| /* |
| * Budget Fair Queueing (BFQ) I/O scheduler. |
| * |
| * Based on ideas and code from CFQ: |
| * Copyright (C) 2003 Jens Axboe <axboe@kernel.dk> |
| * |
| * Copyright (C) 2008 Fabio Checconi <fabio@gandalf.sssup.it> |
| * Paolo Valente <paolo.valente@unimore.it> |
| * |
| * Copyright (C) 2010 Paolo Valente <paolo.valente@unimore.it> |
| * Arianna Avanzini <avanzini@google.com> |
| * |
| * Copyright (C) 2017 Paolo Valente <paolo.valente@linaro.org> |
| * |
| * This program is free software; you can redistribute it and/or |
| * modify it under the terms of the GNU General Public License as |
| * published by the Free Software Foundation; either version 2 of the |
| * License, or (at your option) any later version. |
| * |
| * This program is distributed in the hope that it will be useful, |
| * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| * General Public License for more details. |
| * |
| * BFQ is a proportional-share I/O scheduler, with some extra |
| * low-latency capabilities. BFQ also supports full hierarchical |
| * scheduling through cgroups. Next paragraphs provide an introduction |
| * on BFQ inner workings. Details on BFQ benefits, usage and |
| * limitations can be found in Documentation/block/bfq-iosched.txt. |
| * |
| * BFQ is a proportional-share storage-I/O scheduling algorithm based |
| * on the slice-by-slice service scheme of CFQ. But BFQ assigns |
| * budgets, measured in number of sectors, to processes instead of |
| * time slices. The device is not granted to the in-service process |
| * for a given time slice, but until it has exhausted its assigned |
| * budget. This change from the time to the service domain enables BFQ |
| * to distribute the device throughput among processes as desired, |
| * without any distortion due to throughput fluctuations, or to device |
| * internal queueing. BFQ uses an ad hoc internal scheduler, called |
| * B-WF2Q+, to schedule processes according to their budgets. More |
| * precisely, BFQ schedules queues associated with processes. Each |
| * process/queue is assigned a user-configurable weight, and B-WF2Q+ |
| * guarantees that each queue receives a fraction of the throughput |
| * proportional to its weight. Thanks to the accurate policy of |
| * B-WF2Q+, BFQ can afford to assign high budgets to I/O-bound |
| * processes issuing sequential requests (to boost the throughput), |
| * and yet guarantee a low latency to interactive and soft real-time |
| * applications. |
| * |
| * In particular, to provide these low-latency guarantees, BFQ |
| * explicitly privileges the I/O of two classes of time-sensitive |
| * applications: interactive and soft real-time. This feature enables |
| * BFQ to provide applications in these classes with a very low |
| * latency. Finally, BFQ also features additional heuristics for |
| * preserving both a low latency and a high throughput on NCQ-capable, |
| * rotational or flash-based devices, and to get the job done quickly |
| * for applications consisting in many I/O-bound processes. |
| * |
| * NOTE: if the main or only goal, with a given device, is to achieve |
| * the maximum-possible throughput at all times, then do switch off |
| * all low-latency heuristics for that device, by setting low_latency |
| * to 0. |
| * |
| * BFQ is described in [1], where also a reference to the initial, more |
| * theoretical paper on BFQ can be found. The interested reader can find |
| * in the latter paper full details on the main algorithm, as well as |
| * formulas of the guarantees and formal proofs of all the properties. |
| * With respect to the version of BFQ presented in these papers, this |
| * implementation adds a few more heuristics, such as the one that |
| * guarantees a low latency to soft real-time applications, and a |
| * hierarchical extension based on H-WF2Q+. |
| * |
| * B-WF2Q+ is based on WF2Q+, which is described in [2], together with |
| * H-WF2Q+, while the augmented tree used here to implement B-WF2Q+ |
| * with O(log N) complexity derives from the one introduced with EEVDF |
| * in [3]. |
| * |
| * [1] P. Valente, A. Avanzini, "Evolution of the BFQ Storage I/O |
| * Scheduler", Proceedings of the First Workshop on Mobile System |
| * Technologies (MST-2015), May 2015. |
| * http://algogroup.unimore.it/people/paolo/disk_sched/mst-2015.pdf |
| * |
| * [2] Jon C.R. Bennett and H. Zhang, "Hierarchical Packet Fair Queueing |
| * Algorithms", IEEE/ACM Transactions on Networking, 5(5):675-689, |
| * Oct 1997. |
| * |
| * http://www.cs.cmu.edu/~hzhang/papers/TON-97-Oct.ps.gz |
| * |
| * [3] I. Stoica and H. Abdel-Wahab, "Earliest Eligible Virtual Deadline |
| * First: A Flexible and Accurate Mechanism for Proportional Share |
| * Resource Allocation", technical report. |
| * |
| * http://www.cs.berkeley.edu/~istoica/papers/eevdf-tr-95.pdf |
| */ |
| #include <linux/module.h> |
| #include <linux/slab.h> |
| #include <linux/blkdev.h> |
| #include <linux/cgroup.h> |
| #include <linux/elevator.h> |
| #include <linux/ktime.h> |
| #include <linux/rbtree.h> |
| #include <linux/ioprio.h> |
| #include <linux/sbitmap.h> |
| #include <linux/delay.h> |
| |
| #include "blk.h" |
| #include "blk-mq.h" |
| #include "blk-mq-tag.h" |
| #include "blk-mq-sched.h" |
| #include "bfq-iosched.h" |
| |
| #define BFQ_BFQQ_FNS(name) \ |
| void bfq_mark_bfqq_##name(struct bfq_queue *bfqq) \ |
| { \ |
| __set_bit(BFQQF_##name, &(bfqq)->flags); \ |
| } \ |
| void bfq_clear_bfqq_##name(struct bfq_queue *bfqq) \ |
| { \ |
| __clear_bit(BFQQF_##name, &(bfqq)->flags); \ |
| } \ |
| int bfq_bfqq_##name(const struct bfq_queue *bfqq) \ |
| { \ |
| return test_bit(BFQQF_##name, &(bfqq)->flags); \ |
| } |
| |
| BFQ_BFQQ_FNS(just_created); |
| BFQ_BFQQ_FNS(busy); |
| BFQ_BFQQ_FNS(wait_request); |
| BFQ_BFQQ_FNS(non_blocking_wait_rq); |
| BFQ_BFQQ_FNS(fifo_expire); |
| BFQ_BFQQ_FNS(has_short_ttime); |
| BFQ_BFQQ_FNS(sync); |
| BFQ_BFQQ_FNS(IO_bound); |
| BFQ_BFQQ_FNS(in_large_burst); |
| BFQ_BFQQ_FNS(coop); |
| BFQ_BFQQ_FNS(split_coop); |
| BFQ_BFQQ_FNS(softrt_update); |
| #undef BFQ_BFQQ_FNS \ |
| |
| /* Expiration time of sync (0) and async (1) requests, in ns. */ |
| static const u64 bfq_fifo_expire[2] = { NSEC_PER_SEC / 4, NSEC_PER_SEC / 8 }; |
| |
| /* Maximum backwards seek (magic number lifted from CFQ), in KiB. */ |
| static const int bfq_back_max = 16 * 1024; |
| |
| /* Penalty of a backwards seek, in number of sectors. */ |
| static const int bfq_back_penalty = 2; |
| |
| /* Idling period duration, in ns. */ |
| static u64 bfq_slice_idle = NSEC_PER_SEC / 125; |
| |
| /* Minimum number of assigned budgets for which stats are safe to compute. */ |
| static const int bfq_stats_min_budgets = 194; |
| |
| /* Default maximum budget values, in sectors and number of requests. */ |
| static const int bfq_default_max_budget = 16 * 1024; |
| |
| /* |
| * Async to sync throughput distribution is controlled as follows: |
| * when an async request is served, the entity is charged the number |
| * of sectors of the request, multiplied by the factor below |
| */ |
| static const int bfq_async_charge_factor = 10; |
| |
| /* Default timeout values, in jiffies, approximating CFQ defaults. */ |
| const int bfq_timeout = HZ / 8; |
| |
| static struct kmem_cache *bfq_pool; |
| |
| /* Below this threshold (in ns), we consider thinktime immediate. */ |
| #define BFQ_MIN_TT (2 * NSEC_PER_MSEC) |
| |
| /* hw_tag detection: parallel requests threshold and min samples needed. */ |
| #define BFQ_HW_QUEUE_THRESHOLD 4 |
| #define BFQ_HW_QUEUE_SAMPLES 32 |
| |
| #define BFQQ_SEEK_THR (sector_t)(8 * 100) |
| #define BFQQ_SECT_THR_NONROT (sector_t)(2 * 32) |
| #define BFQQ_CLOSE_THR (sector_t)(8 * 1024) |
| #define BFQQ_SEEKY(bfqq) (hweight32(bfqq->seek_history) > 32/8) |
| |
| /* Min number of samples required to perform peak-rate update */ |
| #define BFQ_RATE_MIN_SAMPLES 32 |
| /* Min observation time interval required to perform a peak-rate update (ns) */ |
| #define BFQ_RATE_MIN_INTERVAL (300*NSEC_PER_MSEC) |
| /* Target observation time interval for a peak-rate update (ns) */ |
| #define BFQ_RATE_REF_INTERVAL NSEC_PER_SEC |
| |
| /* Shift used for peak rate fixed precision calculations. */ |
| #define BFQ_RATE_SHIFT 16 |
| |
| /* |
| * By default, BFQ computes the duration of the weight raising for |
| * interactive applications automatically, using the following formula: |
| * duration = (R / r) * T, where r is the peak rate of the device, and |
| * R and T are two reference parameters. |
| * In particular, R is the peak rate of the reference device (see below), |
| * and T is a reference time: given the systems that are likely to be |
| * installed on the reference device according to its speed class, T is |
| * about the maximum time needed, under BFQ and while reading two files in |
| * parallel, to load typical large applications on these systems. |
| * In practice, the slower/faster the device at hand is, the more/less it |
| * takes to load applications with respect to the reference device. |
| * Accordingly, the longer/shorter BFQ grants weight raising to interactive |
| * applications. |
| * |
| * BFQ uses four different reference pairs (R, T), depending on: |
| * . whether the device is rotational or non-rotational; |
| * . whether the device is slow, such as old or portable HDDs, as well as |
| * SD cards, or fast, such as newer HDDs and SSDs. |
| * |
| * The device's speed class is dynamically (re)detected in |
| * bfq_update_peak_rate() every time the estimated peak rate is updated. |
| * |
| * In the following definitions, R_slow[0]/R_fast[0] and |
| * T_slow[0]/T_fast[0] are the reference values for a slow/fast |
| * rotational device, whereas R_slow[1]/R_fast[1] and |
| * T_slow[1]/T_fast[1] are the reference values for a slow/fast |
| * non-rotational device. Finally, device_speed_thresh are the |
| * thresholds used to switch between speed classes. The reference |
| * rates are not the actual peak rates of the devices used as a |
| * reference, but slightly lower values. The reason for using these |
| * slightly lower values is that the peak-rate estimator tends to |
| * yield slightly lower values than the actual peak rate (it can yield |
| * the actual peak rate only if there is only one process doing I/O, |
| * and the process does sequential I/O). |
| * |
| * Both the reference peak rates and the thresholds are measured in |
| * sectors/usec, left-shifted by BFQ_RATE_SHIFT. |
| */ |
| static int R_slow[2] = {1000, 10700}; |
| static int R_fast[2] = {14000, 33000}; |
| /* |
| * To improve readability, a conversion function is used to initialize the |
| * following arrays, which entails that they can be initialized only in a |
| * function. |
| */ |
| static int T_slow[2]; |
| static int T_fast[2]; |
| static int device_speed_thresh[2]; |
| |
| #define RQ_BIC(rq) icq_to_bic((rq)->elv.priv[0]) |
| #define RQ_BFQQ(rq) ((rq)->elv.priv[1]) |
| |
| struct bfq_queue *bic_to_bfqq(struct bfq_io_cq *bic, bool is_sync) |
| { |
| return bic->bfqq[is_sync]; |
| } |
| |
| void bic_set_bfqq(struct bfq_io_cq *bic, struct bfq_queue *bfqq, bool is_sync) |
| { |
| bic->bfqq[is_sync] = bfqq; |
| } |
| |
| struct bfq_data *bic_to_bfqd(struct bfq_io_cq *bic) |
| { |
| return bic->icq.q->elevator->elevator_data; |
| } |
| |
| /** |
| * icq_to_bic - convert iocontext queue structure to bfq_io_cq. |
| * @icq: the iocontext queue. |
| */ |
| static struct bfq_io_cq *icq_to_bic(struct io_cq *icq) |
| { |
| /* bic->icq is the first member, %NULL will convert to %NULL */ |
| return container_of(icq, struct bfq_io_cq, icq); |
| } |
| |
| /** |
| * bfq_bic_lookup - search into @ioc a bic associated to @bfqd. |
| * @bfqd: the lookup key. |
| * @ioc: the io_context of the process doing I/O. |
| * @q: the request queue. |
| */ |
| static struct bfq_io_cq *bfq_bic_lookup(struct bfq_data *bfqd, |
| struct io_context *ioc, |
| struct request_queue *q) |
| { |
| if (ioc) { |
| unsigned long flags; |
| struct bfq_io_cq *icq; |
| |
| spin_lock_irqsave(q->queue_lock, flags); |
| icq = icq_to_bic(ioc_lookup_icq(ioc, q)); |
| spin_unlock_irqrestore(q->queue_lock, flags); |
| |
| return icq; |
| } |
| |
| return NULL; |
| } |
| |
| /* |
| * Scheduler run of queue, if there are requests pending and no one in the |
| * driver that will restart queueing. |
| */ |
| void bfq_schedule_dispatch(struct bfq_data *bfqd) |
| { |
| if (bfqd->queued != 0) { |
| bfq_log(bfqd, "schedule dispatch"); |
| blk_mq_run_hw_queues(bfqd->queue, true); |
| } |
| } |
| |
| #define bfq_class_idle(bfqq) ((bfqq)->ioprio_class == IOPRIO_CLASS_IDLE) |
| #define bfq_class_rt(bfqq) ((bfqq)->ioprio_class == IOPRIO_CLASS_RT) |
| |
| #define bfq_sample_valid(samples) ((samples) > 80) |
| |
| /* |
| * Lifted from AS - choose which of rq1 and rq2 that is best served now. |
| * We choose the request that is closesr to the head right now. Distance |
| * behind the head is penalized and only allowed to a certain extent. |
| */ |
| static struct request *bfq_choose_req(struct bfq_data *bfqd, |
| struct request *rq1, |
| struct request *rq2, |
| sector_t last) |
| { |
| sector_t s1, s2, d1 = 0, d2 = 0; |
| unsigned long back_max; |
| #define BFQ_RQ1_WRAP 0x01 /* request 1 wraps */ |
| #define BFQ_RQ2_WRAP 0x02 /* request 2 wraps */ |
| unsigned int wrap = 0; /* bit mask: requests behind the disk head? */ |
| |
| if (!rq1 || rq1 == rq2) |
| return rq2; |
| if (!rq2) |
| return rq1; |
| |
| if (rq_is_sync(rq1) && !rq_is_sync(rq2)) |
| return rq1; |
| else if (rq_is_sync(rq2) && !rq_is_sync(rq1)) |
| return rq2; |
| if ((rq1->cmd_flags & REQ_META) && !(rq2->cmd_flags & REQ_META)) |
| return rq1; |
| else if ((rq2->cmd_flags & REQ_META) && !(rq1->cmd_flags & REQ_META)) |
| return rq2; |
| |
| s1 = blk_rq_pos(rq1); |
| s2 = blk_rq_pos(rq2); |
| |
| /* |
| * By definition, 1KiB is 2 sectors. |
| */ |
| back_max = bfqd->bfq_back_max * 2; |
| |
| /* |
| * Strict one way elevator _except_ in the case where we allow |
| * short backward seeks which are biased as twice the cost of a |
| * similar forward seek. |
| */ |
| if (s1 >= last) |
| d1 = s1 - last; |
| else if (s1 + back_max >= last) |
| d1 = (last - s1) * bfqd->bfq_back_penalty; |
| else |
| wrap |= BFQ_RQ1_WRAP; |
| |
| if (s2 >= last) |
| d2 = s2 - last; |
| else if (s2 + back_max >= last) |
| d2 = (last - s2) * bfqd->bfq_back_penalty; |
| else |
| wrap |= BFQ_RQ2_WRAP; |
| |
| /* Found required data */ |
| |
| /* |
| * By doing switch() on the bit mask "wrap" we avoid having to |
| * check two variables for all permutations: --> faster! |
| */ |
| switch (wrap) { |
| case 0: /* common case for CFQ: rq1 and rq2 not wrapped */ |
| if (d1 < d2) |
| return rq1; |
| else if (d2 < d1) |
| return rq2; |
| |
| if (s1 >= s2) |
| return rq1; |
| else |
| return rq2; |
| |
| case BFQ_RQ2_WRAP: |
| return rq1; |
| case BFQ_RQ1_WRAP: |
| return rq2; |
| case BFQ_RQ1_WRAP|BFQ_RQ2_WRAP: /* both rqs wrapped */ |
| default: |
| /* |
| * Since both rqs are wrapped, |
| * start with the one that's further behind head |
| * (--> only *one* back seek required), |
| * since back seek takes more time than forward. |
| */ |
| if (s1 <= s2) |
| return rq1; |
| else |
| return rq2; |
| } |
| } |
| |
| static struct bfq_queue * |
| bfq_rq_pos_tree_lookup(struct bfq_data *bfqd, struct rb_root *root, |
| sector_t sector, struct rb_node **ret_parent, |
| struct rb_node ***rb_link) |
| { |
| struct rb_node **p, *parent; |
| struct bfq_queue *bfqq = NULL; |
| |
| parent = NULL; |
| p = &root->rb_node; |
| while (*p) { |
| struct rb_node **n; |
| |
| parent = *p; |
| bfqq = rb_entry(parent, struct bfq_queue, pos_node); |
| |
| /* |
| * Sort strictly based on sector. Smallest to the left, |
| * largest to the right. |
| */ |
| if (sector > blk_rq_pos(bfqq->next_rq)) |
| n = &(*p)->rb_right; |
| else if (sector < blk_rq_pos(bfqq->next_rq)) |
| n = &(*p)->rb_left; |
| else |
| break; |
| p = n; |
| bfqq = NULL; |
| } |
| |
| *ret_parent = parent; |
| if (rb_link) |
| *rb_link = p; |
| |
| bfq_log(bfqd, "rq_pos_tree_lookup %llu: returning %d", |
