Version:  2.0.40 2.2.26 2.4.37 3.13 3.14 3.15 3.16 3.17 3.18 3.19 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10

Linux/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 100ms slice and after that slice is renewed */
 22 static unsigned long throtl_slice = HZ/10;      /* 100 ms */
 23 
 24 static struct blkcg_policy blkcg_policy_throtl;
 25 
 26 /* A workqueue to queue throttle related work */
 27 static struct workqueue_struct *kthrotld_workqueue;
 28 
 29 /*
 30  * To implement hierarchical throttling, throtl_grps form a tree and bios
 31  * are dispatched upwards level by level until they reach the top and get
 32  * issued.  When dispatching bios from the children and local group at each
 33  * level, if the bios are dispatched into a single bio_list, there's a risk
 34  * of a local or child group which can queue many bios at once filling up
 35  * the list starving others.
 36  *
 37  * To avoid such starvation, dispatched bios are queued separately
 38  * according to where they came from.  When they are again dispatched to
 39  * the parent, they're popped in round-robin order so that no single source
 40  * hogs the dispatch window.
 41  *
 42  * throtl_qnode is used to keep the queued bios separated by their sources.
 43  * Bios are queued to throtl_qnode which in turn is queued to
 44  * throtl_service_queue and then dispatched in round-robin order.
 45  *
 46  * It's also used to track the reference counts on blkg's.  A qnode always
 47  * belongs to a throtl_grp and gets queued on itself or the parent, so
 48  * incrementing the reference of the associated throtl_grp when a qnode is
 49  * queued and decrementing when dequeued is enough to keep the whole blkg
 50  * tree pinned while bios are in flight.
 51  */
 52 struct throtl_qnode {
 53         struct list_head        node;           /* service_queue->queued[] */
 54         struct bio_list         bios;           /* queued bios */
 55         struct throtl_grp       *tg;            /* tg this qnode belongs to */
 56 };
 57 
 58 struct throtl_service_queue {
 59         struct throtl_service_queue *parent_sq; /* the parent service_queue */
 60 
 61         /*
 62          * Bios queued directly to this service_queue or dispatched from
 63          * children throtl_grp's.
 64          */
 65         struct list_head        queued[2];      /* throtl_qnode [READ/WRITE] */
 66         unsigned int            nr_queued[2];   /* number of queued bios */
 67 
 68         /*
 69          * RB tree of active children throtl_grp's, which are sorted by
 70          * their ->disptime.
 71          */
 72         struct rb_root          pending_tree;   /* RB tree of active tgs */
 73         struct rb_node          *first_pending; /* first node in the tree */
 74         unsigned int            nr_pending;     /* # queued in the tree */
 75         unsigned long           first_pending_disptime; /* disptime of the first tg */
 76         struct timer_list       pending_timer;  /* fires on first_pending_disptime */
 77 };
 78 
 79 enum tg_state_flags {
 80         THROTL_TG_PENDING       = 1 << 0,       /* on parent's pending tree */
 81         THROTL_TG_WAS_EMPTY     = 1 << 1,       /* bio_lists[] became non-empty */
 82 };
 83 
 84 #define rb_entry_tg(node)       rb_entry((node), struct throtl_grp, rb_node)
 85 
 86 struct throtl_grp {
 87         /* must be the first member */
 88         struct blkg_policy_data pd;
 89 
 90         /* active throtl group service_queue member */
 91         struct rb_node rb_node;
 92 
 93         /* throtl_data this group belongs to */
 94         struct throtl_data *td;
 95 
 96         /* this group's service queue */
 97         struct throtl_service_queue service_queue;
 98 
 99         /*
100          * qnode_on_self is used when bios are directly queued to this
101          * throtl_grp so that local bios compete fairly with bios
102          * dispatched from children.  qnode_on_parent is used when bios are
103          * dispatched from this throtl_grp into its parent and will compete
104          * with the sibling qnode_on_parents and the parent's
105          * qnode_on_self.
106          */
107         struct throtl_qnode qnode_on_self[2];
108         struct throtl_qnode qnode_on_parent[2];
109 
110         /*
111          * Dispatch time in jiffies. This is the estimated time when group
112          * will unthrottle and is ready to dispatch more bio. It is used as
113          * key to sort active groups in service tree.
114          */
115         unsigned long disptime;
116 
117         unsigned int flags;
118 
119         /* are there any throtl rules between this group and td? */
120         bool has_rules[2];
121 
122         /* bytes per second rate limits */
123         uint64_t bps[2];
124 
125         /* IOPS limits */
126         unsigned int iops[2];
127 
128         /* Number of bytes disptached in current slice */
129         uint64_t bytes_disp[2];
130         /* Number of bio's dispatched in current slice */
131         unsigned int io_disp[2];
132 
133         /* When did we start a new slice */
134         unsigned long slice_start[2];
135         unsigned long slice_end[2];
136 };
137 
138 struct throtl_data
139 {
140         /* service tree for active throtl groups */
141         struct throtl_service_queue service_queue;
142 
143         struct request_queue *queue;
144 
145         /* Total Number of queued bios on READ and WRITE lists */
146         unsigned int nr_queued[2];
147 
148         /* Work for dispatching throttled bios */
149         struct work_struct dispatch_work;
150 };
151 
152 static void throtl_pending_timer_fn(unsigned long arg);
153 
154 static inline struct throtl_grp *pd_to_tg(struct blkg_policy_data *pd)
155 {
156         return pd ? container_of(pd, struct throtl_grp, pd) : NULL;
157 }
158 
159 static inline struct throtl_grp *blkg_to_tg(struct blkcg_gq *blkg)
160 {
161         return pd_to_tg(blkg_to_pd(blkg, &blkcg_policy_throtl));
162 }
163 
164 static inline struct blkcg_gq *tg_to_blkg(struct throtl_grp *tg)
165 {
166         return pd_to_blkg(&tg->pd);
167 }
168 
169 /**
170  * sq_to_tg - return the throl_grp the specified service queue belongs to
171  * @sq: the throtl_service_queue of interest
172  *
173  * Return the throtl_grp @sq belongs to.  If @sq is the top-level one
174  * embedded in throtl_data, %NULL is returned.
175  */
176 static struct throtl_grp *sq_to_tg(struct throtl_service_queue *sq)
177 {
178         if (sq && sq->parent_sq)
179                 return container_of(sq, struct throtl_grp, service_queue);
180         else
181                 return NULL;
182 }
183 
184 /**
185  * sq_to_td - return throtl_data the specified service queue belongs to
186  * @sq: the throtl_service_queue of interest
187  *
188  * A service_queue can be embeded in either a throtl_grp or throtl_data.
189  * Determine the associated throtl_data accordingly and return it.
190  */
191 static struct throtl_data *sq_to_td(struct throtl_service_queue *sq)
192 {
193         struct throtl_grp *tg = sq_to_tg(sq);
194 
195         if (tg)
196                 return tg->td;
197         else
198                 return container_of(sq, struct throtl_data, service_queue);
199 }
200 
201 /**
202  * throtl_log - log debug message via blktrace
203  * @sq: the service_queue being reported
204  * @fmt: printf format string
205  * @args: printf args
206  *
207  * The messages are prefixed with "throtl BLKG_NAME" if @sq belongs to a
208  * throtl_grp; otherwise, just "throtl".
