Root/block/elevator.c

1/*
2 * Block device elevator/IO-scheduler.
3 *
4 * Copyright (C) 2000 Andrea Arcangeli <andrea@suse.de> SuSE
5 *
6 * 30042000 Jens Axboe <axboe@kernel.dk> :
7 *
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
12 * an existing request
13 * - elevator_dequeue_fn, called when a request is taken off the active list
14 *
15 * 20082000 Dave Jones <davej@suse.de> :
16 * Removed tests for max-bomb-segments, which was breaking elvtune
17 * when run without -bN
18 *
19 * Jens:
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
23 *
24 */
25#include <linux/kernel.h>
26#include <linux/fs.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/delay.h>
35#include <linux/blktrace_api.h>
36#include <linux/hash.h>
37#include <linux/uaccess.h>
38
39#include <trace/events/block.h>
40
41#include "blk.h"
42
43static DEFINE_SPINLOCK(elv_list_lock);
44static LIST_HEAD(elv_list);
45
46/*
47 * Merge hash stuff.
48 */
49static const int elv_hash_shift = 6;
50#define ELV_HASH_BLOCK(sec) ((sec) >> 3)
51#define ELV_HASH_FN(sec) \
52        (hash_long(ELV_HASH_BLOCK((sec)), elv_hash_shift))
53#define ELV_HASH_ENTRIES (1 << elv_hash_shift)
54#define rq_hash_key(rq) (blk_rq_pos(rq) + blk_rq_sectors(rq))
55
56/*
57 * Query io scheduler to see if the current process issuing bio may be
58 * merged with rq.
59 */
60static int elv_iosched_allow_merge(struct request *rq, struct bio *bio)
61{
62    struct request_queue *q = rq->q;
63    struct elevator_queue *e = q->elevator;
64
65    if (e->ops->elevator_allow_merge_fn)
66        return e->ops->elevator_allow_merge_fn(q, rq, bio);
67
68    return 1;
69}
70
71/*
72 * can we safely merge with this request?
73 */
74int elv_rq_merge_ok(struct request *rq, struct bio *bio)
75{
76    if (!rq_mergeable(rq))
77        return 0;
78
79    /*
80     * Don't merge file system requests and discard requests
81     */
82    if ((bio->bi_rw & REQ_DISCARD) != (rq->bio->bi_rw & REQ_DISCARD))
83        return 0;
84
85    /*
86     * Don't merge discard requests and secure discard requests
87     */
88    if ((bio->bi_rw & REQ_SECURE) != (rq->bio->bi_rw & REQ_SECURE))
89        return 0;
90
91    /*
92     * different data direction or already started, don't merge
93     */
94    if (bio_data_dir(bio) != rq_data_dir(rq))
95        return 0;
96
97    /*
98     * must be same device and not a special request
99     */
100    if (rq->rq_disk != bio->bi_bdev->bd_disk || rq->special)
101        return 0;
102
103    /*
104     * only merge integrity protected bio into ditto rq
105     */
106    if (bio_integrity(bio) != blk_integrity_rq(rq))
107        return 0;
108
109    if (!elv_iosched_allow_merge(rq, bio))
110        return 0;
111
112    return 1;
113}
114EXPORT_SYMBOL(elv_rq_merge_ok);
115
116static inline int elv_try_merge(struct request *__rq, struct bio *bio)
117{
118    int ret = ELEVATOR_NO_MERGE;
119
120    /*
121     * we can merge and sequence is ok, check if it's possible
122     */
123    if (elv_rq_merge_ok(__rq, bio)) {
124        if (blk_rq_pos(__rq) + blk_rq_sectors(__rq) == bio->bi_sector)
125            ret = ELEVATOR_BACK_MERGE;
126        else if (blk_rq_pos(__rq) - bio_sectors(bio) == bio->bi_sector)
127            ret = ELEVATOR_FRONT_MERGE;
128    }
129
130    return ret;
131}
132
133static struct elevator_type *elevator_find(const char *name)
134{
135    struct elevator_type *e;
136
137    list_for_each_entry(e, &elv_list, list) {
138        if (!strcmp(e->elevator_name, name))
139            return e;
140    }
141
142    return NULL;
143}
144
145static void elevator_put(struct elevator_type *e)
146{
147    module_put(e->elevator_owner);
148}
149
150static struct elevator_type *elevator_get(const char *name)
151{
152    struct elevator_type *e;
153
154    spin_lock(&elv_list_lock);
155
156    e = elevator_find(name);
157    if (!e) {
158        char elv[ELV_NAME_MAX + strlen("-iosched")];
159
160        spin_unlock(&elv_list_lock);
161
162        snprintf(elv, sizeof(elv), "%s-iosched", name);
163
164        request_module("%s", elv);
165        spin_lock(&elv_list_lock);
166        e = elevator_find(name);
167    }
168
169    if (e && !try_module_get(e->elevator_owner))
170        e = NULL;
171
172    spin_unlock(&elv_list_lock);
173
174    return e;
175}
176
177static void *elevator_init_queue(struct request_queue *q,
178                 struct elevator_queue *eq)
179{
180    return eq->ops->elevator_init_fn(q);
181}
182
183static void elevator_attach(struct request_queue *q, struct elevator_queue *eq,
184               void *data)
185{
186    q->elevator = eq;
187    eq->elevator_data = data;
188}
189
190static char chosen_elevator[16];
191
192static int __init elevator_setup(char *str)
193{
194    /*
195     * Be backwards-compatible with previous kernels, so users
196     * won't get the wrong elevator.