| (unsigned long long)sector, |
| bfqq ? bfqq->pid : 0); |
| |
| return bfqq; |
| } |
| |
| void bfq_pos_tree_add_move(struct bfq_data *bfqd, struct bfq_queue *bfqq) |
| { |
| struct rb_node **p, *parent; |
| struct bfq_queue *__bfqq; |
| |
| if (bfqq->pos_root) { |
| rb_erase(&bfqq->pos_node, bfqq->pos_root); |
| bfqq->pos_root = NULL; |
| } |
| |
| if (bfq_class_idle(bfqq)) |
| return; |
| if (!bfqq->next_rq) |
| return; |
| |
| bfqq->pos_root = &bfq_bfqq_to_bfqg(bfqq)->rq_pos_tree; |
| __bfqq = bfq_rq_pos_tree_lookup(bfqd, bfqq->pos_root, |
| blk_rq_pos(bfqq->next_rq), &parent, &p); |
| if (!__bfqq) { |
| rb_link_node(&bfqq->pos_node, parent, p); |
| rb_insert_color(&bfqq->pos_node, bfqq->pos_root); |
| } else |
| bfqq->pos_root = NULL; |
| } |
| |
| /* |
| * Tell whether there are active queues or groups with differentiated weights. |
| */ |
| static bool bfq_differentiated_weights(struct bfq_data *bfqd) |
| { |
| /* |
| * For weights to differ, at least one of the trees must contain |
| * at least two nodes. |
| */ |
| return (!RB_EMPTY_ROOT(&bfqd->queue_weights_tree) && |
| (bfqd->queue_weights_tree.rb_node->rb_left || |
| bfqd->queue_weights_tree.rb_node->rb_right) |
| #ifdef CONFIG_BFQ_GROUP_IOSCHED |
| ) || |
| (!RB_EMPTY_ROOT(&bfqd->group_weights_tree) && |
| (bfqd->group_weights_tree.rb_node->rb_left || |
| bfqd->group_weights_tree.rb_node->rb_right) |
| #endif |
| ); |
| } |
| |
| /* |
| * The following function returns true if every queue must receive the |
| * same share of the throughput (this condition is used when deciding |
| * whether idling may be disabled, see the comments in the function |
| * bfq_bfqq_may_idle()). |
| * |
| * Such a scenario occurs when: |
| * 1) all active queues have the same weight, |
| * 2) all active groups at the same level in the groups tree have the same |
| * weight, |
| * 3) all active groups at the same level in the groups tree have the same |
| * number of children. |
| * |
| * Unfortunately, keeping the necessary state for evaluating exactly the |
| * above symmetry conditions would be quite complex and time-consuming. |
| * Therefore this function evaluates, instead, the following stronger |
| * sub-conditions, for which it is much easier to maintain the needed |
| * state: |
| * 1) all active queues have the same weight, |
| * 2) all active groups have the same weight, |
| * 3) all active groups have at most one active child each. |
| * In particular, the last two conditions are always true if hierarchical |
| * support and the cgroups interface are not enabled, thus no state needs |
| * to be maintained in this case. |
| */ |
| static bool bfq_symmetric_scenario(struct bfq_data *bfqd) |
| { |
| return !bfq_differentiated_weights(bfqd); |
| } |
| |
| /* |
| * If the weight-counter tree passed as input contains no counter for |
| * the weight of the input entity, then add that counter; otherwise just |
| * increment the existing counter. |
| * |
| * Note that weight-counter trees contain few nodes in mostly symmetric |
| * scenarios. For example, if all queues have the same weight, then the |
| * weight-counter tree for the queues may contain at most one node. |
| * This holds even if low_latency is on, because weight-raised queues |
| * are not inserted in the tree. |
| * In most scenarios, the rate at which nodes are created/destroyed |
| * should be low too. |
| */ |
| void bfq_weights_tree_add(struct bfq_data *bfqd, struct bfq_entity *entity, |
| struct rb_root *root) |
| { |
| struct rb_node **new = &(root->rb_node), *parent = NULL; |
| |
| /* |
| * Do not insert if the entity is already associated with a |
| * counter, which happens if: |
| * 1) the entity is associated with a queue, |
| * 2) a request arrival has caused the queue to become both |
| * non-weight-raised, and hence change its weight, and |
| * backlogged; in this respect, each of the two events |
| * causes an invocation of this function, |
| * 3) this is the invocation of this function caused by the |
| * second event. This second invocation is actually useless, |
| * and we handle this fact by exiting immediately. More |
| * efficient or clearer solutions might possibly be adopted. |
| */ |
| if (entity->weight_counter) |
| return; |
| |
| while (*new) { |
| struct bfq_weight_counter *__counter = container_of(*new, |
| struct bfq_weight_counter, |
| weights_node); |
| parent = *new; |
| |
| if (entity->weight == __counter->weight) { |
| entity->weight_counter = __counter; |
| goto inc_counter; |
| } |
| if (entity->weight < __counter->weight) |
| new = &((*new)->rb_left); |
| else |
| new = &((*new)->rb_right); |
| } |
| |
| entity->weight_counter = kzalloc(sizeof(struct bfq_weight_counter), |
| GFP_ATOMIC); |
| |
| /* |
| * In the unlucky event of an allocation failure, we just |
| * exit. This will cause the weight of entity to not be |
| * considered in bfq_differentiated_weights, which, in its |
| * turn, causes the scenario to be deemed wrongly symmetric in |
| * case entity's weight would have been the only weight making |
| * the scenario asymmetric. On the bright side, no unbalance |
| * will however occur when entity becomes inactive again (the |
| * invocation of this function is triggered by an activation |
| * of entity). In fact, bfq_weights_tree_remove does nothing |
| * if !entity->weight_counter. |
| */ |
| if (unlikely(!entity->weight_counter)) |
| return; |
| |
| entity->weight_counter->weight = entity->weight; |
| rb_link_node(&entity->weight_counter->weights_node, parent, new); |
| rb_insert_color(&entity->weight_counter->weights_node, root); |
| |
| inc_counter: |
| entity->weight_counter->num_active++; |
| } |
| |
| /* |
| * Decrement the weight counter associated with the entity, and, if the |
| * counter reaches 0, remove the counter from the tree. |
| * See the comments to the function bfq_weights_tree_add() for considerations |
| * about overhead. |
| */ |
| void bfq_weights_tree_remove(struct bfq_data *bfqd, struct bfq_entity *entity, |
| struct rb_root *root) |
| { |
| if (!entity->weight_counter) |
| return; |
| |
| entity->weight_counter->num_active--; |
| if (entity->weight_counter->num_active > 0) |
| goto reset_entity_pointer; |
| |
| rb_erase(&entity->weight_counter->weights_node, root); |
| kfree(entity->weight_counter); |
| |
| reset_entity_pointer: |
| entity->weight_counter = NULL; |
| } |
| |
| /* |
| * Return expired entry, or NULL to just start from scratch in rbtree. |
| */ |
| static struct request *bfq_check_fifo(struct bfq_queue *bfqq, |
| struct request *last) |
| { |
| struct request *rq; |
| |
| if (bfq_bfqq_fifo_expire(bfqq)) |
| return NULL; |
| |
| bfq_mark_bfqq_fifo_expire(bfqq); |
| |
| rq = rq_entry_fifo(bfqq->fifo.next); |
| |
| if (rq == last || ktime_get_ns() < rq->fifo_time) |
| return NULL; |
| |
| bfq_log_bfqq(bfqq->bfqd, bfqq, "check_fifo: returned %p", rq); |
| return rq; |
| } |
| |
| static struct request *bfq_find_next_rq(struct bfq_data *bfqd, |
| struct bfq_queue *bfqq, |
| struct request *last) |
| { |
| struct rb_node *rbnext = rb_next(&last->rb_node); |
| struct rb_node *rbprev = rb_prev(&last->rb_node); |
| struct request *next, *prev = NULL; |
| |
| /* Follow expired path, else get first next available. */ |
| next = bfq_check_fifo(bfqq, last); |
| if (next) |
| return next; |
| |
| if (rbprev) |
| prev = rb_entry_rq(rbprev); |
| |
| if (rbnext) |
| next = rb_entry_rq(rbnext); |
| else { |
| rbnext = rb_first(&bfqq->sort_list); |
| if (rbnext && rbnext != &last->rb_node) |
| next = rb_entry_rq(rbnext); |
| } |
| |
| return bfq_choose_req(bfqd, next, prev, blk_rq_pos(last)); |
| } |
| |
| /* see the definition of bfq_async_charge_factor for details */ |
| static unsigned long bfq_serv_to_charge(struct request *rq, |
| struct bfq_queue *bfqq) |
| { |
| if (bfq_bfqq_sync(bfqq) || bfqq->wr_coeff > 1) |
| return blk_rq_sectors(rq); |
| |
| /* |
| * If there are no weight-raised queues, then amplify service |
| * by just the async charge factor; otherwise amplify service |
| * by twice the async charge factor, to further reduce latency |
| * for weight-raised queues. |
| */ |
| if (bfqq->bfqd->wr_busy_queues == 0) |
| return blk_rq_sectors(rq) * bfq_async_charge_factor; |
| |
| return blk_rq_sectors(rq) * 2 * bfq_async_charge_factor; |
| } |
| |
| /** |
| * bfq_updated_next_req - update the queue after a new next_rq selection. |
| * @bfqd: the device data the queue belongs to. |
| * @bfqq: the queue to update. |
| * |
| * If the first request of a queue changes we make sure that the queue |
| * has enough budget to serve at least its first request (if the |
| * request has grown). We do this because if the queue has not enough |
| * budget for its first request, it has to go through two dispatch |
| * rounds to actually get it dispatched. |
| */ |
| static void bfq_updated_next_req(struct bfq_data *bfqd, |
| struct bfq_queue *bfqq) |
| { |
| struct bfq_entity *entity = &bfqq->entity; |
| struct request *next_rq = bfqq->next_rq; |
| unsigned long new_budget; |
| |
| if (!next_rq) |
| return; |
| |
| if (bfqq == bfqd->in_service_queue) |
| /* |
| * In order not to break guarantees, budgets cannot be |
| * changed after an entity has been selected. |
| */ |
| return; |
| |
| new_budget = max_t(unsigned long, bfqq->max_budget, |
| bfq_serv_to_charge(next_rq, bfqq)); |
| if (entity->budget != new_budget) { |
| entity->budget = new_budget; |
| bfq_log_bfqq(bfqd, bfqq, "updated next rq: new budget %lu", |
| new_budget); |
| bfq_requeue_bfqq(bfqd, bfqq, false); |
| } |
| } |
| |
| static void |
| bfq_bfqq_resume_state(struct bfq_queue *bfqq, struct bfq_data *bfqd, |
| struct bfq_io_cq *bic, bool bfq_already_existing) |
| { |
| unsigned int old_wr_coeff = bfqq->wr_coeff; |
| bool busy = bfq_already_existing && bfq_bfqq_busy(bfqq); |
| |
| if (bic->saved_has_short_ttime) |
| bfq_mark_bfqq_has_short_ttime(bfqq); |
| else |
| bfq_clear_bfqq_has_short_ttime(bfqq); |
| |
| if (bic->saved_IO_bound) |
| bfq_mark_bfqq_IO_bound(bfqq); |
| else |
| bfq_clear_bfqq_IO_bound(bfqq); |
| |
| bfqq->ttime = bic->saved_ttime; |
| bfqq->wr_coeff = bic->saved_wr_coeff; |
| bfqq->wr_start_at_switch_to_srt = bic->saved_wr_start_at_switch_to_srt; |
| bfqq->last_wr_start_finish = bic->saved_last_wr_start_finish; |
| bfqq->wr_cur_max_time = bic->saved_wr_cur_max_time; |
| |
| if (bfqq->wr_coeff > 1 && (bfq_bfqq_in_large_burst(bfqq) || |
| time_is_before_jiffies(bfqq->last_wr_start_finish + |
| bfqq->wr_cur_max_time))) { |
| bfq_log_bfqq(bfqq->bfqd, bfqq, |
| "resume state: switching off wr"); |
| |
| bfqq->wr_coeff = 1; |
| } |
| |
| /* make sure weight will be updated, however we got here */ |
| bfqq->entity.prio_changed = 1; |
| |
| if (likely(!busy)) |
| return; |
| |
| if (old_wr_coeff == 1 && bfqq->wr_coeff > 1) |
| bfqd->wr_busy_queues++; |
| else if (old_wr_coeff > 1 && bfqq->wr_coeff == 1) |
| bfqd->wr_busy_queues--; |
| } |
| |
| static int bfqq_process_refs(struct bfq_queue *bfqq) |
| { |
| return bfqq->ref - bfqq->allocated - bfqq->entity.on_st; |
| } |
| |
| /* Empty burst list and add just bfqq (see comments on bfq_handle_burst) */ |
| static void bfq_reset_burst_list(struct bfq_data *bfqd, struct bfq_queue *bfqq) |
| { |
| struct bfq_queue *item; |
| struct hlist_node *n; |
| |
| hlist_for_each_entry_safe(item, n, &bfqd->burst_list, burst_list_node) |
| hlist_del_init(&item->burst_list_node); |
| hlist_add_head(&bfqq->burst_list_node, &bfqd->burst_list); |
| bfqd->burst_size = 1; |
| bfqd->burst_parent_entity = bfqq->entity.parent; |
| } |
| |
| /* Add bfqq to the list of queues in current burst (see bfq_handle_burst) */ |
| static void bfq_add_to_burst(struct bfq_data *bfqd, struct bfq_queue *bfqq) |
| { |
| /* Increment burst size to take into account also bfqq */ |
| bfqd->burst_size++; |
| |
| if (bfqd->burst_size == bfqd->bfq_large_burst_thresh) { |
| struct bfq_queue *pos, *bfqq_item; |
| struct hlist_node *n; |
| |
| /* |
| * Enough queues have been activated shortly after each |
| * other to consider this burst as large. |
| */ |
| bfqd->large_burst = true; |
| |
| /* |
| * We can now mark all queues in the burst list as |
| * belonging to a large burst. |
| */ |
| hlist_for_each_entry(bfqq_item, &bfqd->burst_list, |
| burst_list_node) |
| bfq_mark_bfqq_in_large_burst(bfqq_item); |
| bfq_mark_bfqq_in_large_burst(bfqq); |
| |
| /* |
| * From now on, and until the current burst finishes, any |
| * new queue being activated shortly after the last queue |
| * was inserted in the burst can be immediately marked as |
| * belonging to a large burst. So the burst list is not |
| * needed any more. Remove it. |
| */ |
| hlist_for_each_entry_safe(pos, n, &bfqd->burst_list, |
| burst_list_node) |
| hlist_del_init(&pos->burst_list_node); |
| } else /* |
| * Burst not yet large: add bfqq to the burst list. Do |
| * not increment the ref counter for bfqq, because bfqq |
| * is removed from the burst list before freeing bfqq |
| * in put_queue. |
| */ |
| hlist_add_head(&bfqq->burst_list_node, &bfqd->burst_list); |
| } |
| |
| /* |
| * If many queues belonging to the same group happen to be created |
| * shortly after each other, then the processes associated with these |
| * queues have typically a common goal. In particular, bursts of queue |
| * creations are usually caused by services or applications that spawn |
| * many parallel threads/processes. Examples are systemd during boot, |
| * or git grep. To help these processes get their job done as soon as |
| * possible, it is usually better to not grant either weight-raising |
| * or device idling to their queues. |
| * |
| * In this comment we describe, firstly, the reasons why this fact |
| * holds, and, secondly, the next function, which implements the main |
| * steps needed to properly mark these queues so that they can then be |
| * treated in a different way. |
| * |
| * The above services or applications benefit mostly from a high |
| * throughput: the quicker the requests of the activated queues are |
| * cumulatively served, the sooner the target job of these queues gets |
| * completed. As a consequence, weight-raising any of these queues, |
| * which also implies idling the device for it, is almost always |
| * counterproductive. In most cases it just lowers throughput. |
| * |
| * On the other hand, a burst of queue creations may be caused also by |
| * the start of an application that does not consist of a lot of |
| * parallel I/O-bound threads. In fact, with a complex application, |
| * several short processes may need to be executed to start-up the |
| * application. In this respect, to start an application as quickly as |
| * possible, the best thing to do is in any case to privilege the I/O |
| * related to the application with respect to all other |
| * I/O. Therefore, the best strategy to start as quickly as possible |
| * an application that causes a burst of queue creations is to |
| * weight-raise all the queues created during the burst. This is the |
| * exact opposite of the best strategy for the other type of bursts. |
| * |
| * In the end, to take the best action for each of the two cases, the |
| * two types of bursts need to be distinguished. Fortunately, this |
| * seems relatively easy, by looking at the sizes of the bursts. In |
| * particular, we found a threshold such that only bursts with a |
| * larger size than that threshold are apparently caused by |
| * services or commands such as systemd or git grep. For brevity, |
| * hereafter we call just 'large' these bursts. BFQ *does not* |
| * weight-raise queues whose creation occurs in a large burst. In |
| * addition, for each of these queues BFQ performs or does not perform |
| * idling depending on which choice boosts the throughput more. The |
| * exact choice depends on the device and request pattern at |
| * hand. |
| * |
| * Unfortunately, false positives may occur while an interactive task |
| * is starting (e.g., an application is being started). The |
| * consequence is that the queues associated with the task do not |
