summaryrefslogtreecommitdiffstats
path: root/block/kyber-iosched.c
blob: a1660bafc912452a37730ac0ed2bf02f6c8a99bc (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
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
/*
 * The Kyber I/O scheduler. Controls latency by throttling queue depths using
 * scalable techniques.
 *
 * Copyright (C) 2017 Facebook
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public
 * License v2 as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

#include <linux/kernel.h>
#include <linux/blkdev.h>
#include <linux/blk-mq.h>
#include <linux/elevator.h>
#include <linux/module.h>
#include <linux/sbitmap.h>

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

/* Scheduling domains. */
enum {
	KYBER_READ,
	KYBER_SYNC_WRITE,
	KYBER_OTHER, /* Async writes, discard, etc. */
	KYBER_NUM_DOMAINS,
};

enum {
	KYBER_MIN_DEPTH = 256,

	/*
	 * In order to prevent starvation of synchronous requests by a flood of
	 * asynchronous requests, we reserve 25% of requests for synchronous
	 * operations.
	 */
	KYBER_ASYNC_PERCENT = 75,
};

/*
 * Initial device-wide depths for each scheduling domain.
 *
 * Even for fast devices with lots of tags like NVMe, you can saturate
 * the device with only a fraction of the maximum possible queue depth.
 * So, we cap these to a reasonable value.
 */
static const unsigned int kyber_depth[] = {
	[KYBER_READ] = 256,
	[KYBER_SYNC_WRITE] = 128,
	[KYBER_OTHER] = 64,
};

/*
 * Scheduling domain batch sizes. We favor reads.
 */
static const unsigned int kyber_batch_size[] = {
	[KYBER_READ] = 16,
	[KYBER_SYNC_WRITE] = 8,
	[KYBER_OTHER] = 8,
};

/*
 * There is a same mapping between ctx & hctx and kcq & khd,
 * we use request->mq_ctx->index_hw to index the kcq in khd.
 */
struct kyber_ctx_queue {
	/*
	 * Used to ensure operations on rq_list and kcq_map to be an atmoic one.
	 * Also protect the rqs on rq_list when merge.
	 */
	spinlock_t lock;
	struct list_head rq_list[KYBER_NUM_DOMAINS];
} ____cacheline_aligned_in_smp;

struct kyber_queue_data {
	struct request_queue *q;

	struct blk_stat_callback *cb;

	/*
	 * The device is divided into multiple scheduling domains based on the
	 * request type. Each domain has a fixed number of in-flight requests of
	 * that type device-wide, limited by these tokens.
	 */
	struct sbitmap_queue domain_tokens[KYBER_NUM_DOMAINS];

	/*
	 * Async request percentage, converted to per-word depth for
	 * sbitmap_get_shallow().
	 */
	unsigned int async_depth;

	/* Target latencies in nanoseconds. */
	u64 read_lat_nsec, write_lat_nsec;
};

struct kyber_hctx_data {
	spinlock_t lock;
	struct list_head rqs[KYBER_NUM_DOMAINS];
	unsigned int cur_domain;
	unsigned int batching;
	struct kyber_ctx_queue *kcqs;
	struct sbitmap kcq_map[KYBER_NUM_DOMAINS];
	wait_queue_entry_t domain_wait[KYBER_NUM_DOMAINS];
	struct sbq_wait_state *domain_ws[KYBER_NUM_DOMAINS];
	atomic_t wait_index[KYBER_NUM_DOMAINS];
};

static int kyber_domain_wake(wait_queue_entry_t *wait, unsigned mode, int flags,
			     void *key);

static unsigned int kyber_sched_domain(unsigned int op)
{
	if ((op & REQ_OP_MASK) == REQ_OP_READ)
		return KYBER_READ;
	else if ((op & REQ_OP_MASK) == REQ_OP_WRITE && op_is_sync(op))
		return KYBER_SYNC_WRITE;
	else
		return KYBER_OTHER;
}

enum {
	NONE = 0,
	GOOD = 1,
	GREAT = 2,
	BAD = -1,
	AWFUL = -2,
};

