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