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);
728 static unsigned int bfq_wr_duration(struct bfq_data
*bfqd
)
732 if (bfqd
->bfq_wr_max_time
> 0)
733 return bfqd
->bfq_wr_max_time
;
736 do_div(dur
, bfqd
->peak_rate
);
739 * Limit duration between 3 and 13 seconds. Tests show that
740 * higher values than 13 seconds often yield the opposite of
741 * the desired result, i.e., worsen responsiveness by letting
742 * non-interactive and non-soft-real-time applications
743 * preserve weight raising for a too long time interval.
745 * On the other end, lower values than 3 seconds make it
746 * difficult for most interactive tasks to complete their jobs
747 * before weight-raising finishes.
749 if (dur
> msecs_to_jiffies(13000))
750 dur
= msecs_to_jiffies(13000);
751 else if (dur
< msecs_to_jiffies(3000))
752 dur
= msecs_to_jiffies(3000);
757 /* switch back from soft real-time to interactive weight raising */
758 static void switch_back_to_interactive_wr(struct bfq_queue
*bfqq
,
759 struct bfq_data
*bfqd
)
761 bfqq
->wr_coeff
= bfqd
->bfq_wr_coeff
;
762 bfqq
->wr_cur_max_time
= bfq_wr_duration(bfqd
);
763 bfqq
->last_wr_start_finish
= bfqq
->wr_start_at_switch_to_srt
;
767 bfq_bfqq_resume_state(struct bfq_queue
*bfqq
, struct bfq_data
*bfqd
,
768 struct bfq_io_cq
*bic
, bool bfq_already_existing
)
770 unsigned int old_wr_coeff
= bfqq
->wr_coeff
;
771 bool busy
= bfq_already_existing
&& bfq_bfqq_busy(bfqq
);
773 if (bic
->saved_has_short_ttime
)
774 bfq_mark_bfqq_has_short_ttime(bfqq
);
776 bfq_clear_bfqq_has_short_ttime(bfqq
);
778 if (bic
->saved_IO_bound
)
779 bfq_mark_bfqq_IO_bound(bfqq
);
781 bfq_clear_bfqq_IO_bound(bfqq
);
783 bfqq
->ttime
= bic
->saved_ttime
;
784 bfqq
->wr_coeff
= bic
->saved_wr_coeff
;
785 bfqq
->wr_start_at_switch_to_srt
= bic
->saved_wr_start_at_switch_to_srt
;
786 bfqq
->last_wr_start_finish
= bic
->saved_last_wr_start_finish
;
787 bfqq
->wr_cur_max_time
= bic
->saved_wr_cur_max_time
;
789 if (bfqq
->wr_coeff
> 1 && (bfq_bfqq_in_large_burst(bfqq
) ||
790 time_is_before_jiffies(bfqq
->last_wr_start_finish
+
791 bfqq
->wr_cur_max_time
))) {
792 if (bfqq
->wr_cur_max_time
== bfqd
->bfq_wr_rt_max_time
&&
793 !bfq_bfqq_in_large_burst(bfqq
) &&
794 time_is_after_eq_jiffies(bfqq
->wr_start_at_switch_to_srt
+
795 bfq_wr_duration(bfqd
))) {
796 switch_back_to_interactive_wr(bfqq
, bfqd
);
799 bfq_log_bfqq(bfqq
->bfqd
, bfqq
,
800 "resume state: switching off wr");
804 /* make sure weight will be updated, however we got here */
805 bfqq
->entity
.prio_changed
= 1;
810 if (old_wr_coeff
== 1 && bfqq
->wr_coeff
> 1)
811 bfqd
->wr_busy_queues
++;
812 else if (old_wr_coeff
> 1 && bfqq
->wr_coeff
== 1)
813 bfqd
->wr_busy_queues
--;
816 static int bfqq_process_refs(struct bfq_queue
*bfqq
)
818 return bfqq
->ref
- bfqq
->allocated
- bfqq
->entity
.on_st
;
821 /* Empty burst list and add just bfqq (see comments on bfq_handle_burst) */
822 static void bfq_reset_burst_list(struct bfq_data
*bfqd
, struct bfq_queue
*bfqq
)
824 struct bfq_queue
*item
;
825 struct hlist_node
*n
;
827 hlist_for_each_entry_safe(item
, n
, &bfqd
->burst_list
, burst_list_node
)
828 hlist_del_init(&item
->burst_list_node
);
829 hlist_add_head(&bfqq
->burst_list_node
, &bfqd
->burst_list
);
830 bfqd
->burst_size
= 1;
831 bfqd
->burst_parent_entity
= bfqq
->entity
.parent
;
834 /* Add bfqq to the list of queues in current burst (see bfq_handle_burst) */
835 static void bfq_add_to_burst(struct bfq_data
*bfqd
, struct bfq_queue
*bfqq
)
837 /* Increment burst size to take into account also bfqq */
840 if (bfqd
->burst_size
== bfqd
->bfq_large_burst_thresh
) {
841 struct bfq_queue
*pos
, *bfqq_item
;
842 struct hlist_node
*n
;
845 * Enough queues have been activated shortly after each
846 * other to consider this burst as large.
848 bfqd
->large_burst
= true;
851 * We can now mark all queues in the burst list as
852 * belonging to a large burst.
854 hlist_for_each_entry(bfqq_item
, &bfqd
->burst_list
,
856 bfq_mark_bfqq_in_large_burst(bfqq_item
);
857 bfq_mark_bfqq_in_large_burst(bfqq
);
860 * From now on, and until the current burst finishes, any
861 * new queue being activated shortly after the last queue
862 * was inserted in the burst can be immediately marked as
863 * belonging to a large burst. So the burst list is not
864 * needed any more. Remove it.
866 hlist_for_each_entry_safe(pos
, n
, &bfqd
->burst_list
,
868 hlist_del_init(&pos
->burst_list_node
);
870 * Burst not yet large: add bfqq to the burst list. Do
871 * not increment the ref counter for bfqq, because bfqq
872 * is removed from the burst list before freeing bfqq
875 hlist_add_head(&bfqq
->burst_list_node
, &bfqd
->burst_list
);
879 * If many queues belonging to the same group happen to be created
880 * shortly after each other, then the processes associated with these
881 * queues have typically a common goal. In particular, bursts of queue
882 * creations are usually caused by services or applications that spawn
883 * many parallel threads/processes. Examples are systemd during boot,
884 * or git grep. To help these processes get their job done as soon as
885 * possible, it is usually better to not grant either weight-raising
886 * or device idling to their queues.
888 * In this comment we describe, firstly, the reasons why this fact
889 * holds, and, secondly, the next function, which implements the main
890 * steps needed to properly mark these queues so that they can then be
891 * treated in a different way.
893 * The above services or applications benefit mostly from a high
894 * throughput: the quicker the requests of the activated queues are
895 * cumulatively served, the sooner the target job of these queues gets
896 * completed. As a consequence, weight-raising any of these queues,
897 * which also implies idling the device for it, is almost always
898 * counterproductive. In most cases it just lowers throughput.
900 * On the other hand, a burst of queue creations may be caused also by
901 * the start of an application that does not consist of a lot of
902 * parallel I/O-bound threads. In fact, with a complex application,
903 * several short processes may need to be executed to start-up the
904 * application. In this respect, to start an application as quickly as
905 * possible, the best thing to do is in any case to privilege the I/O
906 * related to the application with respect to all other
907 * I/O. Therefore, the best strategy to start as quickly as possible
908 * an application that causes a burst of queue creations is to
909 * weight-raise all the queues created during the burst. This is the
910 * exact opposite of the best strategy for the other type of bursts.
912 * In the end, to take the best action for each of the two cases, the
913 * two types of bursts need to be distinguished. Fortunately, this
914 * seems relatively easy, by looking at the sizes of the bursts. In
915 * particular, we found a threshold such that only bursts with a
916 * larger size than that threshold are apparently caused by
917 * services or commands such as systemd or git grep. For brevity,
918 * hereafter we call just 'large' these bursts. BFQ *does not*
919 * weight-raise queues whose creation occurs in a large burst. In
920 * addition, for each of these queues BFQ performs or does not perform
921 * idling depending on which choice boosts the throughput more. The
922 * exact choice depends on the device and request pattern at
925 * Unfortunately, false positives may occur while an interactive task
926 * is starting (e.g., an application is being started). The
927 * consequence is that the queues associated with the task do not
928 * enjoy weight raising as expected. Fortunately these false positives
929 * are very rare. They typically occur if some service happens to
930 * start doing I/O exactly when the interactive task starts.
932 * Turning back to the next function, it implements all the steps
933 * needed to detect the occurrence of a large burst and to properly
934 * mark all the queues belonging to it (so that they can then be
935 * treated in a different way). This goal is achieved by maintaining a
936 * "burst list" that holds, temporarily, the queues that belong to the
937 * burst in progress. The list is then used to mark these queues as
938 * belonging to a large burst if the burst does become large. The main
939 * steps are the following.
941 * . when the very first queue is created, the queue is inserted into the
942 * list (as it could be the first queue in a possible burst)
944 * . if the current burst has not yet become large, and a queue Q that does
945 * not yet belong to the burst is activated shortly after the last time
946 * at which a new queue entered the burst list, then the function appends
947 * Q to the burst list
949 * . if, as a consequence of the previous step, the burst size reaches
950 * the large-burst threshold, then
952 * . all the queues in the burst list are marked as belonging to a
955 * . the burst list is deleted; in fact, the burst list already served
956 * its purpose (keeping temporarily track of the queues in a burst,
957 * so as to be able to mark them as belonging to a large burst in the
958 * previous sub-step), and now is not needed any more
960 * . the device enters a large-burst mode
962 * . if a queue Q that does not belong to the burst is created while
963 * the device is in large-burst mode and shortly after the last time
964 * at which a queue either entered the burst list or was marked as
965 * belonging to the current large burst, then Q is immediately marked
966 * as belonging to a large burst.
968 * . if a queue Q that does not belong to the burst is created a while
969 * later, i.e., not shortly after, than the last time at which a queue
970 * either entered the burst list or was marked as belonging to the
971 * current large burst, then the current burst is deemed as finished and:
973 * . the large-burst mode is reset if set
975 * . the burst list is emptied
977 * . Q is inserted in the burst list, as Q may be the first queue
978 * in a possible new burst (then the burst list contains just Q
981 static void bfq_handle_burst(struct bfq_data
*bfqd
, struct bfq_queue
*bfqq
)
984 * If bfqq is already in the burst list or is part of a large
985 * burst, or finally has just been split, then there is
986 * nothing else to do.
988 if (!hlist_unhashed(&bfqq
->burst_list_node
) ||
989 bfq_bfqq_in_large_burst(bfqq
) ||
990 time_is_after_eq_jiffies(bfqq
->split_time
+
991 msecs_to_jiffies(10)))
995 * If bfqq's creation happens late enough, or bfqq belongs to
996 * a different group than the burst group, then the current
997 * burst is finished, and related data structures must be
1000 * In this respect, consider the special case where bfqq is
1001 * the very first queue created after BFQ is selected for this
1002 * device. In this case, last_ins_in_burst and
1003 * burst_parent_entity are not yet significant when we get
1004 * here. But it is easy to verify that, whether or not the
1005 * following condition is true, bfqq will end up being
1006 * inserted into the burst list. In particular the list will
1007 * happen to contain only bfqq. And this is exactly what has
1008 * to happen, as bfqq may be the first queue of the first
1011 if (time_is_before_jiffies(bfqd
->last_ins_in_burst
+
1012 bfqd
->bfq_burst_interval
) ||
1013 bfqq
->entity
.parent
!= bfqd
->burst_parent_entity
) {
1014 bfqd
->large_burst
= false;
1015 bfq_reset_burst_list(bfqd
, bfqq
);
1020 * If we get here, then bfqq is being activated shortly after the
1021 * last queue. So, if the current burst is also large, we can mark
1022 * bfqq as belonging to this large burst immediately.
1024 if (bfqd
->large_burst
) {
1025 bfq_mark_bfqq_in_large_burst(bfqq
);
1030 * If we get here, then a large-burst state has not yet been
1031 * reached, but bfqq is being activated shortly after the last
1032 * queue. Then we add bfqq to the burst.
1034 bfq_add_to_burst(bfqd
, bfqq
);
1037 * At this point, bfqq either has been added to the current
1038 * burst or has caused the current burst to terminate and a
1039 * possible new burst to start. In particular, in the second
1040 * case, bfqq has become the first queue in the possible new
1041 * burst. In both cases last_ins_in_burst needs to be moved
1044 bfqd
->last_ins_in_burst
= jiffies
;
1047 static int bfq_bfqq_budget_left(struct bfq_queue
*bfqq
)
1049 struct bfq_entity
*entity
= &bfqq
->entity
;
1051 return entity
->budget
- entity
->service
;
1055 * If enough samples have been computed, return the current max budget
1056 * stored in bfqd, which is dynamically updated according to the
1057 * estimated disk peak rate; otherwise return the default max budget
1059 static int bfq_max_budget(struct bfq_data
*bfqd
)
1061 if (bfqd
->budgets_assigned
< bfq_stats_min_budgets
)
1062 return bfq_default_max_budget
;
1064 return bfqd
->bfq_max_budget
;
1068 * Return min budget, which is a fraction of the current or default
1069 * max budget (trying with 1/32)
1071 static int bfq_min_budget(struct bfq_data
*bfqd
)
1073 if (bfqd
->budgets_assigned
< bfq_stats_min_budgets
)
1074 return bfq_default_max_budget
/ 32;
1076 return bfqd
->bfq_max_budget
/ 32;
1080 * The next function, invoked after the input queue bfqq switches from
1081 * idle to busy, updates the budget of bfqq. The function also tells
1082 * whether the in-service queue should be expired, by returning
1083 * true. The purpose of expiring the in-service queue is to give bfqq
1084 * the chance to possibly preempt the in-service queue, and the reason
1085 * for preempting the in-service queue is to achieve one of the two
1088 * 1. Guarantee to bfqq its reserved bandwidth even if bfqq has
1089 * expired because it has remained idle. In particular, bfqq may have
1090 * expired for one of the following two reasons:
1092 * - BFQQE_NO_MORE_REQUESTS bfqq did not enjoy any device idling
1093 * and did not make it to issue a new request before its last
1094 * request was served;
1096 * - BFQQE_TOO_IDLE bfqq did enjoy device idling, but did not issue
1097 * a new request before the expiration of the idling-time.
1099 * Even if bfqq has expired for one of the above reasons, the process
1100 * associated with the queue may be however issuing requests greedily,
1101 * and thus be sensitive to the bandwidth it receives (bfqq may have
1102 * remained idle for other reasons: CPU high load, bfqq not enjoying
1103 * idling, I/O throttling somewhere in the path from the process to
1104 * the I/O scheduler, ...). But if, after every expiration for one of
1105 * the above two reasons, bfqq has to wait for the service of at least
1106 * one full budget of another queue before being served again, then
1107 * bfqq is likely to get a much lower bandwidth or resource time than
1108 * its reserved ones. To address this issue, two countermeasures need
1111 * First, the budget and the timestamps of bfqq need to be updated in
1112 * a special way on bfqq reactivation: they need to be updated as if
1113 * bfqq did not remain idle and did not expire. In fact, if they are
1114 * computed as if bfqq expired and remained idle until reactivation,
1115 * then the process associated with bfqq is treated as if, instead of
1116 * being greedy, it stopped issuing requests when bfqq remained idle,
1117 * and restarts issuing requests only on this reactivation. In other
1118 * words, the scheduler does not help the process recover the "service
1119 * hole" between bfqq expiration and reactivation. As a consequence,
1120 * the process receives a lower bandwidth than its reserved one. In
1121 * contrast, to recover this hole, the budget must be updated as if
1122 * bfqq was not expired at all before this reactivation, i.e., it must
1123 * be set to the value of the remaining budget when bfqq was
1124 * expired. Along the same line, timestamps need to be assigned the
1125 * value they had the last time bfqq was selected for service, i.e.,
1126 * before last expiration. Thus timestamps need to be back-shifted
1127 * with respect to their normal computation (see [1] for more details
1128 * on this tricky aspect).
1130 * Secondly, to allow the process to recover the hole, the in-service
1131 * queue must be expired too, to give bfqq the chance to preempt it
1132 * immediately. In fact, if bfqq has to wait for a full budget of the
1133 * in-service queue to be completed, then it may become impossible to
1134 * let the process recover the hole, even if the back-shifted
1135 * timestamps of bfqq are lower than those of the in-service queue. If
1136 * this happens for most or all of the holes, then the process may not
1137 * receive its reserved bandwidth. In this respect, it is worth noting
1138 * that, being the service of outstanding requests unpreemptible, a
1139 * little fraction of the holes may however be unrecoverable, thereby
1140 * causing a little loss of bandwidth.
1142 * The last important point is detecting whether bfqq does need this
1143 * bandwidth recovery. In this respect, the next function deems the
1144 * process associated with bfqq greedy, and thus allows it to recover
1145 * the hole, if: 1) the process is waiting for the arrival of a new
1146 * request (which implies that bfqq expired for one of the above two
1147 * reasons), and 2) such a request has arrived soon. The first
1148 * condition is controlled through the flag non_blocking_wait_rq,
1149 * while the second through the flag arrived_in_time. If both
1150 * conditions hold, then the function computes the budget in the
1151 * above-described special way, and signals that the in-service queue
1152 * should be expired. Timestamp back-shifting is done later in
1153 * __bfq_activate_entity.
1155 * 2. Reduce latency. Even if timestamps are not backshifted to let
1156 * the process associated with bfqq recover a service hole, bfqq may
1157 * however happen to have, after being (re)activated, a lower finish
1158 * timestamp than the in-service queue. That is, the next budget of
1159 * bfqq may have to be completed before the one of the in-service
1160 * queue. If this is the case, then preempting the in-service queue
1161 * allows this goal to be achieved, apart from the unpreemptible,
1162 * outstanding requests mentioned above.
1164 * Unfortunately, regardless of which of the above two goals one wants
1165 * to achieve, service trees need first to be updated to know whether
1166 * the in-service queue must be preempted. To have service trees
1167 * correctly updated, the in-service queue must be expired and
1168 * rescheduled, and bfqq must be scheduled too. This is one of the
1169 * most costly operations (in future versions, the scheduling
1170 * mechanism may be re-designed in such a way to make it possible to
1171 * know whether preemption is needed without needing to update service
1172 * trees). In addition, queue preemptions almost always cause random
1173 * I/O, and thus loss of throughput. Because of these facts, the next
1174 * function adopts the following simple scheme to avoid both costly
1175 * operations and too frequent preemptions: it requests the expiration
1176 * of the in-service queue (unconditionally) only for queues that need
1177 * to recover a hole, or that either are weight-raised or deserve to
1180 static bool bfq_bfqq_update_budg_for_activation(struct bfq_data
*bfqd
,
1181 struct bfq_queue
*bfqq
,
1182 bool arrived_in_time
,
1183 bool wr_or_deserves_wr
)
1185 struct bfq_entity
*entity
= &bfqq
->entity
;
1187 if (bfq_bfqq_non_blocking_wait_rq(bfqq
) && arrived_in_time
) {
1189 * We do not clear the flag non_blocking_wait_rq here, as
1190 * the latter is used in bfq_activate_bfqq to signal
1191 * that timestamps need to be back-shifted (and is
1192 * cleared right after).
1196 * In next assignment we rely on that either
1197 * entity->service or entity->budget are not updated
1198 * on expiration if bfqq is empty (see
1199 * __bfq_bfqq_recalc_budget). Thus both quantities
1200 * remain unchanged after such an expiration, and the
1201 * following statement therefore assigns to
1202 * entity->budget the remaining budget on such an
1203 * expiration. For clarity, entity->service is not
1204 * updated on expiration in any case, and, in normal
1205 * operation, is reset only when bfqq is selected for
1206 * service (see bfq_get_next_queue).
1208 entity
->budget
= min_t(unsigned long,
1209 bfq_bfqq_budget_left(bfqq
),
1215 entity
->budget
= max_t(unsigned long, bfqq
->max_budget
,
1216 bfq_serv_to_charge(bfqq
->next_rq
, bfqq
));
1217 bfq_clear_bfqq_non_blocking_wait_rq(bfqq
);
1218 return wr_or_deserves_wr
;
1222 * Return the farthest future time instant according to jiffies
1225 static unsigned long bfq_greatest_from_now(void)
1227 return jiffies
+ MAX_JIFFY_OFFSET
;
1231 * Return the farthest past time instant according to jiffies
1234 static unsigned long bfq_smallest_from_now(void)
1236 return jiffies
- MAX_JIFFY_OFFSET
;
1239 static void bfq_update_bfqq_wr_on_rq_arrival(struct bfq_data
*bfqd
,
1240 struct bfq_queue
*bfqq
,
1241 unsigned int old_wr_coeff
,
1242 bool wr_or_deserves_wr
,
1247 if (old_wr_coeff
== 1 && wr_or_deserves_wr
) {
1248 /* start a weight-raising period */
1250 bfqq
->wr_coeff
= bfqd
->bfq_wr_coeff
;
1251 bfqq
->wr_cur_max_time
= bfq_wr_duration(bfqd
);
1254 * No interactive weight raising in progress
1255 * here: assign minus infinity to
1256 * wr_start_at_switch_to_srt, to make sure
1257 * that, at the end of the soft-real-time
1258 * weight raising periods that is starting
1259 * now, no interactive weight-raising period
1260 * may be wrongly considered as still in
1261 * progress (and thus actually started by
1264 bfqq
->wr_start_at_switch_to_srt
=
1265 bfq_smallest_from_now();
1266 bfqq
->wr_coeff
= bfqd
->bfq_wr_coeff
*
1267 BFQ_SOFTRT_WEIGHT_FACTOR
;
1268 bfqq
->wr_cur_max_time
=
1269 bfqd
->bfq_wr_rt_max_time
;
1273 * If needed, further reduce budget to make sure it is
1274 * close to bfqq's backlog, so as to reduce the
1275 * scheduling-error component due to a too large
1276 * budget. Do not care about throughput consequences,
1277 * but only about latency. Finally, do not assign a
1278 * too small budget either, to avoid increasing
1279 * latency by causing too frequent expirations.
