cregit-Linux how code gets into the kernel

Release 4.18 block/bfq-iosched.c

Directory: block
/*
 * 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;

/*
 * Async to sync throughput distribution is controlled as follows:
 * when an async request is served, the entity is charged the number
 * of sectors of the request, multiplied by the factor below
 */

static const int bfq_async_charge_factor = 10;

/* 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];
}


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void bic_set_bfqq(struct bfq_io_cq *bic, struct bfq_queue *bfqq, bool is_sync)
{
	bic->bfqq[is_sync] = bfqq;
}


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struct bfq_data *bic_to_bfqd(struct bfq_io_cq *bic)
{
	return bic->icq.q->elevator->elevator_data;
}


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/**
 * 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);
}


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/**
 * 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;
}


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/*
 * 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);
	}
}


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#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;
	}
}


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/*
 * 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);
}


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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;
}


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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);
}


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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;
}


Contributors
PersonTokensPropCommitsCommitProp
Arianna Avanzini14594.16%150.00%


Paolo Valente95.84%150.00%


Total154100.00%2100.00%



/*
 * Tell whether there are active queues or groups with differentiated weights.
 */



static bool bfq_differentiated_weights(struct bfq_data *bfqd)
{
	/*
         * For weights to differ, at least one of the trees 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
	       ) ||
	       (!RB_EMPTY_ROOT(&bfqd->group_weights_tree) &&
		(bfqd->group_weights_tree.rb_node->rb_left ||
		 bfqd->group_weights_tree.rb_node->rb_right)
#endif
	       );
}


Contributors
PersonTokensPropCommitsCommitProp
Arianna Avanzini76100.00%1100.00%


Total76100.00%1100.00%



/*
 * 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_bfqq_may_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
 * above symmetry conditions would be quite complex and time-consuming.
 * Therefore this function evaluates, instead, the following stronger
 * sub-conditions, for which it is much easier to maintain the needed
 * state:
 * 1) all active queues have the same weight,
 * 2) all active groups have the same weight,
 * 3) all active groups have at most one active child each.
 * In particular, the last two conditions are always true if hierarchical
 * support and 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_differentiated_weights(bfqd);
}


Contributors
PersonTokensPropCommitsCommitProp
Arianna Avanzini18100.00%1100.00%


Total18100.00%1100.00%



/*
 * If the weight-counter tree passed as input contains no counter for
 * the weight of the input entity, 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_entity *entity,
			  struct rb_root *root)
{
	struct rb_node **new = &(root->rb_node), *parent = NULL;

	/*
         * Do not insert if the entity is already associated with a
         * counter, which happens if:
         *   1) the entity is associated with a queue,
         *   2) 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,
         *   3) 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 (entity->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) {
			entity->weight_counter = __counter;
			goto inc_counter;
		}
		if (entity->weight < __counter->weight)
			new = &((*new)->rb_left);
		else
			new = &((*new)->rb_right);
	}

	entity->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 entity to not be
         * considered in bfq_differentiated_weights, which, in its
         * turn, causes the scenario to be deemed wrongly symmetric in
         * case entity's weight would have been the only weight making
         * the scenario asymmetric. On the bright side, no unbalance
         * will however occur when entity becomes inactive again (the
         * invocation of this function is triggered by an activation
         * of entity). In fact, bfq_weights_tree_remove does nothing
         * if !entity->weight_counter.
         */
	if (unlikely(!entity->weight_counter))
		return;

	entity->weight_counter->weight = entity->weight;
	rb_link_node(&entity->weight_counter->weights_node, parent, new);
	rb_insert_color(&entity->weight_counter->weights_node, root);

inc_counter:
	entity->weight_counter->num_active++;
}


Contributors
PersonTokensPropCommitsCommitProp
Arianna Avanzini19596.53%266.67%


Paolo Valente73.47%133.33%


Total202100.00%3100.00%



/*
 * Decrement the weight counter associated with the entity, 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_entity *entity,
			     struct rb_root *root)
{
	if (!entity->weight_counter)
		return;

	entity->weight_counter->num_active--;
	if (entity->weight_counter->num_active > 0)
		goto reset_entity_pointer;

	rb_erase(&entity->weight_counter->weights_node, root);
	kfree(entity->weight_counter);

reset_entity_pointer:
	entity->weight_counter = NULL;
}


Contributors
PersonTokensPropCommitsCommitProp
Arianna Avanzini5573.33%266.67%


Paolo Valente2026.67%133.33%


Total75100.00%3100.00%



/*
 * 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;
}


Contributors
PersonTokensPropCommitsCommitProp
Arianna Avanzini4960.49%125.00%


Paolo Valente3239.51%375.00%


Total81100.00%4100.00%






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));
}


Contributors
PersonTokensPropCommitsCommitProp
Arianna Avanzini11982.64%150.00%


Paolo Valente2517.36%150.00%


Total144100.00%2100.00%



/* 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);

	/*
         * If there are no weight-raised queues, then amplify service
         * by just the async charge factor; otherwise amplify service
         * by twice the async charge factor, to further reduce latency
         * for weight-raised queues.
         */
	if (bfqq->bfqd->wr_busy_queues == 0)
		return blk_rq_sectors(rq) * bfq_async_charge_factor;

	return blk_rq_sectors(rq) * 2 * bfq_async_charge_factor;
}


Contributors
PersonTokensPropCommitsCommitProp
Arianna Avanzini65100.00%1100.00%


Total65100.00%1100.00%



/**
 * 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);
	}
}


Contributors
PersonTokensPropCommitsCommitProp
Paolo Valente6260.78%250.00%


Arianna Avanzini4039.22%250.00%


Total102100.00%4100.00%






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));
}


Contributors
PersonTokensPropCommitsCommitProp
Paolo Valente5388.33%266.67%


Davide Sapienza711.67%133.33%


Total60100.00%3100.00%



/* 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;
}


Contributors
PersonTokensPropCommitsCommitProp
Paolo Valente41100.00%1100.00%


Total41100.00%1100.00%





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--;
}


Contributors
PersonTokensPropCommitsCommitProp
Paolo Valente13051.18%466.67%


Arianna Avanzini12448.82%233.33%


Total254100.00%6100.00%






static int bfqq_process_refs(struct bfq_queue *bfqq)
{
	return bfqq->ref - bfqq->allocated - bfqq->entity.on_st;
}


Contributors
PersonTokensPropCommitsCommitProp
Arianna Avanzini26100.00%1100.00%


Total26100.00%1100.00%



/* 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;
}


Contributors
PersonTokensPropCommitsCommitProp
Arianna Avanzini73100.00%2100.00%


Total73100.00%2100.00%



/* 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(&