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