2 * Budget Fair Queueing (BFQ) I/O scheduler.
4 * Based on ideas and code from CFQ:
5 * Copyright (C) 2003 Jens Axboe <axboe@kernel.dk>
7 * Copyright (C) 2008 Fabio Checconi <fabio@gandalf.sssup.it>
8 * Paolo Valente <paolo.valente@unimore.it>
10 * Copyright (C) 2010 Paolo Valente <paolo.valente@unimore.it>
11 * Arianna Avanzini <avanzini@google.com>
13 * Copyright (C) 2017 Paolo Valente <paolo.valente@linaro.org>
15 * This program is free software; you can redistribute it and/or
16 * modify it under the terms of the GNU General Public License as
17 * published by the Free Software Foundation; either version 2 of the
18 * License, or (at your option) any later version.
20 * This program is distributed in the hope that it will be useful,
21 * but WITHOUT ANY WARRANTY; without even the implied warranty of
22 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
23 * General Public License for more details.
25 * BFQ is a proportional-share I/O scheduler, with some extra
26 * low-latency capabilities. BFQ also supports full hierarchical
27 * scheduling through cgroups. Next paragraphs provide an introduction
28 * on BFQ inner workings. Details on BFQ benefits, usage and
29 * limitations can be found in Documentation/block/bfq-iosched.txt.
31 * BFQ is a proportional-share storage-I/O scheduling algorithm based
32 * on the slice-by-slice service scheme of CFQ. But BFQ assigns
33 * budgets, measured in number of sectors, to processes instead of
34 * time slices. The device is not granted to the in-service process
35 * for a given time slice, but until it has exhausted its assigned
36 * budget. This change from the time to the service domain enables BFQ
37 * to distribute the device throughput among processes as desired,
38 * without any distortion due to throughput fluctuations, or to device
39 * internal queueing. BFQ uses an ad hoc internal scheduler, called
40 * B-WF2Q+, to schedule processes according to their budgets. More
41 * precisely, BFQ schedules queues associated with processes. Each
42 * process/queue is assigned a user-configurable weight, and B-WF2Q+
43 * guarantees that each queue receives a fraction of the throughput
44 * proportional to its weight. Thanks to the accurate policy of
45 * B-WF2Q+, BFQ can afford to assign high budgets to I/O-bound
46 * processes issuing sequential requests (to boost the throughput),
47 * and yet guarantee a low latency to interactive and soft real-time
50 * In particular, to provide these low-latency guarantees, BFQ
51 * explicitly privileges the I/O of two classes of time-sensitive
52 * applications: interactive and soft real-time. This feature enables
53 * BFQ to provide applications in these classes with a very low
54 * latency. Finally, BFQ also features additional heuristics for
55 * preserving both a low latency and a high throughput on NCQ-capable,
56 * rotational or flash-based devices, and to get the job done quickly
57 * for applications consisting in many I/O-bound processes.
59 * NOTE: if the main or only goal, with a given device, is to achieve
60 * the maximum-possible throughput at all times, then do switch off
61 * all low-latency heuristics for that device, by setting low_latency
64 * BFQ is described in [1], where also a reference to the initial, more
65 * theoretical paper on BFQ can be found. The interested reader can find
66 * in the latter paper full details on the main algorithm, as well as
67 * formulas of the guarantees and formal proofs of all the properties.
68 * With respect to the version of BFQ presented in these papers, this
69 * implementation adds a few more heuristics, such as the one that
70 * guarantees a low latency to soft real-time applications, and a
71 * hierarchical extension based on H-WF2Q+.
73 * B-WF2Q+ is based on WF2Q+, which is described in [2], together with
74 * H-WF2Q+, while the augmented tree used here to implement B-WF2Q+
75 * with O(log N) complexity derives from the one introduced with EEVDF
78 * [1] P. Valente, A. Avanzini, "Evolution of the BFQ Storage I/O
79 * Scheduler", Proceedings of the First Workshop on Mobile System
80 * Technologies (MST-2015), May 2015.
81 * http://algogroup.unimore.it/people/paolo/disk_sched/mst-2015.pdf
83 * [2] Jon C.R. Bennett and H. Zhang, "Hierarchical Packet Fair Queueing
84 * Algorithms", IEEE/ACM Transactions on Networking, 5(5):675-689,
87 * http://www.cs.cmu.edu/~hzhang/papers/TON-97-Oct.ps.gz
89 * [3] I. Stoica and H. Abdel-Wahab, "Earliest Eligible Virtual Deadline
90 * First: A Flexible and Accurate Mechanism for Proportional Share
91 * Resource Allocation", technical report.
93 * http://www.cs.berkeley.edu/~istoica/papers/eevdf-tr-95.pdf
95 #include <linux/module.h>
96 #include <linux/slab.h>
97 #include <linux/blkdev.h>
98 #include <linux/cgroup.h>
99 #include <linux/elevator.h>
100 #include <linux/ktime.h>
101 #include <linux/rbtree.h>
102 #include <linux/ioprio.h>
103 #include <linux/sbitmap.h>
104 #include <linux/delay.h>
108 #include "blk-mq-tag.h"
109 #include "blk-mq-sched.h"
110 #include "bfq-iosched.h"
113 #define BFQ_BFQQ_FNS(name) \
114 void bfq_mark_bfqq_##name(struct bfq_queue *bfqq) \
116 __set_bit(BFQQF_##name, &(bfqq)->flags); \
118 void bfq_clear_bfqq_##name(struct bfq_queue *bfqq) \
120 __clear_bit(BFQQF_##name, &(bfqq)->flags); \
122 int bfq_bfqq_##name(const struct bfq_queue *bfqq) \
124 return test_bit(BFQQF_##name, &(bfqq)->flags); \
127 BFQ_BFQQ_FNS(just_created);
129 BFQ_BFQQ_FNS(wait_request);
130 BFQ_BFQQ_FNS(non_blocking_wait_rq);
131 BFQ_BFQQ_FNS(fifo_expire);
132 BFQ_BFQQ_FNS(has_short_ttime);
134 BFQ_BFQQ_FNS(IO_bound);
135 BFQ_BFQQ_FNS(in_large_burst);
137 BFQ_BFQQ_FNS(split_coop);
138 BFQ_BFQQ_FNS(softrt_update);
139 #undef BFQ_BFQQ_FNS \
141 /* Expiration time of sync (0) and async (1) requests, in ns. */
142 static const u64 bfq_fifo_expire[2] = { NSEC_PER_SEC / 4, NSEC_PER_SEC / 8 };
144 /* Maximum backwards seek (magic number lifted from CFQ), in KiB. */
145 static const int bfq_back_max = 16 * 1024;
147 /* Penalty of a backwards seek, in number of sectors. */
148 static const int bfq_back_penalty = 2;
150 /* Idling period duration, in ns. */
151 static u64 bfq_slice_idle = NSEC_PER_SEC / 125;
153 /* Minimum number of assigned budgets for which stats are safe to compute. */
154 static const int bfq_stats_min_budgets = 194;
156 /* Default maximum budget values, in sectors and number of requests. */
157 static const int bfq_default_max_budget = 16 * 1024;
160 * Async to sync throughput distribution is controlled as follows:
161 * when an async request is served, the entity is charged the number
162 * of sectors of the request, multiplied by the factor below
164 static const int bfq_async_charge_factor = 10;
166 /* Default timeout values, in jiffies, approximating CFQ defaults. */
167 const int bfq_timeout = HZ / 8;
169 static struct kmem_cache *bfq_pool;
171 /* Below this threshold (in ns), we consider thinktime immediate. */
172 #define BFQ_MIN_TT (2 * NSEC_PER_MSEC)
174 /* hw_tag detection: parallel requests threshold and min samples needed. */
175 #define BFQ_HW_QUEUE_THRESHOLD 4
176 #define BFQ_HW_QUEUE_SAMPLES 32
178 #define BFQQ_SEEK_THR (sector_t)(8 * 100)
179 #define BFQQ_SECT_THR_NONROT (sector_t)(2 * 32)
180 #define BFQQ_CLOSE_THR (sector_t)(8 * 1024)
181 #define BFQQ_SEEKY(bfqq) (hweight32(bfqq->seek_history) > 32/8)
183 /* Min number of samples required to perform peak-rate update */
184 #define BFQ_RATE_MIN_SAMPLES 32
185 /* Min observation time interval required to perform a peak-rate update (ns) */
186 #define BFQ_RATE_MIN_INTERVAL (300*NSEC_PER_MSEC)
187 /* Target observation time interval for a peak-rate update (ns) */
188 #define BFQ_RATE_REF_INTERVAL NSEC_PER_SEC
190 /* Shift used for peak rate fixed precision calculations. */
191 #define BFQ_RATE_SHIFT 16
194 * By default, BFQ computes the duration of the weight raising for
195 * interactive applications automatically, using the following formula:
196 * duration = (R / r) * T, where r is the peak rate of the device, and
197 * R and T are two reference parameters.
198 * In particular, R is the peak rate of the reference device (see below),
199 * and T is a reference time: given the systems that are likely to be
200 * installed on the reference device according to its speed class, T is
201 * about the maximum time needed, under BFQ and while reading two files in
202 * parallel, to load typical large applications on these systems.
203 * In practice, the slower/faster the device at hand is, the more/less it
204 * takes to load applications with respect to the reference device.
205 * Accordingly, the longer/shorter BFQ grants weight raising to interactive
208 * BFQ uses four different reference pairs (R, T), depending on:
209 * . whether the device is rotational or non-rotational;
210 * . whether the device is slow, such as old or portable HDDs, as well as
211 * SD cards, or fast, such as newer HDDs and SSDs.
213 * The device's speed class is dynamically (re)detected in
214 * bfq_update_peak_rate() every time the estimated peak rate is updated.
216 * In the following definitions, R_slow[0]/R_fast[0] and
217 * T_slow[0]/T_fast[0] are the reference values for a slow/fast
218 * rotational device, whereas R_slow[1]/R_fast[1] and
219 * T_slow[1]/T_fast[1] are the reference values for a slow/fast
220 * non-rotational device. Finally, device_speed_thresh are the
221 * thresholds used to switch between speed classes. The reference
222 * rates are not the actual peak rates of the devices used as a
223 * reference, but slightly lower values. The reason for using these
224 * slightly lower values is that the peak-rate estimator tends to
225 * yield slightly lower values than the actual peak rate (it can yield
226 * the actual peak rate only if there is only one process doing I/O,
227 * and the process does sequential I/O).
229 * Both the reference peak rates and the thresholds are measured in
230 * sectors/usec, left-shifted by BFQ_RATE_SHIFT.
232 static int R_slow[2] = {1000, 10700};
233 static int R_fast[2] = {14000, 33000};
235 * To improve readability, a conversion function is used to initialize the
236 * following arrays, which entails that they can be initialized only in a
239 static int T_slow[2];
240 static int T_fast[2];
241 static int device_speed_thresh[2];
243 #define RQ_BIC(rq) icq_to_bic((rq)->elv.priv[0])
244 #define RQ_BFQQ(rq) ((rq)->elv.priv[1])
246 struct bfq_queue *bic_to_bfqq(struct bfq_io_cq *bic, bool is_sync)
248 return bic->bfqq[is_sync];
251 void bic_set_bfqq(struct bfq_io_cq *bic, struct bfq_queue *bfqq, bool is_sync)
253 bic->bfqq[is_sync] = bfqq;
256 struct bfq_data *bic_to_bfqd(struct bfq_io_cq *bic)
258 return bic->icq.q->elevator->elevator_data;
262 * icq_to_bic - convert iocontext queue structure to bfq_io_cq.
263 * @icq: the iocontext queue.
265 static struct bfq_io_cq *icq_to_bic(struct io_cq *icq)
267 /* bic->icq is the first member, %NULL will convert to %NULL */
268 return container_of(icq, struct bfq_io_cq, icq);
272 * bfq_bic_lookup - search into @ioc a bic associated to @bfqd.
273 * @bfqd: the lookup key.
274 * @ioc: the io_context of the process doing I/O.
275 * @q: the request queue.
277 static struct bfq_io_cq *bfq_bic_lookup(struct bfq_data *bfqd,
278 struct io_context *ioc,
279 struct request_queue *q)
283 struct bfq_io_cq *icq;
285 spin_lock_irqsave(q->queue_lock, flags);
286 icq = icq_to_bic(ioc_lookup_icq(ioc, q));
287 spin_unlock_irqrestore(q->queue_lock, flags);
296 * Scheduler run of queue, if there are requests pending and no one in the
297 * driver that will restart queueing.
299 void bfq_schedule_dispatch(struct bfq_data *bfqd)
301 if (bfqd->queued != 0) {
302 bfq_log(bfqd, "schedule dispatch");
303 blk_mq_run_hw_queues(bfqd->queue, true);
307 #define bfq_class_idle(bfqq) ((bfqq)->ioprio_class == IOPRIO_CLASS_IDLE)
308 #define bfq_class_rt(bfqq) ((bfqq)->ioprio_class == IOPRIO_CLASS_RT)
310 #define bfq_sample_valid(samples) ((samples) > 80)
313 * Lifted from AS - choose which of rq1 and rq2 that is best served now.
314 * We choose the request that is closesr to the head right now. Distance
315 * behind the head is penalized and only allowed to a certain extent.
317 static struct request *bfq_choose_req(struct bfq_data *bfqd,
322 sector_t s1, s2, d1 = 0, d2 = 0;
323 unsigned long back_max;
324 #define BFQ_RQ1_WRAP 0x01 /* request 1 wraps */
325 #define BFQ_RQ2_WRAP 0x02 /* request 2 wraps */
326 unsigned int wrap = 0; /* bit mask: requests behind the disk head? */
328 if (!rq1 || rq1 == rq2)
333 if (rq_is_sync(rq1) && !rq_is_sync(rq2))
335 else if (rq_is_sync(rq2) && !rq_is_sync(rq1))
337 if ((rq1->cmd_flags & REQ_META) && !(rq2->cmd_flags & REQ_META))
339 else if ((rq2->cmd_flags & REQ_META) && !(rq1->cmd_flags & REQ_META))
342 s1 = blk_rq_pos(rq1);
343 s2 = blk_rq_pos(rq2);
346 * By definition, 1KiB is 2 sectors.
348 back_max = bfqd->bfq_back_max * 2;
351 * Strict one way elevator _except_ in the case where we allow
352 * short backward seeks which are biased as twice the cost of a
353 * similar forward seek.
357 else if (s1 + back_max >= last)
358 d1 = (last - s1) * bfqd->bfq_back_penalty;
360 wrap |= BFQ_RQ1_WRAP;
364 else if (s2 + back_max >= last)
365 d2 = (last - s2) * bfqd->bfq_back_penalty;
367 wrap |= BFQ_RQ2_WRAP;
369 /* Found required data */
372 * By doing switch() on the bit mask "wrap" we avoid having to
373 * check two variables for all permutations: --> faster!
376 case 0: /* common case for CFQ: rq1 and rq2 not wrapped */
391 case BFQ_RQ1_WRAP|BFQ_RQ2_WRAP: /* both rqs wrapped */
394 * Since both rqs are wrapped,
395 * start with the one that's further behind head
396 * (--> only *one* back seek required),
397 * since back seek takes more time than forward.
406 static struct bfq_queue *
407 bfq_rq_pos_tree_lookup(struct bfq_data *bfqd, struct rb_root *root,
408 sector_t sector, struct rb_node **ret_parent,
409 struct rb_node ***rb_link)
411 struct rb_node **p, *parent;
412 struct bfq_queue *bfqq = NULL;
420 bfqq = rb_entry(parent, struct bfq_queue, pos_node);
423 * Sort strictly based on sector. Smallest to the left,
424 * largest to the right.
426 if (sector > blk_rq_pos(bfqq->next_rq))
428 else if (sector < blk_rq_pos(bfqq->next_rq))
436 *ret_parent = parent;
440 bfq_log(bfqd, "rq_pos_tree_lookup %llu: returning %d",
441 (unsigned long long)sector,
442 bfqq ? bfqq->pid : 0);
447 void bfq_pos_tree_add_move(struct bfq_data *bfqd, struct bfq_queue *bfqq)
449 struct rb_node **p, *parent;
450 struct bfq_queue *__bfqq;
452 if (bfqq->pos_root) {
453 rb_erase(&bfqq->pos_node, bfqq->pos_root);
454 bfqq->pos_root = NULL;
457 if (bfq_class_idle(bfqq))
462 bfqq->pos_root = &bfq_bfqq_to_bfqg(bfqq)->rq_pos_tree;
463 __bfqq = bfq_rq_pos_tree_lookup(bfqd, bfqq->pos_root,
464 blk_rq_pos(bfqq->next_rq), &parent, &p);
466 rb_link_node(&bfqq->pos_node, parent, p);
467 rb_insert_color(&bfqq->pos_node, bfqq->pos_root);
469 bfqq->pos_root = NULL;
473 * Tell whether there are active queues or groups with differentiated weights.
475 static bool bfq_differentiated_weights(struct bfq_data *bfqd)
478 * For weights to differ, at least one of the trees must contain
479 * at least two nodes.
481 return (!RB_EMPTY_ROOT(&bfqd->queue_weights_tree) &&
482 (bfqd->queue_weights_tree.rb_node->rb_left ||
483 bfqd->queue_weights_tree.rb_node->rb_right)
484 #ifdef CONFIG_BFQ_GROUP_IOSCHED
486 (!RB_EMPTY_ROOT(&bfqd->group_weights_tree) &&
487 (bfqd->group_weights_tree.rb_node->rb_left ||
488 bfqd->group_weights_tree.rb_node->rb_right)
494 * The following function returns true if every queue must receive the
495 * same share of the throughput (this condition is used when deciding
496 * whether idling may be disabled, see the comments in the function
497 * bfq_bfqq_may_idle()).
499 * Such a scenario occurs when:
500 * 1) all active queues have the same weight,
501 * 2) all active groups at the same level in the groups tree have the same
503 * 3) all active groups at the same level in the groups tree have the same
504 * number of children.
506 * Unfortunately, keeping the necessary state for evaluating exactly the
507 * above symmetry conditions would be quite complex and time-consuming.
508 * Therefore this function evaluates, instead, the following stronger
509 * sub-conditions, for which it is much easier to maintain the needed
511 * 1) all active queues have the same weight,
512 * 2) all active groups have the same weight,
513 * 3) all active groups have at most one active child each.
514 * In particular, the last two conditions are always true if hierarchical
515 * support and the cgroups interface are not enabled, thus no state needs
516 * to be maintained in this case.
518 static bool bfq_symmetric_scenario(struct bfq_data *bfqd)
520 return !bfq_differentiated_weights(bfqd);
524 * If the weight-counter tree passed as input contains no counter for
525 * the weight of the input entity, then add that counter; otherwise just
526 * increment the existing counter.
528 * Note that weight-counter trees contain few nodes in mostly symmetric
529 * scenarios. For example, if all queues have the same weight, then the
530 * weight-counter tree for the queues may contain at most one node.
531 * This holds even if low_latency is on, because weight-raised queues
532 * are not inserted in the tree.
533 * In most scenarios, the rate at which nodes are created/destroyed
536 void bfq_weights_tree_add(struct bfq_data *bfqd, struct bfq_entity *entity,
537 struct rb_root *root)
539 struct rb_node **new = &(root->rb_node), *parent = NULL;
542 * Do not insert if the entity is already associated with a
543 * counter, which happens if:
544 * 1) the entity is associated with a queue,
545 * 2) a request arrival has caused the queue to become both
546 * non-weight-raised, and hence change its weight, and
547 * backlogged; in this respect, each of the two events
548 * causes an invocation of this function,
549 * 3) this is the invocation of this function caused by the
550 * second event. This second invocation is actually useless,
551 * and we handle this fact by exiting immediately. More
552 * efficient or clearer solutions might possibly be adopted.
554 if (entity->weight_counter)
558 struct bfq_weight_counter *__counter = container_of(*new,
559 struct bfq_weight_counter,
563 if (entity->weight == __counter->weight) {
564 entity->weight_counter = __counter;
567 if (entity->weight < __counter->weight)
568 new = &((*new)->rb_left);
570 new = &((*new)->rb_right);
573 entity->weight_counter = kzalloc(sizeof(struct bfq_weight_counter),
577 * In the unlucky event of an allocation failure, we just
578 * exit. This will cause the weight of entity to not be
579 * considered in bfq_differentiated_weights, which, in its
580 * turn, causes the scenario to be deemed wrongly symmetric in
581 * case entity's weight would have been the only weight making
582 * the scenario asymmetric. On the bright side, no unbalance
583 * will however occur when entity becomes inactive again (the
584 * invocation of this function is triggered by an activation
585 * of entity). In fact, bfq_weights_tree_remove does nothing
586 * if !entity->weight_counter.
588 if (unlikely(!entity->weight_counter))
591 entity->weight_counter->weight = entity->weight;
592 rb_link_node(&entity->weight_counter->weights_node, parent, new);
593 rb_insert_color(&entity->weight_counter->weights_node, root);
596 entity->weight_counter->num_active++;
600 * Decrement the weight counter associated with the entity, and, if the
601 * counter reaches 0, remove the counter from the tree.
602 * See the comments to the function bfq_weights_tree_add() for considerations
605 void bfq_weights_tree_remove(struct bfq_data *bfqd, struct bfq_entity *entity,
606 struct rb_root *root)
608 if (!entity->weight_counter)
611 entity->weight_counter->num_active--;
612 if (entity->weight_counter->num_active > 0)
613 goto reset_entity_pointer;
615 rb_erase(&entity->weight_counter->weights_node, root);
616 kfree(entity->weight_counter);
618 reset_entity_pointer:
619 entity->weight_counter = NULL;
623 * Return expired entry, or NULL to just start from scratch in rbtree.
625 static struct request *bfq_check_fifo(struct bfq_queue *bfqq,
626 struct request *last)
630 if (bfq_bfqq_fifo_expire(bfqq))
633 bfq_mark_bfqq_fifo_expire(bfqq);
635 rq = rq_entry_fifo(bfqq->fifo.next);
637 if (rq == last || ktime_get_ns() < rq->fifo_time)
640 bfq_log_bfqq(bfqq->bfqd, bfqq, "check_fifo: returned %p", rq);
644 static struct request *bfq_find_next_rq(struct bfq_data *bfqd,
645 struct bfq_queue *bfqq,
646 struct request *last)
648 struct rb_node *rbnext = rb_next(&last->rb_node);
649 struct rb_node *rbprev = rb_prev(&last->rb_node);
650 struct request *next, *prev = NULL;
652 /* Follow expired path, else get first next available. */
653 next = bfq_check_fifo(bfqq, last);
658 prev = rb_entry_rq(rbprev);
661 next = rb_entry_rq(rbnext);
663 rbnext = rb_first(&bfqq->sort_list);
664 if (rbnext && rbnext != &last->rb_node)
665 next = rb_entry_rq(rbnext);
668 return bfq_choose_req(bfqd, next, prev, blk_rq_pos(last));
671 /* see the definition of bfq_async_charge_factor for details */
672 static unsigned long bfq_serv_to_charge(struct request *rq,
673 struct bfq_queue *bfqq)
675 if (bfq_bfqq_sync(bfqq) || bfqq->wr_coeff > 1)
676 return blk_rq_sectors(rq);
679 * If there are no weight-raised queues, then amplify service
680 * by just the async charge factor; otherwise amplify service
681 * by twice the async charge factor, to further reduce latency
682 * for weight-raised queues.
