2 * Block device elevator/IO-scheduler.
4 * Copyright (C) 2000 Andrea Arcangeli <andrea@suse.de> SuSE
6 * 30042000 Jens Axboe <axboe@kernel.dk> :
8 * Split the elevator a bit so that it is possible to choose a different
9 * one or even write a new "plug in". There are three pieces:
10 * - elevator_fn, inserts a new request in the queue list
11 * - elevator_merge_fn, decides whether a new buffer can be merged with
13 * - elevator_dequeue_fn, called when a request is taken off the active list
15 * 20082000 Dave Jones <davej@suse.de> :
16 * Removed tests for max-bomb-segments, which was breaking elvtune
17 * when run without -bN
20 * - Rework again to work with bio instead of buffer_heads
21 * - loose bi_dev comparisons, partition handling is right now
22 * - completely modularize elevator setup and teardown
25 #include <linux/kernel.h>
27 #include <linux/blkdev.h>
28 #include <linux/elevator.h>
29 #include <linux/bio.h>
30 #include <linux/module.h>
31 #include <linux/slab.h>
32 #include <linux/init.h>
33 #include <linux/compiler.h>
34 #include <linux/blktrace_api.h>
35 #include <linux/hash.h>
36 #include <linux/uaccess.h>
38 #include <trace/events/block.h>
42 static DEFINE_SPINLOCK(elv_list_lock
);
43 static LIST_HEAD(elv_list
);
48 static const int elv_hash_shift
= 6;
49 #define ELV_HASH_BLOCK(sec) ((sec) >> 3)
50 #define ELV_HASH_FN(sec) \
51 (hash_long(ELV_HASH_BLOCK((sec)), elv_hash_shift))
52 #define ELV_HASH_ENTRIES (1 << elv_hash_shift)
53 #define rq_hash_key(rq) (blk_rq_pos(rq) + blk_rq_sectors(rq))
56 * Query io scheduler to see if the current process issuing bio may be
59 static int elv_iosched_allow_merge(struct request
*rq
, struct bio
*bio
)
61 struct request_queue
*q
= rq
->q
;
62 struct elevator_queue
*e
= q
->elevator
;
64 if (e
->type
->ops
.elevator_allow_merge_fn
)
65 return e
->type
->ops
.elevator_allow_merge_fn(q
, rq
, bio
);
71 * can we safely merge with this request?
73 bool elv_rq_merge_ok(struct request
*rq
, struct bio
*bio
)
75 if (!blk_rq_merge_ok(rq
, bio
))
78 if (!elv_iosched_allow_merge(rq
, bio
))
83 EXPORT_SYMBOL(elv_rq_merge_ok
);
85 static struct elevator_type
*elevator_find(const char *name
)
87 struct elevator_type
*e
;
89 list_for_each_entry(e
, &elv_list
, list
) {
90 if (!strcmp(e
->elevator_name
, name
))
97 static void elevator_put(struct elevator_type
*e
)
99 module_put(e
->elevator_owner
);
102 static struct elevator_type
*elevator_get(const char *name
)
104 struct elevator_type
*e
;
106 spin_lock(&elv_list_lock
);
108 e
= elevator_find(name
);
110 spin_unlock(&elv_list_lock
);
111 request_module("%s-iosched", name
);
112 spin_lock(&elv_list_lock
);
113 e
= elevator_find(name
);
116 if (e
&& !try_module_get(e
->elevator_owner
))
119 spin_unlock(&elv_list_lock
);
124 static char chosen_elevator
[ELV_NAME_MAX
];
126 static int __init
elevator_setup(char *str
)
129 * Be backwards-compatible with previous kernels, so users
130 * won't get the wrong elevator.
