block/blk-throttle.c

   1 /*
   2  * Interface for controlling IO bandwidth on a request queue
   3  *
   4  * Copyright (C) 2010 Vivek Goyal <vgoyal@redhat.com>
   5  */
   6
   7 #include <linux/module.h>
   8 #include <linux/slab.h>
   9 #include <linux/blkdev.h>
  10 #include <linux/bio.h>
  11 #include <linux/blktrace_api.h>
  12 #include <linux/blk-cgroup.h>
  13 #include "blk.h"
  14
  15 /* Max dispatch from a group in 1 round */
  16 static int throtl_grp_quantum = 8;
  17
  18 /* Total max dispatch from all groups in one round */
  19 static int throtl_quantum = 32;
  20
  21 /* Throttling is performed over a slice and after that slice is renewed */
  22 #define DFL_THROTL_SLICE_HD (HZ / 10)
  23 #define DFL_THROTL_SLICE_SSD (HZ / 50)
  24 #define MAX_THROTL_SLICE (HZ)
  25 #define MAX_IDLE_TIME (5L * 1000 * 1000) /* 5 s */
  26 #define MIN_THROTL_BPS (320 * 1024)
  27 #define MIN_THROTL_IOPS (10)
  28 #define DFL_LATENCY_TARGET (-1L)
  29 #define DFL_IDLE_THRESHOLD (0)
  30
  31 #define SKIP_LATENCY (((u64)1) << BLK_STAT_RES_SHIFT)
  32
  33 static struct blkcg_policy blkcg_policy_throtl;
  34
  35 /* A workqueue to queue throttle related work */
  36 static struct workqueue_struct *kthrotld_workqueue;
  37
  38 /*
  39  * To implement hierarchical throttling, throtl_grps form a tree and bios
  40  * are dispatched upwards level by level until they reach the top and get
  41  * issued.  When dispatching bios from the children and local group at each
  42  * level, if the bios are dispatched into a single bio_list, there's a risk
  43  * of a local or child group which can queue many bios at once filling up
  44  * the list starving others.
  45  *
  46  * To avoid such starvation, dispatched bios are queued separately
  47  * according to where they came from.  When they are again dispatched to
  48  * the parent, they're popped in round-robin order so that no single source
  49  * hogs the dispatch window.
  50  *
  51  * throtl_qnode is used to keep the queued bios separated by their sources.
  52  * Bios are queued to throtl_qnode which in turn is queued to
  53  * throtl_service_queue and then dispatched in round-robin order.
  54  *
  55  * It's also used to track the reference counts on blkg's.  A qnode always
  56  * belongs to a throtl_grp and gets queued on itself or the parent, so
  57  * incrementing the reference of the associated throtl_grp when a qnode is
  58  * queued and decrementing when dequeued is enough to keep the whole blkg
  59  * tree pinned while bios are in flight.
  60  */
  61 struct throtl_qnode {
  62         struct list_head        node;           /* service_queue->queued[] */
  63         struct bio_list         bios;           /* queued bios */
  64         struct throtl_grp       *tg;            /* tg this qnode belongs to */
  65 };
  66
  67 struct throtl_service_queue {
  68         struct throtl_service_queue *parent_sq; /* the parent service_queue */
  69
  70         /*
  71          * Bios queued directly to this service_queue or dispatched from
  72          * children throtl_grp's.
  73          */
  74         struct list_head        queued[2];      /* throtl_qnode [READ/WRITE] */
  75         unsigned int            nr_queued[2];   /* number of queued bios */
  76
  77         /*
  78          * RB tree of active children throtl_grp's, which are sorted by
  79          * their ->disptime.
  80          */
  81         struct rb_root          pending_tree;   /* RB tree of active tgs */
  82         struct rb_node          *first_pending; /* first node in the tree */
  83         unsigned int            nr_pending;     /* # queued in the tree */
  84         unsigned long           first_pending_disptime; /* disptime of the first tg */
  85         struct timer_list       pending_timer;  /* fires on first_pending_disptime */
  86 };
  87
  88 enum tg_state_flags {
  89         THROTL_TG_PENDING       = 1 << 0,       /* on parent's pending tree */
  90         THROTL_TG_WAS_EMPTY     = 1 << 1,       /* bio_lists[] became non-empty */
  91 };
  92
  93 #define rb_entry_tg(node)       rb_entry((node), struct throtl_grp, rb_node)
  94
  95 enum {
  96         LIMIT_LOW,
  97         LIMIT_MAX,
  98         LIMIT_CNT,
  99 };
 100
 101 struct throtl_grp {
 102         /* must be the first member */
 103         struct blkg_policy_data pd;
 104
 105         /* active throtl group service_queue member */
 106         struct rb_node rb_node;
 107
 108         /* throtl_data this group belongs to */
 109         struct throtl_data *td;
 110
 111         /* this group's service queue */
 112         struct throtl_service_queue service_queue;
 113
 114         /*
 115          * qnode_on_self is used when bios are directly queued to this
 116          * throtl_grp so that local bios compete fairly with bios
 117          * dispatched from children.  qnode_on_parent is used when bios are
 118          * dispatched from this throtl_grp into its parent and will compete
 119          * with the sibling qnode_on_parents and the parent's
 120          * qnode_on_self.
 121          */
 122         struct throtl_qnode qnode_on_self[2];
 123         struct throtl_qnode qnode_on_parent[2];
 124
 125         /*
 126          * Dispatch time in jiffies. This is the estimated time when group
 127          * will unthrottle and is ready to dispatch more bio. It is used as
 128          * key to sort active groups in service tree.
 129          */
 130         unsigned long disptime;
 131
 132         unsigned int flags;
 133
 134         /* are there any throtl rules between this group and td? */
 135         bool has_rules[2];
 136
 137         /* internally used bytes per second rate limits */
 138         uint64_t bps[2][LIMIT_CNT];
 139         /* user configured bps limits */
 140         uint64_t bps_conf[2][LIMIT_CNT];
 141
 142         /* internally used IOPS limits */
 143         unsigned int iops[2][LIMIT_CNT];
 144         /* user configured IOPS limits */
 145         unsigned int iops_conf[2][LIMIT_CNT];
 146
 147         /* Number of bytes disptached in current slice */
 148         uint64_t bytes_disp[2];
 149         /* Number of bio's dispatched in current slice */
 150         unsigned int io_disp[2];
 151
 152         unsigned long last_low_overflow_time[2];
 153
 154         uint64_t last_bytes_disp[2];
 155         unsigned int last_io_disp[2];
 156
 157         unsigned long last_check_time;
 158
 159         unsigned long latency_target; /* us */
 160         unsigned long latency_target_conf; /* us */
 161         /* When did we start a new slice */
 162         unsigned long slice_start[2];
 163         unsigned long slice_end[2];
 164
 165         unsigned long last_finish_time; /* ns / 1024 */
 166         unsigned long checked_last_finish_time; /* ns / 1024 */
 167         unsigned long avg_idletime; /* ns / 1024 */
 168         unsigned long idletime_threshold; /* us */
 169         unsigned long idletime_threshold_conf; /* us */
 170
 171         unsigned int bio_cnt; /* total bios */
 172         unsigned int bad_bio_cnt; /* bios exceeding latency threshold */
 173         unsigned long bio_cnt_reset_time;
 174 };
 175
 176 /* We measure latency for request size from <= 4k to >= 1M */
 177 #define LATENCY_BUCKET_SIZE 9
 178
 179 struct latency_bucket {
 180         unsigned long total_latency; /* ns / 1024 */
 181         int samples;
 182 };
 183
 184 struct avg_latency_bucket {
 185         unsigned long latency; /* ns / 1024 */
 186         bool valid;
 187 };
 188
 189 struct throtl_data
 190 {
 191         /* service tree for active throtl groups */
 192         struct throtl_service_queue service_queue;
 193
 194         struct request_queue *queue;
 195
 196         /* Total Number of queued bios on READ and WRITE lists */
 197         unsigned int nr_queued[2];
 198
 199         unsigned int throtl_slice;
 200
 201         /* Work for dispatching throttled bios */
 202         struct work_struct dispatch_work;
 203         unsigned int limit_index;
 204         bool limit_valid[LIMIT_CNT];
 205
 206         unsigned long low_upgrade_time;
 207         unsigned long low_downgrade_time;
 208
 209         unsigned int scale;
 210
 211         struct latency_bucket tmp_buckets[LATENCY_BUCKET_SIZE];
 212         struct avg_latency_bucket avg_buckets[LATENCY_BUCKET_SIZE];
 213         struct latency_bucket __percpu *latency_buckets;
 214         unsigned long last_calculate_time;
 215
 216         bool track_bio_latency;
 217 };
 218
 219 static void throtl_pending_timer_fn(unsigned long arg);
 220
 221 static inline struct throtl_grp *pd_to_tg(struct blkg_policy_data *pd)
 222 {
 223         return pd ? container_of(pd, struct throtl_grp, pd) : NULL;
 224 }
 225
 226 static inline struct throtl_grp *blkg_to_tg(struct blkcg_gq *blkg)
 227 {
 228         return pd_to_tg(blkg_to_pd(blkg, &blkcg_policy_throtl));
 229 }
 230
 231 static inline struct blkcg_gq *tg_to_blkg(struct throtl_grp *tg)
 232 {
 233         return pd_to_blkg(&tg->pd);
 234 }
 235
 236 /**
 237  * sq_to_tg - return the throl_grp the specified service queue belongs to
 238  * @sq: the throtl_service_queue of interest
 239  *
 240  * Return the throtl_grp @sq belongs to.  If @sq is the top-level one
 241  * embedded in throtl_data, %NULL is returned.
 242  */
 243 static struct throtl_grp *sq_to_tg(struct throtl_service_queue *sq)
 244 {
 245         if (sq && sq->parent_sq)
 246                 return container_of(sq, struct throtl_grp, service_queue);
 247         else
 248                 return NULL;
 249 }
 250
 251 /**
 252  * sq_to_td - return throtl_data the specified service queue belongs to
 253  * @sq: the throtl_service_queue of interest
 254  *
 255  * A service_queue can be embedded in either a throtl_grp or throtl_data.
 256  * Determine the associated throtl_data accordingly and return it.
 257  */
 258 static struct throtl_data *sq_to_td(struct throtl_service_queue *sq)
 259 {
 260         struct throtl_grp *tg = sq_to_tg(sq);
 261
 262         if (tg)
 263                 return tg->td;
 264         else
 265                 return container_of(sq, struct throtl_data, service_queue);
 266 }
 267
 268 /*
 269  * cgroup's limit in LIMIT_MAX is scaled if low limit is set. This scale is to
 270  * make the IO dispatch more smooth.
 271  * Scale up: linearly scale up according to lapsed time since upgrade. For
 272  *           every throtl_slice, the limit scales up 1/2 .low limit till the
 273  *           limit hits .max limit
 274  * Scale down: exponentially scale down if a cgroup doesn't hit its .low limit
 275  */
 276 static uint64_t throtl_adjusted_limit(uint64_t low, struct throtl_data *td)
 277 {
 278         /* arbitrary value to avoid too big scale */
 279         if (td->scale < 4096 && time_after_eq(jiffies,
 280             td->low_upgrade_time + td->scale * td->throtl_slice))
 281                 td->scale = (jiffies - td->low_upgrade_time) / td->throtl_slice;
 282
 283         return low + (low >> 1) * td->scale;
 284 }
 285
 286 static uint64_t tg_bps_limit(struct throtl_grp *tg, int rw)
 287 {
 288         struct blkcg_gq *blkg = tg_to_blkg(tg);
 289         struct throtl_data *td;
 290         uint64_t ret;
 291
 292         if (cgroup_subsys_on_dfl(io_cgrp_subsys) && !blkg->parent)
 293                 return U64_MAX;
 294
 295         td = tg->td;
 296         ret = tg->bps[rw][td->limit_index];
 297         if (ret == 0 && td->limit_index == LIMIT_LOW) {
 298                 /* intermediate node or iops isn't 0 */
 299                 if (!list_empty(&blkg->blkcg->css.children) ||
 300                     tg->iops[rw][td->limit_index])
 301                         return U64_MAX;
 302                 else
 303                         return MIN_THROTL_BPS;
 304         }
 305
 306         if (td->limit_index == LIMIT_MAX && tg->bps[rw][LIMIT_LOW] &&
 307             tg->bps[rw][LIMIT_LOW] != tg->bps[rw][LIMIT_MAX]) {
 308                 uint64_t adjusted;
 309
 310                 adjusted = throtl_adjusted_limit(tg->bps[rw][LIMIT_LOW], td);
 311                 ret = min(tg->bps[rw][LIMIT_MAX], adjusted);
 312         }
 313         return ret;
 314 }
 315
 316 static unsigned int tg_iops_limit(struct throtl_grp *tg, int rw)
 317 {
 318         struct blkcg_gq *blkg = tg_to_blkg(tg);
 319         struct throtl_data *td;
 320         unsigned int ret;
 321
 322         if (cgroup_subsys_on_dfl(io_cgrp_subsys) && !blkg->parent)
 323                 return UINT_MAX;
 324
 325         td = tg->td;
 326         ret = tg->iops[rw][td->limit_index];
 327         if (ret == 0 && tg->td->limit_index == LIMIT_LOW) {
 328                 /* intermediate node or bps isn't 0 */
 329                 if (!list_empty(&blkg->blkcg->css.children) ||
 330                     tg->bps[rw][td->limit_index])
 331                         return UINT_MAX;
 332                 else
 333                         return MIN_THROTL_IOPS;
 334         }
 335
 336         if (td->limit_index == LIMIT_MAX && tg->iops[rw][LIMIT_LOW] &&
 337             tg->iops[rw][LIMIT_LOW] != tg->iops[rw][LIMIT_MAX]) {
 338                 uint64_t adjusted;
 339
 340                 adjusted = throtl_adjusted_limit(tg->iops[rw][LIMIT_LOW], td);
 341                 if (adjusted > UINT_MAX)
 342                         adjusted = UINT_MAX;
 343                 ret = min_t(unsigned int, tg->iops[rw][LIMIT_MAX], adjusted);
 344         }
 345         return ret;
 346 }
 347
 348 #define request_bucket_index(sectors) \
 349         clamp_t(int, order_base_2(sectors) - 3, 0, LATENCY_BUCKET_SIZE - 1)
 350
 351 /**
 352  * throtl_log - log debug message via blktrace
 353  * @sq: the service_queue being reported
 354  * @fmt: printf format string
 355  * @args: printf args
 356  *
 357  * The messages are prefixed with "throtl BLKG_NAME" if @sq belongs to a
 358  * throtl_grp; otherwise, just "throtl".
