2 * linux/drivers/block/elevator.c
4 * Block device elevator/IO-scheduler.
6 * Copyright (C) 2000 Andrea Arcangeli <andrea@suse.de> SuSE
8 * 30042000 Jens Axboe <axboe@suse.de> :
10 * Split the elevator a bit so that it is possible to choose a different
11 * one or even write a new "plug in". There are three pieces:
12 * - elevator_fn, inserts a new request in the queue list
13 * - elevator_merge_fn, decides whether a new buffer can be merged with
15 * - elevator_dequeue_fn, called when a request is taken off the active list
17 * 20082000 Dave Jones <davej@suse.de> :
18 * Removed tests for max-bomb-segments, which was breaking elvtune
19 * when run without -bN
22 * - Rework again to work with bio instead of buffer_heads
23 * - loose bi_dev comparisons, partition handling is right now
24 * - completely modularize elevator setup and teardown
27 #include <linux/kernel.h>
29 #include <linux/blkdev.h>
30 #include <linux/elevator.h>
31 #include <linux/bio.h>
32 #include <linux/config.h>
33 #include <linux/module.h>
34 #include <linux/slab.h>
35 #include <linux/init.h>
36 #include <linux/compiler.h>
38 #include <asm/uaccess.h>
40 static DEFINE_SPINLOCK(elv_list_lock);
41 static LIST_HEAD(elv_list);
44 * can we safely merge with this request?
46 inline int elv_rq_merge_ok(struct request *rq, struct bio *bio)
48 if (!rq_mergeable(rq))
52 * different data direction or already started, don't merge
54 if (bio_data_dir(bio) != rq_data_dir(rq))
58 * same device and no special stuff set, merge is ok
60 if (rq->rq_disk == bio->bi_bdev->bd_disk &&
61 !rq->waiting && !rq->special)
66 EXPORT_SYMBOL(elv_rq_merge_ok);
68 inline int elv_try_merge(struct request *__rq, struct bio *bio)
70 int ret = ELEVATOR_NO_MERGE;
73 * we can merge and sequence is ok, check if it's possible
75 if (elv_rq_merge_ok(__rq, bio)) {
76 if (__rq->sector + __rq->nr_sectors == bio->bi_sector)
77 ret = ELEVATOR_BACK_MERGE;
78 else if (__rq->sector - bio_sectors(bio) == bio->bi_sector)
79 ret = ELEVATOR_FRONT_MERGE;
84 EXPORT_SYMBOL(elv_try_merge);
86 static struct elevator_type *elevator_find(const char *name)
88 struct elevator_type *e = NULL;
89 struct list_head *entry;
91 list_for_each(entry, &elv_list) {
92 struct elevator_type *__e;
94 __e = list_entry(entry, struct elevator_type, list);
96 if (!strcmp(__e->elevator_name, name)) {
105 static void elevator_put(struct elevator_type *e)
107 module_put(e->elevator_owner);
110 static struct elevator_type *elevator_get(const char *name)
112 struct elevator_type *e;
114 spin_lock_irq(&elv_list_lock);
116 e = elevator_find(name);
117 if (e && !try_module_get(e->elevator_owner))
120 spin_unlock_irq(&elv_list_lock);
125 static int elevator_attach(request_queue_t *q, struct elevator_type *e,
126 struct elevator_queue *eq)
130 memset(eq, 0, sizeof(*eq));
132 eq->elevator_type = e;
134 INIT_LIST_HEAD(&q->queue_head);
135 q->last_merge = NULL;
138 q->boundary_rq = NULL;
140 if (eq->ops->elevator_init_fn)
141 ret = eq->ops->elevator_init_fn(q, eq);
146 static char chosen_elevator[16];
148 static void elevator_setup_default(void)
150 struct elevator_type *e;
153 * check if default is set and exists
155 if (chosen_elevator[0] && (e = elevator_get(chosen_elevator))) {
160 #if defined(CONFIG_IOSCHED_AS)
161 strcpy(chosen_elevator, "anticipatory");
162 #elif defined(CONFIG_IOSCHED_DEADLINE)
163 strcpy(chosen_elevator, "deadline");
164 #elif defined(CONFIG_IOSCHED_CFQ)
165 strcpy(chosen_elevator, "cfq");
166 #elif defined(CONFIG_IOSCHED_NOOP)
167 strcpy(chosen_elevator, "noop");
169 #error "You must build at least 1 IO scheduler into the kernel"
173 static int __init elevator_setup(char *str)
