xref: /openbmc/linux/block/blk-throttle.c (revision 4f205687)
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 	/*
149 	 * number of total undestroyed groups
150 	 */
151 	unsigned int nr_undestroyed_grps;
152 
153 	/* Work for dispatching throttled bios */
154 	struct work_struct dispatch_work;
155 };
156 
157 static void throtl_pending_timer_fn(unsigned long arg);
158 
159 static inline struct throtl_grp *pd_to_tg(struct blkg_policy_data *pd)
160 {
161 	return pd ? container_of(pd, struct throtl_grp, pd) : NULL;
162 }
163 
164 static inline struct throtl_grp *blkg_to_tg(struct blkcg_gq *blkg)
165 {
166 	return pd_to_tg(blkg_to_pd(blkg, &blkcg_policy_throtl));
167 }
168 
169 static inline struct blkcg_gq *tg_to_blkg(struct throtl_grp *tg)
170 {
171 	return pd_to_blkg(&tg->pd);
172 }
173 
174 /**
175  * sq_to_tg - return the throl_grp the specified service queue belongs to
176  * @sq: the throtl_service_queue of interest
177  *
178  * Return the throtl_grp @sq belongs to.  If @sq is the top-level one
179  * embedded in throtl_data, %NULL is returned.
180  */
181 static struct throtl_grp *sq_to_tg(struct throtl_service_queue *sq)
182 {
183 	if (sq && sq->parent_sq)
184 		return container_of(sq, struct throtl_grp, service_queue);
185 	else
186 		return NULL;
187 }
188 
189 /**
190  * sq_to_td - return throtl_data the specified service queue belongs to
191  * @sq: the throtl_service_queue of interest
192  *
193  * A service_queue can be embeded in either a throtl_grp or throtl_data.
194  * Determine the associated throtl_data accordingly and return it.
195  */
196 static struct throtl_data *sq_to_td(struct throtl_service_queue *sq)
197 {
198 	struct throtl_grp *tg = sq_to_tg(sq);
199 
200 	if (tg)
201 		return tg->td;
202 	else
203 		return container_of(sq, struct throtl_data, service_queue);
204 }
205 
206 /**
207  * throtl_log - log debug message via blktrace
208  * @sq: the service_queue being reported
209  * @fmt: printf format string
210  * @args: printf args
211  *
212  * The messages are prefixed with "throtl BLKG_NAME" if @sq belongs to a
213  * throtl_grp; otherwise, just "throtl".
214  */
215 #define throtl_log(sq, fmt, args...)	do {				\
216 	struct throtl_grp *__tg = sq_to_tg((sq));			\
217 	struct throtl_data *__td = sq_to_td((sq));			\
218 									\
219 	(void)__td;							\
220 	if (likely(!blk_trace_note_message_enabled(__td->queue)))	\
221 		break;							\
222 	if ((__tg)) {							\
223 		char __pbuf[128];					\
224 									\
225 		blkg_path(tg_to_blkg(__tg), __pbuf, sizeof(__pbuf));	\
226 		blk_add_trace_msg(__td->queue, "throtl %s " fmt, __pbuf, ##args); \
227 	} else {							\
228 		blk_add_trace_msg(__td->queue, "throtl " fmt, ##args);	\
229 	}								\
230 } while (0)
231 
232 static void throtl_qnode_init(struct throtl_qnode *qn, struct throtl_grp *tg)
233 {
234 	INIT_LIST_HEAD(&qn->node);
235 	bio_list_init(&qn->bios);
236 	qn->tg = tg;
237 }
238 
239 /**
240  * throtl_qnode_add_bio - add a bio to a throtl_qnode and activate it
241  * @bio: bio being added
242  * @qn: qnode to add bio to
243  * @queued: the service_queue->queued[] list @qn belongs to
244  *
245  * Add @bio to @qn and put @qn on @queued if it's not already on.
246  * @qn->tg's reference count is bumped when @qn is activated.  See the
247  * comment on top of throtl_qnode definition for details.
248  */
249 static void throtl_qnode_add_bio(struct bio *bio, struct throtl_qnode *qn,
250 				 struct list_head *queued)
251 {
252 	bio_list_add(&qn->bios, bio);
253 	if (list_empty(&qn->node)) {
254 		list_add_tail(&qn->node, queued);
255 		blkg_get(tg_to_blkg(qn->tg));
256 	}
257 }
258 
259 /**
260  * throtl_peek_queued - peek the first bio on a qnode list
261  * @queued: the qnode list to peek
262  */
263 static struct bio *throtl_peek_queued(struct list_head *queued)
264 {
265 	struct throtl_qnode *qn = list_first_entry(queued, struct throtl_qnode, node);
266 	struct bio *bio;
267 
268 	if (list_empty(queued))
269 		return NULL;
270 
271 	bio = bio_list_peek(&qn->bios);
272 	WARN_ON_ONCE(!bio);
273 	return bio;
274 }
275 
276 /**
277  * throtl_pop_queued - pop the first bio form a qnode list
278  * @queued: the qnode list to pop a bio from
279  * @tg_to_put: optional out argument for throtl_grp to put
280  *
281  * Pop the first bio from the qnode list @queued.  After popping, the first
282  * qnode is removed from @queued if empty or moved to the end of @queued so
283  * that the popping order is round-robin.
284  *
285  * When the first qnode is removed, its associated throtl_grp should be put
286  * too.  If @tg_to_put is NULL, this function automatically puts it;
287  * otherwise, *@tg_to_put is set to the throtl_grp to put and the caller is
288  * responsible for putting it.
289  */
290 static struct bio *throtl_pop_queued(struct list_head *queued,
291 				     struct throtl_grp **tg_to_put)
292 {
293 	struct throtl_qnode *qn = list_first_entry(queued, struct throtl_qnode, node);
294 	struct bio *bio;
295 
296 	if (list_empty(queued))
297 		return NULL;
298 
299 	bio = bio_list_pop(&qn->bios);
300 	WARN_ON_ONCE(!bio);
301 
302 	if (bio_list_empty(&qn->bios)) {
303 		list_del_init(&qn->node);
304 		if (tg_to_put)
305 			*tg_to_put = qn->tg;
306 		else
307 			blkg_put(tg_to_blkg(qn->tg));
308 	} else {
309 		list_move_tail(&qn->node, queued);
310 	}
311 
312 	return bio;
313 }
314 
315 /* init a service_queue, assumes the caller zeroed it */
316 static void throtl_service_queue_init(struct throtl_service_queue *sq)
317 {
318 	INIT_LIST_HEAD(&sq->queued[0]);
319 	INIT_LIST_HEAD(&sq->queued[1]);
320 	sq->pending_tree = RB_ROOT;
321 	setup_timer(&sq->pending_timer, throtl_pending_timer_fn,
322 		    (unsigned long)sq);
323 }
324 
325 static struct blkg_policy_data *throtl_pd_alloc(gfp_t gfp, int node)
326 {
327 	struct throtl_grp *tg;
328 	int rw;
329 
330 	tg = kzalloc_node(sizeof(*tg), gfp, node);
331 	if (!tg)
332 		return NULL;
333 
334 	throtl_service_queue_init(&tg->service_queue);
335 
336 	for (rw = READ; rw <= WRITE; rw++) {
337 		throtl_qnode_init(&tg->qnode_on_self[rw], tg);
338 		throtl_qnode_init(&tg->qnode_on_parent[rw], tg);
339 	}
340 
341 	RB_CLEAR_NODE(&tg->rb_node);
342 	tg->bps[READ] = -1;
343 	tg->bps[WRITE] = -1;
344 	tg->iops[READ] = -1;
345 	tg->iops[WRITE] = -1;
346 
347 	return &tg->pd;
348 }
349 
350 static void throtl_pd_init(struct blkg_policy_data *pd)
351 {
352 	struct throtl_grp *tg = pd_to_tg(pd);
353 	struct blkcg_gq *blkg = tg_to_blkg(tg);
354 	struct throtl_data *td = blkg->q->td;
355 	struct throtl_service_queue *sq = &tg->service_queue;
356 
357 	/*
358 	 * If on the default hierarchy, we switch to properly hierarchical
359 	 * behavior where limits on a given throtl_grp are applied to the
360 	 * whole subtree rather than just the group itself.  e.g. If 16M
361 	 * read_bps limit is set on the root group, the whole system can't
362 	 * exceed 16M for the device.