132 strncpy(chosen_elevator
, str
, sizeof(chosen_elevator
) - 1);
136 __setup("elevator=", elevator_setup
);
138 static struct kobj_type elv_ktype
;
140 static struct elevator_queue
*elevator_alloc(struct request_queue
*q
,
141 struct elevator_type
*e
)
143 struct elevator_queue
*eq
;
146 eq
= kmalloc_node(sizeof(*eq
), GFP_KERNEL
| __GFP_ZERO
, q
->node
);
151 kobject_init(&eq
->kobj
, &elv_ktype
);
152 mutex_init(&eq
->sysfs_lock
);
154 eq
->hash
= kmalloc_node(sizeof(struct hlist_head
) * ELV_HASH_ENTRIES
,
155 GFP_KERNEL
, q
->node
);
159 for (i
= 0; i
< ELV_HASH_ENTRIES
; i
++)
160 INIT_HLIST_HEAD(&eq
->hash
[i
]);
169 static void elevator_release(struct kobject
*kobj
)
171 struct elevator_queue
*e
;
173 e
= container_of(kobj
, struct elevator_queue
, kobj
);
174 elevator_put(e
->type
);
179 int elevator_init(struct request_queue
*q
, char *name
)
181 struct elevator_type
*e
= NULL
;
184 if (unlikely(q
->elevator
))
187 INIT_LIST_HEAD(&q
->queue_head
);
188 q
->last_merge
= NULL
;
190 q
->boundary_rq
= NULL
;
193 e
= elevator_get(name
);
198 if (!e
&& *chosen_elevator
) {
199 e
= elevator_get(chosen_elevator
);
201 printk(KERN_ERR
"I/O scheduler %s not found\n",
206 e
= elevator_get(CONFIG_DEFAULT_IOSCHED
);
209 "Default I/O scheduler not found. " \
211 e
= elevator_get("noop");
215 q
->elevator
= elevator_alloc(q
, e
);
219 err
= e
->ops
.elevator_init_fn(q
);
221 kobject_put(&q
->elevator
->kobj
);
227 EXPORT_SYMBOL(elevator_init
);
229 void elevator_exit(struct elevator_queue
*e
)
231 mutex_lock(&e
->sysfs_lock
);
232 if (e
->type
->ops
.elevator_exit_fn
)
233 e
->type
->ops
.elevator_exit_fn(e
);
234 mutex_unlock(&e
->sysfs_lock
);
236 kobject_put(&e
->kobj
);
238 EXPORT_SYMBOL(elevator_exit
);
240 static inline void __elv_rqhash_del(struct request
*rq
)
242 hlist_del_init(&rq
->hash
);
245 static void elv_rqhash_del(struct request_queue
*q
, struct request
*rq
)
248 __elv_rqhash_del(rq
);
251 static void elv_rqhash_add(struct request_queue
*q
, struct request
*rq
)
253 struct elevator_queue
*e
= q
->elevator
;
255 BUG_ON(ELV_ON_HASH(rq
));
256 hlist_add_head(&rq
->hash
, &e
->hash
[ELV_HASH_FN(rq_hash_key(rq
))]);
259 static void elv_rqhash_reposition(struct request_queue
*q
, struct request
*rq
)
261 __elv_rqhash_del(rq
);
262 elv_rqhash_add(q
, rq
);
265 static struct request
*elv_rqhash_find(struct request_queue
*q
, sector_t offset
)
267 struct elevator_queue
*e
= q
->elevator
;
268 struct hlist_head
*hash_list
= &e
->hash
[ELV_HASH_FN(offset
)];
269 struct hlist_node
*entry
, *next
;
272 hlist_for_each_entry_safe(rq
, entry
, next
, hash_list
, hash
) {
273 BUG_ON(!ELV_ON_HASH(rq
));
275 if (unlikely(!rq_mergeable(rq
))) {
276 __elv_rqhash_del(rq
);
280 if (rq_hash_key(rq
) == offset
)
288 * RB-tree support functions for inserting/lookup/removal of requests
289 * in a sorted RB tree.
