summaryrefslogtreecommitdiffstats
path: root/drivers/block/elevator.c
blob: f831f08f839c14d145cb19d322b361c47a08a2e6 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
/*
 *  linux/drivers/block/elevator.c
 *
 *  Block device elevator/IO-scheduler.
 *
 *  Copyright (C) 2000 Andrea Arcangeli <andrea@suse.de> SuSE
 *
 * 30042000 Jens Axboe <axboe@suse.de> :
 *
 * Split the elevator a bit so that it is possible to choose a different
 * one or even write a new "plug in". There are three pieces:
 * - elevator_fn, inserts a new request in the queue list
 * - elevator_merge_fn, decides whether a new buffer can be merged with
 *   an existing request
 * - elevator_dequeue_fn, called when a request is taken off the active list
 *
 * 20082000 Dave Jones <davej@suse.de> :
 * Removed tests for max-bomb-segments, which was breaking elvtune
 *  when run without -bN
 *
 * Jens:
 * - Rework again to work with bio instead of buffer_heads
 * - loose bi_dev comparisons, partition handling is right now
 * - completely modularize elevator setup and teardown
 *
 */
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/blkdev.h>
#include <linux/elevator.h>
#include <linux/bio.h>
#include <linux/config.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/compiler.h>

#include <asm/uaccess.h>

static DEFINE_SPINLOCK(elv_list_lock);
static LIST_HEAD(elv_list);

/*
 * can we safely merge with this request?
 */
inline int elv_rq_merge_ok(struct request *rq, struct bio *bio)
{
	if (!rq_mergeable(rq))
		return 0;

	/*
	 * different data direction or already started, don't merge
	 */
	if (bio_data_dir(bio) != rq_data_dir(rq))
		return 0;

	/*
	 * same device and no special stuff set, merge is ok
	 */
	if (rq->rq_disk == bio->bi_bdev->bd_disk &&
	    !rq->waiting && !rq->special)
		return 1;

	return 0;
}
EXPORT_SYMBOL(elv_rq_merge_ok);

inline int elv_try_merge(struct request *__rq, struct bio *bio)
{
	int ret = ELEVATOR_NO_MERGE;

	/*
	 * we can merge and sequence is ok, check if it's possible
	 */
	if (elv_rq_merge_ok(__rq, bio)) {
		if (__rq->sector + __rq->nr_sectors == bio->bi_sector)
			ret = ELEVATOR_BACK_MERGE;
		else if (__rq->sector - bio_sectors(bio) == bio->bi_sector)
			ret = ELEVATOR_FRONT_MERGE;
	}

	return ret;
}
EXPORT_SYMBOL(elv_try_merge);

inline int elv_try_last_merge(request_queue_t *q, struct bio *bio)
{
	if (q->last_merge)
		return elv_try_merge(q->last_merge, bio);

	return ELEVATOR_NO_MERGE;
}
EXPORT_SYMBOL(elv_try_last_merge);

static struct elevator_type *elevator_find(const char *name)
{
	struct elevator_type *e = NULL;
	struct list_head *entry;

	spin_lock_irq(&elv_list_lock);
	list_for_each(entry, &elv_list) {
		struct elevator_type *__e;

		__e = list_entry(entry, struct elevator_type, list);

		if (!strcmp(__e->elevator_name, name)) {
			e = __e;
			break;
		}
	}
	spin_unlock_irq(&elv_list_lock);

	return e;
}

static void elevator_put(struct elevator_type *e)
{
	module_put(e->elevator_owner);
}

static struct elevator_type *elevator_get(const char *name)
{
	struct elevator_type *e = elevator_find(name);

	if (!e)
		return NULL;
	if (!try_module_get(e->elevator_owner))
		return NULL;

	return e;
}

static int elevator_attach(request_queue_t *q, struct elevator_type *e,
			   struct elevator_queue *eq)
{
	int ret = 0;

	memset(eq, 0, sizeof(*eq));
	eq->ops = &e->ops;
	eq->elevator_type = e;