#define IS_GOOD(status) ((status) > 0)
#define IS_BAD(status) ((status) < 0)

static int kyber_lat_status(struct blk_stat_callback *cb,
			    unsigned int sched_domain, u64 target)
{
	u64 latency;

	if (!cb->stat[sched_domain].nr_samples)
		return NONE;

	latency = cb->stat[sched_domain].mean;
	if (latency >= 2 * target)
		return AWFUL;
	else if (latency > target)
		return BAD;
	else if (latency <= target / 2)
		return GREAT;
	else /* (latency <= target) */
		return GOOD;
}

/*
 * Adjust the read or synchronous write depth given the status of reads and
 * writes. The goal is that the latencies of the two domains are fair (i.e., if
 * one is good, then the other is good).
 */
static void kyber_adjust_rw_depth(struct kyber_queue_data *kqd,
				  unsigned int sched_domain, int this_status,
				  int other_status)
{
	unsigned int orig_depth, depth;

	/*
	 * If this domain had no samples, or reads and writes are both good or
	 * both bad, don't adjust the depth.
	 */
	if (this_status == NONE ||
	    (IS_GOOD(this_status) && IS_GOOD(other_status)) ||
	    (IS_BAD(this_status) && IS_BAD(other_status)))
		return;

	orig_depth = depth = kqd->domain_tokens[sched_domain].sb.depth;

	if (other_status == NONE) {
		depth++;
	} else {
		switch (this_status) {
		case GOOD:
			if (other_status == AWFUL)
				depth -= max(depth / 4, 1U);
			else
				depth -= max(depth / 8, 1U);
			break;
		case GREAT:
			if (other_status == AWFUL)
				depth /= 2;
			else
				depth -= max(depth / 4, 1U);
			break;
		case BAD:
			depth++;
			break;
		case AWFUL:
			if (other_status == GREAT)
				depth += 2;
			else
				depth++;
			break;
		}
	}

	depth = clamp(depth, 1U, kyber_depth[sched_domain]);
	if (depth != orig_depth)
		sbitmap_queue_resize(&kqd->domain_tokens[sched_domain], depth);
}

/*
 * Adjust the depth of other requests given the status of reads and synchronous
 * writes. As long as either domain is doing fine, we don't throttle, but if
 * both domains are doing badly, we throttle heavily.
 */
static void kyber_adjust_other_depth(struct kyber_queue_data *kqd,
				     int read_status, int write_status,
				     bool have_samples)
{
	unsigned int orig_depth, depth;
	int status;

	orig_depth = depth = kqd->domain_tokens[KYBER_OTHER].sb.depth;

	if (read_status == NONE && write_status == NONE) {
		depth += 2;
	} else if (have_samples) {
		if (read_status == NONE)
			status = write_status;
		else if (write_status == NONE)
			status = read_status;
		else
			status = max(read_status, write_status);
		switch (status) {
		case GREAT:
			depth += 2;
			break;
		case GOOD:
			depth++;
			break;
		case BAD:
			depth -= max(depth / 4, 1U);
			break;
		case AWFUL:
			depth /= 2;
			break;
		}
	}

	depth = clamp(depth, 1U, kyber_depth[KYBER_OTHER]);
	if (depth != orig_depth)
		sbitmap_queue_resize(&kqd->domain_tokens[KYBER_OTHER], depth);
}

/*
 * Apply heuristics for limiting queue depths based on gathered latency
 * statistics.
 */
static void kyber_stat_timer_fn(struct blk_stat_callback *cb)
{
	struct kyber_queue_data *kqd = cb->data;
	int read_status, write_status;

	read_status = kyber_lat_status(cb, KYBER_READ, kqd->read_lat_nsec);
	write_status = kyber_lat_status(cb, KYBER_SYNC_WRITE, kqd->write_lat_nsec);

	kyber_adjust_rw_depth(kqd, KYBER_READ, read_status, write_status);
	kyber_adjust_rw_depth(kqd, KYBER_SYNC_WRITE, write_status, read_status);
	kyber_adjust_other_depth(kqd, read_status, write_status,
				 cb->stat[KYBER_OTHER].nr_samples != 0);