291 void elv_rb_add(struct rb_root
*root
, struct request
*rq
)
293 struct rb_node
**p
= &root
->rb_node
;
294 struct rb_node
*parent
= NULL
;
295 struct request
*__rq
;
299 __rq
= rb_entry(parent
, struct request
, rb_node
);
301 if (blk_rq_pos(rq
) < blk_rq_pos(__rq
))
303 else if (blk_rq_pos(rq
) >= blk_rq_pos(__rq
))
307 rb_link_node(&rq
->rb_node
, parent
, p
);
308 rb_insert_color(&rq
->rb_node
, root
);
310 EXPORT_SYMBOL(elv_rb_add
);
312 void elv_rb_del(struct rb_root
*root
, struct request
*rq
)
314 BUG_ON(RB_EMPTY_NODE(&rq
->rb_node
));
315 rb_erase(&rq
->rb_node
, root
);
316 RB_CLEAR_NODE(&rq
->rb_node
);
318 EXPORT_SYMBOL(elv_rb_del
);
320 struct request
*elv_rb_find(struct rb_root
*root
, sector_t sector
)
322 struct rb_node
*n
= root
->rb_node
;
326 rq
= rb_entry(n
, struct request
, rb_node
);
328 if (sector
< blk_rq_pos(rq
))
330 else if (sector
> blk_rq_pos(rq
))
338 EXPORT_SYMBOL(elv_rb_find
);
341 * Insert rq into dispatch queue of q. Queue lock must be held on
342 * entry. rq is sort instead into the dispatch queue. To be used by
343 * specific elevators.
345 void elv_dispatch_sort(struct request_queue
*q
, struct request
*rq
)
348 struct list_head
*entry
;
351 if (q
->last_merge
== rq
)
352 q
->last_merge
= NULL
;
354 elv_rqhash_del(q
, rq
);
358 boundary
= q
->end_sector
;
359 stop_flags
= REQ_SOFTBARRIER
| REQ_STARTED
;
360 list_for_each_prev(entry
, &q
->queue_head
) {
361 struct request
*pos
= list_entry_rq(entry
);
363 if ((rq
->cmd_flags
& REQ_DISCARD
) !=
364 (pos
->cmd_flags
& REQ_DISCARD
))
366 if (rq_data_dir(rq
) != rq_data_dir(pos
))
368 if (pos
->cmd_flags
& stop_flags
)
370 if (blk_rq_pos(rq
) >= boundary
) {
371 if (blk_rq_pos(pos
) < boundary
)
374 if (blk_rq_pos(pos
) >= boundary
)
377 if (blk_rq_pos(rq
) >= blk_rq_pos(pos
))
381 list_add(&rq
->queuelist
, entry
);
383 EXPORT_SYMBOL(elv_dispatch_sort
);
386 * Insert rq into dispatch queue of q. Queue lock must be held on
387 * entry. rq is added to the back of the dispatch queue. To be used by
388 * specific elevators.
390 void elv_dispatch_add_tail(struct request_queue
*q
, struct request
*rq
)
392 if (q
->last_merge
== rq
)
393 q
->last_merge
= NULL
;
395 elv_rqhash_del(q
, rq
);
399 q
->end_sector
= rq_end_sector(rq
);
401 list_add_tail(&rq
->queuelist
, &q
->queue_head
);
403 EXPORT_SYMBOL(elv_dispatch_add_tail
);
405 int elv_merge(struct request_queue
*q
, struct request
**req
, struct bio
*bio
)
407 struct elevator_queue
*e
= q
->elevator
;
408 struct request
*__rq
;
413 * nomerges: No merges at all attempted
414 * noxmerges: Only simple one-hit cache try
415 * merges: All merge tries attempted
417 if (blk_queue_nomerges(q
))
418 return ELEVATOR_NO_MERGE
;
421 * First try one-hit cache.
423 if (q
->last_merge
&& elv_rq_merge_ok(q
->last_merge
, bio
)) {
424 ret
= blk_try_merge(q
->last_merge
, bio
);
425 if (ret
!= ELEVATOR_NO_MERGE
) {
426 *req
= q
->last_merge
;
431 if (blk_queue_noxmerges(q
))
432 return ELEVATOR_NO_MERGE
;
435 * See if our hash lookup can find a potential backmerge.
437 __rq
= elv_rqhash_find(q
, bio
->bi_sector
);
438 if (__rq
&& elv_rq_merge_ok(__rq
, bio
)) {
440 return ELEVATOR_BACK_MERGE
;
443 if (e
->type
->ops
.elevator_merge_fn
)
444 return e
->type
->ops
.elevator_merge_fn(q
, req
, bio
);
446 return ELEVATOR_NO_MERGE
;
450 * Attempt to do an insertion back merge. Only check for the case where
451 * we can append 'rq' to an existing request, so we can throw 'rq' away
454 * Returns true if we merged, false otherwise
456 static bool elv_attempt_insert_merge(struct request_queue
*q
,
459 struct request
*__rq
;
461 if (blk_queue_nomerges(q
))
465 * First try one-hit cache.