| * enjoy weight raising as expected. Fortunately these false positives |
| * are very rare. They typically occur if some service happens to |
| * start doing I/O exactly when the interactive task starts. |
| * |
| * Turning back to the next function, it implements all the steps |
| * needed to detect the occurrence of a large burst and to properly |
| * mark all the queues belonging to it (so that they can then be |
| * treated in a different way). This goal is achieved by maintaining a |
| * "burst list" that holds, temporarily, the queues that belong to the |
| * burst in progress. The list is then used to mark these queues as |
| * belonging to a large burst if the burst does become large. The main |
| * steps are the following. |
| * |
| * . when the very first queue is created, the queue is inserted into the |
| * list (as it could be the first queue in a possible burst) |
| * |
| * . if the current burst has not yet become large, and a queue Q that does |
| * not yet belong to the burst is activated shortly after the last time |
| * at which a new queue entered the burst list, then the function appends |
| * Q to the burst list |
| * |
| * . if, as a consequence of the previous step, the burst size reaches |
| * the large-burst threshold, then |
| * |
| * . all the queues in the burst list are marked as belonging to a |
| * large burst |
| * |
| * . the burst list is deleted; in fact, the burst list already served |
| * its purpose (keeping temporarily track of the queues in a burst, |
| * so as to be able to mark them as belonging to a large burst in the |
| * previous sub-step), and now is not needed any more |
| * |
| * . the device enters a large-burst mode |
| * |
| * . if a queue Q that does not belong to the burst is created while |
| * the device is in large-burst mode and shortly after the last time |
| * at which a queue either entered the burst list or was marked as |
| * belonging to the current large burst, then Q is immediately marked |
| * as belonging to a large burst. |
| * |
| * . if a queue Q that does not belong to the burst is created a while |
| * later, i.e., not shortly after, than the last time at which a queue |
| * either entered the burst list or was marked as belonging to the |
| * current large burst, then the current burst is deemed as finished and: |
| * |
| * . the large-burst mode is reset if set |
| * |
| * . the burst list is emptied |
| * |
| * . Q is inserted in the burst list, as Q may be the first queue |
| * in a possible new burst (then the burst list contains just Q |
| * after this step). |
| */ |
| static void bfq_handle_burst(struct bfq_data *bfqd, struct bfq_queue *bfqq) |
| { |
| /* |
| * If bfqq is already in the burst list or is part of a large |
| * burst, or finally has just been split, then there is |
| * nothing else to do. |
| */ |
| if (!hlist_unhashed(&bfqq->burst_list_node) || |
| bfq_bfqq_in_large_burst(bfqq) || |
| time_is_after_eq_jiffies(bfqq->split_time + |
| msecs_to_jiffies(10))) |
| return; |
| |
| /* |
| * If bfqq's creation happens late enough, or bfqq belongs to |
| * a different group than the burst group, then the current |
| * burst is finished, and related data structures must be |
| * reset. |
| * |
| * In this respect, consider the special case where bfqq is |
| * the very first queue created after BFQ is selected for this |
| * device. In this case, last_ins_in_burst and |
| * burst_parent_entity are not yet significant when we get |
| * here. But it is easy to verify that, whether or not the |
| * following condition is true, bfqq will end up being |
| * inserted into the burst list. In particular the list will |
| * happen to contain only bfqq. And this is exactly what has |
| * to happen, as bfqq may be the first queue of the first |
| * burst. |
| */ |
| if (time_is_before_jiffies(bfqd->last_ins_in_burst + |
| bfqd->bfq_burst_interval) || |
| bfqq->entity.parent != bfqd->burst_parent_entity) { |
| bfqd->large_burst = false; |
| bfq_reset_burst_list(bfqd, bfqq); |
| goto end; |
| } |
| |
| /* |
| * If we get here, then bfqq is being activated shortly after the |
| * last queue. So, if the current burst is also large, we can mark |
| * bfqq as belonging to this large burst immediately. |
| */ |
| if (bfqd->large_burst) { |
| bfq_mark_bfqq_in_large_burst(bfqq); |
| goto end; |
| } |
| |
| /* |
| * If we get here, then a large-burst state has not yet been |
| * reached, but bfqq is being activated shortly after the last |
| * queue. Then we add bfqq to the burst. |
| */ |
| bfq_add_to_burst(bfqd, bfqq); |
| end: |
| /* |
| * At this point, bfqq either has been added to the current |
| * burst or has caused the current burst to terminate and a |
| * possible new burst to start. In particular, in the second |
| * case, bfqq has become the first queue in the possible new |
| * burst. In both cases last_ins_in_burst needs to be moved |
| * forward. |
| */ |
| bfqd->last_ins_in_burst = jiffies; |
| } |
| |
| static int bfq_bfqq_budget_left(struct bfq_queue *bfqq) |
| { |
| struct bfq_entity *entity = &bfqq->entity; |
| |
| return entity->budget - entity->service; |
| } |
| |
| /* |
| * If enough samples have been computed, return the current max budget |
| * stored in bfqd, which is dynamically updated according to the |
| * estimated disk peak rate; otherwise return the default max budget |
| */ |
| static int bfq_max_budget(struct bfq_data *bfqd) |
| { |
| if (bfqd->budgets_assigned < bfq_stats_min_budgets) |
| return bfq_default_max_budget; |
| else |
| return bfqd->bfq_max_budget; |
| } |
| |
| /* |
| * Return min budget, which is a fraction of the current or default |
| * max budget (trying with 1/32) |
| */ |
| static int bfq_min_budget(struct bfq_data *bfqd) |
| { |
| if (bfqd->budgets_assigned < bfq_stats_min_budgets) |
| return bfq_default_max_budget / 32; |
| else |
| return bfqd->bfq_max_budget / 32; |
| } |
| |
| /* |
| * The next function, invoked after the input queue bfqq switches from |
| * idle to busy, updates the budget of bfqq. The function also tells |
| * whether the in-service queue should be expired, by returning |
| * true. The purpose of expiring the in-service queue is to give bfqq |
| * the chance to possibly preempt the in-service queue, and the reason |
| * for preempting the in-service queue is to achieve one of the two |
| * goals below. |
| * |
| * 1. Guarantee to bfqq its reserved bandwidth even if bfqq has |
| * expired because it has remained idle. In particular, bfqq may have |
| * expired for one of the following two reasons: |
| * |
| * - BFQQE_NO_MORE_REQUESTS bfqq did not enjoy any device idling |
| * and did not make it to issue a new request before its last |
| * request was served; |
| * |
| * - BFQQE_TOO_IDLE bfqq did enjoy device idling, but did not issue |
| * a new request before the expiration of the idling-time. |
| * |
| * Even if bfqq has expired for one of the above reasons, the process |
| * associated with the queue may be however issuing requests greedily, |
| * and thus be sensitive to the bandwidth it receives (bfqq may have |
| * remained idle for other reasons: CPU high load, bfqq not enjoying |
| * idling, I/O throttling somewhere in the path from the process to |
| * the I/O scheduler, ...). But if, after every expiration for one of |
| * the above two reasons, bfqq has to wait for the service of at least |
| * one full budget of another queue before being served again, then |
| * bfqq is likely to get a much lower bandwidth or resource time than |
| * its reserved ones. To address this issue, two countermeasures need |
| * to be taken. |
| * |
| * First, the budget and the timestamps of bfqq need to be updated in |
| * a special way on bfqq reactivation: they need to be updated as if |
| * bfqq did not remain idle and did not expire. In fact, if they are |
| * computed as if bfqq expired and remained idle until reactivation, |
| * then the process associated with bfqq is treated as if, instead of |
| * being greedy, it stopped issuing requests when bfqq remained idle, |
| * and restarts issuing requests only on this reactivation. In other |
| * words, the scheduler does not help the process recover the "service |
| * hole" between bfqq expiration and reactivation. As a consequence, |
| * the process receives a lower bandwidth than its reserved one. In |
| * contrast, to recover this hole, the budget must be updated as if |
| * bfqq was not expired at all before this reactivation, i.e., it must |
| * be set to the value of the remaining budget when bfqq was |
| * expired. Along the same line, timestamps need to be assigned the |
| * value they had the last time bfqq was selected for service, i.e., |
| * before last expiration. Thus timestamps need to be back-shifted |
| * with respect to their normal computation (see [1] for more details |
| * on this tricky aspect). |
| * |
| * Secondly, to allow the process to recover the hole, the in-service |
| * queue must be expired too, to give bfqq the chance to preempt it |
| * immediately. In fact, if bfqq has to wait for a full budget of the |
| * in-service queue to be completed, then it may become impossible to |
| * let the process recover the hole, even if the back-shifted |
| * timestamps of bfqq are lower than those of the in-service queue. If |
| * this happens for most or all of the holes, then the process may not |
| * receive its reserved bandwidth. In this respect, it is worth noting |
| * that, being the service of outstanding requests unpreemptible, a |
| * little fraction of the holes may however be unrecoverable, thereby |
| * causing a little loss of bandwidth. |
| * |
| * The last important point is detecting whether bfqq does need this |
| * bandwidth recovery. In this respect, the next function deems the |
| * process associated with bfqq greedy, and thus allows it to recover |
| * the hole, if: 1) the process is waiting for the arrival of a new |
| * request (which implies that bfqq expired for one of the above two |
| * reasons), and 2) such a request has arrived soon. The first |
| * condition is controlled through the flag non_blocking_wait_rq, |
| * while the second through the flag arrived_in_time. If both |
| * conditions hold, then the function computes the budget in the |
| * above-described special way, and signals that the in-service queue |
| * should be expired. Timestamp back-shifting is done later in |
| * __bfq_activate_entity. |
| * |
| * 2. Reduce latency. Even if timestamps are not backshifted to let |
| * the process associated with bfqq recover a service hole, bfqq may |
| * however happen to have, after being (re)activated, a lower finish |
| * timestamp than the in-service queue. That is, the next budget of |
| * bfqq may have to be completed before the one of the in-service |
| * queue. If this is the case, then preempting the in-service queue |
| * allows this goal to be achieved, apart from the unpreemptible, |
| * outstanding requests mentioned above. |
| * |
| * Unfortunately, regardless of which of the above two goals one wants |
| * to achieve, service trees need first to be updated to know whether |
| * the in-service queue must be preempted. To have service trees |
| * correctly updated, the in-service queue must be expired and |
| * rescheduled, and bfqq must be scheduled too. This is one of the |
| * most costly operations (in future versions, the scheduling |
| * mechanism may be re-designed in such a way to make it possible to |
| * know whether preemption is needed without needing to update service |
| * trees). In addition, queue preemptions almost always cause random |
| * I/O, and thus loss of throughput. Because of these facts, the next |
| * function adopts the following simple scheme to avoid both costly |
| * operations and too frequent preemptions: it requests the expiration |
| * of the in-service queue (unconditionally) only for queues that need |
| * to recover a hole, or that either are weight-raised or deserve to |
| * be weight-raised. |
| */ |
| static bool bfq_bfqq_update_budg_for_activation(struct bfq_data *bfqd, |
| struct bfq_queue *bfqq, |
| bool arrived_in_time, |
| bool wr_or_deserves_wr) |
| { |
| struct bfq_entity *entity = &bfqq->entity; |
| |
| if (bfq_bfqq_non_blocking_wait_rq(bfqq) && arrived_in_time) { |
| /* |
| * We do not clear the flag non_blocking_wait_rq here, as |
| * the latter is used in bfq_activate_bfqq to signal |
| * that timestamps need to be back-shifted (and is |
| * cleared right after). |
| */ |
| |
| /* |
| * In next assignment we rely on that either |
| * entity->service or entity->budget are not updated |
| * on expiration if bfqq is empty (see |
| * __bfq_bfqq_recalc_budget). Thus both quantities |
| * remain unchanged after such an expiration, and the |
| * following statement therefore assigns to |
| * entity->budget the remaining budget on such an |
| * expiration. For clarity, entity->service is not |
| * updated on expiration in any case, and, in normal |
| * operation, is reset only when bfqq is selected for |
| * service (see bfq_get_next_queue). |
| */ |
| entity->budget = min_t(unsigned long, |
| bfq_bfqq_budget_left(bfqq), |
| bfqq->max_budget); |
| |
| return true; |
| } |
| |
| entity->budget = max_t(unsigned long, bfqq->max_budget, |
| bfq_serv_to_charge(bfqq->next_rq, bfqq)); |
| bfq_clear_bfqq_non_blocking_wait_rq(bfqq); |
| return wr_or_deserves_wr; |
| } |
| |
| static unsigned int bfq_wr_duration(struct bfq_data *bfqd) |
| { |
| u64 dur; |
| |
| if (bfqd->bfq_wr_max_time > 0) |
| return bfqd->bfq_wr_max_time; |
| |
| dur = bfqd->RT_prod; |
| do_div(dur, bfqd->peak_rate); |
| |
| /* |
| * Limit duration between 3 and 13 seconds. Tests show that |
| * higher values than 13 seconds often yield the opposite of |
| * the desired result, i.e., worsen responsiveness by letting |
| * non-interactive and non-soft-real-time applications |
| * preserve weight raising for a too long time interval. |
| * |
| * On the other end, lower values than 3 seconds make it |
| * difficult for most interactive tasks to complete their jobs |
| * before weight-raising finishes. |
| */ |
| if (dur > msecs_to_jiffies(13000)) |
| dur = msecs_to_jiffies(13000); |
| else if (dur < msecs_to_jiffies(3000)) |
| dur = msecs_to_jiffies(3000); |
| |
| return dur; |
| } |
| |
| static void bfq_update_bfqq_wr_on_rq_arrival(struct bfq_data *bfqd, |
| struct bfq_queue *bfqq, |
| unsigned int old_wr_coeff, |
| bool wr_or_deserves_wr, |
| bool interactive, |
| bool in_burst, |
| bool soft_rt) |
| { |
| if (old_wr_coeff == 1 && wr_or_deserves_wr) { |
| /* start a weight-raising period */ |
| if (interactive) { |
| bfqq->wr_coeff = bfqd->bfq_wr_coeff; |
| bfqq->wr_cur_max_time = bfq_wr_duration(bfqd); |
| } else { |
| bfqq->wr_start_at_switch_to_srt = jiffies; |
| bfqq->wr_coeff = bfqd->bfq_wr_coeff * |
| BFQ_SOFTRT_WEIGHT_FACTOR; |
| bfqq->wr_cur_max_time = |
| bfqd->bfq_wr_rt_max_time; |
| } |
| |
| /* |
| * If needed, further reduce budget to make sure it is |
| * close to bfqq's backlog, so as to reduce the |
| * scheduling-error component due to a too large |
| * budget. Do not care about throughput consequences, |
| * but only about latency. Finally, do not assign a |
| * too small budget either, to avoid increasing |
| * latency by causing too frequent expirations. |
| */ |
| bfqq->entity.budget = min_t(unsigned long, |
| bfqq->entity.budget, |
| 2 * bfq_min_budget(bfqd)); |
| } else if (old_wr_coeff > 1) { |
| if (interactive) { /* update wr coeff and duration */ |
| bfqq->wr_coeff = bfqd->bfq_wr_coeff; |
| bfqq->wr_cur_max_time = bfq_wr_duration(bfqd); |
| } else if (in_burst) |
| bfqq->wr_coeff = 1; |
| else if (soft_rt) { |
| /* |
| * The application is now or still meeting the |
| * requirements for being deemed soft rt. We |
| * can then correctly and safely (re)charge |
| * the weight-raising duration for the |
| * application with the weight-raising |
| * duration for soft rt applications. |
| * |
| * In particular, doing this recharge now, i.e., |