	/*
	 * Continue monitoring latencies if we aren't hitting the targets or
	 * we're still throttling other requests.
	 */
	if (!blk_stat_is_active(kqd->cb) &&
	    ((IS_BAD(read_status) || IS_BAD(write_status) ||
	      kqd->domain_tokens[KYBER_OTHER].sb.depth < kyber_depth[KYBER_OTHER])))
		blk_stat_activate_msecs(kqd->cb, 100);
}

static unsigned int kyber_sched_tags_shift(struct kyber_queue_data *kqd)
{
	/*
	 * All of the hardware queues have the same depth, so we can just grab
	 * the shift of the first one.
	 */
	return kqd->q->queue_hw_ctx[0]->sched_tags->bitmap_tags.sb.shift;
}

static int kyber_bucket_fn(const struct request *rq)
{
	return kyber_sched_domain(rq->cmd_flags);
}

static struct kyber_queue_data *kyber_queue_data_alloc(struct request_queue *q)
{
	struct kyber_queue_data *kqd;
	unsigned int max_tokens;
	unsigned int shift;
	int ret = -ENOMEM;
	int i;

	kqd = kmalloc_node(sizeof(*kqd), GFP_KERNEL, q->node);
	if (!kqd)
		goto err;
	kqd->q = q;

	kqd->cb = blk_stat_alloc_callback(kyber_stat_timer_fn, kyber_bucket_fn,
					  KYBER_NUM_DOMAINS, kqd);
	if (!kqd->cb)
		goto err_kqd;

	/*
	 * The maximum number of tokens for any scheduling domain is at least
	 * the queue depth of a single hardware queue. If the hardware doesn't
	 * have many tags, still provide a reasonable number.
	 */
	max_tokens = max_t(unsigned int, q->tag_set->queue_depth,
			   KYBER_MIN_DEPTH);
	for (i = 0; i < KYBER_NUM_DOMAINS; i++) {
		WARN_ON(!kyber_depth[i]);
		WARN_ON(!kyber_batch_size[i]);
		ret = sbitmap_queue_init_node(&kqd->domain_tokens[i],
					      max_tokens, -1, false, GFP_KERNEL,
					      q->node);
		if (ret) {
			while (--i >= 0)
				sbitmap_queue_free(&kqd->domain_tokens[i]);
			goto err_cb;
		}
		sbitmap_queue_resize(&kqd->domain_tokens[i], kyber_depth[i]);
	}

	shift = kyber_sched_tags_shift(kqd);
	kqd->async_depth = (1U << shift) * KYBER_ASYNC_PERCENT / 100U;

	kqd->read_lat_nsec = 2000000ULL;
	kqd->write_lat_nsec = 10000000ULL;

	return kqd;

err_cb:
	blk_stat_free_callback(kqd->cb);
err_kqd:
	kfree(kqd);
err:
	return ERR_PTR(ret);
}

static int kyber_init_sched(struct request_queue *q, struct elevator_type *e)
{
	struct kyber_queue_data *kqd;
	struct elevator_queue *eq;

	eq = elevator_alloc(q, e);
	if (!eq)
		return -ENOMEM;

	kqd = kyber_queue_data_alloc(q);
	if (IS_ERR(kqd)) {
		kobject_put(&eq->kobj);
		return PTR_ERR(kqd);
	}

	eq->elevator_data = kqd;
	q->elevator = eq;

	blk_stat_add_callback(q, kqd->cb);

	return 0;
}

static void kyber_exit_sched(struct elevator_queue *e)
{
	struct kyber_queue_data *kqd = e->elevator_data;
	struct request_queue *q = kqd->q;
	int i;

	blk_stat_remove_callback(q, kqd->cb);

	for (i = 0; i < KYBER_NUM_DOMAINS; i++)
		sbitmap_queue_free(&kqd->domain_tokens[i]);
	blk_stat_free_callback(kqd->cb);
	kfree(kqd);
}

static void kyber_ctx_queue_init(struct kyber_ctx_queue *kcq)
{
	unsigned int i;

	spin_lock_init(&kcq->lock);
	for (i = 0; i < KYBER_NUM_DOMAINS; i++)
		INIT_LIST_HEAD(&kcq->rq_list[i]);
}

static int kyber_init_hctx(struct blk_mq_hw_ctx *hctx, unsigned int hctx_idx)
{
	struct kyber_queue_data *kqd = hctx->queue->elevator->elevator_data;
	struct kyber_hctx_data *khd;
	int i;