197     */
198    strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1);
199    return 1;
200}
201
202__setup("elevator=", elevator_setup);
203
204static struct kobj_type elv_ktype;
205
206static struct elevator_queue *elevator_alloc(struct request_queue *q,
207                  struct elevator_type *e)
208{
209    struct elevator_queue *eq;
210    int i;
211
212    eq = kmalloc_node(sizeof(*eq), GFP_KERNEL | __GFP_ZERO, q->node);
213    if (unlikely(!eq))
214        goto err;
215
216    eq->ops = &e->ops;
217    eq->elevator_type = e;
218    kobject_init(&eq->kobj, &elv_ktype);
219    mutex_init(&eq->sysfs_lock);
220
221    eq->hash = kmalloc_node(sizeof(struct hlist_head) * ELV_HASH_ENTRIES,
222                    GFP_KERNEL, q->node);
223    if (!eq->hash)
224        goto err;
225
226    for (i = 0; i < ELV_HASH_ENTRIES; i++)
227        INIT_HLIST_HEAD(&eq->hash[i]);
228
229    return eq;
230err:
231    kfree(eq);
232    elevator_put(e);
233    return NULL;
234}
235
236static void elevator_release(struct kobject *kobj)
237{
238    struct elevator_queue *e;
239
240    e = container_of(kobj, struct elevator_queue, kobj);
241    elevator_put(e->elevator_type);
242    kfree(e->hash);
243    kfree(e);
244}
245
246int elevator_init(struct request_queue *q, char *name)
247{
248    struct elevator_type *e = NULL;
249    struct elevator_queue *eq;
250    void *data;
251
252    if (unlikely(q->elevator))
253        return 0;
254
255    INIT_LIST_HEAD(&q->queue_head);
256    q->last_merge = NULL;
257    q->end_sector = 0;
258    q->boundary_rq = NULL;
259
260    if (name) {
261        e = elevator_get(name);
262        if (!e)
263            return -EINVAL;
264    }
265
266    if (!e && *chosen_elevator) {
267        e = elevator_get(chosen_elevator);
268        if (!e)
269            printk(KERN_ERR "I/O scheduler %s not found\n",
270                            chosen_elevator);
271    }
272
273    if (!e) {
274        e = elevator_get(CONFIG_DEFAULT_IOSCHED);
275        if (!e) {
276            printk(KERN_ERR
277                "Default I/O scheduler not found. " \
278                "Using noop.\n");
279            e = elevator_get("noop");
280        }
281    }
282
283    eq = elevator_alloc(q, e);
284    if (!eq)
285        return -ENOMEM;
286
287    data = elevator_init_queue(q, eq);
288    if (!data) {
289        kobject_put(&eq->kobj);
290        return -ENOMEM;
291    }
292
293    elevator_attach(q, eq, data);
294    return 0;
295}
296EXPORT_SYMBOL(elevator_init);
297
298void elevator_exit(struct elevator_queue *e)
299{
300    mutex_lock(&e->sysfs_lock);
301    if (e->ops->elevator_exit_fn)
302        e->ops->elevator_exit_fn(e);
303    e->ops = NULL;
304    mutex_unlock(&e->sysfs_lock);
305
306    kobject_put(&e->kobj);
307}
308EXPORT_SYMBOL(elevator_exit);
309
310static inline void __elv_rqhash_del(struct request *rq)
311{