209  */
210 #define throtl_log(sq, fmt, args...)    do {                            \
211         struct throtl_grp *__tg = sq_to_tg((sq));                       \
212         struct throtl_data *__td = sq_to_td((sq));                      \
213                                                                         \
214         (void)__td;                                                     \
215         if (likely(!blk_trace_note_message_enabled(__td->queue)))       \
216                 break;                                                  \
217         if ((__tg)) {                                                   \
218                 char __pbuf[128];                                       \
219                                                                         \
220                 blkg_path(tg_to_blkg(__tg), __pbuf, sizeof(__pbuf));    \
221                 blk_add_trace_msg(__td->queue, "throtl %s " fmt, __pbuf, ##args); \
222         } else {                                                        \
223                 blk_add_trace_msg(__td->queue, "throtl " fmt, ##args);  \
224         }                                                               \
225 } while (0)
226 
227 static void throtl_qnode_init(struct throtl_qnode *qn, struct throtl_grp *tg)
228 {
229         INIT_LIST_HEAD(&qn->node);
230         bio_list_init(&qn->bios);
231         qn->tg = tg;
232 }
233 
234 /**
235  * throtl_qnode_add_bio - add a bio to a throtl_qnode and activate it
236  * @bio: bio being added
237  * @qn: qnode to add bio to
238  * @queued: the service_queue->queued[] list @qn belongs to
239  *
240  * Add @bio to @qn and put @qn on @queued if it's not already on.
241  * @qn->tg's reference count is bumped when @qn is activated.  See the
242  * comment on top of throtl_qnode definition for details.
243  */
244 static void throtl_qnode_add_bio(struct bio *bio, struct throtl_qnode *qn,
245                                  struct list_head *queued)
246 {
247         bio_list_add(&qn->bios, bio);
248         if (list_empty(&qn->node)) {
249                 list_add_tail(&qn->node, queued);
250                 blkg_get(tg_to_blkg(qn->tg));
251         }
252 }
253 
254 /**
255  * throtl_peek_queued - peek the first bio on a qnode list
256  * @queued: the qnode list to peek
257  */
258 static struct bio *throtl_peek_queued(struct list_head *queued)
259 {
260         struct throtl_qnode *qn = list_first_entry(queued, struct throtl_qnode, node);
261         struct bio *bio;
262 
263         if (list_empty(queued))
264                 return NULL;
265 
266         bio = bio_list_peek(&qn->bios);
267         WARN_ON_ONCE(!bio);
268         return bio;
269 }
270 
271 /**
272  * throtl_pop_queued - pop the first bio form a qnode list
273  * @queued: the qnode list to pop a bio from
274  * @tg_to_put: optional out argument for throtl_grp to put
275  *
276  * Pop the first bio from the qnode list @queued.  After popping, the first
277  * qnode is removed from @queued if empty or moved to the end of @queued so
278  * that the popping order is round-robin.
279  *
280  * When the first qnode is removed, its associated throtl_grp should be put
281  * too.  If @tg_to_put is NULL, this function automatically puts it;
282  * otherwise, *@tg_to_put is set to the throtl_grp to put and the caller is
283  * responsible for putting it.
284  */
285 static struct bio *throtl_pop_queued(struct list_head *queued,
286                                      struct throtl_grp **tg_to_put)
287 {
288         struct throtl_qnode *qn = list_first_entry(queued, struct throtl_qnode, node);
289         struct bio *bio;
290 
291         if (list_empty(queued))
292                 return NULL;
293 
294         bio = bio_list_pop(&qn->bios);
295         WARN_ON_ONCE(!bio);
296 
297         if (bio_list_empty(&qn->bios)) {
298                 list_del_init(&qn->node);
299                 if (tg_to_put)
300                         *tg_to_put = qn->tg;
301                 else
302                         blkg_put(tg_to_blkg(qn->tg));
303         } else {
304                 list_move_tail(&qn->node, queued);
305         }
306 
307         return bio;
308 }
309 
310 /* init a service_queue, assumes the caller zeroed it */
311 static void throtl_service_queue_init(struct throtl_service_queue *sq)
312 {
313         INIT_LIST_HEAD(&sq->queued[0]);
314         INIT_LIST_HEAD(&sq->queued[1]);
315         sq->pending_tree = RB_ROOT;
316         setup_timer(&sq->pending_timer, throtl_pending_timer_fn,
317                     (unsigned long)sq);
318 }
319 
320 static struct blkg_policy_data *throtl_pd_alloc(gfp_t gfp, int node)
321 {
322         struct throtl_grp *tg;
323         int rw;
324 
325         tg = kzalloc_node(sizeof(*tg), gfp, node);
326         if (!tg)
327                 return NULL;
328 
329         throtl_service_queue_init(&tg->service_queue);
330 
331         for (rw = READ; rw <= WRITE; rw++) {
332                 throtl_qnode_init(&tg->qnode_on_self[rw], tg);
333                 throtl_qnode_init(&tg->qnode_on_parent[rw], tg);
334         }
335 
336         RB_CLEAR_NODE(&tg->rb_node);
337         tg->bps[READ] = -1;
338         tg->bps[WRITE] = -1;
339         tg->iops[READ] = -1;
340         tg->iops[WRITE] = -1;
341 
342         return &tg->pd;
343 }
344 
345 static void throtl_pd_init(struct blkg_policy_data *pd)
346 {
347         struct throtl_grp *tg = pd_to_tg(pd);
348         struct blkcg_gq *blkg = tg_to_blkg(tg);
349         struct throtl_data *td = blkg->q->td;
350         struct throtl_service_queue *sq = &tg->service_queue;
351 
352         /*
353          * If on the default hierarchy, we switch to properly hierarchical
354          * behavior where limits on a given throtl_grp are applied to the
355          * whole subtree rather than just the group itself.  e.g. If 16M
356          * read_bps limit is set on the root group, the whole system can't
357          * exceed 16M for the device.
358          *
359          * If not on the default hierarchy, the broken flat hierarchy
360          * behavior is retained where all throtl_grps are treated as if
361          * they're all separate root groups right below throtl_data.
362          * Limits of a group don't interact with limits of other groups
363          * regardless of the position of the group in the hierarchy.
364          */
365         sq->parent_sq = &td->service_queue;
366         if (cgroup_subsys_on_dfl(io_cgrp_subsys) && blkg->parent)
367                 sq->parent_sq = &blkg_to_tg(blkg->parent)->service_queue;
368         tg->td = td;
369 }
370 
371 /*
372  * Set has_rules[] if @tg or any of its parents have limits configured.
373  * This doesn't require walking up to the top of the hierarchy as the
374  * parent's has_rules[] is guaranteed to be correct.
375  */
376 static void tg_update_has_rules(struct throtl_grp *tg)
377 {
378         struct throtl_grp *parent_tg = sq_to_tg(tg->service_queue.parent_sq);
379         int rw;
380 
381         for (rw = READ; rw <= WRITE; rw++)
382                 tg->has_rules[rw] = (parent_tg && parent_tg->has_rules[rw]) ||
383                                     (tg->bps[rw] != -1 || tg->iops[rw] != -1);
384 }
385 
386 static void throtl_pd_online(struct blkg_policy_data *pd)
387 {
388         /*
389          * We don't want new groups to escape the limits of its ancestors.
390          * Update has_rules[] after a new group is brought online.