 359  */
 360 #define throtl_log(sq, fmt, args...)    do {                            \
 361         struct throtl_grp *__tg = sq_to_tg((sq));                       \
 362         struct throtl_data *__td = sq_to_td((sq));                      \
 363                                                                         \
 364         (void)__td;                                                     \
 365         if (likely(!blk_trace_note_message_enabled(__td->queue)))       \
 366                 break;                                                  \
 367         if ((__tg)) {                                                   \
 368                 char __pbuf[128];                                       \
 369                                                                         \
 370                 blkg_path(tg_to_blkg(__tg), __pbuf, sizeof(__pbuf));    \
 371                 blk_add_trace_msg(__td->queue, "throtl %s " fmt, __pbuf, ##args); \
 372         } else {                                                        \
 373                 blk_add_trace_msg(__td->queue, "throtl " fmt, ##args);  \
 374         }                                                               \
 375 } while (0)
 376
 377 static void throtl_qnode_init(struct throtl_qnode *qn, struct throtl_grp *tg)
 378 {
 379         INIT_LIST_HEAD(&qn->node);
 380         bio_list_init(&qn->bios);
 381         qn->tg = tg;
 382 }
 383
 384 /**
 385  * throtl_qnode_add_bio - add a bio to a throtl_qnode and activate it
 386  * @bio: bio being added
 387  * @qn: qnode to add bio to
 388  * @queued: the service_queue->queued[] list @qn belongs to
 389  *
 390  * Add @bio to @qn and put @qn on @queued if it's not already on.
 391  * @qn->tg's reference count is bumped when @qn is activated.  See the
 392  * comment on top of throtl_qnode definition for details.
 393  */
 394 static void throtl_qnode_add_bio(struct bio *bio, struct throtl_qnode *qn,
 395                                  struct list_head *queued)
 396 {
 397         bio_list_add(&qn->bios, bio);
 398         if (list_empty(&qn->node)) {
 399                 list_add_tail(&qn->node, queued);
 400                 blkg_get(tg_to_blkg(qn->tg));
 401         }
 402 }
 403
 404 /**
 405  * throtl_peek_queued - peek the first bio on a qnode list
 406  * @queued: the qnode list to peek
 407  */
 408 static struct bio *throtl_peek_queued(struct list_head *queued)
 409 {
 410         struct throtl_qnode *qn = list_first_entry(queued, struct throtl_qnode, node);
 411         struct bio *bio;
 412
 413         if (list_empty(queued))
 414                 return NULL;
 415
 416         bio = bio_list_peek(&qn->bios);
 417         WARN_ON_ONCE(!bio);
 418         return bio;
 419 }
 420
 421 /**
 422  * throtl_pop_queued - pop the first bio form a qnode list
 423  * @queued: the qnode list to pop a bio from
 424  * @tg_to_put: optional out argument for throtl_grp to put
 425  *
 426  * Pop the first bio from the qnode list @queued.  After popping, the first
 427  * qnode is removed from @queued if empty or moved to the end of @queued so
 428  * that the popping order is round-robin.
 429  *
 430  * When the first qnode is removed, its associated throtl_grp should be put
 431  * too.  If @tg_to_put is NULL, this function automatically puts it;
 432  * otherwise, *@tg_to_put is set to the throtl_grp to put and the caller is
 433  * responsible for putting it.
 434  */
 435 static struct bio *throtl_pop_queued(struct list_head *queued,
 436                                      struct throtl_grp **tg_to_put)
 437 {
 438         struct throtl_qnode *qn = list_first_entry(queued, struct throtl_qnode, node);
 439         struct bio *bio;
 440
 441         if (list_empty(queued))
 442                 return NULL;
 443
 444         bio = bio_list_pop(&qn->bios);
 445         WARN_ON_ONCE(!bio);
 446
 447         if (bio_list_empty(&qn->bios)) {
 448                 list_del_init(&qn->node);
 449                 if (tg_to_put)
 450                         *tg_to_put = qn->tg;
 451                 else
 452                         blkg_put(tg_to_blkg(qn->tg));
 453         } else {
 454                 list_move_tail(&qn->node, queued);
 455         }
 456
 457         return bio;
 458 }
 459
 460 /* init a service_queue, assumes the caller zeroed it */
 461 static void throtl_service_queue_init(struct throtl_service_queue *sq)
 462 {
 463         INIT_LIST_HEAD(&sq->queued[0]);
 464         INIT_LIST_HEAD(&sq->queued[1]);
 465         sq->pending_tree = RB_ROOT;
 466         setup_timer(&sq->pending_timer, throtl_pending_timer_fn,
 467                     (unsigned long)sq);
 468 }
 469
 470 static struct blkg_policy_data *throtl_pd_alloc(gfp_t gfp, int node)
 471 {
 472         struct throtl_grp *tg;
 473         int rw;
 474
 475         tg = kzalloc_node(sizeof(*tg), gfp, node);
 476         if (!tg)
 477                 return NULL;
 478
 479         throtl_service_queue_init(&tg->service_queue);
 480
 481         for (rw = READ; rw <= WRITE; rw++) {
 482                 throtl_qnode_init(&tg->qnode_on_self[rw], tg);
 483                 throtl_qnode_init(&tg->qnode_on_parent[rw], tg);
 484         }
 485
 486         RB_CLEAR_NODE(&tg->rb_node);
 487         tg->bps[READ][LIMIT_MAX] = U64_MAX;
 488         tg->bps[WRITE][LIMIT_MAX] = U64_MAX;
 489         tg->iops[READ][LIMIT_MAX] = UINT_MAX;
 490         tg->iops[WRITE][LIMIT_MAX] = UINT_MAX;
 491         tg->bps_conf[READ][LIMIT_MAX] = U64_MAX;
 492         tg->bps_conf[WRITE][LIMIT_MAX] = U64_MAX;
 493         tg->iops_conf[READ][LIMIT_MAX] = UINT_MAX;
 494         tg->iops_conf[WRITE][LIMIT_MAX] = UINT_MAX;
 495         /* LIMIT_LOW will have default value 0 */
 496
 497         tg->latency_target = DFL_LATENCY_TARGET;
 498         tg->latency_target_conf = DFL_LATENCY_TARGET;
 499         tg->idletime_threshold = DFL_IDLE_THRESHOLD;
 500         tg->idletime_threshold_conf = DFL_IDLE_THRESHOLD;
 501
 502         return &tg->pd;
 503 }
 504
 505 static void throtl_pd_init(struct blkg_policy_data *pd)
 506 {
 507         struct throtl_grp *tg = pd_to_tg(pd);
 508         struct blkcg_gq *blkg = tg_to_blkg(tg);
 509         struct throtl_data *td = blkg->q->td;
 510         struct throtl_service_queue *sq = &tg->service_queue;
 511
 512         /*
 513          * If on the default hierarchy, we switch to properly hierarchical
 514          * behavior where limits on a given throtl_grp are applied to the
 515          * whole subtree rather than just the group itself.  e.g. If 16M
 516          * read_bps limit is set on the root group, the whole system can't
 517          * exceed 16M for the device.
 518          *
 519          * If not on the default hierarchy, the broken flat hierarchy
 520          * behavior is retained where all throtl_grps are treated as if
 521          * they're all separate root groups right below throtl_data.
 522          * Limits of a group don't interact with limits of other groups
 523          * regardless of the position of the group in the hierarchy.
 524          */
 525         sq->parent_sq = &td->service_queue;
 526         if (cgroup_subsys_on_dfl(io_cgrp_subsys) && blkg->parent)
 527                 sq->parent_sq = &blkg_to_tg(blkg->parent)->service_queue;
 528         tg->td = td;
 529 }
 530
 531 /*
 532  * Set has_rules[] if @tg or any of its parents have limits configured.
 533  * This doesn't require walking up to the top of the hierarchy as the
 534  * parent's has_rules[] is guaranteed to be correct.
 535  */
 536 static void tg_update_has_rules(struct throtl_grp *tg)
 537 {
 538         struct throtl_grp *parent_tg = sq_to_tg(tg->service_queue.parent_sq);
 539         struct throtl_data *td = tg->td;
 540         int rw;
 541
 542         for (rw = READ; rw <= WRITE; rw++)
 543                 tg->has_rules[rw] = (parent_tg && parent_tg->has_rules[rw]) ||
 544                         (td->limit_valid[td->limit_index] &&
 545                          (tg_bps_limit(tg, rw) != U64_MAX ||
 546                           tg_iops_limit(tg, rw) != UINT_MAX));
 547 }
 548
 549 static void throtl_pd_online(struct blkg_policy_data *pd)
 550 {
 551         struct throtl_grp *tg = pd_to_tg(pd);
 552         /*
 553          * We don't want new groups to escape the limits of its ancestors.
 554          * Update has_rules[] after a new group is brought online.