312    hlist_del_init(&rq->hash);
313}
314
315static void elv_rqhash_del(struct request_queue *q, struct request *rq)
316{
317    if (ELV_ON_HASH(rq))
318        __elv_rqhash_del(rq);
319}
320
321static void elv_rqhash_add(struct request_queue *q, struct request *rq)
322{
323    struct elevator_queue *e = q->elevator;
324
325    BUG_ON(ELV_ON_HASH(rq));
326    hlist_add_head(&rq->hash, &e->hash[ELV_HASH_FN(rq_hash_key(rq))]);
327}
328
329static void elv_rqhash_reposition(struct request_queue *q, struct request *rq)
330{
331    __elv_rqhash_del(rq);
332    elv_rqhash_add(q, rq);
333}
334
335static struct request *elv_rqhash_find(struct request_queue *q, sector_t offset)
336{
337    struct elevator_queue *e = q->elevator;
338    struct hlist_head *hash_list = &e->hash[ELV_HASH_FN(offset)];
339    struct hlist_node *entry, *next;
340    struct request *rq;
341
342    hlist_for_each_entry_safe(rq, entry, next, hash_list, hash) {
343        BUG_ON(!ELV_ON_HASH(rq));
344
345        if (unlikely(!rq_mergeable(rq))) {
346            __elv_rqhash_del(rq);
347            continue;
348        }
349
350        if (rq_hash_key(rq) == offset)
351            return rq;
352    }
353
354    return NULL;
355}
356
357/*
358 * RB-tree support functions for inserting/lookup/removal of requests
359 * in a sorted RB tree.
360 */
361struct request *elv_rb_add(struct rb_root *root, struct request *rq)
362{
363    struct rb_node **p = &root->rb_node;
364    struct rb_node *parent = NULL;
365    struct request *__rq;
366
367    while (*p) {
368        parent = *p;
369        __rq = rb_entry(parent, struct request, rb_node);
370
371        if (blk_rq_pos(rq) < blk_rq_pos(__rq))
372            p = &(*p)->rb_left;
373        else if (blk_rq_pos(rq) > blk_rq_pos(__rq))
374            p = &(*p)->rb_right;
375        else
376            return __rq;
377    }
378
379    rb_link_node(&rq->rb_node, parent, p);
380    rb_insert_color(&rq->rb_node, root);
381    return NULL;
382}
383EXPORT_SYMBOL(elv_rb_add);
384
385void elv_rb_del(struct rb_root *root, struct request *rq)
386{
387    BUG_ON(RB_EMPTY_NODE(&rq->rb_node));
388    rb_erase(&rq->rb_node, root);
389    RB_CLEAR_NODE(&rq->rb_node);
390}
391EXPORT_SYMBOL(elv_rb_del);
392
393struct request *elv_rb_find(struct rb_root *root, sector_t sector)
394{
395    struct rb_node *n = root->rb_node;
396    struct request *rq;
397
398    while (n) {
399        rq = rb_entry(n, struct request, rb_node);
400
401        if (sector < blk_rq_pos(rq))
402            n = n->rb_left;
403        else if (sector > blk_rq_pos(rq))
404            n = n->rb_right;
405        else
406            return rq;
407    }
408
409    return NULL;
410}
411EXPORT_SYMBOL(elv_rb_find);
412
413/*
414 * Insert rq into dispatch queue of q. Queue lock must be held on
415 * entry. rq is sort instead into the dispatch queue. To be used by
416 * specific elevators.
