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Release 4.15 block/mq-deadline.c

Directory: block
/*
 *  MQ Deadline i/o scheduler - adaptation of the legacy deadline scheduler,
 *  for the blk-mq scheduling framework
 *
 *  Copyright (C) 2016 Jens Axboe <axboe@kernel.dk>
 */
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/blkdev.h>
#include <linux/blk-mq.h>
#include <linux/elevator.h>
#include <linux/bio.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/compiler.h>
#include <linux/rbtree.h>
#include <linux/sbitmap.h>

#include "blk.h"
#include "blk-mq.h"
#include "blk-mq-debugfs.h"
#include "blk-mq-tag.h"
#include "blk-mq-sched.h"

/*
 * See Documentation/block/deadline-iosched.txt
 */

static const int read_expire = HZ / 2;  
/* max time before a read is submitted. */

static const int write_expire = 5 * HZ; 
/* ditto for writes, these limits are SOFT! */

static const int writes_starved = 2;    
/* max times reads can starve a write */

static const int fifo_batch = 16;       
/* # of sequential requests treated as one
                                     by the above parameters. For throughput. */


struct deadline_data {
	/*
         * run time data
         */

	/*
         * requests (deadline_rq s) are present on both sort_list and fifo_list
         */
	
struct rb_root sort_list[2];
	
struct list_head fifo_list[2];

	/*
         * next in sort order. read, write or both are NULL
         */
	
struct request *next_rq[2];
	
unsigned int batching;		/* number of sequential requests made */
	
unsigned int starved;		/* times reads have starved writes */

	/*
         * settings that change how the i/o scheduler behaves
         */
	
int fifo_expire[2];
	
int fifo_batch;
	
int writes_starved;
	
int front_merges;

	
spinlock_t lock;
	
struct list_head dispatch;
};


static inline struct rb_root * deadline_rb_root(struct deadline_data *dd, struct request *rq) { return &dd->sort_list[rq_data_dir(rq)]; }

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/* * get the request after `rq' in sector-sorted order */
static inline struct request * deadline_latter_request(struct request *rq) { struct rb_node *node = rb_next(&rq->rb_node); if (node) return rb_entry_rq(node); return NULL; }

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static void deadline_add_rq_rb(struct deadline_data *dd, struct request *rq) { struct rb_root *root = deadline_rb_root(dd, rq); elv_rb_add(root, rq); }

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static inline void deadline_del_rq_rb(struct deadline_data *dd, struct request *rq) { const int data_dir = rq_data_dir(rq); if (dd->next_rq[data_dir] == rq) dd->next_rq[data_dir] = deadline_latter_request(rq); elv_rb_del(deadline_rb_root(dd, rq), rq); }

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/* * remove rq from rbtree and fifo. */
static void deadline_remove_request(struct request_queue *q, struct request *rq) { struct deadline_data *dd = q->elevator->elevator_data; list_del_init(&rq->queuelist); /* * We might not be on the rbtree, if we are doing an insert merge */ if (!RB_EMPTY_NODE(&rq->rb_node)) deadline_del_rq_rb(dd, rq); elv_rqhash_del(q, rq); if (q->last_merge == rq) q->last_merge = NULL; }

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static void dd_request_merged(struct request_queue *q, struct request *req, enum elv_merge type) { struct deadline_data *dd = q->elevator->elevator_data; /* * if the merge was a front merge, we need to reposition request */ if (type == ELEVATOR_FRONT_MERGE) { elv_rb_del(deadline_rb_root(dd, req), req); deadline_add_rq_rb(dd, req); } }

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static void dd_merged_requests(struct request_queue *q, struct request *req, struct request *next) { /* * if next expires before rq, assign its expire time to rq * and move into next position (next will be deleted) in fifo */ if (!list_empty(&req->queuelist) && !list_empty(&next->queuelist)) { if (time_before((unsigned long)next->fifo_time, (unsigned long)req->fifo_time)) { list_move(&req->queuelist, &next->queuelist); req->fifo_time = next->fifo_time; } } /* * kill knowledge of next, this one is a goner */ deadline_remove_request(q, next); }

