1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * The Kyber I/O scheduler. Controls latency by throttling queue depths using
4 * scalable techniques.
5 *
6 * Copyright (C) 2017 Facebook
7 */
8
9 #include <linux/kernel.h>
10 #include <linux/blkdev.h>
11 #include <linux/module.h>
12 #include <linux/sbitmap.h>
13
14 #include <trace/events/block.h>
15
16 #include "elevator.h"
17 #include "blk.h"
18 #include "blk-mq.h"
19 #include "blk-mq-debugfs.h"
20 #include "blk-mq-sched.h"
21
22 #define CREATE_TRACE_POINTS
23 #include <trace/events/kyber.h>
24
25 /*
26 * Scheduling domains: the device is divided into multiple domains based on the
27 * request type.
28 */
29 enum {
30 KYBER_READ,
31 KYBER_WRITE,
32 KYBER_DISCARD,
33 KYBER_OTHER,
34 KYBER_NUM_DOMAINS,
35 };
36
37 static const char *kyber_domain_names[] = {
38 [KYBER_READ] = "READ",
39 [KYBER_WRITE] = "WRITE",
40 [KYBER_DISCARD] = "DISCARD",
41 [KYBER_OTHER] = "OTHER",
42 };
43
44 enum {
45 /*
46 * In order to prevent starvation of synchronous requests by a flood of
47 * asynchronous requests, we reserve 25% of requests for synchronous
48 * operations.
49 */
50 KYBER_ASYNC_PERCENT = 75,
51 };
52
53 /*
54 * Maximum device-wide depth for each scheduling domain.
55 *
56 * Even for fast devices with lots of tags like NVMe, you can saturate the
57 * device with only a fraction of the maximum possible queue depth. So, we cap
58 * these to a reasonable value.
59 */
60 static const unsigned int kyber_depth[] = {
61 [KYBER_READ] = 256,
62 [KYBER_WRITE] = 128,
63 [KYBER_DISCARD] = 64,
64 [KYBER_OTHER] = 16,
65 };
66
67 /*
68 * Default latency targets for each scheduling domain.
69 */
70 static const u64 kyber_latency_targets[] = {
71 [KYBER_READ] = 2ULL * NSEC_PER_MSEC,
72 [KYBER_WRITE] = 10ULL * NSEC_PER_MSEC,
73 [KYBER_DISCARD] = 5ULL * NSEC_PER_SEC,
74 };
75
76 /*
77 * Batch size (number of requests we'll dispatch in a row) for each scheduling
78 * domain.
79 */
80 static const unsigned int kyber_batch_size[] = {
81 [KYBER_READ] = 16,
82 [KYBER_WRITE] = 8,
83 [KYBER_DISCARD] = 1,
84 [KYBER_OTHER] = 1,
85 };
86
87 /*
88 * Requests latencies are recorded in a histogram with buckets defined relative
89 * to the target latency:
90 *
91 * <= 1/4 * target latency
92 * <= 1/2 * target latency
93 * <= 3/4 * target latency
94 * <= target latency
95 * <= 1 1/4 * target latency
96 * <= 1 1/2 * target latency
97 * <= 1 3/4 * target latency
98 * > 1 3/4 * target latency
99 */
100 enum {
101 /*
102 * The width of the latency histogram buckets is
103 * 1 / (1 << KYBER_LATENCY_SHIFT) * target latency.
104 */
105 KYBER_LATENCY_SHIFT = 2,
106 /*
107 * The first (1 << KYBER_LATENCY_SHIFT) buckets are <= target latency,
108 * thus, "good".
109 */
110 KYBER_GOOD_BUCKETS = 1 << KYBER_LATENCY_SHIFT,
111 /* There are also (1 << KYBER_LATENCY_SHIFT) "bad" buckets. */
112 KYBER_LATENCY_BUCKETS = 2 << KYBER_LATENCY_SHIFT,
113 };
114
115 /*
116 * We measure both the total latency and the I/O latency (i.e., latency after
117 * submitting to the device).
118 */
119 enum {
120 KYBER_TOTAL_LATENCY,
121 KYBER_IO_LATENCY,
122 };
123
124 static const char *kyber_latency_type_names[] = {
125 [KYBER_TOTAL_LATENCY] = "total",
126 [KYBER_IO_LATENCY] = "I/O",
127 };
128
129 /*
130 * Per-cpu latency histograms: total latency and I/O latency for each scheduling
131 * domain except for KYBER_OTHER.
132 */
133 struct kyber_cpu_latency {
134 atomic_t buckets[KYBER_OTHER][2][KYBER_LATENCY_BUCKETS];
135 };
136
137 /*
138 * There is a same mapping between ctx & hctx and kcq & khd,
139 * we use request->mq_ctx->index_hw to index the kcq in khd.
140 */
141 struct kyber_ctx_queue {
142 /*
143 * Used to ensure operations on rq_list and kcq_map to be an atmoic one.
144 * Also protect the rqs on rq_list when merge.
145 */
146 spinlock_t lock;
147 struct list_head rq_list[KYBER_NUM_DOMAINS];
148 } ____cacheline_aligned_in_smp;
149
150 struct kyber_queue_data {
151 struct request_queue *q;
152 dev_t dev;
153
154 /*
155 * Each scheduling domain has a limited number of in-flight requests
156 * device-wide, limited by these tokens.
157 */
158 struct sbitmap_queue domain_tokens[KYBER_NUM_DOMAINS];
159
160 /*
161 * Async request percentage, converted to per-word depth for
162 * sbitmap_get_shallow().