 555          */
 556         tg_update_has_rules(tg);
 557 }
 558
 559 static void blk_throtl_update_limit_valid(struct throtl_data *td)
 560 {
 561         struct cgroup_subsys_state *pos_css;
 562         struct blkcg_gq *blkg;
 563         bool low_valid = false;
 564
 565         rcu_read_lock();
 566         blkg_for_each_descendant_post(blkg, pos_css, td->queue->root_blkg) {
 567                 struct throtl_grp *tg = blkg_to_tg(blkg);
 568
 569                 if (tg->bps[READ][LIMIT_LOW] || tg->bps[WRITE][LIMIT_LOW] ||
 570                     tg->iops[READ][LIMIT_LOW] || tg->iops[WRITE][LIMIT_LOW])
 571                         low_valid = true;
 572         }
 573         rcu_read_unlock();
 574
 575         td->limit_valid[LIMIT_LOW] = low_valid;
 576 }
 577
 578 static void throtl_upgrade_state(struct throtl_data *td);
 579 static void throtl_pd_offline(struct blkg_policy_data *pd)
 580 {
 581         struct throtl_grp *tg = pd_to_tg(pd);
 582
 583         tg->bps[READ][LIMIT_LOW] = 0;
 584         tg->bps[WRITE][LIMIT_LOW] = 0;
 585         tg->iops[READ][LIMIT_LOW] = 0;
 586         tg->iops[WRITE][LIMIT_LOW] = 0;
 587
 588         blk_throtl_update_limit_valid(tg->td);
 589
 590         if (!tg->td->limit_valid[tg->td->limit_index])
 591                 throtl_upgrade_state(tg->td);
 592 }
 593
 594 static void throtl_pd_free(struct blkg_policy_data *pd)
 595 {
 596         struct throtl_grp *tg = pd_to_tg(pd);
 597
 598         del_timer_sync(&tg->service_queue.pending_timer);
 599         kfree(tg);
 600 }
 601
 602 static struct throtl_grp *
 603 throtl_rb_first(struct throtl_service_queue *parent_sq)
 604 {
 605         /* Service tree is empty */
 606         if (!parent_sq->nr_pending)
 607                 return NULL;
 608
 609         if (!parent_sq->first_pending)
 610                 parent_sq->first_pending = rb_first(&parent_sq->pending_tree);
 611
 612         if (parent_sq->first_pending)
 613                 return rb_entry_tg(parent_sq->first_pending);
 614
 615         return NULL;
 616 }
 617
 618 static void rb_erase_init(struct rb_node *n, struct rb_root *root)
 619 {
 620         rb_erase(n, root);
 621         RB_CLEAR_NODE(n);
 622 }
 623
 624 static void throtl_rb_erase(struct rb_node *n,
 625                             struct throtl_service_queue *parent_sq)
 626 {
 627         if (parent_sq->first_pending == n)
 628                 parent_sq->first_pending = NULL;
 629         rb_erase_init(n, &parent_sq->pending_tree);
 630         --parent_sq->nr_pending;
 631 }
 632
 633 static void update_min_dispatch_time(struct throtl_service_queue *parent_sq)
 634 {
 635         struct throtl_grp *tg;
 636
 637         tg = throtl_rb_first(parent_sq);
 638         if (!tg)
 639                 return;
 640
 641         parent_sq->first_pending_disptime = tg->disptime;
 642 }
 643
 644 static void tg_service_queue_add(struct throtl_grp *tg)
 645 {
 646         struct throtl_service_queue *parent_sq = tg->service_queue.parent_sq;
 647         struct rb_node **node = &parent_sq->pending_tree.rb_node;
 648         struct rb_node *parent = NULL;
 649         struct throtl_grp *__tg;
 650         unsigned long key = tg->disptime;
 651         int left = 1;
 652
 653         while (*node != NULL) {
 654                 parent = *node;
 655                 __tg = rb_entry_tg(parent);
 656
 657                 if (time_before(key, __tg->disptime))
 658                         node = &parent->rb_left;
 659                 else {
 660                         node = &parent->rb_right;
 661                         left = 0;
 662                 }
 663         }
 664
 665         if (left)
 666                 parent_sq->first_pending = &tg->rb_node;
 667
 668         rb_link_node(&tg->rb_node, parent, node);
 669         rb_insert_color(&tg->rb_node, &parent_sq->pending_tree);
 670 }
 671
 672 static void __throtl_enqueue_tg(struct throtl_grp *tg)
 673 {
 674         tg_service_queue_add(tg);
 675         tg->flags |= THROTL_TG_PENDING;
 676         tg->service_queue.parent_sq->nr_pending++;
 677 }
 678
 679 static void throtl_enqueue_tg(struct throtl_grp *tg)
 680 {
 681         if (!(tg->flags & THROTL_TG_PENDING))
 682                 __throtl_enqueue_tg(tg);
 683 }
 684
 685 static void __throtl_dequeue_tg(struct throtl_grp *tg)
 686 {
 687         throtl_rb_erase(&tg->rb_node, tg->service_queue.parent_sq);
 688         tg->flags &= ~THROTL_TG_PENDING;
 689 }
 690
 691 static void throtl_dequeue_tg(struct throtl_grp *tg)
 692 {
 693         if (tg->flags & THROTL_TG_PENDING)
 694                 __throtl_dequeue_tg(tg);
 695 }
 696
 697 /* Call with queue lock held */
 698 static void throtl_schedule_pending_timer(struct throtl_service_queue *sq,
 699                                           unsigned long expires)
 700 {
 701         unsigned long max_expire = jiffies + 8 * sq_to_tg(sq)->td->throtl_slice;
 702
 703         /*
 704          * Since we are adjusting the throttle limit dynamically, the sleep
 705          * time calculated according to previous limit might be invalid. It's
 706          * possible the cgroup sleep time is very long and no other cgroups
 707          * have IO running so notify the limit changes. Make sure the cgroup
 708          * doesn't sleep too long to avoid the missed notification.
 709          */
 710         if (time_after(expires, max_expire))
 711                 expires = max_expire;
 712         mod_timer(&sq->pending_timer, expires);
 713         throtl_log(sq, "schedule timer. delay=%lu jiffies=%lu",
 714                    expires - jiffies, jiffies);
 715 }
 716
 717 /**
 718  * throtl_schedule_next_dispatch - schedule the next dispatch cycle
 719  * @sq: the service_queue to schedule dispatch for
 720  * @force: force scheduling
 721  *
 722  * Arm @sq->pending_timer so that the next dispatch cycle starts on the
 723  * dispatch time of the first pending child.  Returns %true if either timer
 724  * is armed or there's no pending child left.  %false if the current
 725  * dispatch window is still open and the caller should continue
 726  * dispatching.
 727  *
 728  * If @force is %true, the dispatch timer is always scheduled and this
 729  * function is guaranteed to return %true.  This is to be used when the
 730  * caller can't dispatch itself and needs to invoke pending_timer
 731  * unconditionally.  Note that forced scheduling is likely to induce short
 732  * delay before dispatch starts even if @sq->first_pending_disptime is not
 733  * in the future and thus shouldn't be used in hot paths.
 734  */
 735 static bool throtl_schedule_next_dispatch(struct throtl_service_queue *sq,
 736                                           bool force)
 737 {
 738         /* any pending children left? */
 739         if (!sq->nr_pending)
 740                 return true;
 741
 742         update_min_dispatch_time(sq);
 743
 744         /* is the next dispatch time in the future? */
 745         if (force || time_after(sq->first_pending_disptime, jiffies)) {
 746                 throtl_schedule_pending_timer(sq, sq->first_pending_disptime);
 747                 return true;
 748         }
 749
 750         /* tell the caller to continue dispatching */
 751         return false;
 752 }
 753
 754 static inline void throtl_start_new_slice_with_credit(struct throtl_grp *tg,
 755                 bool rw, unsigned long start)
 756 {
 757         tg->bytes_disp[rw] = 0;
 758         tg->io_disp[rw] = 0;
 759
 760         /*
 761          * Previous slice has expired. We must have trimmed it after last
 762          * bio dispatch. That means since start of last slice, we never used
 763          * that bandwidth. Do try to make use of that bandwidth while giving
 764          * credit.
 765          */
 766         if (time_after_eq(start, tg->slice_start[rw]))
 767                 tg->slice_start[rw] = start;
 768
 769         tg->slice_end[rw] = jiffies + tg->td->throtl_slice;
 770         throtl_log(&tg->service_queue,
 771                    "[%c] new slice with credit start=%lu end=%lu jiffies=%lu",
 772                    rw == READ ? 'R' : 'W', tg->slice_start[rw],
 773                    tg->slice_end[rw], jiffies);
 774 }
 775
 776 static inline void throtl_start_new_slice(struct throtl_grp *tg, bool rw)
 777 {
 778         tg->bytes_disp[rw] = 0;
 779         tg->io_disp[rw] = 0;
 780         tg->slice_start[rw] = jiffies;
 781         tg->slice_end[rw] = jiffies + tg->td->throtl_slice;
 782         throtl_log(&tg->service_queue,
 783                    "[%c] new slice start=%lu end=%lu jiffies=%lu",
 784                    rw == READ ? 'R' : 'W', tg->slice_start[rw],
 785                    tg->slice_end[rw], jiffies);
 786 }
 787
 788 static inline void throtl_set_slice_end(struct throtl_grp *tg, bool rw,
 789                                         unsigned long jiffy_end)
 790 {
 791         tg->slice_end[rw] = roundup(jiffy_end, tg->td->throtl_slice);
 792 }
 793
 794 static inline void throtl_extend_slice(struct throtl_grp *tg, bool rw,
 795                                        unsigned long jiffy_end)
 796 {
 797         tg->slice_end[rw] = roundup(jiffy_end, tg->td->throtl_slice);
 798         throtl_log(&tg->service_queue,
 799                    "[%c] extend slice start=%lu end=%lu jiffies=%lu",
 800                    rw == READ ? 'R' : 'W', tg->slice_start[rw],
 801                    tg->slice_end[rw], jiffies);
 802 }
 803
 804 /* Determine if previously allocated or extended slice is complete or not */
 805 static bool throtl_slice_used(struct throtl_grp *tg, bool rw)
 806 {
 807         if (time_in_range(jiffies, tg->slice_start[rw], tg->slice_end[rw]))
 808                 return false;
 809
 810         return 1;
 811 }
 812
 813 /* Trim the used slices and adjust slice start accordingly */
 814 static inline void throtl_trim_slice(struct throtl_grp *tg, bool rw)
 815 {
 816         unsigned long nr_slices, time_elapsed, io_trim;
 817         u64 bytes_trim, tmp;
 818
 819         BUG_ON(time_before(tg->slice_end[rw], tg->slice_start[rw]));
 820
 821         /*
 822          * If bps are unlimited (-1), then time slice don't get
 823          * renewed. Don't try to trim the slice if slice is used. A new
 824          * slice will start when appropriate.
 825          */
 826         if (throtl_slice_used(tg, rw))
 827                 return;
 828
 829         /*
 830          * A bio has been dispatched. Also adjust slice_end. It might happen
 831          * that initially cgroup limit was very low resulting in high
 832          * slice_end, but later limit was bumped up and bio was dispached
 833          * sooner, then we need to reduce slice_end. A high bogus slice_end
 834          * is bad because it does not allow new slice to start.
 835          */
 836
 837         throtl_set_slice_end(tg, rw, jiffies + tg->td->throtl_slice);
 838
 839         time_elapsed = jiffies - tg->slice_start[rw];
 840
 841         nr_slices = time_elapsed / tg->td->throtl_slice;
 842
 843         if (!nr_slices)
 844                 return;
 845         tmp = tg_bps_limit(tg, rw) * tg->td->throtl_slice * nr_slices;
 846         do_div(tmp, HZ);
 847         bytes_trim = tmp;
 848
 849         io_trim = (tg_iops_limit(tg, rw) * tg->td->throtl_slice * nr_slices) /
 850                 HZ;
 851
 852         if (!bytes_trim && !io_trim)
 853                 return;
 854
 855         if (tg->bytes_disp[rw] >= bytes_trim)
 856                 tg->bytes_disp[rw] -= bytes_trim;
 857         else
 858                 tg->bytes_disp[rw] = 0;
 859
 860         if (tg->io_disp[rw] >= io_trim)
 861                 tg->io_disp[rw] -= io_trim;
 862         else
 863                 tg->io_disp[rw] = 0;
 864
 865         tg->slice_start[rw] += nr_slices * tg->td->throtl_slice;
 866
 867         throtl_log(&tg->service_queue,
 868                    "[%c] trim slice nr=%lu bytes=%llu io=%lu start=%lu end=%lu jiffies=%lu",
 869                    rw == READ ? 'R' : 'W', nr_slices, bytes_trim, io_trim,
 870                    tg->slice_start[rw], tg->slice_end[rw], jiffies);
 871 }
 872
 873 static bool tg_with_in_iops_limit(struct throtl_grp *tg, struct bio *bio,
 874                                   unsigned long *wait)
 875 {
 876         bool rw = bio_data_dir(bio);
 877         unsigned int io_allowed;
 878         unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd;
 879         u64 tmp;
 880
 881         jiffy_elapsed = jiffy_elapsed_rnd = jiffies - tg->slice_start[rw];
 882
 883         /* Slice has just started. Consider one slice interval */
 884         if (!jiffy_elapsed)
 885                 jiffy_elapsed_rnd = tg->td->throtl_slice;
 886
 887         jiffy_elapsed_rnd = roundup(jiffy_elapsed_rnd, tg->td->throtl_slice);
 888
 889         /*
 890          * jiffy_elapsed_rnd should not be a big value as minimum iops can be
 891          * 1 then at max jiffy elapsed should be equivalent of 1 second as we
 892          * will allow dispatch after 1 second and after that slice should
 893          * have been trimmed.