1281 bfqq
->entity
.budget
= min_t(unsigned long,
1282 bfqq
->entity
.budget
,
1283 2 * bfq_min_budget(bfqd
));
1284 } else if (old_wr_coeff
> 1) {
1285 if (interactive
) { /* update wr coeff and duration */
1286 bfqq
->wr_coeff
= bfqd
->bfq_wr_coeff
;
1287 bfqq
->wr_cur_max_time
= bfq_wr_duration(bfqd
);
1288 } else if (in_burst
)
1292 * The application is now or still meeting the
1293 * requirements for being deemed soft rt. We
1294 * can then correctly and safely (re)charge
1295 * the weight-raising duration for the
1296 * application with the weight-raising
1297 * duration for soft rt applications.
1299 * In particular, doing this recharge now, i.e.,
1300 * before the weight-raising period for the
1301 * application finishes, reduces the probability
1302 * of the following negative scenario:
1303 * 1) the weight of a soft rt application is
1304 * raised at startup (as for any newly
1305 * created application),
1306 * 2) since the application is not interactive,
1307 * at a certain time weight-raising is
1308 * stopped for the application,
1309 * 3) at that time the application happens to
1310 * still have pending requests, and hence
1311 * is destined to not have a chance to be
1312 * deemed soft rt before these requests are
1313 * completed (see the comments to the
1314 * function bfq_bfqq_softrt_next_start()
1315 * for details on soft rt detection),
1316 * 4) these pending requests experience a high
1317 * latency because the application is not
1318 * weight-raised while they are pending.
1320 if (bfqq
->wr_cur_max_time
!=
1321 bfqd
->bfq_wr_rt_max_time
) {
1322 bfqq
->wr_start_at_switch_to_srt
=
1323 bfqq
->last_wr_start_finish
;
1325 bfqq
->wr_cur_max_time
=
1326 bfqd
->bfq_wr_rt_max_time
;
1327 bfqq
->wr_coeff
= bfqd
->bfq_wr_coeff
*
1328 BFQ_SOFTRT_WEIGHT_FACTOR
;
1330 bfqq
->last_wr_start_finish
= jiffies
;
1335 static bool bfq_bfqq_idle_for_long_time(struct bfq_data
*bfqd
,
1336 struct bfq_queue
*bfqq
)
1338 return bfqq
->dispatched
== 0 &&
1339 time_is_before_jiffies(
1340 bfqq
->budget_timeout
+
1341 bfqd
->bfq_wr_min_idle_time
);
1344 static void bfq_bfqq_handle_idle_busy_switch(struct bfq_data
*bfqd
,
1345 struct bfq_queue
*bfqq
,
1350 bool soft_rt
, in_burst
, wr_or_deserves_wr
,
1351 bfqq_wants_to_preempt
,
1352 idle_for_long_time
= bfq_bfqq_idle_for_long_time(bfqd
, bfqq
),
1354 * See the comments on
1355 * bfq_bfqq_update_budg_for_activation for
1356 * details on the usage of the next variable.
1358 arrived_in_time
= ktime_get_ns() <=
1359 bfqq
->ttime
.last_end_request
+
1360 bfqd
->bfq_slice_idle
* 3;
1362 bfqg_stats_update_io_add(bfqq_group(RQ_BFQQ(rq
)), bfqq
, rq
->cmd_flags
);
1365 * bfqq deserves to be weight-raised if:
1367 * - it does not belong to a large burst,
1368 * - it has been idle for enough time or is soft real-time,
1369 * - is linked to a bfq_io_cq (it is not shared in any sense).
1371 in_burst
= bfq_bfqq_in_large_burst(bfqq
);
1372 soft_rt
= bfqd
->bfq_wr_max_softrt_rate
> 0 &&
1374 time_is_before_jiffies(bfqq
->soft_rt_next_start
);
1375 *interactive
= !in_burst
&& idle_for_long_time
;
1376 wr_or_deserves_wr
= bfqd
->low_latency
&&
1377 (bfqq
->wr_coeff
> 1 ||
1378 (bfq_bfqq_sync(bfqq
) &&
1379 bfqq
->bic
&& (*interactive
|| soft_rt
)));
1382 * Using the last flag, update budget and check whether bfqq
1383 * may want to preempt the in-service queue.
1385 bfqq_wants_to_preempt
=
1386 bfq_bfqq_update_budg_for_activation(bfqd
, bfqq
,
1391 * If bfqq happened to be activated in a burst, but has been
1392 * idle for much more than an interactive queue, then we
1393 * assume that, in the overall I/O initiated in the burst, the
1394 * I/O associated with bfqq is finished. So bfqq does not need
1395 * to be treated as a queue belonging to a burst
1396 * anymore. Accordingly, we reset bfqq's in_large_burst flag
1397 * if set, and remove bfqq from the burst list if it's
1398 * there. We do not decrement burst_size, because the fact
1399 * that bfqq does not need to belong to the burst list any
1400 * more does not invalidate the fact that bfqq was created in
1403 if (likely(!bfq_bfqq_just_created(bfqq
)) &&
1404 idle_for_long_time
&&
1405 time_is_before_jiffies(
1406 bfqq
->budget_timeout
+
1407 msecs_to_jiffies(10000))) {
1408 hlist_del_init(&bfqq
->burst_list_node
);
1409 bfq_clear_bfqq_in_large_burst(bfqq
);
1412 bfq_clear_bfqq_just_created(bfqq
);
1415 if (!bfq_bfqq_IO_bound(bfqq
)) {
1416 if (arrived_in_time
) {
1417 bfqq
->requests_within_timer
++;
1418 if (bfqq
->requests_within_timer
>=
1419 bfqd
->bfq_requests_within_timer
)
1420 bfq_mark_bfqq_IO_bound(bfqq
);
1422 bfqq
->requests_within_timer
= 0;
1425 if (bfqd
->low_latency
) {
1426 if (unlikely(time_is_after_jiffies(bfqq
->split_time
)))
1429 jiffies
- bfqd
->bfq_wr_min_idle_time
- 1;
1431 if (time_is_before_jiffies(bfqq
->split_time
+
1432 bfqd
->bfq_wr_min_idle_time
)) {
1433 bfq_update_bfqq_wr_on_rq_arrival(bfqd
, bfqq
,
1440 if (old_wr_coeff
!= bfqq
->wr_coeff
)
1441 bfqq
->entity
.prio_changed
= 1;
1445 bfqq
->last_idle_bklogged
= jiffies
;
1446 bfqq
->service_from_backlogged
= 0;
1447 bfq_clear_bfqq_softrt_update(bfqq
);
1449 bfq_add_bfqq_busy(bfqd
, bfqq
);
1452 * Expire in-service queue only if preemption may be needed
1453 * for guarantees. In this respect, the function
1454 * next_queue_may_preempt just checks a simple, necessary
1455 * condition, and not a sufficient condition based on
1456 * timestamps. In fact, for the latter condition to be
1457 * evaluated, timestamps would need first to be updated, and
1458 * this operation is quite costly (see the comments on the
1459 * function bfq_bfqq_update_budg_for_activation).
1461 if (bfqd
->in_service_queue
&& bfqq_wants_to_preempt
&&
1462 bfqd
->in_service_queue
->wr_coeff
< bfqq
->wr_coeff
&&
1463 next_queue_may_preempt(bfqd
))
1464 bfq_bfqq_expire(bfqd
, bfqd
->in_service_queue
,
1465 false, BFQQE_PREEMPTED
);
1468 static void bfq_add_request(struct request
*rq
)
1470 struct bfq_queue
*bfqq
= RQ_BFQQ(rq
);
1471 struct bfq_data
*bfqd
= bfqq
->bfqd
;
1472 struct request
*next_rq
, *prev
;
1473 unsigned int old_wr_coeff
= bfqq
->wr_coeff
;
1474 bool interactive
= false;
1476 bfq_log_bfqq(bfqd
, bfqq
, "add_request %d", rq_is_sync(rq
));
1477 bfqq
->queued
[rq_is_sync(rq
)]++;
1480 elv_rb_add(&bfqq
->sort_list
, rq
);
1483 * Check if this request is a better next-serve candidate.
1485 prev
= bfqq
->next_rq
;
1486 next_rq
= bfq_choose_req(bfqd
, bfqq
->next_rq
, rq
, bfqd
->last_position
);
1487 bfqq
->next_rq
= next_rq
;
1490 * Adjust priority tree position, if next_rq changes.
1492 if (prev
!= bfqq
->next_rq
)
1493 bfq_pos_tree_add_move(bfqd
, bfqq
);
1495 if (!bfq_bfqq_busy(bfqq
)) /* switching to busy ... */
1496 bfq_bfqq_handle_idle_busy_switch(bfqd
, bfqq
, old_wr_coeff
,
1499 if (bfqd
->low_latency
&& old_wr_coeff
== 1 && !rq_is_sync(rq
) &&
1500 time_is_before_jiffies(
1501 bfqq
->last_wr_start_finish
+
1502 bfqd
->bfq_wr_min_inter_arr_async
)) {
1503 bfqq
->wr_coeff
= bfqd
->bfq_wr_coeff
;
1504 bfqq
->wr_cur_max_time
= bfq_wr_duration(bfqd
);
1506 bfqd
->wr_busy_queues
++;
1507 bfqq
->entity
.prio_changed
= 1;
1509 if (prev
!= bfqq
->next_rq
)
1510 bfq_updated_next_req(bfqd
, bfqq
);
1514 * Assign jiffies to last_wr_start_finish in the following
1517 * . if bfqq is not going to be weight-raised, because, for
1518 * non weight-raised queues, last_wr_start_finish stores the
1519 * arrival time of the last request; as of now, this piece
1520 * of information is used only for deciding whether to
1521 * weight-raise async queues
1523 * . if bfqq is not weight-raised, because, if bfqq is now
1524 * switching to weight-raised, then last_wr_start_finish
1525 * stores the time when weight-raising starts
1527 * . if bfqq is interactive, because, regardless of whether
1528 * bfqq is currently weight-raised, the weight-raising
1529 * period must start or restart (this case is considered
1530 * separately because it is not detected by the above
1531 * conditions, if bfqq is already weight-raised)
1533 * last_wr_start_finish has to be updated also if bfqq is soft
1534 * real-time, because the weight-raising period is constantly
1535 * restarted on idle-to-busy transitions for these queues, but
1536 * this is already done in bfq_bfqq_handle_idle_busy_switch if
1539 if (bfqd
->low_latency
&&
1540 (old_wr_coeff
== 1 || bfqq
->wr_coeff
== 1 || interactive
))
1541 bfqq
->last_wr_start_finish
= jiffies
;
1544 static struct request
*bfq_find_rq_fmerge(struct bfq_data
*bfqd
,
1546 struct request_queue
*q
)
1548 struct bfq_queue
*bfqq
= bfqd
->bio_bfqq
;
1552 return elv_rb_find(&bfqq
->sort_list
, bio_end_sector(bio
));
1557 static sector_t
get_sdist(sector_t last_pos
, struct request
*rq
)
1560 return abs(blk_rq_pos(rq
) - last_pos
);
1565 #if 0 /* Still not clear if we can do without next two functions */
1566 static void bfq_activate_request(struct request_queue
*q
, struct request
*rq
)
1568 struct bfq_data
*bfqd
= q
->elevator
->elevator_data
;
1570 bfqd
->rq_in_driver
++;
1573 static void bfq_deactivate_request(struct request_queue
*q
, struct request
*rq
)
1575 struct bfq_data
*bfqd
= q
->elevator
->elevator_data
;
1577 bfqd
->rq_in_driver
--;
1581 static void bfq_remove_request(struct request_queue
*q
,
1584 struct bfq_queue
*bfqq
= RQ_BFQQ(rq
);
1585 struct bfq_data
*bfqd
= bfqq
->bfqd
;
1586 const int sync
= rq_is_sync(rq
);
1588 if (bfqq
->next_rq
== rq
) {
1589 bfqq
->next_rq
= bfq_find_next_rq(bfqd
, bfqq
, rq
);
1590 bfq_updated_next_req(bfqd
, bfqq
);
1593 if (rq
->queuelist
.prev
!= &rq
->queuelist
)
1594 list_del_init(&rq
->queuelist
);
1595 bfqq
->queued
[sync
]--;
1597 elv_rb_del(&bfqq
->sort_list
, rq
);
1599 elv_rqhash_del(q
, rq
);
1600 if (q
->last_merge
== rq
)
1601 q
->last_merge
= NULL
;
1603 if (RB_EMPTY_ROOT(&bfqq
->sort_list
)) {
1604 bfqq
->next_rq
= NULL
;
1606 if (bfq_bfqq_busy(bfqq
) && bfqq
!= bfqd
->in_service_queue
) {
1607 bfq_del_bfqq_busy(bfqd
, bfqq
, false);
1609 * bfqq emptied. In normal operation, when
1610 * bfqq is empty, bfqq->entity.service and
1611 * bfqq->entity.budget must contain,
1612 * respectively, the service received and the
1613 * budget used last time bfqq emptied. These
1614 * facts do not hold in this case, as at least
1615 * this last removal occurred while bfqq is
1616 * not in service. To avoid inconsistencies,
1617 * reset both bfqq->entity.service and
1618 * bfqq->entity.budget, if bfqq has still a
1619 * process that may issue I/O requests to it.
1621 bfqq
->entity
.budget
= bfqq
->entity
.service
= 0;
1625 * Remove queue from request-position tree as it is empty.
1627 if (bfqq
->pos_root
) {
1628 rb_erase(&bfqq
->pos_node
, bfqq
->pos_root
);
1629 bfqq
->pos_root
= NULL
;
1633 if (rq
->cmd_flags
& REQ_META
)
1634 bfqq
->meta_pending
--;
1636 bfqg_stats_update_io_remove(bfqq_group(bfqq
), rq
->cmd_flags
);
1639 static bool bfq_bio_merge(struct blk_mq_hw_ctx
*hctx
, struct bio
*bio
)
1641 struct request_queue
*q
= hctx
->queue
;
1642 struct bfq_data
*bfqd
= q
->elevator
->elevator_data
;
1643 struct request
*free
= NULL
;
1645 * bfq_bic_lookup grabs the queue_lock: invoke it now and
1646 * store its return value for later use, to avoid nesting
1647 * queue_lock inside the bfqd->lock. We assume that the bic
1648 * returned by bfq_bic_lookup does not go away before
1649 * bfqd->lock is taken.
1651 struct bfq_io_cq
*bic
= bfq_bic_lookup(bfqd
, current
->io_context
, q
);
1654 spin_lock_irq(&bfqd
->lock
);
1657 bfqd
->bio_bfqq
= bic_to_bfqq(bic
, op_is_sync(bio
->bi_opf
));
1659 bfqd
->bio_bfqq
= NULL
;
1660 bfqd
->bio_bic
= bic
;
1662 ret
= blk_mq_sched_try_merge(q
, bio
, &free
);
1665 blk_mq_free_request(free
);
1666 spin_unlock_irq(&bfqd
->lock
);
1671 static int bfq_request_merge(struct request_queue
*q
, struct request
**req
,
1674 struct bfq_data
*bfqd
= q
->elevator
->elevator_data
;
1675 struct request
*__rq
;
1677 __rq
= bfq_find_rq_fmerge(bfqd
, bio
, q
);
1678 if (__rq
&& elv_bio_merge_ok(__rq
, bio
)) {
1680 return ELEVATOR_FRONT_MERGE
;
1683 return ELEVATOR_NO_MERGE
;
1686 static void bfq_request_merged(struct request_queue
*q
, struct request
*req
,
1687 enum elv_merge type
)
1689 if (type
== ELEVATOR_FRONT_MERGE
&&
1690 rb_prev(&req
->rb_node
) &&
1692 blk_rq_pos(container_of(rb_prev(&req
->rb_node
),
1693 struct request
, rb_node
))) {
1694 struct bfq_queue
*bfqq
= RQ_BFQQ(req
);
1695 struct bfq_data
*bfqd
= bfqq
->bfqd
;
1696 struct request
*prev
, *next_rq
;
1698 /* Reposition request in its sort_list */
1699 elv_rb_del(&bfqq
->sort_list
, req
);
1700 elv_rb_add(&bfqq
->sort_list
, req
);
1702 /* Choose next request to be served for bfqq */
1703 prev
= bfqq
->next_rq
;
1704 next_rq
= bfq_choose_req(bfqd
, bfqq
->next_rq
, req
,
1705 bfqd
->last_position
);
1706 bfqq
->next_rq
= next_rq
;
1708 * If next_rq changes, update both the queue's budget to
1709 * fit the new request and the queue's position in its
1712 if (prev
!= bfqq
->next_rq
) {
1713 bfq_updated_next_req(bfqd
, bfqq
);
1714 bfq_pos_tree_add_move(bfqd
, bfqq
);
1719 static void bfq_requests_merged(struct request_queue
*q
, struct request
*rq
,
1720 struct request
*next
)
1722 struct bfq_queue
*bfqq
= RQ_BFQQ(rq
), *next_bfqq
= RQ_BFQQ(next
);
1724 if (!RB_EMPTY_NODE(&rq
->rb_node
))
1726 spin_lock_irq(&bfqq
->bfqd
->lock
);
1729 * If next and rq belong to the same bfq_queue and next is older
1730 * than rq, then reposition rq in the fifo (by substituting next
1731 * with rq). Otherwise, if next and rq belong to different
1732 * bfq_queues, never reposition rq: in fact, we would have to
1733 * reposition it with respect to next's position in its own fifo,
1734 * which would most certainly be too expensive with respect to
1737 if (bfqq
== next_bfqq
&&
1738 !list_empty(&rq
->queuelist
) && !list_empty(&next
->queuelist
) &&
1739 next
->fifo_time
< rq
->fifo_time
) {
1740 list_del_init(&rq
->queuelist
);
1741 list_replace_init(&next
->queuelist
, &rq
->queuelist
);
1742 rq
->fifo_time
= next
->fifo_time
;
1745 if (bfqq
->next_rq
== next
)
1748 bfq_remove_request(q
, next
);
1750 spin_unlock_irq(&bfqq
->bfqd
->lock
);
1752 bfqg_stats_update_io_merged(bfqq_group(bfqq
), next
->cmd_flags
);
1755 /* Must be called with bfqq != NULL */
1756 static void bfq_bfqq_end_wr(struct bfq_queue
*bfqq
)
1758 if (bfq_bfqq_busy(bfqq
))
1759 bfqq
->bfqd
->wr_busy_queues
--;
1761 bfqq
->wr_cur_max_time
= 0;
1762 bfqq
->last_wr_start_finish
= jiffies
;
1764 * Trigger a weight change on the next invocation of
1765 * __bfq_entity_update_weight_prio.
1767 bfqq
->entity
.prio_changed
= 1;
1770 void bfq_end_wr_async_queues(struct bfq_data
*bfqd
,
1771 struct bfq_group
*bfqg
)
1775 for (i
= 0; i
< 2; i
++)
1776 for (j
= 0; j
< IOPRIO_BE_NR
; j
++)
1777 if (bfqg
->async_bfqq
[i
][j
])
1778 bfq_bfqq_end_wr(bfqg
->async_bfqq
[i
][j
]);
1779 if (bfqg
->async_idle_bfqq
)
1780 bfq_bfqq_end_wr(bfqg
->async_idle_bfqq
);
1783 static void bfq_end_wr(struct bfq_data
*bfqd
)
1785 struct bfq_queue
*bfqq
;
1787 spin_lock_irq(&bfqd
->lock
);
1789 list_for_each_entry(bfqq
, &bfqd
->active_list
, bfqq_list
)
1790 bfq_bfqq_end_wr(bfqq
);
1791 list_for_each_entry(bfqq
, &bfqd
->idle_list
, bfqq_list
)
1792 bfq_bfqq_end_wr(bfqq
);
1793 bfq_end_wr_async(bfqd
);
1795 spin_unlock_irq(&bfqd
->lock
);
1798 static sector_t
bfq_io_struct_pos(void *io_struct
, bool request
)
1801 return blk_rq_pos(io_struct
);
1803 return ((struct bio
*)io_struct
)->bi_iter
.bi_sector
;
1806 static int bfq_rq_close_to_sector(void *io_struct
, bool request
,
1809 return abs(bfq_io_struct_pos(io_struct
, request
) - sector
) <=
1813 static struct bfq_queue
*bfqq_find_close(struct bfq_data
*bfqd
,
1814 struct bfq_queue
*bfqq
,
1817 struct rb_root
*root
= &bfq_bfqq_to_bfqg(bfqq
)->rq_pos_tree
;
1818 struct rb_node
*parent
, *node
;
1819 struct bfq_queue
*__bfqq
;
1821 if (RB_EMPTY_ROOT(root
))
1825 * First, if we find a request starting at the end of the last
1826 * request, choose it.