175 strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1);
179 __setup("elevator=", elevator_setup);
181 int elevator_init(request_queue_t *q, char *name)
183 struct elevator_type *e = NULL;
184 struct elevator_queue *eq;
187 elevator_setup_default();
190 name = chosen_elevator;
192 e = elevator_get(name);
196 eq = kmalloc(sizeof(struct elevator_queue), GFP_KERNEL);
198 elevator_put(e->elevator_type);
202 ret = elevator_attach(q, e, eq);
205 elevator_put(e->elevator_type);
211 void elevator_exit(elevator_t *e)
213 if (e->ops->elevator_exit_fn)
214 e->ops->elevator_exit_fn(e);
216 elevator_put(e->elevator_type);
217 e->elevator_type = NULL;
222 * Insert rq into dispatch queue of q. Queue lock must be held on
223 * entry. If sort != 0, rq is sort-inserted; otherwise, rq will be
224 * appended to the dispatch queue. To be used by specific elevators.
226 void elv_dispatch_sort(request_queue_t *q, struct request *rq)
229 struct list_head *entry;
231 if (q->last_merge == rq)
232 q->last_merge = NULL;
234 boundary = q->end_sector;
236 list_for_each_prev(entry, &q->queue_head) {
237 struct request *pos = list_entry_rq(entry);
239 if (pos->flags & (REQ_SOFTBARRIER|REQ_HARDBARRIER|REQ_STARTED))
241 if (rq->sector >= boundary) {
242 if (pos->sector < boundary)
245 if (pos->sector >= boundary)
248 if (rq->sector >= pos->sector)
252 list_add(&rq->queuelist, entry);
255 int elv_merge(request_queue_t *q, struct request **req, struct bio *bio)
257 elevator_t *e = q->elevator;
261 ret = elv_try_merge(q->last_merge, bio);
262 if (ret != ELEVATOR_NO_MERGE) {
263 *req = q->last_merge;
268 if (e->ops->elevator_merge_fn)
269 return e->ops->elevator_merge_fn(q, req, bio);
271 return ELEVATOR_NO_MERGE;
274 void elv_merged_request(request_queue_t *q, struct request *rq)
276 elevator_t *e = q->elevator;
278 if (e->ops->elevator_merged_fn)
279 e->ops->elevator_merged_fn(q, rq);
284 void elv_merge_requests(request_queue_t *q, struct request *rq,
285 struct request *next)
287 elevator_t *e = q->elevator;
289 if (e->ops->elevator_merge_req_fn)
290 e->ops->elevator_merge_req_fn(q, rq, next);
295 void elv_requeue_request(request_queue_t *q, struct request *rq)
297 elevator_t *e = q->elevator;
300 * it already went through dequeue, we need to decrement the
301 * in_flight count again
303 if (blk_account_rq(rq)) {
305 if (blk_sorted_rq(rq) && e->ops->elevator_deactivate_req_fn)
306 e->ops->elevator_deactivate_req_fn(q, rq);
309 rq->flags &= ~REQ_STARTED;
312 * if this is the flush, requeue the original instead and drop the flush
314 if (rq->flags & REQ_BAR_FLUSH) {
315 clear_bit(QUEUE_FLAG_FLUSH, &q->queue_flags);
316 rq = rq->end_io_data;
319 __elv_add_request(q, rq, ELEVATOR_INSERT_FRONT, 0);
322 void __elv_add_request(request_queue_t *q, struct request *rq, int where,
325 if (rq->flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER)) {
327 * barriers implicitly indicate back insertion
329 if (where == ELEVATOR_INSERT_SORT)
330 where = ELEVATOR_INSERT_BACK;
333 * this request is scheduling boundary, update end_sector
335 if (blk_fs_request(rq)) {
336 q->end_sector = rq_end_sector(rq);
346 if (unlikely(test_bit(QUEUE_FLAG_DRAIN, &q->queue_flags))) {
348 * if drain is set, store the request "locally". when the drain
349 * is finished, the requests will be handed ordered to the io
352 list_add_tail(&rq->queuelist, &q->drain_list);
357 case ELEVATOR_INSERT_FRONT:
358 rq->flags |= REQ_SOFTBARRIER;
360 list_add(&rq->queuelist, &q->queue_head);
363 case ELEVATOR_INSERT_BACK:
364 rq->flags |= REQ_SOFTBARRIER;
366 while (q->elevator->ops->elevator_dispatch_fn(q, 1))
368 list_add_tail(&rq->queuelist, &q->queue_head);
370 * We kick the queue here for the following reasons.