| * before the weight-raising period for the |
| * application finishes, reduces the probability |
| * of the following negative scenario: |
| * 1) the weight of a soft rt application is |
| * raised at startup (as for any newly |
| * created application), |
| * 2) since the application is not interactive, |
| * at a certain time weight-raising is |
| * stopped for the application, |
| * 3) at that time the application happens to |
| * still have pending requests, and hence |
| * is destined to not have a chance to be |
| * deemed soft rt before these requests are |
| * completed (see the comments to the |
| * function bfq_bfqq_softrt_next_start() |
| * for details on soft rt detection), |
| * 4) these pending requests experience a high |
| * latency because the application is not |
| * weight-raised while they are pending. |
| */ |
| if (bfqq->wr_cur_max_time != |
| bfqd->bfq_wr_rt_max_time) { |
| bfqq->wr_start_at_switch_to_srt = |
| bfqq->last_wr_start_finish; |
| |
| bfqq->wr_cur_max_time = |
| bfqd->bfq_wr_rt_max_time; |
| bfqq->wr_coeff = bfqd->bfq_wr_coeff * |
| BFQ_SOFTRT_WEIGHT_FACTOR; |
| } |
| bfqq->last_wr_start_finish = jiffies; |
| } |
| } |
| } |
| |
| static bool bfq_bfqq_idle_for_long_time(struct bfq_data *bfqd, |
| struct bfq_queue *bfqq) |
| { |
| return bfqq->dispatched == 0 && |
| time_is_before_jiffies( |
| bfqq->budget_timeout + |
| bfqd->bfq_wr_min_idle_time); |
| } |
| |
| static void bfq_bfqq_handle_idle_busy_switch(struct bfq_data *bfqd, |
| struct bfq_queue *bfqq, |
| int old_wr_coeff, |
| struct request *rq, |
| bool *interactive) |
| { |
| bool soft_rt, in_burst, wr_or_deserves_wr, |
| bfqq_wants_to_preempt, |
| idle_for_long_time = bfq_bfqq_idle_for_long_time(bfqd, bfqq), |
| /* |
| * See the comments on |
| * bfq_bfqq_update_budg_for_activation for |
| * details on the usage of the next variable. |
| */ |
| arrived_in_time = ktime_get_ns() <= |
| bfqq->ttime.last_end_request + |
| bfqd->bfq_slice_idle * 3; |
| |
| bfqg_stats_update_io_add(bfqq_group(RQ_BFQQ(rq)), bfqq, rq->cmd_flags); |
| |
| /* |
| * bfqq deserves to be weight-raised if: |
| * - it is sync, |
| * - it does not belong to a large burst, |
| * - it has been idle for enough time or is soft real-time, |
| * - is linked to a bfq_io_cq (it is not shared in any sense). |
| */ |
| in_burst = bfq_bfqq_in_large_burst(bfqq); |
| soft_rt = bfqd->bfq_wr_max_softrt_rate > 0 && |
| !in_burst && |
| time_is_before_jiffies(bfqq->soft_rt_next_start); |
| *interactive = !in_burst && idle_for_long_time; |
| wr_or_deserves_wr = bfqd->low_latency && |
| (bfqq->wr_coeff > 1 || |
| (bfq_bfqq_sync(bfqq) && |
| bfqq->bic && (*interactive || soft_rt))); |
| |
| /* |
| * Using the last flag, update budget and check whether bfqq |
| * may want to preempt the in-service queue. |
| */ |
| bfqq_wants_to_preempt = |
| bfq_bfqq_update_budg_for_activation(bfqd, bfqq, |
| arrived_in_time, |
| wr_or_deserves_wr); |
| |
| /* |
| * If bfqq happened to be activated in a burst, but has been |
| * idle for much more than an interactive queue, then we |
| * assume that, in the overall I/O initiated in the burst, the |
| * I/O associated with bfqq is finished. So bfqq does not need |
| * to be treated as a queue belonging to a burst |
| * anymore. Accordingly, we reset bfqq's in_large_burst flag |
| * if set, and remove bfqq from the burst list if it's |
| * there. We do not decrement burst_size, because the fact |
| * that bfqq does not need to belong to the burst list any |
| * more does not invalidate the fact that bfqq was created in |
| * a burst. |
| */ |
| if (likely(!bfq_bfqq_just_created(bfqq)) && |
| idle_for_long_time && |
| time_is_before_jiffies( |
| bfqq->budget_timeout + |
| msecs_to_jiffies(10000))) { |
| hlist_del_init(&bfqq->burst_list_node); |
| bfq_clear_bfqq_in_large_burst(bfqq); |
| } |
| |
| bfq_clear_bfqq_just_created(bfqq); |
| |
| |
| if (!bfq_bfqq_IO_bound(bfqq)) { |
| if (arrived_in_time) { |
| bfqq->requests_within_timer++; |
| if (bfqq->requests_within_timer >= |
| bfqd->bfq_requests_within_timer) |
| bfq_mark_bfqq_IO_bound(bfqq); |
| } else |
| bfqq->requests_within_timer = 0; |
| } |
| |
| if (bfqd->low_latency) { |
| if (unlikely(time_is_after_jiffies(bfqq->split_time))) |
| /* wraparound */ |
| bfqq->split_time = |
| jiffies - bfqd->bfq_wr_min_idle_time - 1; |
| |
| if (time_is_before_jiffies(bfqq->split_time + |
| bfqd->bfq_wr_min_idle_time)) { |
| bfq_update_bfqq_wr_on_rq_arrival(bfqd, bfqq, |
| old_wr_coeff, |
| wr_or_deserves_wr, |
| *interactive, |
| in_burst, |
| soft_rt); |
| |
| if (old_wr_coeff != bfqq->wr_coeff) |
| bfqq->entity.prio_changed = 1; |
| } |
| } |
| |
| bfqq->last_idle_bklogged = jiffies; |
| bfqq->service_from_backlogged = 0; |
| bfq_clear_bfqq_softrt_update(bfqq); |
| |
| bfq_add_bfqq_busy(bfqd, bfqq); |
| |
| /* |
| * Expire in-service queue only if preemption may be needed |
| * for guarantees. In this respect, the function |
| * next_queue_may_preempt just checks a simple, necessary |
| * condition, and not a sufficient condition based on |
| * timestamps. In fact, for the latter condition to be |
| * evaluated, timestamps would need first to be updated, and |
| * this operation is quite costly (see the comments on the |
| * function bfq_bfqq_update_budg_for_activation). |
| */ |
| if (bfqd->in_service_queue && bfqq_wants_to_preempt && |
| bfqd->in_service_queue->wr_coeff < bfqq->wr_coeff && |
| next_queue_may_preempt(bfqd)) |
| bfq_bfqq_expire(bfqd, bfqd->in_service_queue, |
| false, BFQQE_PREEMPTED); |
| } |
| |
| static void bfq_add_request(struct request *rq) |
| { |
| struct bfq_queue *bfqq = RQ_BFQQ(rq); |
| struct bfq_data *bfqd = bfqq->bfqd; |
| struct request *next_rq, *prev; |
| unsigned int old_wr_coeff = bfqq->wr_coeff; |
| bool interactive = false; |
| |
| bfq_log_bfqq(bfqd, bfqq, "add_request %d", rq_is_sync(rq)); |
| bfqq->queued[rq_is_sync(rq)]++; |
| bfqd->queued++; |
| |
| elv_rb_add(&bfqq->sort_list, rq); |
| |
| /* |
| * Check if this request is a better next-serve candidate. |
| */ |
| prev = bfqq->next_rq; |
| next_rq = bfq_choose_req(bfqd, bfqq->next_rq, rq, bfqd->last_position); |
| bfqq->next_rq = next_rq; |
| |
| /* |
| * Adjust priority tree position, if next_rq changes. |
| */ |
| if (prev != bfqq->next_rq) |
| bfq_pos_tree_add_move(bfqd, bfqq); |
| |
| if (!bfq_bfqq_busy(bfqq)) /* switching to busy ... */ |
| bfq_bfqq_handle_idle_busy_switch(bfqd, bfqq, old_wr_coeff, |
| rq, &interactive); |
| else { |
| if (bfqd->low_latency && old_wr_coeff == 1 && !rq_is_sync(rq) && |
| time_is_before_jiffies( |
| bfqq->last_wr_start_finish + |
| bfqd->bfq_wr_min_inter_arr_async)) { |
| bfqq->wr_coeff = bfqd->bfq_wr_coeff; |
| bfqq->wr_cur_max_time = bfq_wr_duration(bfqd); |
| |
| bfqd->wr_busy_queues++; |
| bfqq->entity.prio_changed = 1; |
| } |
| if (prev != bfqq->next_rq) |
| bfq_updated_next_req(bfqd, bfqq); |
| } |
| |
| /* |
| * Assign jiffies to last_wr_start_finish in the following |
| * cases: |
| * |
| * . if bfqq is not going to be weight-raised, because, for |
| * non weight-raised queues, last_wr_start_finish stores the |
| * arrival time of the last request; as of now, this piece |
| * of information is used only for deciding whether to |
| * weight-raise async queues |
| * |
| * . if bfqq is not weight-raised, because, if bfqq is now |
| * switching to weight-raised, then last_wr_start_finish |
| * stores the time when weight-raising starts |
| * |
| * . if bfqq is interactive, because, regardless of whether |
| * bfqq is currently weight-raised, the weight-raising |
| * period must start or restart (this case is considered |
| * separately because it is not detected by the above |
| * conditions, if bfqq is already weight-raised) |
| * |
| * last_wr_start_finish has to be updated also if bfqq is soft |
| * real-time, because the weight-raising period is constantly |
| * restarted on idle-to-busy transitions for these queues, but |
| * this is already done in bfq_bfqq_handle_idle_busy_switch if |
| * needed. |
| */ |
| if (bfqd->low_latency && |
| (old_wr_coeff == 1 || bfqq->wr_coeff == 1 || interactive)) |
| bfqq->last_wr_start_finish = jiffies; |
| } |
| |
| static struct request *bfq_find_rq_fmerge(struct bfq_data *bfqd, |
| struct bio *bio, |
| struct request_queue *q) |
| { |
| struct bfq_queue *bfqq = bfqd->bio_bfqq; |
| |
| |
| if (bfqq) |
| return elv_rb_find(&bfqq->sort_list, bio_end_sector(bio)); |
| |
| return NULL; |
| } |
| |
| static sector_t get_sdist(sector_t last_pos, struct request *rq) |
| { |
| if (last_pos) |
| return abs(blk_rq_pos(rq) - last_pos); |
| |
| return 0; |
| } |
| |
| #if 0 /* Still not clear if we can do without next two functions */ |
| static void bfq_activate_request(struct request_queue *q, struct request *rq) |
| { |
| struct bfq_data *bfqd = q->elevator->elevator_data; |
| |
| bfqd->rq_in_driver++; |
| } |
| |
| static void bfq_deactivate_request(struct request_queue *q, struct request *rq) |
| { |
| struct bfq_data *bfqd = q->elevator->elevator_data; |
| |
| bfqd->rq_in_driver--; |
| } |
| #endif |
| |
| static void bfq_remove_request(struct request_queue *q, |
| struct request *rq) |
| { |
| struct bfq_queue *bfqq = RQ_BFQQ(rq); |
| struct bfq_data *bfqd = bfqq->bfqd; |
| const int sync = rq_is_sync(rq); |
| |
| if (bfqq->next_rq == rq) { |
| bfqq->next_rq = bfq_find_next_rq(bfqd, bfqq, rq); |
| bfq_updated_next_req(bfqd, bfqq); |
| } |
| |
| if (rq->queuelist.prev != &rq->queuelist) |
| list_del_init(&rq->queuelist); |
| bfqq->queued[sync]--; |
| bfqd->queued--; |
| elv_rb_del(&bfqq->sort_list, rq); |
| |
| elv_rqhash_del(q, rq); |
| if (q->last_merge == rq) |
| q->last_merge = NULL; |
| |
| if (RB_EMPTY_ROOT(&bfqq->sort_list)) { |
| bfqq->next_rq = NULL; |
| |
| if (bfq_bfqq_busy(bfqq) && bfqq != bfqd->in_service_queue) { |
| bfq_del_bfqq_busy(bfqd, bfqq, false); |
| /* |
| * bfqq emptied. In normal operation, when |
| * bfqq is empty, bfqq->entity.service and |
| * bfqq->entity.budget must contain, |
| * respectively, the service received and the |
| * budget used last time bfqq emptied. These |
| * facts do not hold in this case, as at least |
| * this last removal occurred while bfqq is |
| * not in service. To avoid inconsistencies, |
| * reset both bfqq->entity.service and |
| * bfqq->entity.budget, if bfqq has still a |
| * process that may issue I/O requests to it. |
| */ |
| bfqq->entity.budget = bfqq->entity.service = 0; |
| } |
| |
| /* |
| * Remove queue from request-position tree as it is empty. |
| */ |
| if (bfqq->pos_root) { |
| rb_erase(&bfqq->pos_node, bfqq->pos_root); |
| bfqq->pos_root = NULL; |
| } |
| } |
| |
| if (rq->cmd_flags & REQ_META) |
| bfqq->meta_pending--; |
| |
| bfqg_stats_update_io_remove(bfqq_group(bfqq), rq->cmd_flags); |
| } |
| |
| static bool bfq_bio_merge(struct blk_mq_hw_ctx *hctx, struct bio *bio) |
| { |
| struct request_queue *q = hctx->queue; |
| struct bfq_data *bfqd = q->elevator->elevator_data; |
| struct request *free = NULL; |
| /* |
| * bfq_bic_lookup grabs the queue_lock: invoke it now and |
| * store its return value for later use, to avoid nesting |
| * queue_lock inside the bfqd->lock. We assume that the bic |
| * returned by bfq_bic_lookup does not go away before |
| * bfqd->lock is taken. |
| */ |
| struct bfq_io_cq *bic = bfq_bic_lookup(bfqd, current->io_context, q); |
| bool ret; |
| |
| spin_lock_irq(&bfqd->lock); |
| |
| if (bic) |
| bfqd->bio_bfqq = bic_to_bfqq(bic, op_is_sync(bio->bi_opf)); |
| else |
| bfqd->bio_bfqq = NULL; |
| bfqd->bio_bic = bic; |
| |
| ret = blk_mq_sched_try_merge(q, bio, &free); |
| |
| if (free) |
| blk_mq_free_request(free); |
| spin_unlock_irq(&bfqd->lock); |
| |
| return ret; |
| } |
| |
| static int bfq_request_merge(struct request_queue *q, struct request **req, |
| struct bio *bio) |
| { |
| struct bfq_data *bfqd = q->elevator->elevator_data; |
| struct request *__rq; |
| |
| __rq = bfq_find_rq_fmerge(bfqd, bio, q); |
| if (__rq && elv_bio_merge_ok(__rq, bio)) { |
| *req = __rq; |
| return ELEVATOR_FRONT_MERGE; |
| } |
| |
| return ELEVATOR_NO_MERGE; |
| } |
| |
| static void bfq_request_merged(struct request_queue *q, struct request *req, |
| enum elv_merge type) |
| { |
| if (type == ELEVATOR_FRONT_MERGE && |
| rb_prev(&req->rb_node) && |
| blk_rq_pos(req) < |
| blk_rq_pos(container_of(rb_prev(&req->rb_node), |
| struct request, rb_node))) { |
| struct bfq_queue *bfqq = RQ_BFQQ(req); |
| struct bfq_data *bfqd = bfqq->bfqd; |
| struct request *prev, *next_rq; |
| |
| /* Reposition request in its sort_list */ |
| elv_rb_del(&bfqq->sort_list, req); |
| elv_rb_add(&bfqq->sort_list, req); |
| |
| /* Choose next request to be served for bfqq */ |
| prev = bfqq->next_rq; |
| next_rq = bfq_choose_req(bfqd, bfqq->next_rq, req, |
| bfqd->last_position); |
| bfqq->next_rq = next_rq; |
| /* |
| * If next_rq changes, update both the queue's budget to |
| * fit the new request and the queue's position in its |
| * rq_pos_tree. |
| */ |
| if (prev != bfqq->next_rq) { |
| bfq_updated_next_req(bfqd, bfqq); |
| bfq_pos_tree_add_move(bfqd, bfqq); |
| } |
| } |
| } |
| |
| static void bfq_requests_merged(struct request_queue *q, struct request *rq, |
| struct request *next) |
| { |
| struct bfq_queue *bfqq = RQ_BFQQ(rq), *next_bfqq = RQ_BFQQ(next); |
| |
| if (!RB_EMPTY_NODE(&rq->rb_node)) |
| goto end; |
| spin_lock_irq(&bfqq->bfqd->lock); |
| |
| /* |
| * If next and rq belong to the same bfq_queue and next is older |
| * than rq, then reposition rq in the fifo (by substituting next |
| * with rq). Otherwise, if next and rq belong to different |
| * bfq_queues, never reposition rq: in fact, we would have to |
| * reposition it with respect to next's position in its own fifo, |
| * which would most certainly be too expensive with respect to |
| * the benefits. |
| */ |
| if (bfqq == next_bfqq && |
| !list_empty(&rq->queuelist) && !list_empty(&next->queuelist) && |
| next->fifo_time < rq->fifo_time) { |
| list_del_init(&rq->queuelist); |
| list_replace_init(&next->queuelist, &rq->queuelist); |
| rq->fifo_time = next->fifo_time; |
| } |
| |
| if (bfqq->next_rq == next) |
| bfqq->next_rq = rq; |
| |
| bfq_remove_request(q, next); |
| |
| spin_unlock_irq(&bfqq->bfqd->lock); |
| end: |
| bfqg_stats_update_io_merged(bfqq_group(bfqq), next->cmd_flags); |
| } |
| |
| /* Must be called with bfqq != NULL */ |
| static void bfq_bfqq_end_wr(struct bfq_queue *bfqq) |
| { |
| if (bfq_bfqq_busy(bfqq)) |
| bfqq->bfqd->wr_busy_queues--; |
| bfqq->wr_coeff = 1; |
| bfqq->wr_cur_max_time = 0; |
| bfqq->last_wr_start_finish = jiffies; |
| /* |
| * Trigger a weight change on the next invocation of |
| * __bfq_entity_update_weight_prio. |
| */ |
| bfqq->entity.prio_changed = 1; |
| } |
| |
| void bfq_end_wr_async_queues(struct bfq_data *bfqd, |
| struct bfq_group *bfqg) |
| { |
| int i, j; |
| |
| for (i = 0; i < 2; i++) |
| for (j = 0; j < IOPRIO_BE_NR; j++) |
| if (bfqg->async_bfqq[i][j]) |
| bfq_bfqq_end_wr(bfqg->async_bfqq[i][j]); |
| if (bfqg->async_idle_bfqq) |
| bfq_bfqq_end_wr(bfqg->async_idle_bfqq); |
| } |
| |
| static void bfq_end_wr(struct bfq_data *bfqd) |
| { |
| struct bfq_queue *bfqq; |
| |
| spin_lock_irq(&bfqd->lock); |
| |
| list_for_each_entry(bfqq, &bfqd->active_list, bfqq_list) |
| bfq_bfqq_end_wr(bfqq); |
| list_for_each_entry(bfqq, &bfqd->idle_list, bfqq_list) |
| bfq_bfqq_end_wr(bfqq); |
| bfq_end_wr_async(bfqd); |
| |
| spin_unlock_irq(&bfqd->lock); |
| } |
| |
| static sector_t bfq_io_struct_pos(void *io_struct, bool request) |
| { |
| if (request) |
| return blk_rq_pos(io_struct); |
| else |
| return ((struct bio *)io_struct)->bi_iter.bi_sector; |
| } |
| |
| static int bfq_rq_close_to_sector(void *io_struct, bool request, |
| sector_t sector) |
| { |
| return abs(bfq_io_struct_pos(io_struct, request) - sector) <= |
| BFQQ_CLOSE_THR; |
| } |
| |
| static struct bfq_queue *bfqq_find_close(struct bfq_data *bfqd, |
| struct bfq_queue *bfqq, |
| sector_t sector) |
| { |
| struct rb_root *root = &bfq_bfqq_to_bfqg(bfqq)->rq_pos_tree; |