391          */
392         tg_update_has_rules(pd_to_tg(pd));
393 }
394 
395 static void throtl_pd_free(struct blkg_policy_data *pd)
396 {
397         struct throtl_grp *tg = pd_to_tg(pd);
398 
399         del_timer_sync(&tg->service_queue.pending_timer);
400         kfree(tg);
401 }
402 
403 static struct throtl_grp *
404 throtl_rb_first(struct throtl_service_queue *parent_sq)
405 {
406         /* Service tree is empty */
407         if (!parent_sq->nr_pending)
408                 return NULL;
409 
410         if (!parent_sq->first_pending)
411                 parent_sq->first_pending = rb_first(&parent_sq->pending_tree);
412 
413         if (parent_sq->first_pending)
414                 return rb_entry_tg(parent_sq->first_pending);
415 
416         return NULL;
417 }
418 
419 static void rb_erase_init(struct rb_node *n, struct rb_root *root)
420 {
421         rb_erase(n, root);
422         RB_CLEAR_NODE(n);
423 }
424 
425 static void throtl_rb_erase(struct rb_node *n,
426                             struct throtl_service_queue *parent_sq)
427 {
428         if (parent_sq->first_pending == n)
429                 parent_sq->first_pending = NULL;
430         rb_erase_init(n, &parent_sq->pending_tree);
431         --parent_sq->nr_pending;
432 }
433 
434 static void update_min_dispatch_time(struct throtl_service_queue *parent_sq)
435 {
436         struct throtl_grp *tg;
437 
438         tg = throtl_rb_first(parent_sq);
439         if (!tg)
440                 return;
441 
442         parent_sq->first_pending_disptime = tg->disptime;
443 }
444 
445 static void tg_service_queue_add(struct throtl_grp *tg)
446 {
447         struct throtl_service_queue *parent_sq = tg->service_queue.parent_sq;
448         struct rb_node **node = &parent_sq->pending_tree.rb_node;
449         struct rb_node *parent = NULL;
450         struct throtl_grp *__tg;
451         unsigned long key = tg->disptime;
452         int left = 1;
453 
454         while (*node != NULL) {
455                 parent = *node;
456                 __tg = rb_entry_tg(parent);
457 
458                 if (time_before(key, __tg->disptime))
459                         node = &parent->rb_left;
460                 else {
461                         node = &parent->rb_right;
462                         left = 0;
463                 }
464         }
465 
466         if (left)
467                 parent_sq->first_pending = &tg->rb_node;
468 
469         rb_link_node(&tg->rb_node, parent, node);
470         rb_insert_color(&tg->rb_node, &parent_sq->pending_tree);
471 }
472 
473 static void __throtl_enqueue_tg(struct throtl_grp *tg)
474 {
475         tg_service_queue_add(tg);
476         tg->flags |= THROTL_TG_PENDING;
477         tg->service_queue.parent_sq->nr_pending++;
478 }
479 
480 static void throtl_enqueue_tg(struct throtl_grp *tg)
481 {
482         if (!(tg->flags & THROTL_TG_PENDING))
483                 __throtl_enqueue_tg(tg);
484 }
485 
486 static void __throtl_dequeue_tg(struct throtl_grp *tg)
487 {
488         throtl_rb_erase(&tg->rb_node, tg->service_queue.parent_sq);
489         tg->flags &= ~THROTL_TG_PENDING;
490 }
491 
492 static void throtl_dequeue_tg(struct throtl_grp *tg)
493 {
494         if (tg->flags & THROTL_TG_PENDING)
495                 __throtl_dequeue_tg(tg);
496 }
497 
498 /* Call with queue lock held */
499 static void throtl_schedule_pending_timer(struct throtl_service_queue *sq,
500                                           unsigned long expires)
501 {
502         mod_timer(&sq->pending_timer, expires);
503         throtl_log(sq, "schedule timer. delay=%lu jiffies=%lu",
504                    expires - jiffies, jiffies);
505 }
506 
507 /**
508  * throtl_schedule_next_dispatch - schedule the next dispatch cycle
509  * @sq: the service_queue to schedule dispatch for
510  * @force: force scheduling
511  *
512  * Arm @sq->pending_timer so that the next dispatch cycle starts on the
513  * dispatch time of the first pending child.  Returns %true if either timer
514  * is armed or there's no pending child left.  %false if the current
515  * dispatch window is still open and the caller should continue
516  * dispatching.
517  *
518  * If @force is %true, the dispatch timer is always scheduled and this
519  * function is guaranteed to return %true.  This is to be used when the
520  * caller can't dispatch itself and needs to invoke pending_timer
521  * unconditionally.  Note that forced scheduling is likely to induce short
522  * delay before dispatch starts even if @sq->first_pending_disptime is not
523  * in the future and thus shouldn't be used in hot paths.
524  */
525 static bool throtl_schedule_next_dispatch(struct throtl_service_queue *sq,
526                                           bool force)
527 {
528         /* any pending children left? */
529         if (!sq->nr_pending)
530                 return true;
531 
532         update_min_dispatch_time(sq);
533 
534         /* is the next dispatch time in the future? */
535         if (force || time_after(sq->first_pending_disptime, jiffies)) {
536                 throtl_schedule_pending_timer(sq, sq->first_pending_disptime);
537                 return true;
538         }
539 
540         /* tell the caller to continue dispatching */
541         return false;
542 }
543 
544 static inline void throtl_start_new_slice_with_credit(struct throtl_grp *tg,
545                 bool rw, unsigned long start)
546 {
547         tg->bytes_disp[rw] = 0;
548         tg->io_disp[rw] = 0;
549 
550         /*
551          * Previous slice has expired. We must have trimmed it after last
552          * bio dispatch. That means since start of last slice, we never used
553          * that bandwidth. Do try to make use of that bandwidth while giving
554          * credit.
555          */
556         if (time_after_eq(start, tg->slice_start[rw]))
557                 tg->slice_start[rw] = start;
558 
559         tg->slice_end[rw] = jiffies + throtl_slice;
560         throtl_log(&tg->service_queue,
561                    "[%c] new slice with credit start=%lu end=%lu jiffies=%lu",
562                    rw == READ ? 'R' : 'W', tg->slice_start[rw],
563                    tg->slice_end[rw], jiffies);
564 }
565 
566 static inline void throtl_start_new_slice(struct throtl_grp *tg, bool rw)
567 {
568         tg->bytes_disp[rw] = 0;
569         tg->io_disp[rw] = 0;
570         tg->slice_start[rw] = jiffies;
571         tg->slice_end[rw] = jiffies + throtl_slice;
572         throtl_log(&tg->service_queue,
573                    "[%c] new slice start=%lu end=%lu jiffies=%lu",
574                    rw == READ ? 'R' : 'W', tg->slice_start[rw],
575                    tg->slice_end[rw], jiffies);
576 }
577 
578 static inline void throtl_set_slice_end(struct throtl_grp *tg, bool rw,
579                                         unsigned long jiffy_end)
580 {
581         tg->slice_end[rw] = roundup(jiffy_end, throtl_slice);
582 }
583 
584 static inline void throtl_extend_slice(struct throtl_grp *tg, bool rw,
585                                        unsigned long jiffy_end)
586 {
587         tg->slice_end[rw] = roundup(jiffy_end, throtl_slice);
588         throtl_log(&tg->service_queue,
589                    "[%c] extend slice start=%lu end=%lu jiffies=%lu",
590                    rw == READ ? 'R' : 'W', tg->slice_start[rw],
591                    tg->slice_end[rw], jiffies);
592 }
593 
594 /* Determine if previously allocated or extended slice is complete or not */
595 static bool throtl_slice_used(struct throtl_grp *tg, bool rw)
596 {
597         if (time_in_range(jiffies, tg->slice_start[rw], tg->slice_end[rw]))
598                 return false;
599 
600         return 1;
601 }
602 
603 /* Trim the used slices and adjust slice start accordingly */
604 static inline void throtl_trim_slice(struct throtl_grp *tg, bool rw)
605 {
606         unsigned long nr_slices, time_elapsed, io_trim;
607         u64 bytes_trim, tmp;
608 
609         BUG_ON(time_before(tg->slice_end[rw], tg->slice_start[rw]));
610 
611         /*
612          * If bps are unlimited (-1), then time slice don't get
613          * renewed. Don't try to trim the slice if slice is used. A new
614          * slice will start when appropriate.