684 if (bfqq->bfqd->wr_busy_queues == 0)
685 return blk_rq_sectors(rq) * bfq_async_charge_factor;
687 return blk_rq_sectors(rq) * 2 * bfq_async_charge_factor;
691 * bfq_updated_next_req - update the queue after a new next_rq selection.
692 * @bfqd: the device data the queue belongs to.
693 * @bfqq: the queue to update.
695 * If the first request of a queue changes we make sure that the queue
696 * has enough budget to serve at least its first request (if the
697 * request has grown). We do this because if the queue has not enough
698 * budget for its first request, it has to go through two dispatch
699 * rounds to actually get it dispatched.
701 static void bfq_updated_next_req(struct bfq_data *bfqd,
702 struct bfq_queue *bfqq)
704 struct bfq_entity *entity = &bfqq->entity;
705 struct request *next_rq = bfqq->next_rq;
706 unsigned long new_budget;
711 if (bfqq == bfqd->in_service_queue)
713 * In order not to break guarantees, budgets cannot be
714 * changed after an entity has been selected.
718 new_budget = max_t(unsigned long, bfqq->max_budget,
719 bfq_serv_to_charge(next_rq, bfqq));
720 if (entity->budget != new_budget) {
721 entity->budget = new_budget;
722 bfq_log_bfqq(bfqd, bfqq, "updated next rq: new budget %lu",
724 bfq_requeue_bfqq(bfqd, bfqq, false);
729 bfq_bfqq_resume_state(struct bfq_queue *bfqq, struct bfq_data *bfqd,
730 struct bfq_io_cq *bic, bool bfq_already_existing)
732 unsigned int old_wr_coeff = bfqq->wr_coeff;
733 bool busy = bfq_already_existing && bfq_bfqq_busy(bfqq);
735 if (bic->saved_has_short_ttime)
736 bfq_mark_bfqq_has_short_ttime(bfqq);
738 bfq_clear_bfqq_has_short_ttime(bfqq);
740 if (bic->saved_IO_bound)
741 bfq_mark_bfqq_IO_bound(bfqq);
743 bfq_clear_bfqq_IO_bound(bfqq);
745 bfqq->ttime = bic->saved_ttime;
746 bfqq->wr_coeff = bic->saved_wr_coeff;
747 bfqq->wr_start_at_switch_to_srt = bic->saved_wr_start_at_switch_to_srt;
748 bfqq->last_wr_start_finish = bic->saved_last_wr_start_finish;
749 bfqq->wr_cur_max_time = bic->saved_wr_cur_max_time;
751 if (bfqq->wr_coeff > 1 && (bfq_bfqq_in_large_burst(bfqq) ||
752 time_is_before_jiffies(bfqq->last_wr_start_finish +
753 bfqq->wr_cur_max_time))) {
754 bfq_log_bfqq(bfqq->bfqd, bfqq,
755 "resume state: switching off wr");
760 /* make sure weight will be updated, however we got here */
761 bfqq->entity.prio_changed = 1;
766 if (old_wr_coeff == 1 && bfqq->wr_coeff > 1)
767 bfqd->wr_busy_queues++;
768 else if (old_wr_coeff > 1 && bfqq->wr_coeff == 1)
769 bfqd->wr_busy_queues--;
772 static int bfqq_process_refs(struct bfq_queue *bfqq)
774 return bfqq->ref - bfqq->allocated - bfqq->entity.on_st;
777 /* Empty burst list and add just bfqq (see comments on bfq_handle_burst) */
778 static void bfq_reset_burst_list(struct bfq_data *bfqd, struct bfq_queue *bfqq)
780 struct bfq_queue *item;
781 struct hlist_node *n;
783 hlist_for_each_entry_safe(item, n, &bfqd->burst_list, burst_list_node)
784 hlist_del_init(&item->burst_list_node);
785 hlist_add_head(&bfqq->burst_list_node, &bfqd->burst_list);
786 bfqd->burst_size = 1;
787 bfqd->burst_parent_entity = bfqq->entity.parent;
790 /* Add bfqq to the list of queues in current burst (see bfq_handle_burst) */
791 static void bfq_add_to_burst(struct bfq_data *bfqd, struct bfq_queue *bfqq)
793 /* Increment burst size to take into account also bfqq */
796 if (bfqd->burst_size == bfqd->bfq_large_burst_thresh) {
797 struct bfq_queue *pos, *bfqq_item;
798 struct hlist_node *n;
801 * Enough queues have been activated shortly after each
802 * other to consider this burst as large.
804 bfqd->large_burst = true;
807 * We can now mark all queues in the burst list as
808 * belonging to a large burst.
810 hlist_for_each_entry(bfqq_item, &bfqd->burst_list,
812 bfq_mark_bfqq_in_large_burst(bfqq_item);
813 bfq_mark_bfqq_in_large_burst(bfqq);
816 * From now on, and until the current burst finishes, any
817 * new queue being activated shortly after the last queue
818 * was inserted in the burst can be immediately marked as
819 * belonging to a large burst. So the burst list is not
820 * needed any more. Remove it.
822 hlist_for_each_entry_safe(pos, n, &bfqd->burst_list,
824 hlist_del_init(&pos->burst_list_node);
826 * Burst not yet large: add bfqq to the burst list. Do
827 * not increment the ref counter for bfqq, because bfqq
828 * is removed from the burst list before freeing bfqq
831 hlist_add_head(&bfqq->burst_list_node, &bfqd->burst_list);
835 * If many queues belonging to the same group happen to be created
836 * shortly after each other, then the processes associated with these
837 * queues have typically a common goal. In particular, bursts of queue
838 * creations are usually caused by services or applications that spawn
839 * many parallel threads/processes. Examples are systemd during boot,
840 * or git grep. To help these processes get their job done as soon as
841 * possible, it is usually better to not grant either weight-raising
842 * or device idling to their queues.
844 * In this comment we describe, firstly, the reasons why this fact
845 * holds, and, secondly, the next function, which implements the main
846 * steps needed to properly mark these queues so that they can then be
847 * treated in a different way.
849 * The above services or applications benefit mostly from a high
850 * throughput: the quicker the requests of the activated queues are
851 * cumulatively served, the sooner the target job of these queues gets
852 * completed. As a consequence, weight-raising any of these queues,
853 * which also implies idling the device for it, is almost always
854 * counterproductive. In most cases it just lowers throughput.
856 * On the other hand, a burst of queue creations may be caused also by
857 * the start of an application that does not consist of a lot of
858 * parallel I/O-bound threads. In fact, with a complex application,
859 * several short processes may need to be executed to start-up the
860 * application. In this respect, to start an application as quickly as
861 * possible, the best thing to do is in any case to privilege the I/O
862 * related to the application with respect to all other
863 * I/O. Therefore, the best strategy to start as quickly as possible
864 * an application that causes a burst of queue creations is to
865 * weight-raise all the queues created during the burst. This is the
866 * exact opposite of the best strategy for the other type of bursts.
868 * In the end, to take the best action for each of the two cases, the
869 * two types of bursts need to be distinguished. Fortunately, this
870 * seems relatively easy, by looking at the sizes of the bursts. In
871 * particular, we found a threshold such that only bursts with a
872 * larger size than that threshold are apparently caused by
873 * services or commands such as systemd or git grep. For brevity,
874 * hereafter we call just 'large' these bursts. BFQ *does not*
875 * weight-raise queues whose creation occurs in a large burst. In
876 * addition, for each of these queues BFQ performs or does not perform
877 * idling depending on which choice boosts the throughput more. The
878 * exact choice depends on the device and request pattern at
881 * Unfortunately, false positives may occur while an interactive task
882 * is starting (e.g., an application is being started). The
883 * consequence is that the queues associated with the task do not
884 * enjoy weight raising as expected. Fortunately these false positives
885 * are very rare. They typically occur if some service happens to
886 * start doing I/O exactly when the interactive task starts.
888 * Turning back to the next function, it implements all the steps
889 * needed to detect the occurrence of a large burst and to properly
890 * mark all the queues belonging to it (so that they can then be
891 * treated in a different way). This goal is achieved by maintaining a
892 * "burst list" that holds, temporarily, the queues that belong to the
893 * burst in progress. The list is then used to mark these queues as
894 * belonging to a large burst if the burst does become large. The main
895 * steps are the following.
897 * . when the very first queue is created, the queue is inserted into the
898 * list (as it could be the first queue in a possible burst)
900 * . if the current burst has not yet become large, and a queue Q that does
901 * not yet belong to the burst is activated shortly after the last time
902 * at which a new queue entered the burst list, then the function appends
903 * Q to the burst list
905 * . if, as a consequence of the previous step, the burst size reaches
906 * the large-burst threshold, then
908 * . all the queues in the burst list are marked as belonging to a
911 * . the burst list is deleted; in fact, the burst list already served
912 * its purpose (keeping temporarily track of the queues in a burst,
913 * so as to be able to mark them as belonging to a large burst in the
914 * previous sub-step), and now is not needed any more
916 * . the device enters a large-burst mode
918 * . if a queue Q that does not belong to the burst is created while
919 * the device is in large-burst mode and shortly after the last time
920 * at which a queue either entered the burst list or was marked as
921 * belonging to the current large burst, then Q is immediately marked
922 * as belonging to a large burst.
924 * . if a queue Q that does not belong to the burst is created a while
925 * later, i.e., not shortly after, than the last time at which a queue
926 * either entered the burst list or was marked as belonging to the
927 * current large burst, then the current burst is deemed as finished and:
929 * . the large-burst mode is reset if set
931 * . the burst list is emptied
933 * . Q is inserted in the burst list, as Q may be the first queue
934 * in a possible new burst (then the burst list contains just Q
937 static void bfq_handle_burst(struct bfq_data *bfqd, struct bfq_queue *bfqq)
940 * If bfqq is already in the burst list or is part of a large
941 * burst, or finally has just been split, then there is
942 * nothing else to do.
944 if (!hlist_unhashed(&bfqq->burst_list_node) ||
945 bfq_bfqq_in_large_burst(bfqq) ||
946 time_is_after_eq_jiffies(bfqq->split_time +
947 msecs_to_jiffies(10)))
951 * If bfqq's creation happens late enough, or bfqq belongs to
952 * a different group than the burst group, then the current
953 * burst is finished, and related data structures must be
956 * In this respect, consider the special case where bfqq is
957 * the very first queue created after BFQ is selected for this
958 * device. In this case, last_ins_in_burst and
959 * burst_parent_entity are not yet significant when we get
960 * here. But it is easy to verify that, whether or not the
961 * following condition is true, bfqq will end up being
962 * inserted into the burst list. In particular the list will
963 * happen to contain only bfqq. And this is exactly what has
964 * to happen, as bfqq may be the first queue of the first
967 if (time_is_before_jiffies(bfqd->last_ins_in_burst +
968 bfqd->bfq_burst_interval) ||
969 bfqq->entity.parent != bfqd->burst_parent_entity) {
970 bfqd->large_burst = false;
971 bfq_reset_burst_list(bfqd, bfqq);
976 * If we get here, then bfqq is being activated shortly after the
977 * last queue. So, if the current burst is also large, we can mark
978 * bfqq as belonging to this large burst immediately.
980 if (bfqd->large_burst) {
981 bfq_mark_bfqq_in_large_burst(bfqq);
986 * If we get here, then a large-burst state has not yet been
987 * reached, but bfqq is being activated shortly after the last
988 * queue. Then we add bfqq to the burst.
990 bfq_add_to_burst(bfqd, bfqq);
993 * At this point, bfqq either has been added to the current
994 * burst or has caused the current burst to terminate and a
995 * possible new burst to start. In particular, in the second
996 * case, bfqq has become the first queue in the possible new
997 * burst. In both cases last_ins_in_burst needs to be moved
1000 bfqd->last_ins_in_burst = jiffies;
1003 static int bfq_bfqq_budget_left(struct bfq_queue *bfqq)
1005 struct bfq_entity *entity = &bfqq->entity;
1007 return entity->budget - entity->service;
1011 * If enough samples have been computed, return the current max budget
1012 * stored in bfqd, which is dynamically updated according to the
1013 * estimated disk peak rate; otherwise return the default max budget
1015 static int bfq_max_budget(struct bfq_data *bfqd)
1017 if (bfqd->budgets_assigned < bfq_stats_min_budgets)
1018 return bfq_default_max_budget;
1020 return bfqd->bfq_max_budget;
1024 * Return min budget, which is a fraction of the current or default
1025 * max budget (trying with 1/32)
1027 static int bfq_min_budget(struct bfq_data *bfqd)
1029 if (bfqd->budgets_assigned < bfq_stats_min_budgets)
1030 return bfq_default_max_budget / 32;
1032 return bfqd->bfq_max_budget / 32;
1036 * The next function, invoked after the input queue bfqq switches from
1037 * idle to busy, updates the budget of bfqq. The function also tells
1038 * whether the in-service queue should be expired, by returning
1039 * true. The purpose of expiring the in-service queue is to give bfqq
1040 * the chance to possibly preempt the in-service queue, and the reason
1041 * for preempting the in-service queue is to achieve one of the two
1044 * 1. Guarantee to bfqq its reserved bandwidth even if bfqq has
1045 * expired because it has remained idle. In particular, bfqq may have
1046 * expired for one of the following two reasons:
1048 * - BFQQE_NO_MORE_REQUESTS bfqq did not enjoy any device idling
1049 * and did not make it to issue a new request before its last
1050 * request was served;
1052 * - BFQQE_TOO_IDLE bfqq did enjoy device idling, but did not issue
1053 * a new request before the expiration of the idling-time.
1055 * Even if bfqq has expired for one of the above reasons, the process
1056 * associated with the queue may be however issuing requests greedily,
1057 * and thus be sensitive to the bandwidth it receives (bfqq may have
1058 * remained idle for other reasons: CPU high load, bfqq not enjoying
1059 * idling, I/O throttling somewhere in the path from the process to
1060 * the I/O scheduler, ...). But if, after every expiration for one of
1061 * the above two reasons, bfqq has to wait for the service of at least
1062 * one full budget of another queue before being served again, then
1063 * bfqq is likely to get a much lower bandwidth or resource time than
1064 * its reserved ones. To address this issue, two countermeasures need
1067 * First, the budget and the timestamps of bfqq need to be updated in
1068 * a special way on bfqq reactivation: they need to be updated as if
1069 * bfqq did not remain idle and did not expire. In fact, if they are
1070 * computed as if bfqq expired and remained idle until reactivation,
1071 * then the process associated with bfqq is treated as if, instead of
1072 * being greedy, it stopped issuing requests when bfqq remained idle,
1073 * and restarts issuing requests only on this reactivation. In other
1074 * words, the scheduler does not help the process recover the "service
1075 * hole" between bfqq expiration and reactivation. As a consequence,
1076 * the process receives a lower bandwidth than its reserved one. In
1077 * contrast, to recover this hole, the budget must be updated as if
1078 * bfqq was not expired at all before this reactivation, i.e., it must
1079 * be set to the value of the remaining budget when bfqq was
1080 * expired. Along the same line, timestamps need to be assigned the
1081 * value they had the last time bfqq was selected for service, i.e.,
1082 * before last expiration. Thus timestamps need to be back-shifted
1083 * with respect to their normal computation (see [1] for more details
1084 * on this tricky aspect).
1086 * Secondly, to allow the process to recover the hole, the in-service
1087 * queue must be expired too, to give bfqq the chance to preempt it
1088 * immediately. In fact, if bfqq has to wait for a full budget of the
1089 * in-service queue to be completed, then it may become impossible to
1090 * let the process recover the hole, even if the back-shifted
1091 * timestamps of bfqq are lower than those of the in-service queue. If
1092 * this happens for most or all of the holes, then the process may not
1093 * receive its reserved bandwidth. In this respect, it is worth noting
1094 * that, being the service of outstanding requests unpreemptible, a
1095 * little fraction of the holes may however be unrecoverable, thereby
1096 * causing a little loss of bandwidth.
1098 * The last important point is detecting whether bfqq does need this
1099 * bandwidth recovery. In this respect, the next function deems the
1100 * process associated with bfqq greedy, and thus allows it to recover
1101 * the hole, if: 1) the process is waiting for the arrival of a new
1102 * request (which implies that bfqq expired for one of the above two
1103 * reasons), and 2) such a request has arrived soon. The first
1104 * condition is controlled through the flag non_blocking_wait_rq,
1105 * while the second through the flag arrived_in_time. If both
1106 * conditions hold, then the function computes the budget in the
1107 * above-described special way, and signals that the in-service queue
1108 * should be expired. Timestamp back-shifting is done later in
1109 * __bfq_activate_entity.
1111 * 2. Reduce latency. Even if timestamps are not backshifted to let
1112 * the process associated with bfqq recover a service hole, bfqq may
1113 * however happen to have, after being (re)activated, a lower finish
1114 * timestamp than the in-service queue. That is, the next budget of
1115 * bfqq may have to be completed before the one of the in-service
1116 * queue. If this is the case, then preempting the in-service queue
1117 * allows this goal to be achieved, apart from the unpreemptible,
1118 * outstanding requests mentioned above.
1120 * Unfortunately, regardless of which of the above two goals one wants
1121 * to achieve, service trees need first to be updated to know whether
1122 * the in-service queue must be preempted. To have service trees
1123 * correctly updated, the in-service queue must be expired and
1124 * rescheduled, and bfqq must be scheduled too. This is one of the
1125 * most costly operations (in future versions, the scheduling
1126 * mechanism may be re-designed in such a way to make it possible to
1127 * know whether preemption is needed without needing to update service
1128 * trees). In addition, queue preemptions almost always cause random
1129 * I/O, and thus loss of throughput. Because of these facts, the next
1130 * function adopts the following simple scheme to avoid both costly
1131 * operations and too frequent preemptions: it requests the expiration
1132 * of the in-service queue (unconditionally) only for queues that need
1133 * to recover a hole, or that either are weight-raised or deserve to
1136 static bool bfq_bfqq_update_budg_for_activation(struct bfq_data *bfqd,
1137 struct bfq_queue *bfqq,
1138 bool arrived_in_time,
1139 bool wr_or_deserves_wr)
1141 struct bfq_entity *entity = &bfqq->entity;
1143 if (bfq_bfqq_non_blocking_wait_rq(bfqq) && arrived_in_time) {
1145 * We do not clear the flag non_blocking_wait_rq here, as
1146 * the latter is used in bfq_activate_bfqq to signal
1147 * that timestamps need to be back-shifted (and is
1148 * cleared right after).
1152 * In next assignment we rely on that either
1153 * entity->service or entity->budget are not updated
1154 * on expiration if bfqq is empty (see
1155 * __bfq_bfqq_recalc_budget). Thus both quantities
1156 * remain unchanged after such an expiration, and the
1157 * following statement therefore assigns to
1158 * entity->budget the remaining budget on such an
1159 * expiration. For clarity, entity->service is not
1160 * updated on expiration in any case, and, in normal
1161 * operation, is reset only when bfqq is selected for
1162 * service (see bfq_get_next_queue).
1164 entity->budget = min_t(unsigned long,
1165 bfq_bfqq_budget_left(bfqq),
1171 entity->budget = max_t(unsigned long, bfqq->max_budget,
1172 bfq_serv_to_charge(bfqq->next_rq, bfqq));
1173 bfq_clear_bfqq_non_blocking_wait_rq(bfqq);
1174 return wr_or_deserves_wr;
1177 static unsigned int bfq_wr_duration(struct bfq_data *bfqd)
1181 if (bfqd->bfq_wr_max_time > 0)
1182 return bfqd->bfq_wr_max_time;
1184 dur = bfqd->RT_prod;
1185 do_div(dur, bfqd->peak_rate);
1188 * Limit duration between 3 and 13 seconds. Tests show that
1189 * higher values than 13 seconds often yield the opposite of
1190 * the desired result, i.e., worsen responsiveness by letting
1191 * non-interactive and non-soft-real-time applications
1192 * preserve weight raising for a too long time interval.
1194 * On the other end, lower values than 3 seconds make it
1195 * difficult for most interactive tasks to complete their jobs
1196 * before weight-raising finishes.
1198 if (dur > msecs_to_jiffies(13000))
1199 dur = msecs_to_jiffies(13000);
1200 else if (dur < msecs_to_jiffies(3000))
1201 dur = msecs_to_jiffies(3000);
1206 static void bfq_update_bfqq_wr_on_rq_arrival(struct bfq_data *bfqd,
1207 struct bfq_queue *bfqq,
1208 unsigned int old_wr_coeff,
1209 bool wr_or_deserves_wr,
1214 if (old_wr_coeff == 1 && wr_or_deserves_wr) {
1215 /* start a weight-raising period */
1217 bfqq->wr_coeff = bfqd->bfq_wr_coeff;
1218 bfqq->wr_cur_max_time = bfq_wr_duration(bfqd);
1220 bfqq->wr_start_at_switch_to_srt = jiffies;
1221 bfqq->wr_coeff = bfqd->bfq_wr_coeff *
1222 BFQ_SOFTRT_WEIGHT_FACTOR;
1223 bfqq->wr_cur_max_time =
1224 bfqd->bfq_wr_rt_max_time;
1228 * If needed, further reduce budget to make sure it is
1229 * close to bfqq's backlog, so as to reduce the
1230 * scheduling-error component due to a too large
1231 * budget. Do not care about throughput consequences,
1232 * but only about latency. Finally, do not assign a
1233 * too small budget either, to avoid increasing
1234 * latency by causing too frequent expirations.
1236 bfqq->entity.budget = min_t(unsigned long,
1237 bfqq->entity.budget,
1238 2 * bfq_min_budget(bfqd));
1239 } else if (old_wr_coeff > 1) {
1240 if (interactive) { /* update wr coeff and duration */
1241 bfqq->wr_coeff = bfqd->bfq_wr_coeff;
1242 bfqq->wr_cur_max_time = bfq_wr_duration(bfqd);
1243 } else if (in_burst)
1247 * The application is now or still meeting the
1248 * requirements for being deemed soft rt. We
1249 * can then correctly and safely (re)charge
1250 * the weight-raising duration for the
1251 * application with the weight-raising
1252 * duration for soft rt applications.
