; } spin_unlock_irq(&bfqd->lock); blk_mq_sched_request_inserted(rq); spin_lock_irq(&bfqd->lock); bfqq = bfq_init_rq(rq); if (at_head || blk_rq_is_passthrough(rq)) { if (at_head) list_add(&rq->queuelist, &bfqd->dispatch); else list_add_tail(&rq->queuelist, &bfqd->dispatch); } else { /* bfqq is assumed to be non null here */ idle_timer_disabled = __bfq_insert_request(bfqd, rq); /* * Update bfqq, because, if a queue merge has occurred * in __bfq_insert_request, then rq has been * redirected into a new queue. */ bfqq = RQ_BFQQ(rq); if (rq_mergeable(rq)) { elv_rqhash_add(q, rq); if (!q->last_merge) q->last_merge = rq; } } /* * Cache cmd_flags before releasing scheduler lock, because rq * may disappear afterwards (for example, because of a request * merge). */ cmd_flags = rq->cmd_flags; spin_unlock_irq(&bfqd->lock); bfq_update_insert_stats(q, bfqq, idle_timer_disabled, cmd_flags); } static void bfq_insert_requests(struct blk_mq_hw_ctx *hctx, struct list_head *list, bool at_head) { while (!list_empty(list)) { struct request *rq; rq = list_first_entry(list, struct request, queuelist); list_del_init(&rq->queuelist); bfq_insert_request(hctx, rq, at_head); } } static void bfq_update_hw_tag(struct bfq_data *bfqd) { bfqd->max_rq_in_driver = max_t(int, bfqd->max_rq_in_driver, bfqd->rq_in_driver); if (bfqd->hw_tag == 1) return; /* * This sample is valid if the number of outstanding requests * is large enough to allow a queueing behavior. Note that the * sum is not exact, as it's not taking into account deactivated * requests. */ if (bfqd->rq_in_driver + bfqd->queued < BFQ_HW_QUEUE_THRESHOLD) return; if (bfqd->hw_tag_samples++ < BFQ_HW_QUEUE_SAMPLES) return; bfqd->hw_tag = bfqd->max_rq_in_driver > BFQ_HW_QUEUE_THRESHOLD; bfqd->max_rq_in_driver = 0; bfqd->hw_tag_samples = 0; } static void bfq_completed_request(struct bfq_queue *bfqq, struct bfq_data *bfqd) { u64 now_ns; u32 delta_us; bfq_update_hw_tag(bfqd); bfqd->rq_in_driver--; bfqq->dispatched--; if (!bfqq->dispatched && !bfq_bfqq_busy(bfqq)) { /* * Set budget_timeout (which we overload to store the * time at which the queue remains with no backlog and * no outstanding request; used by the weight-raising * mechanism). */ bfqq->budget_timeout = jiffies; bfq_weights_tree_remove(bfqd, bfqq); } now_ns = ktime_get_ns(); bfqq->ttime.last_end_request = now_ns; /* * Using us instead of ns, to get a reasonable precision in * computing rate in next check. */ delta_us = div_u64(now_ns - bfqd->last_completion, NSEC_PER_USEC); /* * If the request took rather long to complete, and, according * to the maximum request size recorded, this completion latency * implies that the request was certainly served at a very low * rate (less than 1M sectors/sec), then the whole observation * interval that lasts up to this time instant cannot be a * valid time interval for computing a new peak rate. Invoke * bfq_update_rate_reset to have the following three steps * taken: * - close the observation interval at the last (previous) * request dispatch or completion * - compute rate, if possible, for that observation interval * - reset to zero samples, which will trigger a proper * re-initialization of the observation interval on next * dispatch */ if (delta_us > BFQ_MIN_TT/NSEC_PER_USEC && (bfqd->last_rq_max_size<<BFQ_RATE_SHIFT)/delta_us < 1UL<<(BFQ_RATE_SHIFT - 10)) bfq_update_rate_reset(bfqd, NULL); bfqd->last_completion = now_ns; /* * If we are waiting to discover whether the request pattern * of the task associated with the queue is actually * isochronous, and both requisites for this condition to hold * are now satisfied, then compute soft_rt_next_start (see the * comments on the function bfq_bfqq_softrt_next_start()). We * schedule this delayed check when bfqq expires, if it still * has in-flight requests. */ if (bfq_bfqq_softrt_update(bfqq) && bfqq->dispatched == 0 && RB_EMPTY_ROOT(&bfqq->sort_list)) bfqq->soft_rt_next_start = bfq_bfqq_softrt_next_start(bfqd, bfqq); /* * If this is the in-service queue, check if it needs to be expired, * or if we want to idle in case it has no pending requests. */ if (bfqd->in_service_queue == bfqq) { if (bfq_bfqq_must_idle(bfqq)) { if (bfqq->dispatched == 0) bfq_arm_slice_timer(bfqd); /* * If we get here, we do not expire bfqq, even * if bfqq was in budget timeout or had no * more requests (as controlled in the next * conditional instructions). The reason for * not expiring bfqq is as follows. * * Here bfqq->dispatched > 0 holds, but * bfq_bfqq_must_idle() returned true. This * implies that, even if no request arrives * for bfqq before bfqq->dispatched reaches 0, * bfqq will, however, not be expired on the * completion event that causes bfqq->dispatch * to reach zero. In contrast, on this event, * bfqq will start enjoying device idling * (I/O-dispatch plugging). * * But, if we expired bfqq here, bfqq would * not have the chance to enjoy device idling * when bfqq->dispatched finally reaches * zero. This would expose bfqq to violation * of its reserved service guarantees. */ return; } else if (bfq_may_expire_for_budg_timeout(bfqq)) bfq_bfqq_expire(bfqd, bfqq, false, BFQQE_BUDGET_TIMEOUT); else if (RB_EMPTY_ROOT(&bfqq->sort_list) && (bfqq->dispatched == 0 || !bfq_better_to_idle(bfqq))) bfq_bfqq_expire(bfqd, bfqq, false, BFQQE_NO_MORE_REQUESTS); } if (!bfqd->rq_in_driver) bfq_schedule_dispatch(bfqd); } static void bfq_finish_requeue_request_body(struct bfq_queue *bfqq) { bfqq->allocated--; bfq_put_queue(bfqq); } /* * Handle either a requeue or a finish for rq. The things to do are * the same in both cases: all references to rq are to be dropped. In * particular, rq is considered completed from the point of view of * the scheduler. */ static void bfq_finish_requeue_request(struct request *rq) { struct bfq_queue *bfqq = RQ_BFQQ(rq); struct bfq_data *bfqd; /* * Requeue and finish hooks are invoked in blk-mq without * checking whether the involved request is actually still * referenced in the scheduler. To handle this fact, the * following two checks make this function exit in case of * spurious invocations, for which there is nothing to do. * * First, check whether rq has nothing to do with an elevator. */ if (unlikely(!(rq->rq_flags & RQF_ELVPRIV))) return; /* * rq either is not associated with any icq, or is an already * requeued request that has not (yet) been re-inserted into * a bfq_queue. */ if (!rq->elv.icq || !bfqq) return; bfqd = bfqq->bfqd; if (rq->rq_flags & RQF_STARTED) bfqg_stats_update_completion(bfqq_group(bfqq), rq->start_time_ns, rq->io_start_time_ns, rq->cmd_flags); if (likely(rq->rq_flags & RQF_STARTED)) { unsigned long flags; spin_lock_irqsave(&bfqd->lock, flags); bfq_completed_request(bfqq, bfqd); bfq_finish_requeue_request_body(bfqq); spin_unlock_irqrestore(&bfqd->lock, flags); } else { /* * Request rq may be still/already in the scheduler, * in which case we need to remove it (this should * never happen in case of requeue). And we cannot * defer such a check and removal, to avoid * inconsistencies in the time interval from the end * of this function to the start of the deferred work. * This situation seems to occur only in process * context, as a consequence of a merge. In the * current version of the code, this implies that the * lock is held. */ if (!RB_EMPTY_NODE(&rq->rb_node)) { bfq_remove_request(rq->q, rq); bfqg_stats_update_io_remove(bfqq_group(bfqq), rq->cmd_flags); } bfq_finish_requeue_request_body(bfqq); } /* * Reset private fields. In case of a requeue, this allows * this function to correctly do nothing if it is spuriously * invoked again on this same request (see the check at the * beginning of the function). Probably, a better general * design would be to prevent blk-mq from invoking the requeue * or finish hooks of an elevator, for a request that is not * referred by that elevator. * * Resetting