363 	 *
364 	 * If not on the default hierarchy, the broken flat hierarchy
365 	 * behavior is retained where all throtl_grps are treated as if
366 	 * they're all separate root groups right below throtl_data.
367 	 * Limits of a group don't interact with limits of other groups
368 	 * regardless of the position of the group in the hierarchy.
369 	 */
370 	sq->parent_sq = &td->service_queue;
371 	if (cgroup_subsys_on_dfl(io_cgrp_subsys) && blkg->parent)
372 		sq->parent_sq = &blkg_to_tg(blkg->parent)->service_queue;
373 	tg->td = td;
374 }
375 
376 /*
377  * Set has_rules[] if @tg or any of its parents have limits configured.
378  * This doesn't require walking up to the top of the hierarchy as the
379  * parent's has_rules[] is guaranteed to be correct.
380  */
381 static void tg_update_has_rules(struct throtl_grp *tg)
382 {
383 	struct throtl_grp *parent_tg = sq_to_tg(tg->service_queue.parent_sq);
384 	int rw;
385 
386 	for (rw = READ; rw <= WRITE; rw++)
387 		tg->has_rules[rw] = (parent_tg && parent_tg->has_rules[rw]) ||
388 				    (tg->bps[rw] != -1 || tg->iops[rw] != -1);
389 }
390 
391 static void throtl_pd_online(struct blkg_policy_data *pd)
392 {
393 	/*
394 	 * We don't want new groups to escape the limits of its ancestors.
395 	 * Update has_rules[] after a new group is brought online.
396 	 */
397 	tg_update_has_rules(pd_to_tg(pd));
398 }
399 
400 static void throtl_pd_free(struct blkg_policy_data *pd)
401 {
402 	struct throtl_grp *tg = pd_to_tg(pd);
403 
404 	del_timer_sync(&tg->service_queue.pending_timer);
405 	kfree(tg);
406 }
407 
408 static struct throtl_grp *
409 throtl_rb_first(struct throtl_service_queue *parent_sq)
410 {
411 	/* Service tree is empty */
412 	if (!parent_sq->nr_pending)
413 		return NULL;
414 
415 	if (!parent_sq->first_pending)
416 		parent_sq->first_pending = rb_first(&parent_sq->pending_tree);
417 
418 	if (parent_sq->first_pending)
419 		return rb_entry_tg(parent_sq->first_pending);
420 
421 	return NULL;
422 }
423 
424 static void rb_erase_init(struct rb_node *n, struct rb_root *root)
425 {
426 	rb_erase(n, root);
427 	RB_CLEAR_NODE(n);
428 }
429 
430 static void throtl_rb_erase(struct rb_node *n,
431 			    struct throtl_service_queue *parent_sq)
432 {
433 	if (parent_sq->first_pending == n)
434 		parent_sq->first_pending = NULL;
435 	rb_erase_init(n, &parent_sq->pending_tree);
436 	--parent_sq->nr_pending;
437 }
438 
439 static void update_min_dispatch_time(struct throtl_service_queue *parent_sq)
440 {
441 	struct throtl_grp *tg;
442 
443 	tg = throtl_rb_first(parent_sq);
444 	if (!tg)
445 		return;
446 
447 	parent_sq->first_pending_disptime = tg->disptime;
448 }
449 
450 static void tg_service_queue_add(struct throtl_grp *tg)
451 {
452 	struct throtl_service_queue *parent_sq = tg->service_queue.parent_sq;
453 	struct rb_node **node = &parent_sq->pending_tree.rb_node;
454 	struct rb_node *parent = NULL;
455 	struct throtl_grp *__tg;
456 	unsigned long key = tg->disptime;
457 	int left = 1;
458 
459 	while (*node != NULL) {
460 		parent = *node;
461 		__tg = rb_entry_tg(parent);
462 
463 		if (time_before(key, __tg->disptime))
464 			node = &parent->rb_left;
465 		else {
466 			node = &parent->rb_right;
467 			left = 0;
468 		}
469 	}
470 
471 	if (left)
472 		parent_sq->first_pending = &tg->rb_node;
473 
474 	rb_link_node(&tg->rb_node, parent, node);
475 	rb_insert_color(&tg->rb_node, &parent_sq->pending_tree);
476 }
477 
478 static void __throtl_enqueue_tg(struct throtl_grp *tg)
479 {
480 	tg_service_queue_add(tg);
481 	tg->flags |= THROTL_TG_PENDING;
482 	tg->service_queue.parent_sq->nr_pending++;
483 }
484 
485 static void throtl_enqueue_tg(struct throtl_grp *tg)
486 {
487 	if (!(tg->flags & THROTL_TG_PENDING))
488 		__throtl_enqueue_tg(tg);
489 }
490 
491 static void __throtl_dequeue_tg(struct throtl_grp *tg)
492 {
493 	throtl_rb_erase(&tg->rb_node, tg->service_queue.parent_sq);
494 	tg->flags &= ~THROTL_TG_PENDING;
495 }
496 
497 static void throtl_dequeue_tg(struct throtl_grp *tg)
498 {
499 	if (tg->flags & THROTL_TG_PENDING)
500 		__throtl_dequeue_tg(tg);
501 }
502 
503 /* Call with queue lock held */
504 static void throtl_schedule_pending_timer(struct throtl_service_queue *sq,
505 					  unsigned long expires)
506 {
507 	mod_timer(&sq->pending_timer, expires);
508 	throtl_log(sq, "schedule timer. delay=%lu jiffies=%lu",
509 		   expires - jiffies, jiffies);
510 }
511 
512 /**
513  * throtl_schedule_next_dispatch - schedule the next dispatch cycle
514  * @sq: the service_queue to schedule dispatch for
515  * @force: force scheduling
516  *
517  * Arm @sq->pending_timer so that the next dispatch cycle starts on the
518  * dispatch time of the first pending child.  Returns %true if either timer
519  * is armed or there's no pending child left.  %false if the current
520  * dispatch window is still open and the caller should continue
521  * dispatching.