	INIT_LIST_HEAD(&q->queue_head);
	q->last_merge = NULL;
	q->elevator = eq;

	if (eq->ops->elevator_init_fn)
		ret = eq->ops->elevator_init_fn(q, eq);

	return ret;
}

static char chosen_elevator[16];

static void elevator_setup_default(void)
{
	/*
	 * check if default is set and exists
	 */
	if (chosen_elevator[0] && elevator_find(chosen_elevator))
		return;

#if defined(CONFIG_IOSCHED_AS)
	strcpy(chosen_elevator, "anticipatory");
#elif defined(CONFIG_IOSCHED_DEADLINE)
	strcpy(chosen_elevator, "deadline");
#elif defined(CONFIG_IOSCHED_CFQ)
	strcpy(chosen_elevator, "cfq");
#elif defined(CONFIG_IOSCHED_NOOP)
	strcpy(chosen_elevator, "noop");
#else
#error "You must build at least 1 IO scheduler into the kernel"
#endif
}

static int __init elevator_setup(char *str)
{
	strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1);
	return 0;
}

__setup("elevator=", elevator_setup);

int elevator_init(request_queue_t *q, char *name)
{
	struct elevator_type *e = NULL;
	struct elevator_queue *eq;
	int ret = 0;

	elevator_setup_default();

	if (!name)
		name = chosen_elevator;

	e = elevator_get(name);
	if (!e)
		return -EINVAL;

	eq = kmalloc(sizeof(struct elevator_queue), GFP_KERNEL);
	if (!eq) {
		elevator_put(e->elevator_type);
		return -ENOMEM;
	}

	ret = elevator_attach(q, e, eq);
	if (ret) {
		kfree(eq);
		elevator_put(e->elevator_type);
	}

	return ret;
}

void elevator_exit(elevator_t *e)
{
	if (e->ops->elevator_exit_fn)
		e->ops->elevator_exit_fn(e);

	elevator_put(e->elevator_type);
	e->elevator_type = NULL;
	kfree(e);
}

int elv_merge(request_queue_t *q, struct request **req, struct bio *bio)
{
	elevator_t *e = q->elevator;

	if (e->ops->elevator_merge_fn)
		return e->ops->elevator_merge_fn(q, req, bio);

	return ELEVATOR_NO_MERGE;
}

void elv_merged_request(request_queue_t *q, struct request *rq)
{
	elevator_t *e = q->elevator;

	if (e->ops->elevator_merged_fn)
		e->ops->elevator_merged_fn(q, rq);
}

void elv_merge_requests(request_queue_t *q, struct request *rq,
			     struct request *next)
{
	elevator_t *e = q->elevator;

	if (q->last_merge == next)
		q->last_merge = NULL;

	if (e->ops->elevator_merge_req_fn)
		e->ops->elevator_merge_req_fn(q, rq, next);
}

/*
 * For careful internal use by the block layer. Essentially the same as
 * a requeue in that it tells the io scheduler that this request is not
 * active in the driver or hardware anymore, but we don't want the request
 * added back to the scheduler. Function is not exported.
 */
void elv_deactivate_request(request_queue_t *q, struct request *rq)
{
	elevator_t *e = q->elevator;

	/*
	 * it already went through dequeue, we need to decrement the
	 * in_flight count again
	 */
	if (blk_account_rq(rq))
		q->in_flight--;

	rq->flags &= ~REQ_STARTED;

	if (e->ops->elevator_deactivate_req_fn)
		e->ops->elevator_deactivate_req_fn(q, rq);
}

void elv_requeue_request(request_queue_t *q, struct request *rq)
{
	elv_deactivate_request(q, rq);

	/*
	 * if this is the flush, requeue the original instead and drop the flush
	 */
	if (rq->flags & REQ_BAR_FLUSH) {
		clear_bit(QUEUE_FLAG_FLUSH, &q->queue_flags);
		rq = rq->end_io_data;
	}

	/*
	 * the request is prepped and may have some resources allocated.
	 * allowing unprepped requests to pass this one may cause resource
	 * deadlock.  turn on softbarrier.
	 */
	rq->flags |= REQ_SOFTBARRIER;