163 */
164 unsigned int async_depth;
165
166 struct kyber_cpu_latency __percpu *cpu_latency;
167
168 /* Timer for stats aggregation and adjusting domain tokens. */
169 struct timer_list timer;
170
171 unsigned int latency_buckets[KYBER_OTHER][2][KYBER_LATENCY_BUCKETS];
172
173 unsigned long latency_timeout[KYBER_OTHER];
174
175 int domain_p99[KYBER_OTHER];
176
177 /* Target latencies in nanoseconds. */
178 u64 latency_targets[KYBER_OTHER];
179 };
180
181 struct kyber_hctx_data {
182 spinlock_t lock;
183 struct list_head rqs[KYBER_NUM_DOMAINS];
184 unsigned int cur_domain;
185 unsigned int batching;
186 struct kyber_ctx_queue *kcqs;
187 struct sbitmap kcq_map[KYBER_NUM_DOMAINS];
188 struct sbq_wait domain_wait[KYBER_NUM_DOMAINS];
189 struct sbq_wait_state *domain_ws[KYBER_NUM_DOMAINS];
190 atomic_t wait_index[KYBER_NUM_DOMAINS];
191 };
192
193 static int kyber_domain_wake(wait_queue_entry_t *wait, unsigned mode, int flags,
194 void *key);
195
kyber_sched_domain(blk_opf_t opf)196 static unsigned int kyber_sched_domain(blk_opf_t opf)
197 {
198 switch (opf & REQ_OP_MASK) {
199 case REQ_OP_READ:
200 return KYBER_READ;
201 case REQ_OP_WRITE:
202 return KYBER_WRITE;
203 case REQ_OP_DISCARD:
204 return KYBER_DISCARD;
205 default:
206 return KYBER_OTHER;
207 }
208 }
209
flush_latency_buckets(struct kyber_queue_data * kqd,struct kyber_cpu_latency * cpu_latency,unsigned int sched_domain,unsigned int type)210 static void flush_latency_buckets(struct kyber_queue_data *kqd,
211 struct kyber_cpu_latency *cpu_latency,
212 unsigned int sched_domain, unsigned int type)
213 {
214 unsigned int *buckets = kqd->latency_buckets[sched_domain][type];
215 atomic_t *cpu_buckets = cpu_latency->buckets[sched_domain][type];
216 unsigned int bucket;
217
218 for (bucket = 0; bucket < KYBER_LATENCY_BUCKETS; bucket++)
219 buckets[bucket] += atomic_xchg(&cpu_buckets[bucket], 0);
220 }
221
222 /*
223 * Calculate the histogram bucket with the given percentile rank, or -1 if there
224 * aren't enough samples yet.
225 */
calculate_percentile(struct kyber_queue_data * kqd,unsigned int sched_domain,unsigned int type,unsigned int percentile)226 static int calculate_percentile(struct kyber_queue_data *kqd,
227 unsigned int sched_domain, unsigned int type,
228 unsigned int percentile)
229 {
230 unsigned int *buckets = kqd->latency_buckets[sched_domain][type];
231 unsigned int bucket, samples = 0, percentile_samples;
232
233 for (bucket = 0; bucket < KYBER_LATENCY_BUCKETS; bucket++)
234 samples += buckets[bucket];
235
236 if (!samples)
237 return -1;
238
239 /*
240 * We do the calculation once we have 500 samples or one second passes
241 * since the first sample was recorded, whichever comes first.
242 */
243 if (!kqd->latency_timeout[sched_domain])
244 kqd->latency_timeout[sched_domain] = max(jiffies + HZ, 1UL);
245 if (samples < 500 &&
246 time_is_after_jiffies(kqd->latency_timeout[sched_domain])) {
247 return -1;
248 }
249 kqd->latency_timeout[sched_domain] = 0;
250
251 percentile_samples = DIV_ROUND_UP(samples * percentile, 100);
252 for (bucket = 0; bucket < KYBER_LATENCY_BUCKETS - 1; bucket++) {
253 if (buckets[bucket] >= percentile_samples)
254 break;
255 percentile_samples -= buckets[bucket];
256 }
257 memset(buckets, 0, sizeof(kqd->latency_buckets[sched_domain][type]));
258
259 trace_kyber_latency(kqd->dev, kyber_domain_names[sched_domain],
260 kyber_latency_type_names[type], percentile,
261 bucket + 1, 1 << KYBER_LATENCY_SHIFT, samples);
262
263 return bucket;
264 }
265
kyber_resize_domain(struct kyber_queue_data * kqd,unsigned int sched_domain,unsigned int depth)266 static void kyber_resize_domain(struct kyber_queue_data *kqd,
267 unsigned int sched_domain, unsigned int depth)
268 {
269 depth = clamp(depth, 1U, kyber_depth[sched_domain]);
270 if (depth != kqd->domain_tokens[sched_domain].sb.depth) {
271 sbitmap_queue_resize(&kqd->domain_tokens[sched_domain], depth);
272 trace_kyber_adjust(kqd->dev, kyber_domain_names[sched_domain],
273 depth);
274 }
275 }
276
kyber_timer_fn(struct timer_list * t)277 static void kyber_timer_fn(struct timer_list *t)
278 {
279 struct kyber_queue_data *kqd = from_timer(kqd, t, timer);
280 unsigned int sched_domain;
281 int cpu;
282 bool bad = false;
283
284 /* Sum all of the per-cpu latency histograms. */
285 for_each_online_cpu(cpu) {
286 struct kyber_cpu_latency *cpu_latency;
287
288 cpu_latency = per_cpu_ptr(kqd->cpu_latency, cpu);
289 for (sched_domain = 0; sched_domain < KYBER_OTHER; sched_domain++) {
290 flush_latency_buckets(kqd, cpu_latency, sched_domain,
291 KYBER_TOTAL_LATENCY);
292 flush_latency_buckets(kqd, cpu_latency, sched_domain,
293 KYBER_IO_LATENCY);
294 }
295 }
296
297 /*
298 * Check if any domains have a high I/O latency, which might indicate
299 * congestion in the device. Note that we use the p90; we don't want to
300 * be too sensitive to outliers here.
