1// SPDX-License-Identifier: GPL-2.0 2/* 3 * Block rq-qos base io controller 4 * 5 * This works similar to wbt with a few exceptions 6 * 7 * - It's bio based, so the latency covers the whole block layer in addition to 8 * the actual io. 9 * - We will throttle all IO that comes in here if we need to. 10 * - We use the mean latency over the 100ms window. This is because writes can 11 * be particularly fast, which could give us a false sense of the impact of 12 * other workloads on our protected workload. 13 * - By default there's no throttling, we set the queue_depth to UINT_MAX so 14 * that we can have as many outstanding bio's as we're allowed to. Only at 15 * throttle time do we pay attention to the actual queue depth. 16 * 17 * The hierarchy works like the cpu controller does, we track the latency at 18 * every configured node, and each configured node has it's own independent 19 * queue depth. This means that we only care about our latency targets at the 20 * peer level. Some group at the bottom of the hierarchy isn't going to affect 21 * a group at the end of some other path if we're only configred at leaf level. 22 * 23 * Consider the following 24 * 25 * root blkg 26 * / \ 27 * fast (target=5ms) slow (target=10ms) 28 * / \ / \ 29 * a b normal(15ms) unloved 30 * 31 * "a" and "b" have no target, but their combined io under "fast" cannot exceed 32 * an average latency of 5ms. If it does then we will throttle the "slow" 33 * group. In the case of "normal", if it exceeds its 15ms target, we will 34 * throttle "unloved", but nobody else. 35 * 36 * In this example "fast", "slow", and "normal" will be the only groups actually 37 * accounting their io latencies. We have to walk up the heirarchy to the root 38 * on every submit and complete so we can do the appropriate stat recording and 39 * adjust the queue depth of ourselves if needed. 40 * 41 * There are 2 ways we throttle IO. 42 * 43 * 1) Queue depth throttling. As we throttle down we will adjust the maximum 44 * number of IO's we're allowed to have in flight. This starts at (u64)-1 down 45 * to 1. If the group is only ever submitting IO for itself then this is the 46 * only way we throttle. 47 * 48 * 2) Induced delay throttling. This is for the case that a group is generating 49 * IO that has to be issued by the root cg to avoid priority inversion. So think 50 * REQ_META or REQ_SWAP. If we are already at qd == 1 and we're getting a lot 51 * of work done for us on behalf of the root cg and are being asked to scale 52 * down more then we induce a latency at userspace return. We accumulate the 53 * total amount of time we need to be punished by doing 54 * 55 * total_time += min_lat_nsec - actual_io_completion 56 * 57 * and then at throttle time will do 58 * 59 * throttle_time = min(total_time, NSEC_PER_SEC) 60 * 61 * This induced delay will throttle back the activity that is generating the 62 * root cg issued io's, wethere that's some metadata intensive operation or the 63 * group is using so much memory that it is pushing us into swap. 64 * 65 * Copyright (C) 2018 Josef Bacik 66 */ 67#include <linux/kernel.h> 68#include <linux/blk_types.h> 69#include <linux/backing-dev.h> 70#include <linux/module.h> 71#include <linux/timer.h> 72#include <linux/memcontrol.h> 73#include <linux/sched/loadavg.h> 74#include <linux/sched/signal.h> 75#include <trace/events/block.h> 76#include <linux/blk-mq.h> 77#include "blk-rq-qos.h" 78#include "blk-stat.h" 79#include "blk.h" 80 81#define DEFAULT_SCALE_COOKIE 1000000U 82 83static struct blkcg_policy blkcg_policy_iolatency; 84struct iolatency_grp; 85 86struct blk_iolatency { 87 struct rq_qos rqos; 88 struct timer_list timer; 89 90 /* 91 * ->enabled is the master enable switch gating the throttling logic and 92 * inflight tracking. The number of cgroups which have iolat enabled is 93 * tracked in ->enable_cnt, and ->enable is flipped on/off accordingly 94 * from ->enable_work with the request_queue frozen. For details, See 95 * blkiolatency_enable_work_fn(). 