| struct rb_node *parent, *node; |
| struct bfq_queue *__bfqq; |
| |
| if (RB_EMPTY_ROOT(root)) |
| return NULL; |
| |
| /* |
| * First, if we find a request starting at the end of the last |
| * request, choose it. |
| */ |
| __bfqq = bfq_rq_pos_tree_lookup(bfqd, root, sector, &parent, NULL); |
| if (__bfqq) |
| return __bfqq; |
| |
| /* |
| * If the exact sector wasn't found, the parent of the NULL leaf |
| * will contain the closest sector (rq_pos_tree sorted by |
| * next_request position). |
| */ |
| __bfqq = rb_entry(parent, struct bfq_queue, pos_node); |
| if (bfq_rq_close_to_sector(__bfqq->next_rq, true, sector)) |
| return __bfqq; |
| |
| if (blk_rq_pos(__bfqq->next_rq) < sector) |
| node = rb_next(&__bfqq->pos_node); |
| else |
| node = rb_prev(&__bfqq->pos_node); |
| if (!node) |
| return NULL; |
| |
| __bfqq = rb_entry(node, struct bfq_queue, pos_node); |
| if (bfq_rq_close_to_sector(__bfqq->next_rq, true, sector)) |
| return __bfqq; |
| |
| return NULL; |
| } |
| |
| static struct bfq_queue *bfq_find_close_cooperator(struct bfq_data *bfqd, |
| struct bfq_queue *cur_bfqq, |
| sector_t sector) |
| { |
| struct bfq_queue *bfqq; |
| |
| /* |
| * We shall notice if some of the queues are cooperating, |
| * e.g., working closely on the same area of the device. In |
| * that case, we can group them together and: 1) don't waste |
| * time idling, and 2) serve the union of their requests in |
| * the best possible order for throughput. |
| */ |
| bfqq = bfqq_find_close(bfqd, cur_bfqq, sector); |
| if (!bfqq || bfqq == cur_bfqq) |
| return NULL; |
| |
| return bfqq; |
| } |
| |
| static struct bfq_queue * |
| bfq_setup_merge(struct bfq_queue *bfqq, struct bfq_queue *new_bfqq) |
| { |
| int process_refs, new_process_refs; |
| struct bfq_queue *__bfqq; |
| |
| /* |
| * If there are no process references on the new_bfqq, then it is |
| * unsafe to follow the ->new_bfqq chain as other bfqq's in the chain |
| * may have dropped their last reference (not just their last process |
| * reference). |
| */ |
| if (!bfqq_process_refs(new_bfqq)) |
| return NULL; |
| |
| /* Avoid a circular list and skip interim queue merges. */ |
| while ((__bfqq = new_bfqq->new_bfqq)) { |
| if (__bfqq == bfqq) |
| return NULL; |
| new_bfqq = __bfqq; |
| } |
| |
| process_refs = bfqq_process_refs(bfqq); |
| new_process_refs = bfqq_process_refs(new_bfqq); |
| /* |
| * If the process for the bfqq has gone away, there is no |
| * sense in merging the queues. |
| */ |
| if (process_refs == 0 || new_process_refs == 0) |
| return NULL; |
| |
| bfq_log_bfqq(bfqq->bfqd, bfqq, "scheduling merge with queue %d", |
| new_bfqq->pid); |
| |
| /* |
| * Merging is just a redirection: the requests of the process |
| * owning one of the two queues are redirected to the other queue. |
| * The latter queue, in its turn, is set as shared if this is the |
| * first time that the requests of some process are redirected to |
| * it. |
| * |
| * We redirect bfqq to new_bfqq and not the opposite, because |
| * we are in the context of the process owning bfqq, thus we |
| * have the io_cq of this process. So we can immediately |
| * configure this io_cq to redirect the requests of the |
| * process to new_bfqq. In contrast, the io_cq of new_bfqq is |
| * not available any more (new_bfqq->bic == NULL). |
| * |
| * Anyway, even in case new_bfqq coincides with the in-service |
| * queue, redirecting requests the in-service queue is the |
| * best option, as we feed the in-service queue with new |
| * requests close to the last request served and, by doing so, |
| * are likely to increase the throughput. |
| */ |
| bfqq->new_bfqq = new_bfqq; |
| new_bfqq->ref += process_refs; |
| return new_bfqq; |
| } |
| |
| static bool bfq_may_be_close_cooperator(struct bfq_queue *bfqq, |
| struct bfq_queue *new_bfqq) |
| { |
| if (bfq_class_idle(bfqq) || bfq_class_idle(new_bfqq) || |
| (bfqq->ioprio_class != new_bfqq->ioprio_class)) |
| return false; |
| |
| /* |
| * If either of the queues has already been detected as seeky, |
| * then merging it with the other queue is unlikely to lead to |
| * sequential I/O. |
| */ |
| if (BFQQ_SEEKY(bfqq) || BFQQ_SEEKY(new_bfqq)) |
| return false; |
| |
| /* |
| * Interleaved I/O is known to be done by (some) applications |
| * only for reads, so it does not make sense to merge async |
| * queues. |
| */ |
| if (!bfq_bfqq_sync(bfqq) || !bfq_bfqq_sync(new_bfqq)) |
| return false; |
| |
| return true; |
| } |
| |
| /* |
| * If this function returns true, then bfqq cannot be merged. The idea |
| * is that true cooperation happens very early after processes start |
| * to do I/O. Usually, late cooperations are just accidental false |
| * positives. In case bfqq is weight-raised, such false positives |
| * would evidently degrade latency guarantees for bfqq. |
| */ |
| static bool wr_from_too_long(struct bfq_queue *bfqq) |
| { |
| return bfqq->wr_coeff > 1 && |
| time_is_before_jiffies(bfqq->last_wr_start_finish + |
| msecs_to_jiffies(100)); |
| } |
| |
| /* |
| * Attempt to schedule a merge of bfqq with the currently in-service |
| * queue or with a close queue among the scheduled queues. Return |
| * NULL if no merge was scheduled, a pointer to the shared bfq_queue |
| * structure otherwise. |
| * |
| * The OOM queue is not allowed to participate to cooperation: in fact, since |
| * the requests temporarily redirected to the OOM queue could be redirected |
| * again to dedicated queues at any time, the state needed to correctly |
| * handle merging with the OOM queue would be quite complex and expensive |
| * to maintain. Besides, in such a critical condition as an out of memory, |
| * the benefits of queue merging may be little relevant, or even negligible. |
| * |
| * Weight-raised queues can be merged only if their weight-raising |
| * period has just started. In fact cooperating processes are usually |
| * started together. Thus, with this filter we avoid false positives |
| * that would jeopardize low-latency guarantees. |
| * |
| * WARNING: queue merging may impair fairness among non-weight raised |
| * queues, for at least two reasons: 1) the original weight of a |
| * merged queue may change during the merged state, 2) even being the |
| * weight the same, a merged queue may be bloated with many more |
| * requests than the ones produced by its originally-associated |
| * process. |
| */ |
| static struct bfq_queue * |
| bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq, |
| void *io_struct, bool request) |
| { |
| struct bfq_queue *in_service_bfqq, *new_bfqq; |
| |
| if (bfqq->new_bfqq) |
| return bfqq->new_bfqq; |
| |
| if (!io_struct || |
| wr_from_too_long(bfqq) || |
| unlikely(bfqq == &bfqd->oom_bfqq)) |
| return NULL; |
| |
| /* If there is only one backlogged queue, don't search. */ |
| if (bfqd->busy_queues == 1) |
| return NULL; |
| |
| in_service_bfqq = bfqd->in_service_queue; |
| |
| if (!in_service_bfqq || in_service_bfqq == bfqq |
| || wr_from_too_long(in_service_bfqq) || |
| unlikely(in_service_bfqq == &bfqd->oom_bfqq)) |
| goto check_scheduled; |
| |
| if (bfq_rq_close_to_sector(io_struct, request, bfqd->last_position) && |
| bfqq->entity.parent == in_service_bfqq->entity.parent && |
| bfq_may_be_close_cooperator(bfqq, in_service_bfqq)) { |
| new_bfqq = bfq_setup_merge(bfqq, in_service_bfqq); |
| if (new_bfqq) |
| return new_bfqq; |
| } |
| /* |
| * Check whether there is a cooperator among currently scheduled |
| * queues. The only thing we need is that the bio/request is not |
| * NULL, as we need it to establish whether a cooperator exists. |
| */ |
| check_scheduled: |
| new_bfqq = bfq_find_close_cooperator(bfqd, bfqq, |
| bfq_io_struct_pos(io_struct, request)); |
| |
| if (new_bfqq && !wr_from_too_long(new_bfqq) && |
| likely(new_bfqq != &bfqd->oom_bfqq) && |
| bfq_may_be_close_cooperator(bfqq, new_bfqq)) |
| return bfq_setup_merge(bfqq, new_bfqq); |
| |
| return NULL; |
| } |
| |
| static void bfq_bfqq_save_state(struct bfq_queue *bfqq) |
| { |
| struct bfq_io_cq *bic = bfqq->bic; |
| |
| /* |
| * If !bfqq->bic, the queue is already shared or its requests |
| * have already been redirected to a shared queue; both idle window |
| * and weight raising state have already been saved. Do nothing. |
| */ |
| if (!bic) |
| return; |
| |
| bic->saved_ttime = bfqq->ttime; |
| bic->saved_has_short_ttime = bfq_bfqq_has_short_ttime(bfqq); |
| bic->saved_IO_bound = bfq_bfqq_IO_bound(bfqq); |
| bic->saved_in_large_burst = bfq_bfqq_in_large_burst(bfqq); |
| bic->was_in_burst_list = !hlist_unhashed(&bfqq->burst_list_node); |
| bic->saved_wr_coeff = bfqq->wr_coeff; |
| bic->saved_wr_start_at_switch_to_srt = bfqq->wr_start_at_switch_to_srt; |
| bic->saved_last_wr_start_finish = bfqq->last_wr_start_finish; |
| bic->saved_wr_cur_max_time = bfqq->wr_cur_max_time; |
| } |
| |
| static void |
| bfq_merge_bfqqs(struct bfq_data *bfqd, struct bfq_io_cq *bic, |
| struct bfq_queue *bfqq, struct bfq_queue *new_bfqq) |
| { |
| bfq_log_bfqq(bfqd, bfqq, "merging with queue %lu", |
| (unsigned long)new_bfqq->pid); |
| /* Save weight raising and idle window of the merged queues */ |
| bfq_bfqq_save_state(bfqq); |
| bfq_bfqq_save_state(new_bfqq); |
| if (bfq_bfqq_IO_bound(bfqq)) |
| bfq_mark_bfqq_IO_bound(new_bfqq); |
| bfq_clear_bfqq_IO_bound(bfqq); |
| |
| /* |
| * If bfqq is weight-raised, then let new_bfqq inherit |
| * weight-raising. To reduce false positives, neglect the case |
| * where bfqq has just been created, but has not yet made it |
| * to be weight-raised (which may happen because EQM may merge |
| * bfqq even before bfq_add_request is executed for the first |
| * time for bfqq). Handling this case would however be very |
| * easy, thanks to the flag just_created. |
| */ |
| if (new_bfqq->wr_coeff == 1 && bfqq->wr_coeff > 1) { |
| new_bfqq->wr_coeff = bfqq->wr_coeff; |
| new_bfqq->wr_cur_max_time = bfqq->wr_cur_max_time; |
| new_bfqq->last_wr_start_finish = bfqq->last_wr_start_finish; |
| new_bfqq->wr_start_at_switch_to_srt = |
| bfqq->wr_start_at_switch_to_srt; |
| if (bfq_bfqq_busy(new_bfqq)) |
| bfqd->wr_busy_queues++; |
| new_bfqq->entity.prio_changed = 1; |
| } |
| |
| if (bfqq->wr_coeff > 1) { /* bfqq has given its wr to new_bfqq */ |
| bfqq->wr_coeff = 1; |
| bfqq->entity.prio_changed = 1; |
| if (bfq_bfqq_busy(bfqq)) |
| bfqd->wr_busy_queues--; |
| } |
| |
| bfq_log_bfqq(bfqd, new_bfqq, "merge_bfqqs: wr_busy %d", |
| bfqd->wr_busy_queues); |
| |
| /* |
| * Merge queues (that is, let bic redirect its requests to new_bfqq) |
| */ |
| bic_set_bfqq(bic, new_bfqq, 1); |
| bfq_mark_bfqq_coop(new_bfqq); |
| /* |
| * new_bfqq now belongs to at least two bics (it is a shared queue): |
| * set new_bfqq->bic to NULL. bfqq either: |
| * - does not belong to any bic any more, and hence bfqq->bic must |
| * be set to NULL, or |
| * - is a queue whose owning bics have already been redirected to a |
| * different queue, hence the queue is destined to not belong to |
| * any bic soon and bfqq->bic is already NULL (therefore the next |
| * assignment causes no harm). |
| */ |
| new_bfqq->bic = NULL; |
| bfqq->bic = NULL; |
| /* release process reference to bfqq */ |
| bfq_put_queue(bfqq); |
| } |
| |
| static bool bfq_allow_bio_merge(struct request_queue *q, struct request *rq, |
| struct bio *bio) |
| { |
| struct bfq_data *bfqd = q->elevator->elevator_data; |
| bool is_sync = op_is_sync(bio->bi_opf); |
| struct bfq_queue *bfqq = bfqd->bio_bfqq, *new_bfqq; |
| |
| /* |
| * Disallow merge of a sync bio into an async request. |
| */ |
| if (is_sync && !rq_is_sync(rq)) |
| return false; |
| |
| /* |
| * Lookup the bfqq that this bio will be queued with. Allow |
| * merge only if rq is queued there. |
| */ |
| if (!bfqq) |
| return false; |
| |
| /* |
| * We take advantage of this function to perform an early merge |
| * of the queues of possible cooperating processes. |
| */ |
| new_bfqq = bfq_setup_cooperator(bfqd, bfqq, bio, false); |
| if (new_bfqq) { |
| /* |
| * bic still points to bfqq, then it has not yet been |
| * redirected to some other bfq_queue, and a queue |
| * merge beween bfqq and new_bfqq can be safely |
| * fulfillled, i.e., bic can be redirected to new_bfqq |
| * and bfqq can be put. |
| */ |
| bfq_merge_bfqqs(bfqd, bfqd->bio_bic, bfqq, |
| new_bfqq); |
| /* |
| * If we get here, bio will be queued into new_queue, |
| * so use new_bfqq to decide whether bio and rq can be |
| * merged. |
| */ |
| bfqq = new_bfqq; |
| |
| /* |
| * Change also bqfd->bio_bfqq, as |
| * bfqd->bio_bic now points to new_bfqq, and |
| * this function may be invoked again (and then may |
| * use again bqfd->bio_bfqq). |
| */ |
| bfqd->bio_bfqq = bfqq; |
| } |
| |
| return bfqq == RQ_BFQQ(rq); |
| } |
| |
| /* |
| * Set the maximum time for the in-service queue to consume its |
| * budget. This prevents seeky processes from lowering the throughput. |
| * In practice, a time-slice service scheme is used with seeky |
| * processes. |
| */ |
| static void bfq_set_budget_timeout(struct bfq_data *bfqd, |
| struct bfq_queue *bfqq) |
| { |
| unsigned int timeout_coeff; |
| |
| if (bfqq->wr_cur_max_time == bfqd->bfq_wr_rt_max_time) |
| timeout_coeff = 1; |
| else |
| timeout_coeff = bfqq->entity.weight / bfqq->entity.orig_weight; |
| |
| bfqd->last_budget_start = ktime_get(); |
| |
| bfqq->budget_timeout = jiffies + |
| bfqd->bfq_timeout * timeout_coeff; |
| } |
| |
| static void __bfq_set_in_service_queue(struct bfq_data *bfqd, |
| struct bfq_queue *bfqq) |
| { |
| if (bfqq) { |
| bfqg_stats_update_avg_queue_size(bfqq_group(bfqq)); |
| bfq_clear_bfqq_fifo_expire(bfqq); |
| |
| bfqd->budgets_assigned = (bfqd->budgets_assigned * 7 + 256) / 8; |
| |
| if (time_is_before_jiffies(bfqq->last_wr_start_finish) && |
| bfqq->wr_coeff > 1 && |
| bfqq->wr_cur_max_time == bfqd->bfq_wr_rt_max_time && |
| time_is_before_jiffies(bfqq->budget_timeout)) { |
| /* |
| * For soft real-time queues, move the start |
| * of the weight-raising period forward by the |
| * time the queue has not received any |
| * service. Otherwise, a relatively long |
| * service delay is likely to cause the |
| * weight-raising period of the queue to end, |
| * because of the short duration of the |
| * weight-raising period of a soft real-time |
| * queue. It is worth noting that this move |
| * is not so dangerous for the other queues, |
| * because soft real-time queues are not |
| * greedy. |
| * |
| * To not add a further variable, we use the |
| * overloaded field budget_timeout to |
| * determine for how long the queue has not |
| * received service, i.e., how much time has |
| * elapsed since the queue expired. However, |
| * this is a little imprecise, because |
| * budget_timeout is set to jiffies if bfqq |
| * not only expires, but also remains with no |
| * request. |
| */ |
| if (time_after(bfqq->budget_timeout, |
| bfqq->last_wr_start_finish)) |
| bfqq->last_wr_start_finish += |
| jiffies - bfqq->budget_timeout; |
| else |
| bfqq->last_wr_start_finish = jiffies; |
| } |
| |
| bfq_set_budget_timeout(bfqd, bfqq); |
| bfq_log_bfqq(bfqd, bfqq, |
| "set_in_service_queue, cur-budget = %d", |
| bfqq->entity.budget); |
| } |
| |
| bfqd->in_service_queue = bfqq; |
| } |
| |
| /* |
| * Get and set a new queue for service. |
| */ |
| static struct bfq_queue *bfq_set_in_service_queue(struct bfq_data *bfqd) |
| { |
| struct bfq_queue *bfqq = bfq_get_next_queue(bfqd); |
| |
| __bfq_set_in_service_queue(bfqd, bfqq); |
| return bfqq; |
| } |
| |
| static void bfq_arm_slice_timer(struct bfq_data *bfqd) |
| { |
| struct bfq_queue *bfqq = bfqd->in_service_queue; |
| u32 sl; |
| |
| bfq_mark_bfqq_wait_request(bfqq); |
| |
| /* |
| * We don't want to idle for seeks, but we do want to allow |
| * fair distribution of slice time for a process doing back-to-back |
| * seeks. So allow a little bit of time for him to submit a new rq. |
| */ |
| sl = bfqd->bfq_slice_idle; |
| /* |
| * Unless the queue is being weight-raised or the scenario is |
| * asymmetric, grant only minimum idle time if the queue |
| * is seeky. A long idling is preserved for a weight-raised |