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/* * move an entry to dispatch queue */
static void deadline_move_request(struct deadline_data *dd, struct request *rq) { const int data_dir = rq_data_dir(rq); dd->next_rq[READ] = NULL; dd->next_rq[WRITE] = NULL; dd->next_rq[data_dir] = deadline_latter_request(rq); /* * take it off the sort and fifo list */ deadline_remove_request(rq->q, rq); }

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/* * deadline_check_fifo returns 0 if there are no expired requests on the fifo, * 1 otherwise. Requires !list_empty(&dd->fifo_list[data_dir]) */
static inline int deadline_check_fifo(struct deadline_data *dd, int ddir) { struct request *rq = rq_entry_fifo(dd->fifo_list[ddir].next); /* * rq is expired! */ if (time_after_eq(jiffies, (unsigned long)rq->fifo_time)) return 1; return 0; }

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/* * deadline_dispatch_requests selects the best request according to * read/write expire, fifo_batch, etc */
static struct request *__dd_dispatch_request(struct blk_mq_hw_ctx *hctx) { struct deadline_data *dd = hctx->queue->elevator->elevator_data; struct request *rq; bool reads, writes; int data_dir; if (!list_empty(&dd->dispatch)) { rq = list_first_entry(&dd->dispatch, struct request, queuelist); list_del_init(&rq->queuelist); goto done; } reads = !list_empty(&dd->fifo_list[READ]); writes = !list_empty(&dd->fifo_list[WRITE]); /* * batches are currently reads XOR writes */ if (dd->next_rq[WRITE]) rq = dd->next_rq[WRITE]; else rq = dd->next_rq[READ]; if (rq && dd->batching < dd->fifo_batch) /* we have a next request are still entitled to batch */ goto dispatch_request; /* * at this point we are not running a batch. select the appropriate * data direction (read / write) */ if (reads) { BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[READ])); if (writes && (dd->starved++ >= dd->writes_starved)) goto dispatch_writes; data_dir = READ; goto dispatch_find_request; } /* * there are either no reads or writes have been starved */ if (writes) { dispatch_writes: BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[WRITE])); dd->starved = 0; data_dir = WRITE; goto dispatch_find_request; } return NULL; dispatch_find_request: /* * we are not running a batch, find best request for selected data_dir */ if (deadline_check_fifo(dd, data_dir) || !dd->next_rq[data_dir]) { /* * A deadline has expired, the last request was in the other * direction, or we have run out of higher-sectored requests. * Start again from the request with the earliest expiry time. */ rq = rq_entry_fifo(dd->fifo_list[data_dir].next); } else { /* * The last req was the same dir and we have a next request in * sort order. No expired requests so continue on from here. */ rq = dd->next_rq[data_dir]; } dd->batching = 0; dispatch_request: /* * rq is the selected appropriate request. */ dd->batching++; deadline_move_request(dd, rq); done: rq->rq_flags |= RQF_STARTED; return rq; }

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static struct request *dd_dispatch_request(struct blk_mq_hw_ctx *hctx) { struct deadline_data *dd = hctx->queue->elevator->elevator_data; struct request *rq; spin_lock(&dd->lock); rq = __dd_dispatch_request(hctx); spin_unlock(&dd->lock); return rq; }

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static void dd_exit_queue(struct elevator_queue *e) { struct deadline_data *dd = e->elevator_data; BUG_ON(!list_empty(&dd->fifo_list[READ])); BUG_ON(!list_empty(&dd->fifo_list[WRITE])); kfree(dd); }