417 */
418void elv_dispatch_sort(struct request_queue *q, struct request *rq)
419{
420    sector_t boundary;
421    struct list_head *entry;
422    int stop_flags;
423
424    if (q->last_merge == rq)
425        q->last_merge = NULL;
426
427    elv_rqhash_del(q, rq);
428
429    q->nr_sorted--;
430
431    boundary = q->end_sector;
432    stop_flags = REQ_SOFTBARRIER | REQ_STARTED;
433    list_for_each_prev(entry, &q->queue_head) {
434        struct request *pos = list_entry_rq(entry);
435
436        if ((rq->cmd_flags & REQ_DISCARD) !=
437            (pos->cmd_flags & REQ_DISCARD))
438            break;
439        if (rq_data_dir(rq) != rq_data_dir(pos))
440            break;
441        if (pos->cmd_flags & stop_flags)
442            break;
443        if (blk_rq_pos(rq) >= boundary) {
444            if (blk_rq_pos(pos) < boundary)
445                continue;
446        } else {
447            if (blk_rq_pos(pos) >= boundary)
448                break;
449        }
450        if (blk_rq_pos(rq) >= blk_rq_pos(pos))
451            break;
452    }
453
454    list_add(&rq->queuelist, entry);
455}
456EXPORT_SYMBOL(elv_dispatch_sort);
457
458/*
459 * Insert rq into dispatch queue of q. Queue lock must be held on
460 * entry. rq is added to the back of the dispatch queue. To be used by
461 * specific elevators.
462 */
463void elv_dispatch_add_tail(struct request_queue *q, struct request *rq)
464{
465    if (q->last_merge == rq)
466        q->last_merge = NULL;
467
468    elv_rqhash_del(q, rq);
469
470    q->nr_sorted--;
471
472    q->end_sector = rq_end_sector(rq);
473    q->boundary_rq = rq;
474    list_add_tail(&rq->queuelist, &q->queue_head);
475}
476EXPORT_SYMBOL(elv_dispatch_add_tail);
477
478int elv_merge(struct request_queue *q, struct request **req, struct bio *bio)
479{
480    struct elevator_queue *e = q->elevator;
481    struct request *__rq;
482    int ret;
483
484    /*
485     * Levels of merges:
486     * nomerges: No merges at all attempted
487     * noxmerges: Only simple one-hit cache try
488     * merges: All merge tries attempted
489     */
490    if (blk_queue_nomerges(q))
491        return ELEVATOR_NO_MERGE;
492
493    /*
494     * First try one-hit cache.
495     */
496    if (q->last_merge) {
497        ret = elv_try_merge(q->last_merge, bio);
498        if (ret != ELEVATOR_NO_MERGE) {
499            *req = q->last_merge;
500            return ret;
501        }
502    }
503
504    if (blk_queue_noxmerges(q))
505        return ELEVATOR_NO_MERGE;
506
507    /*
508     * See if our hash lookup can find a potential backmerge.
509     */
510    __rq = elv_rqhash_find(q, bio->bi_sector);
511    if (__rq && elv_rq_merge_ok(__rq, bio)) {
512        *req = __rq;
513        return ELEVATOR_BACK_MERGE;
514    }
515
516    if (e->ops->elevator_merge_fn)
517        return e->ops->elevator_merge_fn(q, req, bio);
518
519    return ELEVATOR_NO_MERGE;
520}
521
522void elv_merged_request(struct request_queue *q, struct request *rq, int type)
523{
524    struct elevator_queue *e = q->elevator;
525
526    if (e->ops->elevator_merged_fn)
527        e->ops->elevator_merged_fn(q, rq, type);
528
529    if (type == ELEVATOR_BACK_MERGE)
530        elv_rqhash_reposition(q, rq);
531
532    q->last_merge = rq;
533}
534
535void elv_merge_requests(struct request_queue *q, struct request *rq,
536                 struct request *next)
537{
538    struct elevator_queue *e = q->elevator;
539
540    if (e->ops->elevator_merge_req_fn)
541        e->ops->elevator_merge_req_fn(q, rq, next);
542
543    elv_rqhash_reposition(q, rq);
544    elv_rqhash_del(q, next);
545
546    q->nr_sorted--;
547    q->last_merge = rq;
548}
549
550void elv_bio_merged(struct request_queue *q, struct request *rq,