 894          */
 895
 896         tmp = (u64)tg_iops_limit(tg, rw) * jiffy_elapsed_rnd;
 897         do_div(tmp, HZ);
 898
 899         if (tmp > UINT_MAX)
 900                 io_allowed = UINT_MAX;
 901         else
 902                 io_allowed = tmp;
 903
 904         if (tg->io_disp[rw] + 1 <= io_allowed) {
 905                 if (wait)
 906                         *wait = 0;
 907                 return true;
 908         }
 909
 910         /* Calc approx time to dispatch */
 911         jiffy_wait = ((tg->io_disp[rw] + 1) * HZ) / tg_iops_limit(tg, rw) + 1;
 912
 913         if (jiffy_wait > jiffy_elapsed)
 914                 jiffy_wait = jiffy_wait - jiffy_elapsed;
 915         else
 916                 jiffy_wait = 1;
 917
 918         if (wait)
 919                 *wait = jiffy_wait;
 920         return 0;
 921 }
 922
 923 static bool tg_with_in_bps_limit(struct throtl_grp *tg, struct bio *bio,
 924                                  unsigned long *wait)
 925 {
 926         bool rw = bio_data_dir(bio);
 927         u64 bytes_allowed, extra_bytes, tmp;
 928         unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd;
 929
 930         jiffy_elapsed = jiffy_elapsed_rnd = jiffies - tg->slice_start[rw];
 931
 932         /* Slice has just started. Consider one slice interval */
 933         if (!jiffy_elapsed)
 934                 jiffy_elapsed_rnd = tg->td->throtl_slice;
 935
 936         jiffy_elapsed_rnd = roundup(jiffy_elapsed_rnd, tg->td->throtl_slice);
 937
 938         tmp = tg_bps_limit(tg, rw) * jiffy_elapsed_rnd;
 939         do_div(tmp, HZ);
 940         bytes_allowed = tmp;
 941
 942         if (tg->bytes_disp[rw] + bio->bi_iter.bi_size <= bytes_allowed) {
 943                 if (wait)
 944                         *wait = 0;
 945                 return true;
 946         }
 947
 948         /* Calc approx time to dispatch */
 949         extra_bytes = tg->bytes_disp[rw] + bio->bi_iter.bi_size - bytes_allowed;
 950         jiffy_wait = div64_u64(extra_bytes * HZ, tg_bps_limit(tg, rw));
 951
 952         if (!jiffy_wait)
 953                 jiffy_wait = 1;
 954
 955         /*
 956          * This wait time is without taking into consideration the rounding
 957          * up we did. Add that time also.
 958          */
 959         jiffy_wait = jiffy_wait + (jiffy_elapsed_rnd - jiffy_elapsed);
 960         if (wait)
 961                 *wait = jiffy_wait;
 962         return 0;
 963 }
 964
 965 /*
 966  * Returns whether one can dispatch a bio or not. Also returns approx number
 967  * of jiffies to wait before this bio is with-in IO rate and can be dispatched
 968  */
 969 static bool tg_may_dispatch(struct throtl_grp *tg, struct bio *bio,
 970                             unsigned long *wait)
 971 {
 972         bool rw = bio_data_dir(bio);
 973         unsigned long bps_wait = 0, iops_wait = 0, max_wait = 0;
 974
 975         /*
 976          * Currently whole state machine of group depends on first bio
 977          * queued in the group bio list. So one should not be calling
 978          * this function with a different bio if there are other bios
 979          * queued.
 980          */
 981         BUG_ON(tg->service_queue.nr_queued[rw] &&
 982                bio != throtl_peek_queued(&tg->service_queue.queued[rw]));
 983
 984         /* If tg->bps = -1, then BW is unlimited */
 985         if (tg_bps_limit(tg, rw) == U64_MAX &&
 986             tg_iops_limit(tg, rw) == UINT_MAX) {
 987                 if (wait)
 988                         *wait = 0;
 989                 return true;
 990         }
 991
 992         /*
 993          * If previous slice expired, start a new one otherwise renew/extend
 994          * existing slice to make sure it is at least throtl_slice interval
 995          * long since now. New slice is started only for empty throttle group.
 996          * If there is queued bio, that means there should be an active
 997          * slice and it should be extended instead.
 998          */
 999         if (throtl_slice_used(tg, rw) && !(tg->service_queue.nr_queued[rw]))
1000                 throtl_start_new_slice(tg, rw);
1001         else {
1002                 if (time_before(tg->slice_end[rw],
1003                     jiffies + tg->td->throtl_slice))
1004                         throtl_extend_slice(tg, rw,
1005                                 jiffies + tg->td->throtl_slice);
1006         }
1007
1008         if (tg_with_in_bps_limit(tg, bio, &bps_wait) &&
1009             tg_with_in_iops_limit(tg, bio, &iops_wait)) {
1010                 if (wait)
1011                         *wait = 0;
1012                 return 1;
1013         }
1014
1015         max_wait = max(bps_wait, iops_wait);
1016
1017         if (wait)
1018                 *wait = max_wait;
1019
1020         if (time_before(tg->slice_end[rw], jiffies + max_wait))
1021                 throtl_extend_slice(tg, rw, jiffies + max_wait);
1022
1023         return 0;
1024 }
1025
1026 static void throtl_charge_bio(struct throtl_grp *tg, struct bio *bio)
1027 {
1028         bool rw = bio_data_dir(bio);
1029
1030         /* Charge the bio to the group */
1031         tg->bytes_disp[rw] += bio->bi_iter.bi_size;
1032         tg->io_disp[rw]++;
1033         tg->last_bytes_disp[rw] += bio->bi_iter.bi_size;
1034         tg->last_io_disp[rw]++;
1035
1036         /*
1037          * BIO_THROTTLED is used to prevent the same bio to be throttled
1038          * more than once as a throttled bio will go through blk-throtl the
1039          * second time when it eventually gets issued.  Set it when a bio
1040          * is being charged to a tg.
1041          */
1042         if (!bio_flagged(bio, BIO_THROTTLED))
1043                 bio_set_flag(bio, BIO_THROTTLED);
1044 }
1045
1046 /**
1047  * throtl_add_bio_tg - add a bio to the specified throtl_grp
1048  * @bio: bio to add
1049  * @qn: qnode to use
1050  * @tg: the target throtl_grp
1051  *
1052  * Add @bio to @tg's service_queue using @qn.  If @qn is not specified,
1053  * tg->qnode_on_self[] is used.
1054  */
1055 static void throtl_add_bio_tg(struct bio *bio, struct throtl_qnode *qn,
1056                               struct throtl_grp *tg)
1057 {
1058         struct throtl_service_queue *sq = &tg->service_queue;
1059         bool rw = bio_data_dir(bio);
1060
1061         if (!qn)
1062                 qn = &tg->qnode_on_self[rw];
1063
1064         /*
1065          * If @tg doesn't currently have any bios queued in the same
1066          * direction, queueing @bio can change when @tg should be
1067          * dispatched.  Mark that @tg was empty.  This is automatically
1068          * cleaered on the next tg_update_disptime().
1069          */
1070         if (!sq->nr_queued[rw])
1071                 tg->flags |= THROTL_TG_WAS_EMPTY;
1072
1073         throtl_qnode_add_bio(bio, qn, &sq->queued[rw]);
1074
1075         sq->nr_queued[rw]++;
1076         throtl_enqueue_tg(tg);
1077 }
1078
1079 static void tg_update_disptime(struct throtl_grp *tg)
1080 {
1081         struct throtl_service_queue *sq = &tg->service_queue;
1082         unsigned long read_wait = -1, write_wait = -1, min_wait = -1, disptime;
1083         struct bio *bio;
1084
1085         bio = throtl_peek_queued(&sq->queued[READ]);
1086         if (bio)
1087                 tg_may_dispatch(tg, bio, &read_wait);
1088
1089         bio = throtl_peek_queued(&sq->queued[WRITE]);
1090         if (bio)
1091                 tg_may_dispatch(tg, bio, &write_wait);
1092
1093         min_wait = min(read_wait, write_wait);
1094         disptime = jiffies + min_wait;
1095
1096         /* Update dispatch time */
1097         throtl_dequeue_tg(tg);
1098         tg->disptime = disptime;
1099         throtl_enqueue_tg(tg);
1100
1101         /* see throtl_add_bio_tg() */
1102         tg->flags &= ~THROTL_TG_WAS_EMPTY;
1103 }
1104
1105 static void start_parent_slice_with_credit(struct throtl_grp *child_tg,
1106                                         struct throtl_grp *parent_tg, bool rw)
1107 {
1108         if (throtl_slice_used(parent_tg, rw)) {
1109                 throtl_start_new_slice_with_credit(parent_tg, rw,
1110                                 child_tg->slice_start[rw]);
1111         }
1112
1113 }
1114
1115 static void tg_dispatch_one_bio(struct throtl_grp *tg, bool rw)
1116 {
1117         struct throtl_service_queue *sq = &tg->service_queue;
1118         struct throtl_service_queue *parent_sq = sq->parent_sq;
1119         struct throtl_grp *parent_tg = sq_to_tg(parent_sq);
1120         struct throtl_grp *tg_to_put = NULL;
1121         struct bio *bio;
1122
1123         /*
1124          * @bio is being transferred from @tg to @parent_sq.  Popping a bio
1125          * from @tg may put its reference and @parent_sq might end up
1126          * getting released prematurely.  Remember the tg to put and put it
1127          * after @bio is transferred to @parent_sq.
1128          */
1129         bio = throtl_pop_queued(&sq->queued[rw], &tg_to_put);
1130         sq->nr_queued[rw]--;
1131
1132         throtl_charge_bio(tg, bio);
1133
1134         /*
1135          * If our parent is another tg, we just need to transfer @bio to
1136          * the parent using throtl_add_bio_tg().  If our parent is
1137          * @td->service_queue, @bio is ready to be issued.  Put it on its
1138          * bio_lists[] and decrease total number queued.  The caller is
1139          * responsible for issuing these bios.
1140          */
1141         if (parent_tg) {
1142                 throtl_add_bio_tg(bio, &tg->qnode_on_parent[rw], parent_tg);
1143                 start_parent_slice_with_credit(tg, parent_tg, rw);
1144         } else {
1145                 throtl_qnode_add_bio(bio, &tg->qnode_on_parent[rw],
1146                                      &parent_sq->queued[rw]);
1147                 BUG_ON(tg->td->nr_queued[rw] <= 0);
1148                 tg->td->nr_queued[rw]--;
1149         }
1150
1151         throtl_trim_slice(tg, rw);
1152
1153         if (tg_to_put)
1154                 blkg_put(tg_to_blkg(tg_to_put));
1155 }
1156
1157 static int throtl_dispatch_tg(struct throtl_grp *tg)
1158 {
1159         struct throtl_service_queue *sq = &tg->service_queue;
1160         unsigned int nr_reads = 0, nr_writes = 0;
1161         unsigned int max_nr_reads = throtl_grp_quantum*3/4;
1162         unsigned int max_nr_writes = throtl_grp_quantum - max_nr_reads;
1163         struct bio *bio;
1164
1165         /* Try to dispatch 75% READS and 25% WRITES */
1166
1167         while ((bio = throtl_peek_queued(&sq->queued[READ])) &&
1168                tg_may_dispatch(tg, bio, NULL)) {
1169
1170                 tg_dispatch_one_bio(tg, bio_data_dir(bio));
1171                 nr_reads++;
1172
1173                 if (nr_reads >= max_nr_reads)
1174                         break;
1175         }
1176
1177         while ((bio = throtl_peek_queued(&sq->queued[WRITE])) &&
1178                tg_may_dispatch(tg, bio, NULL)) {
1179
1180                 tg_dispatch_one_bio(tg, bio_data_dir(bio));
1181                 nr_writes++;
1182
1183                 if (nr_writes >= max_nr_writes)
1184                         break;
1185         }
1186
1187         return nr_reads + nr_writes;
1188 }
1189
1190 static int throtl_select_dispatch(struct throtl_service_queue *parent_sq)
1191 {
1192         unsigned int nr_disp = 0;
1193
1194         while (1) {
1195                 struct throtl_grp *tg = throtl_rb_first(parent_sq);
1196                 struct throtl_service_queue *sq = &tg->service_queue;
1197
1198                 if (!tg)
1199                         break;
1200
1201                 if (time_before(jiffies, tg->disptime))
1202                         break;
1203
1204                 throtl_dequeue_tg(tg);
1205
1206                 nr_disp += throtl_dispatch_tg(tg);
1207
1208                 if (sq->nr_queued[0] || sq->nr_queued[1])
1209                         tg_update_disptime(tg);
1210
1211                 if (nr_disp >= throtl_quantum)
1212                         break;
1213         }
1214
1215         return nr_disp;
1216 }
1217
1218 static bool throtl_can_upgrade(struct throtl_data *td,
1219         struct throtl_grp *this_tg);
1220 /**
1221  * throtl_pending_timer_fn - timer function for service_queue->pending_timer
1222  * @arg: the throtl_service_queue being serviced
1223  *
1224  * This timer is armed when a child throtl_grp with active bio's become
1225  * pending and queued on the service_queue's pending_tree and expires when
1226  * the first child throtl_grp should be dispatched.  This function
1227  * dispatches bio's from the children throtl_grps to the parent
1228  * service_queue.
1229  *
1230  * If the parent's parent is another throtl_grp, dispatching is propagated
1231  * by either arming its pending_timer or repeating dispatch directly.  If
1232  * the top-level service_tree is reached, throtl_data->dispatch_work is
1233  * kicked so that the ready bio's are issued.