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/* * initialize elevator private data (deadline_data). */
static int dd_init_queue(struct request_queue *q, struct elevator_type *e) { struct deadline_data *dd; struct elevator_queue *eq; eq = elevator_alloc(q, e); if (!eq) return -ENOMEM; dd = kzalloc_node(sizeof(*dd), GFP_KERNEL, q->node); if (!dd) { kobject_put(&eq->kobj); return -ENOMEM; } eq->elevator_data = dd; INIT_LIST_HEAD(&dd->fifo_list[READ]); INIT_LIST_HEAD(&dd->fifo_list[WRITE]); dd->sort_list[READ] = RB_ROOT; dd->sort_list[WRITE] = RB_ROOT; dd->fifo_expire[READ] = read_expire; dd->fifo_expire[WRITE] = write_expire; dd->writes_starved = writes_starved; dd->front_merges = 1; dd->fifo_batch = fifo_batch; spin_lock_init(&dd->lock); INIT_LIST_HEAD(&dd->dispatch); q->elevator = eq; return 0; }

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static int dd_request_merge(struct request_queue *q, struct request **rq, struct bio *bio) { struct deadline_data *dd = q->elevator->elevator_data; sector_t sector = bio_end_sector(bio); struct request *__rq; if (!dd->front_merges) return ELEVATOR_NO_MERGE; __rq = elv_rb_find(&dd->sort_list[bio_data_dir(bio)], sector); if (__rq) { BUG_ON(sector != blk_rq_pos(__rq)); if (elv_bio_merge_ok(__rq, bio)) { *rq = __rq; return ELEVATOR_FRONT_MERGE; } } return ELEVATOR_NO_MERGE; }

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static bool dd_bio_merge(struct blk_mq_hw_ctx *hctx, struct bio *bio) { struct request_queue *q = hctx->queue; struct deadline_data *dd = q->elevator->elevator_data; struct request *free = NULL; bool ret; spin_lock(&dd->lock); ret = blk_mq_sched_try_merge(q, bio, &free); spin_unlock(&dd->lock); if (free) blk_mq_free_request(free); return ret; }

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/* * add rq to rbtree and fifo */
static void dd_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq, bool at_head) { struct request_queue *q = hctx->queue; struct deadline_data *dd = q->elevator->elevator_data; const int data_dir = rq_data_dir(rq); if (blk_mq_sched_try_insert_merge(q, rq)) return; blk_mq_sched_request_inserted(rq); if (at_head || blk_rq_is_passthrough(rq)) { if (at_head) list_add(&rq->queuelist, &dd->dispatch); else list_add_tail(&rq->queuelist, &dd->dispatch); } else { deadline_add_rq_rb(dd, rq); if (rq_mergeable(rq)) { elv_rqhash_add(q, rq); if (!q->last_merge) q->last_merge = rq; } /* * set expire time and add to fifo list */ rq->fifo_time = jiffies + dd->fifo_expire[data_dir]; list_add_tail(&rq->queuelist, &dd->fifo_list[data_dir]); } }

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static void dd_insert_requests(struct blk_mq_hw_ctx *hctx, struct list_head *list, bool at_head) { struct request_queue *q = hctx->queue; struct deadline_data *dd = q->elevator->elevator_data; spin_lock(&dd->lock); while (!list_empty(list)) { struct request *rq; rq = list_first_entry(list, struct request, queuelist); list_del_init(&rq->queuelist); dd_insert_request(hctx, rq, at_head); } spin_unlock(&dd->lock); }

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static bool dd_has_work(struct blk_mq_hw_ctx *hctx) { struct deadline_data *dd = hctx->queue->elevator->elevator_data; return !list_empty_careful(&dd->dispatch) || !list_empty_careful(&dd->fifo_list[0]) || !list_empty_careful(&dd->fifo_list[1]); }

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/* * sysfs parts below */
static ssize_t deadline_var_show(int var, char *page) { return sprintf(page, "%d\n", var); }