615          */
616         if (throtl_slice_used(tg, rw))
617                 return;
618 
619         /*
620          * A bio has been dispatched. Also adjust slice_end. It might happen
621          * that initially cgroup limit was very low resulting in high
622          * slice_end, but later limit was bumped up and bio was dispached
623          * sooner, then we need to reduce slice_end. A high bogus slice_end
624          * is bad because it does not allow new slice to start.
625          */
626 
627         throtl_set_slice_end(tg, rw, jiffies + throtl_slice);
628 
629         time_elapsed = jiffies - tg->slice_start[rw];
630 
631         nr_slices = time_elapsed / throtl_slice;
632 
633         if (!nr_slices)
634                 return;
635         tmp = tg->bps[rw] * throtl_slice * nr_slices;
636         do_div(tmp, HZ);
637         bytes_trim = tmp;
638 
639         io_trim = (tg->iops[rw] * throtl_slice * nr_slices)/HZ;
640 
641         if (!bytes_trim && !io_trim)
642                 return;
643 
644         if (tg->bytes_disp[rw] >= bytes_trim)
645                 tg->bytes_disp[rw] -= bytes_trim;
646         else
647                 tg->bytes_disp[rw] = 0;
648 
649         if (tg->io_disp[rw] >= io_trim)
650                 tg->io_disp[rw] -= io_trim;
651         else
652                 tg->io_disp[rw] = 0;
653 
654         tg->slice_start[rw] += nr_slices * throtl_slice;
655 
656         throtl_log(&tg->service_queue,
657                    "[%c] trim slice nr=%lu bytes=%llu io=%lu start=%lu end=%lu jiffies=%lu",
658                    rw == READ ? 'R' : 'W', nr_slices, bytes_trim, io_trim,
659                    tg->slice_start[rw], tg->slice_end[rw], jiffies);
660 }
661 
662 static bool tg_with_in_iops_limit(struct throtl_grp *tg, struct bio *bio,
663                                   unsigned long *wait)
664 {
665         bool rw = bio_data_dir(bio);
666         unsigned int io_allowed;
667         unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd;
668         u64 tmp;
669 
670         jiffy_elapsed = jiffy_elapsed_rnd = jiffies - tg->slice_start[rw];
671 
672         /* Slice has just started. Consider one slice interval */
673         if (!jiffy_elapsed)
674                 jiffy_elapsed_rnd = throtl_slice;
675 
676         jiffy_elapsed_rnd = roundup(jiffy_elapsed_rnd, throtl_slice);
677 
678         /*
679          * jiffy_elapsed_rnd should not be a big value as minimum iops can be
680          * 1 then at max jiffy elapsed should be equivalent of 1 second as we
681          * will allow dispatch after 1 second and after that slice should
682          * have been trimmed.
683          */
684 
685         tmp = (u64)tg->iops[rw] * jiffy_elapsed_rnd;
686         do_div(tmp, HZ);
687 
688         if (tmp > UINT_MAX)
689                 io_allowed = UINT_MAX;
690         else
691                 io_allowed = tmp;
692 
693         if (tg->io_disp[rw] + 1 <= io_allowed) {
694                 if (wait)
695                         *wait = 0;
696                 return true;
697         }
698 
699         /* Calc approx time to dispatch */
700         jiffy_wait = ((tg->io_disp[rw] + 1) * HZ)/tg->iops[rw] + 1;
701 
702         if (jiffy_wait > jiffy_elapsed)
703                 jiffy_wait = jiffy_wait - jiffy_elapsed;
704         else
705                 jiffy_wait = 1;
706 
707         if (wait)
708                 *wait = jiffy_wait;
709         return 0;
710 }
711 
712 static bool tg_with_in_bps_limit(struct throtl_grp *tg, struct bio *bio,
713                                  unsigned long *wait)
714 {
715         bool rw = bio_data_dir(bio);
716         u64 bytes_allowed, extra_bytes, tmp;
717         unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd;
718 
719         jiffy_elapsed = jiffy_elapsed_rnd = jiffies - tg->slice_start[rw];
720 
721         /* Slice has just started. Consider one slice interval */
722         if (!jiffy_elapsed)
723                 jiffy_elapsed_rnd = throtl_slice;
724 
725         jiffy_elapsed_rnd = roundup(jiffy_elapsed_rnd, throtl_slice);
726 
727         tmp = tg->bps[rw] * jiffy_elapsed_rnd;
728         do_div(tmp, HZ);
729         bytes_allowed = tmp;
730 
731         if (tg->bytes_disp[rw] + bio->bi_iter.bi_size <= bytes_allowed) {
732                 if (wait)
733                         *wait = 0;
734                 return true;
735         }
736 
737         /* Calc approx time to dispatch */
738         extra_bytes = tg->bytes_disp[rw] + bio->bi_iter.bi_size - bytes_allowed;
739         jiffy_wait = div64_u64(extra_bytes * HZ, tg->bps[rw]);
740 
741         if (!jiffy_wait)
742                 jiffy_wait = 1;
743 
744         /*
745          * This wait time is without taking into consideration the rounding
746          * up we did. Add that time also.
747          */
748         jiffy_wait = jiffy_wait + (jiffy_elapsed_rnd - jiffy_elapsed);
749         if (wait)
750                 *wait = jiffy_wait;
751         return 0;
752 }
753 
754 /*
755  * Returns whether one can dispatch a bio or not. Also returns approx number
756  * of jiffies to wait before this bio is with-in IO rate and can be dispatched
757  */
758 static bool tg_may_dispatch(struct throtl_grp *tg, struct bio *bio,
759                             unsigned long *wait)
760 {
761         bool rw = bio_data_dir(bio);
762         unsigned long bps_wait = 0, iops_wait = 0, max_wait = 0;
763 
764         /*
765          * Currently whole state machine of group depends on first bio
766          * queued in the group bio list. So one should not be calling
767          * this function with a different bio if there are other bios
768          * queued.
769          */
770         BUG_ON(tg->service_queue.nr_queued[rw] &&
771                bio != throtl_peek_queued(&tg->service_queue.queued[rw]));
772 
773         /* If tg->bps = -1, then BW is unlimited */
774         if (tg->bps[rw] == -1 && tg->iops[rw] == -1) {
775                 if (wait)
776                         *wait = 0;
777                 return true;
778         }
779 
780         /*
781          * If previous slice expired, start a new one otherwise renew/extend
782          * existing slice to make sure it is at least throtl_slice interval
783          * long since now. New slice is started only for empty throttle group.
784          * If there is queued bio, that means there should be an active
785          * slice and it should be extended instead.
786          */
787         if (throtl_slice_used(tg, rw) && !(tg->service_queue.nr_queued[rw]))
788                 throtl_start_new_slice(tg, rw);
789         else {
790                 if (time_before(tg->slice_end[rw], jiffies + throtl_slice))
791                         throtl_extend_slice(tg, rw, jiffies + throtl_slice);
792         }
793 
794         if (tg_with_in_bps_limit(tg, bio, &bps_wait) &&
795             tg_with_in_iops_limit(tg, bio, &iops_wait)) {
796                 if (wait)
797                         *wait = 0;
798                 return 1;
799         }
800 
801         max_wait = max(bps_wait, iops_wait);
802 
803         if (wait)
804                 *wait = max_wait;
805 
806         if (time_before(tg->slice_end[rw], jiffies + max_wait))
807                 throtl_extend_slice(tg, rw, jiffies + max_wait);
808 
809         return 0;
810 }
811 
812 static void throtl_charge_bio(struct throtl_grp *tg, struct bio *bio)
813 {
814         bool rw = bio_data_dir(bio);
815 
816         /* Charge the bio to the group */
817         tg->bytes_disp[rw] += bio->bi_iter.bi_size;
818         tg->io_disp[rw]++;
819 
820         /*
821          * BIO_THROTTLED is used to prevent the same bio to be throttled
822          * more than once as a throttled bio will go through blk-throtl the
823          * second time when it eventually gets issued.  Set it when a bio
824          * is being charged to a tg.