301 */
302 for (sched_domain = 0; sched_domain < KYBER_OTHER; sched_domain++) {
303 int p90;
304
305 p90 = calculate_percentile(kqd, sched_domain, KYBER_IO_LATENCY,
306 90);
307 if (p90 >= KYBER_GOOD_BUCKETS)
308 bad = true;
309 }
310
311 /*
312 * Adjust the scheduling domain depths. If we determined that there was
313 * congestion, we throttle all domains with good latencies. Either way,
314 * we ease up on throttling domains with bad latencies.
315 */
316 for (sched_domain = 0; sched_domain < KYBER_OTHER; sched_domain++) {
317 unsigned int orig_depth, depth;
318 int p99;
319
320 p99 = calculate_percentile(kqd, sched_domain,
321 KYBER_TOTAL_LATENCY, 99);
322 /*
323 * This is kind of subtle: different domains will not
324 * necessarily have enough samples to calculate the latency
325 * percentiles during the same window, so we have to remember
326 * the p99 for the next time we observe congestion; once we do,
327 * we don't want to throttle again until we get more data, so we
328 * reset it to -1.
329 */
330 if (bad) {
331 if (p99 < 0)
332 p99 = kqd->domain_p99[sched_domain];
333 kqd->domain_p99[sched_domain] = -1;
334 } else if (p99 >= 0) {
335 kqd->domain_p99[sched_domain] = p99;
336 }
337 if (p99 < 0)
338 continue;
339
340 /*
341 * If this domain has bad latency, throttle less. Otherwise,
342 * throttle more iff we determined that there is congestion.
343 *
344 * The new depth is scaled linearly with the p99 latency vs the
345 * latency target. E.g., if the p99 is 3/4 of the target, then
346 * we throttle down to 3/4 of the current depth, and if the p99
347 * is 2x the target, then we double the depth.
348 */
349 if (bad || p99 >= KYBER_GOOD_BUCKETS) {
350 orig_depth = kqd->domain_tokens[sched_domain].sb.depth;
351 depth = (orig_depth * (p99 + 1)) >> KYBER_LATENCY_SHIFT;
352 kyber_resize_domain(kqd, sched_domain, depth);
353 }
354 }
355 }
356
kyber_queue_data_alloc(struct request_queue * q)357 static struct kyber_queue_data *kyber_queue_data_alloc(struct request_queue *q)
358 {
359 struct kyber_queue_data *kqd;
360 int ret = -ENOMEM;
361 int i;
362
363 kqd = kzalloc_node(sizeof(*kqd), GFP_KERNEL, q->node);
364 if (!kqd)
365 goto err;
366
367 kqd->q = q;
368 kqd->dev = disk_devt(q->disk);
369
370 kqd->cpu_latency = alloc_percpu_gfp(struct kyber_cpu_latency,
371 GFP_KERNEL | __GFP_ZERO);
372 if (!kqd->cpu_latency)
373 goto err_kqd;
374
375 timer_setup(&kqd->timer, kyber_timer_fn, 0);
376
377 for (i = 0; i < KYBER_NUM_DOMAINS; i++) {
378 WARN_ON(!kyber_depth[i]);
379 WARN_ON(!kyber_batch_size[i]);
380 ret = sbitmap_queue_init_node(&kqd->domain_tokens[i],
381 kyber_depth[i], -1, false,
382 GFP_KERNEL, q->node);
383 if (ret) {
384 while (--i >= 0)
385 sbitmap_queue_free(&kqd->domain_tokens[i]);
386 goto err_buckets;
387 }
388 }
389
390 for (i = 0; i < KYBER_OTHER; i++) {
391 kqd->domain_p99[i] = -1;
392 kqd->latency_targets[i] = kyber_latency_targets[i];
393 }
394
395 return kqd;
396
397 err_buckets:
398 free_percpu(kqd->cpu_latency);
399 err_kqd:
400 kfree(kqd);
401 err:
402 return ERR_PTR(ret);
403 }
404
kyber_init_sched(struct request_queue * q,struct elevator_type * e)405 static int kyber_init_sched(struct request_queue *q, struct elevator_type *e)
406 {
407 struct kyber_queue_data *kqd;
408 struct elevator_queue *eq;
409
410 eq = elevator_alloc(q, e);
411 if (!eq)
412 return -ENOMEM;
413
414 kqd = kyber_queue_data_alloc(q);
415 if (IS_ERR(kqd)) {
416 kobject_put(&eq->kobj);
417 return PTR_ERR(kqd);
418 }
419
420 blk_stat_enable_accounting(q);
421
422 blk_queue_flag_clear(QUEUE_FLAG_SQ_SCHED, q);
423
424 eq->elevator_data = kqd;
425 q->elevator = eq;
426
427 return 0;
428 }
429
kyber_exit_sched(struct elevator_queue * e)430 static void kyber_exit_sched(struct elevator_queue *e)
431 {