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static void deadline_var_store(int *var, const char *page) { char *p = (char *) page; *var = simple_strtol(p, &p, 10); }

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#define SHOW_FUNCTION(__FUNC, __VAR, __CONV) \ static ssize_t __FUNC(struct elevator_queue *e, char *page) \ { \ struct deadline_data *dd = e->elevator_data; \ int __data = __VAR; \ if (__CONV) \ __data = jiffies_to_msecs(__data); \ return deadline_var_show(__data, (page)); \ } SHOW_FUNCTION(deadline_read_expire_show, dd->fifo_expire[READ], 1); SHOW_FUNCTION(deadline_write_expire_show, dd->fifo_expire[WRITE], 1); SHOW_FUNCTION(deadline_writes_starved_show, dd->writes_starved, 0); SHOW_FUNCTION(deadline_front_merges_show, dd->front_merges, 0); SHOW_FUNCTION(deadline_fifo_batch_show, dd->fifo_batch, 0); #undef 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 deadline_data *dd = e->elevator_data; \ int __data; \ deadline_var_store(&__data, (page)); \ if (__data < (MIN)) \ __data = (MIN); \ else if (__data > (MAX)) \ __data = (MAX); \ if (__CONV) \ *(__PTR) = msecs_to_jiffies(__data); \ else \ *(__PTR) = __data; \ return count; \ } STORE_FUNCTION(deadline_read_expire_store, &dd->fifo_expire[READ], 0, INT_MAX, 1); STORE_FUNCTION(deadline_write_expire_store, &dd->fifo_expire[WRITE], 0, INT_MAX, 1); STORE_FUNCTION(deadline_writes_starved_store, &dd->writes_starved, INT_MIN, INT_MAX, 0); STORE_FUNCTION(deadline_front_merges_store, &dd->front_merges, 0, 1, 0); STORE_FUNCTION(deadline_fifo_batch_store, &dd->fifo_batch, 0, INT_MAX, 0); #undef STORE_FUNCTION #define DD_ATTR(name) \ __ATTR(name, S_IRUGO|S_IWUSR, deadline_##name##_show, \ deadline_##name##_store) static struct elv_fs_entry deadline_attrs[] = { DD_ATTR(read_expire), DD_ATTR(write_expire), DD_ATTR(writes_starved), DD_ATTR(front_merges), DD_ATTR(fifo_batch), __ATTR_NULL }; #ifdef CONFIG_BLK_DEBUG_FS #define DEADLINE_DEBUGFS_DDIR_ATTRS(ddir, name) \ static void *deadline_##name##_fifo_start(struct seq_file *m, \ loff_t *pos) \ __acquires(&dd->lock) \ { \ struct request_queue *q = m->private; \ struct deadline_data *dd = q->elevator->elevator_data; \ \ spin_lock(&dd->lock); \ return seq_list_start(&dd->fifo_list[ddir], *pos); \ } \ \ static void *deadline_##name##_fifo_next(struct seq_file *m, void *v, \ loff_t *pos) \ { \ struct request_queue *q = m->private; \ struct deadline_data *dd = q->elevator->elevator_data; \ \ return seq_list_next(v, &dd->fifo_list[ddir], pos); \ } \ \ static void deadline_##name##_fifo_stop(struct seq_file *m, void *v) \ __releases(&dd->lock) \ { \ struct request_queue *q = m->private; \ struct deadline_data *dd = q->elevator->elevator_data; \ \ spin_unlock(&dd->lock); \ } \ \ static const struct seq_operations deadline_##name##_fifo_seq_ops = { \ .start = deadline_##name##_fifo_start, \ .next = deadline_##name##_fifo_next, \ .stop = deadline_##name##_fifo_stop, \ .show = blk_mq_debugfs_rq_show, \ }; \ \ static int deadline_##name##_next_rq_show(void *data, \ struct seq_file *m) \ { \ struct request_queue *q = data; \ struct deadline_data *dd = q->elevator->elevator_data; \ struct request *rq = dd->next_rq[ddir]; \ \ if (rq) \ __blk_mq_debugfs_rq_show(m, rq); \ return 0; \ } DEADLINE_DEBUGFS_DDIR_ATTRS(READ, read) DEADLINE_DEBUGFS_DDIR_ATTRS(WRITE, write) #undef DEADLINE_DEBUGFS_DDIR_ATTRS
static int deadline_batching_show(void *data, struct seq_file *m) { struct request_queue *q = data; struct deadline_data *dd = q->elevator->elevator_data; seq_printf(m, "%u\n", dd->batching); return 0; }