467 if (q
->last_merge
&& blk_attempt_req_merge(q
, q
->last_merge
, rq
))
470 if (blk_queue_noxmerges(q
))
474 * See if our hash lookup can find a potential backmerge.
476 __rq
= elv_rqhash_find(q
, blk_rq_pos(rq
));
477 if (__rq
&& blk_attempt_req_merge(q
, __rq
, rq
))
483 void elv_merged_request(struct request_queue
*q
, struct request
*rq
, int type
)
485 struct elevator_queue
*e
= q
->elevator
;
487 if (e
->type
->ops
.elevator_merged_fn
)
488 e
->type
->ops
.elevator_merged_fn(q
, rq
, type
);
490 if (type
== ELEVATOR_BACK_MERGE
)
491 elv_rqhash_reposition(q
, rq
);
496 void elv_merge_requests(struct request_queue
*q
, struct request
*rq
,
497 struct request
*next
)
499 struct elevator_queue
*e
= q
->elevator
;
500 const int next_sorted
= next
->cmd_flags
& REQ_SORTED
;
502 if (next_sorted
&& e
->type
->ops
.elevator_merge_req_fn
)
503 e
->type
->ops
.elevator_merge_req_fn(q
, rq
, next
);
505 elv_rqhash_reposition(q
, rq
);
508 elv_rqhash_del(q
, next
);
515 void elv_bio_merged(struct request_queue
*q
, struct request
*rq
,
518 struct elevator_queue
*e
= q
->elevator
;
520 if (e
->type
->ops
.elevator_bio_merged_fn
)
521 e
->type
->ops
.elevator_bio_merged_fn(q
, rq
, bio
);
524 void elv_requeue_request(struct request_queue
*q
, struct request
*rq
)
527 * it already went through dequeue, we need to decrement the
528 * in_flight count again
530 if (blk_account_rq(rq
)) {
531 q
->in_flight
[rq_is_sync(rq
)]--;
532 if (rq
->cmd_flags
& REQ_SORTED
)
533 elv_deactivate_rq(q
, rq
);
536 rq
->cmd_flags
&= ~REQ_STARTED
;
538 __elv_add_request(q
, rq
, ELEVATOR_INSERT_REQUEUE
);
541 void elv_drain_elevator(struct request_queue
*q
)
545 lockdep_assert_held(q
->queue_lock
);
547 while (q
->elevator
->type
->ops
.elevator_dispatch_fn(q
, 1))
549 if (q
->nr_sorted
&& printed
++ < 10) {
550 printk(KERN_ERR
"%s: forced dispatching is broken "
551 "(nr_sorted=%u), please report this\n",
552 q
->elevator
->type
->elevator_name
, q
->nr_sorted
);
556 void __elv_add_request(struct request_queue
*q
, struct request
*rq
, int where
)
558 trace_block_rq_insert(q
, rq
);
562 if (rq
->cmd_flags
& REQ_SOFTBARRIER
) {
563 /* barriers are scheduling boundary, update end_sector */
564 if (rq
->cmd_type
== REQ_TYPE_FS
||
565 (rq
->cmd_flags
& REQ_DISCARD
)) {
566 q
->end_sector
= rq_end_sector(rq
);
569 } else if (!(rq
->cmd_flags
& REQ_ELVPRIV
) &&
570 (where
== ELEVATOR_INSERT_SORT
||
571 where
== ELEVATOR_INSERT_SORT_MERGE
))
572 where
= ELEVATOR_INSERT_BACK
;
575 case ELEVATOR_INSERT_REQUEUE
:
576 case ELEVATOR_INSERT_FRONT
:
577 rq
->cmd_flags
|= REQ_SOFTBARRIER
;
578 list_add(&rq
->queuelist
, &q
->queue_head
);
581 case ELEVATOR_INSERT_BACK
:
582 rq
->cmd_flags
|= REQ_SOFTBARRIER
;
583 elv_drain_elevator(q
);
584 list_add_tail(&rq
->queuelist
, &q
->queue_head
);
586 * We kick the queue here for the following reasons.