1828 __bfqq
= bfq_rq_pos_tree_lookup(bfqd
, root
, sector
, &parent
, NULL
);
1833 * If the exact sector wasn't found, the parent of the NULL leaf
1834 * will contain the closest sector (rq_pos_tree sorted by
1835 * next_request position).
1837 __bfqq
= rb_entry(parent
, struct bfq_queue
, pos_node
);
1838 if (bfq_rq_close_to_sector(__bfqq
->next_rq
, true, sector
))
1841 if (blk_rq_pos(__bfqq
->next_rq
) < sector
)
1842 node
= rb_next(&__bfqq
->pos_node
);
1844 node
= rb_prev(&__bfqq
->pos_node
);
1848 __bfqq
= rb_entry(node
, struct bfq_queue
, pos_node
);
1849 if (bfq_rq_close_to_sector(__bfqq
->next_rq
, true, sector
))
1855 static struct bfq_queue
*bfq_find_close_cooperator(struct bfq_data
*bfqd
,
1856 struct bfq_queue
*cur_bfqq
,
1859 struct bfq_queue
*bfqq
;
1862 * We shall notice if some of the queues are cooperating,
1863 * e.g., working closely on the same area of the device. In
1864 * that case, we can group them together and: 1) don't waste
1865 * time idling, and 2) serve the union of their requests in
1866 * the best possible order for throughput.
1868 bfqq
= bfqq_find_close(bfqd
, cur_bfqq
, sector
);
1869 if (!bfqq
|| bfqq
== cur_bfqq
)
1875 static struct bfq_queue
*
1876 bfq_setup_merge(struct bfq_queue
*bfqq
, struct bfq_queue
*new_bfqq
)
1878 int process_refs
, new_process_refs
;
1879 struct bfq_queue
*__bfqq
;
1882 * If there are no process references on the new_bfqq, then it is
1883 * unsafe to follow the ->new_bfqq chain as other bfqq's in the chain
1884 * may have dropped their last reference (not just their last process
1887 if (!bfqq_process_refs(new_bfqq
))
1890 /* Avoid a circular list and skip interim queue merges. */
1891 while ((__bfqq
= new_bfqq
->new_bfqq
)) {
1897 process_refs
= bfqq_process_refs(bfqq
);
1898 new_process_refs
= bfqq_process_refs(new_bfqq
);
1900 * If the process for the bfqq has gone away, there is no
1901 * sense in merging the queues.
1903 if (process_refs
== 0 || new_process_refs
== 0)
1906 bfq_log_bfqq(bfqq
->bfqd
, bfqq
, "scheduling merge with queue %d",
1910 * Merging is just a redirection: the requests of the process
1911 * owning one of the two queues are redirected to the other queue.
1912 * The latter queue, in its turn, is set as shared if this is the
1913 * first time that the requests of some process are redirected to
1916 * We redirect bfqq to new_bfqq and not the opposite, because
1917 * we are in the context of the process owning bfqq, thus we
1918 * have the io_cq of this process. So we can immediately
1919 * configure this io_cq to redirect the requests of the
1920 * process to new_bfqq. In contrast, the io_cq of new_bfqq is
1921 * not available any more (new_bfqq->bic == NULL).
1923 * Anyway, even in case new_bfqq coincides with the in-service
1924 * queue, redirecting requests the in-service queue is the
1925 * best option, as we feed the in-service queue with new
1926 * requests close to the last request served and, by doing so,
1927 * are likely to increase the throughput.
1929 bfqq
->new_bfqq
= new_bfqq
;
1930 new_bfqq
->ref
+= process_refs
;
1934 static bool bfq_may_be_close_cooperator(struct bfq_queue
*bfqq
,
1935 struct bfq_queue
*new_bfqq
)
1937 if (bfq_class_idle(bfqq
) || bfq_class_idle(new_bfqq
) ||
1938 (bfqq
->ioprio_class
!= new_bfqq
->ioprio_class
))
1942 * If either of the queues has already been detected as seeky,
1943 * then merging it with the other queue is unlikely to lead to
1946 if (BFQQ_SEEKY(bfqq
) || BFQQ_SEEKY(new_bfqq
))
1950 * Interleaved I/O is known to be done by (some) applications
1951 * only for reads, so it does not make sense to merge async
1954 if (!bfq_bfqq_sync(bfqq
) || !bfq_bfqq_sync(new_bfqq
))
1961 * If this function returns true, then bfqq cannot be merged. The idea
1962 * is that true cooperation happens very early after processes start
1963 * to do I/O. Usually, late cooperations are just accidental false
1964 * positives. In case bfqq is weight-raised, such false positives
1965 * would evidently degrade latency guarantees for bfqq.
1967 static bool wr_from_too_long(struct bfq_queue
*bfqq
)
1969 return bfqq
->wr_coeff
> 1 &&
1970 time_is_before_jiffies(bfqq
->last_wr_start_finish
+
1971 msecs_to_jiffies(100));
1975 * Attempt to schedule a merge of bfqq with the currently in-service
1976 * queue or with a close queue among the scheduled queues. Return
1977 * NULL if no merge was scheduled, a pointer to the shared bfq_queue
1978 * structure otherwise.
1980 * The OOM queue is not allowed to participate to cooperation: in fact, since
1981 * the requests temporarily redirected to the OOM queue could be redirected
1982 * again to dedicated queues at any time, the state needed to correctly
1983 * handle merging with the OOM queue would be quite complex and expensive
1984 * to maintain. Besides, in such a critical condition as an out of memory,
1985 * the benefits of queue merging may be little relevant, or even negligible.
1987 * Weight-raised queues can be merged only if their weight-raising
1988 * period has just started. In fact cooperating processes are usually
1989 * started together. Thus, with this filter we avoid false positives
1990 * that would jeopardize low-latency guarantees.
1992 * WARNING: queue merging may impair fairness among non-weight raised
1993 * queues, for at least two reasons: 1) the original weight of a
1994 * merged queue may change during the merged state, 2) even being the
1995 * weight the same, a merged queue may be bloated with many more
1996 * requests than the ones produced by its originally-associated
1999 static struct bfq_queue
*
2000 bfq_setup_cooperator(struct bfq_data
*bfqd
, struct bfq_queue
*bfqq
,
2001 void *io_struct
, bool request
)
2003 struct bfq_queue
*in_service_bfqq
, *new_bfqq
;
2006 return bfqq
->new_bfqq
;
2009 wr_from_too_long(bfqq
) ||
2010 unlikely(bfqq
== &bfqd
->oom_bfqq
))
2013 /* If there is only one backlogged queue, don't search. */
2014 if (bfqd
->busy_queues
== 1)
2017 in_service_bfqq
= bfqd
->in_service_queue
;
2019 if (!in_service_bfqq
|| in_service_bfqq
== bfqq
2020 || wr_from_too_long(in_service_bfqq
) ||
2021 unlikely(in_service_bfqq
== &bfqd
->oom_bfqq
))
2022 goto check_scheduled
;
2024 if (bfq_rq_close_to_sector(io_struct
, request
, bfqd
->last_position
) &&
2025 bfqq
->entity
.parent
== in_service_bfqq
->entity
.parent
&&
2026 bfq_may_be_close_cooperator(bfqq
, in_service_bfqq
)) {
2027 new_bfqq
= bfq_setup_merge(bfqq
, in_service_bfqq
);
2032 * Check whether there is a cooperator among currently scheduled
2033 * queues. The only thing we need is that the bio/request is not
2034 * NULL, as we need it to establish whether a cooperator exists.
2037 new_bfqq
= bfq_find_close_cooperator(bfqd
, bfqq
,
2038 bfq_io_struct_pos(io_struct
, request
));
2040 if (new_bfqq
&& !wr_from_too_long(new_bfqq
) &&
2041 likely(new_bfqq
!= &bfqd
->oom_bfqq
) &&
2042 bfq_may_be_close_cooperator(bfqq
, new_bfqq
))
2043 return bfq_setup_merge(bfqq
, new_bfqq
);
2048 static void bfq_bfqq_save_state(struct bfq_queue
*bfqq
)
2050 struct bfq_io_cq
*bic
= bfqq
->bic
;
2053 * If !bfqq->bic, the queue is already shared or its requests
2054 * have already been redirected to a shared queue; both idle window
2055 * and weight raising state have already been saved. Do nothing.
2060 bic
->saved_ttime
= bfqq
->ttime
;
2061 bic
->saved_has_short_ttime
= bfq_bfqq_has_short_ttime(bfqq
);
2062 bic
->saved_IO_bound
= bfq_bfqq_IO_bound(bfqq
);
2063 bic
->saved_in_large_burst
= bfq_bfqq_in_large_burst(bfqq
);
2064 bic
->was_in_burst_list
= !hlist_unhashed(&bfqq
->burst_list_node
);
2065 if (unlikely(bfq_bfqq_just_created(bfqq
) &&
2066 !bfq_bfqq_in_large_burst(bfqq
))) {
2068 * bfqq being merged right after being created: bfqq
2069 * would have deserved interactive weight raising, but
2070 * did not make it to be set in a weight-raised state,
2071 * because of this early merge. Store directly the
2072 * weight-raising state that would have been assigned
2073 * to bfqq, so that to avoid that bfqq unjustly fails
2074 * to enjoy weight raising if split soon.
2076 bic
->saved_wr_coeff
= bfqq
->bfqd
->bfq_wr_coeff
;
2077 bic
->saved_wr_cur_max_time
= bfq_wr_duration(bfqq
->bfqd
);
2078 bic
->saved_last_wr_start_finish
= jiffies
;
2080 bic
->saved_wr_coeff
= bfqq
->wr_coeff
;
2081 bic
->saved_wr_start_at_switch_to_srt
=
2082 bfqq
->wr_start_at_switch_to_srt
;
2083 bic
->saved_last_wr_start_finish
= bfqq
->last_wr_start_finish
;
2084 bic
->saved_wr_cur_max_time
= bfqq
->wr_cur_max_time
;
2089 bfq_merge_bfqqs(struct bfq_data
*bfqd
, struct bfq_io_cq
*bic
,
2090 struct bfq_queue
*bfqq
, struct bfq_queue
*new_bfqq
)
2092 bfq_log_bfqq(bfqd
, bfqq
, "merging with queue %lu",
2093 (unsigned long)new_bfqq
->pid
);
2094 /* Save weight raising and idle window of the merged queues */
2095 bfq_bfqq_save_state(bfqq
);
2096 bfq_bfqq_save_state(new_bfqq
);
2097 if (bfq_bfqq_IO_bound(bfqq
))
2098 bfq_mark_bfqq_IO_bound(new_bfqq
);
2099 bfq_clear_bfqq_IO_bound(bfqq
);
2102 * If bfqq is weight-raised, then let new_bfqq inherit
2103 * weight-raising. To reduce false positives, neglect the case
2104 * where bfqq has just been created, but has not yet made it
2105 * to be weight-raised (which may happen because EQM may merge
2106 * bfqq even before bfq_add_request is executed for the first
2107 * time for bfqq). Handling this case would however be very
2108 * easy, thanks to the flag just_created.
2110 if (new_bfqq
->wr_coeff
== 1 && bfqq
->wr_coeff
> 1) {
2111 new_bfqq
->wr_coeff
= bfqq
->wr_coeff
;
2112 new_bfqq
->wr_cur_max_time
= bfqq
->wr_cur_max_time
;
2113 new_bfqq
->last_wr_start_finish
= bfqq
->last_wr_start_finish
;
2114 new_bfqq
->wr_start_at_switch_to_srt
=
2115 bfqq
->wr_start_at_switch_to_srt
;
2116 if (bfq_bfqq_busy(new_bfqq
))
2117 bfqd
->wr_busy_queues
++;
2118 new_bfqq
->entity
.prio_changed
= 1;
2121 if (bfqq
->wr_coeff
> 1) { /* bfqq has given its wr to new_bfqq */
2123 bfqq
->entity
.prio_changed
= 1;
2124 if (bfq_bfqq_busy(bfqq
))
2125 bfqd
->wr_busy_queues
--;
2128 bfq_log_bfqq(bfqd
, new_bfqq
, "merge_bfqqs: wr_busy %d",
2129 bfqd
->wr_busy_queues
);
2132 * Merge queues (that is, let bic redirect its requests to new_bfqq)
2134 bic_set_bfqq(bic
, new_bfqq
, 1);
2135 bfq_mark_bfqq_coop(new_bfqq
);
2137 * new_bfqq now belongs to at least two bics (it is a shared queue):
2138 * set new_bfqq->bic to NULL. bfqq either:
2139 * - does not belong to any bic any more, and hence bfqq->bic must
2140 * be set to NULL, or
2141 * - is a queue whose owning bics have already been redirected to a
2142 * different queue, hence the queue is destined to not belong to
2143 * any bic soon and bfqq->bic is already NULL (therefore the next
2144 * assignment causes no harm).
2146 new_bfqq
->bic
= NULL
;
2148 /* release process reference to bfqq */
2149 bfq_put_queue(bfqq
);
2152 static bool bfq_allow_bio_merge(struct request_queue
*q
, struct request
*rq
,
2155 struct bfq_data
*bfqd
= q
->elevator
->elevator_data
;
2156 bool is_sync
= op_is_sync(bio
->bi_opf
);
2157 struct bfq_queue
*bfqq
= bfqd
->bio_bfqq
, *new_bfqq
;
2160 * Disallow merge of a sync bio into an async request.
2162 if (is_sync
&& !rq_is_sync(rq
))
2166 * Lookup the bfqq that this bio will be queued with. Allow
2167 * merge only if rq is queued there.
2173 * We take advantage of this function to perform an early merge
2174 * of the queues of possible cooperating processes.
2176 new_bfqq
= bfq_setup_cooperator(bfqd
, bfqq
, bio
, false);
2179 * bic still points to bfqq, then it has not yet been
2180 * redirected to some other bfq_queue, and a queue
2181 * merge beween bfqq and new_bfqq can be safely
2182 * fulfillled, i.e., bic can be redirected to new_bfqq
2183 * and bfqq can be put.
2185 bfq_merge_bfqqs(bfqd
, bfqd
->bio_bic
, bfqq
,
2188 * If we get here, bio will be queued into new_queue,
2189 * so use new_bfqq to decide whether bio and rq can be
2195 * Change also bqfd->bio_bfqq, as
2196 * bfqd->bio_bic now points to new_bfqq, and
2197 * this function may be invoked again (and then may
2198 * use again bqfd->bio_bfqq).
2200 bfqd
->bio_bfqq
= bfqq
;
2203 return bfqq
== RQ_BFQQ(rq
);
2207 * Set the maximum time for the in-service queue to consume its
2208 * budget. This prevents seeky processes from lowering the throughput.
2209 * In practice, a time-slice service scheme is used with seeky
2212 static void bfq_set_budget_timeout(struct bfq_data
*bfqd
,
2213 struct bfq_queue
*bfqq
)
2215 unsigned int timeout_coeff
;
2217 if (bfqq
->wr_cur_max_time
== bfqd
->bfq_wr_rt_max_time
)
2220 timeout_coeff
= bfqq
->entity
.weight
/ bfqq
->entity
.orig_weight
;
2222 bfqd
->last_budget_start
= ktime_get();
2224 bfqq
->budget_timeout
= jiffies
+
2225 bfqd
->bfq_timeout
* timeout_coeff
;
2228 static void __bfq_set_in_service_queue(struct bfq_data
*bfqd
,
2229 struct bfq_queue
*bfqq
)
2232 bfqg_stats_update_avg_queue_size(bfqq_group(bfqq
));
2233 bfq_clear_bfqq_fifo_expire(bfqq
);
2235 bfqd
->budgets_assigned
= (bfqd
->budgets_assigned
* 7 + 256) / 8;
2237 if (time_is_before_jiffies(bfqq
->last_wr_start_finish
) &&
2238 bfqq
->wr_coeff
> 1 &&
2239 bfqq
->wr_cur_max_time
== bfqd
->bfq_wr_rt_max_time
&&
2240 time_is_before_jiffies(bfqq
->budget_timeout
)) {
2242 * For soft real-time queues, move the start
2243 * of the weight-raising period forward by the
2244 * time the queue has not received any
2245 * service. Otherwise, a relatively long
2246 * service delay is likely to cause the
2247 * weight-raising period of the queue to end,
2248 * because of the short duration of the
2249 * weight-raising period of a soft real-time
2250 * queue. It is worth noting that this move
2251 * is not so dangerous for the other queues,
2252 * because soft real-time queues are not
2255 * To not add a further variable, we use the
2256 * overloaded field budget_timeout to
2257 * determine for how long the queue has not
2258 * received service, i.e., how much time has
2259 * elapsed since the queue expired. However,
2260 * this is a little imprecise, because
2261 * budget_timeout is set to jiffies if bfqq
2262 * not only expires, but also remains with no
2265 if (time_after(bfqq
->budget_timeout
,
2266 bfqq
->last_wr_start_finish
))
2267 bfqq
->last_wr_start_finish
+=
2268 jiffies
- bfqq
->budget_timeout
;
2270 bfqq
->last_wr_start_finish
= jiffies
;
2273 bfq_set_budget_timeout(bfqd
, bfqq
);
2274 bfq_log_bfqq(bfqd
, bfqq
,
2275 "set_in_service_queue, cur-budget = %d",
2276 bfqq
->entity
.budget
);
2279 bfqd
->in_service_queue
= bfqq
;
2283 * Get and set a new queue for service.
2285 static struct bfq_queue
*bfq_set_in_service_queue(struct bfq_data
*bfqd
)
2287 struct bfq_queue
*bfqq
= bfq_get_next_queue(bfqd
);
2289 __bfq_set_in_service_queue(bfqd
, bfqq
);
2293 static void bfq_arm_slice_timer(struct bfq_data
*bfqd
)
2295 struct bfq_queue
*bfqq
= bfqd
->in_service_queue
;
2298 bfq_mark_bfqq_wait_request(bfqq
);
2301 * We don't want to idle for seeks, but we do want to allow
2302 * fair distribution of slice time for a process doing back-to-back
2303 * seeks. So allow a little bit of time for him to submit a new rq.
2305 sl
= bfqd
->bfq_slice_idle
;
2307 * Unless the queue is being weight-raised or the scenario is
2308 * asymmetric, grant only minimum idle time if the queue
2309 * is seeky. A long idling is preserved for a weight-raised
2310 * queue, or, more in general, in an asymmetric scenario,
2311 * because a long idling is needed for guaranteeing to a queue
2312 * its reserved share of the throughput (in particular, it is
2313 * needed if the queue has a higher weight than some other
2316 if (BFQQ_SEEKY(bfqq
) && bfqq
->wr_coeff
== 1 &&
2317 bfq_symmetric_scenario(bfqd
))
2318 sl
= min_t(u64
, sl
, BFQ_MIN_TT
);
2320 bfqd
->last_idling_start
= ktime_get();
2321 hrtimer_start(&bfqd
->idle_slice_timer
, ns_to_ktime(sl
),
2323 bfqg_stats_set_start_idle_time(bfqq_group(bfqq
));
2327 * In autotuning mode, max_budget is dynamically recomputed as the
2328 * amount of sectors transferred in timeout at the estimated peak
2329 * rate. This enables BFQ to utilize a full timeslice with a full
2330 * budget, even if the in-service queue is served at peak rate. And
2331 * this maximises throughput with sequential workloads.
2333 static unsigned long bfq_calc_max_budget(struct bfq_data
*bfqd
)
2335 return (u64
)bfqd
->peak_rate
* USEC_PER_MSEC
*
2336 jiffies_to_msecs(bfqd
->bfq_timeout
)>>BFQ_RATE_SHIFT
;
2340 * Update parameters related to throughput and responsiveness, as a
2341 * function of the estimated peak rate. See comments on
2342 * bfq_calc_max_budget(), and on T_slow and T_fast arrays.
2344 static void update_thr_responsiveness_params(struct bfq_data
*bfqd
)
2346 int dev_type
= blk_queue_nonrot(bfqd
->queue
);
2348 if (bfqd
->bfq_user_max_budget
== 0)
2349 bfqd
->bfq_max_budget
=
2350 bfq_calc_max_budget(bfqd
);
2352 if (bfqd
->device_speed
== BFQ_BFQD_FAST
&&
2353 bfqd
->peak_rate
< device_speed_thresh
[dev_type
]) {
2354 bfqd
->device_speed
= BFQ_BFQD_SLOW
;
2355 bfqd
->RT_prod
= R_slow
[dev_type
] *
2357 } else if (bfqd
->device_speed
== BFQ_BFQD_SLOW
&&
2358 bfqd
->peak_rate
> device_speed_thresh
[dev_type
]) {
2359 bfqd
->device_speed
= BFQ_BFQD_FAST
;
2360 bfqd
->RT_prod
= R_fast
[dev_type
] *
2365 "dev_type %s dev_speed_class = %s (%llu sects/sec), thresh %llu setcs/sec",
2366 dev_type
== 0 ? "ROT" : "NONROT",
2367 bfqd
->device_speed
== BFQ_BFQD_FAST
? "FAST" : "SLOW",
2368 bfqd
->device_speed
== BFQ_BFQD_FAST
?