522  *
523  * If @force is %true, the dispatch timer is always scheduled and this
524  * function is guaranteed to return %true.  This is to be used when the
525  * caller can't dispatch itself and needs to invoke pending_timer
526  * unconditionally.  Note that forced scheduling is likely to induce short
527  * delay before dispatch starts even if @sq->first_pending_disptime is not
528  * in the future and thus shouldn't be used in hot paths.
529  */
530 static bool throtl_schedule_next_dispatch(struct throtl_service_queue *sq,
531 					  bool force)
532 {
533 	/* any pending children left? */
534 	if (!sq->nr_pending)
535 		return true;
536 
537 	update_min_dispatch_time(sq);
538 
539 	/* is the next dispatch time in the future? */
540 	if (force || time_after(sq->first_pending_disptime, jiffies)) {
541 		throtl_schedule_pending_timer(sq, sq->first_pending_disptime);
542 		return true;
543 	}
544 
545 	/* tell the caller to continue dispatching */
546 	return false;
547 }
548 
549 static inline void throtl_start_new_slice_with_credit(struct throtl_grp *tg,
550 		bool rw, unsigned long start)
551 {
552 	tg->bytes_disp[rw] = 0;
553 	tg->io_disp[rw] = 0;
554 
555 	/*
556 	 * Previous slice has expired. We must have trimmed it after last
557 	 * bio dispatch. That means since start of last slice, we never used
558 	 * that bandwidth. Do try to make use of that bandwidth while giving
559 	 * credit.
560 	 */
561 	if (time_after_eq(start, tg->slice_start[rw]))
562 		tg->slice_start[rw] = start;
563 
564 	tg->slice_end[rw] = jiffies + throtl_slice;
565 	throtl_log(&tg->service_queue,
566 		   "[%c] new slice with credit start=%lu end=%lu jiffies=%lu",
567 		   rw == READ ? 'R' : 'W', tg->slice_start[rw],
568 		   tg->slice_end[rw], jiffies);
569 }
570 
571 static inline void throtl_start_new_slice(struct throtl_grp *tg, bool rw)
572 {
573 	tg->bytes_disp[rw] = 0;
574 	tg->io_disp[rw] = 0;
575 	tg->slice_start[rw] = jiffies;
576 	tg->slice_end[rw] = jiffies + throtl_slice;
577 	throtl_log(&tg->service_queue,
578 		   "[%c] new slice start=%lu end=%lu jiffies=%lu",
579 		   rw == READ ? 'R' : 'W', tg->slice_start[rw],
580 		   tg->slice_end[rw], jiffies);
581 }
582 
583 static inline void throtl_set_slice_end(struct throtl_grp *tg, bool rw,
584 					unsigned long jiffy_end)
585 {
586 	tg->slice_end[rw] = roundup(jiffy_end, throtl_slice);
587 }
588 
589 static inline void throtl_extend_slice(struct throtl_grp *tg, bool rw,
590 				       unsigned long jiffy_end)
591 {
592 	tg->slice_end[rw] = roundup(jiffy_end, throtl_slice);
593 	throtl_log(&tg->service_queue,
594 		   "[%c] extend slice start=%lu end=%lu jiffies=%lu",
595 		   rw == READ ? 'R' : 'W', tg->slice_start[rw],
596 		   tg->slice_end[rw], jiffies);
597 }
598 
599 /* Determine if previously allocated or extended slice is complete or not */
600 static bool throtl_slice_used(struct throtl_grp *tg, bool rw)
601 {
602 	if (time_in_range(jiffies, tg->slice_start[rw], tg->slice_end[rw]))
603 		return false;
604 
605 	return 1;
606 }
607 
608 /* Trim the used slices and adjust slice start accordingly */
609 static inline void throtl_trim_slice(struct throtl_grp *tg, bool rw)
610 {
611 	unsigned long nr_slices, time_elapsed, io_trim;
612 	u64 bytes_trim, tmp;
613 
614 	BUG_ON(time_before(tg->slice_end[rw], tg->slice_start[rw]));
615 
616 	/*
617 	 * If bps are unlimited (-1), then time slice don't get
618 	 * renewed. Don't try to trim the slice if slice is used. A new
619 	 * slice will start when appropriate.
620 	 */
621 	if (throtl_slice_used(tg, rw))
622 		return;
623 
624 	/*
625 	 * A bio has been dispatched. Also adjust slice_end. It might happen
626 	 * that initially cgroup limit was very low resulting in high
627 	 * slice_end, but later limit was bumped up and bio was dispached
628 	 * sooner, then we need to reduce slice_end. A high bogus slice_end
629 	 * is bad because it does not allow new slice to start.
630 	 */
631 
632 	throtl_set_slice_end(tg, rw, jiffies + throtl_slice);
633 
634 	time_elapsed = jiffies - tg->slice_start[rw];
635 
636 	nr_slices = time_elapsed / throtl_slice;
637 
638 	if (!nr_slices)
639 		return;
640 	tmp = tg->bps[rw] * throtl_slice * nr_slices;
641 	do_div(tmp, HZ);
642 	bytes_trim = tmp;
643 
644 	io_trim = (tg->iops[rw] * throtl_slice * nr_slices)/HZ;
645 
646 	if (!bytes_trim && !io_trim)
647 		return;
648 
649 	if (tg->bytes_disp[rw] >= bytes_trim)
650 		tg->bytes_disp[rw] -= bytes_trim;
651 	else
652 		tg->bytes_disp[rw] = 0;
653 
654 	if (tg->io_disp[rw] >= io_trim)
655 		tg->io_disp[rw] -= io_trim;
656 	else
657 		tg->io_disp[rw] = 0;
658 
659 	tg->slice_start[rw] += nr_slices * throtl_slice;
660 
661 	throtl_log(&tg->service_queue,
662 		   "[%c] trim slice nr=%lu bytes=%llu io=%lu start=%lu end=%lu jiffies=%lu",
663 		   rw == READ ? 'R' : 'W', nr_slices, bytes_trim, io_trim,
664 		   tg->slice_start[rw], tg->slice_end[rw], jiffies);
665 }
666 
667 static bool tg_with_in_iops_limit(struct throtl_grp *tg, struct bio *bio,
668 				  unsigned long *wait)
669 {
670 	bool rw = bio_data_dir(bio);
671 	unsigned int io_allowed;
672 	unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd;
673 	u64 tmp;
674 
675 	jiffy_elapsed = jiffy_elapsed_rnd = jiffies - tg->slice_start[rw];
676 
677 	/* Slice has just started. Consider one slice interval */
678 	if (!jiffy_elapsed)
679 		jiffy_elapsed_rnd = throtl_slice;
680 
681 	jiffy_elapsed_rnd = roundup(jiffy_elapsed_rnd, throtl_slice);
682 
683 	/*
684 	 * jiffy_elapsed_rnd should not be a big value as minimum iops can be
685 	 * 1 then at max jiffy elapsed should be equivalent of 1 second as we
686 	 * will allow dispatch after 1 second and after that slice should
687 	 * have been trimmed.