432 struct kyber_queue_data *kqd = e->elevator_data;
433 int i;
434
435 timer_shutdown_sync(&kqd->timer);
436 blk_stat_disable_accounting(kqd->q);
437
438 for (i = 0; i < KYBER_NUM_DOMAINS; i++)
439 sbitmap_queue_free(&kqd->domain_tokens[i]);
440 free_percpu(kqd->cpu_latency);
441 kfree(kqd);
442 }
443
kyber_ctx_queue_init(struct kyber_ctx_queue * kcq)444 static void kyber_ctx_queue_init(struct kyber_ctx_queue *kcq)
445 {
446 unsigned int i;
447
448 spin_lock_init(&kcq->lock);
449 for (i = 0; i < KYBER_NUM_DOMAINS; i++)
450 INIT_LIST_HEAD(&kcq->rq_list[i]);
451 }
452
kyber_depth_updated(struct blk_mq_hw_ctx * hctx)453 static void kyber_depth_updated(struct blk_mq_hw_ctx *hctx)
454 {
455 struct kyber_queue_data *kqd = hctx->queue->elevator->elevator_data;
456 struct blk_mq_tags *tags = hctx->sched_tags;
457 unsigned int shift = tags->bitmap_tags.sb.shift;
458
459 kqd->async_depth = (1U << shift) * KYBER_ASYNC_PERCENT / 100U;
460
461 sbitmap_queue_min_shallow_depth(&tags->bitmap_tags, kqd->async_depth);
462 }
463
kyber_init_hctx(struct blk_mq_hw_ctx * hctx,unsigned int hctx_idx)464 static int kyber_init_hctx(struct blk_mq_hw_ctx *hctx, unsigned int hctx_idx)
465 {
466 struct kyber_hctx_data *khd;
467 int i;
468
469 khd = kmalloc_node(sizeof(*khd), GFP_KERNEL, hctx->numa_node);
470 if (!khd)
471 return -ENOMEM;
472
473 khd->kcqs = kmalloc_array_node(hctx->nr_ctx,
474 sizeof(struct kyber_ctx_queue),
475 GFP_KERNEL, hctx->numa_node);
476 if (!khd->kcqs)
477 goto err_khd;
478
479 for (i = 0; i < hctx->nr_ctx; i++)
480 kyber_ctx_queue_init(&khd->kcqs[i]);
481
482 for (i = 0; i < KYBER_NUM_DOMAINS; i++) {
483 if (sbitmap_init_node(&khd->kcq_map[i], hctx->nr_ctx,
484 ilog2(8), GFP_KERNEL, hctx->numa_node,
485 false, false)) {
486 while (--i >= 0)
487 sbitmap_free(&khd->kcq_map[i]);
488 goto err_kcqs;
489 }
490 }
491
492 spin_lock_init(&khd->lock);
493
494 for (i = 0; i < KYBER_NUM_DOMAINS; i++) {
495 INIT_LIST_HEAD(&khd->rqs[i]);
496 khd->domain_wait[i].sbq = NULL;
497 init_waitqueue_func_entry(&khd->domain_wait[i].wait,
498 kyber_domain_wake);
499 khd->domain_wait[i].wait.private = hctx;
500 INIT_LIST_HEAD(&khd->domain_wait[i].wait.entry);
501 atomic_set(&khd->wait_index[i], 0);
502 }
503
504 khd->cur_domain = 0;
505 khd->batching = 0;
506
507 hctx->sched_data = khd;
508 kyber_depth_updated(hctx);
509
510 return 0;
511
512 err_kcqs:
513 kfree(khd->kcqs);
514 err_khd:
515 kfree(khd);
516 return -ENOMEM;
517 }
518
kyber_exit_hctx(struct blk_mq_hw_ctx * hctx,unsigned int hctx_idx)519 static void kyber_exit_hctx(struct blk_mq_hw_ctx *hctx, unsigned int hctx_idx)
520 {
521 struct kyber_hctx_data *khd = hctx->sched_data;
522 int i;
523
524 for (i = 0; i < KYBER_NUM_DOMAINS; i++)
525 sbitmap_free(&khd->kcq_map[i]);
526 kfree(khd->kcqs);
527 kfree(hctx->sched_data);
528 }
529
rq_get_domain_token(struct request * rq)530 static int rq_get_domain_token(struct request *rq)
531 {
532 return (long)rq->elv.priv[0];
533 }
534
rq_set_domain_token(struct request * rq,int token)535 static void rq_set_domain_token(struct request *rq, int token)
536 {
537 rq->elv.priv[0] = (void *)(long)token;
538 }
539
rq_clear_domain_token(struct kyber_queue_data * kqd,struct request * rq)540 static void rq_clear_domain_token(struct kyber_queue_data *kqd,
541 struct request *rq)
542 {
543 unsigned int sched_domain;
544 int nr;
545
546 nr = rq_get_domain_token(rq);
547 if (nr != -1) {
548 sched_domain = kyber_sched_domain(rq->cmd_flags);
549 sbitmap_queue_clear(&kqd->domain_tokens[sched_domain], nr,
550 rq->mq_ctx->cpu);
551 }
552 }
553
kyber_limit_depth(blk_opf_t opf,struct blk_mq_alloc_data * data)554 static void kyber_limit_depth(blk_opf_t opf, struct blk_mq_alloc_data *data)
555 {
556 /*
557 * We use the scheduler tags as per-hardware queue queueing tokens.