| * queue, or, more in general, in an asymmetric scenario, |
| * because a long idling is needed for guaranteeing to a queue |
| * its reserved share of the throughput (in particular, it is |
| * needed if the queue has a higher weight than some other |
| * queue). |
| */ |
| if (BFQQ_SEEKY(bfqq) && bfqq->wr_coeff == 1 && |
| bfq_symmetric_scenario(bfqd)) |
| sl = min_t(u64, sl, BFQ_MIN_TT); |
| |
| bfqd->last_idling_start = ktime_get(); |
| hrtimer_start(&bfqd->idle_slice_timer, ns_to_ktime(sl), |
| HRTIMER_MODE_REL); |
| bfqg_stats_set_start_idle_time(bfqq_group(bfqq)); |
| } |
| |
| /* |
| * In autotuning mode, max_budget is dynamically recomputed as the |
| * amount of sectors transferred in timeout at the estimated peak |
| * rate. This enables BFQ to utilize a full timeslice with a full |
| * budget, even if the in-service queue is served at peak rate. And |
| * this maximises throughput with sequential workloads. |
| */ |
| static unsigned long bfq_calc_max_budget(struct bfq_data *bfqd) |
| { |
| return (u64)bfqd->peak_rate * USEC_PER_MSEC * |
| jiffies_to_msecs(bfqd->bfq_timeout)>>BFQ_RATE_SHIFT; |
| } |
| |
| /* |
| * Update parameters related to throughput and responsiveness, as a |
| * function of the estimated peak rate. See comments on |
| * bfq_calc_max_budget(), and on T_slow and T_fast arrays. |
| */ |
| static void update_thr_responsiveness_params(struct bfq_data *bfqd) |
| { |
| int dev_type = blk_queue_nonrot(bfqd->queue); |
| |
| if (bfqd->bfq_user_max_budget == 0) |
| bfqd->bfq_max_budget = |
| bfq_calc_max_budget(bfqd); |
| |
| if (bfqd->device_speed == BFQ_BFQD_FAST && |
| bfqd->peak_rate < device_speed_thresh[dev_type]) { |
| bfqd->device_speed = BFQ_BFQD_SLOW; |
| bfqd->RT_prod = R_slow[dev_type] * |
| T_slow[dev_type]; |
| } else if (bfqd->device_speed == BFQ_BFQD_SLOW && |
| bfqd->peak_rate > device_speed_thresh[dev_type]) { |
| bfqd->device_speed = BFQ_BFQD_FAST; |
| bfqd->RT_prod = R_fast[dev_type] * |
| T_fast[dev_type]; |
| } |
| |
| bfq_log(bfqd, |
| "dev_type %s dev_speed_class = %s (%llu sects/sec), thresh %llu setcs/sec", |
| dev_type == 0 ? "ROT" : "NONROT", |
| bfqd->device_speed == BFQ_BFQD_FAST ? "FAST" : "SLOW", |
| bfqd->device_speed == BFQ_BFQD_FAST ? |
| (USEC_PER_SEC*(u64)R_fast[dev_type])>>BFQ_RATE_SHIFT : |
| (USEC_PER_SEC*(u64)R_slow[dev_type])>>BFQ_RATE_SHIFT, |
| (USEC_PER_SEC*(u64)device_speed_thresh[dev_type])>> |
| BFQ_RATE_SHIFT); |
| } |
| |
| static void bfq_reset_rate_computation(struct bfq_data *bfqd, |
| struct request *rq) |
| { |
| if (rq != NULL) { /* new rq dispatch now, reset accordingly */ |
| bfqd->last_dispatch = bfqd->first_dispatch = ktime_get_ns(); |
| bfqd->peak_rate_samples = 1; |
| bfqd->sequential_samples = 0; |
| bfqd->tot_sectors_dispatched = bfqd->last_rq_max_size = |
| blk_rq_sectors(rq); |
| } else /* no new rq dispatched, just reset the number of samples */ |
| bfqd->peak_rate_samples = 0; /* full re-init on next disp. */ |
| |
| bfq_log(bfqd, |
| "reset_rate_computation at end, sample %u/%u tot_sects %llu", |
| bfqd->peak_rate_samples, bfqd->sequential_samples, |
| bfqd->tot_sectors_dispatched); |
| } |
| |
| static void bfq_update_rate_reset(struct bfq_data *bfqd, struct request *rq) |
| { |
| u32 rate, weight, divisor; |
| |
| /* |
| * For the convergence property to hold (see comments on |
| * bfq_update_peak_rate()) and for the assessment to be |
| * reliable, a minimum number of samples must be present, and |
| * a minimum amount of time must have elapsed. If not so, do |
| * not compute new rate. Just reset parameters, to get ready |
| * for a new evaluation attempt. |
| */ |
| if (bfqd->peak_rate_samples < BFQ_RATE_MIN_SAMPLES || |
| bfqd->delta_from_first < BFQ_RATE_MIN_INTERVAL) |
| goto reset_computation; |
| |
| /* |
| * If a new request completion has occurred after last |
| * dispatch, then, to approximate the rate at which requests |
| * have been served by the device, it is more precise to |
| * extend the observation interval to the last completion. |
| */ |
| bfqd->delta_from_first = |
| max_t(u64, bfqd->delta_from_first, |
| bfqd->last_completion - bfqd->first_dispatch); |
| |
| /* |
| * Rate computed in sects/usec, and not sects/nsec, for |
| * precision issues. |
| */ |
| rate = div64_ul(bfqd->tot_sectors_dispatched<<BFQ_RATE_SHIFT, |
| div_u64(bfqd->delta_from_first, NSEC_PER_USEC)); |
| |
| /* |
| * Peak rate not updated if: |
| * - the percentage of sequential dispatches is below 3/4 of the |
| * total, and rate is below the current estimated peak rate |
| * - rate is unreasonably high (> 20M sectors/sec) |
| */ |
| if ((bfqd->sequential_samples < (3 * bfqd->peak_rate_samples)>>2 && |
| rate <= bfqd->peak_rate) || |
| rate > 20<<BFQ_RATE_SHIFT) |
| goto reset_computation; |
| |
| /* |
| * We have to update the peak rate, at last! To this purpose, |
| * we use a low-pass filter. We compute the smoothing constant |
| * of the filter as a function of the 'weight' of the new |
| * measured rate. |
| * |
| * As can be seen in next formulas, we define this weight as a |
| * quantity proportional to how sequential the workload is, |
| * and to how long the observation time interval is. |
| * |
| * The weight runs from 0 to 8. The maximum value of the |
| * weight, 8, yields the minimum value for the smoothing |
| * constant. At this minimum value for the smoothing constant, |
| * the measured rate contributes for half of the next value of |
| * the estimated peak rate. |
| * |
| * So, the first step is to compute the weight as a function |
| * of how sequential the workload is. Note that the weight |
| * cannot reach 9, because bfqd->sequential_samples cannot |
| * become equal to bfqd->peak_rate_samples, which, in its |
| * turn, holds true because bfqd->sequential_samples is not |
| * incremented for the first sample. |
| */ |
| weight = (9 * bfqd->sequential_samples) / bfqd->peak_rate_samples; |
| |
| /* |
| * Second step: further refine the weight as a function of the |
| * duration of the observation interval. |
| */ |
| weight = min_t(u32, 8, |
| div_u64(weight * bfqd->delta_from_first, |
| BFQ_RATE_REF_INTERVAL)); |
| |
| /* |
| * Divisor ranging from 10, for minimum weight, to 2, for |
| * maximum weight. |
| */ |
| divisor = 10 - weight; |
| |
| /* |
| * Finally, update peak rate: |
| * |
| * peak_rate = peak_rate * (divisor-1) / divisor + rate / divisor |
| */ |
| bfqd->peak_rate *= divisor-1; |
| bfqd->peak_rate /= divisor; |
| rate /= divisor; /* smoothing constant alpha = 1/divisor */ |
| |
| bfqd->peak_rate += rate; |
| update_thr_responsiveness_params(bfqd); |
| |
| reset_computation: |
| bfq_reset_rate_computation(bfqd, rq); |
| } |
| |
| /* |
| * Update the read/write peak rate (the main quantity used for |
| * auto-tuning, see update_thr_responsiveness_params()). |
| * |
| * It is not trivial to estimate the peak rate (correctly): because of |
| * the presence of sw and hw queues between the scheduler and the |
| * device components that finally serve I/O requests, it is hard to |
| * say exactly when a given dispatched request is served inside the |
| * device, and for how long. As a consequence, it is hard to know |
| * precisely at what rate a given set of requests is actually served |
| * by the device. |
| * |
| * On the opposite end, the dispatch time of any request is trivially |
| * available, and, from this piece of information, the "dispatch rate" |
| * of requests can be immediately computed. So, the idea in the next |
| * function is to use what is known, namely request dispatch times |
| * (plus, when useful, request completion times), to estimate what is |
| * unknown, namely in-device request service rate. |
| * |
| * The main issue is that, because of the above facts, the rate at |
| * which a certain set of requests is dispatched over a certain time |
| * interval can vary greatly with respect to the rate at which the |
| * same requests are then served. But, since the size of any |
| * intermediate queue is limited, and the service scheme is lossless |
| * (no request is silently dropped), the following obvious convergence |
| * property holds: the number of requests dispatched MUST become |
| * closer and closer to the number of requests completed as the |
| * observation interval grows. This is the key property used in |
| * the next function to estimate the peak service rate as a function |
| * of the observed dispatch rate. The function assumes to be invoked |
| * on every request dispatch. |
| */ |
| static void bfq_update_peak_rate(struct bfq_data *bfqd, struct request *rq) |
| { |
| u64 now_ns = ktime_get_ns(); |
| |
| if (bfqd->peak_rate_samples == 0) { /* first dispatch */ |
| bfq_log(bfqd, "update_peak_rate: goto reset, samples %d", |
| bfqd->peak_rate_samples); |
| bfq_reset_rate_computation(bfqd, rq); |
| goto update_last_values; /* will add one sample */ |
| } |
| |
| /* |
| * Device idle for very long: the observation interval lasting |
| * up to this dispatch cannot be a valid observation interval |
| * for computing a new peak rate (similarly to the late- |
| * completion event in bfq_completed_request()). Go to |
| * update_rate_and_reset to have the following three steps |
| * taken: |
| * - close the observation interval at the last (previous) |
| * request dispatch or completion |
| * - compute rate, if possible, for that observation interval |
| * - start a new observation interval with this dispatch |
| */ |
| if (now_ns - bfqd->last_dispatch > 100*NSEC_PER_MSEC && |
| bfqd->rq_in_driver == 0) |
| goto update_rate_and_reset; |
| |
| /* Update sampling information */ |
| bfqd->peak_rate_samples++; |
| |
| if ((bfqd->rq_in_driver > 0 || |
| now_ns - bfqd->last_completion < BFQ_MIN_TT) |
| && get_sdist(bfqd->last_position, rq) < BFQQ_SEEK_THR) |
| bfqd->sequential_samples++; |
| |
| bfqd->tot_sectors_dispatched += blk_rq_sectors(rq); |
| |
| /* Reset max observed rq size every 32 dispatches */ |
| if (likely(bfqd->peak_rate_samples % 32)) |
| bfqd->last_rq_max_size = |
| max_t(u32, blk_rq_sectors(rq), bfqd->last_rq_max_size); |
| else |
| bfqd->last_rq_max_size = blk_rq_sectors(rq); |
| |
| bfqd->delta_from_first = now_ns - bfqd->first_dispatch; |
| |
| /* Target observation interval not yet reached, go on sampling */ |
| if (bfqd->delta_from_first < BFQ_RATE_REF_INTERVAL) |
| goto update_last_values; |
| |
| update_rate_and_reset: |
| bfq_update_rate_reset(bfqd, rq); |
| update_last_values: |
| bfqd->last_position = blk_rq_pos(rq) + blk_rq_sectors(rq); |
| bfqd->last_dispatch = now_ns; |
| } |
| |
| /* |
| * Remove request from internal lists. |
| */ |
| static void bfq_dispatch_remove(struct request_queue *q, struct request *rq) |
| { |
| struct bfq_queue *bfqq = RQ_BFQQ(rq); |
| |
| /* |
| * For consistency, the next instruction should have been |
| * executed after removing the request from the queue and |
| * dispatching it. We execute instead this instruction before |
| * bfq_remove_request() (and hence introduce a temporary |
| * inconsistency), for efficiency. In fact, should this |
| * dispatch occur for a non in-service bfqq, this anticipated |
| * increment prevents two counters related to bfqq->dispatched |
| * from risking to be, first, uselessly decremented, and then |
| * incremented again when the (new) value of bfqq->dispatched |
| * happens to be taken into account. |
| */ |
| bfqq->dispatched++; |
| bfq_update_peak_rate(q->elevator->elevator_data, rq); |
| |
| bfq_remove_request(q, rq); |
| } |
| |
| static void __bfq_bfqq_expire(struct bfq_data *bfqd, struct bfq_queue *bfqq) |
| { |
| /* |
| * If this bfqq is shared between multiple processes, check |
| * to make sure that those processes are still issuing I/Os |
| * within the mean seek distance. If not, it may be time to |
| * break the queues apart again. |
| */ |
| if (bfq_bfqq_coop(bfqq) && BFQQ_SEEKY(bfqq)) |
| bfq_mark_bfqq_split_coop(bfqq); |
| |
| if (RB_EMPTY_ROOT(&bfqq->sort_list)) { |
| if (bfqq->dispatched == 0) |
| /* |
| * Overloading budget_timeout field to store |
| * the time at which the queue remains with no |
| * backlog and no outstanding request; used by |
| * the weight-raising mechanism. |
| */ |
| bfqq->budget_timeout = jiffies; |
| |
| bfq_del_bfqq_busy(bfqd, bfqq, true); |
| } else { |
| bfq_requeue_bfqq(bfqd, bfqq, true); |
| /* |
| * Resort priority tree of potential close cooperators. |
| */ |
| bfq_pos_tree_add_move(bfqd, bfqq); |
| } |
| |
| /* |
| * All in-service entities must have been properly deactivated |
| * or requeued before executing the next function, which |
| * resets all in-service entites as no more in service. |
| */ |
| __bfq_bfqd_reset_in_service(bfqd); |
| } |
| |
| /** |
| * __bfq_bfqq_recalc_budget - try to adapt the budget to the @bfqq behavior. |
| * @bfqd: device data. |
| * @bfqq: queue to update. |
| * @reason: reason for expiration. |
| * |
| * Handle the feedback on @bfqq budget at queue expiration. |
| * See the body for detailed comments. |
| */ |
| static void __bfq_bfqq_recalc_budget(struct bfq_data *bfqd, |
| struct bfq_queue *bfqq, |
| enum bfqq_expiration reason) |
| { |
| struct request *next_rq; |
| int budget, min_budget; |
| |
| min_budget = bfq_min_budget(bfqd); |
| |
| if (bfqq->wr_coeff == 1) |
| budget = bfqq->max_budget; |
| else /* |
| * Use a constant, low budget for weight-raised queues, |
| * to help achieve a low latency. Keep it slightly higher |
| * than the minimum possible budget, to cause a little |
| * bit fewer expirations. |
| */ |
| budget = 2 * min_budget; |
| |
| bfq_log_bfqq(bfqd, bfqq, "recalc_budg: last budg %d, budg left %d", |
| bfqq->entity.budget, bfq_bfqq_budget_left(bfqq)); |
| bfq_log_bfqq(bfqd, bfqq, "recalc_budg: last max_budg %d, min budg %d", |
| budget, bfq_min_budget(bfqd)); |
| bfq_log_bfqq(bfqd, bfqq, "recalc_budg: sync %d, seeky %d", |
| bfq_bfqq_sync(bfqq), BFQQ_SEEKY(bfqd->in_service_queue)); |
| |
| if (bfq_bfqq_sync(bfqq) && bfqq->wr_coeff == 1) { |
| switch (reason) { |
| /* |
| * Caveat: in all the following cases we trade latency |
| * for throughput. |
| */ |
| case BFQQE_TOO_IDLE: |
| /* |
| * This is the only case where we may reduce |
| * the budget: if there is no request of the |
| * process still waiting for completion, then |
| * we assume (tentatively) that the timer has |
| * expired because the batch of requests of |
| * the process could have been served with a |
| * smaller budget. Hence, betting that |
| * process will behave in the same way when it |
| * becomes backlogged again, we reduce its |
| * next budget. As long as we guess right, |
| * this budget cut reduces the latency |
| * experienced by the process. |
| * |
| * However, if there are still outstanding |
| * requests, then the process may have not yet |
| * issued its next request just because it is |
| * still waiting for the completion of some of |
| * the still outstanding ones. So in this |
| * subcase we do not reduce its budget, on the |
| * contrary we increase it to possibly boost |
| * the throughput, as discussed in the |
| * comments to the BUDGET_TIMEOUT case. |
| */ |
| if (bfqq->dispatched > 0) /* still outstanding reqs */ |
| budget = min(budget * 2, bfqd->bfq_max_budget); |
| else { |
| if (budget > 5 * min_budget) |
| budget -= 4 * min_budget; |
| else |
| budget = min_budget; |
| } |
| break; |
| case BFQQE_BUDGET_TIMEOUT: |
| /* |
| * We double the budget here because it gives |
| * the chance to boost the throughput if this |
| * is not a seeky process (and has bumped into |
| * this timeout because of, e.g., ZBR). |
| */ |
| budget = min(budget * 2, bfqd->bfq_max_budget); |
| break; |
| case BFQQE_BUDGET_EXHAUSTED: |
| /* |
| * The process still has backlog, and did not |
| * let either the budget timeout or the disk |
| * idling timeout expire. Hence it is not |
| * seeky, has a short thinktime and may be |
| * happy with a higher budget too. So |
| * definitely increase the budget of this good |
| * candidate to boost the disk throughput. |
| */ |