688 	 */
689 
690 	tmp = (u64)tg->iops[rw] * jiffy_elapsed_rnd;
691 	do_div(tmp, HZ);
692 
693 	if (tmp > UINT_MAX)
694 		io_allowed = UINT_MAX;
695 	else
696 		io_allowed = tmp;
697 
698 	if (tg->io_disp[rw] + 1 <= io_allowed) {
699 		if (wait)
700 			*wait = 0;
701 		return true;
702 	}
703 
704 	/* Calc approx time to dispatch */
705 	jiffy_wait = ((tg->io_disp[rw] + 1) * HZ)/tg->iops[rw] + 1;
706 
707 	if (jiffy_wait > jiffy_elapsed)
708 		jiffy_wait = jiffy_wait - jiffy_elapsed;
709 	else
710 		jiffy_wait = 1;
711 
712 	if (wait)
713 		*wait = jiffy_wait;
714 	return 0;
715 }
716 
717 static bool tg_with_in_bps_limit(struct throtl_grp *tg, struct bio *bio,
718 				 unsigned long *wait)
719 {
720 	bool rw = bio_data_dir(bio);
721 	u64 bytes_allowed, extra_bytes, tmp;
722 	unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd;
723 
724 	jiffy_elapsed = jiffy_elapsed_rnd = jiffies - tg->slice_start[rw];
725 
726 	/* Slice has just started. Consider one slice interval */
727 	if (!jiffy_elapsed)
728 		jiffy_elapsed_rnd = throtl_slice;
729 
730 	jiffy_elapsed_rnd = roundup(jiffy_elapsed_rnd, throtl_slice);
731 
732 	tmp = tg->bps[rw] * jiffy_elapsed_rnd;
733 	do_div(tmp, HZ);
734 	bytes_allowed = tmp;
735 
736 	if (tg->bytes_disp[rw] + bio->bi_iter.bi_size <= bytes_allowed) {
737 		if (wait)
738 			*wait = 0;
739 		return true;
740 	}
741 
742 	/* Calc approx time to dispatch */
743 	extra_bytes = tg->bytes_disp[rw] + bio->bi_iter.bi_size - bytes_allowed;
744 	jiffy_wait = div64_u64(extra_bytes * HZ, tg->bps[rw]);
745 
746 	if (!jiffy_wait)
747 		jiffy_wait = 1;
748 
749 	/*
750 	 * This wait time is without taking into consideration the rounding
751 	 * up we did. Add that time also.
752 	 */
753 	jiffy_wait = jiffy_wait + (jiffy_elapsed_rnd - jiffy_elapsed);
754 	if (wait)
755 		*wait = jiffy_wait;
756 	return 0;
757 }
758 
759 /*
760  * Returns whether one can dispatch a bio or not. Also returns approx number
761  * of jiffies to wait before this bio is with-in IO rate and can be dispatched
762  */
763 static bool tg_may_dispatch(struct throtl_grp *tg, struct bio *bio,
764 			    unsigned long *wait)
765 {
766 	bool rw = bio_data_dir(bio);
767 	unsigned long bps_wait = 0, iops_wait = 0, max_wait = 0;
768 
769 	/*
770  	 * Currently whole state machine of group depends on first bio
771 	 * queued in the group bio list. So one should not be calling
772 	 * this function with a different bio if there are other bios
773 	 * queued.
774 	 */
775 	BUG_ON(tg->service_queue.nr_queued[rw] &&
776 	       bio != throtl_peek_queued(&tg->service_queue.queued[rw]));
777 
778 	/* If tg->bps = -1, then BW is unlimited */
779 	if (tg->bps[rw] == -1 && tg->iops[rw] == -1) {
780 		if (wait)
781 			*wait = 0;
782 		return true;
783 	}
784 
785 	/*
786 	 * If previous slice expired, start a new one otherwise renew/extend
787 	 * existing slice to make sure it is at least throtl_slice interval
788 	 * long since now.
789 	 */
790 	if (throtl_slice_used(tg, rw))
791 		throtl_start_new_slice(tg, rw);
792 	else {
793 		if (time_before(tg->slice_end[rw], jiffies + throtl_slice))
794 			throtl_extend_slice(tg, rw, jiffies + throtl_slice);
795 	}
796 
797 	if (tg_with_in_bps_limit(tg, bio, &bps_wait) &&
798 	    tg_with_in_iops_limit(tg, bio, &iops_wait)) {
799 		if (wait)
800 			*wait = 0;
801 		return 1;
802 	}
803 
804 	max_wait = max(bps_wait, iops_wait);
805 
806 	if (wait)
807 		*wait = max_wait;
808 
809 	if (time_before(tg->slice_end[rw], jiffies + max_wait))
810 		throtl_extend_slice(tg, rw, jiffies + max_wait);
811 
812 	return 0;
813 }
814 
815 static void throtl_charge_bio(struct throtl_grp *tg, struct bio *bio)
816 {
817 	bool rw = bio_data_dir(bio);
818 
819 	/* Charge the bio to the group */
820 	tg->bytes_disp[rw] += bio->bi_iter.bi_size;
821 	tg->io_disp[rw]++;
822 
823 	/*
824 	 * REQ_THROTTLED is used to prevent the same bio to be throttled
825 	 * more than once as a throttled bio will go through blk-throtl the
826 	 * second time when it eventually gets issued.  Set it when a bio
827 	 * is being charged to a tg.
828 	 */
829 	if (!(bio->bi_rw & REQ_THROTTLED))
830 		bio->bi_rw |= REQ_THROTTLED;
831 }
832 
833 /**
834  * throtl_add_bio_tg - add a bio to the specified throtl_grp
835  * @bio: bio to add
836  * @qn: qnode to use
837  * @tg: the target throtl_grp
838  *
839  * Add @bio to @tg's service_queue using @qn.  If @qn is not specified,
840  * tg->qnode_on_self[] is used.
841  */
842 static void throtl_add_bio_tg(struct bio *bio, struct throtl_qnode *qn,
843 			      struct throtl_grp *tg)
844 {
845 	struct throtl_service_queue *sq = &tg->service_queue;
846 	bool rw = bio_data_dir(bio);
847 
848 	if (!qn)
849 		qn = &tg->qnode_on_self[rw];
850 
851 	/*
852 	 * If @tg doesn't currently have any bios queued in the same
853 	 * direction, queueing @bio can change when @tg should be
854 	 * dispatched.  Mark that @tg was empty.  This is automatically
855 	 * cleaered on the next tg_update_disptime().