825          */
826         if (!bio_flagged(bio, BIO_THROTTLED))
827                 bio_set_flag(bio, BIO_THROTTLED);
828 }
829 
830 /**
831  * throtl_add_bio_tg - add a bio to the specified throtl_grp
832  * @bio: bio to add
833  * @qn: qnode to use
834  * @tg: the target throtl_grp
835  *
836  * Add @bio to @tg's service_queue using @qn.  If @qn is not specified,
837  * tg->qnode_on_self[] is used.
838  */
839 static void throtl_add_bio_tg(struct bio *bio, struct throtl_qnode *qn,
840                               struct throtl_grp *tg)
841 {
842         struct throtl_service_queue *sq = &tg->service_queue;
843         bool rw = bio_data_dir(bio);
844 
845         if (!qn)
846                 qn = &tg->qnode_on_self[rw];
847 
848         /*
849          * If @tg doesn't currently have any bios queued in the same
850          * direction, queueing @bio can change when @tg should be
851          * dispatched.  Mark that @tg was empty.  This is automatically
852          * cleaered on the next tg_update_disptime().
853          */
854         if (!sq->nr_queued[rw])
855                 tg->flags |= THROTL_TG_WAS_EMPTY;
856 
857         throtl_qnode_add_bio(bio, qn, &sq->queued[rw]);
858 
859         sq->nr_queued[rw]++;
860         throtl_enqueue_tg(tg);
861 }
862 
863 static void tg_update_disptime(struct throtl_grp *tg)
864 {
865         struct throtl_service_queue *sq = &tg->service_queue;
866         unsigned long read_wait = -1, write_wait = -1, min_wait = -1, disptime;
867         struct bio *bio;
868 
869         if ((bio = throtl_peek_queued(&sq->queued[READ])))
870                 tg_may_dispatch(tg, bio, &read_wait);
871 
872         if ((bio = throtl_peek_queued(&sq->queued[WRITE])))
873                 tg_may_dispatch(tg, bio, &write_wait);
874 
875         min_wait = min(read_wait, write_wait);
876         disptime = jiffies + min_wait;
877 
878         /* Update dispatch time */
879         throtl_dequeue_tg(tg);
880         tg->disptime = disptime;
881         throtl_enqueue_tg(tg);
882 
883         /* see throtl_add_bio_tg() */
884         tg->flags &= ~THROTL_TG_WAS_EMPTY;
885 }
886 
887 static void start_parent_slice_with_credit(struct throtl_grp *child_tg,
888                                         struct throtl_grp *parent_tg, bool rw)
889 {
890         if (throtl_slice_used(parent_tg, rw)) {
891                 throtl_start_new_slice_with_credit(parent_tg, rw,
892                                 child_tg->slice_start[rw]);
893         }
894 
895 }
896 
897 static void tg_dispatch_one_bio(struct throtl_grp *tg, bool rw)
898 {
899         struct throtl_service_queue *sq = &tg->service_queue;
900         struct throtl_service_queue *parent_sq = sq->parent_sq;
901         struct throtl_grp *parent_tg = sq_to_tg(parent_sq);
902         struct throtl_grp *tg_to_put = NULL;
903         struct bio *bio;
904 
905         /*
906          * @bio is being transferred from @tg to @parent_sq.  Popping a bio
907          * from @tg may put its reference and @parent_sq might end up
908          * getting released prematurely.  Remember the tg to put and put it
909          * after @bio is transferred to @parent_sq.
910          */
911         bio = throtl_pop_queued(&sq->queued[rw], &tg_to_put);
912         sq->nr_queued[rw]--;
913 
914         throtl_charge_bio(tg, bio);
915 
916         /*
917          * If our parent is another tg, we just need to transfer @bio to
918          * the parent using throtl_add_bio_tg().  If our parent is
919          * @td->service_queue, @bio is ready to be issued.  Put it on its
920          * bio_lists[] and decrease total number queued.  The caller is
921          * responsible for issuing these bios.
922          */
923         if (parent_tg) {
924                 throtl_add_bio_tg(bio, &tg->qnode_on_parent[rw], parent_tg);
925                 start_parent_slice_with_credit(tg, parent_tg, rw);
926         } else {
927                 throtl_qnode_add_bio(bio, &tg->qnode_on_parent[rw],
928                                      &parent_sq->queued[rw]);
929                 BUG_ON(tg->td->nr_queued[rw] <= 0);
930                 tg->td->nr_queued[rw]--;
931         }
932 
933         throtl_trim_slice(tg, rw);
934 
935         if (tg_to_put)
936                 blkg_put(tg_to_blkg(tg_to_put));
937 }
938 
939 static int throtl_dispatch_tg(struct throtl_grp *tg)
940 {
941         struct throtl_service_queue *sq = &tg->service_queue;
942         unsigned int nr_reads = 0, nr_writes = 0;
943         unsigned int max_nr_reads = throtl_grp_quantum*3/4;
944         unsigned int max_nr_writes = throtl_grp_quantum - max_nr_reads;
945         struct bio *bio;
946 
947         /* Try to dispatch 75% READS and 25% WRITES */
948 
949         while ((bio = throtl_peek_queued(&sq->queued[READ])) &&
950                tg_may_dispatch(tg, bio, NULL)) {
951 
952                 tg_dispatch_one_bio(tg, bio_data_dir(bio));
953                 nr_reads++;
954 
955                 if (nr_reads >= max_nr_reads)
956                         break;
957         }
958 
959         while ((bio = throtl_peek_queued(&sq->queued[WRITE])) &&
960                tg_may_dispatch(tg, bio, NULL)) {
961 
962                 tg_dispatch_one_bio(tg, bio_data_dir(bio));
963                 nr_writes++;
964 
965                 if (nr_writes >= max_nr_writes)
966                         break;
967         }
968 
969         return nr_reads + nr_writes;
970 }
971 
972 static int throtl_select_dispatch(struct throtl_service_queue *parent_sq)
973 {
974         unsigned int nr_disp = 0;
975 
976         while (1) {
977                 struct throtl_grp *tg = throtl_rb_first(parent_sq);
978                 struct throtl_service_queue *sq = &tg->service_queue;
979 
980                 if (!tg)
981                         break;
982 
983                 if (time_before(jiffies, tg->disptime))
984                         break;
985 
986                 throtl_dequeue_tg(tg);
987 
988                 nr_disp += throtl_dispatch_tg(tg);
989 
990                 if (sq->nr_queued[0] || sq->nr_queued[1])
991                         tg_update_disptime(tg);
992 
993                 if (nr_disp >= throtl_quantum)
994                         break;
995         }
996 
997         return nr_disp;
998 }
999 
1000 /**
1001  * throtl_pending_timer_fn - timer function for service_queue->pending_timer
1002  * @arg: the throtl_service_queue being serviced
1003  *
1004  * This timer is armed when a child throtl_grp with active bio's become
1005  * pending and queued on the service_queue's pending_tree and expires when
1006  * the first child throtl_grp should be dispatched.  This function
1007  * dispatches bio's from the children throtl_grps to the parent
1008  * service_queue.
1009  *
1010  * If the parent's parent is another throtl_grp, dispatching is propagated
1011  * by either arming its pending_timer or repeating dispatch directly.  If
1012  * the top-level service_tree is reached, throtl_data->dispatch_work is
1013  * kicked so that the ready bio's are issued.