371 * - The elevator might have returned NULL previously
372 * to delay requests and returned them now. As the
373 * queue wasn't empty before this request, ll_rw_blk
374 * won't run the queue on return, resulting in hang.
375 * - Usually, back inserted requests won't be merged
376 * with anything. There's no point in delaying queue
383 case ELEVATOR_INSERT_SORT:
384 BUG_ON(!blk_fs_request(rq));
385 rq->flags |= REQ_SORTED;
386 q->elevator->ops->elevator_add_req_fn(q, rq);
387 if (q->last_merge == NULL && rq_mergeable(rq))
392 printk(KERN_ERR "%s: bad insertion point %d\n",
393 __FUNCTION__, where);
397 if (blk_queue_plugged(q)) {
398 int nrq = q->rq.count[READ] + q->rq.count[WRITE]
401 if (nrq >= q->unplug_thresh)
402 __generic_unplug_device(q);
406 void elv_add_request(request_queue_t *q, struct request *rq, int where,
411 spin_lock_irqsave(q->queue_lock, flags);
412 __elv_add_request(q, rq, where, plug);
413 spin_unlock_irqrestore(q->queue_lock, flags);
416 static inline struct request *__elv_next_request(request_queue_t *q)
420 if (unlikely(list_empty(&q->queue_head) &&
421 !q->elevator->ops->elevator_dispatch_fn(q, 0)))
424 rq = list_entry_rq(q->queue_head.next);
427 * if this is a barrier write and the device has to issue a
428 * flush sequence to support it, check how far we are
430 if (blk_fs_request(rq) && blk_barrier_rq(rq)) {
431 BUG_ON(q->ordered == QUEUE_ORDERED_NONE);
433 if (q->ordered == QUEUE_ORDERED_FLUSH &&
434 !blk_barrier_preflush(rq))
435 rq = blk_start_pre_flush(q, rq);
441 struct request *elv_next_request(request_queue_t *q)
446 while ((rq = __elv_next_request(q)) != NULL) {
447 if (!(rq->flags & REQ_STARTED)) {
448 elevator_t *e = q->elevator;
451 * This is the first time the device driver
452 * sees this request (possibly after
453 * requeueing). Notify IO scheduler.
455 if (blk_sorted_rq(rq) &&
456 e->ops->elevator_activate_req_fn)
457 e->ops->elevator_activate_req_fn(q, rq);
460 * just mark as started even if we don't start
461 * it, a request that has been delayed should
462 * not be passed by new incoming requests
464 rq->flags |= REQ_STARTED;
467 if (!q->boundary_rq || q->boundary_rq == rq) {
468 q->end_sector = rq_end_sector(rq);
469 q->boundary_rq = NULL;
472 if ((rq->flags & REQ_DONTPREP) || !q->prep_rq_fn)
475 ret = q->prep_rq_fn(q, rq);
476 if (ret == BLKPREP_OK) {
478 } else if (ret == BLKPREP_DEFER) {
480 * the request may have been (partially) prepped.
481 * we need to keep this request in the front to
482 * avoid resource deadlock. REQ_STARTED will
483 * prevent other fs requests from passing this one.