96 */ 97 bool enabled; 98 atomic_t enable_cnt; 99 struct work_struct enable_work; 100}; 101 102static inline struct blk_iolatency *BLKIOLATENCY(struct rq_qos *rqos) 103{ 104 return container_of(rqos, struct blk_iolatency, rqos); 105} 106 107struct child_latency_info { 108 spinlock_t lock; 109 110 /* Last time we adjusted the scale of everybody. */ 111 u64 last_scale_event; 112 113 /* The latency that we missed. */ 114 u64 scale_lat; 115 116 /* Total io's from all of our children for the last summation. */ 117 u64 nr_samples; 118 119 /* The guy who actually changed the latency numbers. */ 120 struct iolatency_grp *scale_grp; 121 122 /* Cookie to tell if we need to scale up or down. */ 123 atomic_t scale_cookie; 124}; 125 126struct percentile_stats { 127 u64 total; 128 u64 missed; 129}; 130 131struct latency_stat { 132 union { 133 struct percentile_stats ps; 134 struct blk_rq_stat rqs; 135 }; 136}; 137 138struct iolatency_grp { 139 struct blkg_policy_data pd; 140 struct latency_stat __percpu *stats; 141 struct latency_stat cur_stat; 142 struct blk_iolatency *blkiolat; 143 struct rq_depth rq_depth; 144 struct rq_wait rq_wait; 145 atomic64_t window_start; 146 atomic_t scale_cookie; 147 u64 min_lat_nsec; 148 u64 cur_win_nsec; 149 150 /* total running average of our io latency. */ 151 u64 lat_avg; 152 153 /* Our current number of IO's for the last summation. */ 154 u64 nr_samples; 155 156 bool ssd; 157 struct child_latency_info child_lat; 158}; 159 160#define BLKIOLATENCY_MIN_WIN_SIZE (100 * NSEC_PER_MSEC) 161#define BLKIOLATENCY_MAX_WIN_SIZE NSEC_PER_SEC 162/* 163 * These are the constants used to fake the fixed-point moving average 164 * calculation just like load average. The call to calc_load() folds 165 * (FIXED_1 (2048) - exp_factor) * new_sample into lat_avg. The sampling 166 * window size is bucketed to try to approximately calculate average 167 * latency such that 1/exp (decay rate) is [1 min, 2.5 min) when windows 168 * elapse immediately. Note, windows only elapse with IO activity. Idle 169 * periods extend the most recent window. 170 */ 171#define BLKIOLATENCY_NR_EXP_FACTORS 5 172#define BLKIOLATENCY_EXP_BUCKET_SIZE (BLKIOLATENCY_MAX_WIN_SIZE / \ 173 (BLKIOLATENCY_NR_EXP_FACTORS - 1)) 174static const u64 iolatency_exp_factors[BLKIOLATENCY_NR_EXP_FACTORS] = { 175 2045, // exp(1/600) - 600 samples 176 2039, // exp(1/240) - 240 samples 177 2031, // exp(1/120) - 120 samples 178 2023, // exp(1/80) - 80 samples 179 2014, // exp(1/60) - 60 samples 180}; 181 182static inline struct iolatency_grp *pd_to_lat(struct blkg_policy_data *pd) 183{ 184 return pd ? container_of(pd, struct iolatency_grp, pd) : NULL; 185} 186 187static inline struct iolatency_grp *blkg_to_lat(struct blkcg_gq *blkg) 188{ 189 return pd_to_lat(blkg_to_pd(blkg, &blkcg_policy_iolatency)); 190} 191 192static inline struct blkcg_gq *lat_to_blkg(struct iolatency_grp *iolat) 193{ 194 return pd_to_blkg(&iolat->pd); 195} 196 197static inline void latency_stat_init(struct iolatency_grp *iolat, 198 struct latency_stat *stat) 199{ 200 if (iolat->ssd) { 201 stat->ps.total = 0; 202 stat->ps.missed = 0; 203 } else 204 blk_rq_stat_init(&stat->rqs); 205} 206 207static inline void latency_stat_sum(struct iolatency_grp *iolat, 208 struct latency_stat *sum, 209 struct latency_stat *stat) 210{ 211 if (iolat->ssd) { 212 sum->ps.total += stat->ps.total; 213 sum->ps.missed += stat->ps.missed; 214 } else 215 blk_rq_stat_sum(&sum->rqs, &stat->rqs); 216} 217 218static inline void latency_stat_record_time(struct iolatency_grp *iolat, 219 u64 req_time) 220{ 221 struct latency_stat *stat = get_cpu_ptr(iolat->stats); 222 if (iolat->ssd) { 223 if (req_time >= iolat->min_lat_nsec) 224 stat->ps.missed++; 225 stat->ps.total++; 226 } else 227 blk_rq_stat_add(&stat->rqs, req_time); 228 put_cpu_ptr(stat); 229} 230 231static inline bool latency_sum_ok(struct iolatency_grp *iolat, 232 struct latency_stat *stat) 233{ 234 if (iolat->ssd) { 235 u64 thresh = div64_u64(stat->ps.total, 10); 236 thresh = max(thresh, 1ULL); 237 return stat->ps.missed < thresh; 238 } 239 return stat->rqs.mean <= iolat->min_lat_nsec; 240} 241 242static inline u64 latency_stat_samples(struct iolatency_grp *iolat, 243 struct latency_stat *stat) 244{ 245 if (iolat->ssd) 246 return stat->ps.total; 247 return stat->rqs.nr_samples; 248} 249 250static inline void iolat_update_total_lat_avg(struct iolatency_grp *iolat, 251 struct latency_stat *stat) 252{ 253 int exp_idx; 254 255 if (iolat->ssd) 256 return; 257 258 /* 259 * calc_load() takes in a number stored in fixed point representation. 