1014  */
1015 static void throtl_pending_timer_fn(unsigned long arg)
1016 {
1017         struct throtl_service_queue *sq = (void *)arg;
1018         struct throtl_grp *tg = sq_to_tg(sq);
1019         struct throtl_data *td = sq_to_td(sq);
1020         struct request_queue *q = td->queue;
1021         struct throtl_service_queue *parent_sq;
1022         bool dispatched;
1023         int ret;
1024 
1025         spin_lock_irq(q->queue_lock);
1026 again:
1027         parent_sq = sq->parent_sq;
1028         dispatched = false;
1029 
1030         while (true) {
1031                 throtl_log(sq, "dispatch nr_queued=%u read=%u write=%u",
1032                            sq->nr_queued[READ] + sq->nr_queued[WRITE],
1033                            sq->nr_queued[READ], sq->nr_queued[WRITE]);
1034 
1035                 ret = throtl_select_dispatch(sq);
1036                 if (ret) {
1037                         throtl_log(sq, "bios disp=%u", ret);
1038                         dispatched = true;
1039                 }
1040 
1041                 if (throtl_schedule_next_dispatch(sq, false))
1042                         break;
1043 
1044                 /* this dispatch windows is still open, relax and repeat */
1045                 spin_unlock_irq(q->queue_lock);
1046                 cpu_relax();
1047                 spin_lock_irq(q->queue_lock);
1048         }
1049 
1050         if (!dispatched)
1051                 goto out_unlock;
1052 
1053         if (parent_sq) {
1054                 /* @parent_sq is another throl_grp, propagate dispatch */
1055                 if (tg->flags & THROTL_TG_WAS_EMPTY) {
1056                         tg_update_disptime(tg);
1057                         if (!throtl_schedule_next_dispatch(parent_sq, false)) {
1058                                 /* window is already open, repeat dispatching */
1059                                 sq = parent_sq;
1060                                 tg = sq_to_tg(sq);
1061                                 goto again;
1062                         }
1063                 }
1064         } else {
1065                 /* reached the top-level, queue issueing */
1066                 queue_work(kthrotld_workqueue, &td->dispatch_work);
1067         }
1068 out_unlock:
1069         spin_unlock_irq(q->queue_lock);
1070 }
1071 
1072 /**
1073  * blk_throtl_dispatch_work_fn - work function for throtl_data->dispatch_work
1074  * @work: work item being executed
1075  *
1076  * This function is queued for execution when bio's reach the bio_lists[]
1077  * of throtl_data->service_queue.  Those bio's are ready and issued by this
1078  * function.
1079  */
1080 static void blk_throtl_dispatch_work_fn(struct work_struct *work)
1081 {
1082         struct throtl_data *td = container_of(work, struct throtl_data,
1083                                               dispatch_work);
1084         struct throtl_service_queue *td_sq = &td->service_queue;
1085         struct request_queue *q = td->queue;
1086         struct bio_list bio_list_on_stack;
1087         struct bio *bio;
1088         struct blk_plug plug;
1089         int rw;
1090 
1091         bio_list_init(&bio_list_on_stack);
1092 
1093         spin_lock_irq(q->queue_lock);
1094         for (rw = READ; rw <= WRITE; rw++)
1095                 while ((bio = throtl_pop_queued(&td_sq->queued[rw], NULL)))
1096                         bio_list_add(&bio_list_on_stack, bio);
1097         spin_unlock_irq(q->queue_lock);
1098 
1099         if (!bio_list_empty(&bio_list_on_stack)) {
1100                 blk_start_plug(&plug);
1101                 while((bio = bio_list_pop(&bio_list_on_stack)))
1102                         generic_make_request(bio);
1103                 blk_finish_plug(&plug);
1104         }
1105 }
1106 
1107 static u64 tg_prfill_conf_u64(struct seq_file *sf, struct blkg_policy_data *pd,
1108                               int off)
1109 {
1110         struct throtl_grp *tg = pd_to_tg(pd);
1111         u64 v = *(u64 *)((void *)tg + off);
1112 
1113         if (v == -1)
1114                 return 0;
1115         return __blkg_prfill_u64(sf, pd, v);
1116 }
1117 
1118 static u64 tg_prfill_conf_uint(struct seq_file *sf, struct blkg_policy_data *pd,
1119                                int off)
1120 {
1121         struct throtl_grp *tg = pd_to_tg(pd);
1122         unsigned int v = *(unsigned int *)((void *)tg + off);
1123 
1124         if (v == -1)
1125                 return 0;
1126         return __blkg_prfill_u64(sf, pd, v);
1127 }
1128 
1129 static int tg_print_conf_u64(struct seq_file *sf, void *v)
1130 {
1131         blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)), tg_prfill_conf_u64,
1132                           &blkcg_policy_throtl, seq_cft(sf)->private, false);
1133         return 0;
1134 }
1135 
1136 static int tg_print_conf_uint(struct seq_file *sf, void *v)
1137 {
1138         blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)), tg_prfill_conf_uint,
1139                           &blkcg_policy_throtl, seq_cft(sf)->private, false);
1140         return 0;
1141 }
1142 
1143 static void tg_conf_updated(struct throtl_grp *tg)
1144 {
1145         struct throtl_service_queue *sq = &tg->service_queue;
1146         struct cgroup_subsys_state *pos_css;
1147         struct blkcg_gq *blkg;
1148 
1149         throtl_log(&tg->service_queue,
1150                    "limit change rbps=%llu wbps=%llu riops=%u wiops=%u",
1151                    tg->bps[READ], tg->bps[WRITE],
1152                    tg->iops[READ], tg->iops[WRITE]);
1153 
1154         /*
1155          * Update has_rules[] flags for the updated tg's subtree.  A tg is
1156          * considered to have rules if either the tg itself or any of its
1157          * ancestors has rules.  This identifies groups without any
1158          * restrictions in the whole hierarchy and allows them to bypass
1159          * blk-throttle.
1160          */
1161         blkg_for_each_descendant_pre(blkg, pos_css, tg_to_blkg(tg))
1162                 tg_update_has_rules(blkg_to_tg(blkg));
1163 
1164         /*
1165          * We're already holding queue_lock and know @tg is valid.  Let's
1166          * apply the new config directly.
1167          *
1168          * Restart the slices for both READ and WRITES. It might happen
1169          * that a group's limit are dropped suddenly and we don't want to
1170          * account recently dispatched IO with new low rate.
