block/blk-iolatency.c

   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);