487 } else if (ret == BLKPREP_KILL) {
488 int nr_bytes = rq->hard_nr_sectors << 9;
491 nr_bytes = rq->data_len;
493 blkdev_dequeue_request(rq);
494 rq->flags |= REQ_QUIET;
495 end_that_request_chunk(rq, 0, nr_bytes);
496 end_that_request_last(rq);
498 printk(KERN_ERR "%s: bad return=%d\n", __FUNCTION__,
507 void elv_dequeue_request(request_queue_t *q, struct request *rq)
509 BUG_ON(list_empty(&rq->queuelist));
511 list_del_init(&rq->queuelist);
514 * the time frame between a request being removed from the lists
515 * and to it is freed is accounted as io that is in progress at
518 if (blk_account_rq(rq))
522 int elv_queue_empty(request_queue_t *q)
524 elevator_t *e = q->elevator;
526 if (!list_empty(&q->queue_head))
529 if (e->ops->elevator_queue_empty_fn)
530 return e->ops->elevator_queue_empty_fn(q);
535 struct request *elv_latter_request(request_queue_t *q, struct request *rq)
537 struct list_head *next;
539 elevator_t *e = q->elevator;
541 if (e->ops->elevator_latter_req_fn)
542 return e->ops->elevator_latter_req_fn(q, rq);
544 next = rq->queuelist.next;
545 if (next != &q->queue_head && next != &rq->queuelist)
546 return list_entry_rq(next);
551 struct request *elv_former_request(request_queue_t *q, struct request *rq)
553 struct list_head *prev;
555 elevator_t *e = q->elevator;
557 if (e->ops->elevator_former_req_fn)
558 return e->ops->elevator_former_req_fn(q, rq);
560 prev = rq->queuelist.prev;
561 if (prev != &q->queue_head && prev != &rq->queuelist)
562 return list_entry_rq(prev);
567 int elv_set_request(request_queue_t *q, struct request *rq, struct bio *bio,
570 elevator_t *e = q->elevator;
572 if (e->ops->elevator_set_req_fn)
573 return e->ops->elevator_set_req_fn(q, rq, bio, gfp_mask);
575 rq->elevator_private = NULL;
579 void elv_put_request(request_queue_t *q, struct request *rq)
581 elevator_t *e = q->elevator;
583 if (e->ops->elevator_put_req_fn)
584 e->ops->elevator_put_req_fn(q, rq);
587 int elv_may_queue(request_queue_t *q, int rw, struct bio *bio)
589 elevator_t *e = q->elevator;
591 if (e->ops->elevator_may_queue_fn)
592 return e->ops->elevator_may_queue_fn(q, rw, bio);
594 return ELV_MQUEUE_MAY;
597 void elv_completed_request(request_queue_t *q, struct request *rq)
599 elevator_t *e = q->elevator;
602 * request is released from the driver, io must be done
604 if (blk_account_rq(rq)) {
606 if (blk_sorted_rq(rq) && e->ops->elevator_completed_req_fn)
607 e->ops->elevator_completed_req_fn(q, rq);
611 int elv_register_queue(struct request_queue *q)
613 elevator_t *e = q->elevator;
615 e->kobj.parent = kobject_get(&q->kobj);
619 snprintf(e->kobj.name, KOBJ_NAME_LEN, "%s", "iosched");
620 e->kobj.ktype = e->elevator_type->elevator_ktype;
622 return kobject_register(&e->kobj);
625 void elv_unregister_queue(struct request_queue *q)
628 elevator_t *e = q->elevator;
629 kobject_unregister(&e->kobj);
630 kobject_put(&q->kobj);
634 int elv_register(struct elevator_type *e)
636 spin_lock_irq(&elv_list_lock);
637 if (elevator_find(e->elevator_name))
639 list_add_tail(&e->list, &elv_list);
640 spin_unlock_irq(&elv_list_lock);
642 printk(KERN_INFO "io scheduler %s registered", e->elevator_name);
643 if (!strcmp(e->elevator_name, chosen_elevator))
644 printk(" (default)");
648 EXPORT_SYMBOL_GPL(elv_register);
650 void elv_unregister(struct elevator_type *e)
652 spin_lock_irq(&elv_list_lock);
653 list_del_init(&e->list);
654 spin_unlock_irq(&elv_list_lock);
656 EXPORT_SYMBOL_GPL(elv_unregister);
659 * switch to new_e io scheduler. be careful not to introduce deadlocks -
660 * we don't free the old io scheduler, before we have allocated what we
661 * need for the new one. this way we have a chance of going back to the old
662 * one, if the new one fails init for some reason. we also do an intermediate
663 * switch to noop to ensure safety with stack-allocated requests, since they
664 * don't originate from the block layer allocator. noop is safe here, because
665 * it never needs to touch the elevator itself for completion events. DRAIN
666 * flags will make sure we don't touch it for additions either.