551            struct bio *bio)
552{
553    struct elevator_queue *e = q->elevator;
554
555    if (e->ops->elevator_bio_merged_fn)
556        e->ops->elevator_bio_merged_fn(q, rq, bio);
557}
558
559void elv_requeue_request(struct request_queue *q, struct request *rq)
560{
561    /*
562     * it already went through dequeue, we need to decrement the
563     * in_flight count again
564     */
565    if (blk_account_rq(rq)) {
566        q->in_flight[rq_is_sync(rq)]--;
567        if (rq->cmd_flags & REQ_SORTED)
568            elv_deactivate_rq(q, rq);
569    }
570
571    rq->cmd_flags &= ~REQ_STARTED;
572
573    elv_insert(q, rq, ELEVATOR_INSERT_REQUEUE);
574}
575
576void elv_drain_elevator(struct request_queue *q)
577{
578    static int printed;
579    while (q->elevator->ops->elevator_dispatch_fn(q, 1))
580        ;
581    if (q->nr_sorted == 0)
582        return;
583    if (printed++ < 10) {
584        printk(KERN_ERR "%s: forced dispatching is broken "
585               "(nr_sorted=%u), please report this\n",
586               q->elevator->elevator_type->elevator_name, q->nr_sorted);
587    }
588}
589
590/*
591 * Call with queue lock held, interrupts disabled
592 */
593void elv_quiesce_start(struct request_queue *q)
594{
595    if (!q->elevator)
596        return;
597
598    queue_flag_set(QUEUE_FLAG_ELVSWITCH, q);
599
600    /*
601     * make sure we don't have any requests in flight
602     */
603    elv_drain_elevator(q);
604    while (q->rq.elvpriv) {
605        __blk_run_queue(q);
606        spin_unlock_irq(q->queue_lock);
607        msleep(10);
608        spin_lock_irq(q->queue_lock);
609        elv_drain_elevator(q);
610    }
611}
612
613void elv_quiesce_end(struct request_queue *q)
614{
615    queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
616}
617
618void elv_insert(struct request_queue *q, struct request *rq, int where)
619{
620    int unplug_it = 1;
621
622    trace_block_rq_insert(q, rq);
623
624    rq->q = q;
625
626    switch (where) {
627    case ELEVATOR_INSERT_REQUEUE:
628        /*
629         * Most requeues happen because of a busy condition,
630         * don't force unplug of the queue for that case.
631         * Clear unplug_it and fall through.
632         */
633        unplug_it = 0;
634
635    case ELEVATOR_INSERT_FRONT:
636        rq->cmd_flags |= REQ_SOFTBARRIER;
637        list_add(&rq->queuelist, &q->queue_head);
638        break;
639
640    case ELEVATOR_INSERT_BACK:
641        rq->cmd_flags |= REQ_SOFTBARRIER;
642        elv_drain_elevator(q);
643        list_add_tail(&rq->queuelist, &q->queue_head);
644        /*
645         * We kick the queue here for the following reasons.
646         * - The elevator might have returned NULL previously
647         * to delay requests and returned them now. As the
648         * queue wasn't empty before this request, ll_rw_blk
649         * won't run the queue on return, resulting in hang.
650         * - Usually, back inserted requests won't be merged
651         * with anything. There's no point in delaying queue
652         * processing.
653         */
654        __blk_run_queue(q);
655        break;
656
657    case ELEVATOR_INSERT_SORT:
658        BUG_ON(rq->cmd_type != REQ_TYPE_FS &&
659               !(rq->cmd_flags & REQ_DISCARD));
660        rq->cmd_flags |= REQ_SORTED;
661        q->nr_sorted++;
662        if (rq_mergeable(rq)) {
663            elv_rqhash_add(q, rq);
664            if (!q->last_merge)
665                q->last_merge = rq;
666        }
667
668        /*
669         * Some ioscheds (cfq) run q->request_fn directly, so
670         * rq cannot be accessed after calling
671         * elevator_add_req_fn.