1234  */
1235 static void throtl_pending_timer_fn(unsigned long arg)
1236 {
1237         struct throtl_service_queue *sq = (void *)arg;
1238         struct throtl_grp *tg = sq_to_tg(sq);
1239         struct throtl_data *td = sq_to_td(sq);
1240         struct request_queue *q = td->queue;
1241         struct throtl_service_queue *parent_sq;
1242         bool dispatched;
1243         int ret;
1244
1245         spin_lock_irq(q->queue_lock);
1246         if (throtl_can_upgrade(td, NULL))
1247                 throtl_upgrade_state(td);
1248
1249 again:
1250         parent_sq = sq->parent_sq;
1251         dispatched = false;
1252
1253         while (true) {
1254                 throtl_log(sq, "dispatch nr_queued=%u read=%u write=%u",
1255                            sq->nr_queued[READ] + sq->nr_queued[WRITE],
1256                            sq->nr_queued[READ], sq->nr_queued[WRITE]);
1257
1258                 ret = throtl_select_dispatch(sq);
1259                 if (ret) {
1260                         throtl_log(sq, "bios disp=%u", ret);
1261                         dispatched = true;
1262                 }
1263
1264                 if (throtl_schedule_next_dispatch(sq, false))
1265                         break;
1266
1267                 /* this dispatch windows is still open, relax and repeat */
1268                 spin_unlock_irq(q->queue_lock);
1269                 cpu_relax();
1270                 spin_lock_irq(q->queue_lock);
1271         }
1272
1273         if (!dispatched)
1274                 goto out_unlock;
1275
1276         if (parent_sq) {
1277                 /* @parent_sq is another throl_grp, propagate dispatch */
1278                 if (tg->flags & THROTL_TG_WAS_EMPTY) {
1279                         tg_update_disptime(tg);
1280                         if (!throtl_schedule_next_dispatch(parent_sq, false)) {
1281                                 /* window is already open, repeat dispatching */
1282                                 sq = parent_sq;
1283                                 tg = sq_to_tg(sq);
1284                                 goto again;
1285                         }
1286                 }
1287         } else {
1288                 /* reached the top-level, queue issueing */
1289                 queue_work(kthrotld_workqueue, &td->dispatch_work);
1290         }
1291 out_unlock:
1292         spin_unlock_irq(q->queue_lock);
1293 }
1294
1295 /**
1296  * blk_throtl_dispatch_work_fn - work function for throtl_data->dispatch_work
1297  * @work: work item being executed
1298  *
1299  * This function is queued for execution when bio's reach the bio_lists[]
1300  * of throtl_data->service_queue.  Those bio's are ready and issued by this
1301  * function.
1302  */
1303 static void blk_throtl_dispatch_work_fn(struct work_struct *work)
1304 {
1305         struct throtl_data *td = container_of(work, struct throtl_data,
1306                                               dispatch_work);
1307         struct throtl_service_queue *td_sq = &td->service_queue;
1308         struct request_queue *q = td->queue;
1309         struct bio_list bio_list_on_stack;
1310         struct bio *bio;
1311         struct blk_plug plug;
1312         int rw;
1313
1314         bio_list_init(&bio_list_on_stack);
1315
1316         spin_lock_irq(q->queue_lock);
1317         for (rw = READ; rw <= WRITE; rw++)
1318                 while ((bio = throtl_pop_queued(&td_sq->queued[rw], NULL)))
1319                         bio_list_add(&bio_list_on_stack, bio);
1320         spin_unlock_irq(q->queue_lock);
1321
1322         if (!bio_list_empty(&bio_list_on_stack)) {
1323                 blk_start_plug(&plug);
1324                 while((bio = bio_list_pop(&bio_list_on_stack)))
1325                         generic_make_request(bio);
1326                 blk_finish_plug(&plug);
1327         }
1328 }
1329
1330 static u64 tg_prfill_conf_u64(struct seq_file *sf, struct blkg_policy_data *pd,
1331                               int off)
1332 {
1333         struct throtl_grp *tg = pd_to_tg(pd);
1334         u64 v = *(u64 *)((void *)tg + off);
1335
1336         if (v == U64_MAX)
1337                 return 0;
1338         return __blkg_prfill_u64(sf, pd, v);
1339 }
1340
1341 static u64 tg_prfill_conf_uint(struct seq_file *sf, struct blkg_policy_data *pd,
1342                                int off)
1343 {
1344         struct throtl_grp *tg = pd_to_tg(pd);
1345         unsigned int v = *(unsigned int *)((void *)tg + off);
1346
1347         if (v == UINT_MAX)
1348                 return 0;
1349         return __blkg_prfill_u64(sf, pd, v);
1350 }
1351
1352 static int tg_print_conf_u64(struct seq_file *sf, void *v)
1353 {
1354         blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)), tg_prfill_conf_u64,
1355                           &blkcg_policy_throtl, seq_cft(sf)->private, false);
1356         return 0;
1357 }
1358
1359 static int tg_print_conf_uint(struct seq_file *sf, void *v)
1360 {
1361         blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)), tg_prfill_conf_uint,
1362                           &blkcg_policy_throtl, seq_cft(sf)->private, false);
1363         return 0;
1364 }
1365
1366 static void tg_conf_updated(struct throtl_grp *tg, bool global)
1367 {
1368         struct throtl_service_queue *sq = &tg->service_queue;
1369         struct cgroup_subsys_state *pos_css;
1370         struct blkcg_gq *blkg;
1371
1372         throtl_log(&tg->service_queue,
1373                    "limit change rbps=%llu wbps=%llu riops=%u wiops=%u",
1374                    tg_bps_limit(tg, READ), tg_bps_limit(tg, WRITE),
1375                    tg_iops_limit(tg, READ), tg_iops_limit(tg, WRITE));
1376
1377         /*
1378          * Update has_rules[] flags for the updated tg's subtree.  A tg is
1379          * considered to have rules if either the tg itself or any of its
1380          * ancestors has rules.  This identifies groups without any
1381          * restrictions in the whole hierarchy and allows them to bypass
1382          * blk-throttle.
1383          */
1384         blkg_for_each_descendant_pre(blkg, pos_css,
1385                         global ? tg->td->queue->root_blkg : tg_to_blkg(tg)) {
1386                 struct throtl_grp *this_tg = blkg_to_tg(blkg);
1387                 struct throtl_grp *parent_tg;
1388
1389                 tg_update_has_rules(this_tg);
1390                 /* ignore root/second level */
1391                 if (!cgroup_subsys_on_dfl(io_cgrp_subsys) || !blkg->parent ||
1392                     !blkg->parent->parent)
1393                         continue;
1394                 parent_tg = blkg_to_tg(blkg->parent);
1395                 /*
1396                  * make sure all children has lower idle time threshold and
1397                  * higher latency target
1398                  */
1399                 this_tg->idletime_threshold = min(this_tg->idletime_threshold,
1400                                 parent_tg->idletime_threshold);
1401                 this_tg->latency_target = max(this_tg->latency_target,
1402                                 parent_tg->latency_target);
1403         }
1404
1405         /*
1406          * We're already holding queue_lock and know @tg is valid.  Let's
1407          * apply the new config directly.
1408          *
1409          * Restart the slices for both READ and WRITES. It might happen
1410          * that a group's limit are dropped suddenly and we don't want to
1411          * account recently dispatched IO with new low rate.
1412          */
1413         throtl_start_new_slice(tg, 0);
1414         throtl_start_new_slice(tg, 1);
1415
1416         if (tg->flags & THROTL_TG_PENDING) {
1417                 tg_update_disptime(tg);
1418                 throtl_schedule_next_dispatch(sq->parent_sq, true);
1419         }
1420 }
1421
1422 static ssize_t tg_set_conf(struct kernfs_open_file *of,
1423                            char *buf, size_t nbytes, loff_t off, bool is_u64)
1424 {
1425         struct blkcg *blkcg = css_to_blkcg(of_css(of));
1426         struct blkg_conf_ctx ctx;
1427         struct throtl_grp *tg;
1428         int ret;
1429         u64 v;
1430
1431         ret = blkg_conf_prep(blkcg, &blkcg_policy_throtl, buf, &ctx);
1432         if (ret)
1433                 return ret;
1434
1435         ret = -EINVAL;
1436         if (sscanf(ctx.body, "%llu", &v) != 1)
1437                 goto out_finish;
1438         if (!v)
1439                 v = U64_MAX;
1440
1441         tg = blkg_to_tg(ctx.blkg);
1442
1443         if (is_u64)
1444                 *(u64 *)((void *)tg + of_cft(of)->private) = v;
1445         else
1446                 *(unsigned int *)((void *)tg + of_cft(of)->private) = v;
1447
1448         tg_conf_updated(tg, false);
1449         ret = 0;
1450 out_finish:
1451         blkg_conf_finish(&ctx);
1452         return ret ?: nbytes;
1453 }
1454
1455 static ssize_t tg_set_conf_u64(struct kernfs_open_file *of,
1456                                char *buf, size_t nbytes, loff_t off)
1457 {
1458         return tg_set_conf(of, buf, nbytes, off, true);
1459 }
1460
1461 static ssize_t tg_set_conf_uint(struct kernfs_open_file *of,
1462                                 char *buf, size_t nbytes, loff_t off)
1463 {
1464         return tg_set_conf(of, buf, nbytes, off, false);
1465 }
1466
1467 static struct cftype throtl_legacy_files[] = {
1468         {
1469                 .name = "throttle.read_bps_device",
1470                 .private = offsetof(struct throtl_grp, bps[READ][LIMIT_MAX]),
1471                 .seq_show = tg_print_conf_u64,
1472                 .write = tg_set_conf_u64,
1473         },
1474         {
1475                 .name = "throttle.write_bps_device",
1476                 .private = offsetof(struct throtl_grp, bps[WRITE][LIMIT_MAX]),
1477                 .seq_show = tg_print_conf_u64,
1478                 .write = tg_set_conf_u64,
1479         },
1480         {
1481                 .name = "throttle.read_iops_device",
1482                 .private = offsetof(struct throtl_grp, iops[READ][LIMIT_MAX]),
1483                 .seq_show = tg_print_conf_uint,
1484                 .write = tg_set_conf_uint,
1485         },
1486         {
1487                 .name = "throttle.write_iops_device",
1488                 .private = offsetof(struct throtl_grp, iops[WRITE][LIMIT_MAX]),
1489                 .seq_show = tg_print_conf_uint,
1490                 .write = tg_set_conf_uint,
1491         },
1492         {
1493                 .name = "throttle.io_service_bytes",
1494                 .private = (unsigned long)&blkcg_policy_throtl,
1495                 .seq_show = blkg_print_stat_bytes,
1496         },
1497         {
1498                 .name = "throttle.io_serviced",
1499                 .private = (unsigned long)&blkcg_policy_throtl,
1500                 .seq_show = blkg_print_stat_ios,
1501         },
1502         { }     /* terminate */
1503 };
1504
1505 static u64 tg_prfill_limit(struct seq_file *sf, struct blkg_policy_data *pd,
1506                          int off)
1507 {
1508         struct throtl_grp *tg = pd_to_tg(pd);
1509         const char *dname = blkg_dev_name(pd->blkg);
1510         char bufs[4][21] = { "max", "max", "max", "max" };
1511         u64 bps_dft;
1512         unsigned int iops_dft;
1513         char idle_time[26] = "";
1514         char latency_time[26] = "";
1515
1516         if (!dname)
1517                 return 0;
1518
1519         if (off == LIMIT_LOW) {
1520                 bps_dft = 0;
1521                 iops_dft = 0;
1522         } else {
1523                 bps_dft = U64_MAX;
1524                 iops_dft = UINT_MAX;
1525         }
1526
1527         if (tg->bps_conf[READ][off] == bps_dft &&
1528             tg->bps_conf[WRITE][off] == bps_dft &&
1529             tg->iops_conf[READ][off] == iops_dft &&
1530             tg->iops_conf[WRITE][off] == iops_dft &&
1531             (off != LIMIT_LOW ||
1532              (tg->idletime_threshold_conf == DFL_IDLE_THRESHOLD &&
1533               tg->latency_target_conf == DFL_LATENCY_TARGET)))
1534                 return 0;
1535
1536         if (tg->bps_conf[READ][off] != U64_MAX)
1537                 snprintf(bufs[0], sizeof(bufs[0]), "%llu",
1538                         tg->bps_conf[READ][off]);
1539         if (tg->bps_conf[WRITE][off] != U64_MAX)
1540                 snprintf(bufs[1], sizeof(bufs[1]), "%llu",
1541                         tg->bps_conf[WRITE][off]);
1542         if (tg->iops_conf[READ][off] != UINT_MAX)
1543                 snprintf(bufs[2], sizeof(bufs[2]), "%u",
1544                         tg->iops_conf[READ][off]);