| budget = min(budget * 4, bfqd->bfq_max_budget); |
| break; |
| case BFQQE_NO_MORE_REQUESTS: |
| /* |
| * For queues that expire for this reason, it |
| * is particularly important to keep the |
| * budget close to the actual service they |
| * need. Doing so reduces the timestamp |
| * misalignment problem described in the |
| * comments in the body of |
| * __bfq_activate_entity. In fact, suppose |
| * that a queue systematically expires for |
| * BFQQE_NO_MORE_REQUESTS and presents a |
| * new request in time to enjoy timestamp |
| * back-shifting. The larger the budget of the |
| * queue is with respect to the service the |
| * queue actually requests in each service |
| * slot, the more times the queue can be |
| * reactivated with the same virtual finish |
| * time. It follows that, even if this finish |
| * time is pushed to the system virtual time |
| * to reduce the consequent timestamp |
| * misalignment, the queue unjustly enjoys for |
| * many re-activations a lower finish time |
| * than all newly activated queues. |
| * |
| * The service needed by bfqq is measured |
| * quite precisely by bfqq->entity.service. |
| * Since bfqq does not enjoy device idling, |
| * bfqq->entity.service is equal to the number |
| * of sectors that the process associated with |
| * bfqq requested to read/write before waiting |
| * for request completions, or blocking for |
| * other reasons. |
| */ |
| budget = max_t(int, bfqq->entity.service, min_budget); |
| break; |
| default: |
| return; |
| } |
| } else if (!bfq_bfqq_sync(bfqq)) { |
| /* |
| * Async queues get always the maximum possible |
| * budget, as for them we do not care about latency |
| * (in addition, their ability to dispatch is limited |
| * by the charging factor). |
| */ |
| budget = bfqd->bfq_max_budget; |
| } |
| |
| bfqq->max_budget = budget; |
| |
| if (bfqd->budgets_assigned >= bfq_stats_min_budgets && |
| !bfqd->bfq_user_max_budget) |
| bfqq->max_budget = min(bfqq->max_budget, bfqd->bfq_max_budget); |
| |
| /* |
| * If there is still backlog, then assign a new budget, making |
| * sure that it is large enough for the next request. Since |
| * the finish time of bfqq must be kept in sync with the |
| * budget, be sure to call __bfq_bfqq_expire() *after* this |
| * update. |
| * |
| * If there is no backlog, then no need to update the budget; |
| * it will be updated on the arrival of a new request. |
| */ |
| next_rq = bfqq->next_rq; |
| if (next_rq) |
| bfqq->entity.budget = max_t(unsigned long, bfqq->max_budget, |
| bfq_serv_to_charge(next_rq, bfqq)); |
| |
| bfq_log_bfqq(bfqd, bfqq, "head sect: %u, new budget %d", |
| next_rq ? blk_rq_sectors(next_rq) : 0, |
| bfqq->entity.budget); |
| } |
| |
| /* |
| * Return true if the process associated with bfqq is "slow". The slow |
| * flag is used, in addition to the budget timeout, to reduce the |
| * amount of service provided to seeky processes, and thus reduce |
| * their chances to lower the throughput. More details in the comments |
| * on the function bfq_bfqq_expire(). |
| * |
| * An important observation is in order: as discussed in the comments |
| * on the function bfq_update_peak_rate(), with devices with internal |
| * queues, it is hard if ever possible to know when and for how long |
| * an I/O request is processed by the device (apart from the trivial |
| * I/O pattern where a new request is dispatched only after the |
| * previous one has been completed). This makes it hard to evaluate |
| * the real rate at which the I/O requests of each bfq_queue are |
| * served. In fact, for an I/O scheduler like BFQ, serving a |
| * bfq_queue means just dispatching its requests during its service |
| * slot (i.e., until the budget of the queue is exhausted, or the |
| * queue remains idle, or, finally, a timeout fires). But, during the |
| * service slot of a bfq_queue, around 100 ms at most, the device may |
| * be even still processing requests of bfq_queues served in previous |
| * service slots. On the opposite end, the requests of the in-service |
| * bfq_queue may be completed after the service slot of the queue |
| * finishes. |
| * |
| * Anyway, unless more sophisticated solutions are used |
| * (where possible), the sum of the sizes of the requests dispatched |
| * during the service slot of a bfq_queue is probably the only |
| * approximation available for the service received by the bfq_queue |
| * during its service slot. And this sum is the quantity used in this |
| * function to evaluate the I/O speed of a process. |
| */ |
| static bool bfq_bfqq_is_slow(struct bfq_data *bfqd, struct bfq_queue *bfqq, |
| bool compensate, enum bfqq_expiration reason, |
| unsigned long *delta_ms) |
| { |
| ktime_t delta_ktime; |
| u32 delta_usecs; |
| bool slow = BFQQ_SEEKY(bfqq); /* if delta too short, use seekyness */ |
| |
| if (!bfq_bfqq_sync(bfqq)) |
| return false; |
| |
| if (compensate) |
| delta_ktime = bfqd->last_idling_start; |
| else |
| delta_ktime = ktime_get(); |
| delta_ktime = ktime_sub(delta_ktime, bfqd->last_budget_start); |
| delta_usecs = ktime_to_us(delta_ktime); |
| |
| /* don't use too short time intervals */ |
| if (delta_usecs < 1000) { |
| if (blk_queue_nonrot(bfqd->queue)) |
| /* |
| * give same worst-case guarantees as idling |
| * for seeky |
| */ |
| *delta_ms = BFQ_MIN_TT / NSEC_PER_MSEC; |
| else /* charge at least one seek */ |
| *delta_ms = bfq_slice_idle / NSEC_PER_MSEC; |
| |
| return slow; |
| } |
| |
| *delta_ms = delta_usecs / USEC_PER_MSEC; |
| |
| /* |
| * Use only long (> 20ms) intervals to filter out excessive |
| * spikes in service rate estimation. |
| */ |
| if (delta_usecs > 20000) { |
| /* |
| * Caveat for rotational devices: processes doing I/O |
| * in the slower disk zones tend to be slow(er) even |
| * if not seeky. In this respect, the estimated peak |
| * rate is likely to be an average over the disk |
| * surface. Accordingly, to not be too harsh with |
| * unlucky processes, a process is deemed slow only if |
| * its rate has been lower than half of the estimated |
| * peak rate. |
| */ |
| slow = bfqq->entity.service < bfqd->bfq_max_budget / 2; |
| } |
| |
| bfq_log_bfqq(bfqd, bfqq, "bfq_bfqq_is_slow: slow %d", slow); |
| |
| return slow; |
| } |
| |
| /* |
| * To be deemed as soft real-time, an application must meet two |
| * requirements. First, the application must not require an average |
| * bandwidth higher than the approximate bandwidth required to playback or |
| * record a compressed high-definition video. |
| * The next function is invoked on the completion of the last request of a |
| * batch, to compute the next-start time instant, soft_rt_next_start, such |
| * that, if the next request of the application does not arrive before |
| * soft_rt_next_start, then the above requirement on the bandwidth is met. |
| * |
| * The second requirement is that the request pattern of the application is |
| * isochronous, i.e., that, after issuing a request or a batch of requests, |
| * the application stops issuing new requests until all its pending requests |
| * have been completed. After that, the application may issue a new batch, |
| * and so on. |
| * For this reason the next function is invoked to compute |
| * soft_rt_next_start only for applications that meet this requirement, |
| * whereas soft_rt_next_start is set to infinity for applications that do |
| * not. |
| * |
| * Unfortunately, even a greedy application may happen to behave in an |
| * isochronous way if the CPU load is high. In fact, the application may |
| * stop issuing requests while the CPUs are busy serving other processes, |
| * then restart, then stop again for a while, and so on. In addition, if |
| * the disk achieves a low enough throughput with the request pattern |
| * issued by the application (e.g., because the request pattern is random |
| * and/or the device is slow), then the application may meet the above |
| * bandwidth requirement too. To prevent such a greedy application to be |
| * deemed as soft real-time, a further rule is used in the computation of |
| * soft_rt_next_start: soft_rt_next_start must be higher than the current |
| * time plus the maximum time for which the arrival of a request is waited |
| * for when a sync queue becomes idle, namely bfqd->bfq_slice_idle. |
| * This filters out greedy applications, as the latter issue instead their |
| * next request as soon as possible after the last one has been completed |
| * (in contrast, when a batch of requests is completed, a soft real-time |
| * application spends some time processing data). |
| * |
| * Unfortunately, the last filter may easily generate false positives if |
| * only bfqd->bfq_slice_idle is used as a reference time interval and one |
| * or both the following cases occur: |
| * 1) HZ is so low that the duration of a jiffy is comparable to or higher |
| * than bfqd->bfq_slice_idle. This happens, e.g., on slow devices with |
| * HZ=100. |
| * 2) jiffies, instead of increasing at a constant rate, may stop increasing |
| * for a while, then suddenly 'jump' by several units to recover the lost |
| * increments. This seems to happen, e.g., inside virtual machines. |
| * To address this issue, we do not use as a reference time interval just |
| * bfqd->bfq_slice_idle, but bfqd->bfq_slice_idle plus a few jiffies. In |
| * particular we add the minimum number of jiffies for which the filter |
| * seems to be quite precise also in embedded systems and KVM/QEMU virtual |
| * machines. |
| */ |
| static unsigned long bfq_bfqq_softrt_next_start(struct bfq_data *bfqd, |
| struct bfq_queue *bfqq) |
| { |
| return max(bfqq->last_idle_bklogged + |
| HZ * bfqq->service_from_backlogged / |
| bfqd->bfq_wr_max_softrt_rate, |
| jiffies + nsecs_to_jiffies(bfqq->bfqd->bfq_slice_idle) + 4); |
| } |
| |
| /* |
| * Return the farthest future time instant according to jiffies |
| * macros. |
| */ |
| static unsigned long bfq_greatest_from_now(void) |
| { |
| return jiffies + MAX_JIFFY_OFFSET; |
| } |
| |
| /* |
| * Return the farthest past time instant according to jiffies |
| * macros. |
| */ |
| static unsigned long bfq_smallest_from_now(void) |
| { |
| return jiffies - MAX_JIFFY_OFFSET; |
| } |
| |
| /** |
| * bfq_bfqq_expire - expire a queue. |
| * @bfqd: device owning the queue. |
| * @bfqq: the queue to expire. |
| * @compensate: if true, compensate for the time spent idling. |
| * @reason: the reason causing the expiration. |
| * |
| * If the process associated with bfqq does slow I/O (e.g., because it |
| * issues random requests), we charge bfqq with the time it has been |
| * in service instead of the service it has received (see |
| * bfq_bfqq_charge_time for details on how this goal is achieved). As |
| * a consequence, bfqq will typically get higher timestamps upon |
| * reactivation, and hence it will be rescheduled as if it had |
| * received more service than what it has actually received. In the |
| * end, bfqq receives less service in proportion to how slowly its |
| * associated process consumes its budgets (and hence how seriously it |
| * tends to lower the throughput). In addition, this time-charging |
| * strategy guarantees time fairness among slow processes. In |
| * contrast, if the process associated with bfqq is not slow, we |
| * charge bfqq exactly with the service it has received. |
| * |
| * Charging time to the first type of queues and the exact service to |
| * the other has the effect of using the WF2Q+ policy to schedule the |
| * former on a timeslice basis, without violating service domain |
| * guarantees among the latter. |
| */ |
| void bfq_bfqq_expire(struct bfq_data *bfqd, |
| struct bfq_queue *bfqq, |
| bool compensate, |
| enum bfqq_expiration reason) |
| { |
| bool slow; |
| unsigned long delta = 0; |
| struct bfq_entity *entity = &bfqq->entity; |
| int ref; |
| |
| /* |
| * Check whether the process is slow (see bfq_bfqq_is_slow). |
| */ |
| slow = bfq_bfqq_is_slow(bfqd, bfqq, compensate, reason, &delta); |
| |
| /* |
| * Increase service_from_backlogged before next statement, |
| * because the possible next invocation of |
| * bfq_bfqq_charge_time would likely inflate |
| * entity->service. In contrast, service_from_backlogged must |
| * contain real service, to enable the soft real-time |
| * heuristic to correctly compute the bandwidth consumed by |
| * bfqq. |
| */ |
| bfqq->service_from_backlogged += entity->service; |
| |
| /* |
| * As above explained, charge slow (typically seeky) and |
| * timed-out queues with the time and not the service |
| * received, to favor sequential workloads. |
| * |
| * Processes doing I/O in the slower disk zones will tend to |
| * be slow(er) even if not seeky. Therefore, since the |
| * estimated peak rate is actually an average over the disk |
| * surface, these processes may timeout just for bad luck. To |
| * avoid punishing them, do not charge time to processes that |
| * succeeded in consuming at least 2/3 of their budget. This |
| * allows BFQ to preserve enough elasticity to still perform |
| * bandwidth, and not time, distribution with little unlucky |
| * or quasi-sequential processes. |
| */ |
| if (bfqq->wr_coeff == 1 && |
| (slow || |
| (reason == BFQQE_BUDGET_TIMEOUT && |
| bfq_bfqq_budget_left(bfqq) >= entity->budget / 3))) |
| bfq_bfqq_charge_time(bfqd, bfqq, delta); |
| |
| if (reason == BFQQE_TOO_IDLE && |
| entity->service <= 2 * entity->budget / 10) |
| bfq_clear_bfqq_IO_bound(bfqq); |
| |
| if (bfqd->low_latency && bfqq->wr_coeff == 1) |
| bfqq->last_wr_start_finish = jiffies; |
| |
| if (bfqd->low_latency && bfqd->bfq_wr_max_softrt_rate > 0 && |
| RB_EMPTY_ROOT(&bfqq->sort_list)) { |
| /* |
| * If we get here, and there are no outstanding |
| * requests, then the request pattern is isochronous |
| * (see the comments on the function |
| * bfq_bfqq_softrt_next_start()). Thus we can compute |
| * soft_rt_next_start. If, instead, the queue still |
| * has outstanding requests, then we have to wait for |
| * the completion of all the outstanding requests to |
| * discover whether the request pattern is actually |
| * isochronous. |
| */ |
| if (bfqq->dispatched == 0) |
| bfqq->soft_rt_next_start = |
| bfq_bfqq_softrt_next_start(bfqd, bfqq); |
| else { |
| /* |
| * The application is still waiting for the |
| * completion of one or more requests: |
| * prevent it from possibly being incorrectly |
| * deemed as soft real-time by setting its |
| * soft_rt_next_start to infinity. In fact, |
| * without this assignment, the application |
| * would be incorrectly deemed as soft |
| * real-time if: |
| * 1) it issued a new request before the |
| * completion of all its in-flight |
| * requests, and |
| * 2) at that time, its soft_rt_next_start |
| * happened to be in the past. |
| */ |
| bfqq->soft_rt_next_start = |
| bfq_greatest_from_now(); |
| /* |
| * Schedule an update of soft_rt_next_start to when |
| * the task may be discovered to be isochronous. |
| */ |
| bfq_mark_bfqq_softrt_update(bfqq); |
| } |
| } |
| |
| bfq_log_bfqq(bfqd, bfqq, |
| "expire (%d, slow %d, num_disp %d, short_ttime %d)", reason, |
| slow, bfqq->dispatched, bfq_bfqq_has_short_ttime(bfqq)); |
| |
| /* |
| * Increase, decrease or leave budget unchanged according to |
| * reason. |
| */ |
| __bfq_bfqq_recalc_budget(bfqd, bfqq, reason); |
| ref = bfqq->ref; |
| __bfq_bfqq_expire(bfqd, bfqq); |
| |
| /* mark bfqq as waiting a request only if a bic still points to it */ |
| if (ref > 1 && !bfq_bfqq_busy(bfqq) && |
| reason != BFQQE_BUDGET_TIMEOUT && |
| reason != BFQQE_BUDGET_EXHAUSTED) |
| bfq_mark_bfqq_non_blocking_wait_rq(bfqq); |
| } |
| |
| /* |
| * Budget timeout is not implemented through a dedicated timer, but |
| * just checked on request arrivals and completions, as well as on |
| * idle timer expirations. |
| */ |
| static bool bfq_bfqq_budget_timeout(struct bfq_queue *bfqq) |
| { |
| return time_is_before_eq_jiffies(bfqq->budget_timeout); |
| } |
| |
| /* |
| * If we expire a queue that is actively waiting (i.e., with the |
| * device idled) for the arrival of a new request, then we may incur |