558 * Async requests can be limited at this stage.
559 */
560 if (!op_is_sync(opf)) {
561 struct kyber_queue_data *kqd = data->q->elevator->elevator_data;
562
563 data->shallow_depth = kqd->async_depth;
564 }
565 }
566
kyber_bio_merge(struct request_queue * q,struct bio * bio,unsigned int nr_segs)567 static bool kyber_bio_merge(struct request_queue *q, struct bio *bio,
568 unsigned int nr_segs)
569 {
570 struct blk_mq_ctx *ctx = blk_mq_get_ctx(q);
571 struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, bio->bi_opf, ctx);
572 struct kyber_hctx_data *khd = hctx->sched_data;
573 struct kyber_ctx_queue *kcq = &khd->kcqs[ctx->index_hw[hctx->type]];
574 unsigned int sched_domain = kyber_sched_domain(bio->bi_opf);
575 struct list_head *rq_list = &kcq->rq_list[sched_domain];
576 bool merged;
577
578 spin_lock(&kcq->lock);
579 merged = blk_bio_list_merge(hctx->queue, rq_list, bio, nr_segs);
580 spin_unlock(&kcq->lock);
581
582 return merged;
583 }
584
kyber_prepare_request(struct request * rq)585 static void kyber_prepare_request(struct request *rq)
586 {
587 rq_set_domain_token(rq, -1);
588 }
589
kyber_insert_requests(struct blk_mq_hw_ctx * hctx,struct list_head * rq_list,blk_insert_t flags)590 static void kyber_insert_requests(struct blk_mq_hw_ctx *hctx,
591 struct list_head *rq_list,
592 blk_insert_t flags)
593 {
594 struct kyber_hctx_data *khd = hctx->sched_data;
595 struct request *rq, *next;
596
597 list_for_each_entry_safe(rq, next, rq_list, queuelist) {
598 unsigned int sched_domain = kyber_sched_domain(rq->cmd_flags);
599 struct kyber_ctx_queue *kcq = &khd->kcqs[rq->mq_ctx->index_hw[hctx->type]];
600 struct list_head *head = &kcq->rq_list[sched_domain];
601
602 spin_lock(&kcq->lock);
603 trace_block_rq_insert(rq);
604 if (flags & BLK_MQ_INSERT_AT_HEAD)
605 list_move(&rq->queuelist, head);
606 else
607 list_move_tail(&rq->queuelist, head);
608 sbitmap_set_bit(&khd->kcq_map[sched_domain],
609 rq->mq_ctx->index_hw[hctx->type]);
610 spin_unlock(&kcq->lock);
611 }
612 }
613
kyber_finish_request(struct request * rq)614 static void kyber_finish_request(struct request *rq)
615 {
616 struct kyber_queue_data *kqd = rq->q->elevator->elevator_data;
617
618 rq_clear_domain_token(kqd, rq);
619 }
620
add_latency_sample(struct kyber_cpu_latency * cpu_latency,unsigned int sched_domain,unsigned int type,u64 target,u64 latency)621 static void add_latency_sample(struct kyber_cpu_latency *cpu_latency,
622 unsigned int sched_domain, unsigned int type,
623 u64 target, u64 latency)
624 {
625 unsigned int bucket;
626 u64 divisor;
627
628 if (latency > 0) {
629 divisor = max_t(u64, target >> KYBER_LATENCY_SHIFT, 1);
630 bucket = min_t(unsigned int, div64_u64(latency - 1, divisor),
631 KYBER_LATENCY_BUCKETS - 1);
632 } else {
633 bucket = 0;
634 }
635
636 atomic_inc(&cpu_latency->buckets[sched_domain][type][bucket]);
637 }
638
kyber_completed_request(struct request * rq,u64 now)639 static void kyber_completed_request(struct request *rq, u64 now)
640 {
641 struct kyber_queue_data *kqd = rq->q->elevator->elevator_data;
642 struct kyber_cpu_latency *cpu_latency;
643 unsigned int sched_domain;
644 u64 target;
645
646 sched_domain = kyber_sched_domain(rq->cmd_flags);
647 if (sched_domain == KYBER_OTHER)
648 return;
649
650 cpu_latency = get_cpu_ptr(kqd->cpu_latency);
651 target = kqd->latency_targets[sched_domain];
652 add_latency_sample(cpu_latency, sched_domain, KYBER_TOTAL_LATENCY,
653 target, now - rq->start_time_ns);
654 add_latency_sample(cpu_latency, sched_domain, KYBER_IO_LATENCY, target,
655 now - rq->io_start_time_ns);
656 put_cpu_ptr(kqd->cpu_latency);
657
658 timer_reduce(&kqd->timer, jiffies + HZ / 10);
659 }
660
661 struct flush_kcq_data {
662 struct kyber_hctx_data *khd;
663 unsigned int sched_domain;
664 struct list_head *list;
665 };
666
flush_busy_kcq(struct sbitmap * sb,unsigned int bitnr,void * data)667 static bool flush_busy_kcq(struct sbitmap *sb, unsigned int bitnr, void *data)
668 {
669 struct flush_kcq_data *flush_data = data;
670 struct kyber_ctx_queue *kcq = &flush_data->khd->kcqs[bitnr];
671
672 spin_lock(&kcq->lock);
673 list_splice_tail_init(&kcq->rq_list[flush_data->sched_domain],
674 flush_data->list);
675 sbitmap_clear_bit(sb, bitnr);
676 spin_unlock(&kcq->lock);
677
678 return true;
679 }
680
kyber_flush_busy_kcqs(struct kyber_hctx_data * khd,unsigned int sched_domain,struct list_head * list)681 static void kyber_flush_busy_kcqs(struct kyber_hctx_data *khd,
682 unsigned int sched_domain,
683 struct list_head *list)