1171          */
1172         throtl_start_new_slice(tg, 0);
1173         throtl_start_new_slice(tg, 1);
1174 
1175         if (tg->flags & THROTL_TG_PENDING) {
1176                 tg_update_disptime(tg);
1177                 throtl_schedule_next_dispatch(sq->parent_sq, true);
1178         }
1179 }
1180 
1181 static ssize_t tg_set_conf(struct kernfs_open_file *of,
1182                            char *buf, size_t nbytes, loff_t off, bool is_u64)
1183 {
1184         struct blkcg *blkcg = css_to_blkcg(of_css(of));
1185         struct blkg_conf_ctx ctx;
1186         struct throtl_grp *tg;
1187         int ret;
1188         u64 v;
1189 
1190         ret = blkg_conf_prep(blkcg, &blkcg_policy_throtl, buf, &ctx);
1191         if (ret)
1192                 return ret;
1193 
1194         ret = -EINVAL;
1195         if (sscanf(ctx.body, "%llu", &v) != 1)
1196                 goto out_finish;
1197         if (!v)
1198                 v = -1;
1199 
1200         tg = blkg_to_tg(ctx.blkg);
1201 
1202         if (is_u64)
1203                 *(u64 *)((void *)tg + of_cft(of)->private) = v;
1204         else
1205                 *(unsigned int *)((void *)tg + of_cft(of)->private) = v;
1206 
1207         tg_conf_updated(tg);
1208         ret = 0;
1209 out_finish:
1210         blkg_conf_finish(&ctx);
1211         return ret ?: nbytes;
1212 }
1213 
1214 static ssize_t tg_set_conf_u64(struct kernfs_open_file *of,
1215                                char *buf, size_t nbytes, loff_t off)
1216 {
1217         return tg_set_conf(of, buf, nbytes, off, true);
1218 }
1219 
1220 static ssize_t tg_set_conf_uint(struct kernfs_open_file *of,
1221                                 char *buf, size_t nbytes, loff_t off)
1222 {
1223         return tg_set_conf(of, buf, nbytes, off, false);
1224 }
1225 
1226 static struct cftype throtl_legacy_files[] = {
1227         {
1228                 .name = "throttle.read_bps_device",
1229                 .private = offsetof(struct throtl_grp, bps[READ]),
1230                 .seq_show = tg_print_conf_u64,
1231                 .write = tg_set_conf_u64,
1232         },
1233         {
1234                 .name = "throttle.write_bps_device",
1235                 .private = offsetof(struct throtl_grp, bps[WRITE]),
1236                 .seq_show = tg_print_conf_u64,
1237                 .write = tg_set_conf_u64,
1238         },
1239         {
1240                 .name = "throttle.read_iops_device",
1241                 .private = offsetof(struct throtl_grp, iops[READ]),
1242                 .seq_show = tg_print_conf_uint,
1243                 .write = tg_set_conf_uint,
1244         },
1245         {
1246                 .name = "throttle.write_iops_device",
1247                 .private = offsetof(struct throtl_grp, iops[WRITE]),
1248                 .seq_show = tg_print_conf_uint,
1249                 .write = tg_set_conf_uint,
1250         },
1251         {
1252                 .name = "throttle.io_service_bytes",
1253                 .private = (unsigned long)&blkcg_policy_throtl,
1254                 .seq_show = blkg_print_stat_bytes,
1255         },
1256         {
1257                 .name = "throttle.io_serviced",
1258                 .private = (unsigned long)&blkcg_policy_throtl,
1259                 .seq_show = blkg_print_stat_ios,
1260         },
1261         { }     /* terminate */
1262 };
1263 
1264 static u64 tg_prfill_max(struct seq_file *sf, struct blkg_policy_data *pd,
1265                          int off)
1266 {
1267         struct throtl_grp *tg = pd_to_tg(pd);
1268         const char *dname = blkg_dev_name(pd->blkg);
1269         char bufs[4][21] = { "max", "max", "max", "max" };
1270 
1271         if (!dname)
1272                 return 0;
1273         if (tg->bps[READ] == -1 && tg->bps[WRITE] == -1 &&
1274             tg->iops[READ] == -1 && tg->iops[WRITE] == -1)
1275                 return 0;
1276 
1277         if (tg->bps[READ] != -1)
1278                 snprintf(bufs[0], sizeof(bufs[0]), "%llu", tg->bps[READ]);
1279         if (tg->bps[WRITE] != -1)
1280                 snprintf(bufs[1], sizeof(bufs[1]), "%llu", tg->bps[WRITE]);
1281         if (tg->iops[READ] != -1)
1282                 snprintf(bufs[2], sizeof(bufs[2]), "%u", tg->iops[READ]);
1283         if (tg->iops[WRITE] != -1)
1284                 snprintf(bufs[3], sizeof(bufs[3]), "%u", tg->iops[WRITE]);
1285 
1286         seq_printf(sf, "%s rbps=%s wbps=%s riops=%s wiops=%s\n",
1287                    dname, bufs[0], bufs[1], bufs[2], bufs[3]);
1288         return 0;
1289 }
1290 
1291 static int tg_print_max(struct seq_file *sf, void *v)
1292 {
1293         blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)), tg_prfill_max,
1294                           &blkcg_policy_throtl, seq_cft(sf)->private, false);
1295         return 0;
1296 }
1297 
1298 static ssize_t tg_set_max(struct kernfs_open_file *of,
1299                           char *buf, size_t nbytes, loff_t off)
1300 {
1301         struct blkcg *blkcg = css_to_blkcg(of_css(of));
1302         struct blkg_conf_ctx ctx;
1303         struct throtl_grp *tg;
1304         u64 v[4];
1305         int ret;
1306 
1307         ret = blkg_conf_prep(blkcg, &blkcg_policy_throtl, buf, &ctx);
1308         if (ret)
1309                 return ret;
1310 
1311         tg = blkg_to_tg(ctx.blkg);
1312 
1313         v[0] = tg->bps[READ];
1314         v[1] = tg->bps[WRITE];
1315         v[2] = tg->iops[READ];
1316         v[3] = tg->iops[WRITE];
1317 
1318         while (true) {
1319                 char tok[27];   /* wiops=18446744073709551616 */
1320                 char *p;
1321                 u64 val = -1;
1322                 int len;
1323 
1324                 if (sscanf(ctx.body, "%26s%n", tok, &len) != 1)
1325                         break;
1326                 if (tok[0] == '\0')
1327                         break;
1328                 ctx.body += len;
1329 
1330                 ret = -EINVAL;
1331                 p = tok;
1332                 strsep(&p, "=");
1333                 if (!p || (sscanf(p, "%llu", &val) != 1 && strcmp(p, "max")))
1334                         goto out_finish;
1335 
1336                 ret = -ERANGE;
1337                 if (!val)
1338                         goto out_finish;
1339 
1340                 ret = -EINVAL;
1341                 if (!strcmp(tok, "rbps"))
1342                         v[0] = val;
1343                 else if (!strcmp(tok, "wbps"))
1344                         v[1] = val;
1345                 else if (!strcmp(tok, "riops"))
1346                         v[2] = min_t(u64, val, UINT_MAX);
1347                 else if (!strcmp(tok, "wiops"))
1348                         v[3] = min_t(u64, val, UINT_MAX);
1349                 else
1350                         goto out_finish;
1351         }
1352 
1353         tg->bps[READ] = v[0];
1354         tg->bps[WRITE] = v[1];
1355         tg->iops[READ] = v[2];
1356         tg->iops[WRITE] = v[3];
1357 
1358         tg_conf_updated(tg);
1359         ret = 0;
1360 out_finish:
1361         blkg_conf_finish(&ctx);
1362         return ret ?: nbytes;
1363 }
1364 
1365 static struct cftype throtl_files[] = {
1366         {
1367                 .name = "max",
1368                 .flags = CFTYPE_NOT_ON_ROOT,
1369                 .seq_show = tg_print_max,
1370                 .write = tg_set_max,
1371         },
1372         { }     /* terminate */
1373 };
1374 
1375 static void throtl_shutdown_wq(struct request_queue *q)
1376 {
1377         struct throtl_data *td = q->td;
1378 
1379         cancel_work_sync(&td->dispatch_work);
1380 }
1381 
1382 static struct blkcg_policy blkcg_policy_throtl = {
1383         .dfl_cftypes            = throtl_files,
1384         .legacy_cftypes         = throtl_legacy_files,
1385 
1386         .pd_alloc_fn            = throtl_pd_alloc,
1387         .pd_init_fn             = throtl_pd_init,
1388         .pd_online_fn           = throtl_pd_online,
1389         .pd_free_fn             = throtl_pd_free,
1390 };
1391 
1392 bool blk_throtl_bio(struct request_queue *q, struct blkcg_gq *blkg,
1393                     struct bio *bio)
1394 {
1395         struct throtl_qnode *qn = NULL;
1396         struct throtl_grp *tg = blkg_to_tg(blkg ?: q->root_blkg);
1397         struct throtl_service_queue *sq;
1398         bool rw = bio_data_dir(bio);
1399         bool throttled = false;
1400 
1401         WARN_ON_ONCE(!rcu_read_lock_held());
1402 
1403         /* see throtl_charge_bio() */
1404         if (bio_flagged(bio, BIO_THROTTLED) || !tg->has_rules[rw])
1405                 goto out;
1406 
1407         spin_lock_irq(q->queue_lock);
1408 
1409         if (unlikely(blk_queue_bypass(q)))
1410                 goto out_unlock;
1411 
1412         sq = &tg->service_queue;
1413 
1414         while (true) {
1415                 /* throtl is FIFO - if bios are already queued, should queue */
1416                 if (sq->nr_queued[rw])
1417                         break;
1418 
1419                 /* if above limits, break to queue */
1420                 if (!tg_may_dispatch(tg, bio, NULL))
1421                         break;
1422 
1423                 /* within limits, let's charge and dispatch directly */
1424                 throtl_charge_bio(tg, bio);
1425 
1426                 /*
1427                  * We need to trim slice even when bios are not being queued
1428                  * otherwise it might happen that a bio is not queued for
1429                  * a long time and slice keeps on extending and trim is not
1430                  * called for a long time. Now if limits are reduced suddenly
1431                  * we take into account all the IO dispatched so far at new
1432                  * low rate and * newly queued IO gets a really long dispatch
1433                  * time.