587 * - The elevator might have returned NULL previously
588 * to delay requests and returned them now. As the
589 * queue wasn't empty before this request, ll_rw_blk
590 * won't run the queue on return, resulting in hang.
591 * - Usually, back inserted requests won't be merged
592 * with anything. There's no point in delaying queue
598 case ELEVATOR_INSERT_SORT_MERGE
:
600 * If we succeed in merging this request with one in the
601 * queue already, we are done - rq has now been freed,
602 * so no need to do anything further.
604 if (elv_attempt_insert_merge(q
, rq
))
606 case ELEVATOR_INSERT_SORT
:
607 BUG_ON(rq
->cmd_type
!= REQ_TYPE_FS
&&
608 !(rq
->cmd_flags
& REQ_DISCARD
));
609 rq
->cmd_flags
|= REQ_SORTED
;
611 if (rq_mergeable(rq
)) {
612 elv_rqhash_add(q
, rq
);
618 * Some ioscheds (cfq) run q->request_fn directly, so
619 * rq cannot be accessed after calling
620 * elevator_add_req_fn.
622 q
->elevator
->type
->ops
.elevator_add_req_fn(q
, rq
);
625 case ELEVATOR_INSERT_FLUSH
:
626 rq
->cmd_flags
|= REQ_SOFTBARRIER
;
627 blk_insert_flush(rq
);
630 printk(KERN_ERR
"%s: bad insertion point %d\n",
635 EXPORT_SYMBOL(__elv_add_request
);
637 void elv_add_request(struct request_queue
*q
, struct request
*rq
, int where
)
641 spin_lock_irqsave(q
->queue_lock
, flags
);
642 __elv_add_request(q
, rq
, where
);
643 spin_unlock_irqrestore(q
->queue_lock
, flags
);
645 EXPORT_SYMBOL(elv_add_request
);
647 struct request
*elv_latter_request(struct request_queue
*q
, struct request
*rq
)
649 struct elevator_queue
*e
= q
->elevator
;
651 if (e
->type
->ops
.elevator_latter_req_fn
)
652 return e
->type
->ops
.elevator_latter_req_fn(q
, rq
);
656 struct request
*elv_former_request(struct request_queue
*q
, struct request
*rq
)
658 struct elevator_queue
*e
= q
->elevator
;
660 if (e
->type
->ops
.elevator_former_req_fn
)
661 return e
->type
->ops
.elevator_former_req_fn(q
, rq
);
665 int elv_set_request(struct request_queue
*q
, struct request
*rq
, gfp_t gfp_mask
)
667 struct elevator_queue
*e
= q
->elevator
;
669 if (e
->type
->ops
.elevator_set_req_fn
)
670 return e
->type
->ops
.elevator_set_req_fn(q
, rq
, gfp_mask
);
674 void elv_put_request(struct request_queue
*q
, struct request
*rq
)
676 struct elevator_queue
*e
= q
->elevator
;
678 if (e
->type
->ops
.elevator_put_req_fn
)
679 e
->type
->ops
.elevator_put_req_fn(rq
);
682 int elv_may_queue(struct request_queue
*q
, int rw
)
684 struct elevator_queue
*e
= q
->elevator
;
686 if (e
->type
->ops
.elevator_may_queue_fn
)
687 return e
->type
->ops
.elevator_may_queue_fn(q
, rw
);
689 return ELV_MQUEUE_MAY
;
692 void elv_abort_queue(struct request_queue
*q
)
696 blk_abort_flushes(q
);
698 while (!list_empty(&q
->queue_head
)) {
699 rq
= list_entry_rq(q
->queue_head
.next
);
700 rq
->cmd_flags
|= REQ_QUIET
;
701 trace_block_rq_abort(q
, rq
);
703 * Mark this request as started so we don't trigger
704 * any debug logic in the end I/O path.