1545         if (tg->iops_conf[WRITE][off] != UINT_MAX)
1546                 snprintf(bufs[3], sizeof(bufs[3]), "%u",
1547                         tg->iops_conf[WRITE][off]);
1548         if (off == LIMIT_LOW) {
1549                 if (tg->idletime_threshold_conf == ULONG_MAX)
1550                         strcpy(idle_time, " idle=max");
1551                 else
1552                         snprintf(idle_time, sizeof(idle_time), " idle=%lu",
1553                                 tg->idletime_threshold_conf);
1554
1555                 if (tg->latency_target_conf == ULONG_MAX)
1556                         strcpy(latency_time, " latency=max");
1557                 else
1558                         snprintf(latency_time, sizeof(latency_time),
1559                                 " latency=%lu", tg->latency_target_conf);
1560         }
1561
1562         seq_printf(sf, "%s rbps=%s wbps=%s riops=%s wiops=%s%s%s\n",
1563                    dname, bufs[0], bufs[1], bufs[2], bufs[3], idle_time,
1564                    latency_time);
1565         return 0;
1566 }
1567
1568 static int tg_print_limit(struct seq_file *sf, void *v)
1569 {
1570         blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)), tg_prfill_limit,
1571                           &blkcg_policy_throtl, seq_cft(sf)->private, false);
1572         return 0;
1573 }
1574
1575 static ssize_t tg_set_limit(struct kernfs_open_file *of,
1576                           char *buf, size_t nbytes, loff_t off)
1577 {
1578         struct blkcg *blkcg = css_to_blkcg(of_css(of));
1579         struct blkg_conf_ctx ctx;
1580         struct throtl_grp *tg;
1581         u64 v[4];
1582         unsigned long idle_time;
1583         unsigned long latency_time;
1584         int ret;
1585         int index = of_cft(of)->private;
1586
1587         ret = blkg_conf_prep(blkcg, &blkcg_policy_throtl, buf, &ctx);
1588         if (ret)
1589                 return ret;
1590
1591         tg = blkg_to_tg(ctx.blkg);
1592
1593         v[0] = tg->bps_conf[READ][index];
1594         v[1] = tg->bps_conf[WRITE][index];
1595         v[2] = tg->iops_conf[READ][index];
1596         v[3] = tg->iops_conf[WRITE][index];
1597
1598         idle_time = tg->idletime_threshold_conf;
1599         latency_time = tg->latency_target_conf;
1600         while (true) {
1601                 char tok[27];   /* wiops=18446744073709551616 */
1602                 char *p;
1603                 u64 val = U64_MAX;
1604                 int len;
1605
1606                 if (sscanf(ctx.body, "%26s%n", tok, &len) != 1)
1607                         break;
1608                 if (tok[0] == '\0')
1609                         break;
1610                 ctx.body += len;
1611
1612                 ret = -EINVAL;
1613                 p = tok;
1614                 strsep(&p, "=");
1615                 if (!p || (sscanf(p, "%llu", &val) != 1 && strcmp(p, "max")))
1616                         goto out_finish;
1617
1618                 ret = -ERANGE;
1619                 if (!val)
1620                         goto out_finish;
1621
1622                 ret = -EINVAL;
1623                 if (!strcmp(tok, "rbps"))
1624                         v[0] = val;
1625                 else if (!strcmp(tok, "wbps"))
1626                         v[1] = val;
1627                 else if (!strcmp(tok, "riops"))
1628                         v[2] = min_t(u64, val, UINT_MAX);
1629                 else if (!strcmp(tok, "wiops"))
1630                         v[3] = min_t(u64, val, UINT_MAX);
1631                 else if (off == LIMIT_LOW && !strcmp(tok, "idle"))
1632                         idle_time = val;
1633                 else if (off == LIMIT_LOW && !strcmp(tok, "latency"))
1634                         latency_time = val;
1635                 else
1636                         goto out_finish;
1637         }
1638
1639         tg->bps_conf[READ][index] = v[0];
1640         tg->bps_conf[WRITE][index] = v[1];
1641         tg->iops_conf[READ][index] = v[2];
1642         tg->iops_conf[WRITE][index] = v[3];
1643
1644         if (index == LIMIT_MAX) {
1645                 tg->bps[READ][index] = v[0];
1646                 tg->bps[WRITE][index] = v[1];
1647                 tg->iops[READ][index] = v[2];
1648                 tg->iops[WRITE][index] = v[3];
1649         }
1650         tg->bps[READ][LIMIT_LOW] = min(tg->bps_conf[READ][LIMIT_LOW],
1651                 tg->bps_conf[READ][LIMIT_MAX]);
1652         tg->bps[WRITE][LIMIT_LOW] = min(tg->bps_conf[WRITE][LIMIT_LOW],
1653                 tg->bps_conf[WRITE][LIMIT_MAX]);
1654         tg->iops[READ][LIMIT_LOW] = min(tg->iops_conf[READ][LIMIT_LOW],
1655                 tg->iops_conf[READ][LIMIT_MAX]);
1656         tg->iops[WRITE][LIMIT_LOW] = min(tg->iops_conf[WRITE][LIMIT_LOW],
1657                 tg->iops_conf[WRITE][LIMIT_MAX]);
1658         tg->idletime_threshold_conf = idle_time;
1659         tg->latency_target_conf = latency_time;
1660
1661         /* force user to configure all settings for low limit  */
1662         if (!(tg->bps[READ][LIMIT_LOW] || tg->iops[READ][LIMIT_LOW] ||
1663               tg->bps[WRITE][LIMIT_LOW] || tg->iops[WRITE][LIMIT_LOW]) ||
1664             tg->idletime_threshold_conf == DFL_IDLE_THRESHOLD ||
1665             tg->latency_target_conf == DFL_LATENCY_TARGET) {
1666                 tg->bps[READ][LIMIT_LOW] = 0;
1667                 tg->bps[WRITE][LIMIT_LOW] = 0;
1668                 tg->iops[READ][LIMIT_LOW] = 0;
1669                 tg->iops[WRITE][LIMIT_LOW] = 0;
1670                 tg->idletime_threshold = DFL_IDLE_THRESHOLD;
1671                 tg->latency_target = DFL_LATENCY_TARGET;
1672         } else if (index == LIMIT_LOW) {
1673                 tg->idletime_threshold = tg->idletime_threshold_conf;
1674                 tg->latency_target = tg->latency_target_conf;
1675         }
1676
1677         blk_throtl_update_limit_valid(tg->td);
1678         if (tg->td->limit_valid[LIMIT_LOW]) {
1679                 if (index == LIMIT_LOW)
1680                         tg->td->limit_index = LIMIT_LOW;
1681         } else
1682                 tg->td->limit_index = LIMIT_MAX;
1683         tg_conf_updated(tg, index == LIMIT_LOW &&
1684                 tg->td->limit_valid[LIMIT_LOW]);
1685         ret = 0;
1686 out_finish:
1687         blkg_conf_finish(&ctx);
1688         return ret ?: nbytes;
1689 }
1690
1691 static struct cftype throtl_files[] = {
1692 #ifdef CONFIG_BLK_DEV_THROTTLING_LOW
1693         {
1694                 .name = "low",
1695                 .flags = CFTYPE_NOT_ON_ROOT,
1696                 .seq_show = tg_print_limit,
1697                 .write = tg_set_limit,
1698                 .private = LIMIT_LOW,
1699         },
1700 #endif
1701         {
1702                 .name = "max",
1703                 .flags = CFTYPE_NOT_ON_ROOT,
1704                 .seq_show = tg_print_limit,
1705                 .write = tg_set_limit,
1706                 .private = LIMIT_MAX,
1707         },
1708         { }     /* terminate */
1709 };
1710
1711 static void throtl_shutdown_wq(struct request_queue *q)
1712 {
1713         struct throtl_data *td = q->td;
1714
1715         cancel_work_sync(&td->dispatch_work);
1716 }
1717
1718 static struct blkcg_policy blkcg_policy_throtl = {
1719         .dfl_cftypes            = throtl_files,
1720         .legacy_cftypes         = throtl_legacy_files,
1721
1722         .pd_alloc_fn            = throtl_pd_alloc,
1723         .pd_init_fn             = throtl_pd_init,
1724         .pd_online_fn           = throtl_pd_online,
1725         .pd_offline_fn          = throtl_pd_offline,
1726         .pd_free_fn             = throtl_pd_free,
1727 };
1728
1729 static unsigned long __tg_last_low_overflow_time(struct throtl_grp *tg)
1730 {
1731         unsigned long rtime = jiffies, wtime = jiffies;
1732
1733         if (tg->bps[READ][LIMIT_LOW] || tg->iops[READ][LIMIT_LOW])
1734                 rtime = tg->last_low_overflow_time[READ];
1735         if (tg->bps[WRITE][LIMIT_LOW] || tg->iops[WRITE][LIMIT_LOW])
1736                 wtime = tg->last_low_overflow_time[WRITE];
1737         return min(rtime, wtime);
1738 }
1739
1740 /* tg should not be an intermediate node */
1741 static unsigned long tg_last_low_overflow_time(struct throtl_grp *tg)
1742 {
1743         struct throtl_service_queue *parent_sq;
1744         struct throtl_grp *parent = tg;
1745         unsigned long ret = __tg_last_low_overflow_time(tg);
1746
1747         while (true) {
1748                 parent_sq = parent->service_queue.parent_sq;
1749                 parent = sq_to_tg(parent_sq);
1750                 if (!parent)
1751                         break;
1752
1753                 /*
1754                  * The parent doesn't have low limit, it always reaches low
1755                  * limit. Its overflow time is useless for children
1756                  */
1757                 if (!parent->bps[READ][LIMIT_LOW] &&
1758                     !parent->iops[READ][LIMIT_LOW] &&
1759                     !parent->bps[WRITE][LIMIT_LOW] &&
1760                     !parent->iops[WRITE][LIMIT_LOW])
1761                         continue;
1762                 if (time_after(__tg_last_low_overflow_time(parent), ret))
1763                         ret = __tg_last_low_overflow_time(parent);
1764         }
1765         return ret;
1766 }
1767
1768 static bool throtl_tg_is_idle(struct throtl_grp *tg)
1769 {
1770         /*
1771          * cgroup is idle if:
1772          * - single idle is too long, longer than a fixed value (in case user
1773          *   configure a too big threshold) or 4 times of idletime threshold
1774          * - average think time is more than threshold
1775          * - IO latency is largely below threshold
1776          */
1777         unsigned long time;
1778         bool ret;
1779
1780         time = min_t(unsigned long, MAX_IDLE_TIME, 4 * tg->idletime_threshold);
1781         ret = tg->latency_target == DFL_LATENCY_TARGET ||
1782               tg->idletime_threshold == DFL_IDLE_THRESHOLD ||
1783               (ktime_get_ns() >> 10) - tg->last_finish_time > time ||
1784               tg->avg_idletime > tg->idletime_threshold ||
1785               (tg->latency_target && tg->bio_cnt &&
1786                 tg->bad_bio_cnt * 5 < tg->bio_cnt);
1787         throtl_log(&tg->service_queue,
1788                 "avg_idle=%ld, idle_threshold=%ld, bad_bio=%d, total_bio=%d, is_idle=%d, scale=%d",
1789                 tg->avg_idletime, tg->idletime_threshold, tg->bad_bio_cnt,
1790                 tg->bio_cnt, ret, tg->td->scale);
1791         return ret;
1792 }
1793
1794 static bool throtl_tg_can_upgrade(struct throtl_grp *tg)
1795 {
1796         struct throtl_service_queue *sq = &tg->service_queue;
1797         bool read_limit, write_limit;
1798
1799         /*
1800          * if cgroup reaches low limit (if low limit is 0, the cgroup always
1801          * reaches), it's ok to upgrade to next limit
1802          */
1803         read_limit = tg->bps[READ][LIMIT_LOW] || tg->iops[READ][LIMIT_LOW];
1804         write_limit = tg->bps[WRITE][LIMIT_LOW] || tg->iops[WRITE][LIMIT_LOW];
1805         if (!read_limit && !write_limit)
1806                 return true;
1807         if (read_limit && sq->nr_queued[READ] &&
1808             (!write_limit || sq->nr_queued[WRITE]))
1809                 return true;
1810         if (write_limit && sq->nr_queued[WRITE] &&
1811             (!read_limit || sq->nr_queued[READ]))
1812                 return true;
1813
1814         if (time_after_eq(jiffies,
1815                 tg_last_low_overflow_time(tg) + tg->td->throtl_slice) &&
1816             throtl_tg_is_idle(tg))
1817                 return true;
1818         return false;
1819 }
1820
1821 static bool throtl_hierarchy_can_upgrade(struct throtl_grp *tg)
1822 {
1823         while (true) {
1824                 if (throtl_tg_can_upgrade(tg))
1825                         return true;
1826                 tg = sq_to_tg(tg->service_queue.parent_sq);
1827                 if (!tg || !tg_to_blkg(tg)->parent)
1828                         return false;
1829         }
1830         return false;
1831 }
1832
1833 static bool throtl_can_upgrade(struct throtl_data *td,
1834         struct throtl_grp *this_tg)
1835 {
1836         struct cgroup_subsys_state *pos_css;
1837         struct blkcg_gq *blkg;
1838
1839         if (td->limit_index != LIMIT_LOW)
1840                 return false;
1841
1842         if (time_before(jiffies, td->low_downgrade_time + td->throtl_slice))
1843                 return false;
1844
1845         rcu_read_lock();
1846         blkg_for_each_descendant_post(blkg, pos_css, td->queue->root_blkg) {