684 {
685 struct flush_kcq_data data = {
686 .khd = khd,
687 .sched_domain = sched_domain,
688 .list = list,
689 };
690
691 sbitmap_for_each_set(&khd->kcq_map[sched_domain],
692 flush_busy_kcq, &data);
693 }
694
kyber_domain_wake(wait_queue_entry_t * wqe,unsigned mode,int flags,void * key)695 static int kyber_domain_wake(wait_queue_entry_t *wqe, unsigned mode, int flags,
696 void *key)
697 {
698 struct blk_mq_hw_ctx *hctx = READ_ONCE(wqe->private);
699 struct sbq_wait *wait = container_of(wqe, struct sbq_wait, wait);
700
701 sbitmap_del_wait_queue(wait);
702 blk_mq_run_hw_queue(hctx, true);
703 return 1;
704 }
705
kyber_get_domain_token(struct kyber_queue_data * kqd,struct kyber_hctx_data * khd,struct blk_mq_hw_ctx * hctx)706 static int kyber_get_domain_token(struct kyber_queue_data *kqd,
707 struct kyber_hctx_data *khd,
708 struct blk_mq_hw_ctx *hctx)
709 {
710 unsigned int sched_domain = khd->cur_domain;
711 struct sbitmap_queue *domain_tokens = &kqd->domain_tokens[sched_domain];
712 struct sbq_wait *wait = &khd->domain_wait[sched_domain];
713 struct sbq_wait_state *ws;
714 int nr;
715
716 nr = __sbitmap_queue_get(domain_tokens);
717
718 /*
719 * If we failed to get a domain token, make sure the hardware queue is
720 * run when one becomes available. Note that this is serialized on
721 * khd->lock, but we still need to be careful about the waker.
722 */
723 if (nr < 0 && list_empty_careful(&wait->wait.entry)) {
724 ws = sbq_wait_ptr(domain_tokens,
725 &khd->wait_index[sched_domain]);
726 khd->domain_ws[sched_domain] = ws;
727 sbitmap_add_wait_queue(domain_tokens, ws, wait);
728
729 /*
730 * Try again in case a token was freed before we got on the wait
731 * queue.
732 */
733 nr = __sbitmap_queue_get(domain_tokens);
734 }
735
736 /*
737 * If we got a token while we were on the wait queue, remove ourselves
738 * from the wait queue to ensure that all wake ups make forward
739 * progress. It's possible that the waker already deleted the entry
740 * between the !list_empty_careful() check and us grabbing the lock, but
741 * list_del_init() is okay with that.
742 */
743 if (nr >= 0 && !list_empty_careful(&wait->wait.entry)) {
744 ws = khd->domain_ws[sched_domain];
745 spin_lock_irq(&ws->wait.lock);
746 sbitmap_del_wait_queue(wait);
747 spin_unlock_irq(&ws->wait.lock);
748 }
749
750 return nr;
751 }
752
753 static struct request *
kyber_dispatch_cur_domain(struct kyber_queue_data * kqd,struct kyber_hctx_data * khd,struct blk_mq_hw_ctx * hctx)754 kyber_dispatch_cur_domain(struct kyber_queue_data *kqd,
755 struct kyber_hctx_data *khd,
756 struct blk_mq_hw_ctx *hctx)
757 {
758 struct list_head *rqs;
759 struct request *rq;
760 int nr;
761
762 rqs = &khd->rqs[khd->cur_domain];
763
764 /*
765 * If we already have a flushed request, then we just need to get a
766 * token for it. Otherwise, if there are pending requests in the kcqs,
767 * flush the kcqs, but only if we can get a token. If not, we should
768 * leave the requests in the kcqs so that they can be merged. Note that
769 * khd->lock serializes the flushes, so if we observed any bit set in
770 * the kcq_map, we will always get a request.
771 */
772 rq = list_first_entry_or_null(rqs, struct request, queuelist);
773 if (rq) {
774 nr = kyber_get_domain_token(kqd, khd, hctx);
775 if (nr >= 0) {
776 khd->batching++;
777 rq_set_domain_token(rq, nr);
778 list_del_init(&rq->queuelist);
779 return rq;
780 } else {
781 trace_kyber_throttled(kqd->dev,
782 kyber_domain_names[khd->cur_domain]);
783 }
784 } else if (sbitmap_any_bit_set(&khd->kcq_map[khd->cur_domain])) {
785 nr = kyber_get_domain_token(kqd, khd, hctx);
786 if (nr >= 0) {
787 kyber_flush_busy_kcqs(khd, khd->cur_domain, rqs);
788 rq = list_first_entry(rqs, struct request, queuelist);
789 khd->batching++;
790 rq_set_domain_token(rq, nr);
791 list_del_init(&rq->queuelist);
792 return rq;
793 } else {
794 trace_kyber_throttled(kqd->dev,
795 kyber_domain_names[khd->cur_domain]);
796 }
797 }
798
799 /* There were either no pending requests or no tokens. */
800 return NULL;
801 }
802
kyber_dispatch_request(struct blk_mq_hw_ctx * hctx)803 static struct request *kyber_dispatch_request(struct blk_mq_hw_ctx *hctx)
804 {
805 struct kyber_queue_data *kqd = hctx->queue->elevator->elevator_data;
806 struct kyber_hctx_data *khd = hctx->sched_data;
807 struct request *rq;
808 int i;
809
810 spin_lock(&khd->lock);
811
812 /*
813 * First, if we are still entitled to batch, try to dispatch a request
814 * from the batch.