672         */
673        q->elevator->ops->elevator_add_req_fn(q, rq);
674        break;
675
676    default:
677        printk(KERN_ERR "%s: bad insertion point %d\n",
678               __func__, where);
679        BUG();
680    }
681
682    if (unplug_it && blk_queue_plugged(q)) {
683        int nrq = q->rq.count[BLK_RW_SYNC] + q->rq.count[BLK_RW_ASYNC]
684                - queue_in_flight(q);
685
686        if (nrq >= q->unplug_thresh)
687            __generic_unplug_device(q);
688    }
689}
690
691void __elv_add_request(struct request_queue *q, struct request *rq, int where,
692               int plug)
693{
694    if (rq->cmd_flags & REQ_SOFTBARRIER) {
695        /* barriers are scheduling boundary, update end_sector */
696        if (rq->cmd_type == REQ_TYPE_FS ||
697            (rq->cmd_flags & REQ_DISCARD)) {
698            q->end_sector = rq_end_sector(rq);
699            q->boundary_rq = rq;
700        }
701    } else if (!(rq->cmd_flags & REQ_ELVPRIV) &&
702            where == ELEVATOR_INSERT_SORT)
703        where = ELEVATOR_INSERT_BACK;
704
705    if (plug)
706        blk_plug_device(q);
707
708    elv_insert(q, rq, where);
709}
710EXPORT_SYMBOL(__elv_add_request);
711
712void elv_add_request(struct request_queue *q, struct request *rq, int where,
713             int plug)
714{
715    unsigned long flags;
716
717    spin_lock_irqsave(q->queue_lock, flags);
718    __elv_add_request(q, rq, where, plug);
719    spin_unlock_irqrestore(q->queue_lock, flags);
720}
721EXPORT_SYMBOL(elv_add_request);
722
723int elv_queue_empty(struct request_queue *q)
724{
725    struct elevator_queue *e = q->elevator;
726
727    if (!list_empty(&q->queue_head))
728        return 0;
729
730    if (e->ops->elevator_queue_empty_fn)
731        return e->ops->elevator_queue_empty_fn(q);
732
733    return 1;
734}
735EXPORT_SYMBOL(elv_queue_empty);
736
737struct request *elv_latter_request(struct request_queue *q, struct request *rq)
738{
739    struct elevator_queue *e = q->elevator;
740
741    if (e->ops->elevator_latter_req_fn)
742        return e->ops->elevator_latter_req_fn(q, rq);
743    return NULL;
744}
745
746struct request *elv_former_request(struct request_queue *q, struct request *rq)
747{
748    struct elevator_queue *e = q->elevator;
749
750    if (e->ops->elevator_former_req_fn)
751        return e->ops->elevator_former_req_fn(q, rq);
752    return NULL;
753}
754
755int elv_set_request(struct request_queue *q, struct request *rq, gfp_t gfp_mask)
756{
757    struct elevator_queue *e = q->elevator;
758
759    if (e->ops->elevator_set_req_fn)
760        return e->ops->elevator_set_req_fn(q, rq, gfp_mask);
761
762    rq->elevator_private = NULL;
763    return 0;
764}
765
766void elv_put_request(struct request_queue *q, struct request *rq)
767{
768    struct elevator_queue *e = q->elevator;
769
770    if (e->ops->elevator_put_req_fn)
771        e->ops->elevator_put_req_fn(rq);
772}
773
774int elv_may_queue(struct request_queue *q, int rw)
775{
776    struct elevator_queue *e = q->elevator;
777
778    if (e->ops->elevator_may_queue_fn)
779        return e->ops->elevator_may_queue_fn(q, rw);
780
781    return ELV_MQUEUE_MAY;
782}
783
784void elv_abort_queue(struct request_queue *q)
785{
786    struct request *rq;
787
788    while (!list_empty(&q->queue_head)) {
789        rq = list_entry_rq(q->queue_head.next);
790        rq->cmd_flags |= REQ_QUIET;
791        trace_block_rq_abort(q, rq);
792        /*
793         * Mark this request as started so we don't trigger
794         * any debug logic in the end I/O path.
