block/blk-iolatency.c

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

DEFINITIONS