856 	 */
857 	if (!sq->nr_queued[rw])
858 		tg->flags |= THROTL_TG_WAS_EMPTY;
859 
860 	throtl_qnode_add_bio(bio, qn, &sq->queued[rw]);
861 
862 	sq->nr_queued[rw]++;
863 	throtl_enqueue_tg(tg);
864 }
865 
866 static void tg_update_disptime(struct throtl_grp *tg)
867 {
868 	struct throtl_service_queue *sq = &tg->service_queue;
869 	unsigned long read_wait = -1, write_wait = -1, min_wait = -1, disptime;
870 	struct bio *bio;
871 
872 	if ((bio = throtl_peek_queued(&sq->queued[READ])))
873 		tg_may_dispatch(tg, bio, &read_wait);
874 
875 	if ((bio = throtl_peek_queued(&sq->queued[WRITE])))
876 		tg_may_dispatch(tg, bio, &write_wait);
877 
878 	min_wait = min(read_wait, write_wait);
879 	disptime = jiffies + min_wait;
880 
881 	/* Update dispatch time */
882 	throtl_dequeue_tg(tg);
883 	tg->disptime = disptime;
884 	throtl_enqueue_tg(tg);
885 
886 	/* see throtl_add_bio_tg() */
887 	tg->flags &= ~THROTL_TG_WAS_EMPTY;
888 }
889 
890 static void start_parent_slice_with_credit(struct throtl_grp *child_tg,
891 					struct throtl_grp *parent_tg, bool rw)
892 {
893 	if (throtl_slice_used(parent_tg, rw)) {
894 		throtl_start_new_slice_with_credit(parent_tg, rw,
895 				child_tg->slice_start[rw]);
896 	}
897 
898 }
899 
900 static void tg_dispatch_one_bio(struct throtl_grp *tg, bool rw)
901 {
902 	struct throtl_service_queue *sq = &tg->service_queue;
903 	struct throtl_service_queue *parent_sq = sq->parent_sq;
904 	struct throtl_grp *parent_tg = sq_to_tg(parent_sq);
905 	struct throtl_grp *tg_to_put = NULL;
906 	struct bio *bio;
907 
908 	/*
909 	 * @bio is being transferred from @tg to @parent_sq.  Popping a bio
910 	 * from @tg may put its reference and @parent_sq might end up
911 	 * getting released prematurely.  Remember the tg to put and put it
912 	 * after @bio is transferred to @parent_sq.
913 	 */
914 	bio = throtl_pop_queued(&sq->queued[rw], &tg_to_put);
915 	sq->nr_queued[rw]--;
916 
917 	throtl_charge_bio(tg, bio);
918 
919 	/*
920 	 * If our parent is another tg, we just need to transfer @bio to
921 	 * the parent using throtl_add_bio_tg().  If our parent is
922 	 * @td->service_queue, @bio is ready to be issued.  Put it on its
923 	 * bio_lists[] and decrease total number queued.  The caller is
924 	 * responsible for issuing these bios.
925 	 */
926 	if (parent_tg) {
927 		throtl_add_bio_tg(bio, &tg->qnode_on_parent[rw], parent_tg);
928 		start_parent_slice_with_credit(tg, parent_tg, rw);
929 	} else {
930 		throtl_qnode_add_bio(bio, &tg->qnode_on_parent[rw],
931 				     &parent_sq->queued[rw]);
932 		BUG_ON(tg->td->nr_queued[rw] <= 0);
933 		tg->td->nr_queued[rw]--;
934 	}
935 
936 	throtl_trim_slice(tg, rw);
937 
938 	if (tg_to_put)
939 		blkg_put(tg_to_blkg(tg_to_put));
940 }
941 
942 static int throtl_dispatch_tg(struct throtl_grp *tg)
943 {
944 	struct throtl_service_queue *sq = &tg->service_queue;
945 	unsigned int nr_reads = 0, nr_writes = 0;
946 	unsigned int max_nr_reads = throtl_grp_quantum*3/4;
947 	unsigned int max_nr_writes = throtl_grp_quantum - max_nr_reads;
948 	struct bio *bio;
949 
950 	/* Try to dispatch 75% READS and 25% WRITES */
951 
952 	while ((bio = throtl_peek_queued(&sq->queued[READ])) &&
953 	       tg_may_dispatch(tg, bio, NULL)) {
954 
955 		tg_dispatch_one_bio(tg, bio_data_dir(bio));
956 		nr_reads++;
957 
958 		if (nr_reads >= max_nr_reads)
959 			break;
960 	}
961 
962 	while ((bio = throtl_peek_queued(&sq->queued[WRITE])) &&
963 	       tg_may_dispatch(tg, bio, NULL)) {
964 
965 		tg_dispatch_one_bio(tg, bio_data_dir(bio));
966 		nr_writes++;
967 
968 		if (nr_writes >= max_nr_writes)
969 			break;
970 	}
971 
972 	return nr_reads + nr_writes;
973 }
974 
975 static int throtl_select_dispatch(struct throtl_service_queue *parent_sq)
976 {
977 	unsigned int nr_disp = 0;
978 
979 	while (1) {
980 		struct throtl_grp *tg = throtl_rb_first(parent_sq);
981 		struct throtl_service_queue *sq = &tg->service_queue;
982 
983 		if (!tg)
984 			break;
985 
986 		if (time_before(jiffies, tg->disptime))
987 			break;
988 
989 		throtl_dequeue_tg(tg);
990 
991 		nr_disp += throtl_dispatch_tg(tg);
992 
993 		if (sq->nr_queued[0] || sq->nr_queued[1])
994 			tg_update_disptime(tg);
995 
996 		if (nr_disp >= throtl_quantum)
997 			break;
998 	}
999 
1000 	return nr_disp;
1001 }
1002 
1003 /**
1004  * throtl_pending_timer_fn - timer function for service_queue->pending_timer
1005  * @arg: the throtl_service_queue being serviced
1006  *
1007  * This timer is armed when a child throtl_grp with active bio's become
1008  * pending and queued on the service_queue's pending_tree and expires when
1009  * the first child throtl_grp should be dispatched.  This function
1010  * dispatches bio's from the children throtl_grps to the parent
1011  * service_queue.
1012  *
1013  * If the parent's parent is another throtl_grp, dispatching is propagated
1014  * by either arming its pending_timer or repeating dispatch directly.  If
1015  * the top-level service_tree is reached, throtl_data->dispatch_work is
1016  * kicked so that the ready bio's are issued.
1017  */
1018 static void throtl_pending_timer_fn(unsigned long arg)
1019 {
1020 	struct throtl_service_queue *sq = (void *)arg;
1021 	struct throtl_grp *tg = sq_to_tg(sq);
1022 	struct throtl_data *td = sq_to_td(sq);
1023 	struct request_queue *q = td->queue;
1024 	struct throtl_service_queue *parent_sq;
1025 	bool dispatched;
1026 	int ret;
1027 
1028 	spin_lock_irq(q->queue_lock);
1029 again:
1030 	parent_sq = sq->parent_sq;
1031 	dispatched = false;
1032 
1033 	while (true) {
1034 		throtl_log(sq, "dispatch nr_queued=%u read=%u write=%u",
1035 			   sq->nr_queued[READ] + sq->nr_queued[WRITE],
1036 			   sq->nr_queued[READ], sq->nr_queued[WRITE]);
1037 
1038 		ret = throtl_select_dispatch(sq);
1039 		if (ret) {
1040 			throtl_log(sq, "bios disp=%u", ret);
1041 			dispatched = true;
1042 		}
1043 
1044 		if (throtl_schedule_next_dispatch(sq, false))
1045 			break;
1046 
1047 		/* this dispatch windows is still open, relax and repeat */
1048 		spin_unlock_irq(q->queue_lock);
1049 		cpu_relax();
1050 		spin_lock_irq(q->queue_lock);
1051 	}
1052 
1053 	if (!dispatched)
1054 		goto out_unlock;
1055 
1056 	if (parent_sq) {
1057 		/* @parent_sq is another throl_grp, propagate dispatch */
1058 		if (tg->flags & THROTL_TG_WAS_EMPTY) {
1059 			tg_update_disptime(tg);
1060 			if (!throtl_schedule_next_dispatch(parent_sq, false)) {
1061 				/* window is already open, repeat dispatching */
1062 				sq = parent_sq;
1063 				tg = sq_to_tg(sq);
1064 				goto again;
1065 			}
1066 		}
1067 	} else {
1068 		/* reached the top-level, queue issueing */
1069 		queue_work(kthrotld_workqueue, &td->dispatch_work);
1070 	}
1071 out_unlock:
1072 	spin_unlock_irq(q->queue_lock);
1073 }
1074 
1075 /**
1076  * blk_throtl_dispatch_work_fn - work function for throtl_data->dispatch_work
1077  * @work: work item being executed
1078  *
1079  * This function is queued for execution when bio's reach the bio_lists[]
1080  * of throtl_data->service_queue.  Those bio's are ready and issued by this
1081  * function.