	khd = kmalloc_node(sizeof(*khd), GFP_KERNEL, hctx->numa_node);
	if (!khd)
		return -ENOMEM;

	khd->kcqs = kmalloc_array_node(hctx->nr_ctx,
				       sizeof(struct kyber_ctx_queue),
				       GFP_KERNEL, hctx->numa_node);
	if (!khd->kcqs)
		goto err_khd;

	for (i = 0; i < hctx->nr_ctx; i++)
		kyber_ctx_queue_init(&khd->kcqs[i]);

	for (i = 0; i < KYBER_NUM_DOMAINS; i++) {
		if (sbitmap_init_node(&khd->kcq_map[i], hctx->nr_ctx,
				      ilog2(8), GFP_KERNEL, hctx->numa_node)) {
			while (--i >= 0)
				sbitmap_free(&khd->kcq_map[i]);
			goto err_kcqs;
		}
	}

	spin_lock_init(&khd->lock);

	for (i = 0; i < KYBER_NUM_DOMAINS; i++) {
		INIT_LIST_HEAD(&khd->rqs[i]);
		init_waitqueue_func_entry(&khd->domain_wait[i],
					  kyber_domain_wake);
		khd->domain_wait[i].private = hctx;
		INIT_LIST_HEAD(&khd->domain_wait[i].entry);
		atomic_set(&khd->wait_index[i], 0);
	}

	khd->cur_domain = 0;
	khd->batching = 0;

	hctx->sched_data = khd;
	sbitmap_queue_min_shallow_depth(&hctx->sched_tags->bitmap_tags,
					kqd->async_depth);

	return 0;

err_kcqs:
	kfree(khd->kcqs);
err_khd:
	kfree(khd);
	return -ENOMEM;
}

static void kyber_exit_hctx(struct blk_mq_hw_ctx *hctx, unsigned int hctx_idx)
{
	struct kyber_hctx_data *khd = hctx->sched_data;
	int i;

	for (i = 0; i < KYBER_NUM_DOMAINS; i++)
		sbitmap_free(&khd->kcq_map[i]);
	kfree(khd->kcqs);
	kfree(hctx->sched_data);
}

static int rq_get_domain_token(struct request *rq)
{
	return (long)rq->elv.priv[0];
}

static void rq_set_domain_token(struct request *rq, int token)
{
	rq->elv.priv[0] = (void *)(long)token;
}

static void rq_clear_domain_token(struct kyber_queue_data *kqd,
				  struct request *rq)
{
	unsigned int sched_domain;
	int nr;

	nr = rq_get_domain_token(rq);
	if (nr != -1) {
		sched_domain = kyber_sched_domain(rq->cmd_flags);
		sbitmap_queue_clear(&kqd->domain_tokens[sched_domain], nr,
				    rq->mq_ctx->cpu);
	}
}

static void kyber_limit_depth(unsigned int op, struct blk_mq_alloc_data *data)
{
	/*
	 * We use the scheduler tags as per-hardware queue queueing tokens.
	 * Async requests can be limited at this stage.
	 */
	if (!op_is_sync(op)) {
		struct kyber_queue_data *kqd = data->q->elevator->elevator_data;

		data->shallow_depth = kqd->async_depth;
	}
}

static bool kyber_bio_merge(struct blk_mq_hw_ctx *hctx, struct bio *bio)
{
	struct kyber_hctx_data *khd = hctx->sched_data;
	struct blk_mq_ctx *ctx = blk_mq_get_ctx(hctx->queue);
	struct kyber_ctx_queue *kcq = &khd->kcqs[ctx->index_hw];
	unsigned int sched_domain = kyber_sched_domain(bio->bi_opf);
	struct list_head *rq_list = &kcq->rq_list[sched_domain];
	bool merged;

	spin_lock(&kcq->lock);
	merged = blk_mq_bio_list_merge(hctx->queue, rq_list, bio);
	spin_unlock(&kcq->lock);
	blk_mq_put_ctx(ctx);

	return merged;
}

static void kyber_prepare_request(struct request *rq, struct bio *bio)
{
	rq_set_domain_token(rq, -1);
}