	/*
	 * if iosched has an explicit requeue hook, then use that. otherwise
	 * just put the request at the front of the queue
	 */
	if (q->elevator->ops->elevator_requeue_req_fn)
		q->elevator->ops->elevator_requeue_req_fn(q, rq);
	else
		__elv_add_request(q, rq, ELEVATOR_INSERT_FRONT, 0);
}

void __elv_add_request(request_queue_t *q, struct request *rq, int where,
		       int plug)
{
	/*
	 * barriers implicitly indicate back insertion
	 */
	if (rq->flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER) &&
	    where == ELEVATOR_INSERT_SORT)
		where = ELEVATOR_INSERT_BACK;

	if (plug)
		blk_plug_device(q);

	rq->q = q;

	if (!test_bit(QUEUE_FLAG_DRAIN, &q->queue_flags)) {
		q->elevator->ops->elevator_add_req_fn(q, rq, where);

		if (blk_queue_plugged(q)) {
			int nrq = q->rq.count[READ] + q->rq.count[WRITE]
				  - q->in_flight;

			if (nrq >= q->unplug_thresh)
				__generic_unplug_device(q);
		}
	} else
		/*
		 * if drain is set, store the request "locally". when the drain
		 * is finished, the requests will be handed ordered to the io
		 * scheduler
		 */
		list_add_tail(&rq->queuelist, &q->drain_list);
}

void elv_add_request(request_queue_t *q, struct request *rq, int where,
		     int plug)
{
	unsigned long flags;

	spin_lock_irqsave(q->queue_lock, flags);
	__elv_add_request(q, rq, where, plug);
	spin_unlock_irqrestore(q->queue_lock, flags);
}

static inline struct request *__elv_next_request(request_queue_t *q)
{
	struct request *rq = q->elevator->ops->elevator_next_req_fn(q);

	/*
	 * if this is a barrier write and the device has to issue a
	 * flush sequence to support it, check how far we are
	 */
	if (rq && blk_fs_request(rq) && blk_barrier_rq(rq)) {
		BUG_ON(q->ordered == QUEUE_ORDERED_NONE);

		if (q->ordered == QUEUE_ORDERED_FLUSH &&
		    !blk_barrier_preflush(rq))
			rq = blk_start_pre_flush(q, rq);
	}

	return rq;
}

struct request *elv_next_request(request_queue_t *q)
{
	struct request *rq;
	int ret;

	while ((rq = __elv_next_request(q)) != NULL) {
		/*
		 * just mark as started even if we don't start it, a request
		 * that has been delayed should not be passed by new incoming
		 * requests
		 */
		rq->flags |= REQ_STARTED;

		if (rq == q->last_merge)
			q->last_merge = NULL;

		if ((rq->flags & REQ_DONTPREP) || !q->prep_rq_fn)
			break;

		ret = q->prep_rq_fn(q, rq);
		if (ret == BLKPREP_OK) {
			break;
		} else if (ret == BLKPREP_DEFER) {
			/*
			 * the request may have been (partially) prepped.
			 * we need to keep this request in the front to
			 * avoid resource deadlock.  turn on softbarrier.
			 */
			rq->flags |= REQ_SOFTBARRIER;
			rq = NULL;
			break;
		} else if (ret == BLKPREP_KILL) {
			int nr_bytes = rq->hard_nr_sectors << 9;

			if (!nr_bytes)
				nr_bytes = rq->data_len;

			blkdev_dequeue_request(rq);
			rq->flags |= REQ_QUIET;
			end_that_request_chunk(rq, 0, nr_bytes);
			end_that_request_last(rq);
		} else {
			printk(KERN_ERR "%s: bad return=%d\n", __FUNCTION__,
								ret);
			break;
		}
	}

	return rq;
}

void elv_remove_request(request_queue_t *q, struct request *rq)
{
	elevator_t *e = q->elevator;

	/*
	 * the time frame between a request being removed from the lists
	 * and to it is freed is accounted as io that is in progress at
	 * the driver side. note that we only account requests that the
	 * driver has seen (REQ_STARTED set), to avoid false accounting
	 * for request-request merges
	 */
	if (blk_account_rq(rq))
		q->in_flight++;