668 static void elevator_switch(request_queue_t *q, struct elevator_type *new_e)
670 elevator_t *e = kmalloc(sizeof(elevator_t), GFP_KERNEL);
671 struct elevator_type *noop_elevator = NULL;
672 elevator_t *old_elevator;
678 * first step, drain requests from the block freelist
680 blk_wait_queue_drained(q, 0);
683 * unregister old elevator data
685 elv_unregister_queue(q);
686 old_elevator = q->elevator;
689 * next step, switch to noop since it uses no private rq structures
690 * and doesn't allocate any memory for anything. then wait for any
691 * non-fs requests in-flight
693 noop_elevator = elevator_get("noop");
694 spin_lock_irq(q->queue_lock);
695 elevator_attach(q, noop_elevator, e);
696 spin_unlock_irq(q->queue_lock);
698 blk_wait_queue_drained(q, 1);
701 * attach and start new elevator
703 if (elevator_attach(q, new_e, e))
706 if (elv_register_queue(q))
710 * finally exit old elevator and start queue again
712 elevator_exit(old_elevator);
713 blk_finish_queue_drain(q);
714 elevator_put(noop_elevator);
719 * switch failed, exit the new io scheduler and reattach the old
720 * one again (along with re-adding the sysfs dir)
724 q->elevator = old_elevator;
725 elv_register_queue(q);
726 blk_finish_queue_drain(q);
729 elevator_put(noop_elevator);
731 printk(KERN_ERR "elevator: switch to %s failed\n",new_e->elevator_name);
734 ssize_t elv_iosched_store(request_queue_t *q, const char *name, size_t count)
736 char elevator_name[ELV_NAME_MAX];
737 struct elevator_type *e;
739 memset(elevator_name, 0, sizeof(elevator_name));
740 strncpy(elevator_name, name, sizeof(elevator_name));
742 if (elevator_name[strlen(elevator_name) - 1] == '\n')
743 elevator_name[strlen(elevator_name) - 1] = '\0';
745 e = elevator_get(elevator_name);
747 printk(KERN_ERR "elevator: type %s not found\n", elevator_name);
751 if (!strcmp(elevator_name, q->elevator->elevator_type->elevator_name))
754 elevator_switch(q, e);
758 ssize_t elv_iosched_show(request_queue_t *q, char *name)
760 elevator_t *e = q->elevator;
761 struct elevator_type *elv = e->elevator_type;
762 struct list_head *entry;
765 spin_lock_irq(q->queue_lock);
766 list_for_each(entry, &elv_list) {
767 struct elevator_type *__e;
769 __e = list_entry(entry, struct elevator_type, list);
770 if (!strcmp(elv->elevator_name, __e->elevator_name))
771 len += sprintf(name+len, "[%s] ", elv->elevator_name);
773 len += sprintf(name+len, "%s ", __e->elevator_name);
775 spin_unlock_irq(q->queue_lock);
777 len += sprintf(len+name, "\n");
781 EXPORT_SYMBOL(elv_dispatch_sort);
782 EXPORT_SYMBOL(elv_add_request);
783 EXPORT_SYMBOL(__elv_add_request);
784 EXPORT_SYMBOL(elv_requeue_request);
785 EXPORT_SYMBOL(elv_next_request);
786 EXPORT_SYMBOL(elv_dequeue_request);
787 EXPORT_SYMBOL(elv_queue_empty);
788 EXPORT_SYMBOL(elv_completed_request);
789 EXPORT_SYMBOL(elevator_exit);
790 EXPORT_SYMBOL(elevator_init);