1847                 struct throtl_grp *tg = blkg_to_tg(blkg);
1848
1849                 if (tg == this_tg)
1850                         continue;
1851                 if (!list_empty(&tg_to_blkg(tg)->blkcg->css.children))
1852                         continue;
1853                 if (!throtl_hierarchy_can_upgrade(tg)) {
1854                         rcu_read_unlock();
1855                         return false;
1856                 }
1857         }
1858         rcu_read_unlock();
1859         return true;
1860 }
1861
1862 static void throtl_upgrade_check(struct throtl_grp *tg)
1863 {
1864         unsigned long now = jiffies;
1865
1866         if (tg->td->limit_index != LIMIT_LOW)
1867                 return;
1868
1869         if (time_after(tg->last_check_time + tg->td->throtl_slice, now))
1870                 return;
1871
1872         tg->last_check_time = now;
1873
1874         if (!time_after_eq(now,
1875              __tg_last_low_overflow_time(tg) + tg->td->throtl_slice))
1876                 return;
1877
1878         if (throtl_can_upgrade(tg->td, NULL))
1879                 throtl_upgrade_state(tg->td);
1880 }
1881
1882 static void throtl_upgrade_state(struct throtl_data *td)
1883 {
1884         struct cgroup_subsys_state *pos_css;
1885         struct blkcg_gq *blkg;
1886
1887         throtl_log(&td->service_queue, "upgrade to max");
1888         td->limit_index = LIMIT_MAX;
1889         td->low_upgrade_time = jiffies;
1890         td->scale = 0;
1891         rcu_read_lock();
1892         blkg_for_each_descendant_post(blkg, pos_css, td->queue->root_blkg) {
1893                 struct throtl_grp *tg = blkg_to_tg(blkg);
1894                 struct throtl_service_queue *sq = &tg->service_queue;
1895
1896                 tg->disptime = jiffies - 1;
1897                 throtl_select_dispatch(sq);
1898                 throtl_schedule_next_dispatch(sq, false);
1899         }
1900         rcu_read_unlock();
1901         throtl_select_dispatch(&td->service_queue);
1902         throtl_schedule_next_dispatch(&td->service_queue, false);
1903         queue_work(kthrotld_workqueue, &td->dispatch_work);
1904 }
1905
1906 static void throtl_downgrade_state(struct throtl_data *td, int new)
1907 {
1908         td->scale /= 2;
1909
1910         throtl_log(&td->service_queue, "downgrade, scale %d", td->scale);
1911         if (td->scale) {
1912                 td->low_upgrade_time = jiffies - td->scale * td->throtl_slice;
1913                 return;
1914         }
1915
1916         td->limit_index = new;
1917         td->low_downgrade_time = jiffies;
1918 }
1919
1920 static bool throtl_tg_can_downgrade(struct throtl_grp *tg)
1921 {
1922         struct throtl_data *td = tg->td;
1923         unsigned long now = jiffies;
1924
1925         /*
1926          * If cgroup is below low limit, consider downgrade and throttle other
1927          * cgroups
1928          */
1929         if (time_after_eq(now, td->low_upgrade_time + td->throtl_slice) &&
1930             time_after_eq(now, tg_last_low_overflow_time(tg) +
1931                                         td->throtl_slice) &&
1932             (!throtl_tg_is_idle(tg) ||
1933              !list_empty(&tg_to_blkg(tg)->blkcg->css.children)))
1934                 return true;
1935         return false;
1936 }
1937
1938 static bool throtl_hierarchy_can_downgrade(struct throtl_grp *tg)
1939 {
1940         while (true) {
1941                 if (!throtl_tg_can_downgrade(tg))
1942                         return false;
1943                 tg = sq_to_tg(tg->service_queue.parent_sq);
1944                 if (!tg || !tg_to_blkg(tg)->parent)
1945                         break;
1946         }
1947         return true;
1948 }
1949
1950 static void throtl_downgrade_check(struct throtl_grp *tg)
1951 {
1952         uint64_t bps;
1953         unsigned int iops;
1954         unsigned long elapsed_time;
1955         unsigned long now = jiffies;
1956
1957         if (tg->td->limit_index != LIMIT_MAX ||
1958             !tg->td->limit_valid[LIMIT_LOW])
1959                 return;
1960         if (!list_empty(&tg_to_blkg(tg)->blkcg->css.children))
1961                 return;
1962         if (time_after(tg->last_check_time + tg->td->throtl_slice, now))
1963                 return;
1964
1965         elapsed_time = now - tg->last_check_time;
1966         tg->last_check_time = now;
1967
1968         if (time_before(now, tg_last_low_overflow_time(tg) +
1969                         tg->td->throtl_slice))
1970                 return;
1971
1972         if (tg->bps[READ][LIMIT_LOW]) {
1973                 bps = tg->last_bytes_disp[READ] * HZ;
1974                 do_div(bps, elapsed_time);
1975                 if (bps >= tg->bps[READ][LIMIT_LOW])
1976                         tg->last_low_overflow_time[READ] = now;
1977         }
1978
1979         if (tg->bps[WRITE][LIMIT_LOW]) {
1980                 bps = tg->last_bytes_disp[WRITE] * HZ;
1981                 do_div(bps, elapsed_time);
1982                 if (bps >= tg->bps[WRITE][LIMIT_LOW])
1983                         tg->last_low_overflow_time[WRITE] = now;
1984         }
1985
1986         if (tg->iops[READ][LIMIT_LOW]) {
1987                 iops = tg->last_io_disp[READ] * HZ / elapsed_time;
1988                 if (iops >= tg->iops[READ][LIMIT_LOW])
1989                         tg->last_low_overflow_time[READ] = now;
1990         }
1991
1992         if (tg->iops[WRITE][LIMIT_LOW]) {
1993                 iops = tg->last_io_disp[WRITE] * HZ / elapsed_time;
1994                 if (iops >= tg->iops[WRITE][LIMIT_LOW])
1995                         tg->last_low_overflow_time[WRITE] = now;
1996         }
1997
1998         /*
1999          * If cgroup is below low limit, consider downgrade and throttle other
2000          * cgroups
2001          */
2002         if (throtl_hierarchy_can_downgrade(tg))
2003                 throtl_downgrade_state(tg->td, LIMIT_LOW);
2004
2005         tg->last_bytes_disp[READ] = 0;
2006         tg->last_bytes_disp[WRITE] = 0;
2007         tg->last_io_disp[READ] = 0;
2008         tg->last_io_disp[WRITE] = 0;
2009 }
2010
2011 static void blk_throtl_update_idletime(struct throtl_grp *tg)
2012 {
2013         unsigned long now = ktime_get_ns() >> 10;
2014         unsigned long last_finish_time = tg->last_finish_time;
2015
2016         if (now <= last_finish_time || last_finish_time == 0 ||
2017             last_finish_time == tg->checked_last_finish_time)
2018                 return;
2019
2020         tg->avg_idletime = (tg->avg_idletime * 7 + now - last_finish_time) >> 3;
2021         tg->checked_last_finish_time = last_finish_time;
2022 }
2023
2024 #ifdef CONFIG_BLK_DEV_THROTTLING_LOW
2025 static void throtl_update_latency_buckets(struct throtl_data *td)
2026 {
2027         struct avg_latency_bucket avg_latency[LATENCY_BUCKET_SIZE];
2028         int i, cpu;
2029         unsigned long last_latency = 0;
2030         unsigned long latency;
2031
2032         if (!blk_queue_nonrot(td->queue))
2033                 return;
2034         if (time_before(jiffies, td->last_calculate_time + HZ))
2035                 return;
2036         td->last_calculate_time = jiffies;
2037
2038         memset(avg_latency, 0, sizeof(avg_latency));
2039         for (i = 0; i < LATENCY_BUCKET_SIZE; i++) {
2040                 struct latency_bucket *tmp = &td->tmp_buckets[i];
2041
2042                 for_each_possible_cpu(cpu) {
2043                         struct latency_bucket *bucket;
2044
2045                         /* this isn't race free, but ok in practice */
2046                         bucket = per_cpu_ptr(td->latency_buckets, cpu);
2047                         tmp->total_latency += bucket[i].total_latency;
2048                         tmp->samples += bucket[i].samples;
2049                         bucket[i].total_latency = 0;
2050                         bucket[i].samples = 0;
2051                 }
2052
2053                 if (tmp->samples >= 32) {
2054                         int samples = tmp->samples;
2055
2056                         latency = tmp->total_latency;
2057
2058                         tmp->total_latency = 0;
2059                         tmp->samples = 0;
2060                         latency /= samples;
2061                         if (latency == 0)
2062                                 continue;
2063                         avg_latency[i].latency = latency;
2064                 }
2065         }
2066
2067         for (i = 0; i < LATENCY_BUCKET_SIZE; i++) {
2068                 if (!avg_latency[i].latency) {
2069                         if (td->avg_buckets[i].latency < last_latency)
2070                                 td->avg_buckets[i].latency = last_latency;
2071                         continue;
2072                 }
2073
2074                 if (!td->avg_buckets[i].valid)
2075                         latency = avg_latency[i].latency;
2076                 else
2077                         latency = (td->avg_buckets[i].latency * 7 +
2078                                 avg_latency[i].latency) >> 3;
2079
2080                 td->avg_buckets[i].latency = max(latency, last_latency);
2081                 td->avg_buckets[i].valid = true;
2082                 last_latency = td->avg_buckets[i].latency;
2083         }
2084
2085         for (i = 0; i < LATENCY_BUCKET_SIZE; i++)
2086                 throtl_log(&td->service_queue,
2087                         "Latency bucket %d: latency=%ld, valid=%d", i,
2088                         td->avg_buckets[i].latency, td->avg_buckets[i].valid);
2089 }
2090 #else
2091 static inline void throtl_update_latency_buckets(struct throtl_data *td)
2092 {
2093 }
2094 #endif
2095
2096 static void blk_throtl_assoc_bio(struct throtl_grp *tg, struct bio *bio)
2097 {
2098 #ifdef CONFIG_BLK_DEV_THROTTLING_LOW
2099         int ret;
2100
2101         ret = bio_associate_current(bio);
2102         if (ret == 0 || ret == -EBUSY)
2103                 bio->bi_cg_private = tg;
2104         blk_stat_set_issue(&bio->bi_issue_stat, bio_sectors(bio));
2105 #else
2106         bio_associate_current(bio);
2107 #endif
2108 }
2109
2110 bool blk_throtl_bio(struct request_queue *q, struct blkcg_gq *blkg,
2111                     struct bio *bio)
2112 {
2113         struct throtl_qnode *qn = NULL;
2114         struct throtl_grp *tg = blkg_to_tg(blkg ?: q->root_blkg);
2115         struct throtl_service_queue *sq;
2116         bool rw = bio_data_dir(bio);
2117         bool throttled = false;
2118         struct throtl_data *td = tg->td;
2119
2120         WARN_ON_ONCE(!rcu_read_lock_held());
2121
2122         /* see throtl_charge_bio() */
2123         if (bio_flagged(bio, BIO_THROTTLED) || !tg->has_rules[rw])
2124                 goto out;
2125
2126         spin_lock_irq(q->queue_lock);
2127
2128         throtl_update_latency_buckets(td);
2129
2130         if (unlikely(blk_queue_bypass(q)))
2131                 goto out_unlock;
2132
2133         blk_throtl_assoc_bio(tg, bio);
2134         blk_throtl_update_idletime(tg);
2135
2136         sq = &tg->service_queue;
2137
2138 again:
2139         while (true) {
2140                 if (tg->last_low_overflow_time[rw] == 0)
2141                         tg->last_low_overflow_time[rw] = jiffies;
2142                 throtl_downgrade_check(tg);
2143                 throtl_upgrade_check(tg);
2144                 /* throtl is FIFO - if bios are already queued, should queue */
2145                 if (sq->nr_queued[rw])
2146                         break;
2147
2148                 /* if above limits, break to queue */
2149                 if (!tg_may_dispatch(tg, bio, NULL)) {
2150                         tg->last_low_overflow_time[rw] = jiffies;
2151                         if (throtl_can_upgrade(td, tg)) {
2152                                 throtl_upgrade_state(td);
2153                                 goto again;
2154                         }
2155                         break;
2156                 }
2157
2158                 /* within limits, let's charge and dispatch directly */
2159                 throtl_charge_bio(tg, bio);
2160
2161                 /*
2162                  * We need to trim slice even when bios are not being queued
2163                  * otherwise it might happen that a bio is not queued for
2164                  * a long time and slice keeps on extending and trim is not
2165                  * called for a long time. Now if limits are reduced suddenly
2166                  * we take into account all the IO dispatched so far at new
2167                  * low rate and * newly queued IO gets a really long dispatch
2168                  * time.