795         */
796        blk_start_request(rq);
797        __blk_end_request_all(rq, -EIO);
798    }
799}
800EXPORT_SYMBOL(elv_abort_queue);
801
802void elv_completed_request(struct request_queue *q, struct request *rq)
803{
804    struct elevator_queue *e = q->elevator;
805
806    /*
807     * request is released from the driver, io must be done
808     */
809    if (blk_account_rq(rq)) {
810        q->in_flight[rq_is_sync(rq)]--;
811        if ((rq->cmd_flags & REQ_SORTED) &&
812            e->ops->elevator_completed_req_fn)
813            e->ops->elevator_completed_req_fn(q, rq);
814    }
815}
816
817#define to_elv(atr) container_of((atr), struct elv_fs_entry, attr)
818
819static ssize_t
820elv_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
821{
822    struct elv_fs_entry *entry = to_elv(attr);
823    struct elevator_queue *e;
824    ssize_t error;
825
826    if (!entry->show)
827        return -EIO;
828
829    e = container_of(kobj, struct elevator_queue, kobj);
830    mutex_lock(&e->sysfs_lock);
831    error = e->ops ? entry->show(e, page) : -ENOENT;
832    mutex_unlock(&e->sysfs_lock);
833    return error;
834}
835
836static ssize_t
837elv_attr_store(struct kobject *kobj, struct attribute *attr,
838           const char *page, size_t length)
839{
840    struct elv_fs_entry *entry = to_elv(attr);
841    struct elevator_queue *e;
842    ssize_t error;
843
844    if (!entry->store)
845        return -EIO;
846
847    e = container_of(kobj, struct elevator_queue, kobj);
848    mutex_lock(&e->sysfs_lock);
849    error = e->ops ? entry->store(e, page, length) : -ENOENT;
850    mutex_unlock(&e->sysfs_lock);
851    return error;
852}
853
854static const struct sysfs_ops elv_sysfs_ops = {
855    .show = elv_attr_show,
856    .store = elv_attr_store,
857};
858
859static struct kobj_type elv_ktype = {
860    .sysfs_ops = &elv_sysfs_ops,
861    .release = elevator_release,
862};
863
864int elv_register_queue(struct request_queue *q)
865{
866    struct elevator_queue *e = q->elevator;
867    int error;
868
869    error = kobject_add(&e->kobj, &q->kobj, "%s", "iosched");
870    if (!error) {
871        struct elv_fs_entry *attr = e->elevator_type->elevator_attrs;
872        if (attr) {
873            while (attr->attr.name) {
874                if (sysfs_create_file(&e->kobj, &attr->attr))
875                    break;
876                attr++;
877            }
878        }
879        kobject_uevent(&e->kobj, KOBJ_ADD);
880        e->registered = 1;
881    }
882    return error;
883}
884EXPORT_SYMBOL(elv_register_queue);
885
886static void __elv_unregister_queue(struct elevator_queue *e)
887{
888    kobject_uevent(&e->kobj, KOBJ_REMOVE);
889    kobject_del(&e->kobj);
890    e->registered = 0;
891}
892
893void elv_unregister_queue(struct request_queue *q)
894{
895    if (q)
896        __elv_unregister_queue(q->elevator);
897}
898EXPORT_SYMBOL(elv_unregister_queue);
899
900void elv_register(struct elevator_type *e)
901{
902    char *def = "";
903
904    spin_lock(&elv_list_lock);
905    BUG_ON(elevator_find(e->elevator_name));
906    list_add_tail(&e->list, &elv_list);
907    spin_unlock(&elv_list_lock);
908
909    if (!strcmp(e->elevator_name, chosen_elevator) ||
910            (!*chosen_elevator &&
911             !strcmp(e->elevator_name, CONFIG_DEFAULT_IOSCHED)))
912                def = " (default)";
913
914    printk(KERN_INFO "io scheduler %s registered%s\n", e->elevator_name,
915                                def);
916}
917EXPORT_SYMBOL_GPL(elv_register);
918
919void elv_unregister(struct elevator_type *e)
920{
921    struct task_struct *g, *p;
922
923    /*
924     * Iterate every thread in the process to remove the io contexts.
925     */
926    if (e->ops.trim) {
927        read_lock(&tasklist_lock);
928        do_each_thread(g, p) {
929            task_lock(p);
930            if (p->io_context)
931                e->ops.trim(p->io_context);
932            task_unlock(p);
933        } while_each_thread(g, p);
934        read_unlock(&tasklist_lock);
935    }
936
937    spin_lock(&elv_list_lock);
938    list_del_init(&e->list);
939    spin_unlock(&elv_list_lock);
940}
941EXPORT_SYMBOL_GPL(elv_unregister);
942
943/*
944 * switch to new_e io scheduler. be careful not to introduce deadlocks -
945 * we don't free the old io scheduler, before we have allocated what we
946 * need for the new one. this way we have a chance of going back to the old
947 * one, if the new one fails init for some reason.
948 */
949static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
950{
951    struct elevator_queue *old_elevator, *e;
952    void *data;
953    int err;
954
955    /*
956     * Allocate new elevator
957     */
958    e = elevator_alloc(q, new_e);
959    if (!e)
960        return -ENOMEM;
961
962    data = elevator_init_queue(q, e);
963    if (!data) {
964        kobject_put(&e->kobj);
965        return -ENOMEM;
966    }
967
968    /*
969     * Turn on BYPASS and drain all requests w/ elevator private data
970     */
971    spin_lock_irq(q->queue_lock);
972    elv_quiesce_start(q);
973
974    /*
975     * Remember old elevator.