260 * Because we are using this for IO time in ns, the values stored 261 * are significantly larger than the FIXED_1 denominator (2048). 262 * Therefore, rounding errors in the calculation are negligible and 263 * can be ignored. 264 */ 265 exp_idx = min_t(int, BLKIOLATENCY_NR_EXP_FACTORS - 1, 266 div64_u64(iolat->cur_win_nsec, 267 BLKIOLATENCY_EXP_BUCKET_SIZE)); 268 iolat->lat_avg = calc_load(iolat->lat_avg, 269 iolatency_exp_factors[exp_idx], 270 stat->rqs.mean); 271} 272 273static void iolat_cleanup_cb(struct rq_wait *rqw, void *private_data) 274{ 275 atomic_dec(&rqw->inflight); 276 wake_up(&rqw->wait); 277} 278 279static bool iolat_acquire_inflight(struct rq_wait *rqw, void *private_data) 280{ 281 struct iolatency_grp *iolat = private_data; 282 return rq_wait_inc_below(rqw, iolat->rq_depth.max_depth); 283} 284 285static void __blkcg_iolatency_throttle(struct rq_qos *rqos, 286 struct iolatency_grp *iolat, 287 bool issue_as_root, 288 bool use_memdelay) 289{ 290 struct rq_wait *rqw = &iolat->rq_wait; 291 unsigned use_delay = atomic_read(&lat_to_blkg(iolat)->use_delay); 292 293 if (use_delay) 294 blkcg_schedule_throttle(rqos->q, use_memdelay); 295 296 /* 297 * To avoid priority inversions we want to just take a slot if we are 298 * issuing as root. If we're being killed off there's no point in 299 * delaying things, we may have been killed by OOM so throttling may 300 * make recovery take even longer, so just let the IO's through so the 301 * task can go away. 302 */ 303 if (issue_as_root || fatal_signal_pending(current)) { 304 atomic_inc(&rqw->inflight); 305 return; 306 } 307 308 rq_qos_wait(rqw, iolat, iolat_acquire_inflight, iolat_cleanup_cb); 309} 310 311#define SCALE_DOWN_FACTOR 2 312#define SCALE_UP_FACTOR 4 313 314static inline unsigned long scale_amount(unsigned long qd, bool up) 315{ 316 return max(up ? qd >> SCALE_UP_FACTOR : qd >> SCALE_DOWN_FACTOR, 1UL); 317} 318 319/* 320 * We scale the qd down faster than we scale up, so we need to use this helper 321 * to adjust the scale_cookie accordingly so we don't prematurely get 322 * scale_cookie at DEFAULT_SCALE_COOKIE and unthrottle too much. 323 * 324 * Each group has their own local copy of the last scale cookie they saw, so if 325 * the global scale cookie goes up or down they know which way they need to go 326 * based on their last knowledge of it. 327 */ 328static void scale_cookie_change(struct blk_iolatency *blkiolat, 329 struct child_latency_info *lat_info, 330 bool up) 331{ 332 unsigned long qd = blkiolat->rqos.q->nr_requests; 333 unsigned long scale = scale_amount(qd, up); 334 unsigned long old = atomic_read(&lat_info->scale_cookie); 335 unsigned long max_scale = qd << 1; 336 unsigned long diff = 0; 337 338 if (old < DEFAULT_SCALE_COOKIE) 339 diff = DEFAULT_SCALE_COOKIE - old; 340 341 if (up) { 342 if (scale + old > DEFAULT_SCALE_COOKIE) 343 atomic_set(&lat_info->scale_cookie, 344 DEFAULT_SCALE_COOKIE); 345 else if (diff > qd) 346 atomic_inc(&lat_info->scale_cookie); 347 else 348 atomic_add(scale, &lat_info->scale_cookie); 349 } else { 350 /* 351 * We don't want to dig a hole so deep that it takes us hours to 352 * dig out of it. Just enough that we don't throttle/unthrottle 353 * with jagged workloads but can still unthrottle once pressure 354 * has sufficiently dissipated. 355 */ 356 if (diff > qd) { 357 if (diff < max_scale) 358 atomic_dec(&lat_info->scale_cookie); 359 } else { 360 atomic_sub(scale, &lat_info->scale_cookie); 361 } 362 } 363} 364 365/* 366 * Change the queue depth of the iolatency_grp. We add/subtract 1/16th of the 367 * queue depth at a time so we don't get wild swings and hopefully dial in to 368 * fairer distribution of the overall queue depth. 