static void kyber_insert_requests(struct blk_mq_hw_ctx *hctx,
				  struct list_head *rq_list, bool at_head)
{
	struct kyber_hctx_data *khd = hctx->sched_data;
	struct request *rq, *next;

	list_for_each_entry_safe(rq, next, rq_list, queuelist) {
		unsigned int sched_domain = kyber_sched_domain(rq->cmd_flags);
		struct kyber_ctx_queue *kcq = &khd->kcqs[rq->mq_ctx->index_hw];
		struct list_head *head = &kcq->rq_list[sched_domain];

		spin_lock(&kcq->lock);
		if (at_head)
			list_move(&rq->queuelist, head);
		else
			list_move_tail(&rq->queuelist, head);
		sbitmap_set_bit(&khd->kcq_map[sched_domain],
				rq->mq_ctx->index_hw);
		blk_mq_sched_request_inserted(rq);
		spin_unlock(&kcq->lock);
	}
}

static void kyber_finish_request(struct request *rq)
{
	struct kyber_queue_data *kqd = rq->q->elevator->elevator_data;

	rq_clear_domain_token(kqd, rq);
}

static void kyber_completed_request(struct request *rq)
{
	struct request_queue *q = rq->q;
	struct kyber_queue_data *kqd = q->elevator->elevator_data;
	unsigned int sched_domain;
	u64 now, latency, target;

	/*
	 * Check if this request met our latency goal. If not, quickly gather
	 * some statistics and start throttling.
	 */
	sched_domain = kyber_sched_domain(rq->cmd_flags);
	switch (sched_domain) {
	case KYBER_READ:
		target = kqd->read_lat_nsec;
		break;
	case KYBER_SYNC_WRITE:
		target = kqd->write_lat_nsec;
		break;
	default:
		return;
	}

	/* If we are already monitoring latencies, don't check again. */
	if (blk_stat_is_active(kqd->cb))
		return;

	now = ktime_get_ns();
	if (now < rq->io_start_time_ns)
		return;

	latency = now - rq->io_start_time_ns;

	if (latency > target)
		blk_stat_activate_msecs(kqd->cb, 10);
}

struct flush_kcq_data {
	struct kyber_hctx_data *khd;
	unsigned int sched_domain;
	struct list_head *list;
};

static bool flush_busy_kcq(struct sbitmap *sb, unsigned int bitnr, void *data)
{
	struct flush_kcq_data *flush_data = data;
	struct kyber_ctx_queue *kcq = &flush_data->khd->kcqs[bitnr];

	spin_lock(&kcq->lock);
	list_splice_tail_init(&kcq->rq_list[flush_data->sched_domain],
			      flush_data->list);
	sbitmap_clear_bit(sb, bitnr);
	spin_unlock(&kcq->lock);

	return true;
}

static void kyber_flush_busy_kcqs(struct kyber_hctx_data *khd,
				  unsigned int sched_domain,
				  struct list_head *list)
{
	struct flush_kcq_data data = {
		.khd = khd,
		.sched_domain = sched_domain,
		.list = list,
	};

	sbitmap_for_each_set(&khd->kcq_map[sched_domain],
			     flush_busy_kcq, &data);
}

static int kyber_domain_wake(wait_queue_entry_t *wait, unsigned mode, int flags,
			     void *key)
{
	struct blk_mq_hw_ctx *hctx = READ_ONCE(wait->private);

	list_del_init(&wait->entry);
	blk_mq_run_hw_queue(hctx, true);
	return 1;
}

static int kyber_get_domain_token(struct kyber_queue_data *kqd,
				  struct kyber_hctx_data *khd,
				  struct blk_mq_hw_ctx *hctx)
{
	unsigned int sched_domain = khd->cur_domain;
	struct sbitmap_queue *domain_tokens = &kqd->domain_tokens[sched_domain];
	wait_queue_entry_t *wait = &khd->domain_wait[sched_domain];
	struct sbq_wait_state *ws;
	int nr;

	nr = __sbitmap_queue_get(domain_tokens);