	/*
	 * the main clearing point for q->last_merge is on retrieval of
	 * request by driver (it calls elv_next_request()), but it _can_
	 * also happen here if a request is added to the queue but later
	 * deleted without ever being given to driver (merged with another
	 * request).
	 */
	if (rq == q->last_merge)
		q->last_merge = NULL;

	if (e->ops->elevator_remove_req_fn)
		e->ops->elevator_remove_req_fn(q, rq);
}

int elv_queue_empty(request_queue_t *q)
{
	elevator_t *e = q->elevator;

	if (e->ops->elevator_queue_empty_fn)
		return e->ops->elevator_queue_empty_fn(q);

	return list_empty(&q->queue_head);
}

struct request *elv_latter_request(request_queue_t *q, struct request *rq)
{
	struct list_head *next;

	elevator_t *e = q->elevator;

	if (e->ops->elevator_latter_req_fn)
		return e->ops->elevator_latter_req_fn(q, rq);

	next = rq->queuelist.next;
	if (next != &q->queue_head && next != &rq->queuelist)
		return list_entry_rq(next);

	return NULL;
}

struct request *elv_former_request(request_queue_t *q, struct request *rq)
{
	struct list_head *prev;

	elevator_t *e = q->elevator;

	if (e->ops->elevator_former_req_fn)
		return e->ops->elevator_former_req_fn(q, rq);

	prev = rq->queuelist.prev;
	if (prev != &q->queue_head && prev != &rq->queuelist)
		return list_entry_rq(prev);

	return NULL;
}

int elv_set_request(request_queue_t *q, struct request *rq, int gfp_mask)
{
	elevator_t *e = q->elevator;

	if (e->ops->elevator_set_req_fn)
		return e->ops->elevator_set_req_fn(q, rq, gfp_mask);

	rq->elevator_private = NULL;
	return 0;
}

void elv_put_request(request_queue_t *q, struct request *rq)
{
	elevator_t *e = q->elevator;

	if (e->ops->elevator_put_req_fn)
		e->ops->elevator_put_req_fn(q, rq);
}

int elv_may_queue(request_queue_t *q, int rw)
{
	elevator_t *e = q->elevator;

	if (e->ops->elevator_may_queue_fn)
		return e->ops->elevator_may_queue_fn(q, rw);

	return ELV_MQUEUE_MAY;
}

void elv_completed_request(request_queue_t *q, struct request *rq)
{
	elevator_t *e = q->elevator;

	/*
	 * request is released from the driver, io must be done
	 */
	if (blk_account_rq(rq))
		q->in_flight--;

	if (e->ops->elevator_completed_req_fn)
		e->ops->elevator_completed_req_fn(q, rq);
}

int elv_register_queue(struct request_queue *q)
{
	elevator_t *e = q->elevator;

	e->kobj.parent = kobject_get(&q->kobj);
	if (!e->kobj.parent)
		return -EBUSY;

	snprintf(e->kobj.name, KOBJ_NAME_LEN, "%s", "iosched");
	e->kobj.ktype = e->elevator_type->elevator_ktype;

	return kobject_register(&e->kobj);
}

void elv_unregister_queue(struct request_queue *q)
{
	if (q) {
		elevator_t *e = q->elevator;
		kobject_unregister(&e->kobj);
		kobject_put(&q->kobj);
	}
}

int elv_register(struct elevator_type *e)
{
	if (elevator_find(e->elevator_name))
		BUG();

	spin_lock_irq(&elv_list_lock);
	list_add_tail(&e->list, &elv_list);
	spin_unlock_irq(&elv_list_lock);

	printk(KERN_INFO "io scheduler %s registered", e->elevator_name);
	if (!strcmp(e->elevator_name, chosen_elevator))
		printk(" (default)");
	printk("\n");
	return 0;
}
EXPORT_SYMBOL_GPL(elv_register);

void elv_unregister(struct elevator_type *e)
{
	spin_lock_irq(&elv_list_lock);
	list_del_init(&e->list);
	spin_unlock_irq(&elv_list_lock);
}
EXPORT_SYMBOL_GPL(elv_unregister);