the following fields would break the * request-insertion logic if rq is re-inserted into a bfq * internal queue, without a re-preparation. Here we assume * that re-insertions of requeued requests, without * re-preparation, can happen only for pass_through or at_head * requests (which are not re-inserted into bfq internal * queues). */ rq->elv.priv[0] = NULL; rq->elv.priv[1] = NULL; } /* * Returns NULL if a new bfqq should be allocated, or the old bfqq if this * was the last process referring to that bfqq. */ static struct bfq_queue * bfq_split_bfqq(struct bfq_io_cq *bic, struct bfq_queue *bfqq) { bfq_log_bfqq(bfqq->bfqd, bfqq, "splitting queue"); if (bfqq_process_refs(bfqq) == 1) { bfqq->pid = current->pid; bfq_clear_bfqq_coop(bfqq); bfq_clear_bfqq_split_coop(bfqq); return bfqq; } bic_set_bfqq(bic, NULL, 1); bfq_put_cooperator(bfqq); bfq_put_queue(bfqq); return NULL; } static struct bfq_queue *bfq_get_bfqq_handle_split(struct bfq_data *bfqd, struct bfq_io_cq *bic, struct bio *bio, bool split, bool is_sync, bool *new_queue) { struct bfq_queue *bfqq = bic_to_bfqq(bic, is_sync); if (likely(bfqq && bfqq != &bfqd->oom_bfqq)) return bfqq; if (new_queue) *new_queue = true; if (bfqq) bfq_put_queue(bfqq); bfqq = bfq_get_queue(bfqd, bio, is_sync, bic); bic_set_bfqq(bic, bfqq, is_sync); if (split && is_sync) { if ((bic->was_in_burst_list && bfqd->large_burst) || bic->saved_in_large_burst) bfq_mark_bfqq_in_large_burst(bfqq); else { bfq_clear_bfqq_in_large_burst(bfqq); if (bic->was_in_burst_list) /* * If bfqq was in the current * burst list before being * merged, then we have to add * it back. And we do not need * to increase burst_size, as * we did not decrement * burst_size when we removed * bfqq from the burst list as * a consequence of a merge * (see comments in * bfq_put_queue). In this * respect, it would be rather * costly to know whether the * current burst list is still * the same burst list from * which bfqq was removed on * the merge. To avoid this * cost, if bfqq was in a * burst list, then we add * bfqq to the current burst * list without any further * check. This can cause * inappropriate insertions, * but rarely enough to not * harm the detection of large * bursts significantly. */ hlist_add_head(&bfqq->burst_list_node, &bfqd->burst_list); } bfqq->split_time = jiffies; } return bfqq; } /* * Only reset private fields. The actual request preparation will be * performed by bfq_init_rq, when rq is either inserted or merged. See * comments on bfq_init_rq for the reason behind this delayed * preparation. */ static void bfq_prepare_request(struct request *rq, struct bio *bio) { /* * Regardless of whether we have an icq attached, we have to * clear the scheduler pointers, as they might point to * previously allocated bic/bfqq structs. */ rq->elv.priv[0] = rq->elv.priv[1] = NULL; } /* * If needed, init rq, allocate bfq data structures associated with * rq, and increment reference counters in the destination bfq_queue * for rq. Return the destination bfq_queue for rq, or NULL is rq is * not associated with any bfq_queue. * * This function is invoked by the functions that perform rq insertion * or merging. One may have expected the above preparation operations * to be performed in bfq_prepare_request, and not delayed to when rq * is inserted or merged. The rationale behind this delayed * preparation is that, after the prepare_request hook is invoked for * rq, rq may still be transformed into a request with no icq, i.e., a * request not associated with any queue. No bfq hook is invoked to * signal this tranformation. As a consequence, should these * preparation operations be performed when the prepare_request hook * is invoked, and should rq be transformed one moment later, bfq * would end up in an inconsistent state, because it would have * incremented some queue counters for an rq destined to * transformation, without any chance to correctly