	/*
	 * If we failed to get a domain token, make sure the hardware queue is
	 * run when one becomes available. Note that this is serialized on
	 * khd->lock, but we still need to be careful about the waker.
	 */
	if (nr < 0 && list_empty_careful(&wait->entry)) {
		ws = sbq_wait_ptr(domain_tokens,
				  &khd->wait_index[sched_domain]);
		khd->domain_ws[sched_domain] = ws;
		add_wait_queue(&ws->wait, wait);

		/*
		 * Try again in case a token was freed before we got on the wait
		 * queue.
		 */
		nr = __sbitmap_queue_get(domain_tokens);
	}

	/*
	 * If we got a token while we were on the wait queue, remove ourselves
	 * from the wait queue to ensure that all wake ups make forward
	 * progress. It's possible that the waker already deleted the entry
	 * between the !list_empty_careful() check and us grabbing the lock, but
	 * list_del_init() is okay with that.
	 */
	if (nr >= 0 && !list_empty_careful(&wait->entry)) {
		ws = khd->domain_ws[sched_domain];
		spin_lock_irq(&ws->wait.lock);
		list_del_init(&wait->entry);
		spin_unlock_irq(&ws->wait.lock);
	}

	return nr;
}

static struct request *
kyber_dispatch_cur_domain(struct kyber_queue_data *kqd,
			  struct kyber_hctx_data *khd,
			  struct blk_mq_hw_ctx *hctx)
{
	struct list_head *rqs;
	struct request *rq;
	int nr;

	rqs = &khd->rqs[khd->cur_domain];

	/*
	 * If we already have a flushed request, then we just need to get a
	 * token for it. Otherwise, if there are pending requests in the kcqs,
	 * flush the kcqs, but only if we can get a token. If not, we should
	 * leave the requests in the kcqs so that they can be merged. Note that
	 * khd->lock serializes the flushes, so if we observed any bit set in
	 * the kcq_map, we will always get a request.
	 */
	rq = list_first_entry_or_null(rqs, struct request, queuelist);
	if (rq) {
		nr = kyber_get_domain_token(kqd, khd, hctx);
		if (nr >= 0) {
			khd->batching++;
			rq_set_domain_token(rq, nr);
			list_del_init(&rq->queuelist);
			return rq;
		}
	} else if (sbitmap_any_bit_set(&khd->kcq_map[khd->cur_domain])) {
		nr = kyber_get_domain_token(kqd, khd, hctx);
		if (nr >= 0) {
			kyber_flush_busy_kcqs(khd, khd->cur_domain, rqs);
			rq = list_first_entry(rqs, struct request, queuelist);
			khd->batching++;
			rq_set_domain_token(rq, nr);
			list_del_init(&rq->queuelist);
			return rq;
		}
	}

	/* There were either no pending requests or no tokens. */
	return NULL;
}

static struct request *kyber_dispatch_request(struct blk_mq_hw_ctx *hctx)
{
	struct kyber_queue_data *kqd = hctx->queue->elevator->elevator_data;
	struct kyber_hctx_data *khd = hctx->sched_data;
	struct request *rq;
	int i;

	spin_lock(&khd->lock);

	/*
	 * First, if we are still entitled to batch, try to dispatch a request
	 * from the batch.
	 */
	if (khd->batching < kyber_batch_size[khd->cur_domain]) {
		rq = kyber_dispatch_cur_domain(kqd, khd, hctx);
		if (rq)
			goto out;
	}

	/*
	 * Either,
	 * 1. We were no longer entitled to a batch.
	 * 2. The domain we were batching didn't have any requests.
	 * 3. The domain we were batching was out of tokens.
	 *
	 * Start another batch. Note that this wraps back around to the original
	 * domain if no other domains have requests or tokens.
	 */
	khd->batching = 0;
	for (i = 0; i < KYBER_NUM_DOMAINS; i++) {
		if (khd->cur_domain == KYBER_NUM_DOMAINS - 1)
			khd->cur_domain = 0;
		else
			khd->cur_domain++;

		rq = kyber_dispatch_cur_domain(kqd, khd, hctx);
		if (rq)
			goto out;
	}

	rq = NULL;
out:
	spin_unlock(&khd->lock);
	return rq;
}

static bool kyber_has_work(struct blk_mq_hw_ctx *hctx)
{
	struct kyber_hctx_data *khd = hctx->sched_data;
	int i;