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static int deadline_starved_show(void *data, struct seq_file *m) { struct request_queue *q = data; struct deadline_data *dd = q->elevator->elevator_data; seq_printf(m, "%u\n", dd->starved); return 0; }

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static void *deadline_dispatch_start(struct seq_file *m, loff_t *pos) __acquires(&dd->lock

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) { struct request_queue *q = m->private; struct deadline_data *dd = q->elevator->elevator_data; spin_lock(&dd->lock); return seq_list_start(&dd->dispatch, *pos); }
static void *deadline_dispatch_next(struct seq_file *m, void *v, loff_t *pos) { struct request_queue *q = m->private; struct deadline_data *dd = q->elevator->elevator_data; return seq_list_next(v, &dd->dispatch, pos); }

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static void deadline_dispatch_stop(struct seq_file *m, void *v) __releases(&dd->lock

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) { struct request_queue *q = m->private; struct deadline_data *dd = q->elevator->elevator_data; spin_unlock(&dd->lock); } static const struct seq_operations deadline_dispatch_seq_ops = { .start = deadline_dispatch_start, .next = deadline_dispatch_next, .stop = deadline_dispatch_stop, .show = blk_mq_debugfs_rq_show, }; #define DEADLINE_QUEUE_DDIR_ATTRS(name) \ {#name "_fifo_list", 0400, .seq_ops = &deadline_##name##_fifo_seq_ops}, \ {#name "_next_rq", 0400, deadline_##name##_next_rq_show} static const struct blk_mq_debugfs_attr deadline_queue_debugfs_attrs[] = { DEADLINE_QUEUE_DDIR_ATTRS(read), DEADLINE_QUEUE_DDIR_ATTRS(write), {"batching", 0400, deadline_batching_show}, {"starved", 0400, deadline_starved_show}, {"dispatch", 0400, .seq_ops = &deadline_dispatch_seq_ops}, {}, }; #undef DEADLINE_QUEUE_DDIR_ATTRS #endif static struct elevator_type mq_deadline = { .ops.mq = { .insert_requests = dd_insert_requests, .dispatch_request = dd_dispatch_request, .next_request = elv_rb_latter_request, .former_request = elv_rb_former_request, .bio_merge = dd_bio_merge, .request_merge = dd_request_merge, .requests_merged = dd_merged_requests, .request_merged = dd_request_merged, .has_work = dd_has_work, .init_sched = dd_init_queue, .exit_sched = dd_exit_queue, }, .uses_mq = true, #ifdef CONFIG_BLK_DEBUG_FS .queue_debugfs_attrs = deadline_queue_debugfs_attrs, #endif .elevator_attrs = deadline_attrs, .elevator_name = "mq-deadline", .elevator_alias = "deadline", .elevator_owner = THIS_MODULE, }; MODULE_ALIAS("mq-deadline-iosched");
static int __init deadline_init(void) { return elv_register(&mq_deadline); }

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static void __exit deadline_exit(void) { elv_unregister(&mq_deadline); }

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module_init(deadline_init); module_exit(deadline_exit); MODULE_AUTHOR("Jens Axboe"); MODULE_LICENSE("GPL"); MODULE_DESCRIPTION("MQ deadline IO scheduler");

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