1082  */
1083 static void blk_throtl_dispatch_work_fn(struct work_struct *work)
1084 {
1085 	struct throtl_data *td = container_of(work, struct throtl_data,
1086 					      dispatch_work);
1087 	struct throtl_service_queue *td_sq = &td->service_queue;
1088 	struct request_queue *q = td->queue;
1089 	struct bio_list bio_list_on_stack;
1090 	struct bio *bio;
1091 	struct blk_plug plug;
1092 	int rw;
1093 
1094 	bio_list_init(&bio_list_on_stack);
1095 
1096 	spin_lock_irq(q->queue_lock);
1097 	for (rw = READ; rw <= WRITE; rw++)
1098 		while ((bio = throtl_pop_queued(&td_sq->queued[rw], NULL)))
1099 			bio_list_add(&bio_list_on_stack, bio);
1100 	spin_unlock_irq(q->queue_lock);
1101 
1102 	if (!bio_list_empty(&bio_list_on_stack)) {
1103 		blk_start_plug(&plug);
1104 		while((bio = bio_list_pop(&bio_list_on_stack)))
1105 			generic_make_request(bio);
1106 		blk_finish_plug(&plug);
1107 	}
1108 }
1109 
1110 static u64 tg_prfill_conf_u64(struct seq_file *sf, struct blkg_policy_data *pd,
1111 			      int off)
1112 {
1113 	struct throtl_grp *tg = pd_to_tg(pd);
1114 	u64 v = *(u64 *)((void *)tg + off);
1115 
1116 	if (v == -1)
1117 		return 0;
1118 	return __blkg_prfill_u64(sf, pd, v);
1119 }
1120 
1121 static u64 tg_prfill_conf_uint(struct seq_file *sf, struct blkg_policy_data *pd,
1122 			       int off)
1123 {
1124 	struct throtl_grp *tg = pd_to_tg(pd);
1125 	unsigned int v = *(unsigned int *)((void *)tg + off);
1126 
1127 	if (v == -1)
1128 		return 0;
1129 	return __blkg_prfill_u64(sf, pd, v);
1130 }
1131 
1132 static int tg_print_conf_u64(struct seq_file *sf, void *v)
1133 {
1134 	blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)), tg_prfill_conf_u64,
1135 			  &blkcg_policy_throtl, seq_cft(sf)->private, false);
1136 	return 0;
1137 }
1138 
1139 static int tg_print_conf_uint(struct seq_file *sf, void *v)
1140 {
1141 	blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)), tg_prfill_conf_uint,
1142 			  &blkcg_policy_throtl, seq_cft(sf)->private, false);
1143 	return 0;
1144 }
1145 
1146 static void tg_conf_updated(struct throtl_grp *tg)
1147 {
1148 	struct throtl_service_queue *sq = &tg->service_queue;
1149 	struct cgroup_subsys_state *pos_css;
1150 	struct blkcg_gq *blkg;
1151 
1152 	throtl_log(&tg->service_queue,
1153 		   "limit change rbps=%llu wbps=%llu riops=%u wiops=%u",
1154 		   tg->bps[READ], tg->bps[WRITE],
1155 		   tg->iops[READ], tg->iops[WRITE]);
1156 
1157 	/*
1158 	 * Update has_rules[] flags for the updated tg's subtree.  A tg is
1159 	 * considered to have rules if either the tg itself or any of its
1160 	 * ancestors has rules.  This identifies groups without any
1161 	 * restrictions in the whole hierarchy and allows them to bypass
1162 	 * blk-throttle.
1163 	 */
1164 	blkg_for_each_descendant_pre(blkg, pos_css, tg_to_blkg(tg))
1165 		tg_update_has_rules(blkg_to_tg(blkg));
1166 
1167 	/*
1168 	 * We're already holding queue_lock and know @tg is valid.  Let's
1169 	 * apply the new config directly.
1170 	 *
1171 	 * Restart the slices for both READ and WRITES. It might happen
1172 	 * that a group's limit are dropped suddenly and we don't want to
1173 	 * account recently dispatched IO with new low rate.
1174 	 */
1175 	throtl_start_new_slice(tg, 0);
1176 	throtl_start_new_slice(tg, 1);
1177 
1178 	if (tg->flags & THROTL_TG_PENDING) {
1179 		tg_update_disptime(tg);
1180 		throtl_schedule_next_dispatch(sq->parent_sq, true);
1181 	}
1182 }
1183 
1184 static ssize_t tg_set_conf(struct kernfs_open_file *of,
1185 			   char *buf, size_t nbytes, loff_t off, bool is_u64)
1186 {
1187 	struct blkcg *blkcg = css_to_blkcg(of_css(of));
1188 	struct blkg_conf_ctx ctx;
1189 	struct throtl_grp *tg;
1190 	int ret;
1191 	u64 v;
1192 
1193 	ret = blkg_conf_prep(blkcg, &blkcg_policy_throtl, buf, &ctx);
1194 	if (ret)
1195 		return ret;
1196 
1197 	ret = -EINVAL;
1198 	if (sscanf(ctx.body, "%llu", &v) != 1)
1199 		goto out_finish;
1200 	if (!v)
1201 		v = -1;
1202 
1203 	tg = blkg_to_tg(ctx.blkg);
1204 
1205 	if (is_u64)
1206 		*(u64 *)((void *)tg + of_cft(of)->private) = v;
1207 	else
1208 		*(unsigned int *)((void *)tg + of_cft(of)->private) = v;
1209 
1210 	tg_conf_updated(tg);
1211 	ret = 0;
1212 out_finish:
1213 	blkg_conf_finish(&ctx);
1214 	return ret ?: nbytes;
1215 }
1216 
1217 static ssize_t tg_set_conf_u64(struct kernfs_open_file *of,
1218 			       char *buf, size_t nbytes, loff_t off)
1219 {
1220 	return tg_set_conf(of, buf, nbytes, off, true);
1221 }
1222 
1223 static ssize_t tg_set_conf_uint(struct kernfs_open_file *of,
1224 				char *buf, size_t nbytes, loff_t off)
1225 {
1226 	return tg_set_conf(of, buf, nbytes, off, false);
1227 }
1228 
1229 static struct cftype throtl_legacy_files[] = {
1230 	{
1231 		.name = "throttle.read_bps_device",
1232 		.private = offsetof(struct throtl_grp, bps[READ]),
1233 		.seq_show = tg_print_conf_u64,
1234 		.write = tg_set_conf_u64,
1235 	},
1236 	{
1237 		.name = "throttle.write_bps_device",
1238 		.private = offsetof(struct throtl_grp, bps[WRITE]),
1239 		.seq_show = tg_print_conf_u64,
1240 		.write = tg_set_conf_u64,
1241 	},
1242 	{
1243 		.name = "throttle.read_iops_device",
1244 		.private = offsetof(struct throtl_grp, iops[READ]),
1245 		.seq_show = tg_print_conf_uint,
1246 		.write = tg_set_conf_uint,
1247 	},
1248 	{
1249 		.name = "throttle.write_iops_device",
1250 		.private = offsetof(struct throtl_grp, iops[WRITE]),