	for (i = 0; i < KYBER_NUM_DOMAINS; i++) {
		if (!list_empty_careful(&khd->rqs[i]) ||
		    sbitmap_any_bit_set(&khd->kcq_map[i]))
			return true;
	}

	return false;
}

#define KYBER_LAT_SHOW_STORE(op)					\
static ssize_t kyber_##op##_lat_show(struct elevator_queue *e,		\
				     char *page)			\
{									\
	struct kyber_queue_data *kqd = e->elevator_data;		\
									\
	return sprintf(page, "%llu\n", kqd->op##_lat_nsec);		\
}									\
									\
static ssize_t kyber_##op##_lat_store(struct elevator_queue *e,		\
				      const char *page, size_t count)	\
{									\
	struct kyber_queue_data *kqd = e->elevator_data;		\
	unsigned long long nsec;					\
	int ret;							\
									\
	ret = kstrtoull(page, 10, &nsec);				\
	if (ret)							\
		return ret;						\
									\
	kqd->op##_lat_nsec = nsec;					\
									\
	return count;							\
}
KYBER_LAT_SHOW_STORE(read);
KYBER_LAT_SHOW_STORE(write);
#undef KYBER_LAT_SHOW_STORE

#define KYBER_LAT_ATTR(op) __ATTR(op##_lat_nsec, 0644, kyber_##op##_lat_show, kyber_##op##_lat_store)
static struct elv_fs_entry kyber_sched_attrs[] = {
	KYBER_LAT_ATTR(read),
	KYBER_LAT_ATTR(write),
	__ATTR_NULL
};
#undef KYBER_LAT_ATTR

#ifdef CONFIG_BLK_DEBUG_FS
#define KYBER_DEBUGFS_DOMAIN_ATTRS(domain, name)			\
static int kyber_##name##_tokens_show(void *data, struct seq_file *m)	\
{									\
	struct request_queue *q = data;					\
	struct kyber_queue_data *kqd = q->elevator->elevator_data;	\
									\
	sbitmap_queue_show(&kqd->domain_tokens[domain], m);		\
	return 0;							\
}									\
									\
static void *kyber_##name##_rqs_start(struct seq_file *m, loff_t *pos)	\
	__acquires(&khd->lock)						\
{									\
	struct blk_mq_hw_ctx *hctx = m->private;			\
	struct kyber_hctx_data *khd = hctx->sched_data;			\
									\
	spin_lock(&khd->lock);						\
	return seq_list_start(&khd->rqs[domain], *pos);			\
}									\
									\
static void *kyber_##name##_rqs_next(struct seq_file *m, void *v,	\
				     loff_t *pos)			\
{									\
	struct blk_mq_hw_ctx *hctx = m->private;			\
	struct kyber_hctx_data *khd = hctx->sched_data;			\
									\
	return seq_list_next(v, &khd->rqs[domain], pos);		\
}									\
									\
static void kyber_##name##_rqs_stop(struct seq_file *m, void *v)	\
	__releases(&khd->lock)						\
{									\
	struct blk_mq_hw_ctx *hctx = m->private;			\
	struct kyber_hctx_data *khd = hctx->sched_data;			\
									\
	spin_unlock(&khd->lock);					\
}									\
									\
static const struct seq_operations kyber_##name##_rqs_seq_ops = {	\
	.start	= kyber_##name##_rqs_start,				\
	.next	= kyber_##name##_rqs_next,				\
	.stop	= kyber_##name##_rqs_stop,				\
	.show	= blk_mq_debugfs_rq_show,				\
};									\
									\
static int kyber_##name##_waiting_show(void *data, struct seq_file *m)	\
{									\
	struct blk_mq_hw_ctx *hctx = data;				\
	struct kyber_hctx_data *khd = hctx->sched_data;			\
	wait_queue_entry_t *wait = &khd->domain_wait[domain];		\
									\
	seq_printf(m, "%d\n", !list_empty_careful(&wait->entry));	\
	return 0;							\
}
KYBER_DEBUGFS_DOMAIN_ATTRS(KYBER_READ, read)
KYBER_DEBUGFS_DOMAIN_ATTRS(KYBER_SYNC_WRITE, sync_write)
KYBER_DEBUGFS_DOMAIN_ATTRS(KYBER_OTHER, other)
#undef KYBER_DEBUGFS_DOMAIN_ATTRS