2169                  *
2170                  * So keep on trimming slice even if bio is not queued.
2171                  */
2172                 throtl_trim_slice(tg, rw);
2173
2174                 /*
2175                  * @bio passed through this layer without being throttled.
2176                  * Climb up the ladder.  If we''re already at the top, it
2177                  * can be executed directly.
2178                  */
2179                 qn = &tg->qnode_on_parent[rw];
2180                 sq = sq->parent_sq;
2181                 tg = sq_to_tg(sq);
2182                 if (!tg)
2183                         goto out_unlock;
2184         }
2185
2186         /* out-of-limit, queue to @tg */
2187         throtl_log(sq, "[%c] bio. bdisp=%llu sz=%u bps=%llu iodisp=%u iops=%u queued=%d/%d",
2188                    rw == READ ? 'R' : 'W',
2189                    tg->bytes_disp[rw], bio->bi_iter.bi_size,
2190                    tg_bps_limit(tg, rw),
2191                    tg->io_disp[rw], tg_iops_limit(tg, rw),
2192                    sq->nr_queued[READ], sq->nr_queued[WRITE]);
2193
2194         tg->last_low_overflow_time[rw] = jiffies;
2195
2196         td->nr_queued[rw]++;
2197         throtl_add_bio_tg(bio, qn, tg);
2198         throttled = true;
2199
2200         /*
2201          * Update @tg's dispatch time and force schedule dispatch if @tg
2202          * was empty before @bio.  The forced scheduling isn't likely to
2203          * cause undue delay as @bio is likely to be dispatched directly if
2204          * its @tg's disptime is not in the future.
2205          */
2206         if (tg->flags & THROTL_TG_WAS_EMPTY) {
2207                 tg_update_disptime(tg);
2208                 throtl_schedule_next_dispatch(tg->service_queue.parent_sq, true);
2209         }
2210
2211 out_unlock:
2212         spin_unlock_irq(q->queue_lock);
2213 out:
2214         /*
2215          * As multiple blk-throtls may stack in the same issue path, we
2216          * don't want bios to leave with the flag set.  Clear the flag if
2217          * being issued.
2218          */
2219         if (!throttled)
2220                 bio_clear_flag(bio, BIO_THROTTLED);
2221
2222 #ifdef CONFIG_BLK_DEV_THROTTLING_LOW
2223         if (throttled || !td->track_bio_latency)
2224                 bio->bi_issue_stat.stat |= SKIP_LATENCY;
2225 #endif
2226         return throttled;
2227 }
2228
2229 #ifdef CONFIG_BLK_DEV_THROTTLING_LOW
2230 static void throtl_track_latency(struct throtl_data *td, sector_t size,
2231         int op, unsigned long time)
2232 {
2233         struct latency_bucket *latency;
2234         int index;
2235
2236         if (!td || td->limit_index != LIMIT_LOW || op != REQ_OP_READ ||
2237             !blk_queue_nonrot(td->queue))
2238                 return;
2239
2240         index = request_bucket_index(size);
2241
2242         latency = get_cpu_ptr(td->latency_buckets);
2243         latency[index].total_latency += time;
2244         latency[index].samples++;
2245         put_cpu_ptr(td->latency_buckets);
2246 }
2247
2248 void blk_throtl_stat_add(struct request *rq, u64 time_ns)
2249 {
2250         struct request_queue *q = rq->q;
2251         struct throtl_data *td = q->td;
2252
2253         throtl_track_latency(td, blk_stat_size(&rq->issue_stat),
2254                 req_op(rq), time_ns >> 10);
2255 }
2256
2257 void blk_throtl_bio_endio(struct bio *bio)
2258 {
2259         struct throtl_grp *tg;
2260         u64 finish_time_ns;
2261         unsigned long finish_time;
2262         unsigned long start_time;
2263         unsigned long lat;
2264
2265         tg = bio->bi_cg_private;
2266         if (!tg)
2267                 return;
2268         bio->bi_cg_private = NULL;
2269
2270         finish_time_ns = ktime_get_ns();
2271         tg->last_finish_time = finish_time_ns >> 10;
2272
2273         start_time = blk_stat_time(&bio->bi_issue_stat) >> 10;
2274         finish_time = __blk_stat_time(finish_time_ns) >> 10;
2275         if (!start_time || finish_time <= start_time)
2276                 return;
2277
2278         lat = finish_time - start_time;
2279         /* this is only for bio based driver */
2280         if (!(bio->bi_issue_stat.stat & SKIP_LATENCY))
2281                 throtl_track_latency(tg->td, blk_stat_size(&bio->bi_issue_stat),
2282                         bio_op(bio), lat);
2283
2284         if (tg->latency_target) {
2285                 int bucket;
2286                 unsigned int threshold;
2287
2288                 bucket = request_bucket_index(
2289                         blk_stat_size(&bio->bi_issue_stat));
2290                 threshold = tg->td->avg_buckets[bucket].latency +
2291                         tg->latency_target;
2292                 if (lat > threshold)
2293                         tg->bad_bio_cnt++;
2294                 /*
2295                  * Not race free, could get wrong count, which means cgroups
2296                  * will be throttled
2297                  */
2298                 tg->bio_cnt++;
2299         }
2300
2301         if (time_after(jiffies, tg->bio_cnt_reset_time) || tg->bio_cnt > 1024) {
2302                 tg->bio_cnt_reset_time = tg->td->throtl_slice + jiffies;
2303                 tg->bio_cnt /= 2;
2304                 tg->bad_bio_cnt /= 2;
2305         }
2306 }
2307 #endif
2308
2309 /*
2310  * Dispatch all bios from all children tg's queued on @parent_sq.  On
2311  * return, @parent_sq is guaranteed to not have any active children tg's
2312  * and all bios from previously active tg's are on @parent_sq->bio_lists[].
2313  */
2314 static void tg_drain_bios(struct throtl_service_queue *parent_sq)
2315 {
2316         struct throtl_grp *tg;
2317
2318         while ((tg = throtl_rb_first(parent_sq))) {
2319                 struct throtl_service_queue *sq = &tg->service_queue;
2320                 struct bio *bio;
2321
2322                 throtl_dequeue_tg(tg);
2323
2324                 while ((bio = throtl_peek_queued(&sq->queued[READ])))
2325                         tg_dispatch_one_bio(tg, bio_data_dir(bio));
2326                 while ((bio = throtl_peek_queued(&sq->queued[WRITE])))
2327                         tg_dispatch_one_bio(tg, bio_data_dir(bio));
2328         }
2329 }
2330
2331 /**
2332  * blk_throtl_drain - drain throttled bios
2333  * @q: request_queue to drain throttled bios for
2334  *
2335  * Dispatch all currently throttled bios on @q through ->make_request_fn().
2336  */
2337 void blk_throtl_drain(struct request_queue *q)
2338         __releases(q->queue_lock) __acquires(q->queue_lock)
2339 {
2340         struct throtl_data *td = q->td;
2341         struct blkcg_gq *blkg;
2342         struct cgroup_subsys_state *pos_css;
2343         struct bio *bio;
2344         int rw;
2345
2346         queue_lockdep_assert_held(q);
2347         rcu_read_lock();
2348
2349         /*
2350          * Drain each tg while doing post-order walk on the blkg tree, so
2351          * that all bios are propagated to td->service_queue.  It'd be
2352          * better to walk service_queue tree directly but blkg walk is
2353          * easier.
2354          */
2355         blkg_for_each_descendant_post(blkg, pos_css, td->queue->root_blkg)
2356                 tg_drain_bios(&blkg_to_tg(blkg)->service_queue);
2357
2358         /* finally, transfer bios from top-level tg's into the td */
2359         tg_drain_bios(&td->service_queue);
2360
2361         rcu_read_unlock();
2362         spin_unlock_irq(q->queue_lock);
2363
2364         /* all bios now should be in td->service_queue, issue them */
2365         for (rw = READ; rw <= WRITE; rw++)
2366                 while ((bio = throtl_pop_queued(&td->service_queue.queued[rw],
2367                                                 NULL)))
2368                         generic_make_request(bio);
2369
2370         spin_lock_irq(q->queue_lock);
2371 }
2372
2373 int blk_throtl_init(struct request_queue *q)
2374 {
2375         struct throtl_data *td;
2376         int ret;
2377
2378         td = kzalloc_node(sizeof(*td), GFP_KERNEL, q->node);
2379         if (!td)
2380                 return -ENOMEM;
2381         td->latency_buckets = __alloc_percpu(sizeof(struct latency_bucket) *
2382                 LATENCY_BUCKET_SIZE, __alignof__(u64));
2383         if (!td->latency_buckets) {
2384                 kfree(td);
2385                 return -ENOMEM;
2386         }
2387
2388         INIT_WORK(&td->dispatch_work, blk_throtl_dispatch_work_fn);
2389         throtl_service_queue_init(&td->service_queue);
2390
2391         q->td = td;
2392         td->queue = q;
2393
2394         td->limit_valid[LIMIT_MAX] = true;
2395         td->limit_index = LIMIT_MAX;
2396         td->low_upgrade_time = jiffies;
2397         td->low_downgrade_time = jiffies;
2398
2399         /* activate policy */
2400         ret = blkcg_activate_policy(q, &blkcg_policy_throtl);
2401         if (ret) {
2402                 free_percpu(td->latency_buckets);
2403                 kfree(td);
2404         }
2405         return ret;
2406 }
2407
2408 void blk_throtl_exit(struct request_queue *q)
2409 {
2410         BUG_ON(!q->td);
2411         throtl_shutdown_wq(q);
2412         blkcg_deactivate_policy(q, &blkcg_policy_throtl);
2413         free_percpu(q->td->latency_buckets);
2414         kfree(q->td);
2415 }
2416
2417 void blk_throtl_register_queue(struct request_queue *q)
2418 {
2419         struct throtl_data *td;
2420
2421         td = q->td;
2422         BUG_ON(!td);
2423
2424         if (blk_queue_nonrot(q))
2425                 td->throtl_slice = DFL_THROTL_SLICE_SSD;
2426         else
2427                 td->throtl_slice = DFL_THROTL_SLICE_HD;
2428 #ifndef CONFIG_BLK_DEV_THROTTLING_LOW
2429         /* if no low limit, use previous default */
2430         td->throtl_slice = DFL_THROTL_SLICE_HD;
2431 #endif
2432
2433         td->track_bio_latency = !q->mq_ops && !q->request_fn;
2434         if (!td->track_bio_latency)
2435                 blk_stat_enable_accounting(q);
2436 }
2437
2438 #ifdef CONFIG_BLK_DEV_THROTTLING_LOW
2439 ssize_t blk_throtl_sample_time_show(struct request_queue *q, char *page)
2440 {
2441         if (!q->td)
2442                 return -EINVAL;
2443         return sprintf(page, "%u\n", jiffies_to_msecs(q->td->throtl_slice));
2444 }
2445
2446 ssize_t blk_throtl_sample_time_store(struct request_queue *q,
2447         const char *page, size_t count)
2448 {
2449         unsigned long v;
2450         unsigned long t;
2451
2452         if (!q->td)
2453                 return -EINVAL;
2454         if (kstrtoul(page, 10, &v))
2455                 return -EINVAL;
2456         t = msecs_to_jiffies(v);
2457         if (t == 0 || t > MAX_THROTL_SLICE)
2458                 return -EINVAL;
2459         q->td->throtl_slice = t;
2460         return count;
2461 }
2462 #endif
2463
2464 static int __init throtl_init(void)
2465 {
2466         kthrotld_workqueue = alloc_workqueue("kthrotld", WQ_MEM_RECLAIM, 0);
2467         if (!kthrotld_workqueue)
2468                 panic("Failed to create kthrotld\n");
2469
2470         return blkcg_policy_register(&blkcg_policy_throtl);
2471 }
2472
2473 module_init(throtl_init);