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