static int kyber_async_depth_show(void *data, struct seq_file *m)
{
	struct request_queue *q = data;
	struct kyber_queue_data *kqd = q->elevator->elevator_data;

	seq_printf(m, "%u\n", kqd->async_depth);
	return 0;
}

static int kyber_cur_domain_show(void *data, struct seq_file *m)
{
	struct blk_mq_hw_ctx *hctx = data;
	struct kyber_hctx_data *khd = hctx->sched_data;

	switch (khd->cur_domain) {
	case KYBER_READ:
		seq_puts(m, "READ\n");
		break;
	case KYBER_SYNC_WRITE:
		seq_puts(m, "SYNC_WRITE\n");
		break;
	case KYBER_OTHER:
		seq_puts(m, "OTHER\n");
		break;
	default:
		seq_printf(m, "%u\n", khd->cur_domain);
		break;
	}
	return 0;
}

static int kyber_batching_show(void *data, struct seq_file *m)
{
	struct blk_mq_hw_ctx *hctx = data;
	struct kyber_hctx_data *khd = hctx->sched_data;

	seq_printf(m, "%u\n", khd->batching);
	return 0;
}

#define KYBER_QUEUE_DOMAIN_ATTRS(name)	\
	{#name "_tokens", 0400, kyber_##name##_tokens_show}
static const struct blk_mq_debugfs_attr kyber_queue_debugfs_attrs[] = {
	KYBER_QUEUE_DOMAIN_ATTRS(read),
	KYBER_QUEUE_DOMAIN_ATTRS(sync_write),
	KYBER_QUEUE_DOMAIN_ATTRS(other),
	{"async_depth", 0400, kyber_async_depth_show},
	{},
};
#undef KYBER_QUEUE_DOMAIN_ATTRS

#define KYBER_HCTX_DOMAIN_ATTRS(name)					\
	{#name "_rqs", 0400, .seq_ops = &kyber_##name##_rqs_seq_ops},	\
	{#name "_waiting", 0400, kyber_##name##_waiting_show}
static const struct blk_mq_debugfs_attr kyber_hctx_debugfs_attrs[] = {
	KYBER_HCTX_DOMAIN_ATTRS(read),
	KYBER_HCTX_DOMAIN_ATTRS(sync_write),
	KYBER_HCTX_DOMAIN_ATTRS(other),
	{"cur_domain", 0400, kyber_cur_domain_show},
	{"batching", 0400, kyber_batching_show},
	{},
};
#undef KYBER_HCTX_DOMAIN_ATTRS
#endif

static struct elevator_type kyber_sched = {
	.ops.mq = {
		.init_sched = kyber_init_sched,
		.exit_sched = kyber_exit_sched,
		.init_hctx = kyber_init_hctx,
		.exit_hctx = kyber_exit_hctx,
		.limit_depth = kyber_limit_depth,
		.bio_merge = kyber_bio_merge,
		.prepare_request = kyber_prepare_request,
		.insert_requests = kyber_insert_requests,
		.finish_request = kyber_finish_request,
		.requeue_request = kyber_finish_request,
		.completed_request = kyber_completed_request,
		.dispatch_request = kyber_dispatch_request,
		.has_work = kyber_has_work,
	},
	.uses_mq = true,
#ifdef CONFIG_BLK_DEBUG_FS
	.queue_debugfs_attrs = kyber_queue_debugfs_attrs,
	.hctx_debugfs_attrs = kyber_hctx_debugfs_attrs,
#endif
	.elevator_attrs = kyber_sched_attrs,
	.elevator_name = "kyber",
	.elevator_owner = THIS_MODULE,
};

static int __init kyber_init(void)
{
	return elv_register(&kyber_sched);
}

static void __exit kyber_exit(void)
{
	elv_unregister(&kyber_sched);
}

module_init(kyber_init);
module_exit(kyber_exit);

MODULE_AUTHOR("Omar Sandoval");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Kyber I/O scheduler");