2369 (USEC_PER_SEC
*(u64
)R_fast
[dev_type
])>>BFQ_RATE_SHIFT
:
2370 (USEC_PER_SEC
*(u64
)R_slow
[dev_type
])>>BFQ_RATE_SHIFT
,
2371 (USEC_PER_SEC
*(u64
)device_speed_thresh
[dev_type
])>>
2375 static void bfq_reset_rate_computation(struct bfq_data
*bfqd
,
2378 if (rq
!= NULL
) { /* new rq dispatch now, reset accordingly */
2379 bfqd
->last_dispatch
= bfqd
->first_dispatch
= ktime_get_ns();
2380 bfqd
->peak_rate_samples
= 1;
2381 bfqd
->sequential_samples
= 0;
2382 bfqd
->tot_sectors_dispatched
= bfqd
->last_rq_max_size
=
2384 } else /* no new rq dispatched, just reset the number of samples */
2385 bfqd
->peak_rate_samples
= 0; /* full re-init on next disp. */
2388 "reset_rate_computation at end, sample %u/%u tot_sects %llu",
2389 bfqd
->peak_rate_samples
, bfqd
->sequential_samples
,
2390 bfqd
->tot_sectors_dispatched
);
2393 static void bfq_update_rate_reset(struct bfq_data
*bfqd
, struct request
*rq
)
2395 u32 rate
, weight
, divisor
;
2398 * For the convergence property to hold (see comments on
2399 * bfq_update_peak_rate()) and for the assessment to be
2400 * reliable, a minimum number of samples must be present, and
2401 * a minimum amount of time must have elapsed. If not so, do
2402 * not compute new rate. Just reset parameters, to get ready
2403 * for a new evaluation attempt.
2405 if (bfqd
->peak_rate_samples
< BFQ_RATE_MIN_SAMPLES
||
2406 bfqd
->delta_from_first
< BFQ_RATE_MIN_INTERVAL
)
2407 goto reset_computation
;
2410 * If a new request completion has occurred after last
2411 * dispatch, then, to approximate the rate at which requests
2412 * have been served by the device, it is more precise to
2413 * extend the observation interval to the last completion.
2415 bfqd
->delta_from_first
=
2416 max_t(u64
, bfqd
->delta_from_first
,
2417 bfqd
->last_completion
- bfqd
->first_dispatch
);
2420 * Rate computed in sects/usec, and not sects/nsec, for
2423 rate
= div64_ul(bfqd
->tot_sectors_dispatched
<<BFQ_RATE_SHIFT
,
2424 div_u64(bfqd
->delta_from_first
, NSEC_PER_USEC
));
2427 * Peak rate not updated if:
2428 * - the percentage of sequential dispatches is below 3/4 of the
2429 * total, and rate is below the current estimated peak rate
2430 * - rate is unreasonably high (> 20M sectors/sec)
2432 if ((bfqd
->sequential_samples
< (3 * bfqd
->peak_rate_samples
)>>2 &&
2433 rate
<= bfqd
->peak_rate
) ||
2434 rate
> 20<<BFQ_RATE_SHIFT
)
2435 goto reset_computation
;
2438 * We have to update the peak rate, at last! To this purpose,
2439 * we use a low-pass filter. We compute the smoothing constant
2440 * of the filter as a function of the 'weight' of the new
2443 * As can be seen in next formulas, we define this weight as a
2444 * quantity proportional to how sequential the workload is,
2445 * and to how long the observation time interval is.
2447 * The weight runs from 0 to 8. The maximum value of the
2448 * weight, 8, yields the minimum value for the smoothing
2449 * constant. At this minimum value for the smoothing constant,
2450 * the measured rate contributes for half of the next value of
2451 * the estimated peak rate.
2453 * So, the first step is to compute the weight as a function
2454 * of how sequential the workload is. Note that the weight
2455 * cannot reach 9, because bfqd->sequential_samples cannot
2456 * become equal to bfqd->peak_rate_samples, which, in its
2457 * turn, holds true because bfqd->sequential_samples is not
2458 * incremented for the first sample.
2460 weight
= (9 * bfqd
->sequential_samples
) / bfqd
->peak_rate_samples
;
2463 * Second step: further refine the weight as a function of the
2464 * duration of the observation interval.
2466 weight
= min_t(u32
, 8,
2467 div_u64(weight
* bfqd
->delta_from_first
,
2468 BFQ_RATE_REF_INTERVAL
));
2471 * Divisor ranging from 10, for minimum weight, to 2, for
2474 divisor
= 10 - weight
;
2477 * Finally, update peak rate:
2479 * peak_rate = peak_rate * (divisor-1) / divisor + rate / divisor
2481 bfqd
->peak_rate
*= divisor
-1;
2482 bfqd
->peak_rate
/= divisor
;
2483 rate
/= divisor
; /* smoothing constant alpha = 1/divisor */
2485 bfqd
->peak_rate
+= rate
;
2486 update_thr_responsiveness_params(bfqd
);
2489 bfq_reset_rate_computation(bfqd
, rq
);
2493 * Update the read/write peak rate (the main quantity used for
2494 * auto-tuning, see update_thr_responsiveness_params()).
2496 * It is not trivial to estimate the peak rate (correctly): because of
2497 * the presence of sw and hw queues between the scheduler and the
2498 * device components that finally serve I/O requests, it is hard to
2499 * say exactly when a given dispatched request is served inside the
2500 * device, and for how long. As a consequence, it is hard to know
2501 * precisely at what rate a given set of requests is actually served
2504 * On the opposite end, the dispatch time of any request is trivially
2505 * available, and, from this piece of information, the "dispatch rate"
2506 * of requests can be immediately computed. So, the idea in the next
2507 * function is to use what is known, namely request dispatch times
2508 * (plus, when useful, request completion times), to estimate what is
2509 * unknown, namely in-device request service rate.
2511 * The main issue is that, because of the above facts, the rate at
2512 * which a certain set of requests is dispatched over a certain time
2513 * interval can vary greatly with respect to the rate at which the
2514 * same requests are then served. But, since the size of any
2515 * intermediate queue is limited, and the service scheme is lossless
2516 * (no request is silently dropped), the following obvious convergence
2517 * property holds: the number of requests dispatched MUST become
2518 * closer and closer to the number of requests completed as the
2519 * observation interval grows. This is the key property used in
2520 * the next function to estimate the peak service rate as a function
2521 * of the observed dispatch rate. The function assumes to be invoked
2522 * on every request dispatch.
2524 static void bfq_update_peak_rate(struct bfq_data
*bfqd
, struct request
*rq
)
2526 u64 now_ns
= ktime_get_ns();
2528 if (bfqd
->peak_rate_samples
== 0) { /* first dispatch */
2529 bfq_log(bfqd
, "update_peak_rate: goto reset, samples %d",
2530 bfqd
->peak_rate_samples
);
2531 bfq_reset_rate_computation(bfqd
, rq
);
2532 goto update_last_values
; /* will add one sample */
2536 * Device idle for very long: the observation interval lasting
2537 * up to this dispatch cannot be a valid observation interval
2538 * for computing a new peak rate (similarly to the late-
2539 * completion event in bfq_completed_request()). Go to
2540 * update_rate_and_reset to have the following three steps
2542 * - close the observation interval at the last (previous)
2543 * request dispatch or completion
2544 * - compute rate, if possible, for that observation interval
2545 * - start a new observation interval with this dispatch
2547 if (now_ns
- bfqd
->last_dispatch
> 100*NSEC_PER_MSEC
&&
2548 bfqd
->rq_in_driver
== 0)
2549 goto update_rate_and_reset
;
2551 /* Update sampling information */
2552 bfqd
->peak_rate_samples
++;
2554 if ((bfqd
->rq_in_driver
> 0 ||
2555 now_ns
- bfqd
->last_completion
< BFQ_MIN_TT
)
2556 && get_sdist(bfqd
->last_position
, rq
) < BFQQ_SEEK_THR
)
2557 bfqd
->sequential_samples
++;
2559 bfqd
->tot_sectors_dispatched
+= blk_rq_sectors(rq
);
2561 /* Reset max observed rq size every 32 dispatches */
2562 if (likely(bfqd
->peak_rate_samples
% 32))
2563 bfqd
->last_rq_max_size
=
2564 max_t(u32
, blk_rq_sectors(rq
), bfqd
->last_rq_max_size
);
2566 bfqd
->last_rq_max_size
= blk_rq_sectors(rq
);
2568 bfqd
->delta_from_first
= now_ns
- bfqd
->first_dispatch
;
2570 /* Target observation interval not yet reached, go on sampling */
2571 if (bfqd
->delta_from_first
< BFQ_RATE_REF_INTERVAL
)
2572 goto update_last_values
;
2574 update_rate_and_reset
:
2575 bfq_update_rate_reset(bfqd
, rq
);
2577 bfqd
->last_position
= blk_rq_pos(rq
) + blk_rq_sectors(rq
);
2578 bfqd
->last_dispatch
= now_ns
;
2582 * Remove request from internal lists.
2584 static void bfq_dispatch_remove(struct request_queue
*q
, struct request
*rq
)
2586 struct bfq_queue
*bfqq
= RQ_BFQQ(rq
);
2589 * For consistency, the next instruction should have been
2590 * executed after removing the request from the queue and
2591 * dispatching it. We execute instead this instruction before
2592 * bfq_remove_request() (and hence introduce a temporary
2593 * inconsistency), for efficiency. In fact, should this
2594 * dispatch occur for a non in-service bfqq, this anticipated
2595 * increment prevents two counters related to bfqq->dispatched
2596 * from risking to be, first, uselessly decremented, and then
2597 * incremented again when the (new) value of bfqq->dispatched
2598 * happens to be taken into account.
2601 bfq_update_peak_rate(q
->elevator
->elevator_data
, rq
);
2603 bfq_remove_request(q
, rq
);
2606 static void __bfq_bfqq_expire(struct bfq_data
*bfqd
, struct bfq_queue
*bfqq
)
2609 * If this bfqq is shared between multiple processes, check
2610 * to make sure that those processes are still issuing I/Os
2611 * within the mean seek distance. If not, it may be time to
2612 * break the queues apart again.
2614 if (bfq_bfqq_coop(bfqq
) && BFQQ_SEEKY(bfqq
))
2615 bfq_mark_bfqq_split_coop(bfqq
);
2617 if (RB_EMPTY_ROOT(&bfqq
->sort_list
)) {
2618 if (bfqq
->dispatched
== 0)
2620 * Overloading budget_timeout field to store
2621 * the time at which the queue remains with no
2622 * backlog and no outstanding request; used by
2623 * the weight-raising mechanism.
2625 bfqq
->budget_timeout
= jiffies
;
2627 bfq_del_bfqq_busy(bfqd
, bfqq
, true);
2629 bfq_requeue_bfqq(bfqd
, bfqq
, true);
2631 * Resort priority tree of potential close cooperators.
2633 bfq_pos_tree_add_move(bfqd
, bfqq
);
2637 * All in-service entities must have been properly deactivated
2638 * or requeued before executing the next function, which
2639 * resets all in-service entites as no more in service.
2641 __bfq_bfqd_reset_in_service(bfqd
);
2645 * __bfq_bfqq_recalc_budget - try to adapt the budget to the @bfqq behavior.
2646 * @bfqd: device data.
2647 * @bfqq: queue to update.
2648 * @reason: reason for expiration.
2650 * Handle the feedback on @bfqq budget at queue expiration.
2651 * See the body for detailed comments.
2653 static void __bfq_bfqq_recalc_budget(struct bfq_data
*bfqd
,
2654 struct bfq_queue
*bfqq
,
2655 enum bfqq_expiration reason
)
2657 struct request
*next_rq
;
2658 int budget
, min_budget
;
2660 min_budget
= bfq_min_budget(bfqd
);
2662 if (bfqq
->wr_coeff
== 1)
2663 budget
= bfqq
->max_budget
;
2665 * Use a constant, low budget for weight-raised queues,
2666 * to help achieve a low latency. Keep it slightly higher
2667 * than the minimum possible budget, to cause a little
2668 * bit fewer expirations.
2670 budget
= 2 * min_budget
;
2672 bfq_log_bfqq(bfqd
, bfqq
, "recalc_budg: last budg %d, budg left %d",
2673 bfqq
->entity
.budget
, bfq_bfqq_budget_left(bfqq
));
2674 bfq_log_bfqq(bfqd
, bfqq
, "recalc_budg: last max_budg %d, min budg %d",
2675 budget
, bfq_min_budget(bfqd
));
2676 bfq_log_bfqq(bfqd
, bfqq
, "recalc_budg: sync %d, seeky %d",
2677 bfq_bfqq_sync(bfqq
), BFQQ_SEEKY(bfqd
->in_service_queue
));
2679 if (bfq_bfqq_sync(bfqq
) && bfqq
->wr_coeff
== 1) {
2682 * Caveat: in all the following cases we trade latency
2685 case BFQQE_TOO_IDLE
:
2687 * This is the only case where we may reduce
2688 * the budget: if there is no request of the
2689 * process still waiting for completion, then
2690 * we assume (tentatively) that the timer has
2691 * expired because the batch of requests of
2692 * the process could have been served with a
2693 * smaller budget. Hence, betting that
2694 * process will behave in the same way when it
2695 * becomes backlogged again, we reduce its
2696 * next budget. As long as we guess right,
2697 * this budget cut reduces the latency
2698 * experienced by the process.
2700 * However, if there are still outstanding
2701 * requests, then the process may have not yet
2702 * issued its next request just because it is
2703 * still waiting for the completion of some of
2704 * the still outstanding ones. So in this
2705 * subcase we do not reduce its budget, on the
2706 * contrary we increase it to possibly boost
2707 * the throughput, as discussed in the
2708 * comments to the BUDGET_TIMEOUT case.
2710 if (bfqq
->dispatched
> 0) /* still outstanding reqs */
2711 budget
= min(budget
* 2, bfqd
->bfq_max_budget
);
2713 if (budget
> 5 * min_budget
)
2714 budget
-= 4 * min_budget
;
2716 budget
= min_budget
;
2719 case BFQQE_BUDGET_TIMEOUT
:
2721 * We double the budget here because it gives
2722 * the chance to boost the throughput if this
2723 * is not a seeky process (and has bumped into
2724 * this timeout because of, e.g., ZBR).
2726 budget
= min(budget
* 2, bfqd
->bfq_max_budget
);
2728 case BFQQE_BUDGET_EXHAUSTED
:
2730 * The process still has backlog, and did not
2731 * let either the budget timeout or the disk
2732 * idling timeout expire. Hence it is not
2733 * seeky, has a short thinktime and may be
2734 * happy with a higher budget too. So
2735 * definitely increase the budget of this good
2736 * candidate to boost the disk throughput.
2738 budget
= min(budget
* 4, bfqd
->bfq_max_budget
);
2740 case BFQQE_NO_MORE_REQUESTS
:
2742 * For queues that expire for this reason, it
2743 * is particularly important to keep the
2744 * budget close to the actual service they
2745 * need. Doing so reduces the timestamp
2746 * misalignment problem described in the
2747 * comments in the body of
2748 * __bfq_activate_entity. In fact, suppose
2749 * that a queue systematically expires for
2750 * BFQQE_NO_MORE_REQUESTS and presents a
2751 * new request in time to enjoy timestamp
2752 * back-shifting. The larger the budget of the
2753 * queue is with respect to the service the
2754 * queue actually requests in each service
2755 * slot, the more times the queue can be
2756 * reactivated with the same virtual finish
2757 * time. It follows that, even if this finish
2758 * time is pushed to the system virtual time
2759 * to reduce the consequent timestamp
2760 * misalignment, the queue unjustly enjoys for
2761 * many re-activations a lower finish time
2762 * than all newly activated queues.
2764 * The service needed by bfqq is measured
2765 * quite precisely by bfqq->entity.service.
2766 * Since bfqq does not enjoy device idling,
2767 * bfqq->entity.service is equal to the number
2768 * of sectors that the process associated with
2769 * bfqq requested to read/write before waiting
2770 * for request completions, or blocking for
2773 budget
= max_t(int, bfqq
->entity
.service
, min_budget
);
2778 } else if (!bfq_bfqq_sync(bfqq
)) {
2780 * Async queues get always the maximum possible
2781 * budget, as for them we do not care about latency
2782 * (in addition, their ability to dispatch is limited
2783 * by the charging factor).
2785 budget
= bfqd
->bfq_max_budget
;
2788 bfqq
->max_budget
= budget
;
2790 if (bfqd
->budgets_assigned
>= bfq_stats_min_budgets
&&
2791 !bfqd
->bfq_user_max_budget
)
2792 bfqq
->max_budget
= min(bfqq
->max_budget
, bfqd
->bfq_max_budget
);
2795 * If there is still backlog, then assign a new budget, making
2796 * sure that it is large enough for the next request. Since
2797 * the finish time of bfqq must be kept in sync with the
2798 * budget, be sure to call __bfq_bfqq_expire() *after* this
2801 * If there is no backlog, then no need to update the budget;
2802 * it will be updated on the arrival of a new request.
2804 next_rq
= bfqq
->next_rq
;
2806 bfqq
->entity
.budget
= max_t(unsigned long, bfqq
->max_budget
,
2807 bfq_serv_to_charge(next_rq
, bfqq
));
2809 bfq_log_bfqq(bfqd
, bfqq
, "head sect: %u, new budget %d",
2810 next_rq
? blk_rq_sectors(next_rq
) : 0,
2811 bfqq
->entity
.budget
);
2815 * Return true if the process associated with bfqq is "slow". The slow
2816 * flag is used, in addition to the budget timeout, to reduce the
2817 * amount of service provided to seeky processes, and thus reduce
2818 * their chances to lower the throughput. More details in the comments
2819 * on the function bfq_bfqq_expire().
2821 * An important observation is in order: as discussed in the comments
2822 * on the function bfq_update_peak_rate(), with devices with internal
2823 * queues, it is hard if ever possible to know when and for how long
2824 * an I/O request is processed by the device (apart from the trivial
2825 * I/O pattern where a new request is dispatched only after the
2826 * previous one has been completed). This makes it hard to evaluate
2827 * the real rate at which the I/O requests of each bfq_queue are
2828 * served. In fact, for an I/O scheduler like BFQ, serving a
2829 * bfq_queue means just dispatching its requests during its service
2830 * slot (i.e., until the budget of the queue is exhausted, or the
2831 * queue remains idle, or, finally, a timeout fires). But, during the
2832 * service slot of a bfq_queue, around 100 ms at most, the device may
2833 * be even still processing requests of bfq_queues served in previous
2834 * service slots. On the opposite end, the requests of the in-service
2835 * bfq_queue may be completed after the service slot of the queue
2838 * Anyway, unless more sophisticated solutions are used
2839 * (where possible), the sum of the sizes of the requests dispatched
2840 * during the service slot of a bfq_queue is probably the only
2841 * approximation available for the service received by the bfq_queue
2842 * during its service slot. And this sum is the quantity used in this
2843 * function to evaluate the I/O speed of a process.
2845 static bool bfq_bfqq_is_slow(struct bfq_data
*bfqd
, struct bfq_queue
*bfqq
,
2846 bool compensate
, enum bfqq_expiration reason
,
2847 unsigned long *delta_ms
)
2849 ktime_t delta_ktime
;
2851 bool slow
= BFQQ_SEEKY(bfqq
); /* if delta too short, use seekyness */
2853 if (!bfq_bfqq_sync(bfqq
))
2857 delta_ktime
= bfqd
->last_idling_start
;
2859 delta_ktime
= ktime_get();
2860 delta_ktime
= ktime_sub(delta_ktime
, bfqd
->last_budget_start
);
2861 delta_usecs
= ktime_to_us(delta_ktime
);
2863 /* don't use too short time intervals */
2864 if (delta_usecs
< 1000) {
2865 if (blk_queue_nonrot(bfqd
->queue
))
2867 * give same worst-case guarantees as idling
2870 *delta_ms
= BFQ_MIN_TT
/ NSEC_PER_MSEC
;
2871 else /* charge at least one seek */
2872 *delta_ms
= bfq_slice_idle
/ NSEC_PER_MSEC
;
2877 *delta_ms
= delta_usecs
/ USEC_PER_MSEC
;
2880 * Use only long (> 20ms) intervals to filter out excessive
2881 * spikes in service rate estimation.