369 */ 370static void scale_change(struct iolatency_grp *iolat, bool up) 371{ 372 unsigned long qd = iolat->blkiolat->rqos.q->nr_requests; 373 unsigned long scale = scale_amount(qd, up); 374 unsigned long old = iolat->rq_depth.max_depth; 375 376 if (old > qd) 377 old = qd; 378 379 if (up) { 380 if (old == 1 && blkcg_unuse_delay(lat_to_blkg(iolat))) 381 return; 382 383 if (old < qd) { 384 old += scale; 385 old = min(old, qd); 386 iolat->rq_depth.max_depth = old; 387 wake_up_all(&iolat->rq_wait.wait); 388 } 389 } else { 390 old >>= 1; 391 iolat->rq_depth.max_depth = max(old, 1UL); 392 } 393} 394 395/* Check our parent and see if the scale cookie has changed. */ 396static void check_scale_change(struct iolatency_grp *iolat) 397{ 398 struct iolatency_grp *parent; 399 struct child_latency_info *lat_info; 400 unsigned int cur_cookie; 401 unsigned int our_cookie = atomic_read(&iolat->scale_cookie); 402 u64 scale_lat; 403 unsigned int old; 404 int direction = 0; 405 406 if (lat_to_blkg(iolat)->parent == NULL) 407 return; 408 409 parent = blkg_to_lat(lat_to_blkg(iolat)->parent); 410 if (!parent) 411 return; 412 413 lat_info = &parent->child_lat; 414 cur_cookie = atomic_read(&lat_info->scale_cookie); 415 scale_lat = READ_ONCE(lat_info->scale_lat); 416 417 if (cur_cookie < our_cookie) 418 direction = -1; 419 else if (cur_cookie > our_cookie) 420 direction = 1; 421 else 422 return; 423 424 old = atomic_cmpxchg(&iolat->scale_cookie, our_cookie, cur_cookie); 425 426 /* Somebody beat us to the punch, just bail. */ 427 if (old != our_cookie) 428 return; 429 430 if (direction < 0 && iolat->min_lat_nsec) { 431 u64 samples_thresh; 432 433 if (!scale_lat || iolat->min_lat_nsec <= scale_lat) 434 return; 435 436 /* 437 * Sometimes high priority groups are their own worst enemy, so 438 * instead of taking it out on some poor other group that did 5% 439 * or less of the IO's for the last summation just skip this 440 * scale down event. 441 */ 442 samples_thresh = lat_info->nr_samples * 5; 443 samples_thresh = max(1ULL, div64_u64(samples_thresh, 100)); 444 if (iolat->nr_samples <= samples_thresh) 445 return; 446 } 447 448 /* We're as low as we can go. */ 449 if (iolat->rq_depth.max_depth == 1 && direction < 0) { 450 blkcg_use_delay(lat_to_blkg(iolat)); 451 return; 452 } 453 454 /* We're back to the default cookie, unthrottle all the things. */ 455 if (cur_cookie == DEFAULT_SCALE_COOKIE) { 456 blkcg_clear_delay(lat_to_blkg(iolat)); 457 iolat->rq_depth.max_depth = UINT_MAX; 458 wake_up_all(&iolat->rq_wait.wait); 459 return; 460 } 461 462 scale_change(iolat, direction > 0); 463} 464 465static void blkcg_iolatency_throttle(struct rq_qos *rqos, struct bio *bio) 466{ 467 struct blk_iolatency *blkiolat = BLKIOLATENCY(rqos); 468 struct blkcg_gq *blkg = bio->bi_blkg; 469 bool issue_as_root = bio_issue_as_root_blkg(bio); 470 471 if (!blkiolat->enabled) 472 return; 473 474 while (blkg && blkg->parent) { 475 struct iolatency_grp *iolat = blkg_to_lat(blkg); 476 if (!iolat) { 477 blkg = blkg->parent; 478 continue; 479 } 480 481 check_scale_change(iolat); 482 __blkcg_iolatency_throttle(rqos, iolat, issue_as_root, 483 (bio->bi_opf & REQ_SWAP) == REQ_SWAP); 484 blkg = blkg->parent; 485 } 486 if (!timer_pending(&blkiolat->timer)) 487 mod_timer(&blkiolat->timer, jiffies + HZ); 488} 489 490static void iolatency_record_time(struct iolatency_grp *iolat, 491 struct bio_issue *issue, u64 now, 492 bool issue_as_root) 493{ 494 u64 start = bio_issue_time(issue); 495 u64 req_time; 496 497 /* 498 * Have to do this so we are truncated to the correct time that our 499 * issue is truncated to. 500 */ 501 now = __bio_issue_time(now); 502 503 if (now <= start) 504 return; 505 506 req_time = now - start; 507 508 /* 509 * We don't want to count issue_as_root bio's in the cgroups latency 510 * statistics as it could skew the numbers downwards. 