1254 * In particular, doing this recharge now, i.e.,
1255 * before the weight-raising period for the
1256 * application finishes, reduces the probability
1257 * of the following negative scenario:
1258 * 1) the weight of a soft rt application is
1259 * raised at startup (as for any newly
1260 * created application),
1261 * 2) since the application is not interactive,
1262 * at a certain time weight-raising is
1263 * stopped for the application,
1264 * 3) at that time the application happens to
1265 * still have pending requests, and hence
1266 * is destined to not have a chance to be
1267 * deemed soft rt before these requests are
1268 * completed (see the comments to the
1269 * function bfq_bfqq_softrt_next_start()
1270 * for details on soft rt detection),
1271 * 4) these pending requests experience a high
1272 * latency because the application is not
1273 * weight-raised while they are pending.
1275 if (bfqq->wr_cur_max_time !=
1276 bfqd->bfq_wr_rt_max_time) {
1277 bfqq->wr_start_at_switch_to_srt =
1278 bfqq->last_wr_start_finish;
1280 bfqq->wr_cur_max_time =
1281 bfqd->bfq_wr_rt_max_time;
1282 bfqq->wr_coeff = bfqd->bfq_wr_coeff *
1283 BFQ_SOFTRT_WEIGHT_FACTOR;
1285 bfqq->last_wr_start_finish = jiffies;
1290 static bool bfq_bfqq_idle_for_long_time(struct bfq_data *bfqd,
1291 struct bfq_queue *bfqq)
1293 return bfqq->dispatched == 0 &&
1294 time_is_before_jiffies(
1295 bfqq->budget_timeout +
1296 bfqd->bfq_wr_min_idle_time);
1299 static void bfq_bfqq_handle_idle_busy_switch(struct bfq_data *bfqd,
1300 struct bfq_queue *bfqq,
1305 bool soft_rt, in_burst, wr_or_deserves_wr,
1306 bfqq_wants_to_preempt,
1307 idle_for_long_time = bfq_bfqq_idle_for_long_time(bfqd, bfqq),
1309 * See the comments on
1310 * bfq_bfqq_update_budg_for_activation for
1311 * details on the usage of the next variable.
1313 arrived_in_time = ktime_get_ns() <=
1314 bfqq->ttime.last_end_request +
1315 bfqd->bfq_slice_idle * 3;
1317 bfqg_stats_update_io_add(bfqq_group(RQ_BFQQ(rq)), bfqq, rq->cmd_flags);
1320 * bfqq deserves to be weight-raised if:
1322 * - it does not belong to a large burst,
1323 * - it has been idle for enough time or is soft real-time,
1324 * - is linked to a bfq_io_cq (it is not shared in any sense).
1326 in_burst = bfq_bfqq_in_large_burst(bfqq);
1327 soft_rt = bfqd->bfq_wr_max_softrt_rate > 0 &&
1329 time_is_before_jiffies(bfqq->soft_rt_next_start);
1330 *interactive = !in_burst && idle_for_long_time;
1331 wr_or_deserves_wr = bfqd->low_latency &&
1332 (bfqq->wr_coeff > 1 ||
1333 (bfq_bfqq_sync(bfqq) &&
1334 bfqq->bic && (*interactive || soft_rt)));
1337 * Using the last flag, update budget and check whether bfqq
1338 * may want to preempt the in-service queue.
1340 bfqq_wants_to_preempt =
1341 bfq_bfqq_update_budg_for_activation(bfqd, bfqq,
1346 * If bfqq happened to be activated in a burst, but has been
1347 * idle for much more than an interactive queue, then we
1348 * assume that, in the overall I/O initiated in the burst, the
1349 * I/O associated with bfqq is finished. So bfqq does not need
1350 * to be treated as a queue belonging to a burst
1351 * anymore. Accordingly, we reset bfqq's in_large_burst flag
1352 * if set, and remove bfqq from the burst list if it's
1353 * there. We do not decrement burst_size, because the fact
1354 * that bfqq does not need to belong to the burst list any
1355 * more does not invalidate the fact that bfqq was created in
1358 if (likely(!bfq_bfqq_just_created(bfqq)) &&
1359 idle_for_long_time &&
1360 time_is_before_jiffies(
1361 bfqq->budget_timeout +
1362 msecs_to_jiffies(10000))) {
1363 hlist_del_init(&bfqq->burst_list_node);
1364 bfq_clear_bfqq_in_large_burst(bfqq);
1367 bfq_clear_bfqq_just_created(bfqq);
1370 if (!bfq_bfqq_IO_bound(bfqq)) {
1371 if (arrived_in_time) {
1372 bfqq->requests_within_timer++;
1373 if (bfqq->requests_within_timer >=
1374 bfqd->bfq_requests_within_timer)
1375 bfq_mark_bfqq_IO_bound(bfqq);
1377 bfqq->requests_within_timer = 0;
1380 if (bfqd->low_latency) {
1381 if (unlikely(time_is_after_jiffies(bfqq->split_time)))
1384 jiffies - bfqd->bfq_wr_min_idle_time - 1;
1386 if (time_is_before_jiffies(bfqq->split_time +
1387 bfqd->bfq_wr_min_idle_time)) {
1388 bfq_update_bfqq_wr_on_rq_arrival(bfqd, bfqq,
1395 if (old_wr_coeff != bfqq->wr_coeff)
1396 bfqq->entity.prio_changed = 1;
1400 bfqq->last_idle_bklogged = jiffies;
1401 bfqq->service_from_backlogged = 0;
1402 bfq_clear_bfqq_softrt_update(bfqq);
1404 bfq_add_bfqq_busy(bfqd, bfqq);
1407 * Expire in-service queue only if preemption may be needed
1408 * for guarantees. In this respect, the function
1409 * next_queue_may_preempt just checks a simple, necessary
1410 * condition, and not a sufficient condition based on
1411 * timestamps. In fact, for the latter condition to be
1412 * evaluated, timestamps would need first to be updated, and
1413 * this operation is quite costly (see the comments on the
1414 * function bfq_bfqq_update_budg_for_activation).
1416 if (bfqd->in_service_queue && bfqq_wants_to_preempt &&
1417 bfqd->in_service_queue->wr_coeff < bfqq->wr_coeff &&
1418 next_queue_may_preempt(bfqd))
1419 bfq_bfqq_expire(bfqd, bfqd->in_service_queue,
1420 false, BFQQE_PREEMPTED);
1423 static void bfq_add_request(struct request *rq)
1425 struct bfq_queue *bfqq = RQ_BFQQ(rq);
1426 struct bfq_data *bfqd = bfqq->bfqd;
1427 struct request *next_rq, *prev;
1428 unsigned int old_wr_coeff = bfqq->wr_coeff;
1429 bool interactive = false;
1431 bfq_log_bfqq(bfqd, bfqq, "add_request %d", rq_is_sync(rq));
1432 bfqq->queued[rq_is_sync(rq)]++;
1435 elv_rb_add(&bfqq->sort_list, rq);
1438 * Check if this request is a better next-serve candidate.
1440 prev = bfqq->next_rq;
1441 next_rq = bfq_choose_req(bfqd, bfqq->next_rq, rq, bfqd->last_position);
1442 bfqq->next_rq = next_rq;
1445 * Adjust priority tree position, if next_rq changes.
1447 if (prev != bfqq->next_rq)
1448 bfq_pos_tree_add_move(bfqd, bfqq);
1450 if (!bfq_bfqq_busy(bfqq)) /* switching to busy ... */
1451 bfq_bfqq_handle_idle_busy_switch(bfqd, bfqq, old_wr_coeff,
1454 if (bfqd->low_latency && old_wr_coeff == 1 && !rq_is_sync(rq) &&
1455 time_is_before_jiffies(
1456 bfqq->last_wr_start_finish +
1457 bfqd->bfq_wr_min_inter_arr_async)) {
1458 bfqq->wr_coeff = bfqd->bfq_wr_coeff;
1459 bfqq->wr_cur_max_time = bfq_wr_duration(bfqd);
1461 bfqd->wr_busy_queues++;
1462 bfqq->entity.prio_changed = 1;
1464 if (prev != bfqq->next_rq)
1465 bfq_updated_next_req(bfqd, bfqq);
1469 * Assign jiffies to last_wr_start_finish in the following
1472 * . if bfqq is not going to be weight-raised, because, for
1473 * non weight-raised queues, last_wr_start_finish stores the
1474 * arrival time of the last request; as of now, this piece
1475 * of information is used only for deciding whether to
1476 * weight-raise async queues
1478 * . if bfqq is not weight-raised, because, if bfqq is now
1479 * switching to weight-raised, then last_wr_start_finish
1480 * stores the time when weight-raising starts
1482 * . if bfqq is interactive, because, regardless of whether
1483 * bfqq is currently weight-raised, the weight-raising
1484 * period must start or restart (this case is considered
1485 * separately because it is not detected by the above
1486 * conditions, if bfqq is already weight-raised)
1488 * last_wr_start_finish has to be updated also if bfqq is soft
1489 * real-time, because the weight-raising period is constantly
1490 * restarted on idle-to-busy transitions for these queues, but
1491 * this is already done in bfq_bfqq_handle_idle_busy_switch if
1494 if (bfqd->low_latency &&
1495 (old_wr_coeff == 1 || bfqq->wr_coeff == 1 || interactive))
1496 bfqq->last_wr_start_finish = jiffies;
1499 static struct request *bfq_find_rq_fmerge(struct bfq_data *bfqd,
1501 struct request_queue *q)
1503 struct bfq_queue *bfqq = bfqd->bio_bfqq;
1507 return elv_rb_find(&bfqq->sort_list, bio_end_sector(bio));
1512 static sector_t get_sdist(sector_t last_pos, struct request *rq)
1515 return abs(blk_rq_pos(rq) - last_pos);
1520 #if 0 /* Still not clear if we can do without next two functions */
1521 static void bfq_activate_request(struct request_queue *q, struct request *rq)
1523 struct bfq_data *bfqd = q->elevator->elevator_data;
1525 bfqd->rq_in_driver++;
1528 static void bfq_deactivate_request(struct request_queue *q, struct request *rq)
1530 struct bfq_data *bfqd = q->elevator->elevator_data;
1532 bfqd->rq_in_driver--;
1536 static void bfq_remove_request(struct request_queue *q,
1539 struct bfq_queue *bfqq = RQ_BFQQ(rq);
1540 struct bfq_data *bfqd = bfqq->bfqd;
1541 const int sync = rq_is_sync(rq);
1543 if (bfqq->next_rq == rq) {
1544 bfqq->next_rq = bfq_find_next_rq(bfqd, bfqq, rq);
1545 bfq_updated_next_req(bfqd, bfqq);
1548 if (rq->queuelist.prev != &rq->queuelist)
1549 list_del_init(&rq->queuelist);
1550 bfqq->queued[sync]--;
1552 elv_rb_del(&bfqq->sort_list, rq);
1554 elv_rqhash_del(q, rq);
1555 if (q->last_merge == rq)
1556 q->last_merge = NULL;
1558 if (RB_EMPTY_ROOT(&bfqq->sort_list)) {
1559 bfqq->next_rq = NULL;
1561 if (bfq_bfqq_busy(bfqq) && bfqq != bfqd->in_service_queue) {
1562 bfq_del_bfqq_busy(bfqd, bfqq, false);
1564 * bfqq emptied. In normal operation, when
1565 * bfqq is empty, bfqq->entity.service and
1566 * bfqq->entity.budget must contain,
1567 * respectively, the service received and the
1568 * budget used last time bfqq emptied. These
1569 * facts do not hold in this case, as at least
1570 * this last removal occurred while bfqq is
1571 * not in service. To avoid inconsistencies,
1572 * reset both bfqq->entity.service and
1573 * bfqq->entity.budget, if bfqq has still a
1574 * process that may issue I/O requests to it.
1576 bfqq->entity.budget = bfqq->entity.service = 0;
1580 * Remove queue from request-position tree as it is empty.
1582 if (bfqq->pos_root) {
1583 rb_erase(&bfqq->pos_node, bfqq->pos_root);
1584 bfqq->pos_root = NULL;
1588 if (rq->cmd_flags & REQ_META)
1589 bfqq->meta_pending--;
1591 bfqg_stats_update_io_remove(bfqq_group(bfqq), rq->cmd_flags);
1594 static bool bfq_bio_merge(struct blk_mq_hw_ctx *hctx, struct bio *bio)
1596 struct request_queue *q = hctx->queue;
1597 struct bfq_data *bfqd = q->elevator->elevator_data;
1598 struct request *free = NULL;
1600 * bfq_bic_lookup grabs the queue_lock: invoke it now and
1601 * store its return value for later use, to avoid nesting
1602 * queue_lock inside the bfqd->lock. We assume that the bic
1603 * returned by bfq_bic_lookup does not go away before
1604 * bfqd->lock is taken.
1606 struct bfq_io_cq *bic = bfq_bic_lookup(bfqd, current->io_context, q);
1609 spin_lock_irq(&bfqd->lock);
1612 bfqd->bio_bfqq = bic_to_bfqq(bic, op_is_sync(bio->bi_opf));
1614 bfqd->bio_bfqq = NULL;
1615 bfqd->bio_bic = bic;
1617 ret = blk_mq_sched_try_merge(q, bio, &free);
1620 blk_mq_free_request(free);
1621 spin_unlock_irq(&bfqd->lock);
1626 static int bfq_request_merge(struct request_queue *q, struct request **req,
1629 struct bfq_data *bfqd = q->elevator->elevator_data;
1630 struct request *__rq;
1632 __rq = bfq_find_rq_fmerge(bfqd, bio, q);
1633 if (__rq && elv_bio_merge_ok(__rq, bio)) {
1635 return ELEVATOR_FRONT_MERGE;
1638 return ELEVATOR_NO_MERGE;
1641 static void bfq_request_merged(struct request_queue *q, struct request *req,
1642 enum elv_merge type)
1644 if (type == ELEVATOR_FRONT_MERGE &&
1645 rb_prev(&req->rb_node) &&
1647 blk_rq_pos(container_of(rb_prev(&req->rb_node),
1648 struct request, rb_node))) {
1649 struct bfq_queue *bfqq = RQ_BFQQ(req);
1650 struct bfq_data *bfqd = bfqq->bfqd;
1651 struct request *prev, *next_rq;
1653 /* Reposition request in its sort_list */
1654 elv_rb_del(&bfqq->sort_list, req);
1655 elv_rb_add(&bfqq->sort_list, req);
1657 /* Choose next request to be served for bfqq */
1658 prev = bfqq->next_rq;
1659 next_rq = bfq_choose_req(bfqd, bfqq->next_rq, req,
1660 bfqd->last_position);
1661 bfqq->next_rq = next_rq;
1663 * If next_rq changes, update both the queue's budget to
1664 * fit the new request and the queue's position in its
1667 if (prev != bfqq->next_rq) {
1668 bfq_updated_next_req(bfqd, bfqq);
1669 bfq_pos_tree_add_move(bfqd, bfqq);
1674 static void bfq_requests_merged(struct request_queue *q, struct request *rq,
1675 struct request *next)
1677 struct bfq_queue *bfqq = RQ_BFQQ(rq), *next_bfqq = RQ_BFQQ(next);
1679 if (!RB_EMPTY_NODE(&rq->rb_node))
1681 spin_lock_irq(&bfqq->bfqd->lock);
1684 * If next and rq belong to the same bfq_queue and next is older
1685 * than rq, then reposition rq in the fifo (by substituting next
1686 * with rq). Otherwise, if next and rq belong to different
1687 * bfq_queues, never reposition rq: in fact, we would have to
1688 * reposition it with respect to next's position in its own fifo,
1689 * which would most certainly be too expensive with respect to
1692 if (bfqq == next_bfqq &&
1693 !list_empty(&rq->queuelist) && !list_empty(&next->queuelist) &&
1694 next->fifo_time < rq->fifo_time) {
1695 list_del_init(&rq->queuelist);
1696 list_replace_init(&next->queuelist, &rq->queuelist);
1697 rq->fifo_time = next->fifo_time;
1700 if (bfqq->next_rq == next)
1703 bfq_remove_request(q, next);
1705 spin_unlock_irq(&bfqq->bfqd->lock);
1707 bfqg_stats_update_io_merged(bfqq_group(bfqq), next->cmd_flags);
1710 /* Must be called with bfqq != NULL */
1711 static void bfq_bfqq_end_wr(struct bfq_queue *bfqq)
1713 if (bfq_bfqq_busy(bfqq))
1714 bfqq->bfqd->wr_busy_queues--;
1716 bfqq->wr_cur_max_time = 0;
1717 bfqq->last_wr_start_finish = jiffies;
1719 * Trigger a weight change on the next invocation of
1720 * __bfq_entity_update_weight_prio.
1722 bfqq->entity.prio_changed = 1;
1725 void bfq_end_wr_async_queues(struct bfq_data *bfqd,
1726 struct bfq_group *bfqg)
1730 for (i = 0; i < 2; i++)
1731 for (j = 0; j < IOPRIO_BE_NR; j++)
1732 if (bfqg->async_bfqq[i][j])
1733 bfq_bfqq_end_wr(bfqg->async_bfqq[i][j]);
1734 if (bfqg->async_idle_bfqq)
1735 bfq_bfqq_end_wr(bfqg->async_idle_bfqq);
1738 static void bfq_end_wr(struct bfq_data *bfqd)
1740 struct bfq_queue *bfqq;
1742 spin_lock_irq(&bfqd->lock);
1744 list_for_each_entry(bfqq, &bfqd->active_list, bfqq_list)
1745 bfq_bfqq_end_wr(bfqq);
1746 list_for_each_entry(bfqq, &bfqd->idle_list, bfqq_list)
1747 bfq_bfqq_end_wr(bfqq);
1748 bfq_end_wr_async(bfqd);
1750 spin_unlock_irq(&bfqd->lock);
1753 static sector_t bfq_io_struct_pos(void *io_struct, bool request)
1756 return blk_rq_pos(io_struct);
1758 return ((struct bio *)io_struct)->bi_iter.bi_sector;
1761 static int bfq_rq_close_to_sector(void *io_struct, bool request,
1764 return abs(bfq_io_struct_pos(io_struct, request) - sector) <=
1768 static struct bfq_queue *bfqq_find_close(struct bfq_data *bfqd,
1769 struct bfq_queue *bfqq,
1772 struct rb_root *root = &bfq_bfqq_to_bfqg(bfqq)->rq_pos_tree;
1773 struct rb_node *parent, *node;
1774 struct bfq_queue *__bfqq;
1776 if (RB_EMPTY_ROOT(root))
1780 * First, if we find a request starting at the end of the last
1781 * request, choose it.
1783 __bfqq = bfq_rq_pos_tree_lookup(bfqd, root, sector, &parent, NULL);
1788 * If the exact sector wasn't found, the parent of the NULL leaf
1789 * will contain the closest sector (rq_pos_tree sorted by
1790 * next_request position).
1792 __bfqq = rb_entry(parent, struct bfq_queue, pos_node);
1793 if (bfq_rq_close_to_sector(__bfqq->next_rq, true, sector))
1796 if (blk_rq_pos(__bfqq->next_rq) < sector)
1797 node = rb_next(&__bfqq->pos_node);
1799 node = rb_prev(&__bfqq->pos_node);
1803 __bfqq = rb_entry(node, struct bfq_queue, pos_node);
1804 if (bfq_rq_close_to_sector(__bfqq->next_rq, true, sector))
1810 static struct bfq_queue *bfq_find_close_cooperator(struct bfq_data *bfqd,
1811 struct bfq_queue *cur_bfqq,
1814 struct bfq_queue *bfqq;
1817 * We shall notice if some of the queues are cooperating,
1818 * e.g., working closely on the same area of the device. In
1819 * that case, we can group them together and: 1) don't waste
1820 * time idling, and 2) serve the union of their requests in
1821 * the best possible order for throughput.
1823 bfqq = bfqq_find_close(bfqd, cur_bfqq, sector);
1824 if (!bfqq || bfqq == cur_bfqq)
1830 static struct bfq_queue *
1831 bfq_setup_merge(struct bfq_queue *bfqq, struct bfq_queue *new_bfqq)
1833 int process_refs, new_process_refs;
1834 struct bfq_queue *__bfqq;
1837 * If there are no process references on the new_bfqq, then it is
1838 * unsafe to follow the ->new_bfqq chain as other bfqq's in the chain
1839 * may have dropped their last reference (not just their last process
1842 if (!bfqq_process_refs(new_bfqq))
1845 /* Avoid a circular list and skip interim queue merges. */
1846 while ((__bfqq = new_bfqq->new_bfqq)) {
1852 process_refs = bfqq_process_refs(bfqq);
1853 new_process_refs = bfqq_process_refs(new_bfqq);
1855 * If the process for the bfqq has gone away, there is no
1856 * sense in merging the queues.
1858 if (process_refs == 0 || new_process_refs == 0)
1861 bfq_log_bfqq(bfqq->bfqd, bfqq, "scheduling merge with queue %d",
1865 * Merging is just a redirection: the requests of the process
1866 * owning one of the two queues are redirected to the other queue.
1867 * The latter queue, in its turn, is set as shared if this is the
1868 * first time that the requests of some process are redirected to
1871 * We redirect bfqq to new_bfqq and not the opposite, because
1872 * we are in the context of the process owning bfqq, thus we
1873 * have the io_cq of this process. So we can immediately
1874 * configure this io_cq to redirect the requests of the
1875 * process to new_bfqq. In contrast, the io_cq of new_bfqq is
1876 * not available any more (new_bfqq->bic == NULL).
1878 * Anyway, even in case new_bfqq coincides with the in-service
1879 * queue, redirecting requests the in-service queue is the
1880 * best option, as we feed the in-service queue with new
1881 * requests close to the last request served and, by doing so,
1882 * are likely to increase the throughput.
1884 bfqq->new_bfqq = new_bfqq;
1885 new_bfqq->ref += process_refs;
1889 static bool bfq_may_be_close_cooperator(struct bfq_queue *bfqq,
1890 struct bfq_queue *new_bfqq)
1892 if (bfq_class_idle(bfqq) || bfq_class_idle(new_bfqq) ||
1893 (bfqq->ioprio_class != new_bfqq->ioprio_class))
1897 * If either of the queues has already been detected as seeky,
1898 * then merging it with the other queue is unlikely to lead to
1901 if (BFQQ_SEEKY(bfqq) || BFQQ_SEEKY(new_bfqq))
1905 * Interleaved I/O is known to be done by (some) applications
1906 * only for reads, so it does not make sense to merge async
1909 if (!bfq_bfqq_sync(bfqq) || !bfq_bfqq_sync(new_bfqq))
1916 * If this function returns true, then bfqq cannot be merged. The idea
1917 * is that true cooperation happens very early after processes start
1918 * to do I/O. Usually, late cooperations are just accidental false
1919 * positives. In case bfqq is weight-raised, such false positives
1920 * would evidently degrade latency guarantees for bfqq.
1922 static bool wr_from_too_long(struct bfq_queue *bfqq)
1924 return bfqq->wr_coeff > 1 &&
1925 time_is_before_jiffies(bfqq->last_wr_start_finish +
1926 msecs_to_jiffies(100));
1930 * Attempt to schedule a merge of bfqq with the currently in-service
1931 * queue or with a close queue among the scheduled queues. Return
1932 * NULL if no merge was scheduled, a pointer to the shared bfq_queue
1933 * structure otherwise.