1434                  *
1435                  * So keep on trimming slice even if bio is not queued.
1436                  */
1437                 throtl_trim_slice(tg, rw);
1438 
1439                 /*
1440                  * @bio passed through this layer without being throttled.
1441                  * Climb up the ladder.  If we''re already at the top, it
1442                  * can be executed directly.
1443                  */
1444                 qn = &tg->qnode_on_parent[rw];
1445                 sq = sq->parent_sq;
1446                 tg = sq_to_tg(sq);
1447                 if (!tg)
1448                         goto out_unlock;
1449         }
1450 
1451         /* out-of-limit, queue to @tg */
1452         throtl_log(sq, "[%c] bio. bdisp=%llu sz=%u bps=%llu iodisp=%u iops=%u queued=%d/%d",
1453                    rw == READ ? 'R' : 'W',
1454                    tg->bytes_disp[rw], bio->bi_iter.bi_size, tg->bps[rw],
1455                    tg->io_disp[rw], tg->iops[rw],
1456                    sq->nr_queued[READ], sq->nr_queued[WRITE]);
1457 
1458         bio_associate_current(bio);
1459         tg->td->nr_queued[rw]++;
1460         throtl_add_bio_tg(bio, qn, tg);
1461         throttled = true;
1462 
1463         /*
1464          * Update @tg's dispatch time and force schedule dispatch if @tg
1465          * was empty before @bio.  The forced scheduling isn't likely to
1466          * cause undue delay as @bio is likely to be dispatched directly if
1467          * its @tg's disptime is not in the future.
1468          */
1469         if (tg->flags & THROTL_TG_WAS_EMPTY) {
1470                 tg_update_disptime(tg);
1471                 throtl_schedule_next_dispatch(tg->service_queue.parent_sq, true);
1472         }
1473 
1474 out_unlock:
1475         spin_unlock_irq(q->queue_lock);
1476 out:
1477         /*
1478          * As multiple blk-throtls may stack in the same issue path, we
1479          * don't want bios to leave with the flag set.  Clear the flag if
1480          * being issued.
1481          */
1482         if (!throttled)
1483                 bio_clear_flag(bio, BIO_THROTTLED);
1484         return throttled;
1485 }
1486 
1487 /*
1488  * Dispatch all bios from all children tg's queued on @parent_sq.  On
1489  * return, @parent_sq is guaranteed to not have any active children tg's
1490  * and all bios from previously active tg's are on @parent_sq->bio_lists[].
1491  */
1492 static void tg_drain_bios(struct throtl_service_queue *parent_sq)
1493 {
1494         struct throtl_grp *tg;
1495 
1496         while ((tg = throtl_rb_first(parent_sq))) {
1497                 struct throtl_service_queue *sq = &tg->service_queue;
1498                 struct bio *bio;
1499 
1500                 throtl_dequeue_tg(tg);
1501 
1502                 while ((bio = throtl_peek_queued(&sq->queued[READ])))
1503                         tg_dispatch_one_bio(tg, bio_data_dir(bio));
1504                 while ((bio = throtl_peek_queued(&sq->queued[WRITE])))
1505                         tg_dispatch_one_bio(tg, bio_data_dir(bio));
1506         }
1507 }
1508 
1509 /**
1510  * blk_throtl_drain - drain throttled bios
1511  * @q: request_queue to drain throttled bios for
1512  *
1513  * Dispatch all currently throttled bios on @q through ->make_request_fn().
1514  */
1515 void blk_throtl_drain(struct request_queue *q)
1516         __releases(q->queue_lock) __acquires(q->queue_lock)
1517 {
1518         struct throtl_data *td = q->td;
1519         struct blkcg_gq *blkg;
1520         struct cgroup_subsys_state *pos_css;
1521         struct bio *bio;
1522         int rw;
1523 
1524         queue_lockdep_assert_held(q);
1525         rcu_read_lock();
1526 
1527         /*
1528          * Drain each tg while doing post-order walk on the blkg tree, so
1529          * that all bios are propagated to td->service_queue.  It'd be
1530          * better to walk service_queue tree directly but blkg walk is
1531          * easier.
1532          */
1533         blkg_for_each_descendant_post(blkg, pos_css, td->queue->root_blkg)
1534                 tg_drain_bios(&blkg_to_tg(blkg)->service_queue);
1535 
1536         /* finally, transfer bios from top-level tg's into the td */
1537         tg_drain_bios(&td->service_queue);
1538 
1539         rcu_read_unlock();
1540         spin_unlock_irq(q->queue_lock);
1541 
1542         /* all bios now should be in td->service_queue, issue them */
1543         for (rw = READ; rw <= WRITE; rw++)
1544                 while ((bio = throtl_pop_queued(&td->service_queue.queued[rw],
1545                                                 NULL)))
1546                         generic_make_request(bio);
1547 
1548         spin_lock_irq(q->queue_lock);
1549 }
1550 
1551 int blk_throtl_init(struct request_queue *q)
1552 {
1553         struct throtl_data *td;
1554         int ret;
1555 
1556         td = kzalloc_node(sizeof(*td), GFP_KERNEL, q->node);
1557         if (!td)
1558                 return -ENOMEM;
1559 
1560         INIT_WORK(&td->dispatch_work, blk_throtl_dispatch_work_fn);
1561         throtl_service_queue_init(&td->service_queue);
1562 
1563         q->td = td;
1564         td->queue = q;
1565 
1566         /* activate policy */
1567         ret = blkcg_activate_policy(q, &blkcg_policy_throtl);
1568         if (ret)
1569                 kfree(td);
1570         return ret;
1571 }
1572 
1573 void blk_throtl_exit(struct request_queue *q)
1574 {
1575         BUG_ON(!q->td);
1576         throtl_shutdown_wq(q);
1577         blkcg_deactivate_policy(q, &blkcg_policy_throtl);
1578         kfree(q->td);
1579 }
1580 
1581 static int __init throtl_init(void)
1582 {
1583         kthrotld_workqueue = alloc_workqueue("kthrotld", WQ_MEM_RECLAIM, 0);
1584         if (!kthrotld_workqueue)
1585                 panic("Failed to create kthrotld\n");
1586 
1587         return blkcg_policy_register(&blkcg_policy_throtl);
1588 }
1589 
1590 module_init(throtl_init);
1591 

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