lower these * counters back. In contrast, no transformation can still happen for * rq after rq has been inserted or merged. So, it is safe to execute * these preparation operations when rq is finally inserted or merged. */ static struct bfq_queue *bfq_init_rq(struct request *rq) { struct request_queue *q = rq->q; struct bio *bio = rq->bio; struct bfq_data *bfqd = q->elevator->elevator_data; struct bfq_io_cq *bic; const int is_sync = rq_is_sync(rq); struct bfq_queue *bfqq; bool new_queue = false; bool bfqq_already_existing = false, split = false; if (unlikely(!rq->elv.icq)) return NULL; /* * Assuming that elv.priv[1] is set only if everything is set * for this rq. This holds true, because this function is * invoked only for insertion or merging, and, after such * events, a request cannot be manipulated any longer before * being removed from bfq. */ if (rq->elv.priv[1]) return rq->elv.priv[1]; bic = icq_to_bic(rq->elv.icq); bfq_check_ioprio_change(bic, bio); bfq_bic_update_cgroup(bic, bio); bfqq = bfq_get_bfqq_handle_split(bfqd, bic, bio, false, is_sync, &new_queue); if (likely(!new_queue)) { /* If the queue was seeky for too long, break it apart. */ if (bfq_bfqq_coop(bfqq) && bfq_bfqq_split_coop(bfqq)) { bfq_log_bfqq(bfqd, bfqq, "breaking apart bfqq"); /* Update bic before losing reference to bfqq */ if (bfq_bfqq_in_large_burst(bfqq)) bic->saved_in_large_burst = true; bfqq = bfq_split_bfqq(bic, bfqq); split = true; if (!bfqq) bfqq = bfq_get_bfqq_handle_split(bfqd, bic, bio, true, is_sync, NULL); else bfqq_already_existing = true; } } bfqq->allocated++; bfqq->ref++; bfq_log_bfqq(bfqd, bfqq, "get_request %p: bfqq %p, %d", rq, bfqq, bfqq->ref); rq->elv.priv[0] = bic; rq->elv.priv[1] = bfqq; /* * If a bfq_queue has only one process reference, it is owned * by only this bic: we can then set bfqq->bic = bic. in * addition, if the queue has also just been split, we have to * resume its state. */ if (likely(bfqq != &bfqd->oom_bfqq) && bfqq_process_refs(bfqq) == 1) { bfqq->bic = bic; if (split) { /* * The queue has just been split from a shared * queue: restore the idle window and the * possible weight raising period. */ bfq_bfqq_resume_state(bfqq, bfqd, bic, bfqq_already_existing); } } if (unlikely(bfq_bfqq_just_created(bfqq))) bfq_handle_burst(bfqd, bfqq); return bfqq; } static void bfq_idle_slice_timer_body(struct bfq_queue *bfqq) { struct bfq_data *bfqd = bfqq->bfqd; enum bfqq_expiration reason; unsigned long flags; spin_lock_irqsave(&bfqd->lock, flags); bfq_clear_bfqq_wait_request(bfqq); if (bfqq != bfqd->in_service_queue) { spin_unlock_irqrestore(&bfqd->lock, flags); return; } if (bfq_bfqq_budget_timeout(bfqq)) /* * Also here the queue can be safely expired * for budget timeout without wasting * guarantees */ reason = BFQQE_BUDGET_TIMEOUT; else if (bfqq->queued[0] == 0 && bfqq->queued[1] == 0) /* * The queue may not be empty upon timer expiration, * because we may not disable the timer when the * first request of the in-service queue arrives * during disk idling. */ reason = BFQQE_TOO_IDLE; else goto schedule_dispatch; bfq_bfqq_expire(bfqd, bfqq, true, reason); schedule_dispatch: spin_unlock_irqrestore(&bfqd->lock, flags); bfq_schedule_dispatch(bfqd); } /* * Handler of the expiration of the timer running if the in-service queue * is idling inside its time slice. */ static enum hrtimer_restart bfq_idle_slice_timer(struct hrtimer *timer) { struct bfq_data *bfqd = container_of(timer, struct bfq_data, idle_slice_timer); struct bfq_queue *bfqq = bfqd->in_service_queue; /* * Theoretical race here: the in-service queue can be NULL or * different from the queue that was idling if a new request * arrives for the current queue and there is a full dispatch * cycle that changes the in-service queue. This can hardly * happen, but in the worst case we just expire a queue too * early. */ if (bfqq) bfq_idle_slice_timer_body(bfqq); return HRTIMER_NORESTART; } static