1935 * The OOM queue is not allowed to participate to cooperation: in fact, since
1936 * the requests temporarily redirected to the OOM queue could be redirected
1937 * again to dedicated queues at any time, the state needed to correctly
1938 * handle merging with the OOM queue would be quite complex and expensive
1939 * to maintain. Besides, in such a critical condition as an out of memory,
1940 * the benefits of queue merging may be little relevant, or even negligible.
1942 * Weight-raised queues can be merged only if their weight-raising
1943 * period has just started. In fact cooperating processes are usually
1944 * started together. Thus, with this filter we avoid false positives
1945 * that would jeopardize low-latency guarantees.
1947 * WARNING: queue merging may impair fairness among non-weight raised
1948 * queues, for at least two reasons: 1) the original weight of a
1949 * merged queue may change during the merged state, 2) even being the
1950 * weight the same, a merged queue may be bloated with many more
1951 * requests than the ones produced by its originally-associated
1954 static struct bfq_queue *
1955 bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq,
1956 void *io_struct, bool request)
1958 struct bfq_queue *in_service_bfqq, *new_bfqq;
1961 return bfqq->new_bfqq;
1964 wr_from_too_long(bfqq) ||
1965 unlikely(bfqq == &bfqd->oom_bfqq))
1968 /* If there is only one backlogged queue, don't search. */
1969 if (bfqd->busy_queues == 1)
1972 in_service_bfqq = bfqd->in_service_queue;
1974 if (!in_service_bfqq || in_service_bfqq == bfqq
1975 || wr_from_too_long(in_service_bfqq) ||
1976 unlikely(in_service_bfqq == &bfqd->oom_bfqq))
1977 goto check_scheduled;
1979 if (bfq_rq_close_to_sector(io_struct, request, bfqd->last_position) &&
1980 bfqq->entity.parent == in_service_bfqq->entity.parent &&
1981 bfq_may_be_close_cooperator(bfqq, in_service_bfqq)) {
1982 new_bfqq = bfq_setup_merge(bfqq, in_service_bfqq);
1987 * Check whether there is a cooperator among currently scheduled
1988 * queues. The only thing we need is that the bio/request is not
1989 * NULL, as we need it to establish whether a cooperator exists.
1992 new_bfqq = bfq_find_close_cooperator(bfqd, bfqq,
1993 bfq_io_struct_pos(io_struct, request));
1995 if (new_bfqq && !wr_from_too_long(new_bfqq) &&
1996 likely(new_bfqq != &bfqd->oom_bfqq) &&
1997 bfq_may_be_close_cooperator(bfqq, new_bfqq))
1998 return bfq_setup_merge(bfqq, new_bfqq);
2003 static void bfq_bfqq_save_state(struct bfq_queue *bfqq)
2005 struct bfq_io_cq *bic = bfqq->bic;
2008 * If !bfqq->bic, the queue is already shared or its requests
2009 * have already been redirected to a shared queue; both idle window
2010 * and weight raising state have already been saved. Do nothing.
2015 bic->saved_ttime = bfqq->ttime;
2016 bic->saved_has_short_ttime = bfq_bfqq_has_short_ttime(bfqq);
2017 bic->saved_IO_bound = bfq_bfqq_IO_bound(bfqq);
2018 bic->saved_in_large_burst = bfq_bfqq_in_large_burst(bfqq);
2019 bic->was_in_burst_list = !hlist_unhashed(&bfqq->burst_list_node);
2020 bic->saved_wr_coeff = bfqq->wr_coeff;
2021 bic->saved_wr_start_at_switch_to_srt = bfqq->wr_start_at_switch_to_srt;
2022 bic->saved_last_wr_start_finish = bfqq->last_wr_start_finish;
2023 bic->saved_wr_cur_max_time = bfqq->wr_cur_max_time;
2027 bfq_merge_bfqqs(struct bfq_data *bfqd, struct bfq_io_cq *bic,
2028 struct bfq_queue *bfqq, struct bfq_queue *new_bfqq)
2030 bfq_log_bfqq(bfqd, bfqq, "merging with queue %lu",
2031 (unsigned long)new_bfqq->pid);
2032 /* Save weight raising and idle window of the merged queues */
2033 bfq_bfqq_save_state(bfqq);
2034 bfq_bfqq_save_state(new_bfqq);
2035 if (bfq_bfqq_IO_bound(bfqq))
2036 bfq_mark_bfqq_IO_bound(new_bfqq);
2037 bfq_clear_bfqq_IO_bound(bfqq);
2040 * If bfqq is weight-raised, then let new_bfqq inherit
2041 * weight-raising. To reduce false positives, neglect the case
2042 * where bfqq has just been created, but has not yet made it
2043 * to be weight-raised (which may happen because EQM may merge
2044 * bfqq even before bfq_add_request is executed for the first
2045 * time for bfqq). Handling this case would however be very
2046 * easy, thanks to the flag just_created.
2048 if (new_bfqq->wr_coeff == 1 && bfqq->wr_coeff > 1) {
2049 new_bfqq->wr_coeff = bfqq->wr_coeff;
2050 new_bfqq->wr_cur_max_time = bfqq->wr_cur_max_time;
2051 new_bfqq->last_wr_start_finish = bfqq->last_wr_start_finish;
2052 new_bfqq->wr_start_at_switch_to_srt =
2053 bfqq->wr_start_at_switch_to_srt;
2054 if (bfq_bfqq_busy(new_bfqq))
2055 bfqd->wr_busy_queues++;
2056 new_bfqq->entity.prio_changed = 1;
2059 if (bfqq->wr_coeff > 1) { /* bfqq has given its wr to new_bfqq */
2061 bfqq->entity.prio_changed = 1;
2062 if (bfq_bfqq_busy(bfqq))
2063 bfqd->wr_busy_queues--;
2066 bfq_log_bfqq(bfqd, new_bfqq, "merge_bfqqs: wr_busy %d",
2067 bfqd->wr_busy_queues);
2070 * Merge queues (that is, let bic redirect its requests to new_bfqq)
2072 bic_set_bfqq(bic, new_bfqq, 1);
2073 bfq_mark_bfqq_coop(new_bfqq);
2075 * new_bfqq now belongs to at least two bics (it is a shared queue):
2076 * set new_bfqq->bic to NULL. bfqq either:
2077 * - does not belong to any bic any more, and hence bfqq->bic must
2078 * be set to NULL, or
2079 * - is a queue whose owning bics have already been redirected to a
2080 * different queue, hence the queue is destined to not belong to
2081 * any bic soon and bfqq->bic is already NULL (therefore the next
2082 * assignment causes no harm).
2084 new_bfqq->bic = NULL;
2086 /* release process reference to bfqq */
2087 bfq_put_queue(bfqq);
2090 static bool bfq_allow_bio_merge(struct request_queue *q, struct request *rq,
2093 struct bfq_data *bfqd = q->elevator->elevator_data;
2094 bool is_sync = op_is_sync(bio->bi_opf);
2095 struct bfq_queue *bfqq = bfqd->bio_bfqq, *new_bfqq;
2098 * Disallow merge of a sync bio into an async request.
2100 if (is_sync && !rq_is_sync(rq))
2104 * Lookup the bfqq that this bio will be queued with. Allow
2105 * merge only if rq is queued there.
2111 * We take advantage of this function to perform an early merge
2112 * of the queues of possible cooperating processes.
2114 new_bfqq = bfq_setup_cooperator(bfqd, bfqq, bio, false);
2117 * bic still points to bfqq, then it has not yet been
2118 * redirected to some other bfq_queue, and a queue
2119 * merge beween bfqq and new_bfqq can be safely
2120 * fulfillled, i.e., bic can be redirected to new_bfqq
2121 * and bfqq can be put.
2123 bfq_merge_bfqqs(bfqd, bfqd->bio_bic, bfqq,
2126 * If we get here, bio will be queued into new_queue,
2127 * so use new_bfqq to decide whether bio and rq can be
2133 * Change also bqfd->bio_bfqq, as
2134 * bfqd->bio_bic now points to new_bfqq, and
2135 * this function may be invoked again (and then may
2136 * use again bqfd->bio_bfqq).
2138 bfqd->bio_bfqq = bfqq;
2141 return bfqq == RQ_BFQQ(rq);
2145 * Set the maximum time for the in-service queue to consume its
2146 * budget. This prevents seeky processes from lowering the throughput.
2147 * In practice, a time-slice service scheme is used with seeky
2150 static void bfq_set_budget_timeout(struct bfq_data *bfqd,
2151 struct bfq_queue *bfqq)
2153 unsigned int timeout_coeff;
2155 if (bfqq->wr_cur_max_time == bfqd->bfq_wr_rt_max_time)
2158 timeout_coeff = bfqq->entity.weight / bfqq->entity.orig_weight;
2160 bfqd->last_budget_start = ktime_get();
2162 bfqq->budget_timeout = jiffies +
2163 bfqd->bfq_timeout * timeout_coeff;
2166 static void __bfq_set_in_service_queue(struct bfq_data *bfqd,
2167 struct bfq_queue *bfqq)
2170 bfqg_stats_update_avg_queue_size(bfqq_group(bfqq));
2171 bfq_clear_bfqq_fifo_expire(bfqq);
2173 bfqd->budgets_assigned = (bfqd->budgets_assigned * 7 + 256) / 8;
2175 if (time_is_before_jiffies(bfqq->last_wr_start_finish) &&
2176 bfqq->wr_coeff > 1 &&
2177 bfqq->wr_cur_max_time == bfqd->bfq_wr_rt_max_time &&
2178 time_is_before_jiffies(bfqq->budget_timeout)) {
2180 * For soft real-time queues, move the start
2181 * of the weight-raising period forward by the
2182 * time the queue has not received any
2183 * service. Otherwise, a relatively long
2184 * service delay is likely to cause the
2185 * weight-raising period of the queue to end,
2186 * because of the short duration of the
2187 * weight-raising period of a soft real-time
2188 * queue. It is worth noting that this move
2189 * is not so dangerous for the other queues,
2190 * because soft real-time queues are not
2193 * To not add a further variable, we use the
2194 * overloaded field budget_timeout to
2195 * determine for how long the queue has not
2196 * received service, i.e., how much time has
2197 * elapsed since the queue expired. However,
2198 * this is a little imprecise, because
2199 * budget_timeout is set to jiffies if bfqq
2200 * not only expires, but also remains with no
2203 if (time_after(bfqq->budget_timeout,
2204 bfqq->last_wr_start_finish))
2205 bfqq->last_wr_start_finish +=
2206 jiffies - bfqq->budget_timeout;
2208 bfqq->last_wr_start_finish = jiffies;
2211 bfq_set_budget_timeout(bfqd, bfqq);
2212 bfq_log_bfqq(bfqd, bfqq,
2213 "set_in_service_queue, cur-budget = %d",
2214 bfqq->entity.budget);
2217 bfqd->in_service_queue = bfqq;
2221 * Get and set a new queue for service.
2223 static struct bfq_queue *bfq_set_in_service_queue(struct bfq_data *bfqd)
2225 struct bfq_queue *bfqq = bfq_get_next_queue(bfqd);
2227 __bfq_set_in_service_queue(bfqd, bfqq);
2231 static void bfq_arm_slice_timer(struct bfq_data *bfqd)
2233 struct bfq_queue *bfqq = bfqd->in_service_queue;
2236 bfq_mark_bfqq_wait_request(bfqq);
2239 * We don't want to idle for seeks, but we do want to allow
2240 * fair distribution of slice time for a process doing back-to-back
2241 * seeks. So allow a little bit of time for him to submit a new rq.
2243 sl = bfqd->bfq_slice_idle;
2245 * Unless the queue is being weight-raised or the scenario is
2246 * asymmetric, grant only minimum idle time if the queue
2247 * is seeky. A long idling is preserved for a weight-raised
2248 * queue, or, more in general, in an asymmetric scenario,
2249 * because a long idling is needed for guaranteeing to a queue
2250 * its reserved share of the throughput (in particular, it is
2251 * needed if the queue has a higher weight than some other
2254 if (BFQQ_SEEKY(bfqq) && bfqq->wr_coeff == 1 &&
2255 bfq_symmetric_scenario(bfqd))
2256 sl = min_t(u64, sl, BFQ_MIN_TT);
2258 bfqd->last_idling_start = ktime_get();
2259 hrtimer_start(&bfqd->idle_slice_timer, ns_to_ktime(sl),
2261 bfqg_stats_set_start_idle_time(bfqq_group(bfqq));
2265 * In autotuning mode, max_budget is dynamically recomputed as the
2266 * amount of sectors transferred in timeout at the estimated peak
2267 * rate. This enables BFQ to utilize a full timeslice with a full
2268 * budget, even if the in-service queue is served at peak rate. And
2269 * this maximises throughput with sequential workloads.
2271 static unsigned long bfq_calc_max_budget(struct bfq_data *bfqd)
2273 return (u64)bfqd->peak_rate * USEC_PER_MSEC *
2274 jiffies_to_msecs(bfqd->bfq_timeout)>>BFQ_RATE_SHIFT;
2278 * Update parameters related to throughput and responsiveness, as a
2279 * function of the estimated peak rate. See comments on
2280 * bfq_calc_max_budget(), and on T_slow and T_fast arrays.
2282 static void update_thr_responsiveness_params(struct bfq_data *bfqd)
2284 int dev_type = blk_queue_nonrot(bfqd->queue);
2286 if (bfqd->bfq_user_max_budget == 0)
2287 bfqd->bfq_max_budget =
2288 bfq_calc_max_budget(bfqd);
2290 if (bfqd->device_speed == BFQ_BFQD_FAST &&
2291 bfqd->peak_rate < device_speed_thresh[dev_type]) {
2292 bfqd->device_speed = BFQ_BFQD_SLOW;
2293 bfqd->RT_prod = R_slow[dev_type] *
2295 } else if (bfqd->device_speed == BFQ_BFQD_SLOW &&
2296 bfqd->peak_rate > device_speed_thresh[dev_type]) {
2297 bfqd->device_speed = BFQ_BFQD_FAST;
2298 bfqd->RT_prod = R_fast[dev_type] *
2303 "dev_type %s dev_speed_class = %s (%llu sects/sec), thresh %llu setcs/sec",
2304 dev_type == 0 ? "ROT" : "NONROT",
2305 bfqd->device_speed == BFQ_BFQD_FAST ? "FAST" : "SLOW",
2306 bfqd->device_speed == BFQ_BFQD_FAST ?
2307 (USEC_PER_SEC*(u64)R_fast[dev_type])>>BFQ_RATE_SHIFT :
2308 (USEC_PER_SEC*(u64)R_slow[dev_type])>>BFQ_RATE_SHIFT,
2309 (USEC_PER_SEC*(u64)device_speed_thresh[dev_type])>>
2313 static void bfq_reset_rate_computation(struct bfq_data *bfqd,
2316 if (rq != NULL) { /* new rq dispatch now, reset accordingly */
2317 bfqd->last_dispatch = bfqd->first_dispatch = ktime_get_ns();
2318 bfqd->peak_rate_samples = 1;
2319 bfqd->sequential_samples = 0;
2320 bfqd->tot_sectors_dispatched = bfqd->last_rq_max_size =
2322 } else /* no new rq dispatched, just reset the number of samples */
2323 bfqd->peak_rate_samples = 0; /* full re-init on next disp. */
2326 "reset_rate_computation at end, sample %u/%u tot_sects %llu",
2327 bfqd->peak_rate_samples, bfqd->sequential_samples,
2328 bfqd->tot_sectors_dispatched);
2331 static void bfq_update_rate_reset(struct bfq_data *bfqd, struct request *rq)
2333 u32 rate, weight, divisor;
2336 * For the convergence property to hold (see comments on
2337 * bfq_update_peak_rate()) and for the assessment to be
2338 * reliable, a minimum number of samples must be present, and
2339 * a minimum amount of time must have elapsed. If not so, do
2340 * not compute new rate. Just reset parameters, to get ready
2341 * for a new evaluation attempt.
2343 if (bfqd->peak_rate_samples < BFQ_RATE_MIN_SAMPLES ||
2344 bfqd->delta_from_first < BFQ_RATE_MIN_INTERVAL)
2345 goto reset_computation;
2348 * If a new request completion has occurred after last
2349 * dispatch, then, to approximate the rate at which requests
2350 * have been served by the device, it is more precise to
2351 * extend the observation interval to the last completion.
2353 bfqd->delta_from_first =
2354 max_t(u64, bfqd->delta_from_first,
2355 bfqd->last_completion - bfqd->first_dispatch);
2358 * Rate computed in sects/usec, and not sects/nsec, for
2361 rate = div64_ul(bfqd->tot_sectors_dispatched<<BFQ_RATE_SHIFT,
2362 div_u64(bfqd->delta_from_first, NSEC_PER_USEC));
2365 * Peak rate not updated if:
2366 * - the percentage of sequential dispatches is below 3/4 of the
2367 * total, and rate is below the current estimated peak rate
2368 * - rate is unreasonably high (> 20M sectors/sec)
2370 if ((bfqd->sequential_samples < (3 * bfqd->peak_rate_samples)>>2 &&
2371 rate <= bfqd->peak_rate) ||
2372 rate > 20<<BFQ_RATE_SHIFT)
2373 goto reset_computation;
2376 * We have to update the peak rate, at last! To this purpose,
2377 * we use a low-pass filter. We compute the smoothing constant
2378 * of the filter as a function of the 'weight' of the new
2381 * As can be seen in next formulas, we define this weight as a
2382 * quantity proportional to how sequential the workload is,
2383 * and to how long the observation time interval is.
2385 * The weight runs from 0 to 8. The maximum value of the
2386 * weight, 8, yields the minimum value for the smoothing
2387 * constant. At this minimum value for the smoothing constant,
2388 * the measured rate contributes for half of the next value of
2389 * the estimated peak rate.
2391 * So, the first step is to compute the weight as a function
2392 * of how sequential the workload is. Note that the weight
2393 * cannot reach 9, because bfqd->sequential_samples cannot
2394 * become equal to bfqd->peak_rate_samples, which, in its
2395 * turn, holds true because bfqd->sequential_samples is not
2396 * incremented for the first sample.
2398 weight = (9 * bfqd->sequential_samples) / bfqd->peak_rate_samples;
2401 * Second step: further refine the weight as a function of the
2402 * duration of the observation interval.
2404 weight = min_t(u32, 8,
2405 div_u64(weight * bfqd->delta_from_first,
2406 BFQ_RATE_REF_INTERVAL));
2409 * Divisor ranging from 10, for minimum weight, to 2, for
2412 divisor = 10 - weight;
2415 * Finally, update peak rate:
2417 * peak_rate = peak_rate * (divisor-1) / divisor + rate / divisor
2419 bfqd->peak_rate *= divisor-1;
2420 bfqd->peak_rate /= divisor;
2421 rate /= divisor; /* smoothing constant alpha = 1/divisor */
2423 bfqd->peak_rate += rate;
2424 update_thr_responsiveness_params(bfqd);
2427 bfq_reset_rate_computation(bfqd, rq);
2431 * Update the read/write peak rate (the main quantity used for
2432 * auto-tuning, see update_thr_responsiveness_params()).
2434 * It is not trivial to estimate the peak rate (correctly): because of
2435 * the presence of sw and hw queues between the scheduler and the
2436 * device components that finally serve I/O requests, it is hard to
2437 * say exactly when a given dispatched request is served inside the
2438 * device, and for how long. As a consequence, it is hard to know
2439 * precisely at what rate a given set of requests is actually served
2442 * On the opposite end, the dispatch time of any request is trivially
2443 * available, and, from this piece of information, the "dispatch rate"
2444 * of requests can be immediately computed. So, the idea in the next
2445 * function is to use what is known, namely request dispatch times
2446 * (plus, when useful, request completion times), to estimate what is
2447 * unknown, namely in-device request service rate.
2449 * The main issue is that, because of the above facts, the rate at
2450 * which a certain set of requests is dispatched over a certain time
2451 * interval can vary greatly with respect to the rate at which the
2452 * same requests are then served. But, since the size of any
2453 * intermediate queue is limited, and the service scheme is lossless
2454 * (no request is silently dropped), the following obvious convergence
2455 * property holds: the number of requests dispatched MUST become
2456 * closer and closer to the number of requests completed as the
2457 * observation interval grows. This is the key property used in
2458 * the next function to estimate the peak service rate as a function
2459 * of the observed dispatch rate. The function assumes to be invoked
2460 * on every request dispatch.
2462 static void bfq_update_peak_rate(struct bfq_data *bfqd, struct request *rq)
2464 u64 now_ns = ktime_get_ns();
2466 if (bfqd->peak_rate_samples == 0) { /* first dispatch */
2467 bfq_log(bfqd, "update_peak_rate: goto reset, samples %d",
2468 bfqd->peak_rate_samples);
2469 bfq_reset_rate_computation(bfqd, rq);
2470 goto update_last_values; /* will add one sample */
2474 * Device idle for very long: the observation interval lasting
2475 * up to this dispatch cannot be a valid observation interval
2476 * for computing a new peak rate (similarly to the late-
2477 * completion event in bfq_completed_request()). Go to
2478 * update_rate_and_reset to have the following three steps
2480 * - close the observation interval at the last (previous)
2481 * request dispatch or completion
2482 * - compute rate, if possible, for that observation interval
2483 * - start a new observation interval with this dispatch
2485 if (now_ns - bfqd->last_dispatch > 100*NSEC_PER_MSEC &&
2486 bfqd->rq_in_driver == 0)
2487 goto update_rate_and_reset;
2489 /* Update sampling information */
2490 bfqd->peak_rate_samples++;
2492 if ((bfqd->rq_in_driver > 0 ||
2493 now_ns - bfqd->last_completion < BFQ_MIN_TT)
2494 && get_sdist(bfqd->last_position, rq) < BFQQ_SEEK_THR)
2495 bfqd->sequential_samples++;
2497 bfqd->tot_sectors_dispatched += blk_rq_sectors(rq);
2499 /* Reset max observed rq size every 32 dispatches */
2500 if (likely(bfqd->peak_rate_samples % 32))
2501 bfqd->last_rq_max_size =
2502 max_t(u32, blk_rq_sectors(rq), bfqd->last_rq_max_size);
2504 bfqd->last_rq_max_size = blk_rq_sectors(rq);
2506 bfqd->delta_from_first = now_ns - bfqd->first_dispatch;
2508 /* Target observation interval not yet reached, go on sampling */
2509 if (bfqd->delta_from_first < BFQ_RATE_REF_INTERVAL)
2510 goto update_last_values;
2512 update_rate_and_reset:
2513 bfq_update_rate_reset(bfqd, rq);
2515 bfqd->last_position = blk_rq_pos(rq) + blk_rq_sectors(rq);
2516 bfqd->last_dispatch = now_ns;
2520 * Remove request from internal lists.