1251 		.seq_show = tg_print_conf_uint,
1252 		.write = tg_set_conf_uint,
1253 	},
1254 	{
1255 		.name = "throttle.io_service_bytes",
1256 		.private = (unsigned long)&blkcg_policy_throtl,
1257 		.seq_show = blkg_print_stat_bytes,
1258 	},
1259 	{
1260 		.name = "throttle.io_serviced",
1261 		.private = (unsigned long)&blkcg_policy_throtl,
1262 		.seq_show = blkg_print_stat_ios,
1263 	},
1264 	{ }	/* terminate */
1265 };
1266 
1267 static u64 tg_prfill_max(struct seq_file *sf, struct blkg_policy_data *pd,
1268 			 int off)
1269 {
1270 	struct throtl_grp *tg = pd_to_tg(pd);
1271 	const char *dname = blkg_dev_name(pd->blkg);
1272 	char bufs[4][21] = { "max", "max", "max", "max" };
1273 
1274 	if (!dname)
1275 		return 0;
1276 	if (tg->bps[READ] == -1 && tg->bps[WRITE] == -1 &&
1277 	    tg->iops[READ] == -1 && tg->iops[WRITE] == -1)
1278 		return 0;
1279 
1280 	if (tg->bps[READ] != -1)
1281 		snprintf(bufs[0], sizeof(bufs[0]), "%llu", tg->bps[READ]);
1282 	if (tg->bps[WRITE] != -1)
1283 		snprintf(bufs[1], sizeof(bufs[1]), "%llu", tg->bps[WRITE]);
1284 	if (tg->iops[READ] != -1)
1285 		snprintf(bufs[2], sizeof(bufs[2]), "%u", tg->iops[READ]);
1286 	if (tg->iops[WRITE] != -1)
1287 		snprintf(bufs[3], sizeof(bufs[3]), "%u", tg->iops[WRITE]);
1288 
1289 	seq_printf(sf, "%s rbps=%s wbps=%s riops=%s wiops=%s\n",
1290 		   dname, bufs[0], bufs[1], bufs[2], bufs[3]);
1291 	return 0;
1292 }
1293 
1294 static int tg_print_max(struct seq_file *sf, void *v)
1295 {
1296 	blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)), tg_prfill_max,
1297 			  &blkcg_policy_throtl, seq_cft(sf)->private, false);
1298 	return 0;
1299 }
1300 
1301 static ssize_t tg_set_max(struct kernfs_open_file *of,
1302 			  char *buf, size_t nbytes, loff_t off)
1303 {
1304 	struct blkcg *blkcg = css_to_blkcg(of_css(of));
1305 	struct blkg_conf_ctx ctx;
1306 	struct throtl_grp *tg;
1307 	u64 v[4];
1308 	int ret;
1309 
1310 	ret = blkg_conf_prep(blkcg, &blkcg_policy_throtl, buf, &ctx);
1311 	if (ret)
1312 		return ret;
1313 
1314 	tg = blkg_to_tg(ctx.blkg);
1315 
1316 	v[0] = tg->bps[READ];
1317 	v[1] = tg->bps[WRITE];
1318 	v[2] = tg->iops[READ];
1319 	v[3] = tg->iops[WRITE];
1320 
1321 	while (true) {
1322 		char tok[27];	/* wiops=18446744073709551616 */
1323 		char *p;
1324 		u64 val = -1;
1325 		int len;
1326 
1327 		if (sscanf(ctx.body, "%26s%n", tok, &len) != 1)
1328 			break;
1329 		if (tok[0] == '\0')
1330 			break;
1331 		ctx.body += len;
1332 
1333 		ret = -EINVAL;
1334 		p = tok;
1335 		strsep(&p, "=");
1336 		if (!p || (sscanf(p, "%llu", &val) != 1 && strcmp(p, "max")))
1337 			goto out_finish;
1338 
1339 		ret = -ERANGE;
1340 		if (!val)
1341 			goto out_finish;
1342 
1343 		ret = -EINVAL;
1344 		if (!strcmp(tok, "rbps"))
1345 			v[0] = val;
1346 		else if (!strcmp(tok, "wbps"))
1347 			v[1] = val;
1348 		else if (!strcmp(tok, "riops"))
1349 			v[2] = min_t(u64, val, UINT_MAX);
1350 		else if (!strcmp(tok, "wiops"))
1351 			v[3] = min_t(u64, val, UINT_MAX);
1352 		else
1353 			goto out_finish;
1354 	}
1355 
1356 	tg->bps[READ] = v[0];
1357 	tg->bps[WRITE] = v[1];
1358 	tg->iops[READ] = v[2];
1359 	tg->iops[WRITE] = v[3];
1360 
1361 	tg_conf_updated(tg);
1362 	ret = 0;
1363 out_finish:
1364 	blkg_conf_finish(&ctx);
1365 	return ret ?: nbytes;
1366 }
1367 
1368 static struct cftype throtl_files[] = {
1369 	{
1370 		.name = "max",
1371 		.flags = CFTYPE_NOT_ON_ROOT,
1372 		.seq_show = tg_print_max,
1373 		.write = tg_set_max,
1374 	},
1375 	{ }	/* terminate */
1376 };
1377 
1378 static void throtl_shutdown_wq(struct request_queue *q)
1379 {
1380 	struct throtl_data *td = q->td;
1381 
1382 	cancel_work_sync(&td->dispatch_work);
1383 }
1384 
1385 static struct blkcg_policy blkcg_policy_throtl = {
1386 	.dfl_cftypes		= throtl_files,
1387 	.legacy_cftypes		= throtl_legacy_files,
1388 
1389 	.pd_alloc_fn		= throtl_pd_alloc,
1390 	.pd_init_fn		= throtl_pd_init,
1391 	.pd_online_fn		= throtl_pd_online,
1392 	.pd_free_fn		= throtl_pd_free,
1393 };
1394 
1395 bool blk_throtl_bio(struct request_queue *q, struct blkcg_gq *blkg,
1396 		    struct bio *bio)
1397 {
1398 	struct throtl_qnode *qn = NULL;
1399 	struct throtl_grp *tg = blkg_to_tg(blkg ?: q->root_blkg);
1400 	struct throtl_service_queue *sq;
1401 	bool rw = bio_data_dir(bio);
1402 	bool throttled = false;
1403 
1404 	WARN_ON_ONCE(!rcu_read_lock_held());
1405 
1406 	/* see throtl_charge_bio() */
1407 	if ((bio->bi_rw & REQ_THROTTLED) || !tg->has_rules[rw])
1408 		goto out;
1409 
1410 	spin_lock_irq(q->queue_lock);
1411 
1412 	if (unlikely(blk_queue_bypass(q)))
1413 		goto out_unlock;
1414 
1415 	sq = &tg->service_queue;
1416 
1417 	while (true) {
1418 		/* throtl is FIFO - if bios are already queued, should queue */
1419 		if (sq->nr_queued[rw])
1420 			break;
1421 
1422 		/* if above limits, break to queue */
1423 		if (!tg_may_dispatch(tg, bio, NULL))
1424 			break;
1425 
1426 		/* within limits, let's charge and dispatch directly */
1427 		throtl_charge_bio(tg, bio);
1428 
1429 		/*
1430 		 * We need to trim slice even when bios are not being queued
1431 		 * otherwise it might happen that a bio is not queued for
1432 		 * a long time and slice keeps on extending and trim is not
1433 		 * called for a long time. Now if limits are reduced suddenly
1434 		 * we take into account all the IO dispatched so far at new
1435 		 * low rate and * newly queued IO gets a really long dispatch
1436 		 * time.