void __bfq_put_async_bfqq(struct bfq_data *bfqd, struct bfq_queue **bfqq_ptr) { struct bfq_queue *bfqq = *bfqq_ptr; bfq_log(bfqd, "put_async_bfqq: %p", bfqq); if (bfqq) { bfq_bfqq_move(bfqd, bfqq, bfqd->root_group); bfq_log_bfqq(bfqd, bfqq, "put_async_bfqq: putting %p, %d", bfqq, bfqq->ref); bfq_put_queue(bfqq); *bfqq_ptr = NULL; } } /* * Release all the bfqg references to its async queues. If we are * deallocating the group these queues may still contain requests, so * we reparent them to the root cgroup (i.e., the only one that will * exist for sure until all the requests on a device are gone). */ void bfq_put_async_queues(struct bfq_data *bfqd, struct bfq_group *bfqg) { int i, j; for (i = 0; i < 2; i++) for (j = 0; j < IOPRIO_BE_NR; j++) __bfq_put_async_bfqq(bfqd, &bfqg->async_bfqq[i][j]); __bfq_put_async_bfqq(bfqd, &bfqg->async_idle_bfqq); } /* * See the comments on bfq_limit_depth for the purpose of * the depths set in the function. Return minimum shallow depth we'll use. */ static unsigned int bfq_update_depths(struct bfq_data *bfqd, struct sbitmap_queue *bt) { unsigned int i, j, min_shallow = UINT_MAX; /* * In-word depths if no bfq_queue is being weight-raised: * leaving 25% of tags only for sync reads. * * In next formulas, right-shift the value * (1U<<bt->sb.shift), instead of computing directly * (1U<<(bt->sb.shift - something)), to be robust against * any possible value of bt->sb.shift, without having to * limit 'something'. */ /* no more than 50% of tags for async I/O */ bfqd->word_depths[0][0] = max((1U << bt->sb.shift) >> 1, 1U); /* * no more than 75% of tags for sync writes (25% extra tags * w.r.t. async I/O, to prevent async I/O from starving sync * writes) */ bfqd->word_depths[0][1] = max(((1U << bt->sb.shift) * 3) >> 2, 1U); /* * In-word depths in case some bfq_queue is being weight- * raised: leaving ~63% of tags for sync reads. This is the * highest percentage for which, in our tests, application * start-up times didn't suffer from any regression due to tag * shortage. */ /* no more than ~18% of tags for async I/O */ bfqd->word_depths[1][0] = max(((1U << bt->sb.shift) * 3) >> 4, 1U); /* no more than ~37% of tags for sync writes (~20% extra tags) */ bfqd->word_depths[1][1] = max(((1U << bt->sb.shift) * 6) >> 4, 1U); for (i = 0; i < 2; i++) for (j = 0; j < 2; j++) min_shallow = min(min_shallow, bfqd->word_depths[i][j]); return min_shallow; } static int bfq_init_hctx(struct blk_mq_hw_ctx *hctx, unsigned int index) { struct bfq_data *bfqd = hctx->queue->elevator->elevator_data; struct blk_mq_tags *tags = hctx->sched_tags; unsigned int min_shallow; min_shallow = bfq_update_depths(bfqd, &tags->bitmap_tags); sbitmap_queue_min_shallow_depth(&tags->bitmap_tags, min_shallow); return 0; } static void bfq_exit_queue(struct elevator_queue *e) { struct bfq_data *bfqd = e->elevator_data; struct bfq_queue *bfqq, *n; hrtimer_cancel(&bfqd->idle_slice_timer); spin_lock_irq(&bfqd->lock); list_for_each_entry_safe(bfqq, n, &bfqd->idle_list, bfqq_list) bfq_deactivate_bfqq(bfqd, bfqq, false, false); spin_unlock_irq(&bfqd->lock); hrtimer_cancel(&bfqd->idle_slice_timer); #ifdef CONFIG_BFQ_GROUP_IOSCHED /* release oom-queue reference to root group */ bfqg_and_blkg_put(bfqd->root_group); blkcg_deactivate_policy(bfqd->queue, &blkcg_policy_bfq); #else spin_lock_irq(&bfqd->lock); bfq_put_async_queues(bfqd, bfqd->root_group); kfree(bfqd->root_group); spin_unlock_irq(&bfqd->lock); #endif kfree(bfqd); } static void bfq_init_root_group(struct bfq_group *root_group, struct bfq_data *bfqd) { int i; #ifdef CONFIG_BFQ_GROUP_IOSCHED root_group->entity.parent = NULL; root_group->my_entity = NULL; root_group->bfqd = bfqd; #endif root_group->rq_pos_tree = RB_ROOT; for (i = 0; i < BFQ_IOPRIO_CLASSES; i++) root_group->sched_data.service_tree[i] = BFQ_SERVICE_TREE_INIT; root_group->sched_data.bfq_class_idle_last_service = jiffies; } static int bfq_init_queue(struct