2522 static void bfq_dispatch_remove(struct request_queue *q, struct request *rq)
2524 struct bfq_queue *bfqq = RQ_BFQQ(rq);
2527 * For consistency, the next instruction should have been
2528 * executed after removing the request from the queue and
2529 * dispatching it. We execute instead this instruction before
2530 * bfq_remove_request() (and hence introduce a temporary
2531 * inconsistency), for efficiency. In fact, should this
2532 * dispatch occur for a non in-service bfqq, this anticipated
2533 * increment prevents two counters related to bfqq->dispatched
2534 * from risking to be, first, uselessly decremented, and then
2535 * incremented again when the (new) value of bfqq->dispatched
2536 * happens to be taken into account.
2539 bfq_update_peak_rate(q->elevator->elevator_data, rq);
2541 bfq_remove_request(q, rq);
2544 static void __bfq_bfqq_expire(struct bfq_data *bfqd, struct bfq_queue *bfqq)
2547 * If this bfqq is shared between multiple processes, check
2548 * to make sure that those processes are still issuing I/Os
2549 * within the mean seek distance. If not, it may be time to
2550 * break the queues apart again.
2552 if (bfq_bfqq_coop(bfqq) && BFQQ_SEEKY(bfqq))
2553 bfq_mark_bfqq_split_coop(bfqq);
2555 if (RB_EMPTY_ROOT(&bfqq->sort_list)) {
2556 if (bfqq->dispatched == 0)
2558 * Overloading budget_timeout field to store
2559 * the time at which the queue remains with no
2560 * backlog and no outstanding request; used by
2561 * the weight-raising mechanism.
2563 bfqq->budget_timeout = jiffies;
2565 bfq_del_bfqq_busy(bfqd, bfqq, true);
2567 bfq_requeue_bfqq(bfqd, bfqq, true);
2569 * Resort priority tree of potential close cooperators.
2571 bfq_pos_tree_add_move(bfqd, bfqq);
2575 * All in-service entities must have been properly deactivated
2576 * or requeued before executing the next function, which
2577 * resets all in-service entites as no more in service.
2579 __bfq_bfqd_reset_in_service(bfqd);
2583 * __bfq_bfqq_recalc_budget - try to adapt the budget to the @bfqq behavior.
2584 * @bfqd: device data.
2585 * @bfqq: queue to update.
2586 * @reason: reason for expiration.
2588 * Handle the feedback on @bfqq budget at queue expiration.
2589 * See the body for detailed comments.
2591 static void __bfq_bfqq_recalc_budget(struct bfq_data *bfqd,
2592 struct bfq_queue *bfqq,
2593 enum bfqq_expiration reason)
2595 struct request *next_rq;
2596 int budget, min_budget;
2598 min_budget = bfq_min_budget(bfqd);
2600 if (bfqq->wr_coeff == 1)
2601 budget = bfqq->max_budget;
2603 * Use a constant, low budget for weight-raised queues,
2604 * to help achieve a low latency. Keep it slightly higher
2605 * than the minimum possible budget, to cause a little
2606 * bit fewer expirations.
2608 budget = 2 * min_budget;
2610 bfq_log_bfqq(bfqd, bfqq, "recalc_budg: last budg %d, budg left %d",
2611 bfqq->entity.budget, bfq_bfqq_budget_left(bfqq));
2612 bfq_log_bfqq(bfqd, bfqq, "recalc_budg: last max_budg %d, min budg %d",
2613 budget, bfq_min_budget(bfqd));
2614 bfq_log_bfqq(bfqd, bfqq, "recalc_budg: sync %d, seeky %d",
2615 bfq_bfqq_sync(bfqq), BFQQ_SEEKY(bfqd->in_service_queue));
2617 if (bfq_bfqq_sync(bfqq) && bfqq->wr_coeff == 1) {
2620 * Caveat: in all the following cases we trade latency
2623 case BFQQE_TOO_IDLE:
2625 * This is the only case where we may reduce
2626 * the budget: if there is no request of the
2627 * process still waiting for completion, then
2628 * we assume (tentatively) that the timer has
2629 * expired because the batch of requests of
2630 * the process could have been served with a
2631 * smaller budget. Hence, betting that
2632 * process will behave in the same way when it
2633 * becomes backlogged again, we reduce its
2634 * next budget. As long as we guess right,
2635 * this budget cut reduces the latency
2636 * experienced by the process.
2638 * However, if there are still outstanding
2639 * requests, then the process may have not yet
2640 * issued its next request just because it is
2641 * still waiting for the completion of some of
2642 * the still outstanding ones. So in this
2643 * subcase we do not reduce its budget, on the
2644 * contrary we increase it to possibly boost
2645 * the throughput, as discussed in the
2646 * comments to the BUDGET_TIMEOUT case.
2648 if (bfqq->dispatched > 0) /* still outstanding reqs */
2649 budget = min(budget * 2, bfqd->bfq_max_budget);
2651 if (budget > 5 * min_budget)
2652 budget -= 4 * min_budget;
2654 budget = min_budget;
2657 case BFQQE_BUDGET_TIMEOUT:
2659 * We double the budget here because it gives
2660 * the chance to boost the throughput if this
2661 * is not a seeky process (and has bumped into
2662 * this timeout because of, e.g., ZBR).
2664 budget = min(budget * 2, bfqd->bfq_max_budget);
2666 case BFQQE_BUDGET_EXHAUSTED:
2668 * The process still has backlog, and did not
2669 * let either the budget timeout or the disk
2670 * idling timeout expire. Hence it is not
2671 * seeky, has a short thinktime and may be
2672 * happy with a higher budget too. So
2673 * definitely increase the budget of this good
2674 * candidate to boost the disk throughput.
2676 budget = min(budget * 4, bfqd->bfq_max_budget);
2678 case BFQQE_NO_MORE_REQUESTS:
2680 * For queues that expire for this reason, it
2681 * is particularly important to keep the
2682 * budget close to the actual service they
2683 * need. Doing so reduces the timestamp
2684 * misalignment problem described in the
2685 * comments in the body of
2686 * __bfq_activate_entity. In fact, suppose
2687 * that a queue systematically expires for
2688 * BFQQE_NO_MORE_REQUESTS and presents a
2689 * new request in time to enjoy timestamp
2690 * back-shifting. The larger the budget of the
2691 * queue is with respect to the service the
2692 * queue actually requests in each service
2693 * slot, the more times the queue can be
2694 * reactivated with the same virtual finish
2695 * time. It follows that, even if this finish
2696 * time is pushed to the system virtual time
2697 * to reduce the consequent timestamp
2698 * misalignment, the queue unjustly enjoys for
2699 * many re-activations a lower finish time
2700 * than all newly activated queues.
2702 * The service needed by bfqq is measured
2703 * quite precisely by bfqq->entity.service.
2704 * Since bfqq does not enjoy device idling,
2705 * bfqq->entity.service is equal to the number
2706 * of sectors that the process associated with
2707 * bfqq requested to read/write before waiting
2708 * for request completions, or blocking for
2711 budget = max_t(int, bfqq->entity.service, min_budget);
2716 } else if (!bfq_bfqq_sync(bfqq)) {
2718 * Async queues get always the maximum possible
2719 * budget, as for them we do not care about latency
2720 * (in addition, their ability to dispatch is limited
2721 * by the charging factor).
2723 budget = bfqd->bfq_max_budget;
2726 bfqq->max_budget = budget;
2728 if (bfqd->budgets_assigned >= bfq_stats_min_budgets &&
2729 !bfqd->bfq_user_max_budget)
2730 bfqq->max_budget = min(bfqq->max_budget, bfqd->bfq_max_budget);
2733 * If there is still backlog, then assign a new budget, making
2734 * sure that it is large enough for the next request. Since
2735 * the finish time of bfqq must be kept in sync with the
2736 * budget, be sure to call __bfq_bfqq_expire() *after* this
2739 * If there is no backlog, then no need to update the budget;
2740 * it will be updated on the arrival of a new request.
2742 next_rq = bfqq->next_rq;
2744 bfqq->entity.budget = max_t(unsigned long, bfqq->max_budget,
2745 bfq_serv_to_charge(next_rq, bfqq));
2747 bfq_log_bfqq(bfqd, bfqq, "head sect: %u, new budget %d",
2748 next_rq ? blk_rq_sectors(next_rq) : 0,
2749 bfqq->entity.budget);
2753 * Return true if the process associated with bfqq is "slow". The slow
2754 * flag is used, in addition to the budget timeout, to reduce the
2755 * amount of service provided to seeky processes, and thus reduce
2756 * their chances to lower the throughput. More details in the comments
2757 * on the function bfq_bfqq_expire().
2759 * An important observation is in order: as discussed in the comments
2760 * on the function bfq_update_peak_rate(), with devices with internal
2761 * queues, it is hard if ever possible to know when and for how long
2762 * an I/O request is processed by the device (apart from the trivial
2763 * I/O pattern where a new request is dispatched only after the
2764 * previous one has been completed). This makes it hard to evaluate
2765 * the real rate at which the I/O requests of each bfq_queue are
2766 * served. In fact, for an I/O scheduler like BFQ, serving a
2767 * bfq_queue means just dispatching its requests during its service
2768 * slot (i.e., until the budget of the queue is exhausted, or the
2769 * queue remains idle, or, finally, a timeout fires). But, during the
2770 * service slot of a bfq_queue, around 100 ms at most, the device may
2771 * be even still processing requests of bfq_queues served in previous
2772 * service slots. On the opposite end, the requests of the in-service
2773 * bfq_queue may be completed after the service slot of the queue
2776 * Anyway, unless more sophisticated solutions are used
2777 * (where possible), the sum of the sizes of the requests dispatched
2778 * during the service slot of a bfq_queue is probably the only
2779 * approximation available for the service received by the bfq_queue
2780 * during its service slot. And this sum is the quantity used in this
2781 * function to evaluate the I/O speed of a process.
2783 static bool bfq_bfqq_is_slow(struct bfq_data *bfqd, struct bfq_queue *bfqq,
2784 bool compensate, enum bfqq_expiration reason,
2785 unsigned long *delta_ms)
2787 ktime_t delta_ktime;
2789 bool slow = BFQQ_SEEKY(bfqq); /* if delta too short, use seekyness */
2791 if (!bfq_bfqq_sync(bfqq))
2795 delta_ktime = bfqd->last_idling_start;
2797 delta_ktime = ktime_get();
2798 delta_ktime = ktime_sub(delta_ktime, bfqd->last_budget_start);
2799 delta_usecs = ktime_to_us(delta_ktime);
2801 /* don't use too short time intervals */
2802 if (delta_usecs < 1000) {
2803 if (blk_queue_nonrot(bfqd->queue))
2805 * give same worst-case guarantees as idling
2808 *delta_ms = BFQ_MIN_TT / NSEC_PER_MSEC;
2809 else /* charge at least one seek */
2810 *delta_ms = bfq_slice_idle / NSEC_PER_MSEC;
2815 *delta_ms = delta_usecs / USEC_PER_MSEC;
2818 * Use only long (> 20ms) intervals to filter out excessive
2819 * spikes in service rate estimation.
2821 if (delta_usecs > 20000) {
2823 * Caveat for rotational devices: processes doing I/O
2824 * in the slower disk zones tend to be slow(er) even
2825 * if not seeky. In this respect, the estimated peak
2826 * rate is likely to be an average over the disk
2827 * surface. Accordingly, to not be too harsh with
2828 * unlucky processes, a process is deemed slow only if
2829 * its rate has been lower than half of the estimated
2832 slow = bfqq->entity.service < bfqd->bfq_max_budget / 2;
2835 bfq_log_bfqq(bfqd, bfqq, "bfq_bfqq_is_slow: slow %d", slow);
2841 * To be deemed as soft real-time, an application must meet two
2842 * requirements. First, the application must not require an average
2843 * bandwidth higher than the approximate bandwidth required to playback or
2844 * record a compressed high-definition video.
2845 * The next function is invoked on the completion of the last request of a
2846 * batch, to compute the next-start time instant, soft_rt_next_start, such
2847 * that, if the next request of the application does not arrive before
2848 * soft_rt_next_start, then the above requirement on the bandwidth is met.
2850 * The second requirement is that the request pattern of the application is
2851 * isochronous, i.e., that, after issuing a request or a batch of requests,
2852 * the application stops issuing new requests until all its pending requests
2853 * have been completed. After that, the application may issue a new batch,
2855 * For this reason the next function is invoked to compute
2856 * soft_rt_next_start only for applications that meet this requirement,
2857 * whereas soft_rt_next_start is set to infinity for applications that do
2860 * Unfortunately, even a greedy application may happen to behave in an
2861 * isochronous way if the CPU load is high. In fact, the application may
2862 * stop issuing requests while the CPUs are busy serving other processes,
2863 * then restart, then stop again for a while, and so on. In addition, if
2864 * the disk achieves a low enough throughput with the request pattern
2865 * issued by the application (e.g., because the request pattern is random
2866 * and/or the device is slow), then the application may meet the above
2867 * bandwidth requirement too. To prevent such a greedy application to be
2868 * deemed as soft real-time, a further rule is used in the computation of
2869 * soft_rt_next_start: soft_rt_next_start must be higher than the current
2870 * time plus the maximum time for which the arrival of a request is waited
2871 * for when a sync queue becomes idle, namely bfqd->bfq_slice_idle.
2872 * This filters out greedy applications, as the latter issue instead their
2873 * next request as soon as possible after the last one has been completed
2874 * (in contrast, when a batch of requests is completed, a soft real-time
2875 * application spends some time processing data).
2877 * Unfortunately, the last filter may easily generate false positives if
2878 * only bfqd->bfq_slice_idle is used as a reference time interval and one
2879 * or both the following cases occur:
2880 * 1) HZ is so low that the duration of a jiffy is comparable to or higher
2881 * than bfqd->bfq_slice_idle. This happens, e.g., on slow devices with
2883 * 2) jiffies, instead of increasing at a constant rate, may stop increasing
2884 * for a while, then suddenly 'jump' by several units to recover the lost
2885 * increments. This seems to happen, e.g., inside virtual machines.
2886 * To address this issue, we do not use as a reference time interval just
2887 * bfqd->bfq_slice_idle, but bfqd->bfq_slice_idle plus a few jiffies. In
2888 * particular we add the minimum number of jiffies for which the filter
2889 * seems to be quite precise also in embedded systems and KVM/QEMU virtual
2892 static unsigned long bfq_bfqq_softrt_next_start(struct bfq_data *bfqd,
2893 struct bfq_queue *bfqq)
2895 return max(bfqq->last_idle_bklogged +
2896 HZ * bfqq->service_from_backlogged /
2897 bfqd->bfq_wr_max_softrt_rate,
2898 jiffies + nsecs_to_jiffies(bfqq->bfqd->bfq_slice_idle) + 4);
2902 * Return the farthest future time instant according to jiffies
2905 static unsigned long bfq_greatest_from_now(void)
2907 return jiffies + MAX_JIFFY_OFFSET;
2911 * Return the farthest past time instant according to jiffies
2914 static unsigned long bfq_smallest_from_now(void)
2916 return jiffies - MAX_JIFFY_OFFSET;
2920 * bfq_bfqq_expire - expire a queue.
2921 * @bfqd: device owning the queue.
2922 * @bfqq: the queue to expire.
2923 * @compensate: if true, compensate for the time spent idling.
2924 * @reason: the reason causing the expiration.
2926 * If the process associated with bfqq does slow I/O (e.g., because it
2927 * issues random requests), we charge bfqq with the time it has been
2928 * in service instead of the service it has received (see
2929 * bfq_bfqq_charge_time for details on how this goal is achieved). As
2930 * a consequence, bfqq will typically get higher timestamps upon
2931 * reactivation, and hence it will be rescheduled as if it had
2932 * received more service than what it has actually received. In the
2933 * end, bfqq receives less service in proportion to how slowly its
2934 * associated process consumes its budgets (and hence how seriously it
2935 * tends to lower the throughput). In addition, this time-charging
2936 * strategy guarantees time fairness among slow processes. In
2937 * contrast, if the process associated with bfqq is not slow, we
2938 * charge bfqq exactly with the service it has received.
2940 * Charging time to the first type of queues and the exact service to
2941 * the other has the effect of using the WF2Q+ policy to schedule the
2942 * former on a timeslice basis, without violating service domain
2943 * guarantees among the latter.
2945 void bfq_bfqq_expire(struct bfq_data *bfqd,
2946 struct bfq_queue *bfqq,
2948 enum bfqq_expiration reason)
2951 unsigned long delta = 0;
2952 struct bfq_entity *entity = &bfqq->entity;
2956 * Check whether the process is slow (see bfq_bfqq_is_slow).
2958 slow = bfq_bfqq_is_slow(bfqd, bfqq, compensate, reason, &delta);
2961 * Increase service_from_backlogged before next statement,
2962 * because the possible next invocation of
2963 * bfq_bfqq_charge_time would likely inflate
2964 * entity->service. In contrast, service_from_backlogged must
2965 * contain real service, to enable the soft real-time
2966 * heuristic to correctly compute the bandwidth consumed by
2969 bfqq->service_from_backlogged += entity->service;
2972 * As above explained, charge slow (typically seeky) and
2973 * timed-out queues with the time and not the service
2974 * received, to favor sequential workloads.
2976 * Processes doing I/O in the slower disk zones will tend to
2977 * be slow(er) even if not seeky. Therefore, since the
2978 * estimated peak rate is actually an average over the disk
2979 * surface, these processes may timeout just for bad luck. To
2980 * avoid punishing them, do not charge time to processes that
2981 * succeeded in consuming at least 2/3 of their budget. This
2982 * allows BFQ to preserve enough elasticity to still perform
2983 * bandwidth, and not time, distribution with little unlucky
2984 * or quasi-sequential processes.
2986 if (bfqq->wr_coeff == 1 &&
2988 (reason == BFQQE_BUDGET_TIMEOUT &&
2989 bfq_bfqq_budget_left(bfqq) >= entity->budget / 3)))
2990 bfq_bfqq_charge_time(bfqd, bfqq, delta);
2992 if (reason == BFQQE_TOO_IDLE &&
2993 entity->service <= 2 * entity->budget / 10)
2994 bfq_clear_bfqq_IO_bound(bfqq);
2996 if (bfqd->low_latency && bfqq->wr_coeff == 1)
2997 bfqq->last_wr_start_finish = jiffies;
2999 if (bfqd->low_latency && bfqd->bfq_wr_max_softrt_rate > 0 &&
3000 RB_EMPTY_ROOT(&bfqq->sort_list)) {
3002 * If we get here, and there are no outstanding
3003 * requests, then the request pattern is isochronous
3004 * (see the comments on the function
3005 * bfq_bfqq_softrt_next_start()). Thus we can compute
3006 * soft_rt_next_start. If, instead, the queue still
3007 * has outstanding requests, then we have to wait for
3008 * the completion of all the outstanding requests to
3009 * discover whether the request pattern is actually
3012 if (bfqq->dispatched == 0)
3013 bfqq->soft_rt_next_start =
3014 bfq_bfqq_softrt_next_start(bfqd, bfqq);
3017 * The application is still waiting for the
3018 * completion of one or more requests:
3019 * prevent it from possibly being incorrectly
3020 * deemed as soft real-time by setting its
3021 * soft_rt_next_start to infinity. In fact,
3022 * without this assignment, the application
3023 * would be incorrectly deemed as soft
3025 * 1) it issued a new request before the
3026 * completion of all its in-flight
3028 * 2) at that time, its soft_rt_next_start
3029 * happened to be in the past.
3031 bfqq->soft_rt_next_start =
3032 bfq_greatest_from_now();
3034 * Schedule an update of soft_rt_next_start to when
3035 * the task may be discovered to be isochronous.
3037 bfq_mark_bfqq_softrt_update(bfqq);
3041 bfq_log_bfqq(bfqd, bfqq,
3042 "expire (%d, slow %d, num_disp %d, short_ttime %d)", reason,
3043 slow, bfqq->dispatched, bfq_bfqq_has_short_ttime(bfqq));
3046 * Increase, decrease or leave budget unchanged according to
3049 __bfq_bfqq_recalc_budget(bfqd, bfqq, reason);
3051 __bfq_bfqq_expire(bfqd, bfqq);
3053 /* mark bfqq as waiting a request only if a bic still points to it */
3054 if (ref > 1 && !bfq_bfqq_busy(bfqq) &&
3055 reason != BFQQE_BUDGET_TIMEOUT &&
3056 reason != BFQQE_BUDGET_EXHAUSTED)
3057 bfq_mark_bfqq_non_blocking_wait_rq(bfqq);
3061 * Budget timeout is not implemented through a dedicated timer, but
3062 * just checked on request arrivals and completions, as well as on
3063 * idle timer expirations.
3065 static bool bfq_bfqq_budget_timeout(struct bfq_queue *bfqq)
3067 return time_is_before_eq_jiffies(bfqq->budget_timeout);
3071 * If we expire a queue that is actively waiting (i.e., with the
3072 * device idled) for the arrival of a new request, then we may incur
3073 * the timestamp misalignment problem described in the body of the
3074 * function __bfq_activate_entity. Hence we return true only if this
3075 * condition does not hold, or if the queue is slow enough to deserve
3076 * only to be kicked off for preserving a high throughput.
3078 static bool bfq_may_expire_for_budg_timeout(struct bfq_queue *bfqq)
3080 bfq_log_bfqq(bfqq->bfqd, bfqq,
3081 "may_budget_timeout: wait_request %d left %d timeout %d",
3082 bfq_bfqq_wait_request(bfqq),
3083 bfq_bfqq_budget_left(bfqq) >= bfqq->entity.budget / 3,
3084 bfq_bfqq_budget_timeout(bfqq));
3086 return (!bfq_bfqq_wait_request(bfqq) ||
3087 bfq_bfqq_budget_left(bfqq) >= bfqq->entity.budget / 3)
3089 bfq_bfqq_budget_timeout(bfqq);
3093 * For a queue that becomes empty, device idling is allowed only if
3094 * this function returns true for the queue. As a consequence, since
3095 * device idling plays a critical role in both throughput boosting and
3096 * service guarantees, the return value of this function plays a
3097 * critical role in both these aspects as well.
3099 * In a nutshell, this function returns true only if idling is
3100 * beneficial for throughput or, even if detrimental for throughput,
3101 * idling is however necessary to preserve service guarantees (low
3102 * latency, desired throughput distribution, ...). In particular, on
3103 * NCQ-capable devices, this function tries to return false, so as to
3104 * help keep the drives' internal queues full, whenever this helps the
3105 * device boost the throughput without causing any service-guarantee
3108 * In more detail, the return value of this function is obtained by,
3109 * first, computing a number of boolean variables that take into
3110 * account throughput and service-guarantee issues, and, then,
3111 * combining these variables in a logical expression. Most of the
3112 * issues taken into account are not trivial. We discuss these issues
3113 * individually while introducing the variables.