815 */
816 if (khd->batching < kyber_batch_size[khd->cur_domain]) {
817 rq = kyber_dispatch_cur_domain(kqd, khd, hctx);
818 if (rq)
819 goto out;
820 }
821
822 /*
823 * Either,
824 * 1. We were no longer entitled to a batch.
825 * 2. The domain we were batching didn't have any requests.
826 * 3. The domain we were batching was out of tokens.
827 *
828 * Start another batch. Note that this wraps back around to the original
829 * domain if no other domains have requests or tokens.
830 */
831 khd->batching = 0;
832 for (i = 0; i < KYBER_NUM_DOMAINS; i++) {
833 if (khd->cur_domain == KYBER_NUM_DOMAINS - 1)
834 khd->cur_domain = 0;
835 else
836 khd->cur_domain++;
837
838 rq = kyber_dispatch_cur_domain(kqd, khd, hctx);
839 if (rq)
840 goto out;
841 }
842
843 rq = NULL;
844 out:
845 spin_unlock(&khd->lock);
846 return rq;
847 }
848
kyber_has_work(struct blk_mq_hw_ctx * hctx)849 static bool kyber_has_work(struct blk_mq_hw_ctx *hctx)
850 {
851 struct kyber_hctx_data *khd = hctx->sched_data;
852 int i;
853
854 for (i = 0; i < KYBER_NUM_DOMAINS; i++) {
855 if (!list_empty_careful(&khd->rqs[i]) ||
856 sbitmap_any_bit_set(&khd->kcq_map[i]))
857 return true;
858 }
859
860 return false;
861 }
862
863 #define KYBER_LAT_SHOW_STORE(domain, name) \
864 static ssize_t kyber_##name##_lat_show(struct elevator_queue *e, \
865 char *page) \
866 { \
867 struct kyber_queue_data *kqd = e->elevator_data; \
868 \
869 return sprintf(page, "%llu\n", kqd->latency_targets[domain]); \
870 } \
871 \
872 static ssize_t kyber_##name##_lat_store(struct elevator_queue *e, \
873 const char *page, size_t count) \
874 { \
875 struct kyber_queue_data *kqd = e->elevator_data; \
876 unsigned long long nsec; \
877 int ret; \
878 \
879 ret = kstrtoull(page, 10, &nsec); \
880 if (ret) \
881 return ret; \
882 \
883 kqd->latency_targets[domain] = nsec; \
884 \
885 return count; \
886 }
887 KYBER_LAT_SHOW_STORE(KYBER_READ, read);
888 KYBER_LAT_SHOW_STORE(KYBER_WRITE, write);
889 #undef KYBER_LAT_SHOW_STORE
890
891 #define KYBER_LAT_ATTR(op) __ATTR(op##_lat_nsec, 0644, kyber_##op##_lat_show, kyber_##op##_lat_store)
892 static struct elv_fs_entry kyber_sched_attrs[] = {
893 KYBER_LAT_ATTR(read),
894 KYBER_LAT_ATTR(write),
895 __ATTR_NULL
896 };
897 #undef KYBER_LAT_ATTR
898
899 #ifdef CONFIG_BLK_DEBUG_FS
900 #define KYBER_DEBUGFS_DOMAIN_ATTRS(domain, name) \
901 static int kyber_##name##_tokens_show(void *data, struct seq_file *m) \
902 { \
903 struct request_queue *q = data; \
904 struct kyber_queue_data *kqd = q->elevator->elevator_data; \
905 \
906 sbitmap_queue_show(&kqd->domain_tokens[domain], m); \
907 return 0; \
908 } \
909 \
910 static void *kyber_##name##_rqs_start(struct seq_file *m, loff_t *pos) \
911 __acquires(&khd->lock) \
912 { \
913 struct blk_mq_hw_ctx *hctx = m->private; \
914 struct kyber_hctx_data *khd = hctx->sched_data; \
915 \
916 spin_lock(&khd->lock); \
917 return seq_list_start(&khd->rqs[domain], *pos); \
918 } \
919 \
920 static void *kyber_##name##_rqs_next(struct seq_file *m, void *v, \
921 loff_t *pos) \
922 { \
923 struct blk_mq_hw_ctx *hctx = m->private; \
924 struct kyber_hctx_data *khd = hctx->sched_data; \
925 \
926 return seq_list_next(v, &khd->rqs[domain], pos); \
927 } \
928 \
929 static void kyber_##name##_rqs_stop(struct seq_file *m, void *v) \
930 __releases(&khd->lock) \
931 { \
932 struct blk_mq_hw_ctx *hctx = m->private; \
933 struct kyber_hctx_data *khd = hctx->sched_data; \
934 \
935 spin_unlock(&khd->lock); \
936 } \
937 \
938 static const struct seq_operations kyber_##name##_rqs_seq_ops = { \
939 .start = kyber_##name##_rqs_start, \
940 .next = kyber_##name##_rqs_next, \
941 .stop = kyber_##name##_rqs_stop, \
942 .show = blk_mq_debugfs_rq_show, \
943 }; \
944 \