request_queue *q, struct elevator_type *e) { struct bfq_data *bfqd; struct elevator_queue *eq; eq = elevator_alloc(q, e); if (!eq) return -ENOMEM; bfqd = kzalloc_node(sizeof(*bfqd), GFP_KERNEL, q->node); if (!bfqd) { kobject_put(&eq->kobj); return -ENOMEM; } eq->elevator_data = bfqd; spin_lock_irq(q->queue_lock); q->elevator = eq; spin_unlock_irq(q->queue_lock); /* * Our fallback bfqq if bfq_find_alloc_queue() runs into OOM issues. * Grab a permanent reference to it, so that the normal code flow * will not attempt to free it. */ bfq_init_bfqq(bfqd, &bfqd->oom_bfqq, NULL, 1, 0); bfqd->oom_bfqq.ref++; bfqd->oom_bfqq.new_ioprio = BFQ_DEFAULT_QUEUE_IOPRIO; bfqd->oom_bfqq.new_ioprio_class = IOPRIO_CLASS_BE; bfqd->oom_bfqq.entity.new_weight = bfq_ioprio_to_weight(bfqd->oom_bfqq.new_ioprio); /* oom_bfqq does not participate to bursts */ bfq_clear_bfqq_just_created(&bfqd->oom_bfqq); /* * Trigger weight initialization, according to ioprio, at the * oom_bfqq's first activation. The oom_bfqq's ioprio and ioprio * class won't be changed any more. */ bfqd->oom_bfqq.entity.prio_changed = 1; bfqd->queue = q; INIT_LIST_HEAD(&bfqd->dispatch); hrtimer_init(&bfqd->idle_slice_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL); bfqd->idle_slice_timer.function = bfq_idle_slice_timer; bfqd->queue_weights_tree = RB_ROOT; bfqd->num_groups_with_pending_reqs = 0; INIT_LIST_HEAD(&bfqd->active_list); INIT_LIST_HEAD(&bfqd->idle_list); INIT_HLIST_HEAD(&bfqd->burst_list); bfqd->hw_tag = -1; bfqd->bfq_max_budget = bfq_default_max_budget; bfqd->bfq_fifo_expire[0] = bfq_fifo_expire[0]; bfqd->bfq_fifo_expire[1] = bfq_fifo_expire[1]; bfqd->bfq_back_max = bfq_back_max; bfqd->bfq_back_penalty = bfq_back_penalty; bfqd->bfq_slice_idle = bfq_slice_idle; bfqd->bfq_timeout = bfq_timeout; bfqd->bfq_requests_within_timer = 120; bfqd->bfq_large_burst_thresh = 8; bfqd->bfq_burst_interval = msecs_to_jiffies(180); bfqd->low_latency = true; /* * Trade-off between responsiveness and fairness. */ bfqd->bfq_wr_coeff = 30; bfqd->bfq_wr_rt_max_time = msecs_to_jiffies(300); bfqd->bfq_wr_max_time = 0; bfqd->bfq_wr_min_idle_time = msecs_to_jiffies(2000); bfqd->bfq_wr_min_inter_arr_async = msecs_to_jiffies(500); bfqd->bfq_wr_max_softrt_rate = 7000; /* * Approximate rate required * to playback or record a * high-definition compressed * video. */ bfqd->wr_busy_queues = 0; /* * Begin by assuming, optimistically, that the device peak * rate is equal to 2/3 of the highest reference rate. */ bfqd->rate_dur_prod = ref_rate[blk_queue_nonrot(bfqd->queue)] * ref_wr_duration[blk_queue_nonrot(bfqd->queue)]; bfqd->peak_rate = ref_rate[blk_queue_nonrot(bfqd->queue)] * 2 / 3; spin_lock_init(&bfqd->lock); /* * The invocation of the next bfq_create_group_hierarchy * function is the head of a chain of function calls * (bfq_create_group_hierarchy->blkcg_activate_policy-> * blk_mq_freeze_queue) that may lead to the invocation of the * has_work hook function. For this reason, * bfq_create_group_hierarchy is invoked only after all * scheduler data has been initialized, apart from the fields * that can be initialized only after invoking * bfq_create_group_hierarchy. This, in particular, enables * has_work to correctly return false. Of course, to avoid * other inconsistencies, the blk-mq stack must then refrain * from invoking further scheduler hooks before this init * function is finished. */ bfqd->root_group = bfq_create_group_hierarchy(bfqd, q->node); if (!bfqd->root_group) goto out_free; bfq_init_root_group(bfqd->root_group, bfqd); bfq_init_entity(&bfqd->oom_bfqq.entity, bfqd->root_group); wbt_disable_default(q); return 0; out_free: kfree(bfqd); kobject_put(&eq->kobj); return -ENOMEM; } static void bfq_slab_kill(void) { kmem_cache_destroy(bfq_pool); } static int __init bfq_slab_setup(void) { bfq_pool = KMEM_CACHE(bfq_queue, 0); if (!bfq_pool) return -ENOMEM; return 0; } static ssize_t bfq_var_show(unsigned