2883 if (delta_usecs
> 20000) {
2885 * Caveat for rotational devices: processes doing I/O
2886 * in the slower disk zones tend to be slow(er) even
2887 * if not seeky. In this respect, the estimated peak
2888 * rate is likely to be an average over the disk
2889 * surface. Accordingly, to not be too harsh with
2890 * unlucky processes, a process is deemed slow only if
2891 * its rate has been lower than half of the estimated
2894 slow
= bfqq
->entity
.service
< bfqd
->bfq_max_budget
/ 2;
2897 bfq_log_bfqq(bfqd
, bfqq
, "bfq_bfqq_is_slow: slow %d", slow
);
2903 * To be deemed as soft real-time, an application must meet two
2904 * requirements. First, the application must not require an average
2905 * bandwidth higher than the approximate bandwidth required to playback or
2906 * record a compressed high-definition video.
2907 * The next function is invoked on the completion of the last request of a
2908 * batch, to compute the next-start time instant, soft_rt_next_start, such
2909 * that, if the next request of the application does not arrive before
2910 * soft_rt_next_start, then the above requirement on the bandwidth is met.
2912 * The second requirement is that the request pattern of the application is
2913 * isochronous, i.e., that, after issuing a request or a batch of requests,
2914 * the application stops issuing new requests until all its pending requests
2915 * have been completed. After that, the application may issue a new batch,
2917 * For this reason the next function is invoked to compute
2918 * soft_rt_next_start only for applications that meet this requirement,
2919 * whereas soft_rt_next_start is set to infinity for applications that do
2922 * Unfortunately, even a greedy application may happen to behave in an
2923 * isochronous way if the CPU load is high. In fact, the application may
2924 * stop issuing requests while the CPUs are busy serving other processes,
2925 * then restart, then stop again for a while, and so on. In addition, if
2926 * the disk achieves a low enough throughput with the request pattern
2927 * issued by the application (e.g., because the request pattern is random
2928 * and/or the device is slow), then the application may meet the above
2929 * bandwidth requirement too. To prevent such a greedy application to be
2930 * deemed as soft real-time, a further rule is used in the computation of
2931 * soft_rt_next_start: soft_rt_next_start must be higher than the current
2932 * time plus the maximum time for which the arrival of a request is waited
2933 * for when a sync queue becomes idle, namely bfqd->bfq_slice_idle.
2934 * This filters out greedy applications, as the latter issue instead their
2935 * next request as soon as possible after the last one has been completed
2936 * (in contrast, when a batch of requests is completed, a soft real-time
2937 * application spends some time processing data).
2939 * Unfortunately, the last filter may easily generate false positives if
2940 * only bfqd->bfq_slice_idle is used as a reference time interval and one
2941 * or both the following cases occur:
2942 * 1) HZ is so low that the duration of a jiffy is comparable to or higher
2943 * than bfqd->bfq_slice_idle. This happens, e.g., on slow devices with
2945 * 2) jiffies, instead of increasing at a constant rate, may stop increasing
2946 * for a while, then suddenly 'jump' by several units to recover the lost
2947 * increments. This seems to happen, e.g., inside virtual machines.
2948 * To address this issue, we do not use as a reference time interval just
2949 * bfqd->bfq_slice_idle, but bfqd->bfq_slice_idle plus a few jiffies. In
2950 * particular we add the minimum number of jiffies for which the filter
2951 * seems to be quite precise also in embedded systems and KVM/QEMU virtual
2954 static unsigned long bfq_bfqq_softrt_next_start(struct bfq_data
*bfqd
,
2955 struct bfq_queue
*bfqq
)
2957 return max(bfqq
->last_idle_bklogged
+
2958 HZ
* bfqq
->service_from_backlogged
/
2959 bfqd
->bfq_wr_max_softrt_rate
,
2960 jiffies
+ nsecs_to_jiffies(bfqq
->bfqd
->bfq_slice_idle
) + 4);
2964 * bfq_bfqq_expire - expire a queue.
2965 * @bfqd: device owning the queue.
2966 * @bfqq: the queue to expire.
2967 * @compensate: if true, compensate for the time spent idling.
2968 * @reason: the reason causing the expiration.
2970 * If the process associated with bfqq does slow I/O (e.g., because it
2971 * issues random requests), we charge bfqq with the time it has been
2972 * in service instead of the service it has received (see
2973 * bfq_bfqq_charge_time for details on how this goal is achieved). As
2974 * a consequence, bfqq will typically get higher timestamps upon
2975 * reactivation, and hence it will be rescheduled as if it had
2976 * received more service than what it has actually received. In the
2977 * end, bfqq receives less service in proportion to how slowly its
2978 * associated process consumes its budgets (and hence how seriously it
2979 * tends to lower the throughput). In addition, this time-charging
2980 * strategy guarantees time fairness among slow processes. In
2981 * contrast, if the process associated with bfqq is not slow, we
2982 * charge bfqq exactly with the service it has received.
2984 * Charging time to the first type of queues and the exact service to
2985 * the other has the effect of using the WF2Q+ policy to schedule the
2986 * former on a timeslice basis, without violating service domain
2987 * guarantees among the latter.
2989 void bfq_bfqq_expire(struct bfq_data
*bfqd
,
2990 struct bfq_queue
*bfqq
,
2992 enum bfqq_expiration reason
)
2995 unsigned long delta
= 0;
2996 struct bfq_entity
*entity
= &bfqq
->entity
;
3000 * Check whether the process is slow (see bfq_bfqq_is_slow).
3002 slow
= bfq_bfqq_is_slow(bfqd
, bfqq
, compensate
, reason
, &delta
);
3005 * Increase service_from_backlogged before next statement,
3006 * because the possible next invocation of
3007 * bfq_bfqq_charge_time would likely inflate
3008 * entity->service. In contrast, service_from_backlogged must
3009 * contain real service, to enable the soft real-time
3010 * heuristic to correctly compute the bandwidth consumed by
3013 bfqq
->service_from_backlogged
+= entity
->service
;
3016 * As above explained, charge slow (typically seeky) and
3017 * timed-out queues with the time and not the service
3018 * received, to favor sequential workloads.
3020 * Processes doing I/O in the slower disk zones will tend to
3021 * be slow(er) even if not seeky. Therefore, since the
3022 * estimated peak rate is actually an average over the disk
3023 * surface, these processes may timeout just for bad luck. To
3024 * avoid punishing them, do not charge time to processes that
3025 * succeeded in consuming at least 2/3 of their budget. This
3026 * allows BFQ to preserve enough elasticity to still perform
3027 * bandwidth, and not time, distribution with little unlucky
3028 * or quasi-sequential processes.
3030 if (bfqq
->wr_coeff
== 1 &&
3032 (reason
== BFQQE_BUDGET_TIMEOUT
&&
3033 bfq_bfqq_budget_left(bfqq
) >= entity
->budget
/ 3)))
3034 bfq_bfqq_charge_time(bfqd
, bfqq
, delta
);
3036 if (reason
== BFQQE_TOO_IDLE
&&
3037 entity
->service
<= 2 * entity
->budget
/ 10)
3038 bfq_clear_bfqq_IO_bound(bfqq
);
3040 if (bfqd
->low_latency
&& bfqq
->wr_coeff
== 1)
3041 bfqq
->last_wr_start_finish
= jiffies
;
3043 if (bfqd
->low_latency
&& bfqd
->bfq_wr_max_softrt_rate
> 0 &&
3044 RB_EMPTY_ROOT(&bfqq
->sort_list
)) {
3046 * If we get here, and there are no outstanding
3047 * requests, then the request pattern is isochronous
3048 * (see the comments on the function
3049 * bfq_bfqq_softrt_next_start()). Thus we can compute
3050 * soft_rt_next_start. If, instead, the queue still
3051 * has outstanding requests, then we have to wait for
3052 * the completion of all the outstanding requests to
3053 * discover whether the request pattern is actually
3056 if (bfqq
->dispatched
== 0)
3057 bfqq
->soft_rt_next_start
=
3058 bfq_bfqq_softrt_next_start(bfqd
, bfqq
);
3061 * The application is still waiting for the
3062 * completion of one or more requests:
3063 * prevent it from possibly being incorrectly
3064 * deemed as soft real-time by setting its
3065 * soft_rt_next_start to infinity. In fact,
3066 * without this assignment, the application
3067 * would be incorrectly deemed as soft
3069 * 1) it issued a new request before the
3070 * completion of all its in-flight
3072 * 2) at that time, its soft_rt_next_start
3073 * happened to be in the past.
3075 bfqq
->soft_rt_next_start
=
3076 bfq_greatest_from_now();
3078 * Schedule an update of soft_rt_next_start to when
3079 * the task may be discovered to be isochronous.
3081 bfq_mark_bfqq_softrt_update(bfqq
);
3085 bfq_log_bfqq(bfqd
, bfqq
,
3086 "expire (%d, slow %d, num_disp %d, short_ttime %d)", reason
,
3087 slow
, bfqq
->dispatched
, bfq_bfqq_has_short_ttime(bfqq
));
3090 * Increase, decrease or leave budget unchanged according to
3093 __bfq_bfqq_recalc_budget(bfqd
, bfqq
, reason
);
3095 __bfq_bfqq_expire(bfqd
, bfqq
);
3097 /* mark bfqq as waiting a request only if a bic still points to it */
3098 if (ref
> 1 && !bfq_bfqq_busy(bfqq
) &&
3099 reason
!= BFQQE_BUDGET_TIMEOUT
&&
3100 reason
!= BFQQE_BUDGET_EXHAUSTED
)
3101 bfq_mark_bfqq_non_blocking_wait_rq(bfqq
);
3105 * Budget timeout is not implemented through a dedicated timer, but
3106 * just checked on request arrivals and completions, as well as on
3107 * idle timer expirations.
3109 static bool bfq_bfqq_budget_timeout(struct bfq_queue
*bfqq
)
3111 return time_is_before_eq_jiffies(bfqq
->budget_timeout
);
3115 * If we expire a queue that is actively waiting (i.e., with the
3116 * device idled) for the arrival of a new request, then we may incur
3117 * the timestamp misalignment problem described in the body of the
3118 * function __bfq_activate_entity. Hence we return true only if this
3119 * condition does not hold, or if the queue is slow enough to deserve
3120 * only to be kicked off for preserving a high throughput.
3122 static bool bfq_may_expire_for_budg_timeout(struct bfq_queue
*bfqq
)
3124 bfq_log_bfqq(bfqq
->bfqd
, bfqq
,
3125 "may_budget_timeout: wait_request %d left %d timeout %d",
3126 bfq_bfqq_wait_request(bfqq
),
3127 bfq_bfqq_budget_left(bfqq
) >= bfqq
->entity
.budget
/ 3,
3128 bfq_bfqq_budget_timeout(bfqq
));
3130 return (!bfq_bfqq_wait_request(bfqq
) ||
3131 bfq_bfqq_budget_left(bfqq
) >= bfqq
->entity
.budget
/ 3)
3133 bfq_bfqq_budget_timeout(bfqq
);
3137 * For a queue that becomes empty, device idling is allowed only if
3138 * this function returns true for the queue. As a consequence, since
3139 * device idling plays a critical role in both throughput boosting and
3140 * service guarantees, the return value of this function plays a
3141 * critical role in both these aspects as well.
3143 * In a nutshell, this function returns true only if idling is
3144 * beneficial for throughput or, even if detrimental for throughput,
3145 * idling is however necessary to preserve service guarantees (low
3146 * latency, desired throughput distribution, ...). In particular, on
3147 * NCQ-capable devices, this function tries to return false, so as to
3148 * help keep the drives' internal queues full, whenever this helps the
3149 * device boost the throughput without causing any service-guarantee
3152 * In more detail, the return value of this function is obtained by,
3153 * first, computing a number of boolean variables that take into
3154 * account throughput and service-guarantee issues, and, then,
3155 * combining these variables in a logical expression. Most of the
3156 * issues taken into account are not trivial. We discuss these issues
3157 * individually while introducing the variables.
3159 static bool bfq_bfqq_may_idle(struct bfq_queue
*bfqq
)
3161 struct bfq_data
*bfqd
= bfqq
->bfqd
;
3162 bool rot_without_queueing
=
3163 !blk_queue_nonrot(bfqd
->queue
) && !bfqd
->hw_tag
,
3164 bfqq_sequential_and_IO_bound
,
3165 idling_boosts_thr
, idling_boosts_thr_without_issues
,
3166 idling_needed_for_service_guarantees
,
3167 asymmetric_scenario
;
3169 if (bfqd
->strict_guarantees
)
3173 * Idling is performed only if slice_idle > 0. In addition, we
3176 * (b) bfqq is in the idle io prio class: in this case we do
3177 * not idle because we want to minimize the bandwidth that
3178 * queues in this class can steal to higher-priority queues
3180 if (bfqd
->bfq_slice_idle
== 0 || !bfq_bfqq_sync(bfqq
) ||
3181 bfq_class_idle(bfqq
))
3184 bfqq_sequential_and_IO_bound
= !BFQQ_SEEKY(bfqq
) &&
3185 bfq_bfqq_IO_bound(bfqq
) && bfq_bfqq_has_short_ttime(bfqq
);
3188 * The next variable takes into account the cases where idling
3189 * boosts the throughput.
3191 * The value of the variable is computed considering, first, that
3192 * idling is virtually always beneficial for the throughput if:
3193 * (a) the device is not NCQ-capable and rotational, or
3194 * (b) regardless of the presence of NCQ, the device is rotational and
3195 * the request pattern for bfqq is I/O-bound and sequential, or
3196 * (c) regardless of whether it is rotational, the device is
3197 * not NCQ-capable and the request pattern for bfqq is
3198 * I/O-bound and sequential.
3200 * Secondly, and in contrast to the above item (b), idling an
3201 * NCQ-capable flash-based device would not boost the
3202 * throughput even with sequential I/O; rather it would lower
3203 * the throughput in proportion to how fast the device
3204 * is. Accordingly, the next variable is true if any of the
3205 * above conditions (a), (b) or (c) is true, and, in
3206 * particular, happens to be false if bfqd is an NCQ-capable
3207 * flash-based device.
3209 idling_boosts_thr
= rot_without_queueing
||
3210 ((!blk_queue_nonrot(bfqd
->queue
) || !bfqd
->hw_tag
) &&
3211 bfqq_sequential_and_IO_bound
);
3214 * The value of the next variable,
3215 * idling_boosts_thr_without_issues, is equal to that of
3216 * idling_boosts_thr, unless a special case holds. In this
3217 * special case, described below, idling may cause problems to
3218 * weight-raised queues.
3220 * When the request pool is saturated (e.g., in the presence
3221 * of write hogs), if the processes associated with
3222 * non-weight-raised queues ask for requests at a lower rate,
3223 * then processes associated with weight-raised queues have a
3224 * higher probability to get a request from the pool
3225 * immediately (or at least soon) when they need one. Thus
3226 * they have a higher probability to actually get a fraction
3227 * of the device throughput proportional to their high
3228 * weight. This is especially true with NCQ-capable drives,
3229 * which enqueue several requests in advance, and further
3230 * reorder internally-queued requests.
3232 * For this reason, we force to false the value of
3233 * idling_boosts_thr_without_issues if there are weight-raised
3234 * busy queues. In this case, and if bfqq is not weight-raised,
3235 * this guarantees that the device is not idled for bfqq (if,
3236 * instead, bfqq is weight-raised, then idling will be
3237 * guaranteed by another variable, see below). Combined with
3238 * the timestamping rules of BFQ (see [1] for details), this
3239 * behavior causes bfqq, and hence any sync non-weight-raised
3240 * queue, to get a lower number of requests served, and thus
3241 * to ask for a lower number of requests from the request
3242 * pool, before the busy weight-raised queues get served
3243 * again. This often mitigates starvation problems in the
3244 * presence of heavy write workloads and NCQ, thereby
3245 * guaranteeing a higher application and system responsiveness
3246 * in these hostile scenarios.
3248 idling_boosts_thr_without_issues
= idling_boosts_thr
&&
3249 bfqd
->wr_busy_queues
== 0;
3252 * There is then a case where idling must be performed not
3253 * for throughput concerns, but to preserve service
3256 * To introduce this case, we can note that allowing the drive
3257 * to enqueue more than one request at a time, and hence
3258 * delegating de facto final scheduling decisions to the
3259 * drive's internal scheduler, entails loss of control on the
3260 * actual request service order. In particular, the critical
3261 * situation is when requests from different processes happen
3262 * to be present, at the same time, in the internal queue(s)
3263 * of the drive. In such a situation, the drive, by deciding
3264 * the service order of the internally-queued requests, does
3265 * determine also the actual throughput distribution among
3266 * these processes. But the drive typically has no notion or
3267 * concern about per-process throughput distribution, and
3268 * makes its decisions only on a per-request basis. Therefore,
3269 * the service distribution enforced by the drive's internal
3270 * scheduler is likely to coincide with the desired
3271 * device-throughput distribution only in a completely
3272 * symmetric scenario where:
3273 * (i) each of these processes must get the same throughput as
3275 * (ii) all these processes have the same I/O pattern
3276 (either sequential or random).
3277 * In fact, in such a scenario, the drive will tend to treat
3278 * the requests of each of these processes in about the same
3279 * way as the requests of the others, and thus to provide
3280 * each of these processes with about the same throughput
3281 * (which is exactly the desired throughput distribution). In
3282 * contrast, in any asymmetric scenario, device idling is
3283 * certainly needed to guarantee that bfqq receives its
3284 * assigned fraction of the device throughput (see [1] for
3287 * We address this issue by controlling, actually, only the
3288 * symmetry sub-condition (i), i.e., provided that
3289 * sub-condition (i) holds, idling is not performed,
3290 * regardless of whether sub-condition (ii) holds. In other
3291 * words, only if sub-condition (i) holds, then idling is
3292 * allowed, and the device tends to be prevented from queueing
3293 * many requests, possibly of several processes. The reason
3294 * for not controlling also sub-condition (ii) is that we
3295 * exploit preemption to preserve guarantees in case of
3296 * symmetric scenarios, even if (ii) does not hold, as
3297 * explained in the next two paragraphs.
3299 * Even if a queue, say Q, is expired when it remains idle, Q
3300 * can still preempt the new in-service queue if the next
3301 * request of Q arrives soon (see the comments on
3302 * bfq_bfqq_update_budg_for_activation). If all queues and
3303 * groups have the same weight, this form of preemption,
3304 * combined with the hole-recovery heuristic described in the
3305 * comments on function bfq_bfqq_update_budg_for_activation,
3306 * are enough to preserve a correct bandwidth distribution in
3307 * the mid term, even without idling. In fact, even if not
3308 * idling allows the internal queues of the device to contain
3309 * many requests, and thus to reorder requests, we can rather
3310 * safely assume that the internal scheduler still preserves a
3311 * minimum of mid-term fairness. The motivation for using
3312 * preemption instead of idling is that, by not idling,
3313 * service guarantees are preserved without minimally
3314 * sacrificing throughput. In other words, both a high
3315 * throughput and its desired distribution are obtained.
3317 * More precisely, this preemption-based, idleless approach
3318 * provides fairness in terms of IOPS, and not sectors per
3319 * second. This can be seen with a simple example. Suppose
3320 * that there are two queues with the same weight, but that
3321 * the first queue receives requests of 8 sectors, while the
3322 * second queue receives requests of 1024 sectors. In
3323 * addition, suppose that each of the two queues contains at
3324 * most one request at a time, which implies that each queue
3325 * always remains idle after it is served. Finally, after
3326 * remaining idle, each queue receives very quickly a new
3327 * request. It follows that the two queues are served
3328 * alternatively, preempting each other if needed. This
3329 * implies that, although both queues have the same weight,
3330 * the queue with large requests receives a service that is
3331 * 1024/8 times as high as the service received by the other
3334 * On the other hand, device idling is performed, and thus
3335 * pure sector-domain guarantees are provided, for the
3336 * following queues, which are likely to need stronger
3337 * throughput guarantees: weight-raised queues, and queues
3338 * with a higher weight than other queues. When such queues
3339 * are active, sub-condition (i) is false, which triggers
3342 * According to the above considerations, the next variable is
3343 * true (only) if sub-condition (i) holds. To compute the
3344 * value of this variable, we not only use the return value of
3345 * the function bfq_symmetric_scenario(), but also check
3346 * whether bfqq is being weight-raised, because
3347 * bfq_symmetric_scenario() does not take into account also
3348 * weight-raised queues (see comments on
3349 * bfq_weights_tree_add()).
3351 * As a side note, it is worth considering that the above
3352 * device-idling countermeasures may however fail in the
3353 * following unlucky scenario: if idling is (correctly)
3354 * disabled in a time period during which all symmetry
3355 * sub-conditions hold, and hence the device is allowed to
3356 * enqueue many requests, but at some later point in time some
3357 * sub-condition stops to hold, then it may become impossible
3358 * to let requests be served in the desired order until all
3359 * the requests already queued in the device have been served.
3361 asymmetric_scenario
= bfqq
->wr_coeff
> 1 ||
3362 !bfq_symmetric_scenario(bfqd
);
3365 * Finally, there is a case where maximizing throughput is the
3366 * best choice even if it may cause unfairness toward
3367 * bfqq. Such a case is when bfqq became active in a burst of
3368 * queue activations. Queues that became active during a large
3369 * burst benefit only from throughput, as discussed in the
3370 * comments on bfq_handle_burst. Thus, if bfqq became active
3371 * in a burst and not idling the device maximizes throughput,
3372 * then the device must no be idled, because not idling the
3373 * device provides bfqq and all other queues in the burst with
3374 * maximum benefit. Combining this and the above case, we can
3375 * now establish when idling is actually needed to preserve
3376 * service guarantees.