511 */ 512 if (unlikely(issue_as_root && iolat->rq_depth.max_depth != UINT_MAX)) { 513 u64 sub = iolat->min_lat_nsec; 514 if (req_time < sub) 515 blkcg_add_delay(lat_to_blkg(iolat), now, sub - req_time); 516 return; 517 } 518 519 latency_stat_record_time(iolat, req_time); 520} 521 522#define BLKIOLATENCY_MIN_ADJUST_TIME (500 * NSEC_PER_MSEC) 523#define BLKIOLATENCY_MIN_GOOD_SAMPLES 5 524 525static void iolatency_check_latencies(struct iolatency_grp *iolat, u64 now) 526{ 527 struct blkcg_gq *blkg = lat_to_blkg(iolat); 528 struct iolatency_grp *parent; 529 struct child_latency_info *lat_info; 530 struct latency_stat stat; 531 unsigned long flags; 532 int cpu; 533 534 latency_stat_init(iolat, &stat); 535 preempt_disable(); 536 for_each_online_cpu(cpu) { 537 struct latency_stat *s; 538 s = per_cpu_ptr(iolat->stats, cpu); 539 latency_stat_sum(iolat, &stat, s); 540 latency_stat_init(iolat, s); 541 } 542 preempt_enable(); 543 544 parent = blkg_to_lat(blkg->parent); 545 if (!parent) 546 return; 547 548 lat_info = &parent->child_lat; 549 550 iolat_update_total_lat_avg(iolat, &stat); 551 552 /* Everything is ok and we don't need to adjust the scale. */ 553 if (latency_sum_ok(iolat, &stat) && 554 atomic_read(&lat_info->scale_cookie) == DEFAULT_SCALE_COOKIE) 555 return; 556 557 /* Somebody beat us to the punch, just bail. */ 558 spin_lock_irqsave(&lat_info->lock, flags); 559 560 latency_stat_sum(iolat, &iolat->cur_stat, &stat); 561 lat_info->nr_samples -= iolat->nr_samples; 562 lat_info->nr_samples += latency_stat_samples(iolat, &iolat->cur_stat); 563 iolat->nr_samples = latency_stat_samples(iolat, &iolat->cur_stat); 564 565 if ((lat_info->last_scale_event >= now || 566 now - lat_info->last_scale_event < BLKIOLATENCY_MIN_ADJUST_TIME)) 567 goto out; 568 569 if (latency_sum_ok(iolat, &iolat->cur_stat) && 570 latency_sum_ok(iolat, &stat)) { 571 if (latency_stat_samples(iolat, &iolat->cur_stat) < 572 BLKIOLATENCY_MIN_GOOD_SAMPLES) 573 goto out; 574 if (lat_info->scale_grp == iolat) { 575 lat_info->last_scale_event = now; 576 scale_cookie_change(iolat->blkiolat, lat_info, true); 577 } 578 } else if (lat_info->scale_lat == 0 || 579 lat_info->scale_lat >= iolat->min_lat_nsec) { 580 lat_info->last_scale_event = now; 581 if (!lat_info->scale_grp || 582 lat_info->scale_lat > iolat->min_lat_nsec) { 583 WRITE_ONCE(lat_info->scale_lat, iolat->min_lat_nsec); 584 lat_info->scale_grp = iolat; 585 } 586 scale_cookie_change(iolat->blkiolat, lat_info, false); 587 } 588 latency_stat_init(iolat, &iolat->cur_stat); 589out: 590 spin_unlock_irqrestore(&lat_info->lock, flags); 591} 592 593static void blkcg_iolatency_done_bio(struct rq_qos *rqos, struct bio *bio) 594{ 595 struct blkcg_gq *blkg; 596 struct rq_wait *rqw; 597 struct iolatency_grp *iolat; 598 u64 window_start; 599 u64 now; 600 bool issue_as_root = bio_issue_as_root_blkg(bio); 601 int inflight = 0; 602 603 blkg = bio->bi_blkg; 604 if (!blkg || !bio_flagged(bio, BIO_TRACKED)) 605 return; 606 607 iolat = blkg_to_lat(bio->bi_blkg); 608 if (!iolat) 609 return; 610 611 if (!iolat->blkiolat->enabled) 612 return; 613 614 now = ktime_to_ns(ktime_get()); 615 while (blkg && blkg->parent) { 616 iolat = blkg_to_lat(blkg); 617 if (!iolat) { 618 blkg = blkg->parent; 619 continue; 620 } 621 rqw = &iolat->rq_wait; 622 623 inflight = atomic_dec_return(&rqw->inflight); 624 WARN_ON_ONCE(inflight < 0); 625 /* 626 * If bi_status is BLK_STS_AGAIN, the bio wasn't actually 627 * submitted, so do not account for it. 628 */ 629 if (iolat->min_lat_nsec && bio->bi_status != BLK_STS_AGAIN) { 630 iolatency_record_time(iolat, &bio->bi_issue, now, 631 issue_as_root); 632 window_start = atomic64_read(&iolat->window_start); 633 if (now > window_start && 634 (now - window_start) >= iolat->cur_win_nsec) { 635 if (atomic64_cmpxchg(&iolat->window_start, 636 window_start, now) == window_start) 637 iolatency_check_latencies(iolat, now); 638 } 639 } 640 wake_up(&rqw->wait); 641 blkg = blkg->parent; 642 } 643} 644 645static void blkcg_iolatency_exit(struct rq_qos *rqos) 646{ 647 struct blk_iolatency *blkiolat = BLKIOLATENCY(rqos); 648 649 del_timer_sync(&blkiolat->timer); 650 flush_work(&blkiolat->enable_work); 651 blkcg_deactivate_policy(rqos->q, &blkcg_policy_iolatency); 652 kfree(blkiolat); 653} 654 655static struct rq_qos_ops blkcg_iolatency_ops = { 656 .throttle = blkcg_iolatency_throttle, 657 .done_bio = blkcg_iolatency_done_bio, 658 .exit = blkcg_iolatency_exit, 659}; 660 661static void blkiolatency_timer_fn(struct timer_list *t) 662{ 663 struct blk_iolatency *blkiolat = from_timer(blkiolat, t, timer); 664 struct blkcg_gq *blkg; 665 struct cgroup_subsys_state *pos_css; 666 u64 now = ktime_to_ns(ktime_get()); 667 668 rcu_read_lock(); 669 blkg_for_each_descendant_pre(blkg, pos_css, 670 blkiolat->rqos.q->root_blkg) { 671 struct iolatency_grp *iolat; 672 struct child_latency_info *lat_info; 673 unsigned long flags; 674 u64 cookie; 675 676 /* 677 * We could be exiting, don't access the pd unless we have a 678 * ref on the blkg. 679 */ 680 if (!blkg_tryget(blkg)) 681 continue; 682 683 iolat = blkg_to_lat(blkg); 684 if (!iolat) 685 goto next; 686 687 lat_info = &iolat->child_lat; 688 cookie = atomic_read(&lat_info->scale_cookie); 689 690 if (cookie >= DEFAULT_SCALE_COOKIE) 691 goto next; 692 693 spin_lock_irqsave(&lat_info->lock, flags); 694 if (lat_info->last_scale_event >= now) 695 goto next_lock; 696 697 /* 698 * We scaled down but don't have a scale_grp, scale up and carry 699 * on. 700 */ 701 if (lat_info->scale_grp == NULL) { 702 scale_cookie_change(iolat->blkiolat, lat_info, true); 703 goto next_lock; 704 } 705 706 /* 707 * It's been 5 seconds since our last scale event, clear the 708 * scale grp in case the group that needed the scale down isn't 709 * doing any IO currently. 710 */ 711 if (now - lat_info->last_scale_event >= 712 ((u64)NSEC_PER_SEC * 5)) 713 lat_info->scale_grp = NULL; 714next_lock: 715 spin_unlock_irqrestore(&lat_info->lock, flags); 716next: 717 blkg_put(blkg); 718 } 719 rcu_read_unlock(); 720} 721 722/** 723 * blkiolatency_enable_work_fn - Enable or disable iolatency on the device 724 * @work: enable_work of the blk_iolatency of interest 725 * 726 * iolatency needs to keep track of the number of in-flight IOs per cgroup. This 727 * is relatively expensive as it involves walking up the hierarchy twice for 728 * every IO. Thus, if iolatency is not enabled in any cgroup for the device, we 729 * want to disable the in-flight tracking. 730 * 731 * We have to make sure that the counting is balanced - we don't want to leak 732 * the in-flight counts by disabling accounting in the completion path while IOs 733 * are in flight. This is achieved by ensuring that no IO is in flight by 734 * freezing the queue while flipping ->enabled. As this requires a sleepable 735 * context, ->enabled flipping is punted to this work function. 736 */ 737static void blkiolatency_enable_work_fn(struct work_struct *work) 738{ 739 struct blk_iolatency *blkiolat = container_of(work, struct blk_iolatency, 740 enable_work); 741 bool enabled; 742 743 /* 744 * There can only be one instance of this function running for @blkiolat 745 * and it's guaranteed to be executed at least once after the latest 746 * ->enabled_cnt modification. Acting on the latest ->enable_cnt is 747 * sufficient. 748 * 749 * Also, we know @blkiolat is safe to access as ->enable_work is flushed 750 * in blkcg_iolatency_exit(). 751 */ 752 enabled = atomic_read(&blkiolat->enable_cnt); 753 if (enabled != blkiolat->enabled) { 754 blk_mq_freeze_queue(blkiolat->rqos.q); 755 blkiolat->enabled = enabled; 756 blk_mq_unfreeze_queue(blkiolat->rqos.q); 757 } 758} 759 760int blk_iolatency_init(struct request_queue *q) 761{ 762 struct blk_iolatency *blkiolat; 763 struct rq_qos *rqos; 764 int ret; 765 766 blkiolat = kzalloc(sizeof(*blkiolat), GFP_KERNEL); 767 if (!blkiolat) 768 return -ENOMEM; 769 770 rqos = &blkiolat->rqos; 771 rqos->id = RQ_QOS_LATENCY; 772 rqos->ops = &blkcg_iolatency_ops; 773 rqos->q = q; 774 775 rq_qos_add(q, rqos); 776 777 ret = blkcg_activate_policy(q, &blkcg_policy_iolatency); 778 if (ret) { 