| * the timestamp misalignment problem described in the body of the |
| * function __bfq_activate_entity. Hence we return true only if this |
| * condition does not hold, or if the queue is slow enough to deserve |
| * only to be kicked off for preserving a high throughput. |
| */ |
| static bool bfq_may_expire_for_budg_timeout(struct bfq_queue *bfqq) |
| { |
| bfq_log_bfqq(bfqq->bfqd, bfqq, |
| "may_budget_timeout: wait_request %d left %d timeout %d", |
| bfq_bfqq_wait_request(bfqq), |
| bfq_bfqq_budget_left(bfqq) >= bfqq->entity.budget / 3, |
| bfq_bfqq_budget_timeout(bfqq)); |
| |
| return (!bfq_bfqq_wait_request(bfqq) || |
| bfq_bfqq_budget_left(bfqq) >= bfqq->entity.budget / 3) |
| && |
| bfq_bfqq_budget_timeout(bfqq); |
| } |
| |
| /* |
| * For a queue that becomes empty, device idling is allowed only if |
| * this function returns true for the queue. As a consequence, since |
| * device idling plays a critical role in both throughput boosting and |
| * service guarantees, the return value of this function plays a |
| * critical role in both these aspects as well. |
| * |
| * In a nutshell, this function returns true only if idling is |
| * beneficial for throughput or, even if detrimental for throughput, |
| * idling is however necessary to preserve service guarantees (low |
| * latency, desired throughput distribution, ...). In particular, on |
| * NCQ-capable devices, this function tries to return false, so as to |
| * help keep the drives' internal queues full, whenever this helps the |
| * device boost the throughput without causing any service-guarantee |
| * issue. |
| * |
| * In more detail, the return value of this function is obtained by, |
| * first, computing a number of boolean variables that take into |
| * account throughput and service-guarantee issues, and, then, |
| * combining these variables in a logical expression. Most of the |
| * issues taken into account are not trivial. We discuss these issues |
| * individually while introducing the variables. |
| */ |
| static bool bfq_bfqq_may_idle(struct bfq_queue *bfqq) |
| { |
| struct bfq_data *bfqd = bfqq->bfqd; |
| bool rot_without_queueing = |
| !blk_queue_nonrot(bfqd->queue) && !bfqd->hw_tag, |
| bfqq_sequential_and_IO_bound, |
| idling_boosts_thr, idling_boosts_thr_without_issues, |
| idling_needed_for_service_guarantees, |
| asymmetric_scenario; |
| |
| if (bfqd->strict_guarantees) |
| return true; |
| |
| /* |
| * Idling is performed only if slice_idle > 0. In addition, we |
| * do not idle if |
| * (a) bfqq is async |
| * (b) bfqq is in the idle io prio class: in this case we do |
| * not idle because we want to minimize the bandwidth that |
| * queues in this class can steal to higher-priority queues |
| */ |
| if (bfqd->bfq_slice_idle == 0 || !bfq_bfqq_sync(bfqq) || |
| bfq_class_idle(bfqq)) |
| return false; |
| |
| bfqq_sequential_and_IO_bound = !BFQQ_SEEKY(bfqq) && |
| bfq_bfqq_IO_bound(bfqq) && bfq_bfqq_has_short_ttime(bfqq); |
| |
| /* |
| * The next variable takes into account the cases where idling |
| * boosts the throughput. |
| * |
| * The value of the variable is computed considering, first, that |
| * idling is virtually always beneficial for the throughput if: |
| * (a) the device is not NCQ-capable and rotational, or |
| * (b) regardless of the presence of NCQ, the device is rotational and |
| * the request pattern for bfqq is I/O-bound and sequential, or |
| * (c) regardless of whether it is rotational, the device is |
| * not NCQ-capable and the request pattern for bfqq is |
| * I/O-bound and sequential. |
| * |
| * Secondly, and in contrast to the above item (b), idling an |
| * NCQ-capable flash-based device would not boost the |
| * throughput even with sequential I/O; rather it would lower |
| * the throughput in proportion to how fast the device |
| * is. Accordingly, the next variable is true if any of the |
| * above conditions (a), (b) or (c) is true, and, in |
| * particular, happens to be false if bfqd is an NCQ-capable |
| * flash-based device. |
| */ |
| idling_boosts_thr = rot_without_queueing || |
| ((!blk_queue_nonrot(bfqd->queue) || !bfqd->hw_tag) && |
| bfqq_sequential_and_IO_bound); |
| |
| /* |
| * The value of the next variable, |
| * idling_boosts_thr_without_issues, is equal to that of |
| * idling_boosts_thr, unless a special case holds. In this |
| * special case, described below, idling may cause problems to |
| * weight-raised queues. |
| * |
| * When the request pool is saturated (e.g., in the presence |
| * of write hogs), if the processes associated with |
| * non-weight-raised queues ask for requests at a lower rate, |
| * then processes associated with weight-raised queues have a |
| * higher probability to get a request from the pool |
| * immediately (or at least soon) when they need one. Thus |
| * they have a higher probability to actually get a fraction |
| * of the device throughput proportional to their high |
| * weight. This is especially true with NCQ-capable drives, |
| * which enqueue several requests in advance, and further |
| * reorder internally-queued requests. |
| * |
| * For this reason, we force to false the value of |
| * idling_boosts_thr_without_issues if there are weight-raised |
| * busy queues. In this case, and if bfqq is not weight-raised, |
| * this guarantees that the device is not idled for bfqq (if, |
| * instead, bfqq is weight-raised, then idling will be |
| * guaranteed by another variable, see below). Combined with |
| * the timestamping rules of BFQ (see [1] for details), this |
| * behavior causes bfqq, and hence any sync non-weight-raised |
| * queue, to get a lower number of requests served, and thus |
| * to ask for a lower number of requests from the request |
| * pool, before the busy weight-raised queues get served |
| * again. This often mitigates starvation problems in the |
| * presence of heavy write workloads and NCQ, thereby |
| * guaranteeing a higher application and system responsiveness |
| * in these hostile scenarios. |
| */ |
| idling_boosts_thr_without_issues = idling_boosts_thr && |
| bfqd->wr_busy_queues == 0; |
| |
| /* |
| * There is then a case where idling must be performed not |
| * for throughput concerns, but to preserve service |
| * guarantees. |
| * |
| * To introduce this case, we can note that allowing the drive |
| * to enqueue more than one request at a time, and hence |
| * delegating de facto final scheduling decisions to the |
| * drive's internal scheduler, entails loss of control on the |
| * actual request service order. In particular, the critical |
| * situation is when requests from different processes happen |
| * to be present, at the same time, in the internal queue(s) |
| * of the drive. In such a situation, the drive, by deciding |
| * the service order of the internally-queued requests, does |
| * determine also the actual throughput distribution among |
| * these processes. But the drive typically has no notion or |
| * concern about per-process throughput distribution, and |
| * makes its decisions only on a per-request basis. Therefore, |
| * the service distribution enforced by the drive's internal |
| * scheduler is likely to coincide with the desired |
| * device-throughput distribution only in a completely |
| * symmetric scenario where: |
| * (i) each of these processes must get the same throughput as |
| * the others; |
| * (ii) all these processes have the same I/O pattern |
| (either sequential or random). |
| * In fact, in such a scenario, the drive will tend to treat |
| * the requests of each of these processes in about the same |
| * way as the requests of the others, and thus to provide |
| * each of these processes with about the same throughput |
| * (which is exactly the desired throughput distribution). In |
| * contrast, in any asymmetric scenario, device idling is |
| * certainly needed to guarantee that bfqq receives its |
| * assigned fraction of the device throughput (see [1] for |
| * details). |
| * |
| * We address this issue by controlling, actually, only the |
| * symmetry sub-condition (i), i.e., provided that |
| * sub-condition (i) holds, idling is not performed, |
| * regardless of whether sub-condition (ii) holds. In other |
| * words, only if sub-condition (i) holds, then idling is |
| * allowed, and the device tends to be prevented from queueing |
| * many requests, possibly of several processes. The reason |
| * for not controlling also sub-condition (ii) is that we |
| * exploit preemption to preserve guarantees in case of |
| * symmetric scenarios, even if (ii) does not hold, as |
| * explained in the next two paragraphs. |
| * |
| * Even if a queue, say Q, is expired when it remains idle, Q |
| * can still preempt the new in-service queue if the next |
| * request of Q arrives soon (see the comments on |
| * bfq_bfqq_update_budg_for_activation). If all queues and |
| * groups have the same weight, this form of preemption, |
| * combined with the hole-recovery heuristic described in the |
| * comments on function bfq_bfqq_update_budg_for_activation, |
| * are enough to preserve a correct bandwidth distribution in |
| * the mid term, even without idling. In fact, even if not |
| * idling allows the internal queues of the device to contain |
| * many requests, and thus to reorder requests, we can rather |
| * safely assume that the internal scheduler still preserves a |
| * minimum of mid-term fairness. The motivation for using |
| * preemption instead of idling is that, by not idling, |
| * service guarantees are preserved without minimally |
| * sacrificing throughput. In other words, both a high |
| * throughput and its desired distribution are obtained. |
| * |
| * More precisely, this preemption-based, idleless approach |
| * provides fairness in terms of IOPS, and not sectors per |
| * second. This can be seen with a simple example. Suppose |
| * that there are two queues with the same weight, but that |
| * the first queue receives requests of 8 sectors, while the |
| * second queue receives requests of 1024 sectors. In |
| * addition, suppose that each of the two queues contains at |
| * most one request at a time, which implies that each queue |
| * always remains idle after it is served. Finally, after |
| * remaining idle, each queue receives very quickly a new |
| * request. It follows that the two queues are served |
| * alternatively, preempting each other if needed. This |
| * implies that, although both queues have the same weight, |
| * the queue with large requests receives a service that is |
| * 1024/8 times as high as the service received by the other |
| * queue. |
| * |
| * On the other hand, device idling is performed, and thus |
| * pure sector-domain guarantees are provided, for the |
| * following queues, which are likely to need stronger |
| * throughput guarantees: weight-raised queues, and queues |
| * with a higher weight than other queues. When such queues |
| * are active, sub-condition (i) is false, which triggers |
| * device idling. |
| * |
| * According to the above considerations, the next variable is |
| * true (only) if sub-condition (i) holds. To compute the |
| * value of this variable, we not only use the return value of |
| * the function bfq_symmetric_scenario(), but also check |
| * whether bfqq is being weight-raised, because |
| * bfq_symmetric_scenario() does not take into account also |
| * weight-raised queues (see comments on |
| * bfq_weights_tree_add()). |
| * |
| * As a side note, it is worth considering that the above |
| * device-idling countermeasures may however fail in the |
| * following unlucky scenario: if idling is (correctly) |
| * disabled in a time period during which all symmetry |
| * sub-conditions hold, and hence the device is allowed to |
| * enqueue many requests, but at some later point in time some |
| * sub-condition stops to hold, then it may become impossible |
| * to let requests be served in the desired order until all |
| * the requests already queued in the device have been served. |
| */ |
| asymmetric_scenario = bfqq->wr_coeff > 1 || |
| !bfq_symmetric_scenario(bfqd); |
| |
| /* |
| * Finally, there is a case where maximizing throughput is the |
| * best choice even if it may cause unfairness toward |
| * bfqq. Such a case is when bfqq became active in a burst of |
| * queue activations. Queues that became active during a large |
| * burst benefit only from throughput, as discussed in the |
| * comments on bfq_handle_burst. Thus, if bfqq became active |
| * in a burst and not idling the device maximizes throughput, |
| * then the device must no be idled, because not idling the |
| * device provides bfqq and all other queues in the burst with |
| * maximum benefit. Combining this and the above case, we can |
| * now establish when idling is actually needed to preserve |
| * service guarantees. |
| */ |
| idling_needed_for_service_guarantees = |
| asymmetric_scenario && !bfq_bfqq_in_large_burst(bfqq); |
| |
| /* |
| * We have now all the components we need to compute the |
| * return value of the function, which is true only if idling |
| * either boosts the throughput (without issues), or is |
| * necessary to preserve service guarantees. |
| */ |
| return idling_boosts_thr_without_issues || |
| idling_needed_for_service_guarantees; |
| } |
| |
| /* |
| * If the in-service queue is empty but the function bfq_bfqq_may_idle |
| * returns true, then: |
| * 1) the queue must remain in service and cannot be expired, and |
| * 2) the device must be idled to wait for the possible arrival of a new |
| * request for the queue. |
| * See the comments on the function bfq_bfqq_may_idle for the reasons |
| * why performing device idling is the best choice to boost the throughput |
| * and preserve service guarantees when bfq_bfqq_may_idle itself |
| * returns true. |
| */ |
| static bool bfq_bfqq_must_idle(struct bfq_queue *bfqq) |
| { |
| return RB_EMPTY_ROOT(&bfqq->sort_list) && bfq_bfqq_may_idle(bfqq); |
| } |
| |
| /* |
| * Select a queue for service. If we have a current queue in service, |
| * check whether to continue servicing it, or retrieve and set a new one. |
| */ |
| static struct bfq_queue *bfq_select_queue(struct bfq_data *bfqd) |
| { |
| struct bfq_queue *bfqq; |
| struct request *next_rq; |
| enum bfqq_expiration reason = BFQQE_BUDGET_TIMEOUT; |
| |
| bfqq = bfqd->in_service_queue; |
| if (!bfqq) |
| goto new_queue; |
| |
| bfq_log_bfqq(bfqd, bfqq, "select_queue: already in-service queue"); |
| |
| if (bfq_may_expire_for_budg_timeout(bfqq) && |
| !bfq_bfqq_wait_request(bfqq) && |
| !bfq_bfqq_must_idle(bfqq)) |
| goto expire; |
| |
| check_queue: |
| /* |
| * This loop is rarely executed more than once. Even when it |
| * happens, it is much more convenient to re-execute this loop |
| * than to return NULL and trigger a new dispatch to get a |
| * request served. |
| */ |
| next_rq = bfqq->next_rq; |
| /* |
| * If bfqq has requests queued and it has enough budget left to |
| * serve them, keep the queue, otherwise expire it. |
| */ |
| if (next_rq) { |
| if (bfq_serv_to_charge(next_rq, bfqq) > |
| bfq_bfqq_budget_left(bfqq)) { |
| /* |
| * Expire the queue for budget exhaustion, |
| * which makes sure that the next budget is |
| * enough to serve the next request, even if |
| * it comes from the fifo expired path. |
| */ |
| reason = BFQQE_BUDGET_EXHAUSTED; |
| goto expire; |
| } else { |
| /* |
| * The idle timer may be pending because we may |
| * not disable disk idling even when a new request |
| * arrives. |
| */ |
| if (bfq_bfqq_wait_request(bfqq)) { |
| /* |
| * If we get here: 1) at least a new request |
| * has arrived but we have not disabled the |
| * timer because the request was too small, |
| * 2) then the block layer has unplugged |
| * the device, causing the dispatch to be |
| * invoked. |
| * |
| * Since the device is unplugged, now the |
| * requests are probably large enough to |
| * provide a reasonable throughput. |
| * So we disable idling. |
|