706 blk_start_request(rq
);
707 __blk_end_request_all(rq
, -EIO
);
710 EXPORT_SYMBOL(elv_abort_queue
);
712 void elv_completed_request(struct request_queue
*q
, struct request
*rq
)
714 struct elevator_queue
*e
= q
->elevator
;
717 * request is released from the driver, io must be done
719 if (blk_account_rq(rq
)) {
720 q
->in_flight
[rq_is_sync(rq
)]--;
721 if ((rq
->cmd_flags
& REQ_SORTED
) &&
722 e
->type
->ops
.elevator_completed_req_fn
)
723 e
->type
->ops
.elevator_completed_req_fn(q
, rq
);
727 #define to_elv(atr) container_of((atr), struct elv_fs_entry, attr)
730 elv_attr_show(struct kobject
*kobj
, struct attribute
*attr
, char *page
)
732 struct elv_fs_entry
*entry
= to_elv(attr
);
733 struct elevator_queue
*e
;
739 e
= container_of(kobj
, struct elevator_queue
, kobj
);
740 mutex_lock(&e
->sysfs_lock
);
741 error
= e
->type
? entry
->show(e
, page
) : -ENOENT
;
742 mutex_unlock(&e
->sysfs_lock
);
747 elv_attr_store(struct kobject
*kobj
, struct attribute
*attr
,
748 const char *page
, size_t length
)
750 struct elv_fs_entry
*entry
= to_elv(attr
);
751 struct elevator_queue
*e
;
757 e
= container_of(kobj
, struct elevator_queue
, kobj
);
758 mutex_lock(&e
->sysfs_lock
);
759 error
= e
->type
? entry
->store(e
, page
, length
) : -ENOENT
;
760 mutex_unlock(&e
->sysfs_lock
);
764 static const struct sysfs_ops elv_sysfs_ops
= {
765 .show
= elv_attr_show
,
766 .store
= elv_attr_store
,
769 static struct kobj_type elv_ktype
= {
770 .sysfs_ops
= &elv_sysfs_ops
,
771 .release
= elevator_release
,
774 int elv_register_queue(struct request_queue
*q
)
776 struct elevator_queue
*e
= q
->elevator
;
779 error
= kobject_add(&e
->kobj
, &q
->kobj
, "%s", "iosched");
781 struct elv_fs_entry
*attr
= e
->type
->elevator_attrs
;
783 while (attr
->attr
.name
) {
784 if (sysfs_create_file(&e
->kobj
, &attr
->attr
))
789 kobject_uevent(&e
->kobj
, KOBJ_ADD
);
794 EXPORT_SYMBOL(elv_register_queue
);
796 void elv_unregister_queue(struct request_queue
*q
)
799 struct elevator_queue
*e
= q
->elevator
;
801 kobject_uevent(&e
->kobj
, KOBJ_REMOVE
);
802 kobject_del(&e
->kobj
);
806 EXPORT_SYMBOL(elv_unregister_queue
);
808 int elv_register(struct elevator_type
*e
)
812 /* create icq_cache if requested */
814 if (WARN_ON(e
->icq_size
< sizeof(struct io_cq
)) ||
815 WARN_ON(e
->icq_align
< __alignof__(struct io_cq
)))
818 snprintf(e
->icq_cache_name
, sizeof(e
->icq_cache_name
),
819 "%s_io_cq", e
->elevator_name
);
820 e
->icq_cache
= kmem_cache_create(e
->icq_cache_name
, e
->icq_size
,
821 e
->icq_align
, 0, NULL
);
826 /* register, don't allow duplicate names */
827 spin_lock(&elv_list_lock
);
828 if (elevator_find(e
->elevator_name
)) {
829 spin_unlock(&elv_list_lock
);
831 kmem_cache_destroy(e
->icq_cache
);
834 list_add_tail(&e
->list
, &elv_list
);
835 spin_unlock(&elv_list_lock
);
837 /* print pretty message */
838 if (!strcmp(e
->elevator_name
, chosen_elevator
) ||
839 (!*chosen_elevator
&&
840 !strcmp(e
->elevator_name
, CONFIG_DEFAULT_IOSCHED
)))
843 printk(KERN_INFO
"io scheduler %s registered%s\n", e
->elevator_name
,
847 EXPORT_SYMBOL_GPL(elv_register
);
849 void elv_unregister(struct elevator_type
*e
)
852 spin_lock(&elv_list_lock
);
853 list_del_init(&e
->list
);
854 spin_unlock(&elv_list_lock
);
857 * Destroy icq_cache if it exists. icq's are RCU managed. Make
858 * sure all RCU operations are complete before proceeding.