779 rq_qos_del(q, rqos); 780 kfree(blkiolat); 781 return ret; 782 } 783 784 timer_setup(&blkiolat->timer, blkiolatency_timer_fn, 0); 785 INIT_WORK(&blkiolat->enable_work, blkiolatency_enable_work_fn); 786 787 return 0; 788} 789 790static void iolatency_set_min_lat_nsec(struct blkcg_gq *blkg, u64 val) 791{ 792 struct iolatency_grp *iolat = blkg_to_lat(blkg); 793 struct blk_iolatency *blkiolat = iolat->blkiolat; 794 u64 oldval = iolat->min_lat_nsec; 795 796 iolat->min_lat_nsec = val; 797 iolat->cur_win_nsec = max_t(u64, val << 4, BLKIOLATENCY_MIN_WIN_SIZE); 798 iolat->cur_win_nsec = min_t(u64, iolat->cur_win_nsec, 799 BLKIOLATENCY_MAX_WIN_SIZE); 800 801 if (!oldval && val) { 802 if (atomic_inc_return(&blkiolat->enable_cnt) == 1) 803 schedule_work(&blkiolat->enable_work); 804 } 805 if (oldval && !val) { 806 blkcg_clear_delay(blkg); 807 if (atomic_dec_return(&blkiolat->enable_cnt) == 0) 808 schedule_work(&blkiolat->enable_work); 809 } 810} 811 812static void iolatency_clear_scaling(struct blkcg_gq *blkg) 813{ 814 if (blkg->parent) { 815 struct iolatency_grp *iolat = blkg_to_lat(blkg->parent); 816 struct child_latency_info *lat_info; 817 if (!iolat) 818 return; 819 820 lat_info = &iolat->child_lat; 821 spin_lock(&lat_info->lock); 822 atomic_set(&lat_info->scale_cookie, DEFAULT_SCALE_COOKIE); 823 lat_info->last_scale_event = 0; 824 lat_info->scale_grp = NULL; 825 lat_info->scale_lat = 0; 826 spin_unlock(&lat_info->lock); 827 } 828} 829 830static ssize_t iolatency_set_limit(struct kernfs_open_file *of, char *buf, 831 size_t nbytes, loff_t off) 832{ 833 struct blkcg *blkcg = css_to_blkcg(of_css(of)); 834 struct blkcg_gq *blkg; 835 struct blkg_conf_ctx ctx; 836 struct iolatency_grp *iolat; 837 char *p, *tok; 838 u64 lat_val = 0; 839 u64 oldval; 840 int ret; 841 842 ret = blkg_conf_prep(blkcg, &blkcg_policy_iolatency, buf, &ctx); 843 if (ret) 844 return ret; 845 846 iolat = blkg_to_lat(ctx.blkg); 847 p = ctx.body; 848 849 ret = -EINVAL; 850 while ((tok = strsep(&p, " "))) { 851 char key[16]; 852 char val[21]; /* 18446744073709551616 */ 853 854 if (sscanf(tok, "%15[^=]=%20s", key, val) != 2) 855 goto out; 856 857 if (!strcmp(key, "target")) { 858 u64 v; 859 860 if (!strcmp(val, "max")) 861 lat_val = 0; 862 else if (sscanf(val, "%llu", &v) == 1) 863 lat_val = v * NSEC_PER_USEC; 864 else 865 goto out; 866 } else { 867 goto out; 868 } 869 } 870 871 /* Walk up the tree to see if our new val is lower than it should be. */ 872 blkg = ctx.blkg; 873 oldval = iolat->min_lat_nsec; 874 875 iolatency_set_min_lat_nsec(blkg, lat_val); 876 if (oldval != iolat->min_lat_nsec) 877 iolatency_clear_scaling(blkg); 878 ret = 0; 879out: 880 blkg_conf_finish(&ctx); 881 return ret ?: nbytes; 882} 883 884static u64 iolatency_prfill_limit(struct seq_file *sf, 885 struct blkg_policy_data *pd, int off) 886{ 887 struct iolatency_grp *iolat = pd_to_lat(pd); 888 const char *dname = blkg_dev_name(pd->blkg); 889 890 if (!dname || !iolat->min_lat_nsec) 891 return 0; 892 seq_printf(sf, "%s target=%llu\n", 893 dname, div_u64(iolat->min_lat_nsec, NSEC_PER_USEC)); 894 return 0; 895} 896 897static int iolatency_print_limit(struct seq_file *sf, void *v) 898{ 899 blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)), 900 iolatency_prfill_limit, 901 &blkcg_policy_iolatency, seq_cft(sf)->private, false); 902 return 0; 903} 904 905static size_t iolatency_ssd_stat(struct iolatency_grp *iolat, char *buf, 906 size_t size) 907{ 908 struct latency_stat stat; 909 int cpu; 910 911 latency_stat_init(iolat, &stat); 912 preempt_disable(); 913 for_each_online_cpu(cpu) { 914 struct latency_stat *s; 915 s = per_cpu_ptr(iolat->stats, cpu); 916 latency_stat_sum(iolat, &stat, s); 917 } 918 preempt_enable(); 919 920 if (iolat->rq_depth.max_depth == UINT_MAX) 921 return scnprintf(buf, size, " missed=%llu total=%llu depth=max", 922 (unsigned long long)stat.ps.missed, 923 (unsigned long long)stat.ps.total); 924 return scnprintf(buf, size, " missed=%llu total=%llu depth=%u", 925 (unsigned long long)stat.ps.missed, 926 (unsigned long