3378 idling_needed_for_service_guarantees
=
3379 asymmetric_scenario
&& !bfq_bfqq_in_large_burst(bfqq
);
3382 * We have now all the components we need to compute the
3383 * return value of the function, which is true only if idling
3384 * either boosts the throughput (without issues), or is
3385 * necessary to preserve service guarantees.
3387 return idling_boosts_thr_without_issues
||
3388 idling_needed_for_service_guarantees
;
3392 * If the in-service queue is empty but the function bfq_bfqq_may_idle
3393 * returns true, then:
3394 * 1) the queue must remain in service and cannot be expired, and
3395 * 2) the device must be idled to wait for the possible arrival of a new
3396 * request for the queue.
3397 * See the comments on the function bfq_bfqq_may_idle for the reasons
3398 * why performing device idling is the best choice to boost the throughput
3399 * and preserve service guarantees when bfq_bfqq_may_idle itself
3402 static bool bfq_bfqq_must_idle(struct bfq_queue
*bfqq
)
3404 return RB_EMPTY_ROOT(&bfqq
->sort_list
) && bfq_bfqq_may_idle(bfqq
);
3408 * Select a queue for service. If we have a current queue in service,
3409 * check whether to continue servicing it, or retrieve and set a new one.
3411 static struct bfq_queue
*bfq_select_queue(struct bfq_data
*bfqd
)
3413 struct bfq_queue
*bfqq
;
3414 struct request
*next_rq
;
3415 enum bfqq_expiration reason
= BFQQE_BUDGET_TIMEOUT
;
3417 bfqq
= bfqd
->in_service_queue
;
3421 bfq_log_bfqq(bfqd
, bfqq
, "select_queue: already in-service queue");
3423 if (bfq_may_expire_for_budg_timeout(bfqq
) &&
3424 !bfq_bfqq_wait_request(bfqq
) &&
3425 !bfq_bfqq_must_idle(bfqq
))
3430 * This loop is rarely executed more than once. Even when it
3431 * happens, it is much more convenient to re-execute this loop
3432 * than to return NULL and trigger a new dispatch to get a
3435 next_rq
= bfqq
->next_rq
;
3437 * If bfqq has requests queued and it has enough budget left to
3438 * serve them, keep the queue, otherwise expire it.
3441 if (bfq_serv_to_charge(next_rq
, bfqq
) >
3442 bfq_bfqq_budget_left(bfqq
)) {
3444 * Expire the queue for budget exhaustion,
3445 * which makes sure that the next budget is
3446 * enough to serve the next request, even if
3447 * it comes from the fifo expired path.
3449 reason
= BFQQE_BUDGET_EXHAUSTED
;
3453 * The idle timer may be pending because we may
3454 * not disable disk idling even when a new request
3457 if (bfq_bfqq_wait_request(bfqq
)) {
3459 * If we get here: 1) at least a new request
3460 * has arrived but we have not disabled the
3461 * timer because the request was too small,
3462 * 2) then the block layer has unplugged
3463 * the device, causing the dispatch to be
3466 * Since the device is unplugged, now the
3467 * requests are probably large enough to
3468 * provide a reasonable throughput.
3469 * So we disable idling.
3471 bfq_clear_bfqq_wait_request(bfqq
);
3472 hrtimer_try_to_cancel(&bfqd
->idle_slice_timer
);
3473 bfqg_stats_update_idle_time(bfqq_group(bfqq
));
3480 * No requests pending. However, if the in-service queue is idling
3481 * for a new request, or has requests waiting for a completion and
3482 * may idle after their completion, then keep it anyway.
3484 if (bfq_bfqq_wait_request(bfqq
) ||
3485 (bfqq
->dispatched
!= 0 && bfq_bfqq_may_idle(bfqq
))) {
3490 reason
= BFQQE_NO_MORE_REQUESTS
;
3492 bfq_bfqq_expire(bfqd
, bfqq
, false, reason
);
3494 bfqq
= bfq_set_in_service_queue(bfqd
);
3496 bfq_log_bfqq(bfqd
, bfqq
, "select_queue: checking new queue");
3501 bfq_log_bfqq(bfqd
, bfqq
, "select_queue: returned this queue");
3503 bfq_log(bfqd
, "select_queue: no queue returned");
3508 static void bfq_update_wr_data(struct bfq_data
*bfqd
, struct bfq_queue
*bfqq
)
3510 struct bfq_entity
*entity
= &bfqq
->entity
;
3512 if (bfqq
->wr_coeff
> 1) { /* queue is being weight-raised */
3513 bfq_log_bfqq(bfqd
, bfqq
,
3514 "raising period dur %u/%u msec, old coeff %u, w %d(%d)",
3515 jiffies_to_msecs(jiffies
- bfqq
->last_wr_start_finish
),
3516 jiffies_to_msecs(bfqq
->wr_cur_max_time
),
3518 bfqq
->entity
.weight
, bfqq
->entity
.orig_weight
);
3520 if (entity
->prio_changed
)
3521 bfq_log_bfqq(bfqd
, bfqq
, "WARN: pending prio change");
3524 * If the queue was activated in a burst, or too much
3525 * time has elapsed from the beginning of this
3526 * weight-raising period, then end weight raising.
3528 if (bfq_bfqq_in_large_burst(bfqq
))
3529 bfq_bfqq_end_wr(bfqq
);
3530 else if (time_is_before_jiffies(bfqq
->last_wr_start_finish
+
3531 bfqq
->wr_cur_max_time
)) {
3532 if (bfqq
->wr_cur_max_time
!= bfqd
->bfq_wr_rt_max_time
||
3533 time_is_before_jiffies(bfqq
->wr_start_at_switch_to_srt
+
3534 bfq_wr_duration(bfqd
)))
3535 bfq_bfqq_end_wr(bfqq
);
3537 switch_back_to_interactive_wr(bfqq
, bfqd
);
3538 bfqq
->entity
.prio_changed
= 1;
3543 * To improve latency (for this or other queues), immediately
3544 * update weight both if it must be raised and if it must be
3545 * lowered. Since, entity may be on some active tree here, and
3546 * might have a pending change of its ioprio class, invoke
3547 * next function with the last parameter unset (see the
3548 * comments on the function).
3550 if ((entity
->weight
> entity
->orig_weight
) != (bfqq
->wr_coeff
> 1))
3551 __bfq_entity_update_weight_prio(bfq_entity_service_tree(entity
),
3556 * Dispatch next request from bfqq.
3558 static struct request
*bfq_dispatch_rq_from_bfqq(struct bfq_data
*bfqd
,
3559 struct bfq_queue
*bfqq
)
3561 struct request
*rq
= bfqq
->next_rq
;
3562 unsigned long service_to_charge
;
3564 service_to_charge
= bfq_serv_to_charge(rq
, bfqq
);
3566 bfq_bfqq_served(bfqq
, service_to_charge
);
3568 bfq_dispatch_remove(bfqd
->queue
, rq
);
3571 * If weight raising has to terminate for bfqq, then next
3572 * function causes an immediate update of bfqq's weight,
3573 * without waiting for next activation. As a consequence, on
3574 * expiration, bfqq will be timestamped as if has never been
3575 * weight-raised during this service slot, even if it has
3576 * received part or even most of the service as a
3577 * weight-raised queue. This inflates bfqq's timestamps, which
3578 * is beneficial, as bfqq is then more willing to leave the
3579 * device immediately to possible other weight-raised queues.
3581 bfq_update_wr_data(bfqd
, bfqq
);
3584 * Expire bfqq, pretending that its budget expired, if bfqq
3585 * belongs to CLASS_IDLE and other queues are waiting for
3588 if (bfqd
->busy_queues
> 1 && bfq_class_idle(bfqq
))
3594 bfq_bfqq_expire(bfqd
, bfqq
, false, BFQQE_BUDGET_EXHAUSTED
);
3598 static bool bfq_has_work(struct blk_mq_hw_ctx
*hctx
)
3600 struct bfq_data
*bfqd
= hctx
->queue
->elevator
->elevator_data
;
3603 * Avoiding lock: a race on bfqd->busy_queues should cause at
3604 * most a call to dispatch for nothing
3606 return !list_empty_careful(&bfqd
->dispatch
) ||
3607 bfqd
->busy_queues
> 0;
3610 static struct request
*__bfq_dispatch_request(struct blk_mq_hw_ctx
*hctx
)
3612 struct bfq_data
*bfqd
= hctx
->queue
->elevator
->elevator_data
;
3613 struct request
*rq
= NULL
;
3614 struct bfq_queue
*bfqq
= NULL
;
3616 if (!list_empty(&bfqd
->dispatch
)) {
3617 rq
= list_first_entry(&bfqd
->dispatch
, struct request
,
3619 list_del_init(&rq
->queuelist
);
3625 * Increment counters here, because this
3626 * dispatch does not follow the standard
3627 * dispatch flow (where counters are
3632 goto inc_in_driver_start_rq
;
3636 * We exploit the put_rq_private hook to decrement
3637 * rq_in_driver, but put_rq_private will not be
3638 * invoked on this request. So, to avoid unbalance,
3639 * just start this request, without incrementing
3640 * rq_in_driver. As a negative consequence,
3641 * rq_in_driver is deceptively lower than it should be
3642 * while this request is in service. This may cause
3643 * bfq_schedule_dispatch to be invoked uselessly.
3645 * As for implementing an exact solution, the
3646 * put_request hook, if defined, is probably invoked
3647 * also on this request. So, by exploiting this hook,
3648 * we could 1) increment rq_in_driver here, and 2)
3649 * decrement it in put_request. Such a solution would
3650 * let the value of the counter be always accurate,
3651 * but it would entail using an extra interface
3652 * function. This cost seems higher than the benefit,
3653 * being the frequency of non-elevator-private
3654 * requests very low.
3659 bfq_log(bfqd
, "dispatch requests: %d busy queues", bfqd
->busy_queues
);
3661 if (bfqd
->busy_queues
== 0)
3665 * Force device to serve one request at a time if
3666 * strict_guarantees is true. Forcing this service scheme is
3667 * currently the ONLY way to guarantee that the request
3668 * service order enforced by the scheduler is respected by a
3669 * queueing device. Otherwise the device is free even to make
3670 * some unlucky request wait for as long as the device
3673 * Of course, serving one request at at time may cause loss of
3676 if (bfqd
->strict_guarantees
&& bfqd
->rq_in_driver
> 0)
3679 bfqq
= bfq_select_queue(bfqd
);
3683 rq
= bfq_dispatch_rq_from_bfqq(bfqd
, bfqq
);
3686 inc_in_driver_start_rq
:
3687 bfqd
->rq_in_driver
++;
3689 rq
->rq_flags
|= RQF_STARTED
;
3695 static struct request
*bfq_dispatch_request(struct blk_mq_hw_ctx
*hctx
)
3697 struct bfq_data
*bfqd
= hctx
->queue
->elevator
->elevator_data
;
3700 spin_lock_irq(&bfqd
->lock
);
3702 rq
= __bfq_dispatch_request(hctx
);
3703 spin_unlock_irq(&bfqd
->lock
);
3709 * Task holds one reference to the queue, dropped when task exits. Each rq
3710 * in-flight on this queue also holds a reference, dropped when rq is freed.
3712 * Scheduler lock must be held here. Recall not to use bfqq after calling
3713 * this function on it.
3715 void bfq_put_queue(struct bfq_queue
*bfqq
)
3717 #ifdef CONFIG_BFQ_GROUP_IOSCHED
3718 struct bfq_group
*bfqg
= bfqq_group(bfqq
);
3722 bfq_log_bfqq(bfqq
->bfqd
, bfqq
, "put_queue: %p %d",
3729 if (bfq_bfqq_sync(bfqq
) && !hlist_unhashed(&bfqq
->burst_list_node
)) {
3730 hlist_del_init(&bfqq
->burst_list_node
);
3731 bfqq
->bfqd
->burst_size
--;
3734 kmem_cache_free(bfq_pool
, bfqq
);
3735 #ifdef CONFIG_BFQ_GROUP_IOSCHED
3736 bfqg_and_blkg_put(bfqg
);
3740 static void bfq_put_cooperator(struct bfq_queue
*bfqq
)
3742 struct bfq_queue
*__bfqq
, *next
;
3745 * If this queue was scheduled to merge with another queue, be
3746 * sure to drop the reference taken on that queue (and others in
3747 * the merge chain). See bfq_setup_merge and bfq_merge_bfqqs.
3749 __bfqq
= bfqq
->new_bfqq
;
3753 next
= __bfqq
->new_bfqq
;
3754 bfq_put_queue(__bfqq
);
3759 static void bfq_exit_bfqq(struct bfq_data
*bfqd
, struct bfq_queue
*bfqq
)
3761 if (bfqq
== bfqd
->in_service_queue
) {
3762 __bfq_bfqq_expire(bfqd
, bfqq
);
3763 bfq_schedule_dispatch(bfqd
);
3766 bfq_log_bfqq(bfqd
, bfqq
, "exit_bfqq: %p, %d", bfqq
, bfqq
->ref
);
3768 bfq_put_cooperator(bfqq
);
3770 bfq_put_queue(bfqq
); /* release process reference */
3773 static void bfq_exit_icq_bfqq(struct bfq_io_cq
*bic
, bool is_sync
)
3775 struct bfq_queue
*bfqq
= bic_to_bfqq(bic
, is_sync
);
3776 struct bfq_data
*bfqd
;
3779 bfqd
= bfqq
->bfqd
; /* NULL if scheduler already exited */
3782 unsigned long flags
;
3784 spin_lock_irqsave(&bfqd
->lock
, flags
);
3785 bfq_exit_bfqq(bfqd
, bfqq
);
3786 bic_set_bfqq(bic
, NULL
, is_sync
);
3787 spin_unlock_irqrestore(&bfqd
->lock
, flags
);
3791 static void bfq_exit_icq(struct io_cq
*icq
)
3793 struct bfq_io_cq
*bic
= icq_to_bic(icq
);
3795 bfq_exit_icq_bfqq(bic
, true);
3796 bfq_exit_icq_bfqq(bic
, false);
3800 * Update the entity prio values; note that the new values will not
3801 * be used until the next (re)activation.
3804 bfq_set_next_ioprio_data(struct bfq_queue
*bfqq
, struct bfq_io_cq
*bic
)
3806 struct task_struct
*tsk
= current
;
3808 struct bfq_data
*bfqd
= bfqq
->bfqd
;
3813 ioprio_class
= IOPRIO_PRIO_CLASS(bic
->ioprio
);
3814 switch (ioprio_class
) {
3816 dev_err(bfqq
->bfqd
->queue
->backing_dev_info
->dev
,
3817 "bfq: bad prio class %d\n", ioprio_class
);
3819 case IOPRIO_CLASS_NONE
:
3821 * No prio set, inherit CPU scheduling settings.
3823 bfqq
->new_ioprio
= task_nice_ioprio(tsk
);
3824 bfqq
->new_ioprio_class
= task_nice_ioclass(tsk
);
3826 case IOPRIO_CLASS_RT
:
3827 bfqq
->new_ioprio
= IOPRIO_PRIO_DATA(bic
->ioprio
);
3828 bfqq
->new_ioprio_class
= IOPRIO_CLASS_RT
;
3830 case IOPRIO_CLASS_BE
:
3831 bfqq
->new_ioprio
= IOPRIO_PRIO_DATA(bic
->ioprio
);
3832 bfqq
->new_ioprio_class
= IOPRIO_CLASS_BE
;
3834 case IOPRIO_CLASS_IDLE
:
3835 bfqq
->new_ioprio_class
= IOPRIO_CLASS_IDLE
;
3836 bfqq
->new_ioprio
= 7;
3840 if (bfqq
->new_ioprio
>= IOPRIO_BE_NR
) {
3841 pr_crit("bfq_set_next_ioprio_data: new_ioprio %d\n",
3843 bfqq
->new_ioprio
= IOPRIO_BE_NR
;
3846 bfqq
->entity
.new_weight
= bfq_ioprio_to_weight(bfqq
->new_ioprio
);
3847 bfqq
->entity
.prio_changed
= 1;
3850 static struct bfq_queue
*bfq_get_queue(struct bfq_data
*bfqd
,
3851 struct bio
*bio
, bool is_sync
,
3852 struct bfq_io_cq
*bic
);
3854 static void bfq_check_ioprio_change(struct bfq_io_cq
*bic
, struct bio
*bio
)
3856 struct bfq_data
*bfqd
= bic_to_bfqd(bic
);
3857 struct bfq_queue
*bfqq
;
3858 int ioprio
= bic
->icq
.ioc
->ioprio
;
3861 * This condition may trigger on a newly created bic, be sure to
3862 * drop the lock before returning.
3864 if (unlikely(!bfqd
) || likely(bic
->ioprio
== ioprio
))
3867 bic
->ioprio
= ioprio
;
3869 bfqq
= bic_to_bfqq(bic
, false);
3871 /* release process reference on this queue */
3872 bfq_put_queue(bfqq
);
3873 bfqq
= bfq_get_queue(bfqd
, bio
, BLK_RW_ASYNC
, bic
);
3874 bic_set_bfqq(bic
, bfqq
, false);
3877 bfqq
= bic_to_bfqq(bic
, true);
3879 bfq_set_next_ioprio_data(bfqq
, bic
);
3882 static void bfq_init_bfqq(struct bfq_data
*bfqd
, struct bfq_queue
*bfqq
,
3883 struct bfq_io_cq
*bic
, pid_t pid
, int is_sync
)
3885 RB_CLEAR_NODE(&bfqq
->entity
.rb_node
);
3886 INIT_LIST_HEAD(&bfqq
->fifo
);
3887 INIT_HLIST_NODE(&bfqq
->burst_list_node
);
3893 bfq_set_next_ioprio_data(bfqq
, bic
);
3897 * No need to mark as has_short_ttime if in
3898 * idle_class, because no device idling is performed
3899 * for queues in idle class
3901 if (!bfq_class_idle(bfqq
))
3902 /* tentatively mark as has_short_ttime */
3903 bfq_mark_bfqq_has_short_ttime(bfqq
);
3904 bfq_mark_bfqq_sync(bfqq
);
3905 bfq_mark_bfqq_just_created(bfqq
);
3907 bfq_clear_bfqq_sync(bfqq
);
3909 /* set end request to minus infinity from now */
3910 bfqq
->ttime
.last_end_request
= ktime_get_ns() + 1;
3912 bfq_mark_bfqq_IO_bound(bfqq
);
3916 /* Tentative initial value to trade off between thr and lat */
3917 bfqq
->max_budget
= (2 * bfq_max_budget(bfqd
)) / 3;
3918 bfqq
->budget_timeout
= bfq_smallest_from_now();
3921 bfqq
->last_wr_start_finish
= jiffies
;
3922 bfqq
->wr_start_at_switch_to_srt
= bfq_smallest_from_now();
3923 bfqq
->split_time
= bfq_smallest_from_now();
3926 * Set to the value for which bfqq will not be deemed as
3927 * soft rt when it becomes backlogged.
3929 bfqq
->soft_rt_next_start
= bfq_greatest_from_now();
3931 /* first request is almost certainly seeky */
3932 bfqq
->seek_history
= 1;
3935 static struct bfq_queue
**bfq_async_queue_prio(struct bfq_data
*bfqd
,
3936 struct bfq_group
*bfqg
,
3937 int ioprio_class
, int ioprio
)
3939 switch (ioprio_class
) {
3940 case IOPRIO_CLASS_RT
:
3941 return &bfqg
->async_bfqq
[0][ioprio
];
3942 case IOPRIO_CLASS_NONE
:
3943 ioprio
= IOPRIO_NORM
;
3945 case IOPRIO_CLASS_BE
:
3946 return &bfqg
->async_bfqq
[1][ioprio
];
3947 case IOPRIO_CLASS_IDLE
:
3948 return &bfqg
->async_idle_bfqq
;
3954 static struct bfq_queue
*bfq_get_queue(struct bfq_data
*bfqd
,
3955 struct bio
*bio
, bool is_sync
,
3956 struct bfq_io_cq
*bic
)
3958 const int ioprio
= IOPRIO_PRIO_DATA(bic
->ioprio
);
3959 const int ioprio_class
= IOPRIO_PRIO_CLASS(bic
->ioprio
);
3960 struct bfq_queue
**async_bfqq
= NULL
;
3961 struct bfq_queue
*bfqq
;
3962 struct bfq_group
*bfqg
;
3966 bfqg
= bfq_find_set_group(bfqd
, bio_blkcg(bio
));
3968 bfqq
= &bfqd
->oom_bfqq
;
3973 async_bfqq
= bfq_async_queue_prio(bfqd
, bfqg
, ioprio_class
,
3980 bfqq
= kmem_cache_alloc_node(bfq_pool
,
3981 GFP_NOWAIT
| __GFP_ZERO
| __GFP_NOWARN
,
3985 bfq_init_bfqq(bfqd
, bfqq
, bic
, current
->pid
,
3987 bfq_init_entity(&bfqq
->entity
, bfqg
);
3988 bfq_log_bfqq(bfqd
, bfqq
, "allocated");
3990 bfqq
= &bfqd
->oom_bfqq
;
3991 bfq_log_bfqq(bfqd
, bfqq
, "using oom bfqq");
3996 * Pin the queue now that it's allocated, scheduler exit will
4001 * Extra group reference, w.r.t. sync
4002 * queue. This extra reference is removed
4003 * only if bfqq->bfqg disappears, to
4004 * guarantee that this queue is not freed
4005 * until its group goes away.