1437 		 *
1438 		 * So keep on trimming slice even if bio is not queued.
1439 		 */
1440 		throtl_trim_slice(tg, rw);
1441 
1442 		/*
1443 		 * @bio passed through this layer without being throttled.
1444 		 * Climb up the ladder.  If we''re already at the top, it
1445 		 * can be executed directly.
1446 		 */
1447 		qn = &tg->qnode_on_parent[rw];
1448 		sq = sq->parent_sq;
1449 		tg = sq_to_tg(sq);
1450 		if (!tg)
1451 			goto out_unlock;
1452 	}
1453 
1454 	/* out-of-limit, queue to @tg */
1455 	throtl_log(sq, "[%c] bio. bdisp=%llu sz=%u bps=%llu iodisp=%u iops=%u queued=%d/%d",
1456 		   rw == READ ? 'R' : 'W',
1457 		   tg->bytes_disp[rw], bio->bi_iter.bi_size, tg->bps[rw],
1458 		   tg->io_disp[rw], tg->iops[rw],
1459 		   sq->nr_queued[READ], sq->nr_queued[WRITE]);
1460 
1461 	bio_associate_current(bio);
1462 	tg->td->nr_queued[rw]++;
1463 	throtl_add_bio_tg(bio, qn, tg);
1464 	throttled = true;
1465 
1466 	/*
1467 	 * Update @tg's dispatch time and force schedule dispatch if @tg
1468 	 * was empty before @bio.  The forced scheduling isn't likely to
1469 	 * cause undue delay as @bio is likely to be dispatched directly if
1470 	 * its @tg's disptime is not in the future.
1471 	 */
1472 	if (tg->flags & THROTL_TG_WAS_EMPTY) {
1473 		tg_update_disptime(tg);
1474 		throtl_schedule_next_dispatch(tg->service_queue.parent_sq, true);
1475 	}
1476 
1477 out_unlock:
1478 	spin_unlock_irq(q->queue_lock);
1479 out:
1480 	/*
1481 	 * As multiple blk-throtls may stack in the same issue path, we
1482 	 * don't want bios to leave with the flag set.  Clear the flag if
1483 	 * being issued.
1484 	 */
1485 	if (!throttled)
1486 		bio->bi_rw &= ~REQ_THROTTLED;
1487 	return throttled;
1488 }
1489 
1490 /*
1491  * Dispatch all bios from all children tg's queued on @parent_sq.  On
1492  * return, @parent_sq is guaranteed to not have any active children tg's
1493  * and all bios from previously active tg's are on @parent_sq->bio_lists[].
1494  */
1495 static void tg_drain_bios(struct throtl_service_queue *parent_sq)
1496 {
1497 	struct throtl_grp *tg;
1498 
1499 	while ((tg = throtl_rb_first(parent_sq))) {
1500 		struct throtl_service_queue *sq = &tg->service_queue;
1501 		struct bio *bio;
1502 
1503 		throtl_dequeue_tg(tg);
1504 
1505 		while ((bio = throtl_peek_queued(&sq->queued[READ])))
1506 			tg_dispatch_one_bio(tg, bio_data_dir(bio));
1507 		while ((bio = throtl_peek_queued(&sq->queued[WRITE])))
1508 			tg_dispatch_one_bio(tg, bio_data_dir(bio));
1509 	}
1510 }
1511 
1512 /**
1513  * blk_throtl_drain - drain throttled bios
1514  * @q: request_queue to drain throttled bios for
1515  *
1516  * Dispatch all currently throttled bios on @q through ->make_request_fn().
1517  */
1518 void blk_throtl_drain(struct request_queue *q)
1519 	__releases(q->queue_lock) __acquires(q->queue_lock)
1520 {
1521 	struct throtl_data *td = q->td;
1522 	struct blkcg_gq *blkg;
1523 	struct cgroup_subsys_state *pos_css;
1524 	struct bio *bio;
1525 	int rw;
1526 
1527 	queue_lockdep_assert_held(q);
1528 	rcu_read_lock();
1529 
1530 	/*
1531 	 * Drain each tg while doing post-order walk on the blkg tree, so
1532 	 * that all bios are propagated to td->service_queue.  It'd be
1533 	 * better to walk service_queue tree directly but blkg walk is
1534 	 * easier.
1535 	 */
1536 	blkg_for_each_descendant_post(blkg, pos_css, td->queue->root_blkg)
1537 		tg_drain_bios(&blkg_to_tg(blkg)->service_queue);
1538 
1539 	/* finally, transfer bios from top-level tg's into the td */
1540 	tg_drain_bios(&td->service_queue);
1541 
1542 	rcu_read_unlock();
1543 	spin_unlock_irq(q->queue_lock);
1544 
1545 	/* all bios now should be in td->service_queue, issue them */
1546 	for (rw = READ; rw <= WRITE; rw++)
1547 		while ((bio = throtl_pop_queued(&td->service_queue.queued[rw],
1548 						NULL)))
1549 			generic_make_request(bio);
1550 
1551 	spin_lock_irq(q->queue_lock);
1552 }
1553 
1554 int blk_throtl_init(struct request_queue *q)
1555 {
1556 	struct throtl_data *td;
1557 	int ret;
1558 
1559 	td = kzalloc_node(sizeof(*td), GFP_KERNEL, q->node);
1560 	if (!td)
1561 		return -ENOMEM;
1562 
1563 	INIT_WORK(&td->dispatch_work, blk_throtl_dispatch_work_fn);
1564 	throtl_service_queue_init(&td->service_queue);
1565 
1566 	q->td = td;
1567 	td->queue = q;
1568 
1569 	/* activate policy */
1570 	ret = blkcg_activate_policy(q, &blkcg_policy_throtl);
1571 	if (ret)
1572 		kfree(td);
1573 	return ret;
1574 }
1575 
1576 void blk_throtl_exit(struct request_queue *q)
1577 {
1578 	BUG_ON(!q->td);
1579 	throtl_shutdown_wq(q);
1580 	blkcg_deactivate_policy(q, &blkcg_policy_throtl);
1581 	kfree(q->td);
1582 }
1583 
1584 static int __init throtl_init(void)
1585 {
1586 	kthrotld_workqueue = alloc_workqueue("kthrotld", WQ_MEM_RECLAIM, 0);
1587 	if (!kthrotld_workqueue)
1588 		panic("Failed to create kthrotld\n");
1589 
1590 	return blkcg_policy_register(&blkcg_policy_throtl);
1591 }
1592 
1593 module_init(throtl_init);
1594