976     */
977    old_elevator = q->elevator;
978
979    /*
980     * attach and start new elevator
981     */
982    elevator_attach(q, e, data);
983
984    spin_unlock_irq(q->queue_lock);
985
986    if (old_elevator->registered) {
987        __elv_unregister_queue(old_elevator);
988
989        err = elv_register_queue(q);
990        if (err)
991            goto fail_register;
992    }
993
994    /*
995     * finally exit old elevator and turn off BYPASS.
996     */
997    elevator_exit(old_elevator);
998    spin_lock_irq(q->queue_lock);
999    elv_quiesce_end(q);
1000    spin_unlock_irq(q->queue_lock);
1001
1002    blk_add_trace_msg(q, "elv switch: %s", e->elevator_type->elevator_name);
1003
1004    return 0;
1005
1006fail_register:
1007    /*
1008     * switch failed, exit the new io scheduler and reattach the old
1009     * one again (along with re-adding the sysfs dir)
1010     */
1011    elevator_exit(e);
1012    q->elevator = old_elevator;
1013    elv_register_queue(q);
1014
1015    spin_lock_irq(q->queue_lock);
1016    queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
1017    spin_unlock_irq(q->queue_lock);
1018
1019    return err;
1020}
1021
1022/*
1023 * Switch this queue to the given IO scheduler.
1024 */
1025int elevator_change(struct request_queue *q, const char *name)
1026{
1027    char elevator_name[ELV_NAME_MAX];
1028    struct elevator_type *e;
1029
1030    if (!q->elevator)
1031        return -ENXIO;
1032
1033    strlcpy(elevator_name, name, sizeof(elevator_name));
1034    e = elevator_get(strstrip(elevator_name));
1035    if (!e) {
1036        printk(KERN_ERR "elevator: type %s not found\n", elevator_name);
1037        return -EINVAL;
1038    }
1039
1040    if (!strcmp(elevator_name, q->elevator->elevator_type->elevator_name)) {
1041        elevator_put(e);
1042        return 0;
1043    }
1044
1045    return elevator_switch(q, e);
1046}
1047EXPORT_SYMBOL(elevator_change);
1048
1049ssize_t elv_iosched_store(struct request_queue *q, const char *name,
1050              size_t count)
1051{
1052    int ret;
1053
1054    if (!q->elevator)
1055        return count;
1056
1057    ret = elevator_change(q, name);
1058    if (!ret)
1059        return count;
1060
1061    printk(KERN_ERR "elevator: switch to %s failed\n", name);
1062    return ret;
1063}
1064
1065ssize_t elv_iosched_show(struct request_queue *q, char *name)
1066{
1067    struct elevator_queue *e = q->elevator;
1068    struct elevator_type *elv;
1069    struct elevator_type *__e;
1070    int len = 0;
1071
1072    if (!q->elevator || !blk_queue_stackable(q))
1073        return sprintf(name, "none\n");
1074
1075    elv = e->elevator_type;
1076
1077    spin_lock(&elv_list_lock);
1078    list_for_each_entry(__e, &elv_list, list) {
1079        if (!strcmp(elv->elevator_name, __e->elevator_name))
1080            len += sprintf(name+len, "[%s] ", elv->elevator_name);
1081        else
1082            len += sprintf(name+len, "%s ", __e->elevator_name);
1083    }
1084    spin_unlock(&elv_list_lock);
1085
1086    len += sprintf(len+name, "\n");
1087    return len;
1088}
1089
1090struct request *elv_rb_former_request(struct request_queue *q,
1091                      struct request *rq)
1092{
1093    struct rb_node *rbprev = rb_prev(&rq->rb_node);
1094
1095    if (rbprev)
1096        return rb_entry_rq(rbprev);
1097
1098    return NULL;
1099}
1100EXPORT_SYMBOL(elv_rb_former_request);
1101
1102struct request *elv_rb_latter_request(struct request_queue *q,
1103                      struct request *rq)
1104{
1105    struct rb_node *rbnext = rb_next(&rq->rb_node);
1106
1107    if (rbnext)
1108        return rb_entry_rq(rbnext);
1109
1110    return NULL;
1111}
1112EXPORT_SYMBOL(elv_rb_latter_request);
1113

Archive Download this file



interactive