4007 bfq_log_bfqq(bfqd
, bfqq
, "get_queue, bfqq not in async: %p, %d",
4013 bfqq
->ref
++; /* get a process reference to this queue */
4014 bfq_log_bfqq(bfqd
, bfqq
, "get_queue, at end: %p, %d", bfqq
, bfqq
->ref
);
4019 static void bfq_update_io_thinktime(struct bfq_data
*bfqd
,
4020 struct bfq_queue
*bfqq
)
4022 struct bfq_ttime
*ttime
= &bfqq
->ttime
;
4023 u64 elapsed
= ktime_get_ns() - bfqq
->ttime
.last_end_request
;
4025 elapsed
= min_t(u64
, elapsed
, 2ULL * bfqd
->bfq_slice_idle
);
4027 ttime
->ttime_samples
= (7*bfqq
->ttime
.ttime_samples
+ 256) / 8;
4028 ttime
->ttime_total
= div_u64(7*ttime
->ttime_total
+ 256*elapsed
, 8);
4029 ttime
->ttime_mean
= div64_ul(ttime
->ttime_total
+ 128,
4030 ttime
->ttime_samples
);
4034 bfq_update_io_seektime(struct bfq_data
*bfqd
, struct bfq_queue
*bfqq
,
4037 bfqq
->seek_history
<<= 1;
4038 bfqq
->seek_history
|=
4039 get_sdist(bfqq
->last_request_pos
, rq
) > BFQQ_SEEK_THR
&&
4040 (!blk_queue_nonrot(bfqd
->queue
) ||
4041 blk_rq_sectors(rq
) < BFQQ_SECT_THR_NONROT
);
4044 static void bfq_update_has_short_ttime(struct bfq_data
*bfqd
,
4045 struct bfq_queue
*bfqq
,
4046 struct bfq_io_cq
*bic
)
4048 bool has_short_ttime
= true;
4051 * No need to update has_short_ttime if bfqq is async or in
4052 * idle io prio class, or if bfq_slice_idle is zero, because
4053 * no device idling is performed for bfqq in this case.
4055 if (!bfq_bfqq_sync(bfqq
) || bfq_class_idle(bfqq
) ||
4056 bfqd
->bfq_slice_idle
== 0)
4059 /* Idle window just restored, statistics are meaningless. */
4060 if (time_is_after_eq_jiffies(bfqq
->split_time
+
4061 bfqd
->bfq_wr_min_idle_time
))
4064 /* Think time is infinite if no process is linked to
4065 * bfqq. Otherwise check average think time to
4066 * decide whether to mark as has_short_ttime
4068 if (atomic_read(&bic
->icq
.ioc
->active_ref
) == 0 ||
4069 (bfq_sample_valid(bfqq
->ttime
.ttime_samples
) &&
4070 bfqq
->ttime
.ttime_mean
> bfqd
->bfq_slice_idle
))
4071 has_short_ttime
= false;
4073 bfq_log_bfqq(bfqd
, bfqq
, "update_has_short_ttime: has_short_ttime %d",
4076 if (has_short_ttime
)
4077 bfq_mark_bfqq_has_short_ttime(bfqq
);
4079 bfq_clear_bfqq_has_short_ttime(bfqq
);
4083 * Called when a new fs request (rq) is added to bfqq. Check if there's
4084 * something we should do about it.
4086 static void bfq_rq_enqueued(struct bfq_data
*bfqd
, struct bfq_queue
*bfqq
,
4089 struct bfq_io_cq
*bic
= RQ_BIC(rq
);
4091 if (rq
->cmd_flags
& REQ_META
)
4092 bfqq
->meta_pending
++;
4094 bfq_update_io_thinktime(bfqd
, bfqq
);
4095 bfq_update_has_short_ttime(bfqd
, bfqq
, bic
);
4096 bfq_update_io_seektime(bfqd
, bfqq
, rq
);
4098 bfq_log_bfqq(bfqd
, bfqq
,
4099 "rq_enqueued: has_short_ttime=%d (seeky %d)",
4100 bfq_bfqq_has_short_ttime(bfqq
), BFQQ_SEEKY(bfqq
));
4102 bfqq
->last_request_pos
= blk_rq_pos(rq
) + blk_rq_sectors(rq
);
4104 if (bfqq
== bfqd
->in_service_queue
&& bfq_bfqq_wait_request(bfqq
)) {
4105 bool small_req
= bfqq
->queued
[rq_is_sync(rq
)] == 1 &&
4106 blk_rq_sectors(rq
) < 32;
4107 bool budget_timeout
= bfq_bfqq_budget_timeout(bfqq
);
4110 * There is just this request queued: if the request
4111 * is small and the queue is not to be expired, then
4114 * In this way, if the device is being idled to wait
4115 * for a new request from the in-service queue, we
4116 * avoid unplugging the device and committing the
4117 * device to serve just a small request. On the
4118 * contrary, we wait for the block layer to decide
4119 * when to unplug the device: hopefully, new requests
4120 * will be merged to this one quickly, then the device
4121 * will be unplugged and larger requests will be
4124 if (small_req
&& !budget_timeout
)
4128 * A large enough request arrived, or the queue is to
4129 * be expired: in both cases disk idling is to be
4130 * stopped, so clear wait_request flag and reset
4133 bfq_clear_bfqq_wait_request(bfqq
);
4134 hrtimer_try_to_cancel(&bfqd
->idle_slice_timer
);
4135 bfqg_stats_update_idle_time(bfqq_group(bfqq
));
4138 * The queue is not empty, because a new request just
4139 * arrived. Hence we can safely expire the queue, in
4140 * case of budget timeout, without risking that the
4141 * timestamps of the queue are not updated correctly.
4142 * See [1] for more details.
4145 bfq_bfqq_expire(bfqd
, bfqq
, false,
4146 BFQQE_BUDGET_TIMEOUT
);
4150 static void __bfq_insert_request(struct bfq_data
*bfqd
, struct request
*rq
)
4152 struct bfq_queue
*bfqq
= RQ_BFQQ(rq
),
4153 *new_bfqq
= bfq_setup_cooperator(bfqd
, bfqq
, rq
, true);
4156 if (bic_to_bfqq(RQ_BIC(rq
), 1) != bfqq
)
4157 new_bfqq
= bic_to_bfqq(RQ_BIC(rq
), 1);
4159 * Release the request's reference to the old bfqq
4160 * and make sure one is taken to the shared queue.
4162 new_bfqq
->allocated
++;
4166 * If the bic associated with the process
4167 * issuing this request still points to bfqq
4168 * (and thus has not been already redirected
4169 * to new_bfqq or even some other bfq_queue),
4170 * then complete the merge and redirect it to
4173 if (bic_to_bfqq(RQ_BIC(rq
), 1) == bfqq
)
4174 bfq_merge_bfqqs(bfqd
, RQ_BIC(rq
),
4177 bfq_clear_bfqq_just_created(bfqq
);
4179 * rq is about to be enqueued into new_bfqq,
4180 * release rq reference on bfqq
4182 bfq_put_queue(bfqq
);
4183 rq
->elv
.priv
[1] = new_bfqq
;
4187 bfq_add_request(rq
);
4189 rq
->fifo_time
= ktime_get_ns() + bfqd
->bfq_fifo_expire
[rq_is_sync(rq
)];
4190 list_add_tail(&rq
->queuelist
, &bfqq
->fifo
);
4192 bfq_rq_enqueued(bfqd
, bfqq
, rq
);
4195 static void bfq_insert_request(struct blk_mq_hw_ctx
*hctx
, struct request
*rq
,
4198 struct request_queue
*q
= hctx
->queue
;
4199 struct bfq_data
*bfqd
= q
->elevator
->elevator_data
;
4201 spin_lock_irq(&bfqd
->lock
);
4202 if (blk_mq_sched_try_insert_merge(q
, rq
)) {
4203 spin_unlock_irq(&bfqd
->lock
);
4207 spin_unlock_irq(&bfqd
->lock
);
4209 blk_mq_sched_request_inserted(rq
);
4211 spin_lock_irq(&bfqd
->lock
);
4212 if (at_head
|| blk_rq_is_passthrough(rq
)) {
4214 list_add(&rq
->queuelist
, &bfqd
->dispatch
);
4216 list_add_tail(&rq
->queuelist
, &bfqd
->dispatch
);
4218 __bfq_insert_request(bfqd
, rq
);
4220 if (rq_mergeable(rq
)) {
4221 elv_rqhash_add(q
, rq
);
4227 spin_unlock_irq(&bfqd
->lock
);
4230 static void bfq_insert_requests(struct blk_mq_hw_ctx
*hctx
,
4231 struct list_head
*list
, bool at_head
)
4233 while (!list_empty(list
)) {
4236 rq
= list_first_entry(list
, struct request
, queuelist
);
4237 list_del_init(&rq
->queuelist
);
4238 bfq_insert_request(hctx
, rq
, at_head
);
4242 static void bfq_update_hw_tag(struct bfq_data
*bfqd
)
4244 bfqd
->max_rq_in_driver
= max_t(int, bfqd
->max_rq_in_driver
,
4245 bfqd
->rq_in_driver
);
4247 if (bfqd
->hw_tag
== 1)
4251 * This sample is valid if the number of outstanding requests
4252 * is large enough to allow a queueing behavior. Note that the
4253 * sum is not exact, as it's not taking into account deactivated
4256 if (bfqd
->rq_in_driver
+ bfqd
->queued
< BFQ_HW_QUEUE_THRESHOLD
)
4259 if (bfqd
->hw_tag_samples
++ < BFQ_HW_QUEUE_SAMPLES
)
4262 bfqd
->hw_tag
= bfqd
->max_rq_in_driver
> BFQ_HW_QUEUE_THRESHOLD
;
4263 bfqd
->max_rq_in_driver
= 0;
4264 bfqd
->hw_tag_samples
= 0;
4267 static void bfq_completed_request(struct bfq_queue
*bfqq
, struct bfq_data
*bfqd
)
4272 bfq_update_hw_tag(bfqd
);
4274 bfqd
->rq_in_driver
--;
4277 if (!bfqq
->dispatched
&& !bfq_bfqq_busy(bfqq
)) {
4279 * Set budget_timeout (which we overload to store the
4280 * time at which the queue remains with no backlog and
4281 * no outstanding request; used by the weight-raising
4284 bfqq
->budget_timeout
= jiffies
;
4286 bfq_weights_tree_remove(bfqd
, &bfqq
->entity
,
4287 &bfqd
->queue_weights_tree
);
4290 now_ns
= ktime_get_ns();
4292 bfqq
->ttime
.last_end_request
= now_ns
;
4295 * Using us instead of ns, to get a reasonable precision in
4296 * computing rate in next check.
4298 delta_us
= div_u64(now_ns
- bfqd
->last_completion
, NSEC_PER_USEC
);
4301 * If the request took rather long to complete, and, according
4302 * to the maximum request size recorded, this completion latency
4303 * implies that the request was certainly served at a very low
4304 * rate (less than 1M sectors/sec), then the whole observation
4305 * interval that lasts up to this time instant cannot be a
4306 * valid time interval for computing a new peak rate. Invoke
4307 * bfq_update_rate_reset to have the following three steps
4309 * - close the observation interval at the last (previous)
4310 * request dispatch or completion
4311 * - compute rate, if possible, for that observation interval
4312 * - reset to zero samples, which will trigger a proper
4313 * re-initialization of the observation interval on next
4316 if (delta_us
> BFQ_MIN_TT
/NSEC_PER_USEC
&&
4317 (bfqd
->last_rq_max_size
<<BFQ_RATE_SHIFT
)/delta_us
<
4318 1UL<<(BFQ_RATE_SHIFT
- 10))
4319 bfq_update_rate_reset(bfqd
, NULL
);
4320 bfqd
->last_completion
= now_ns
;
4323 * If we are waiting to discover whether the request pattern
4324 * of the task associated with the queue is actually
4325 * isochronous, and both requisites for this condition to hold
4326 * are now satisfied, then compute soft_rt_next_start (see the
4327 * comments on the function bfq_bfqq_softrt_next_start()). We
4328 * schedule this delayed check when bfqq expires, if it still
4329 * has in-flight requests.
4331 if (bfq_bfqq_softrt_update(bfqq
) && bfqq
->dispatched
== 0 &&
4332 RB_EMPTY_ROOT(&bfqq
->sort_list
))
4333 bfqq
->soft_rt_next_start
=
4334 bfq_bfqq_softrt_next_start(bfqd
, bfqq
);
4337 * If this is the in-service queue, check if it needs to be expired,
4338 * or if we want to idle in case it has no pending requests.
4340 if (bfqd
->in_service_queue
== bfqq
) {
4341 if (bfqq
->dispatched
== 0 && bfq_bfqq_must_idle(bfqq
)) {
4342 bfq_arm_slice_timer(bfqd
);
4344 } else if (bfq_may_expire_for_budg_timeout(bfqq
))
4345 bfq_bfqq_expire(bfqd
, bfqq
, false,
4346 BFQQE_BUDGET_TIMEOUT
);
4347 else if (RB_EMPTY_ROOT(&bfqq
->sort_list
) &&
4348 (bfqq
->dispatched
== 0 ||
4349 !bfq_bfqq_may_idle(bfqq
)))
4350 bfq_bfqq_expire(bfqd
, bfqq
, false,
4351 BFQQE_NO_MORE_REQUESTS
);
4354 if (!bfqd
->rq_in_driver
)
4355 bfq_schedule_dispatch(bfqd
);
4358 static void bfq_put_rq_priv_body(struct bfq_queue
*bfqq
)
4362 bfq_put_queue(bfqq
);
4365 static void bfq_finish_request(struct request
*rq
)
4367 struct bfq_queue
*bfqq
;
4368 struct bfq_data
*bfqd
;
4376 if (rq
->rq_flags
& RQF_STARTED
)
4377 bfqg_stats_update_completion(bfqq_group(bfqq
),
4378 rq_start_time_ns(rq
),
4379 rq_io_start_time_ns(rq
),
4382 if (likely(rq
->rq_flags
& RQF_STARTED
)) {
4383 unsigned long flags
;
4385 spin_lock_irqsave(&bfqd
->lock
, flags
);
4387 bfq_completed_request(bfqq
, bfqd
);
4388 bfq_put_rq_priv_body(bfqq
);
4390 spin_unlock_irqrestore(&bfqd
->lock
, flags
);
4393 * Request rq may be still/already in the scheduler,
4394 * in which case we need to remove it. And we cannot
4395 * defer such a check and removal, to avoid
4396 * inconsistencies in the time interval from the end
4397 * of this function to the start of the deferred work.
4398 * This situation seems to occur only in process
4399 * context, as a consequence of a merge. In the
4400 * current version of the code, this implies that the
4404 if (!RB_EMPTY_NODE(&rq
->rb_node
))
4405 bfq_remove_request(rq
->q
, rq
);
4406 bfq_put_rq_priv_body(bfqq
);
4409 rq
->elv
.priv
[0] = NULL
;
4410 rq
->elv
.priv
[1] = NULL
;
4414 * Returns NULL if a new bfqq should be allocated, or the old bfqq if this
4415 * was the last process referring to that bfqq.
4417 static struct bfq_queue
*
4418 bfq_split_bfqq(struct bfq_io_cq
*bic
, struct bfq_queue
*bfqq
)
4420 bfq_log_bfqq(bfqq
->bfqd
, bfqq
, "splitting queue");
4422 if (bfqq_process_refs(bfqq
) == 1) {
4423 bfqq
->pid
= current
->pid
;
4424 bfq_clear_bfqq_coop(bfqq
);
4425 bfq_clear_bfqq_split_coop(bfqq
);
4429 bic_set_bfqq(bic
, NULL
, 1);
4431 bfq_put_cooperator(bfqq
);
4433 bfq_put_queue(bfqq
);
4437 static struct bfq_queue
*bfq_get_bfqq_handle_split(struct bfq_data
*bfqd
,
4438 struct bfq_io_cq
*bic
,
4440 bool split
, bool is_sync
,
4443 struct bfq_queue
*bfqq
= bic_to_bfqq(bic
, is_sync
);
4445 if (likely(bfqq
&& bfqq
!= &bfqd
->oom_bfqq
))
4452 bfq_put_queue(bfqq
);
4453 bfqq
= bfq_get_queue(bfqd
, bio
, is_sync
, bic
);
4455 bic_set_bfqq(bic
, bfqq
, is_sync
);
4456 if (split
&& is_sync
) {
4457 if ((bic
->was_in_burst_list
&& bfqd
->large_burst
) ||
4458 bic
->saved_in_large_burst
)
4459 bfq_mark_bfqq_in_large_burst(bfqq
);
4461 bfq_clear_bfqq_in_large_burst(bfqq
);
4462 if (bic
->was_in_burst_list
)
4463 hlist_add_head(&bfqq
->burst_list_node
,
4466 bfqq
->split_time
= jiffies
;
4473 * Allocate bfq data structures associated with this request.
4475 static void bfq_prepare_request(struct request
*rq
, struct bio
*bio
)
4477 struct request_queue
*q
= rq
->q
;
4478 struct bfq_data
*bfqd
= q
->elevator
->elevator_data
;
4479 struct bfq_io_cq
*bic
;
4480 const int is_sync
= rq_is_sync(rq
);
4481 struct bfq_queue
*bfqq
;
4482 bool new_queue
= false;
4483 bool bfqq_already_existing
= false, split
= false;
4487 bic
= icq_to_bic(rq
->elv
.icq
);
4489 spin_lock_irq(&bfqd
->lock
);
4491 bfq_check_ioprio_change(bic
, bio
);
4493 bfq_bic_update_cgroup(bic
, bio
);
4495 bfqq
= bfq_get_bfqq_handle_split(bfqd
, bic
, bio
, false, is_sync
,
4498 if (likely(!new_queue
)) {
4499 /* If the queue was seeky for too long, break it apart. */
4500 if (bfq_bfqq_coop(bfqq
) && bfq_bfqq_split_coop(bfqq
)) {
4501 bfq_log_bfqq(bfqd
, bfqq
, "breaking apart bfqq");
4503 /* Update bic before losing reference to bfqq */
4504 if (bfq_bfqq_in_large_burst(bfqq
))
4505 bic
->saved_in_large_burst
= true;
4507 bfqq
= bfq_split_bfqq(bic
, bfqq
);
4511 bfqq
= bfq_get_bfqq_handle_split(bfqd
, bic
, bio
,
4515 bfqq_already_existing
= true;
4521 bfq_log_bfqq(bfqd
, bfqq
, "get_request %p: bfqq %p, %d",
4522 rq
, bfqq
, bfqq
->ref
);
4524 rq
->elv
.priv
[0] = bic
;
4525 rq
->elv
.priv
[1] = bfqq
;
4528 * If a bfq_queue has only one process reference, it is owned
4529 * by only this bic: we can then set bfqq->bic = bic. in
4530 * addition, if the queue has also just been split, we have to
4533 if (likely(bfqq
!= &bfqd
->oom_bfqq
) && bfqq_process_refs(bfqq
) == 1) {
4537 * The queue has just been split from a shared
4538 * queue: restore the idle window and the
4539 * possible weight raising period.
4541 bfq_bfqq_resume_state(bfqq
, bfqd
, bic
,
4542 bfqq_already_existing
);
4546 if (unlikely(bfq_bfqq_just_created(bfqq
)))
4547 bfq_handle_burst(bfqd
, bfqq
);
4549 spin_unlock_irq(&bfqd
->lock
);
4552 static void bfq_idle_slice_timer_body(struct bfq_queue
*bfqq
)
4554 struct bfq_data
*bfqd
= bfqq
->bfqd
;
4555 enum bfqq_expiration reason
;
4556 unsigned long flags
;
4558 spin_lock_irqsave(&bfqd
->lock
, flags
);
4559 bfq_clear_bfqq_wait_request(bfqq
);
4561 if (bfqq
!= bfqd
->in_service_queue
) {
4562 spin_unlock_irqrestore(&bfqd
->lock
, flags
);
4566 if (bfq_bfqq_budget_timeout(bfqq
))
4568 * Also here the queue can be safely expired
4569 * for budget timeout without wasting
4572 reason
= BFQQE_BUDGET_TIMEOUT
;
4573 else if (bfqq
->queued
[0] == 0 && bfqq
->queued
[1] == 0)
4575 * The queue may not be empty upon timer expiration,
4576 * because we may not disable the timer when the
4577 * first request of the in-service queue arrives
4578 * during disk idling.