862 kmem_cache_destroy(e
->icq_cache
);
866 EXPORT_SYMBOL_GPL(elv_unregister
);
869 * switch to new_e io scheduler. be careful not to introduce deadlocks -
870 * we don't free the old io scheduler, before we have allocated what we
871 * need for the new one. this way we have a chance of going back to the old
872 * one, if the new one fails init for some reason.
874 static int elevator_switch(struct request_queue
*q
, struct elevator_type
*new_e
)
876 struct elevator_queue
*old
= q
->elevator
;
877 bool registered
= old
->registered
;
881 * Turn on BYPASS and drain all requests w/ elevator private data.
882 * Block layer doesn't call into a quiesced elevator - all requests
883 * are directly put on the dispatch list without elevator data
884 * using INSERT_BACK. All requests have SOFTBARRIER set and no
885 * merge happens either.
887 blk_queue_bypass_start(q
);
889 /* unregister and clear all auxiliary data of the old elevator */
891 elv_unregister_queue(q
);
893 spin_lock_irq(q
->queue_lock
);
895 spin_unlock_irq(q
->queue_lock
);
897 /* allocate, init and register new elevator */
899 q
->elevator
= elevator_alloc(q
, new_e
);
903 err
= new_e
->ops
.elevator_init_fn(q
);
905 kobject_put(&q
->elevator
->kobj
);
910 err
= elv_register_queue(q
);
915 /* done, kill the old one and finish */
917 blk_queue_bypass_end(q
);
919 blk_add_trace_msg(q
, "elv switch: %s", new_e
->elevator_name
);
924 elevator_exit(q
->elevator
);
926 /* switch failed, restore and re-register old elevator */
928 elv_register_queue(q
);
929 blk_queue_bypass_end(q
);
935 * Switch this queue to the given IO scheduler.
937 int elevator_change(struct request_queue
*q
, const char *name
)
939 char elevator_name
[ELV_NAME_MAX
];
940 struct elevator_type
*e
;
945 strlcpy(elevator_name
, name
, sizeof(elevator_name
));
946 e
= elevator_get(strstrip(elevator_name
));
948 printk(KERN_ERR
"elevator: type %s not found\n", elevator_name
);
952 if (!strcmp(elevator_name
, q
->elevator
->type
->elevator_name
)) {
957 return elevator_switch(q
, e
);
959 EXPORT_SYMBOL(elevator_change
);
961 ssize_t
elv_iosched_store(struct request_queue
*q
, const char *name
,
969 ret
= elevator_change(q
, name
);
973 printk(KERN_ERR
"elevator: switch to %s failed\n", name
);
977 ssize_t
elv_iosched_show(struct request_queue
*q
, char *name
)
979 struct elevator_queue
*e
= q
->elevator
;
980 struct elevator_type
*elv
;
981 struct elevator_type
*__e
;
984 if (!q
->elevator
|| !blk_queue_stackable(q
))
985 return sprintf(name
, "none\n");
989 spin_lock(&elv_list_lock
);
990 list_for_each_entry(__e
, &elv_list
, list
) {
991 if (!strcmp(elv
->elevator_name
, __e
->elevator_name
))
992 len
+= sprintf(name
+len
, "[%s] ", elv
->elevator_name
);
994 len
+= sprintf(name
+len
, "%s ", __e
->elevator_name
);
996 spin_unlock(&elv_list_lock
);
998 len
+= sprintf(len
+name
, "\n");
1002 struct request
*elv_rb_former_request(struct request_queue
*q
,
1005 struct rb_node
*rbprev
= rb_prev(&rq
->rb_node
);
1008 return rb_entry_rq(rbprev
);
1012 EXPORT_SYMBOL(elv_rb_former_request
);
1014 struct request
*elv_rb_latter_request(struct request_queue
*q
,
1017 struct rb_node
*rbnext
= rb_next(&rq
->rb_node
);
1020 return rb_entry_rq(rbnext
);
1024 EXPORT_SYMBOL(elv_rb_latter_request
);