int var, char *page) { return sprintf(page, "%u\n", var); } static int bfq_var_store(unsigned long *var, const char *page) { unsigned long new_val; int ret = kstrtoul(page, 10, &new_val); if (ret) return ret; *var = new_val; return 0; } #define SHOW_FUNCTION(__FUNC, __VAR, __CONV) \ static ssize_t __FUNC(struct elevator_queue *e, char *page) \ { \ struct bfq_data *bfqd = e->elevator_data; \ u64 __data = __VAR; \ if (__CONV == 1) \ __data = jiffies_to_msecs(__data); \ else if (__CONV == 2) \ __data = div_u64(__data, NSEC_PER_MSEC); \ return bfq_var_show(__data, (page)); \ } SHOW_FUNCTION(bfq_fifo_expire_sync_show, bfqd->bfq_fifo_expire[1], 2); SHOW_FUNCTION(bfq_fifo_expire_async_show, bfqd->bfq_fifo_expire[0], 2); SHOW_FUNCTION(bfq_back_seek_max_show, bfqd->bfq_back_max, 0); SHOW_FUNCTION(bfq_back_seek_penalty_show, bfqd->bfq_back_penalty, 0); SHOW_FUNCTION(bfq_slice_idle_show, bfqd->bfq_slice_idle, 2); SHOW_FUNCTION(bfq_max_budget_show, bfqd->bfq_user_max_budget, 0); SHOW_FUNCTION(bfq_timeout_sync_show, bfqd->bfq_timeout, 1); SHOW_FUNCTION(bfq_strict_guarantees_show, bfqd->strict_guarantees, 0); SHOW_FUNCTION(bfq_low_latency_show, bfqd->low_latency, 0); #undef SHOW_FUNCTION #define USEC_SHOW_FUNCTION(__FUNC, __VAR) \ static ssize_t __FUNC(struct elevator_queue *e, char *page) \ { \ struct bfq_data *bfqd = e->elevator_data; \ u64 __data = __VAR; \ __data = div_u64(__data, NSEC_PER_USEC); \ return bfq_var_show(__data, (page)); \ } USEC_SHOW_FUNCTION(bfq_slice_idle_us_show, bfqd->bfq_slice_idle); #undef USEC_SHOW_FUNCTION #define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV) \ static ssize_t \ __FUNC(struct elevator_queue *e, const char *page, size_t count) \ { \ struct bfq_data *bfqd = e->elevator_data; \ unsigned long __data, __min = (MIN), __max = (MAX); \ int ret; \ \ ret = bfq_var_store(&__data, (page)); \ if (ret) \ return ret; \ if (__data < __min) \ __data = __min; \ else if (__data > __max) \ __data = __max; \ if (__CONV == 1) \ *(__PTR) = msecs_to_jiffies(__data); \ else if (__CONV == 2) \ *(__PTR) = (u64)__data * NSEC_PER_MSEC; \ else \ *(__PTR) = __data; \ return count; \ } STORE_FUNCTION(bfq_fifo_expire_sync_store, &bfqd->bfq_fifo_expire[1], 1, INT_MAX, 2); STORE_FUNCTION(bfq_fifo_expire_async_store, &bfqd->bfq_fifo_expire[0], 1, INT_MAX, 2); STORE_FUNCTION(bfq_back_seek_max_store, &bfqd->bfq_back_max, 0, INT_MAX, 0); STORE_FUNCTION(bfq_back_seek_penalty_store, &bfqd->bfq_back_penalty, 1, INT_MAX, 0); STORE_FUNCTION(bfq_slice_idle_store, &bfqd->bfq_slice_idle, 0, INT_MAX, 2); #undef STORE_FUNCTION #define USEC_STORE_FUNCTION(__FUNC, __PTR, MIN, MAX) \ static ssize_t __FUNC(struct elevator_queue *e, const char *page, size_t count)\ { \ struct bfq_data *bfqd = e->elevator_data; \ unsigned long __data, __min = (MIN), __max = (MAX); \ int ret; \ \ ret = bfq_var_store(&__data, (page)); \ if (ret) \ return ret; \ if (__data < __min) \ __data = __min; \ else if (__data > __max) \ __data = __max; \ *(__PTR) = (u64)__data * NSEC_PER_USEC; \ return count; \ } USEC_STORE_FUNCTION(bfq_slice_idle_us_store, &bfqd->bfq_slice_idle, 0, UINT_MAX); #undef USEC_STORE_FUNCTION static ssize_t bfq_max_budget_store(struct elevator_queue *e, const char *page, size_t count) { struct bfq_data *bfqd = e->elevator_data; unsigned long __data; int ret; ret = bfq_var_store(&__data, (page)); if (ret) return ret; if (__data == 0) bfqd->bfq_max_budget = bfq_calc_max_budget(bfqd); else { if (__data > INT_MAX) __data = INT_MAX; bfqd->bfq_max_budget = __data; } bfqd->bfq_user_max_budget = __data; return count; } /* * Leaving this name to preserve name compatibility with cfq * parameters, but this timeout is used for both sync and async. */ static ssize_t bfq_timeout_sync_store(struct elevator_queue *e, const char *page, size_t count) { struct bfq_data *bfqd = e->elevator_data; unsigned long __data; int ret; ret = bfq_var_store(&__data, (page)); if (ret) return ret; if (__data < 1) __data = 1; else if (__data > INT_MAX) __data = INT_MAX; bfqd->bfq_timeout = msecs_to_jiffies(__data); if (bfqd->bfq_user_max_budget == 0) bfqd->bfq_max_budget = bfq_calc_max_budget(bfqd); return count; } static ssize_t bfq_strict_guarantees_store(struct elevator_queue *e, const char *page, size_t count) { struct bfq_data *bfqd = e->elevator_data; unsigned long __data; int ret; ret = bfq_var_store(&__data, (page)); if (ret) return ret; if (__data > 1) __data = 1; if (!bfqd->strict_guarantees && __data == 1 && bfqd->bfq_slice_idle < 8 * NSEC_PER_MSEC) bfqd->bfq_slice_idle = 8 * NSEC_PER_MSEC; bfqd->strict_guarantees = __data; return count; } static ssize_t bfq_low_latency_store(struct elevator_queue *e, const char *page, size_t count) { struct bfq_data *bfqd = e->elevator_data; unsigned long __data; int ret; ret = bfq_var_store(&__data, (page)); if (ret) return ret; if (__data > 1) __data = 1; if (__data == 0 && bfqd->low_latency != 0) bfq_end_wr(bfqd); bfqd->low_latency = __data; return count; } #define BFQ_ATTR(name) \ __ATTR(name, 0644, bfq_##name##_show, bfq_##name##_store) static struct elv_fs_entry bfq_attrs[] = { BFQ_ATTR(fifo_expire_sync), BFQ_ATTR(fifo_expire_async), BFQ_ATTR(back_seek_max), BFQ_ATTR(back_seek_penalty), BFQ_ATTR(slice_idle), BFQ_ATTR(slice_idle_us), BFQ_ATTR(max_budget), BFQ_ATTR(timeout_sync), BFQ_ATTR(strict_guarantees), BFQ_ATTR(low_latency), __ATTR_NULL }; static struct elevator_type iosched_bfq_mq = { .ops.mq = { .limit_depth = bfq_limit_depth, .prepare_request = bfq_prepare_request, .requeue_request = bfq_finish_requeue_request, .finish_request = bfq_finish_requeue_request, .exit_icq = bfq_exit_icq, .insert_requests = bfq_insert_requests, .dispatch_request = bfq_dispatch_request, .next_request = elv_rb_latter_request, .former_request = elv_rb_former_request, .allow_merge = bfq_allow_bio_merge, .bio_merge = bfq_bio_merge, .request_merge = bfq_request_merge, .requests_merged = bfq_requests_merged, .request_merged = bfq_request_merged, .has_work = bfq_has_work, .init_hctx = bfq_init_hctx, .init_sched = bfq_init_queue, .exit_sched = bfq_exit_queue, }, .uses_mq = true, .icq_size = sizeof(struct bfq_io_cq), .icq_align = __alignof__(struct bfq_io_cq), .elevator_attrs = bfq_attrs, .elevator_name = "bfq", .elevator_owner = THIS_MODULE, }; MODULE_ALIAS("bfq-iosched"); static int __init bfq_init(void) { int ret; #ifdef CONFIG_BFQ_GROUP_IOSCHED ret = blkcg_policy_register(&blkcg_policy_bfq); if (ret) return ret; #endif ret = -ENOMEM; if (bfq_slab_setup()) goto err_pol_unreg; /* * Times to load large popular applications for the typical * systems installed on the reference devices (see the * comments before the definition of the next * array). Actually, we use slightly lower values, as the * estimated peak rate tends to be smaller than the actual * peak rate. The reason for this last fact is that estimates * are computed over much shorter time intervals than the long * intervals typically used for benchmarking. Why? First, to * adapt more quickly to variations. Second, because an I/O * scheduler cannot rely on a peak-rate-evaluation workload to * be run for a long time. */ ref_wr_duration[0] = msecs_to_jiffies(7000); /* actually 8 sec */ ref_wr_duration[1] = msecs_to_jiffies(2500); /* actually 3 sec */ ret = elv_register(&iosched_bfq_mq); if (ret) goto slab_kill; return 0; slab_kill: bfq_slab_kill(); err_pol_unreg: #ifdef CONFIG_BFQ_GROUP_IOSCHED blkcg_policy_unregister(&blkcg_policy_bfq); #endif return ret; } static void __exit bfq_exit(void) { elv_unregister(&iosched_bfq_mq); #ifdef CONFIG_BFQ_GROUP_IOSCHED blkcg_policy_unregister(&blkcg_policy_bfq); #endif bfq_slab_kill(); } module_init(bfq_init); module_exit(bfq_exit); MODULE_AUTHOR("Paolo Valente"); MODULE_LICENSE("GPL"); MODULE_DESCRIPTION("MQ Budget Fair Queueing I/O Scheduler");
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