4580 reason
= BFQQE_TOO_IDLE
;
4582 goto schedule_dispatch
;
4584 bfq_bfqq_expire(bfqd
, bfqq
, true, reason
);
4587 spin_unlock_irqrestore(&bfqd
->lock
, flags
);
4588 bfq_schedule_dispatch(bfqd
);
4592 * Handler of the expiration of the timer running if the in-service queue
4593 * is idling inside its time slice.
4595 static enum hrtimer_restart
bfq_idle_slice_timer(struct hrtimer
*timer
)
4597 struct bfq_data
*bfqd
= container_of(timer
, struct bfq_data
,
4599 struct bfq_queue
*bfqq
= bfqd
->in_service_queue
;
4602 * Theoretical race here: the in-service queue can be NULL or
4603 * different from the queue that was idling if a new request
4604 * arrives for the current queue and there is a full dispatch
4605 * cycle that changes the in-service queue. This can hardly
4606 * happen, but in the worst case we just expire a queue too
4610 bfq_idle_slice_timer_body(bfqq
);
4612 return HRTIMER_NORESTART
;
4615 static void __bfq_put_async_bfqq(struct bfq_data
*bfqd
,
4616 struct bfq_queue
**bfqq_ptr
)
4618 struct bfq_queue
*bfqq
= *bfqq_ptr
;
4620 bfq_log(bfqd
, "put_async_bfqq: %p", bfqq
);
4622 bfq_bfqq_move(bfqd
, bfqq
, bfqd
->root_group
);
4624 bfq_log_bfqq(bfqd
, bfqq
, "put_async_bfqq: putting %p, %d",
4626 bfq_put_queue(bfqq
);
4632 * Release all the bfqg references to its async queues. If we are
4633 * deallocating the group these queues may still contain requests, so
4634 * we reparent them to the root cgroup (i.e., the only one that will
4635 * exist for sure until all the requests on a device are gone).
4637 void bfq_put_async_queues(struct bfq_data
*bfqd
, struct bfq_group
*bfqg
)
4641 for (i
= 0; i
< 2; i
++)
4642 for (j
= 0; j
< IOPRIO_BE_NR
; j
++)
4643 __bfq_put_async_bfqq(bfqd
, &bfqg
->async_bfqq
[i
][j
]);
4645 __bfq_put_async_bfqq(bfqd
, &bfqg
->async_idle_bfqq
);
4648 static void bfq_exit_queue(struct elevator_queue
*e
)
4650 struct bfq_data
*bfqd
= e
->elevator_data
;
4651 struct bfq_queue
*bfqq
, *n
;
4653 hrtimer_cancel(&bfqd
->idle_slice_timer
);
4655 spin_lock_irq(&bfqd
->lock
);
4656 list_for_each_entry_safe(bfqq
, n
, &bfqd
->idle_list
, bfqq_list
)
4657 bfq_deactivate_bfqq(bfqd
, bfqq
, false, false);
4658 spin_unlock_irq(&bfqd
->lock
);
4660 hrtimer_cancel(&bfqd
->idle_slice_timer
);
4662 #ifdef CONFIG_BFQ_GROUP_IOSCHED
4663 blkcg_deactivate_policy(bfqd
->queue
, &blkcg_policy_bfq
);
4665 spin_lock_irq(&bfqd
->lock
);
4666 bfq_put_async_queues(bfqd
, bfqd
->root_group
);
4667 kfree(bfqd
->root_group
);
4668 spin_unlock_irq(&bfqd
->lock
);
4674 static void bfq_init_root_group(struct bfq_group
*root_group
,
4675 struct bfq_data
*bfqd
)
4679 #ifdef CONFIG_BFQ_GROUP_IOSCHED
4680 root_group
->entity
.parent
= NULL
;
4681 root_group
->my_entity
= NULL
;
4682 root_group
->bfqd
= bfqd
;
4684 root_group
->rq_pos_tree
= RB_ROOT
;
4685 for (i
= 0; i
< BFQ_IOPRIO_CLASSES
; i
++)
4686 root_group
->sched_data
.service_tree
[i
] = BFQ_SERVICE_TREE_INIT
;
4687 root_group
->sched_data
.bfq_class_idle_last_service
= jiffies
;
4690 static int bfq_init_queue(struct request_queue
*q
, struct elevator_type
*e
)
4692 struct bfq_data
*bfqd
;
4693 struct elevator_queue
*eq
;
4695 eq
= elevator_alloc(q
, e
);
4699 bfqd
= kzalloc_node(sizeof(*bfqd
), GFP_KERNEL
, q
->node
);
4701 kobject_put(&eq
->kobj
);
4704 eq
->elevator_data
= bfqd
;
4706 spin_lock_irq(q
->queue_lock
);
4708 spin_unlock_irq(q
->queue_lock
);
4711 * Our fallback bfqq if bfq_find_alloc_queue() runs into OOM issues.
4712 * Grab a permanent reference to it, so that the normal code flow
4713 * will not attempt to free it.
4715 bfq_init_bfqq(bfqd
, &bfqd
->oom_bfqq
, NULL
, 1, 0);
4716 bfqd
->oom_bfqq
.ref
++;
4717 bfqd
->oom_bfqq
.new_ioprio
= BFQ_DEFAULT_QUEUE_IOPRIO
;
4718 bfqd
->oom_bfqq
.new_ioprio_class
= IOPRIO_CLASS_BE
;
4719 bfqd
->oom_bfqq
.entity
.new_weight
=
4720 bfq_ioprio_to_weight(bfqd
->oom_bfqq
.new_ioprio
);
4722 /* oom_bfqq does not participate to bursts */
4723 bfq_clear_bfqq_just_created(&bfqd
->oom_bfqq
);
4726 * Trigger weight initialization, according to ioprio, at the
4727 * oom_bfqq's first activation. The oom_bfqq's ioprio and ioprio
4728 * class won't be changed any more.
4730 bfqd
->oom_bfqq
.entity
.prio_changed
= 1;
4734 INIT_LIST_HEAD(&bfqd
->dispatch
);
4736 hrtimer_init(&bfqd
->idle_slice_timer
, CLOCK_MONOTONIC
,
4738 bfqd
->idle_slice_timer
.function
= bfq_idle_slice_timer
;
4740 bfqd
->queue_weights_tree
= RB_ROOT
;
4741 bfqd
->group_weights_tree
= RB_ROOT
;
4743 INIT_LIST_HEAD(&bfqd
->active_list
);
4744 INIT_LIST_HEAD(&bfqd
->idle_list
);
4745 INIT_HLIST_HEAD(&bfqd
->burst_list
);
4749 bfqd
->bfq_max_budget
= bfq_default_max_budget
;
4751 bfqd
->bfq_fifo_expire
[0] = bfq_fifo_expire
[0];
4752 bfqd
->bfq_fifo_expire
[1] = bfq_fifo_expire
[1];
4753 bfqd
->bfq_back_max
= bfq_back_max
;
4754 bfqd
->bfq_back_penalty
= bfq_back_penalty
;
4755 bfqd
->bfq_slice_idle
= bfq_slice_idle
;
4756 bfqd
->bfq_timeout
= bfq_timeout
;
4758 bfqd
->bfq_requests_within_timer
= 120;
4760 bfqd
->bfq_large_burst_thresh
= 8;
4761 bfqd
->bfq_burst_interval
= msecs_to_jiffies(180);
4763 bfqd
->low_latency
= true;
4766 * Trade-off between responsiveness and fairness.
4768 bfqd
->bfq_wr_coeff
= 30;
4769 bfqd
->bfq_wr_rt_max_time
= msecs_to_jiffies(300);
4770 bfqd
->bfq_wr_max_time
= 0;
4771 bfqd
->bfq_wr_min_idle_time
= msecs_to_jiffies(2000);
4772 bfqd
->bfq_wr_min_inter_arr_async
= msecs_to_jiffies(500);
4773 bfqd
->bfq_wr_max_softrt_rate
= 7000; /*
4774 * Approximate rate required
4775 * to playback or record a
4776 * high-definition compressed
4779 bfqd
->wr_busy_queues
= 0;
4782 * Begin by assuming, optimistically, that the device is a
4783 * high-speed one, and that its peak rate is equal to 2/3 of
4784 * the highest reference rate.
4786 bfqd
->RT_prod
= R_fast
[blk_queue_nonrot(bfqd
->queue
)] *
4787 T_fast
[blk_queue_nonrot(bfqd
->queue
)];
4788 bfqd
->peak_rate
= R_fast
[blk_queue_nonrot(bfqd
->queue
)] * 2 / 3;
4789 bfqd
->device_speed
= BFQ_BFQD_FAST
;
4791 spin_lock_init(&bfqd
->lock
);
4794 * The invocation of the next bfq_create_group_hierarchy
4795 * function is the head of a chain of function calls
4796 * (bfq_create_group_hierarchy->blkcg_activate_policy->
4797 * blk_mq_freeze_queue) that may lead to the invocation of the
4798 * has_work hook function. For this reason,
4799 * bfq_create_group_hierarchy is invoked only after all
4800 * scheduler data has been initialized, apart from the fields
4801 * that can be initialized only after invoking
4802 * bfq_create_group_hierarchy. This, in particular, enables
4803 * has_work to correctly return false. Of course, to avoid
4804 * other inconsistencies, the blk-mq stack must then refrain
4805 * from invoking further scheduler hooks before this init
4806 * function is finished.
4808 bfqd
->root_group
= bfq_create_group_hierarchy(bfqd
, q
->node
);
4809 if (!bfqd
->root_group
)
4811 bfq_init_root_group(bfqd
->root_group
, bfqd
);
4812 bfq_init_entity(&bfqd
->oom_bfqq
.entity
, bfqd
->root_group
);
4814 wbt_disable_default(q
);
4819 kobject_put(&eq
->kobj
);
4823 static void bfq_slab_kill(void)
4825 kmem_cache_destroy(bfq_pool
);
4828 static int __init
bfq_slab_setup(void)
4830 bfq_pool
= KMEM_CACHE(bfq_queue
, 0);
4836 static ssize_t
bfq_var_show(unsigned int var
, char *page
)
4838 return sprintf(page
, "%u\n", var
);
4841 static int bfq_var_store(unsigned long *var
, const char *page
)
4843 unsigned long new_val
;
4844 int ret
= kstrtoul(page
, 10, &new_val
);
4852 #define SHOW_FUNCTION(__FUNC, __VAR, __CONV) \
4853 static ssize_t __FUNC(struct elevator_queue *e, char *page) \
4855 struct bfq_data *bfqd = e->elevator_data; \
4856 u64 __data = __VAR; \
4858 __data = jiffies_to_msecs(__data); \
4859 else if (__CONV == 2) \
4860 __data = div_u64(__data, NSEC_PER_MSEC); \
4861 return bfq_var_show(__data, (page)); \
4863 SHOW_FUNCTION(bfq_fifo_expire_sync_show
, bfqd
->bfq_fifo_expire
[1], 2);
4864 SHOW_FUNCTION(bfq_fifo_expire_async_show
, bfqd
->bfq_fifo_expire
[0], 2);
4865 SHOW_FUNCTION(bfq_back_seek_max_show
, bfqd
->bfq_back_max
, 0);
4866 SHOW_FUNCTION(bfq_back_seek_penalty_show
, bfqd
->bfq_back_penalty
, 0);
4867 SHOW_FUNCTION(bfq_slice_idle_show
, bfqd
->bfq_slice_idle
, 2);
4868 SHOW_FUNCTION(bfq_max_budget_show
, bfqd
->bfq_user_max_budget
, 0);
4869 SHOW_FUNCTION(bfq_timeout_sync_show
, bfqd
->bfq_timeout
, 1);
4870 SHOW_FUNCTION(bfq_strict_guarantees_show
, bfqd
->strict_guarantees
, 0);
4871 SHOW_FUNCTION(bfq_low_latency_show
, bfqd
->low_latency
, 0);
4872 #undef SHOW_FUNCTION
4874 #define USEC_SHOW_FUNCTION(__FUNC, __VAR) \
4875 static ssize_t __FUNC(struct elevator_queue *e, char *page) \
4877 struct bfq_data *bfqd = e->elevator_data; \
4878 u64 __data = __VAR; \
4879 __data = div_u64(__data, NSEC_PER_USEC); \
4880 return bfq_var_show(__data, (page)); \
4882 USEC_SHOW_FUNCTION(bfq_slice_idle_us_show
, bfqd
->bfq_slice_idle
);
4883 #undef USEC_SHOW_FUNCTION
4885 #define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV) \
4887 __FUNC(struct elevator_queue *e, const char *page, size_t count) \
4889 struct bfq_data *bfqd = e->elevator_data; \
4890 unsigned long __data, __min = (MIN), __max = (MAX); \
4893 ret = bfq_var_store(&__data, (page)); \
4896 if (__data < __min) \
4898 else if (__data > __max) \
4901 *(__PTR) = msecs_to_jiffies(__data); \
4902 else if (__CONV == 2) \
4903 *(__PTR) = (u64)__data * NSEC_PER_MSEC; \
4905 *(__PTR) = __data; \
4908 STORE_FUNCTION(bfq_fifo_expire_sync_store
, &bfqd
->bfq_fifo_expire
[1], 1,
4910 STORE_FUNCTION(bfq_fifo_expire_async_store
, &bfqd
->bfq_fifo_expire
[0], 1,
4912 STORE_FUNCTION(bfq_back_seek_max_store
, &bfqd
->bfq_back_max
, 0, INT_MAX
, 0);
4913 STORE_FUNCTION(bfq_back_seek_penalty_store
, &bfqd
->bfq_back_penalty
, 1,
4915 STORE_FUNCTION(bfq_slice_idle_store
, &bfqd
->bfq_slice_idle
, 0, INT_MAX
, 2);
4916 #undef STORE_FUNCTION
4918 #define USEC_STORE_FUNCTION(__FUNC, __PTR, MIN, MAX) \
4919 static ssize_t __FUNC(struct elevator_queue *e, const char *page, size_t count)\
4921 struct bfq_data *bfqd = e->elevator_data; \
4922 unsigned long __data, __min = (MIN), __max = (MAX); \
4925 ret = bfq_var_store(&__data, (page)); \
4928 if (__data < __min) \
4930 else if (__data > __max) \
4932 *(__PTR) = (u64)__data * NSEC_PER_USEC; \
4935 USEC_STORE_FUNCTION(bfq_slice_idle_us_store
, &bfqd
->bfq_slice_idle
, 0,
4937 #undef USEC_STORE_FUNCTION
4939 static ssize_t
bfq_max_budget_store(struct elevator_queue
*e
,
4940 const char *page
, size_t count
)
4942 struct bfq_data
*bfqd
= e
->elevator_data
;
4943 unsigned long __data
;
4946 ret
= bfq_var_store(&__data
, (page
));
4951 bfqd
->bfq_max_budget
= bfq_calc_max_budget(bfqd
);
4953 if (__data
> INT_MAX
)
4955 bfqd
->bfq_max_budget
= __data
;
4958 bfqd
->bfq_user_max_budget
= __data
;
4964 * Leaving this name to preserve name compatibility with cfq
4965 * parameters, but this timeout is used for both sync and async.
4967 static ssize_t
bfq_timeout_sync_store(struct elevator_queue
*e
,
4968 const char *page
, size_t count
)
4970 struct bfq_data
*bfqd
= e
->elevator_data
;
4971 unsigned long __data
;
4974 ret
= bfq_var_store(&__data
, (page
));
4980 else if (__data
> INT_MAX
)
4983 bfqd
->bfq_timeout
= msecs_to_jiffies(__data
);
4984 if (bfqd
->bfq_user_max_budget
== 0)
4985 bfqd
->bfq_max_budget
= bfq_calc_max_budget(bfqd
);
4990 static ssize_t
bfq_strict_guarantees_store(struct elevator_queue
*e
,
4991 const char *page
, size_t count
)
4993 struct bfq_data
*bfqd
= e
->elevator_data
;
4994 unsigned long __data
;
4997 ret
= bfq_var_store(&__data
, (page
));
5003 if (!bfqd
->strict_guarantees
&& __data
== 1
5004 && bfqd
->bfq_slice_idle
< 8 * NSEC_PER_MSEC
)
5005 bfqd
->bfq_slice_idle
= 8 * NSEC_PER_MSEC
;
5007 bfqd
->strict_guarantees
= __data
;
5012 static ssize_t
bfq_low_latency_store(struct elevator_queue
*e
,
5013 const char *page
, size_t count
)
5015 struct bfq_data
*bfqd
= e
->elevator_data
;
5016 unsigned long __data
;
5019 ret
= bfq_var_store(&__data
, (page
));
5025 if (__data
== 0 && bfqd
->low_latency
!= 0)
5027 bfqd
->low_latency
= __data
;
5032 #define BFQ_ATTR(name) \
5033 __ATTR(name, 0644, bfq_##name##_show, bfq_##name##_store)
5035 static struct elv_fs_entry bfq_attrs
[] = {
5036 BFQ_ATTR(fifo_expire_sync
),
5037 BFQ_ATTR(fifo_expire_async
),
5038 BFQ_ATTR(back_seek_max
),
5039 BFQ_ATTR(back_seek_penalty
),
5040 BFQ_ATTR(slice_idle
),
5041 BFQ_ATTR(slice_idle_us
),
5042 BFQ_ATTR(max_budget
),
5043 BFQ_ATTR(timeout_sync
),
5044 BFQ_ATTR(strict_guarantees
),
5045 BFQ_ATTR(low_latency
),
5049 static struct elevator_type iosched_bfq_mq
= {
5051 .prepare_request
= bfq_prepare_request
,
5052 .finish_request
= bfq_finish_request
,
5053 .exit_icq
= bfq_exit_icq
,
5054 .insert_requests
= bfq_insert_requests
,
5055 .dispatch_request
= bfq_dispatch_request
,
5056 .next_request
= elv_rb_latter_request
,
5057 .former_request
= elv_rb_former_request
,
5058 .allow_merge
= bfq_allow_bio_merge
,
5059 .bio_merge
= bfq_bio_merge
,
5060 .request_merge
= bfq_request_merge
,
5061 .requests_merged
= bfq_requests_merged
,
5062 .request_merged
= bfq_request_merged
,
5063 .has_work
= bfq_has_work
,
5064 .init_sched
= bfq_init_queue
,
5065 .exit_sched
= bfq_exit_queue
,
5069 .icq_size
= sizeof(struct bfq_io_cq
),
5070 .icq_align
= __alignof__(struct bfq_io_cq
),
5071 .elevator_attrs
= bfq_attrs
,
5072 .elevator_name
= "bfq",
5073 .elevator_owner
= THIS_MODULE
,
5075 MODULE_ALIAS("bfq-iosched");
5077 static int __init
bfq_init(void)
5081 #ifdef CONFIG_BFQ_GROUP_IOSCHED
5082 ret
= blkcg_policy_register(&blkcg_policy_bfq
);
5088 if (bfq_slab_setup())
5092 * Times to load large popular applications for the typical
5093 * systems installed on the reference devices (see the
5094 * comments before the definitions of the next two
5095 * arrays). Actually, we use slightly slower values, as the
5096 * estimated peak rate tends to be smaller than the actual
5097 * peak rate. The reason for this last fact is that estimates
5098 * are computed over much shorter time intervals than the long
5099 * intervals typically used for benchmarking. Why? First, to
5100 * adapt more quickly to variations. Second, because an I/O
5101 * scheduler cannot rely on a peak-rate-evaluation workload to
5102 * be run for a long time.
5104 T_slow
[0] = msecs_to_jiffies(3500); /* actually 4 sec */
5105 T_slow
[1] = msecs_to_jiffies(6000); /* actually 6.5 sec */
5106 T_fast
[0] = msecs_to_jiffies(7000); /* actually 8 sec */
5107 T_fast
[1] = msecs_to_jiffies(2500); /* actually 3 sec */
5110 * Thresholds that determine the switch between speed classes
5111 * (see the comments before the definition of the array
5112 * device_speed_thresh). These thresholds are biased towards
5113 * transitions to the fast class. This is safer than the
5114 * opposite bias. In fact, a wrong transition to the slow
5115 * class results in short weight-raising periods, because the
5116 * speed of the device then tends to be higher that the
5117 * reference peak rate. On the opposite end, a wrong
5118 * transition to the fast class tends to increase
5119 * weight-raising periods, because of the opposite reason.
5121 device_speed_thresh
[0] = (4 * R_slow
[0]) / 3;
5122 device_speed_thresh
[1] = (4 * R_slow
[1]) / 3;
5124 ret
= elv_register(&iosched_bfq_mq
);
5133 #ifdef CONFIG_BFQ_GROUP_IOSCHED
5134 blkcg_policy_unregister(&blkcg_policy_bfq
);
5139 static void __exit
bfq_exit(void)
5141 elv_unregister(&iosched_bfq_mq
);
5142 #ifdef CONFIG_BFQ_GROUP_IOSCHED
5143 blkcg_policy_unregister(&blkcg_policy_bfq
);
5148 module_init(bfq_init
);
5149 module_exit(bfq_exit
);
5151 MODULE_AUTHOR("Paolo Valente");
5152 MODULE_LICENSE("GPL");
5153 MODULE_DESCRIPTION("MQ Budget Fair Queueing I/O Scheduler");