3115 static bool bfq_bfqq_may_idle(struct bfq_queue *bfqq)
3117 struct bfq_data *bfqd = bfqq->bfqd;
3118 bool rot_without_queueing =
3119 !blk_queue_nonrot(bfqd->queue) && !bfqd->hw_tag,
3120 bfqq_sequential_and_IO_bound,
3121 idling_boosts_thr, idling_boosts_thr_without_issues,
3122 idling_needed_for_service_guarantees,
3123 asymmetric_scenario;
3125 if (bfqd->strict_guarantees)
3129 * Idling is performed only if slice_idle > 0. In addition, we
3132 * (b) bfqq is in the idle io prio class: in this case we do
3133 * not idle because we want to minimize the bandwidth that
3134 * queues in this class can steal to higher-priority queues
3136 if (bfqd->bfq_slice_idle == 0 || !bfq_bfqq_sync(bfqq) ||
3137 bfq_class_idle(bfqq))
3140 bfqq_sequential_and_IO_bound = !BFQQ_SEEKY(bfqq) &&
3141 bfq_bfqq_IO_bound(bfqq) && bfq_bfqq_has_short_ttime(bfqq);
3144 * The next variable takes into account the cases where idling
3145 * boosts the throughput.
3147 * The value of the variable is computed considering, first, that
3148 * idling is virtually always beneficial for the throughput if:
3149 * (a) the device is not NCQ-capable and rotational, or
3150 * (b) regardless of the presence of NCQ, the device is rotational and
3151 * the request pattern for bfqq is I/O-bound and sequential, or
3152 * (c) regardless of whether it is rotational, the device is
3153 * not NCQ-capable and the request pattern for bfqq is
3154 * I/O-bound and sequential.
3156 * Secondly, and in contrast to the above item (b), idling an
3157 * NCQ-capable flash-based device would not boost the
3158 * throughput even with sequential I/O; rather it would lower
3159 * the throughput in proportion to how fast the device
3160 * is. Accordingly, the next variable is true if any of the
3161 * above conditions (a), (b) or (c) is true, and, in
3162 * particular, happens to be false if bfqd is an NCQ-capable
3163 * flash-based device.
3165 idling_boosts_thr = rot_without_queueing ||
3166 ((!blk_queue_nonrot(bfqd->queue) || !bfqd->hw_tag) &&
3167 bfqq_sequential_and_IO_bound);
3170 * The value of the next variable,
3171 * idling_boosts_thr_without_issues, is equal to that of
3172 * idling_boosts_thr, unless a special case holds. In this
3173 * special case, described below, idling may cause problems to
3174 * weight-raised queues.
3176 * When the request pool is saturated (e.g., in the presence
3177 * of write hogs), if the processes associated with
3178 * non-weight-raised queues ask for requests at a lower rate,
3179 * then processes associated with weight-raised queues have a
3180 * higher probability to get a request from the pool
3181 * immediately (or at least soon) when they need one. Thus
3182 * they have a higher probability to actually get a fraction
3183 * of the device throughput proportional to their high
3184 * weight. This is especially true with NCQ-capable drives,
3185 * which enqueue several requests in advance, and further
3186 * reorder internally-queued requests.
3188 * For this reason, we force to false the value of
3189 * idling_boosts_thr_without_issues if there are weight-raised
3190 * busy queues. In this case, and if bfqq is not weight-raised,
3191 * this guarantees that the device is not idled for bfqq (if,
3192 * instead, bfqq is weight-raised, then idling will be
3193 * guaranteed by another variable, see below). Combined with
3194 * the timestamping rules of BFQ (see [1] for details), this
3195 * behavior causes bfqq, and hence any sync non-weight-raised
3196 * queue, to get a lower number of requests served, and thus
3197 * to ask for a lower number of requests from the request
3198 * pool, before the busy weight-raised queues get served
3199 * again. This often mitigates starvation problems in the
3200 * presence of heavy write workloads and NCQ, thereby
3201 * guaranteeing a higher application and system responsiveness
3202 * in these hostile scenarios.
3204 idling_boosts_thr_without_issues = idling_boosts_thr &&
3205 bfqd->wr_busy_queues == 0;
3208 * There is then a case where idling must be performed not
3209 * for throughput concerns, but to preserve service
3212 * To introduce this case, we can note that allowing the drive
3213 * to enqueue more than one request at a time, and hence
3214 * delegating de facto final scheduling decisions to the
3215 * drive's internal scheduler, entails loss of control on the
3216 * actual request service order. In particular, the critical
3217 * situation is when requests from different processes happen
3218 * to be present, at the same time, in the internal queue(s)
3219 * of the drive. In such a situation, the drive, by deciding
3220 * the service order of the internally-queued requests, does
3221 * determine also the actual throughput distribution among
3222 * these processes. But the drive typically has no notion or
3223 * concern about per-process throughput distribution, and
3224 * makes its decisions only on a per-request basis. Therefore,
3225 * the service distribution enforced by the drive's internal
3226 * scheduler is likely to coincide with the desired
3227 * device-throughput distribution only in a completely
3228 * symmetric scenario where:
3229 * (i) each of these processes must get the same throughput as
3231 * (ii) all these processes have the same I/O pattern
3232 (either sequential or random).
3233 * In fact, in such a scenario, the drive will tend to treat
3234 * the requests of each of these processes in about the same
3235 * way as the requests of the others, and thus to provide
3236 * each of these processes with about the same throughput
3237 * (which is exactly the desired throughput distribution). In
3238 * contrast, in any asymmetric scenario, device idling is
3239 * certainly needed to guarantee that bfqq receives its
3240 * assigned fraction of the device throughput (see [1] for
3243 * We address this issue by controlling, actually, only the
3244 * symmetry sub-condition (i), i.e., provided that
3245 * sub-condition (i) holds, idling is not performed,
3246 * regardless of whether sub-condition (ii) holds. In other
3247 * words, only if sub-condition (i) holds, then idling is
3248 * allowed, and the device tends to be prevented from queueing
3249 * many requests, possibly of several processes. The reason
3250 * for not controlling also sub-condition (ii) is that we
3251 * exploit preemption to preserve guarantees in case of
3252 * symmetric scenarios, even if (ii) does not hold, as
3253 * explained in the next two paragraphs.
3255 * Even if a queue, say Q, is expired when it remains idle, Q
3256 * can still preempt the new in-service queue if the next
3257 * request of Q arrives soon (see the comments on
3258 * bfq_bfqq_update_budg_for_activation). If all queues and
3259 * groups have the same weight, this form of preemption,
3260 * combined with the hole-recovery heuristic described in the
3261 * comments on function bfq_bfqq_update_budg_for_activation,
3262 * are enough to preserve a correct bandwidth distribution in
3263 * the mid term, even without idling. In fact, even if not
3264 * idling allows the internal queues of the device to contain
3265 * many requests, and thus to reorder requests, we can rather
3266 * safely assume that the internal scheduler still preserves a
3267 * minimum of mid-term fairness. The motivation for using
3268 * preemption instead of idling is that, by not idling,
3269 * service guarantees are preserved without minimally
3270 * sacrificing throughput. In other words, both a high
3271 * throughput and its desired distribution are obtained.
3273 * More precisely, this preemption-based, idleless approach
3274 * provides fairness in terms of IOPS, and not sectors per
3275 * second. This can be seen with a simple example. Suppose
3276 * that there are two queues with the same weight, but that
3277 * the first queue receives requests of 8 sectors, while the
3278 * second queue receives requests of 1024 sectors. In
3279 * addition, suppose that each of the two queues contains at
3280 * most one request at a time, which implies that each queue
3281 * always remains idle after it is served. Finally, after
3282 * remaining idle, each queue receives very quickly a new
3283 * request. It follows that the two queues are served
3284 * alternatively, preempting each other if needed. This
3285 * implies that, although both queues have the same weight,
3286 * the queue with large requests receives a service that is
3287 * 1024/8 times as high as the service received by the other
3290 * On the other hand, device idling is performed, and thus
3291 * pure sector-domain guarantees are provided, for the
3292 * following queues, which are likely to need stronger
3293 * throughput guarantees: weight-raised queues, and queues
3294 * with a higher weight than other queues. When such queues
3295 * are active, sub-condition (i) is false, which triggers
3298 * According to the above considerations, the next variable is
3299 * true (only) if sub-condition (i) holds. To compute the
3300 * value of this variable, we not only use the return value of
3301 * the function bfq_symmetric_scenario(), but also check
3302 * whether bfqq is being weight-raised, because
3303 * bfq_symmetric_scenario() does not take into account also
3304 * weight-raised queues (see comments on
3305 * bfq_weights_tree_add()).
3307 * As a side note, it is worth considering that the above
3308 * device-idling countermeasures may however fail in the
3309 * following unlucky scenario: if idling is (correctly)
3310 * disabled in a time period during which all symmetry
3311 * sub-conditions hold, and hence the device is allowed to
3312 * enqueue many requests, but at some later point in time some
3313 * sub-condition stops to hold, then it may become impossible
3314 * to let requests be served in the desired order until all
3315 * the requests already queued in the device have been served.
3317 asymmetric_scenario = bfqq->wr_coeff > 1 ||
3318 !bfq_symmetric_scenario(bfqd);
3321 * Finally, there is a case where maximizing throughput is the
3322 * best choice even if it may cause unfairness toward
3323 * bfqq. Such a case is when bfqq became active in a burst of
3324 * queue activations. Queues that became active during a large
3325 * burst benefit only from throughput, as discussed in the
3326 * comments on bfq_handle_burst. Thus, if bfqq became active
3327 * in a burst and not idling the device maximizes throughput,
3328 * then the device must no be idled, because not idling the
3329 * device provides bfqq and all other queues in the burst with
3330 * maximum benefit. Combining this and the above case, we can
3331 * now establish when idling is actually needed to preserve
3332 * service guarantees.
3334 idling_needed_for_service_guarantees =
3335 asymmetric_scenario && !bfq_bfqq_in_large_burst(bfqq);
3338 * We have now all the components we need to compute the
3339 * return value of the function, which is true only if idling
3340 * either boosts the throughput (without issues), or is
3341 * necessary to preserve service guarantees.
3343 return idling_boosts_thr_without_issues ||
3344 idling_needed_for_service_guarantees;
3348 * If the in-service queue is empty but the function bfq_bfqq_may_idle
3349 * returns true, then:
3350 * 1) the queue must remain in service and cannot be expired, and
3351 * 2) the device must be idled to wait for the possible arrival of a new
3352 * request for the queue.
3353 * See the comments on the function bfq_bfqq_may_idle for the reasons
3354 * why performing device idling is the best choice to boost the throughput
3355 * and preserve service guarantees when bfq_bfqq_may_idle itself
3358 static bool bfq_bfqq_must_idle(struct bfq_queue *bfqq)
3360 return RB_EMPTY_ROOT(&bfqq->sort_list) && bfq_bfqq_may_idle(bfqq);
3364 * Select a queue for service. If we have a current queue in service,
3365 * check whether to continue servicing it, or retrieve and set a new one.
3367 static struct bfq_queue *bfq_select_queue(struct bfq_data *bfqd)
3369 struct bfq_queue *bfqq;
3370 struct request *next_rq;
3371 enum bfqq_expiration reason = BFQQE_BUDGET_TIMEOUT;
3373 bfqq = bfqd->in_service_queue;
3377 bfq_log_bfqq(bfqd, bfqq, "select_queue: already in-service queue");
3379 if (bfq_may_expire_for_budg_timeout(bfqq) &&
3380 !bfq_bfqq_wait_request(bfqq) &&
3381 !bfq_bfqq_must_idle(bfqq))
3386 * This loop is rarely executed more than once. Even when it
3387 * happens, it is much more convenient to re-execute this loop
3388 * than to return NULL and trigger a new dispatch to get a
3391 next_rq = bfqq->next_rq;
3393 * If bfqq has requests queued and it has enough budget left to
3394 * serve them, keep the queue, otherwise expire it.
3397 if (bfq_serv_to_charge(next_rq, bfqq) >
3398 bfq_bfqq_budget_left(bfqq)) {
3400 * Expire the queue for budget exhaustion,
3401 * which makes sure that the next budget is
3402 * enough to serve the next request, even if
3403 * it comes from the fifo expired path.
3405 reason = BFQQE_BUDGET_EXHAUSTED;
3409 * The idle timer may be pending because we may
3410 * not disable disk idling even when a new request
3413 if (bfq_bfqq_wait_request(bfqq)) {
3415 * If we get here: 1) at least a new request
3416 * has arrived but we have not disabled the
3417 * timer because the request was too small,
3418 * 2) then the block layer has unplugged
3419 * the device, causing the dispatch to be
3422 * Since the device is unplugged, now the
3423 * requests are probably large enough to
3424 * provide a reasonable throughput.
3425 * So we disable idling.
3427 bfq_clear_bfqq_wait_request(bfqq);
3428 hrtimer_try_to_cancel(&bfqd->idle_slice_timer);
3429 bfqg_stats_update_idle_time(bfqq_group(bfqq));
3436 * No requests pending. However, if the in-service queue is idling
3437 * for a new request, or has requests waiting for a completion and
3438 * may idle after their completion, then keep it anyway.
3440 if (bfq_bfqq_wait_request(bfqq) ||
3441 (bfqq->dispatched != 0 && bfq_bfqq_may_idle(bfqq))) {
3446 reason = BFQQE_NO_MORE_REQUESTS;
3448 bfq_bfqq_expire(bfqd, bfqq, false, reason);
3450 bfqq = bfq_set_in_service_queue(bfqd);
3452 bfq_log_bfqq(bfqd, bfqq, "select_queue: checking new queue");
3457 bfq_log_bfqq(bfqd, bfqq, "select_queue: returned this queue");
3459 bfq_log(bfqd, "select_queue: no queue returned");
3464 static void bfq_update_wr_data(struct bfq_data *bfqd, struct bfq_queue *bfqq)
3466 struct bfq_entity *entity = &bfqq->entity;
3468 if (bfqq->wr_coeff > 1) { /* queue is being weight-raised */
3469 bfq_log_bfqq(bfqd, bfqq,
3470 "raising period dur %u/%u msec, old coeff %u, w %d(%d)",
3471 jiffies_to_msecs(jiffies - bfqq->last_wr_start_finish),
3472 jiffies_to_msecs(bfqq->wr_cur_max_time),
3474 bfqq->entity.weight, bfqq->entity.orig_weight);
3476 if (entity->prio_changed)
3477 bfq_log_bfqq(bfqd, bfqq, "WARN: pending prio change");
3480 * If the queue was activated in a burst, or too much
3481 * time has elapsed from the beginning of this
3482 * weight-raising period, then end weight raising.
3484 if (bfq_bfqq_in_large_burst(bfqq))
3485 bfq_bfqq_end_wr(bfqq);
3486 else if (time_is_before_jiffies(bfqq->last_wr_start_finish +
3487 bfqq->wr_cur_max_time)) {
3488 if (bfqq->wr_cur_max_time != bfqd->bfq_wr_rt_max_time ||
3489 time_is_before_jiffies(bfqq->wr_start_at_switch_to_srt +
3490 bfq_wr_duration(bfqd)))
3491 bfq_bfqq_end_wr(bfqq);
3493 /* switch back to interactive wr */
3494 bfqq->wr_coeff = bfqd->bfq_wr_coeff;
3495 bfqq->wr_cur_max_time = bfq_wr_duration(bfqd);
3496 bfqq->last_wr_start_finish =
3497 bfqq->wr_start_at_switch_to_srt;
3498 bfqq->entity.prio_changed = 1;
3503 * To improve latency (for this or other queues), immediately
3504 * update weight both if it must be raised and if it must be
3505 * lowered. Since, entity may be on some active tree here, and
3506 * might have a pending change of its ioprio class, invoke
3507 * next function with the last parameter unset (see the
3508 * comments on the function).
3510 if ((entity->weight > entity->orig_weight) != (bfqq->wr_coeff > 1))
3511 __bfq_entity_update_weight_prio(bfq_entity_service_tree(entity),
3516 * Dispatch next request from bfqq.
3518 static struct request *bfq_dispatch_rq_from_bfqq(struct bfq_data *bfqd,
3519 struct bfq_queue *bfqq)
3521 struct request *rq = bfqq->next_rq;
3522 unsigned long service_to_charge;
3524 service_to_charge = bfq_serv_to_charge(rq, bfqq);
3526 bfq_bfqq_served(bfqq, service_to_charge);
3528 bfq_dispatch_remove(bfqd->queue, rq);
3531 * If weight raising has to terminate for bfqq, then next
3532 * function causes an immediate update of bfqq's weight,
3533 * without waiting for next activation. As a consequence, on
3534 * expiration, bfqq will be timestamped as if has never been
3535 * weight-raised during this service slot, even if it has
3536 * received part or even most of the service as a
3537 * weight-raised queue. This inflates bfqq's timestamps, which
3538 * is beneficial, as bfqq is then more willing to leave the
3539 * device immediately to possible other weight-raised queues.
3541 bfq_update_wr_data(bfqd, bfqq);
3544 * Expire bfqq, pretending that its budget expired, if bfqq
3545 * belongs to CLASS_IDLE and other queues are waiting for
3548 if (bfqd->busy_queues > 1 && bfq_class_idle(bfqq))
3554 bfq_bfqq_expire(bfqd, bfqq, false, BFQQE_BUDGET_EXHAUSTED);
3558 static bool bfq_has_work(struct blk_mq_hw_ctx *hctx)
3560 struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;
3563 * Avoiding lock: a race on bfqd->busy_queues should cause at
3564 * most a call to dispatch for nothing
3566 return !list_empty_careful(&bfqd->dispatch) ||
3567 bfqd->busy_queues > 0;
3570 static struct request *__bfq_dispatch_request(struct blk_mq_hw_ctx *hctx)
3572 struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;
3573 struct request *rq = NULL;
3574 struct bfq_queue *bfqq = NULL;
3576 if (!list_empty(&bfqd->dispatch)) {
3577 rq = list_first_entry(&bfqd->dispatch, struct request,
3579 list_del_init(&rq->queuelist);
3585 * Increment counters here, because this
3586 * dispatch does not follow the standard
3587 * dispatch flow (where counters are
3592 goto inc_in_driver_start_rq;
3596 * We exploit the put_rq_private hook to decrement
3597 * rq_in_driver, but put_rq_private will not be
3598 * invoked on this request. So, to avoid unbalance,
3599 * just start this request, without incrementing
3600 * rq_in_driver. As a negative consequence,
3601 * rq_in_driver is deceptively lower than it should be
3602 * while this request is in service. This may cause
3603 * bfq_schedule_dispatch to be invoked uselessly.
3605 * As for implementing an exact solution, the
3606 * put_request hook, if defined, is probably invoked
3607 * also on this request. So, by exploiting this hook,
3608 * we could 1) increment rq_in_driver here, and 2)
3609 * decrement it in put_request. Such a solution would
3610 * let the value of the counter be always accurate,
3611 * but it would entail using an extra interface
3612 * function. This cost seems higher than the benefit,
3613 * being the frequency of non-elevator-private
3614 * requests very low.
3619 bfq_log(bfqd, "dispatch requests: %d busy queues", bfqd->busy_queues);
3621 if (bfqd->busy_queues == 0)
3625 * Force device to serve one request at a time if
3626 * strict_guarantees is true. Forcing this service scheme is
3627 * currently the ONLY way to guarantee that the request
3628 * service order enforced by the scheduler is respected by a
3629 * queueing device. Otherwise the device is free even to make
3630 * some unlucky request wait for as long as the device
3633 * Of course, serving one request at at time may cause loss of
3636 if (bfqd->strict_guarantees && bfqd->rq_in_driver > 0)
3639 bfqq = bfq_select_queue(bfqd);
3643 rq = bfq_dispatch_rq_from_bfqq(bfqd, bfqq);
3646 inc_in_driver_start_rq:
3647 bfqd->rq_in_driver++;
3649 rq->rq_flags |= RQF_STARTED;
3655 static struct request *bfq_dispatch_request(struct blk_mq_hw_ctx *hctx)
3657 struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;
3660 spin_lock_irq(&bfqd->lock);
3662 rq = __bfq_dispatch_request(hctx);
3663 spin_unlock_irq(&bfqd->lock);
3669 * Task holds one reference to the queue, dropped when task exits. Each rq
3670 * in-flight on this queue also holds a reference, dropped when rq is freed.
3672 * Scheduler lock must be held here. Recall not to use bfqq after calling
3673 * this function on it.
3675 void bfq_put_queue(struct bfq_queue *bfqq)
3677 #ifdef CONFIG_BFQ_GROUP_IOSCHED
3678 struct bfq_group *bfqg = bfqq_group(bfqq);
3682 bfq_log_bfqq(bfqq->bfqd, bfqq, "put_queue: %p %d",
3689 if (bfq_bfqq_sync(bfqq))
3691 * The fact that this queue is being destroyed does not
3692 * invalidate the fact that this queue may have been
3693 * activated during the current burst. As a consequence,
3694 * although the queue does not exist anymore, and hence
3695 * needs to be removed from the burst list if there,
3696 * the burst size has not to be decremented.
3698 hlist_del_init(&bfqq->burst_list_node);
3700 kmem_cache_free(bfq_pool, bfqq);
3701 #ifdef CONFIG_BFQ_GROUP_IOSCHED
3702 bfqg_and_blkg_put(bfqg);
3706 static void bfq_put_cooperator(struct bfq_queue *bfqq)
3708 struct bfq_queue *__bfqq, *next;
3711 * If this queue was scheduled to merge with another queue, be
3712 * sure to drop the reference taken on that queue (and others in
3713 * the merge chain). See bfq_setup_merge and bfq_merge_bfqqs.
3715 __bfqq = bfqq->new_bfqq;
3719 next = __bfqq->new_bfqq;
3720 bfq_put_queue(__bfqq);
3725 static void bfq_exit_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq)
3727 if (bfqq == bfqd->in_service_queue) {
3728 __bfq_bfqq_expire(bfqd, bfqq);
3729 bfq_schedule_dispatch(bfqd);
3732 bfq_log_bfqq(bfqd, bfqq, "exit_bfqq: %p, %d", bfqq, bfqq->ref);
3734 bfq_put_cooperator(bfqq);
3736 bfq_put_queue(bfqq); /* release process reference */
3739 static void bfq_exit_icq_bfqq(struct bfq_io_cq *bic, bool is_sync)
3741 struct bfq_queue *bfqq = bic_to_bfqq(bic, is_sync);
3742 struct bfq_data *bfqd;
3745 bfqd = bfqq->bfqd; /* NULL if scheduler already exited */
3748 unsigned long flags;
3750 spin_lock_irqsave(&bfqd->lock, flags);
3751 bfq_exit_bfqq(bfqd, bfqq);
3752 bic_set_bfqq(bic, NULL, is_sync);
3753 spin_unlock_irqrestore(&bfqd->lock, flags);
3757 static void bfq_exit_icq(struct io_cq *icq)
3759 struct bfq_io_cq *bic = icq_to_bic(icq);
3761 bfq_exit_icq_bfqq(bic, true);
3762 bfq_exit_icq_bfqq(bic, false);
3766 * Update the entity prio values; note that the new values will not
3767 * be used until the next (re)activation.