/*
 * switch to new_e io scheduler. be careful not to introduce deadlocks -
 * we don't free the old io scheduler, before we have allocated what we
 * need for the new one. this way we have a chance of going back to the old
 * one, if the new one fails init for some reason. we also do an intermediate
 * switch to noop to ensure safety with stack-allocated requests, since they
 * don't originate from the block layer allocator. noop is safe here, because
 * it never needs to touch the elevator itself for completion events. DRAIN
 * flags will make sure we don't touch it for additions either.
 */
static void elevator_switch(request_queue_t *q, struct elevator_type *new_e)
{
	elevator_t *e = kmalloc(sizeof(elevator_t), GFP_KERNEL);
	struct elevator_type *noop_elevator = NULL;
	elevator_t *old_elevator;

	if (!e)
		goto error;

	/*
	 * first step, drain requests from the block freelist
	 */
	blk_wait_queue_drained(q, 0);

	/*
	 * unregister old elevator data
	 */
	elv_unregister_queue(q);
	old_elevator = q->elevator;

	/*
 	 * next step, switch to noop since it uses no private rq structures
	 * and doesn't allocate any memory for anything. then wait for any
	 * non-fs requests in-flight
 	 */
	noop_elevator = elevator_get("noop");
	spin_lock_irq(q->queue_lock);
	elevator_attach(q, noop_elevator, e);
	spin_unlock_irq(q->queue_lock);

	blk_wait_queue_drained(q, 1);

	/*
	 * attach and start new elevator
	 */
	if (elevator_attach(q, new_e, e))
		goto fail;

	if (elv_register_queue(q))
		goto fail_register;

	/*
	 * finally exit old elevator and start queue again
	 */
	elevator_exit(old_elevator);
	blk_finish_queue_drain(q);
	elevator_put(noop_elevator);
	return;

fail_register:
	/*
	 * switch failed, exit the new io scheduler and reattach the old
	 * one again (along with re-adding the sysfs dir)
	 */
	elevator_exit(e);
fail:
	q->elevator = old_elevator;
	elv_register_queue(q);
	blk_finish_queue_drain(q);
error:
	if (noop_elevator)
		elevator_put(noop_elevator);
	elevator_put(new_e);
	printk(KERN_ERR "elevator: switch to %s failed\n",new_e->elevator_name);
}

ssize_t elv_iosched_store(request_queue_t *q, const char *name, size_t count)
{
	char elevator_name[ELV_NAME_MAX];
	struct elevator_type *e;

	memset(elevator_name, 0, sizeof(elevator_name));
	strncpy(elevator_name, name, sizeof(elevator_name));

	if (elevator_name[strlen(elevator_name) - 1] == '\n')
		elevator_name[strlen(elevator_name) - 1] = '\0';

	e = elevator_get(elevator_name);
	if (!e) {
		printk(KERN_ERR "elevator: type %s not found\n", elevator_name);
		return -EINVAL;
	}

	if (!strcmp(elevator_name, q->elevator->elevator_type->elevator_name))
		return count;

	elevator_switch(q, e);
	return count;
}

ssize_t elv_iosched_show(request_queue_t *q, char *name)
{
	elevator_t *e = q->elevator;
	struct elevator_type *elv = e->elevator_type;
	struct list_head *entry;
	int len = 0;

	spin_lock_irq(q->queue_lock);
	list_for_each(entry, &elv_list) {
		struct elevator_type *__e;

		__e = list_entry(entry, struct elevator_type, list);
		if (!strcmp(elv->elevator_name, __e->elevator_name))
			len += sprintf(name+len, "[%s] ", elv->elevator_name);
		else
			len += sprintf(name+len, "%s ", __e->elevator_name);
	}
	spin_unlock_irq(q->queue_lock);

	len += sprintf(len+name, "\n");
	return len;
}

EXPORT_SYMBOL(elv_add_request);
EXPORT_SYMBOL(__elv_add_request);
EXPORT_SYMBOL(elv_requeue_request);
EXPORT_SYMBOL(elv_next_request);
EXPORT_SYMBOL(elv_remove_request);
EXPORT_SYMBOL(elv_queue_empty);
EXPORT_SYMBOL(elv_completed_request);
EXPORT_SYMBOL(elevator_exit);
EXPORT_SYMBOL(elevator_init);