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