long)stat.ps.total, 927 iolat->rq_depth.max_depth); 928} 929 930static size_t iolatency_pd_stat(struct blkg_policy_data *pd, char *buf, 931 size_t size) 932{ 933 struct iolatency_grp *iolat = pd_to_lat(pd); 934 unsigned long long avg_lat; 935 unsigned long long cur_win; 936 937 if (!blkcg_debug_stats) 938 return 0; 939 940 if (iolat->ssd) 941 return iolatency_ssd_stat(iolat, buf, size); 942 943 avg_lat = div64_u64(iolat->lat_avg, NSEC_PER_USEC); 944 cur_win = div64_u64(iolat->cur_win_nsec, NSEC_PER_MSEC); 945 if (iolat->rq_depth.max_depth == UINT_MAX) 946 return scnprintf(buf, size, " depth=max avg_lat=%llu win=%llu", 947 avg_lat, cur_win); 948 949 return scnprintf(buf, size, " depth=%u avg_lat=%llu win=%llu", 950 iolat->rq_depth.max_depth, avg_lat, cur_win); 951} 952 953 954static struct blkg_policy_data *iolatency_pd_alloc(gfp_t gfp, 955 struct request_queue *q, 956 struct blkcg *blkcg) 957{ 958 struct iolatency_grp *iolat; 959 960 iolat = kzalloc_node(sizeof(*iolat), gfp, q->node); 961 if (!iolat) 962 return NULL; 963 iolat->stats = __alloc_percpu_gfp(sizeof(struct latency_stat), 964 __alignof__(struct latency_stat), gfp); 965 if (!iolat->stats) { 966 kfree(iolat); 967 return NULL; 968 } 969 return &iolat->pd; 970} 971 972static void iolatency_pd_init(struct blkg_policy_data *pd) 973{ 974 struct iolatency_grp *iolat = pd_to_lat(pd); 975 struct blkcg_gq *blkg = lat_to_blkg(iolat); 976 struct rq_qos *rqos = blkcg_rq_qos(blkg->q); 977 struct blk_iolatency *blkiolat = BLKIOLATENCY(rqos); 978 u64 now = ktime_to_ns(ktime_get()); 979 int cpu; 980 981 if (blk_queue_nonrot(blkg->q)) 982 iolat->ssd = true; 983 else 984 iolat->ssd = false; 985 986 for_each_possible_cpu(cpu) { 987 struct latency_stat *stat; 988 stat = per_cpu_ptr(iolat->stats, cpu); 989 latency_stat_init(iolat, stat); 990 } 991 992 latency_stat_init(iolat, &iolat->cur_stat); 993 rq_wait_init(&iolat->rq_wait); 994 spin_lock_init(&iolat->child_lat.lock); 995 iolat->rq_depth.queue_depth = blkg->q->nr_requests; 996 iolat->rq_depth.max_depth = UINT_MAX; 997 iolat->rq_depth.default_depth = iolat->rq_depth.queue_depth; 998 iolat->blkiolat = blkiolat; 999 iolat->cur_win_nsec = 100 * NSEC_PER_MSEC; 1000 atomic64_set(&iolat->window_start, now); 1001 1002 /* 1003 * We init things in list order, so the pd for the parent may not be 1004 * init'ed yet for whatever reason. 1005 */ 1006 if (blkg->parent && blkg_to_pd(blkg->parent, &blkcg_policy_iolatency)) { 1007 struct iolatency_grp *parent = blkg_to_lat(blkg->parent); 1008 atomic_set(&iolat->scale_cookie, 1009 atomic_read(&parent->child_lat.scale_cookie)); 1010 } else { 1011 atomic_set(&iolat->scale_cookie, DEFAULT_SCALE_COOKIE); 1012 } 1013 1014 atomic_set(&iolat->child_lat.scale_cookie, DEFAULT_SCALE_COOKIE); 1015} 1016 1017static void iolatency_pd_offline(struct blkg_policy_data *pd) 1018{ 1019 struct iolatency_grp *iolat = pd_to_lat(pd); 1020 struct blkcg_gq *blkg = lat_to_blkg(iolat); 1021 1022 iolatency_set_min_lat_nsec(blkg, 0); 1023 iolatency_clear_scaling(blkg); 1024} 1025 1026static void iolatency_pd_free(struct blkg_policy_data *pd) 1027{ 1028 struct iolatency_grp *iolat = pd_to_lat(pd); 1029 free_percpu(iolat->stats); 1030 kfree(iolat); 1031} 1032 1033static struct cftype iolatency_files[] = { 1034 { 1035 .name = "latency", 1036 .flags = CFTYPE_NOT_ON_ROOT, 1037 .seq_show = iolatency_print_limit, 1038 .write = iolatency_set_limit, 1039 }, 1040 {} 1041}; 1042 1043static struct blkcg_policy blkcg_policy_iolatency = { 1044 .dfl_cftypes = iolatency_files, 1045 .pd_alloc_fn = iolatency_pd_alloc, 1046 .pd_init_fn = iolatency_pd_init, 1047 .pd_offline_fn = iolatency_pd_offline, 1048 .pd_free_fn = iolatency_pd_free, 1049 .pd_stat_fn = iolatency_pd_stat, 1050}; 1051 1052static int __init iolatency_init(void) 1053{ 1054 return blkcg_policy_register(&blkcg_policy_iolatency); 1055} 1056 1057static void __exit iolatency_exit(void) 1058{ 1059 blkcg_policy_unregister(&blkcg_policy_iolatency); 1060} 1061 1062module_init(iolatency_init); 1063module_exit(iolatency_exit); 1064