3770 bfq_set_next_ioprio_data(struct bfq_queue *bfqq, struct bfq_io_cq *bic)
3772 struct task_struct *tsk = current;
3774 struct bfq_data *bfqd = bfqq->bfqd;
3779 ioprio_class = IOPRIO_PRIO_CLASS(bic->ioprio);
3780 switch (ioprio_class) {
3782 dev_err(bfqq->bfqd->queue->backing_dev_info->dev,
3783 "bfq: bad prio class %d\n", ioprio_class);
3785 case IOPRIO_CLASS_NONE:
3787 * No prio set, inherit CPU scheduling settings.
3789 bfqq->new_ioprio = task_nice_ioprio(tsk);
3790 bfqq->new_ioprio_class = task_nice_ioclass(tsk);
3792 case IOPRIO_CLASS_RT:
3793 bfqq->new_ioprio = IOPRIO_PRIO_DATA(bic->ioprio);
3794 bfqq->new_ioprio_class = IOPRIO_CLASS_RT;
3796 case IOPRIO_CLASS_BE:
3797 bfqq->new_ioprio = IOPRIO_PRIO_DATA(bic->ioprio);
3798 bfqq->new_ioprio_class = IOPRIO_CLASS_BE;
3800 case IOPRIO_CLASS_IDLE:
3801 bfqq->new_ioprio_class = IOPRIO_CLASS_IDLE;
3802 bfqq->new_ioprio = 7;
3806 if (bfqq->new_ioprio >= IOPRIO_BE_NR) {
3807 pr_crit("bfq_set_next_ioprio_data: new_ioprio %d\n",
3809 bfqq->new_ioprio = IOPRIO_BE_NR;
3812 bfqq->entity.new_weight = bfq_ioprio_to_weight(bfqq->new_ioprio);
3813 bfqq->entity.prio_changed = 1;
3816 static struct bfq_queue *bfq_get_queue(struct bfq_data *bfqd,
3817 struct bio *bio, bool is_sync,
3818 struct bfq_io_cq *bic);
3820 static void bfq_check_ioprio_change(struct bfq_io_cq *bic, struct bio *bio)
3822 struct bfq_data *bfqd = bic_to_bfqd(bic);
3823 struct bfq_queue *bfqq;
3824 int ioprio = bic->icq.ioc->ioprio;
3827 * This condition may trigger on a newly created bic, be sure to
3828 * drop the lock before returning.
3830 if (unlikely(!bfqd) || likely(bic->ioprio == ioprio))
3833 bic->ioprio = ioprio;
3835 bfqq = bic_to_bfqq(bic, false);
3837 /* release process reference on this queue */
3838 bfq_put_queue(bfqq);
3839 bfqq = bfq_get_queue(bfqd, bio, BLK_RW_ASYNC, bic);
3840 bic_set_bfqq(bic, bfqq, false);
3843 bfqq = bic_to_bfqq(bic, true);
3845 bfq_set_next_ioprio_data(bfqq, bic);
3848 static void bfq_init_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq,
3849 struct bfq_io_cq *bic, pid_t pid, int is_sync)
3851 RB_CLEAR_NODE(&bfqq->entity.rb_node);
3852 INIT_LIST_HEAD(&bfqq->fifo);
3853 INIT_HLIST_NODE(&bfqq->burst_list_node);
3859 bfq_set_next_ioprio_data(bfqq, bic);
3863 * No need to mark as has_short_ttime if in
3864 * idle_class, because no device idling is performed
3865 * for queues in idle class
3867 if (!bfq_class_idle(bfqq))
3868 /* tentatively mark as has_short_ttime */
3869 bfq_mark_bfqq_has_short_ttime(bfqq);
3870 bfq_mark_bfqq_sync(bfqq);
3871 bfq_mark_bfqq_just_created(bfqq);
3873 bfq_clear_bfqq_sync(bfqq);
3875 /* set end request to minus infinity from now */
3876 bfqq->ttime.last_end_request = ktime_get_ns() + 1;
3878 bfq_mark_bfqq_IO_bound(bfqq);
3882 /* Tentative initial value to trade off between thr and lat */
3883 bfqq->max_budget = (2 * bfq_max_budget(bfqd)) / 3;
3884 bfqq->budget_timeout = bfq_smallest_from_now();
3887 bfqq->last_wr_start_finish = jiffies;
3888 bfqq->wr_start_at_switch_to_srt = bfq_smallest_from_now();
3889 bfqq->split_time = bfq_smallest_from_now();
3892 * Set to the value for which bfqq will not be deemed as
3893 * soft rt when it becomes backlogged.
3895 bfqq->soft_rt_next_start = bfq_greatest_from_now();
3897 /* first request is almost certainly seeky */
3898 bfqq->seek_history = 1;
3901 static struct bfq_queue **bfq_async_queue_prio(struct bfq_data *bfqd,
3902 struct bfq_group *bfqg,
3903 int ioprio_class, int ioprio)
3905 switch (ioprio_class) {
3906 case IOPRIO_CLASS_RT:
3907 return &bfqg->async_bfqq[0][ioprio];
3908 case IOPRIO_CLASS_NONE:
3909 ioprio = IOPRIO_NORM;
3911 case IOPRIO_CLASS_BE:
3912 return &bfqg->async_bfqq[1][ioprio];
3913 case IOPRIO_CLASS_IDLE:
3914 return &bfqg->async_idle_bfqq;
3920 static struct bfq_queue *bfq_get_queue(struct bfq_data *bfqd,
3921 struct bio *bio, bool is_sync,
3922 struct bfq_io_cq *bic)
3924 const int ioprio = IOPRIO_PRIO_DATA(bic->ioprio);
3925 const int ioprio_class = IOPRIO_PRIO_CLASS(bic->ioprio);
3926 struct bfq_queue **async_bfqq = NULL;
3927 struct bfq_queue *bfqq;
3928 struct bfq_group *bfqg;
3932 bfqg = bfq_find_set_group(bfqd, bio_blkcg(bio));
3934 bfqq = &bfqd->oom_bfqq;
3939 async_bfqq = bfq_async_queue_prio(bfqd, bfqg, ioprio_class,
3946 bfqq = kmem_cache_alloc_node(bfq_pool,
3947 GFP_NOWAIT | __GFP_ZERO | __GFP_NOWARN,
3951 bfq_init_bfqq(bfqd, bfqq, bic, current->pid,
3953 bfq_init_entity(&bfqq->entity, bfqg);
3954 bfq_log_bfqq(bfqd, bfqq, "allocated");
3956 bfqq = &bfqd->oom_bfqq;
3957 bfq_log_bfqq(bfqd, bfqq, "using oom bfqq");
3962 * Pin the queue now that it's allocated, scheduler exit will
3967 * Extra group reference, w.r.t. sync
3968 * queue. This extra reference is removed
3969 * only if bfqq->bfqg disappears, to
3970 * guarantee that this queue is not freed
3971 * until its group goes away.
3973 bfq_log_bfqq(bfqd, bfqq, "get_queue, bfqq not in async: %p, %d",
3979 bfqq->ref++; /* get a process reference to this queue */
3980 bfq_log_bfqq(bfqd, bfqq, "get_queue, at end: %p, %d", bfqq, bfqq->ref);
3985 static void bfq_update_io_thinktime(struct bfq_data *bfqd,
3986 struct bfq_queue *bfqq)
3988 struct bfq_ttime *ttime = &bfqq->ttime;
3989 u64 elapsed = ktime_get_ns() - bfqq->ttime.last_end_request;
3991 elapsed = min_t(u64, elapsed, 2ULL * bfqd->bfq_slice_idle);
3993 ttime->ttime_samples = (7*bfqq->ttime.ttime_samples + 256) / 8;
3994 ttime->ttime_total = div_u64(7*ttime->ttime_total + 256*elapsed, 8);
3995 ttime->ttime_mean = div64_ul(ttime->ttime_total + 128,
3996 ttime->ttime_samples);
4000 bfq_update_io_seektime(struct bfq_data *bfqd, struct bfq_queue *bfqq,
4003 bfqq->seek_history <<= 1;
4004 bfqq->seek_history |=
4005 get_sdist(bfqq->last_request_pos, rq) > BFQQ_SEEK_THR &&
4006 (!blk_queue_nonrot(bfqd->queue) ||
4007 blk_rq_sectors(rq) < BFQQ_SECT_THR_NONROT);
4010 static void bfq_update_has_short_ttime(struct bfq_data *bfqd,
4011 struct bfq_queue *bfqq,
4012 struct bfq_io_cq *bic)
4014 bool has_short_ttime = true;
4017 * No need to update has_short_ttime if bfqq is async or in
4018 * idle io prio class, or if bfq_slice_idle is zero, because
4019 * no device idling is performed for bfqq in this case.
4021 if (!bfq_bfqq_sync(bfqq) || bfq_class_idle(bfqq) ||
4022 bfqd->bfq_slice_idle == 0)
4025 /* Idle window just restored, statistics are meaningless. */
4026 if (time_is_after_eq_jiffies(bfqq->split_time +
4027 bfqd->bfq_wr_min_idle_time))
4030 /* Think time is infinite if no process is linked to
4031 * bfqq. Otherwise check average think time to
4032 * decide whether to mark as has_short_ttime
4034 if (atomic_read(&bic->icq.ioc->active_ref) == 0 ||
4035 (bfq_sample_valid(bfqq->ttime.ttime_samples) &&
4036 bfqq->ttime.ttime_mean > bfqd->bfq_slice_idle))
4037 has_short_ttime = false;
4039 bfq_log_bfqq(bfqd, bfqq, "update_has_short_ttime: has_short_ttime %d",
4042 if (has_short_ttime)
4043 bfq_mark_bfqq_has_short_ttime(bfqq);
4045 bfq_clear_bfqq_has_short_ttime(bfqq);
4049 * Called when a new fs request (rq) is added to bfqq. Check if there's
4050 * something we should do about it.
4052 static void bfq_rq_enqueued(struct bfq_data *bfqd, struct bfq_queue *bfqq,
4055 struct bfq_io_cq *bic = RQ_BIC(rq);
4057 if (rq->cmd_flags & REQ_META)
4058 bfqq->meta_pending++;
4060 bfq_update_io_thinktime(bfqd, bfqq);
4061 bfq_update_has_short_ttime(bfqd, bfqq, bic);
4062 bfq_update_io_seektime(bfqd, bfqq, rq);
4064 bfq_log_bfqq(bfqd, bfqq,
4065 "rq_enqueued: has_short_ttime=%d (seeky %d)",
4066 bfq_bfqq_has_short_ttime(bfqq), BFQQ_SEEKY(bfqq));
4068 bfqq->last_request_pos = blk_rq_pos(rq) + blk_rq_sectors(rq);
4070 if (bfqq == bfqd->in_service_queue && bfq_bfqq_wait_request(bfqq)) {
4071 bool small_req = bfqq->queued[rq_is_sync(rq)] == 1 &&
4072 blk_rq_sectors(rq) < 32;
4073 bool budget_timeout = bfq_bfqq_budget_timeout(bfqq);
4076 * There is just this request queued: if the request
4077 * is small and the queue is not to be expired, then
4080 * In this way, if the device is being idled to wait
4081 * for a new request from the in-service queue, we
4082 * avoid unplugging the device and committing the
4083 * device to serve just a small request. On the
4084 * contrary, we wait for the block layer to decide
4085 * when to unplug the device: hopefully, new requests
4086 * will be merged to this one quickly, then the device
4087 * will be unplugged and larger requests will be
4090 if (small_req && !budget_timeout)
4094 * A large enough request arrived, or the queue is to
4095 * be expired: in both cases disk idling is to be
4096 * stopped, so clear wait_request flag and reset
4099 bfq_clear_bfqq_wait_request(bfqq);
4100 hrtimer_try_to_cancel(&bfqd->idle_slice_timer);
4101 bfqg_stats_update_idle_time(bfqq_group(bfqq));
4104 * The queue is not empty, because a new request just
4105 * arrived. Hence we can safely expire the queue, in
4106 * case of budget timeout, without risking that the
4107 * timestamps of the queue are not updated correctly.
4108 * See [1] for more details.
4111 bfq_bfqq_expire(bfqd, bfqq, false,
4112 BFQQE_BUDGET_TIMEOUT);
4116 static void __bfq_insert_request(struct bfq_data *bfqd, struct request *rq)
4118 struct bfq_queue *bfqq = RQ_BFQQ(rq),
4119 *new_bfqq = bfq_setup_cooperator(bfqd, bfqq, rq, true);
4122 if (bic_to_bfqq(RQ_BIC(rq), 1) != bfqq)
4123 new_bfqq = bic_to_bfqq(RQ_BIC(rq), 1);
4125 * Release the request's reference to the old bfqq
4126 * and make sure one is taken to the shared queue.
4128 new_bfqq->allocated++;
4131 bfq_clear_bfqq_just_created(bfqq);
4133 * If the bic associated with the process
4134 * issuing this request still points to bfqq
4135 * (and thus has not been already redirected
4136 * to new_bfqq or even some other bfq_queue),
4137 * then complete the merge and redirect it to
4140 if (bic_to_bfqq(RQ_BIC(rq), 1) == bfqq)
4141 bfq_merge_bfqqs(bfqd, RQ_BIC(rq),
4144 * rq is about to be enqueued into new_bfqq,
4145 * release rq reference on bfqq
4147 bfq_put_queue(bfqq);
4148 rq->elv.priv[1] = new_bfqq;
4152 bfq_add_request(rq);
4154 rq->fifo_time = ktime_get_ns() + bfqd->bfq_fifo_expire[rq_is_sync(rq)];
4155 list_add_tail(&rq->queuelist, &bfqq->fifo);
4157 bfq_rq_enqueued(bfqd, bfqq, rq);
4160 static void bfq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
4163 struct request_queue *q = hctx->queue;
4164 struct bfq_data *bfqd = q->elevator->elevator_data;
4166 spin_lock_irq(&bfqd->lock);
4167 if (blk_mq_sched_try_insert_merge(q, rq)) {
4168 spin_unlock_irq(&bfqd->lock);
4172 spin_unlock_irq(&bfqd->lock);
4174 blk_mq_sched_request_inserted(rq);
4176 spin_lock_irq(&bfqd->lock);
4177 if (at_head || blk_rq_is_passthrough(rq)) {
4179 list_add(&rq->queuelist, &bfqd->dispatch);
4181 list_add_tail(&rq->queuelist, &bfqd->dispatch);
4183 __bfq_insert_request(bfqd, rq);
4185 if (rq_mergeable(rq)) {
4186 elv_rqhash_add(q, rq);
4192 spin_unlock_irq(&bfqd->lock);
4195 static void bfq_insert_requests(struct blk_mq_hw_ctx *hctx,
4196 struct list_head *list, bool at_head)
4198 while (!list_empty(list)) {
4201 rq = list_first_entry(list, struct request, queuelist);
4202 list_del_init(&rq->queuelist);
4203 bfq_insert_request(hctx, rq, at_head);
4207 static void bfq_update_hw_tag(struct bfq_data *bfqd)
4209 bfqd->max_rq_in_driver = max_t(int, bfqd->max_rq_in_driver,
4210 bfqd->rq_in_driver);
4212 if (bfqd->hw_tag == 1)
4216 * This sample is valid if the number of outstanding requests
4217 * is large enough to allow a queueing behavior. Note that the
4218 * sum is not exact, as it's not taking into account deactivated
4221 if (bfqd->rq_in_driver + bfqd->queued < BFQ_HW_QUEUE_THRESHOLD)
4224 if (bfqd->hw_tag_samples++ < BFQ_HW_QUEUE_SAMPLES)
4227 bfqd->hw_tag = bfqd->max_rq_in_driver > BFQ_HW_QUEUE_THRESHOLD;
4228 bfqd->max_rq_in_driver = 0;
4229 bfqd->hw_tag_samples = 0;
4232 static void bfq_completed_request(struct bfq_queue *bfqq, struct bfq_data *bfqd)
4237 bfq_update_hw_tag(bfqd);
4239 bfqd->rq_in_driver--;
4242 if (!bfqq->dispatched && !bfq_bfqq_busy(bfqq)) {
4244 * Set budget_timeout (which we overload to store the
4245 * time at which the queue remains with no backlog and
4246 * no outstanding request; used by the weight-raising
4249 bfqq->budget_timeout = jiffies;
4251 bfq_weights_tree_remove(bfqd, &bfqq->entity,
4252 &bfqd->queue_weights_tree);
4255 now_ns = ktime_get_ns();
4257 bfqq->ttime.last_end_request = now_ns;
4260 * Using us instead of ns, to get a reasonable precision in
4261 * computing rate in next check.
4263 delta_us = div_u64(now_ns - bfqd->last_completion, NSEC_PER_USEC);
4266 * If the request took rather long to complete, and, according
4267 * to the maximum request size recorded, this completion latency
4268 * implies that the request was certainly served at a very low
4269 * rate (less than 1M sectors/sec), then the whole observation
4270 * interval that lasts up to this time instant cannot be a
4271 * valid time interval for computing a new peak rate. Invoke
4272 * bfq_update_rate_reset to have the following three steps
4274 * - close the observation interval at the last (previous)
4275 * request dispatch or completion
4276 * - compute rate, if possible, for that observation interval
4277 * - reset to zero samples, which will trigger a proper
4278 * re-initialization of the observation interval on next
4281 if (delta_us > BFQ_MIN_TT/NSEC_PER_USEC &&
4282 (bfqd->last_rq_max_size<<BFQ_RATE_SHIFT)/delta_us <
4283 1UL<<(BFQ_RATE_SHIFT - 10))
4284 bfq_update_rate_reset(bfqd, NULL);
4285 bfqd->last_completion = now_ns;
4288 * If we are waiting to discover whether the request pattern
4289 * of the task associated with the queue is actually
4290 * isochronous, and both requisites for this condition to hold
4291 * are now satisfied, then compute soft_rt_next_start (see the
4292 * comments on the function bfq_bfqq_softrt_next_start()). We
4293 * schedule this delayed check when bfqq expires, if it still
4294 * has in-flight requests.
4296 if (bfq_bfqq_softrt_update(bfqq) && bfqq->dispatched == 0 &&
4297 RB_EMPTY_ROOT(&bfqq->sort_list))
4298 bfqq->soft_rt_next_start =
4299 bfq_bfqq_softrt_next_start(bfqd, bfqq);
4302 * If this is the in-service queue, check if it needs to be expired,
4303 * or if we want to idle in case it has no pending requests.
4305 if (bfqd->in_service_queue == bfqq) {
4306 if (bfqq->dispatched == 0 && bfq_bfqq_must_idle(bfqq)) {
4307 bfq_arm_slice_timer(bfqd);
4309 } else if (bfq_may_expire_for_budg_timeout(bfqq))
4310 bfq_bfqq_expire(bfqd, bfqq, false,
4311 BFQQE_BUDGET_TIMEOUT);
4312 else if (RB_EMPTY_ROOT(&bfqq->sort_list) &&
4313 (bfqq->dispatched == 0 ||
4314 !bfq_bfqq_may_idle(bfqq)))
4315 bfq_bfqq_expire(bfqd, bfqq, false,
4316 BFQQE_NO_MORE_REQUESTS);
4319 if (!bfqd->rq_in_driver)
4320 bfq_schedule_dispatch(bfqd);
4323 static void bfq_put_rq_priv_body(struct bfq_queue *bfqq)
4327 bfq_put_queue(bfqq);
4330 static void bfq_finish_request(struct request *rq)
4332 struct bfq_queue *bfqq;
4333 struct bfq_data *bfqd;
4341 if (rq->rq_flags & RQF_STARTED)
4342 bfqg_stats_update_completion(bfqq_group(bfqq),
4343 rq_start_time_ns(rq),
4344 rq_io_start_time_ns(rq),
4347 if (likely(rq->rq_flags & RQF_STARTED)) {
4348 unsigned long flags;
4350 spin_lock_irqsave(&bfqd->lock, flags);
4352 bfq_completed_request(bfqq, bfqd);
4353 bfq_put_rq_priv_body(bfqq);
4355 spin_unlock_irqrestore(&bfqd->lock, flags);
4358 * Request rq may be still/already in the scheduler,
4359 * in which case we need to remove it. And we cannot
4360 * defer such a check and removal, to avoid
4361 * inconsistencies in the time interval from the end
4362 * of this function to the start of the deferred work.
4363 * This situation seems to occur only in process
4364 * context, as a consequence of a merge. In the
4365 * current version of the code, this implies that the
4369 if (!RB_EMPTY_NODE(&rq->rb_node))
4370 bfq_remove_request(rq->q, rq);
4371 bfq_put_rq_priv_body(bfqq);
4374 rq->elv.priv[0] = NULL;
4375 rq->elv.priv[1] = NULL;
4379 * Returns NULL if a new bfqq should be allocated, or the old bfqq if this
4380 * was the last process referring to that bfqq.
4382 static struct bfq_queue *
4383 bfq_split_bfqq(struct bfq_io_cq *bic, struct bfq_queue *bfqq)
4385 bfq_log_bfqq(bfqq->bfqd, bfqq, "splitting queue");
4387 if (bfqq_process_refs(bfqq) == 1) {
4388 bfqq->pid = current->pid;
4389 bfq_clear_bfqq_coop(bfqq);
4390 bfq_clear_bfqq_split_coop(bfqq);
4394 bic_set_bfqq(bic, NULL, 1);
4396 bfq_put_cooperator(bfqq);
4398 bfq_put_queue(bfqq);
4402 static struct bfq_queue *bfq_get_bfqq_handle_split(struct bfq_data *bfqd,
4403 struct bfq_io_cq *bic,
4405 bool split, bool is_sync,
4408 struct bfq_queue *bfqq = bic_to_bfqq(bic, is_sync);
4410 if (likely(bfqq && bfqq != &bfqd->oom_bfqq))
4417 bfq_put_queue(bfqq);
4418 bfqq = bfq_get_queue(bfqd, bio, is_sync, bic);
4420 bic_set_bfqq(bic, bfqq, is_sync);
4421 if (split && is_sync) {
4422 if ((bic->was_in_burst_list && bfqd->large_burst) ||
4423 bic->saved_in_large_burst)
4424 bfq_mark_bfqq_in_large_burst(bfqq);
4426 bfq_clear_bfqq_in_large_burst(bfqq);
4427 if (bic->was_in_burst_list)
4428 hlist_add_head(&bfqq->burst_list_node,
4431 bfqq->split_time = jiffies;
4438 * Allocate bfq data structures associated with this request.