945 static int kyber_##name##_waiting_show(void *data, struct seq_file *m) \
946 { \
947 struct blk_mq_hw_ctx *hctx = data; \
948 struct kyber_hctx_data *khd = hctx->sched_data; \
949 wait_queue_entry_t *wait = &khd->domain_wait[domain].wait; \
950 \
951 seq_printf(m, "%d\n", !list_empty_careful(&wait->entry)); \
952 return 0; \
953 }
KYBER_DEBUGFS_DOMAIN_ATTRS(KYBER_READ,read)954 KYBER_DEBUGFS_DOMAIN_ATTRS(KYBER_READ, read)
955 KYBER_DEBUGFS_DOMAIN_ATTRS(KYBER_WRITE, write)
956 KYBER_DEBUGFS_DOMAIN_ATTRS(KYBER_DISCARD, discard)
957 KYBER_DEBUGFS_DOMAIN_ATTRS(KYBER_OTHER, other)
958 #undef KYBER_DEBUGFS_DOMAIN_ATTRS
959
960 static int kyber_async_depth_show(void *data, struct seq_file *m)
961 {
962 struct request_queue *q = data;
963 struct kyber_queue_data *kqd = q->elevator->elevator_data;
964
965 seq_printf(m, "%u\n", kqd->async_depth);
966 return 0;
967 }
968
kyber_cur_domain_show(void * data,struct seq_file * m)969 static int kyber_cur_domain_show(void *data, struct seq_file *m)
970 {
971 struct blk_mq_hw_ctx *hctx = data;
972 struct kyber_hctx_data *khd = hctx->sched_data;
973
974 seq_printf(m, "%s\n", kyber_domain_names[khd->cur_domain]);
975 return 0;
976 }
977
kyber_batching_show(void * data,struct seq_file * m)978 static int kyber_batching_show(void *data, struct seq_file *m)
979 {
980 struct blk_mq_hw_ctx *hctx = data;
981 struct kyber_hctx_data *khd = hctx->sched_data;
982
983 seq_printf(m, "%u\n", khd->batching);
984 return 0;
985 }
986
987 #define KYBER_QUEUE_DOMAIN_ATTRS(name) \
988 {#name "_tokens", 0400, kyber_##name##_tokens_show}
989 static const struct blk_mq_debugfs_attr kyber_queue_debugfs_attrs[] = {
990 KYBER_QUEUE_DOMAIN_ATTRS(read),
991 KYBER_QUEUE_DOMAIN_ATTRS(write),
992 KYBER_QUEUE_DOMAIN_ATTRS(discard),
993 KYBER_QUEUE_DOMAIN_ATTRS(other),
994 {"async_depth", 0400, kyber_async_depth_show},
995 {},
996 };
997 #undef KYBER_QUEUE_DOMAIN_ATTRS
998
999 #define KYBER_HCTX_DOMAIN_ATTRS(name) \
1000 {#name "_rqs", 0400, .seq_ops = &kyber_##name##_rqs_seq_ops}, \
1001 {#name "_waiting", 0400, kyber_##name##_waiting_show}
1002 static const struct blk_mq_debugfs_attr kyber_hctx_debugfs_attrs[] = {
1003 KYBER_HCTX_DOMAIN_ATTRS(read),
1004 KYBER_HCTX_DOMAIN_ATTRS(write),
1005 KYBER_HCTX_DOMAIN_ATTRS(discard),
1006 KYBER_HCTX_DOMAIN_ATTRS(other),
1007 {"cur_domain", 0400, kyber_cur_domain_show},
1008 {"batching", 0400, kyber_batching_show},
1009 {},
1010 };
1011 #undef KYBER_HCTX_DOMAIN_ATTRS
1012 #endif
1013
1014 static struct elevator_type kyber_sched = {
1015 .ops = {
1016 .init_sched = kyber_init_sched,
1017 .exit_sched = kyber_exit_sched,
1018 .init_hctx = kyber_init_hctx,
1019 .exit_hctx = kyber_exit_hctx,
1020 .limit_depth = kyber_limit_depth,
1021 .bio_merge = kyber_bio_merge,
1022 .prepare_request = kyber_prepare_request,
1023 .insert_requests = kyber_insert_requests,
1024 .finish_request = kyber_finish_request,
1025 .requeue_request = kyber_finish_request,
1026 .completed_request = kyber_completed_request,
1027 .dispatch_request = kyber_dispatch_request,
1028 .has_work = kyber_has_work,
1029 .depth_updated = kyber_depth_updated,
1030 },
1031 #ifdef CONFIG_BLK_DEBUG_FS
1032 .queue_debugfs_attrs = kyber_queue_debugfs_attrs,
1033 .hctx_debugfs_attrs = kyber_hctx_debugfs_attrs,
1034 #endif
1035 .elevator_attrs = kyber_sched_attrs,
1036 .elevator_name = "kyber",
1037 .elevator_owner = THIS_MODULE,
1038 };
1039
kyber_init(void)1040 static int __init kyber_init(void)
1041 {
1042 return elv_register(&kyber_sched);
1043 }
1044
kyber_exit(void)1045 static void __exit kyber_exit(void)
1046 {
1047 elv_unregister(&kyber_sched);
1048 }
1049
1050 module_init(kyber_init);
1051 module_exit(kyber_exit);
1052
1053 MODULE_AUTHOR("Omar Sandoval");
1054 MODULE_LICENSE("GPL");
1055 MODULE_DESCRIPTION("Kyber I/O scheduler");
1056