4440 static void bfq_prepare_request(struct request *rq, struct bio *bio)
4442 struct request_queue *q = rq->q;
4443 struct bfq_data *bfqd = q->elevator->elevator_data;
4444 struct bfq_io_cq *bic;
4445 const int is_sync = rq_is_sync(rq);
4446 struct bfq_queue *bfqq;
4447 bool new_queue = false;
4448 bool bfqq_already_existing = false, split = false;
4452 bic = icq_to_bic(rq->elv.icq);
4454 spin_lock_irq(&bfqd->lock);
4456 bfq_check_ioprio_change(bic, bio);
4458 bfq_bic_update_cgroup(bic, bio);
4460 bfqq = bfq_get_bfqq_handle_split(bfqd, bic, bio, false, is_sync,
4463 if (likely(!new_queue)) {
4464 /* If the queue was seeky for too long, break it apart. */
4465 if (bfq_bfqq_coop(bfqq) && bfq_bfqq_split_coop(bfqq)) {
4466 bfq_log_bfqq(bfqd, bfqq, "breaking apart bfqq");
4468 /* Update bic before losing reference to bfqq */
4469 if (bfq_bfqq_in_large_burst(bfqq))
4470 bic->saved_in_large_burst = true;
4472 bfqq = bfq_split_bfqq(bic, bfqq);
4476 bfqq = bfq_get_bfqq_handle_split(bfqd, bic, bio,
4480 bfqq_already_existing = true;
4486 bfq_log_bfqq(bfqd, bfqq, "get_request %p: bfqq %p, %d",
4487 rq, bfqq, bfqq->ref);
4489 rq->elv.priv[0] = bic;
4490 rq->elv.priv[1] = bfqq;
4493 * If a bfq_queue has only one process reference, it is owned
4494 * by only this bic: we can then set bfqq->bic = bic. in
4495 * addition, if the queue has also just been split, we have to
4498 if (likely(bfqq != &bfqd->oom_bfqq) && bfqq_process_refs(bfqq) == 1) {
4502 * The queue has just been split from a shared
4503 * queue: restore the idle window and the
4504 * possible weight raising period.
4506 bfq_bfqq_resume_state(bfqq, bfqd, bic,
4507 bfqq_already_existing);
4511 if (unlikely(bfq_bfqq_just_created(bfqq)))
4512 bfq_handle_burst(bfqd, bfqq);
4514 spin_unlock_irq(&bfqd->lock);
4517 static void bfq_idle_slice_timer_body(struct bfq_queue *bfqq)
4519 struct bfq_data *bfqd = bfqq->bfqd;
4520 enum bfqq_expiration reason;
4521 unsigned long flags;
4523 spin_lock_irqsave(&bfqd->lock, flags);
4524 bfq_clear_bfqq_wait_request(bfqq);
4526 if (bfqq != bfqd->in_service_queue) {
4527 spin_unlock_irqrestore(&bfqd->lock, flags);
4531 if (bfq_bfqq_budget_timeout(bfqq))
4533 * Also here the queue can be safely expired
4534 * for budget timeout without wasting
4537 reason = BFQQE_BUDGET_TIMEOUT;
4538 else if (bfqq->queued[0] == 0 && bfqq->queued[1] == 0)
4540 * The queue may not be empty upon timer expiration,
4541 * because we may not disable the timer when the
4542 * first request of the in-service queue arrives
4543 * during disk idling.
4545 reason = BFQQE_TOO_IDLE;
4547 goto schedule_dispatch;
4549 bfq_bfqq_expire(bfqd, bfqq, true, reason);
4552 spin_unlock_irqrestore(&bfqd->lock, flags);
4553 bfq_schedule_dispatch(bfqd);
4557 * Handler of the expiration of the timer running if the in-service queue
4558 * is idling inside its time slice.
4560 static enum hrtimer_restart bfq_idle_slice_timer(struct hrtimer *timer)
4562 struct bfq_data *bfqd = container_of(timer, struct bfq_data,
4564 struct bfq_queue *bfqq = bfqd->in_service_queue;
4567 * Theoretical race here: the in-service queue can be NULL or
4568 * different from the queue that was idling if a new request
4569 * arrives for the current queue and there is a full dispatch
4570 * cycle that changes the in-service queue. This can hardly
4571 * happen, but in the worst case we just expire a queue too
4575 bfq_idle_slice_timer_body(bfqq);
4577 return HRTIMER_NORESTART;
4580 static void __bfq_put_async_bfqq(struct bfq_data *bfqd,
4581 struct bfq_queue **bfqq_ptr)
4583 struct bfq_queue *bfqq = *bfqq_ptr;
4585 bfq_log(bfqd, "put_async_bfqq: %p", bfqq);
4587 bfq_bfqq_move(bfqd, bfqq, bfqd->root_group);
4589 bfq_log_bfqq(bfqd, bfqq, "put_async_bfqq: putting %p, %d",
4591 bfq_put_queue(bfqq);
4597 * Release all the bfqg references to its async queues. If we are
4598 * deallocating the group these queues may still contain requests, so
4599 * we reparent them to the root cgroup (i.e., the only one that will
4600 * exist for sure until all the requests on a device are gone).
4602 void bfq_put_async_queues(struct bfq_data *bfqd, struct bfq_group *bfqg)
4606 for (i = 0; i < 2; i++)
4607 for (j = 0; j < IOPRIO_BE_NR; j++)
4608 __bfq_put_async_bfqq(bfqd, &bfqg->async_bfqq[i][j]);
4610 __bfq_put_async_bfqq(bfqd, &bfqg->async_idle_bfqq);
4613 static void bfq_exit_queue(struct elevator_queue *e)
4615 struct bfq_data *bfqd = e->elevator_data;
4616 struct bfq_queue *bfqq, *n;
4618 hrtimer_cancel(&bfqd->idle_slice_timer);
4620 spin_lock_irq(&bfqd->lock);
4621 list_for_each_entry_safe(bfqq, n, &bfqd->idle_list, bfqq_list)
4622 bfq_deactivate_bfqq(bfqd, bfqq, false, false);
4623 spin_unlock_irq(&bfqd->lock);
4625 hrtimer_cancel(&bfqd->idle_slice_timer);
4627 #ifdef CONFIG_BFQ_GROUP_IOSCHED
4628 blkcg_deactivate_policy(bfqd->queue, &blkcg_policy_bfq);
4630 spin_lock_irq(&bfqd->lock);
4631 bfq_put_async_queues(bfqd, bfqd->root_group);
4632 kfree(bfqd->root_group);
4633 spin_unlock_irq(&bfqd->lock);
4639 static void bfq_init_root_group(struct bfq_group *root_group,
4640 struct bfq_data *bfqd)
4644 #ifdef CONFIG_BFQ_GROUP_IOSCHED
4645 root_group->entity.parent = NULL;
4646 root_group->my_entity = NULL;
4647 root_group->bfqd = bfqd;
4649 root_group->rq_pos_tree = RB_ROOT;
4650 for (i = 0; i < BFQ_IOPRIO_CLASSES; i++)
4651 root_group->sched_data.service_tree[i] = BFQ_SERVICE_TREE_INIT;
4652 root_group->sched_data.bfq_class_idle_last_service = jiffies;
4655 static int bfq_init_queue(struct request_queue *q, struct elevator_type *e)
4657 struct bfq_data *bfqd;
4658 struct elevator_queue *eq;
4660 eq = elevator_alloc(q, e);
4664 bfqd = kzalloc_node(sizeof(*bfqd), GFP_KERNEL, q->node);
4666 kobject_put(&eq->kobj);
4669 eq->elevator_data = bfqd;
4671 spin_lock_irq(q->queue_lock);
4673 spin_unlock_irq(q->queue_lock);
4676 * Our fallback bfqq if bfq_find_alloc_queue() runs into OOM issues.
4677 * Grab a permanent reference to it, so that the normal code flow
4678 * will not attempt to free it.
4680 bfq_init_bfqq(bfqd, &bfqd->oom_bfqq, NULL, 1, 0);
4681 bfqd->oom_bfqq.ref++;
4682 bfqd->oom_bfqq.new_ioprio = BFQ_DEFAULT_QUEUE_IOPRIO;
4683 bfqd->oom_bfqq.new_ioprio_class = IOPRIO_CLASS_BE;
4684 bfqd->oom_bfqq.entity.new_weight =
4685 bfq_ioprio_to_weight(bfqd->oom_bfqq.new_ioprio);
4687 /* oom_bfqq does not participate to bursts */
4688 bfq_clear_bfqq_just_created(&bfqd->oom_bfqq);
4691 * Trigger weight initialization, according to ioprio, at the
4692 * oom_bfqq's first activation. The oom_bfqq's ioprio and ioprio
4693 * class won't be changed any more.
4695 bfqd->oom_bfqq.entity.prio_changed = 1;
4699 INIT_LIST_HEAD(&bfqd->dispatch);
4701 hrtimer_init(&bfqd->idle_slice_timer, CLOCK_MONOTONIC,
4703 bfqd->idle_slice_timer.function = bfq_idle_slice_timer;
4705 bfqd->queue_weights_tree = RB_ROOT;
4706 bfqd->group_weights_tree = RB_ROOT;
4708 INIT_LIST_HEAD(&bfqd->active_list);
4709 INIT_LIST_HEAD(&bfqd->idle_list);
4710 INIT_HLIST_HEAD(&bfqd->burst_list);
4714 bfqd->bfq_max_budget = bfq_default_max_budget;
4716 bfqd->bfq_fifo_expire[0] = bfq_fifo_expire[0];
4717 bfqd->bfq_fifo_expire[1] = bfq_fifo_expire[1];
4718 bfqd->bfq_back_max = bfq_back_max;
4719 bfqd->bfq_back_penalty = bfq_back_penalty;
4720 bfqd->bfq_slice_idle = bfq_slice_idle;
4721 bfqd->bfq_timeout = bfq_timeout;
4723 bfqd->bfq_requests_within_timer = 120;
4725 bfqd->bfq_large_burst_thresh = 8;
4726 bfqd->bfq_burst_interval = msecs_to_jiffies(180);
4728 bfqd->low_latency = true;
4731 * Trade-off between responsiveness and fairness.
4733 bfqd->bfq_wr_coeff = 30;
4734 bfqd->bfq_wr_rt_max_time = msecs_to_jiffies(300);
4735 bfqd->bfq_wr_max_time = 0;
4736 bfqd->bfq_wr_min_idle_time = msecs_to_jiffies(2000);
4737 bfqd->bfq_wr_min_inter_arr_async = msecs_to_jiffies(500);
4738 bfqd->bfq_wr_max_softrt_rate = 7000; /*
4739 * Approximate rate required
4740 * to playback or record a
4741 * high-definition compressed
4744 bfqd->wr_busy_queues = 0;
4747 * Begin by assuming, optimistically, that the device is a
4748 * high-speed one, and that its peak rate is equal to 2/3 of
4749 * the highest reference rate.
4751 bfqd->RT_prod = R_fast[blk_queue_nonrot(bfqd->queue)] *
4752 T_fast[blk_queue_nonrot(bfqd->queue)];
4753 bfqd->peak_rate = R_fast[blk_queue_nonrot(bfqd->queue)] * 2 / 3;
4754 bfqd->device_speed = BFQ_BFQD_FAST;
4756 spin_lock_init(&bfqd->lock);
4759 * The invocation of the next bfq_create_group_hierarchy
4760 * function is the head of a chain of function calls
4761 * (bfq_create_group_hierarchy->blkcg_activate_policy->
4762 * blk_mq_freeze_queue) that may lead to the invocation of the
4763 * has_work hook function. For this reason,
4764 * bfq_create_group_hierarchy is invoked only after all
4765 * scheduler data has been initialized, apart from the fields
4766 * that can be initialized only after invoking
4767 * bfq_create_group_hierarchy. This, in particular, enables
4768 * has_work to correctly return false. Of course, to avoid
4769 * other inconsistencies, the blk-mq stack must then refrain
4770 * from invoking further scheduler hooks before this init
4771 * function is finished.
4773 bfqd->root_group = bfq_create_group_hierarchy(bfqd, q->node);
4774 if (!bfqd->root_group)
4776 bfq_init_root_group(bfqd->root_group, bfqd);
4777 bfq_init_entity(&bfqd->oom_bfqq.entity, bfqd->root_group);
4779 wbt_disable_default(q);
4784 kobject_put(&eq->kobj);
4788 static void bfq_slab_kill(void)
4790 kmem_cache_destroy(bfq_pool);
4793 static int __init bfq_slab_setup(void)
4795 bfq_pool = KMEM_CACHE(bfq_queue, 0);
4801 static ssize_t bfq_var_show(unsigned int var, char *page)
4803 return sprintf(page, "%u\n", var);
4806 static int bfq_var_store(unsigned long *var, const char *page)
4808 unsigned long new_val;
4809 int ret = kstrtoul(page, 10, &new_val);
4817 #define SHOW_FUNCTION(__FUNC, __VAR, __CONV) \
4818 static ssize_t __FUNC(struct elevator_queue *e, char *page) \
4820 struct bfq_data *bfqd = e->elevator_data; \
4821 u64 __data = __VAR; \
4823 __data = jiffies_to_msecs(__data); \
4824 else if (__CONV == 2) \
4825 __data = div_u64(__data, NSEC_PER_MSEC); \
4826 return bfq_var_show(__data, (page)); \
4828 SHOW_FUNCTION(bfq_fifo_expire_sync_show, bfqd->bfq_fifo_expire[1], 2);
4829 SHOW_FUNCTION(bfq_fifo_expire_async_show, bfqd->bfq_fifo_expire[0], 2);
4830 SHOW_FUNCTION(bfq_back_seek_max_show, bfqd->bfq_back_max, 0);
4831 SHOW_FUNCTION(bfq_back_seek_penalty_show, bfqd->bfq_back_penalty, 0);
4832 SHOW_FUNCTION(bfq_slice_idle_show, bfqd->bfq_slice_idle, 2);
4833 SHOW_FUNCTION(bfq_max_budget_show, bfqd->bfq_user_max_budget, 0);
4834 SHOW_FUNCTION(bfq_timeout_sync_show, bfqd->bfq_timeout, 1);
4835 SHOW_FUNCTION(bfq_strict_guarantees_show, bfqd->strict_guarantees, 0);
4836 SHOW_FUNCTION(bfq_low_latency_show, bfqd->low_latency, 0);
4837 #undef SHOW_FUNCTION
4839 #define USEC_SHOW_FUNCTION(__FUNC, __VAR) \
4840 static ssize_t __FUNC(struct elevator_queue *e, char *page) \
4842 struct bfq_data *bfqd = e->elevator_data; \
4843 u64 __data = __VAR; \
4844 __data = div_u64(__data, NSEC_PER_USEC); \
4845 return bfq_var_show(__data, (page)); \
4847 USEC_SHOW_FUNCTION(bfq_slice_idle_us_show, bfqd->bfq_slice_idle);
4848 #undef USEC_SHOW_FUNCTION
4850 #define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV) \
4852 __FUNC(struct elevator_queue *e, const char *page, size_t count) \
4854 struct bfq_data *bfqd = e->elevator_data; \
4855 unsigned long __data, __min = (MIN), __max = (MAX); \
4858 ret = bfq_var_store(&__data, (page)); \
4861 if (__data < __min) \
4863 else if (__data > __max) \
4866 *(__PTR) = msecs_to_jiffies(__data); \
4867 else if (__CONV == 2) \
4868 *(__PTR) = (u64)__data * NSEC_PER_MSEC; \
4870 *(__PTR) = __data; \
4873 STORE_FUNCTION(bfq_fifo_expire_sync_store, &bfqd->bfq_fifo_expire[1], 1,
4875 STORE_FUNCTION(bfq_fifo_expire_async_store, &bfqd->bfq_fifo_expire[0], 1,
4877 STORE_FUNCTION(bfq_back_seek_max_store, &bfqd->bfq_back_max, 0, INT_MAX, 0);
4878 STORE_FUNCTION(bfq_back_seek_penalty_store, &bfqd->bfq_back_penalty, 1,
4880 STORE_FUNCTION(bfq_slice_idle_store, &bfqd->bfq_slice_idle, 0, INT_MAX, 2);
4881 #undef STORE_FUNCTION
4883 #define USEC_STORE_FUNCTION(__FUNC, __PTR, MIN, MAX) \
4884 static ssize_t __FUNC(struct elevator_queue *e, const char *page, size_t count)\
4886 struct bfq_data *bfqd = e->elevator_data; \
4887 unsigned long __data, __min = (MIN), __max = (MAX); \
4890 ret = bfq_var_store(&__data, (page)); \
4893 if (__data < __min) \
4895 else if (__data > __max) \
4897 *(__PTR) = (u64)__data * NSEC_PER_USEC; \
4900 USEC_STORE_FUNCTION(bfq_slice_idle_us_store, &bfqd->bfq_slice_idle, 0,
4902 #undef USEC_STORE_FUNCTION
4904 static ssize_t bfq_max_budget_store(struct elevator_queue *e,
4905 const char *page, size_t count)
4907 struct bfq_data *bfqd = e->elevator_data;
4908 unsigned long __data;
4911 ret = bfq_var_store(&__data, (page));
4916 bfqd->bfq_max_budget = bfq_calc_max_budget(bfqd);
4918 if (__data > INT_MAX)
4920 bfqd->bfq_max_budget = __data;
4923 bfqd->bfq_user_max_budget = __data;
4929 * Leaving this name to preserve name compatibility with cfq
4930 * parameters, but this timeout is used for both sync and async.
4932 static ssize_t bfq_timeout_sync_store(struct elevator_queue *e,
4933 const char *page, size_t count)
4935 struct bfq_data *bfqd = e->elevator_data;
4936 unsigned long __data;
4939 ret = bfq_var_store(&__data, (page));
4945 else if (__data > INT_MAX)
4948 bfqd->bfq_timeout = msecs_to_jiffies(__data);
4949 if (bfqd->bfq_user_max_budget == 0)
4950 bfqd->bfq_max_budget = bfq_calc_max_budget(bfqd);
4955 static ssize_t bfq_strict_guarantees_store(struct elevator_queue *e,
4956 const char *page, size_t count)
4958 struct bfq_data *bfqd = e->elevator_data;
4959 unsigned long __data;
4962 ret = bfq_var_store(&__data, (page));
4968 if (!bfqd->strict_guarantees && __data == 1
4969 && bfqd->bfq_slice_idle < 8 * NSEC_PER_MSEC)
4970 bfqd->bfq_slice_idle = 8 * NSEC_PER_MSEC;
4972 bfqd->strict_guarantees = __data;
4977 static ssize_t bfq_low_latency_store(struct elevator_queue *e,
4978 const char *page, size_t count)
4980 struct bfq_data *bfqd = e->elevator_data;
4981 unsigned long __data;
4984 ret = bfq_var_store(&__data, (page));
4990 if (__data == 0 && bfqd->low_latency != 0)
4992 bfqd->low_latency = __data;
4997 #define BFQ_ATTR(name) \
4998 __ATTR(name, 0644, bfq_##name##_show, bfq_##name##_store)
5000 static struct elv_fs_entry bfq_attrs[] = {
5001 BFQ_ATTR(fifo_expire_sync),
5002 BFQ_ATTR(fifo_expire_async),
5003 BFQ_ATTR(back_seek_max),
5004 BFQ_ATTR(back_seek_penalty),
5005 BFQ_ATTR(slice_idle),
5006 BFQ_ATTR(slice_idle_us),
5007 BFQ_ATTR(max_budget),
5008 BFQ_ATTR(timeout_sync),
5009 BFQ_ATTR(strict_guarantees),
5010 BFQ_ATTR(low_latency),
5014 static struct elevator_type iosched_bfq_mq = {
5016 .prepare_request = bfq_prepare_request,
5017 .finish_request = bfq_finish_request,
5018 .exit_icq = bfq_exit_icq,
5019 .insert_requests = bfq_insert_requests,
5020 .dispatch_request = bfq_dispatch_request,
5021 .next_request = elv_rb_latter_request,
5022 .former_request = elv_rb_former_request,
5023 .allow_merge = bfq_allow_bio_merge,
5024 .bio_merge = bfq_bio_merge,
5025 .request_merge = bfq_request_merge,
5026 .requests_merged = bfq_requests_merged,
5027 .request_merged = bfq_request_merged,
5028 .has_work = bfq_has_work,
5029 .init_sched = bfq_init_queue,
5030 .exit_sched = bfq_exit_queue,
5034 .icq_size = sizeof(struct bfq_io_cq),
5035 .icq_align = __alignof__(struct bfq_io_cq),
5036 .elevator_attrs = bfq_attrs,
5037 .elevator_name = "bfq",
5038 .elevator_owner = THIS_MODULE,
5040 MODULE_ALIAS("bfq-iosched");
5042 static int __init bfq_init(void)
5046 #ifdef CONFIG_BFQ_GROUP_IOSCHED
5047 ret = blkcg_policy_register(&blkcg_policy_bfq);
5053 if (bfq_slab_setup())
5057 * Times to load large popular applications for the typical
5058 * systems installed on the reference devices (see the
5059 * comments before the definitions of the next two
5060 * arrays). Actually, we use slightly slower values, as the
5061 * estimated peak rate tends to be smaller than the actual
5062 * peak rate. The reason for this last fact is that estimates
5063 * are computed over much shorter time intervals than the long
5064 * intervals typically used for benchmarking. Why? First, to
5065 * adapt more quickly to variations. Second, because an I/O
5066 * scheduler cannot rely on a peak-rate-evaluation workload to
5067 * be run for a long time.
5069 T_slow[0] = msecs_to_jiffies(3500); /* actually 4 sec */
5070 T_slow[1] = msecs_to_jiffies(6000); /* actually 6.5 sec */
5071 T_fast[0] = msecs_to_jiffies(7000); /* actually 8 sec */
5072 T_fast[1] = msecs_to_jiffies(2500); /* actually 3 sec */
5075 * Thresholds that determine the switch between speed classes
5076 * (see the comments before the definition of the array
5077 * device_speed_thresh). These thresholds are biased towards
5078 * transitions to the fast class. This is safer than the
5079 * opposite bias. In fact, a wrong transition to the slow
5080 * class results in short weight-raising periods, because the
5081 * speed of the device then tends to be higher that the
5082 * reference peak rate. On the opposite end, a wrong
5083 * transition to the fast class tends to increase
5084 * weight-raising periods, because of the opposite reason.
5086 device_speed_thresh[0] = (4 * R_slow[0]) / 3;
5087 device_speed_thresh[1] = (4 * R_slow[1]) / 3;
5089 ret = elv_register(&iosched_bfq_mq);
5098 #ifdef CONFIG_BFQ_GROUP_IOSCHED
5099 blkcg_policy_unregister(&blkcg_policy_bfq);
5104 static void __exit bfq_exit(void)
5106 elv_unregister(&iosched_bfq_mq);
5107 #ifdef CONFIG_BFQ_GROUP_IOSCHED
5108 blkcg_policy_unregister(&blkcg_policy_bfq);
5113 module_init(bfq_init);
5114 module_exit(bfq_exit);
5116 MODULE_AUTHOR("Paolo Valente");
5117 MODULE_LICENSE("GPL");
5118 MODULE_DESCRIPTION("MQ Budget Fair Queueing I/O Scheduler");