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diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c new file mode 100644 index 000000000..6687b805b --- /dev/null +++ b/block/bfq-iosched.c @@ -0,0 +1,6900 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * 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> + * + * 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.rst. + * + * 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. In more detail, BFQ + * behaves this way if the low_latency parameter is set (default + * configuration). This feature enables BFQ to provide applications in + * these classes with a very low latency. + * + * To implement this feature, BFQ constantly tries to detect whether + * the I/O requests in a bfq_queue come from an interactive or a soft + * real-time application. For brevity, in these cases, the queue is + * said to be interactive or soft real-time. In both cases, BFQ + * privileges the service of the queue, over that of non-interactive + * and non-soft-real-time queues. This privileging is performed, + * mainly, by raising the weight of the queue. So, for brevity, we + * call just weight-raising periods the time periods during which a + * queue is privileged, because deemed interactive or soft real-time. + * + * The detection of soft real-time queues/applications is described in + * detail in the comments on the function + * bfq_bfqq_softrt_next_start. On the other hand, the detection of an + * interactive queue works as follows: a queue is deemed interactive + * if it is constantly non empty only for a limited time interval, + * after which it does become empty. The queue may be deemed + * interactive again (for a limited time), if it restarts being + * constantly non empty, provided that this happens only after the + * queue has remained empty for a given minimum idle time. + * + * By default, BFQ computes automatically the above maximum time + * interval, i.e., the time interval after which a constantly + * non-empty queue stops being deemed interactive. Since a queue is + * weight-raised while it is deemed interactive, this maximum time + * interval happens to coincide with the (maximum) duration of the + * weight-raising for interactive queues. + * + * 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 + * ones that guarantee a low latency to interactive and 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 <linux/backing-dev.h> + +#include "blk.h" +#include "blk-mq.h" +#include "blk-mq-tag.h" +#include "blk-mq-sched.h" +#include "bfq-iosched.h" +#include "blk-wbt.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); +BFQ_BFQQ_FNS(has_waker); +#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; + +/* + * When a sync request is dispatched, the queue that contains that + * request, and all the ancestor entities of that queue, are charged + * with the number of sectors of the request. In contrast, if the + * request is async, then the queue and its ancestor entities are + * charged with the number of sectors of the request, multiplied by + * the factor below. This throttles the bandwidth for async I/O, + * w.r.t. to sync I/O, and it is done to counter the tendency of async + * writes to steal I/O throughput to reads. + * + * The current value of this parameter is the result of a tuning with + * several hardware and software configurations. We tried to find the + * lowest value for which writes do not cause noticeable problems to + * reads. In fact, the lower this parameter, the stabler I/O control, + * in the following respect. The lower this parameter is, the less + * the bandwidth enjoyed by a group decreases + * - when the group does writes, w.r.t. to when it does reads; + * - when other groups do reads, w.r.t. to when they do writes. + */ +static const int bfq_async_charge_factor = 3; + +/* Default timeout values, in jiffies, approximating CFQ defaults. */ +const int bfq_timeout = HZ / 8; + +/* + * Time limit for merging (see comments in bfq_setup_cooperator). Set + * to the slowest value that, in our tests, proved to be effective in + * removing false positives, while not causing true positives to miss + * queue merging. + * + * As can be deduced from the low time limit below, queue merging, if + * successful, happens at the very beginning of the I/O of the involved + * cooperating processes, as a consequence of the arrival of the very + * first requests from each cooperator. After that, there is very + * little chance to find cooperators. + */ +static const unsigned long bfq_merge_time_limit = HZ/10; + +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 3 +#define BFQ_HW_QUEUE_SAMPLES 32 + +#define BFQQ_SEEK_THR (sector_t)(8 * 100) +#define BFQQ_SECT_THR_NONROT (sector_t)(2 * 32) +#define BFQ_RQ_SEEKY(bfqd, last_pos, rq) \ + (get_sdist(last_pos, rq) > \ + BFQQ_SEEK_THR && \ + (!blk_queue_nonrot(bfqd->queue) || \ + blk_rq_sectors(rq) < BFQQ_SECT_THR_NONROT)) +#define BFQQ_CLOSE_THR (sector_t)(8 * 1024) +#define BFQQ_SEEKY(bfqq) (hweight32(bfqq->seek_history) > 19) +/* + * Sync random I/O is likely to be confused with soft real-time I/O, + * because it is characterized by limited throughput and apparently + * isochronous arrival pattern. To avoid false positives, queues + * containing only random (seeky) I/O are prevented from being tagged + * as soft real-time. + */ +#define BFQQ_TOTALLY_SEEKY(bfqq) (bfqq->seek_history == -1) + +/* 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. + * With + * - the current shift: 16 positions + * - the current type used to store rate: u32 + * - the current unit of measure for rate: [sectors/usec], or, more precisely, + * [(sectors/usec) / 2^BFQ_RATE_SHIFT] to take into account the shift, + * the range of rates that can be stored is + * [1 / 2^BFQ_RATE_SHIFT, 2^(32 - BFQ_RATE_SHIFT)] sectors/usec = + * [1 / 2^16, 2^16] sectors/usec = [15e-6, 65536] sectors/usec = + * [15, 65G] sectors/sec + * Which, assuming a sector size of 512B, corresponds to a range of + * [7.5K, 33T] B/sec + */ +#define BFQ_RATE_SHIFT 16 + +/* + * When configured for computing the duration of the weight-raising + * for interactive queues automatically (see the comments at the + * beginning of this file), BFQ does it using the following formula: + * duration = (ref_rate / r) * ref_wr_duration, + * where r is the peak rate of the device, and ref_rate and + * ref_wr_duration are two reference parameters. In particular, + * ref_rate is the peak rate of the reference storage device (see + * below), and ref_wr_duration is about the maximum time needed, with + * BFQ and while reading two files in parallel, to load typical large + * applications on the reference device (see the comments on + * max_service_from_wr below, for more details on how ref_wr_duration + * is obtained). 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 two different reference pairs (ref_rate, ref_wr_duration), + * depending on whether the device is rotational or non-rotational. + * + * In the following definitions, ref_rate[0] and ref_wr_duration[0] + * are the reference values for a rotational device, whereas + * ref_rate[1] and ref_wr_duration[1] are the reference values for a + * non-rotational device. The reference rates are not the actual peak + * rates of the devices used as a reference, but slightly lower + * values. The reason for using 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). + * + * The reference peak rates are measured in sectors/usec, left-shifted + * by BFQ_RATE_SHIFT. + */ +static int ref_rate[2] = {14000, 33000}; +/* + * To improve readability, a conversion function is used to initialize + * the following array, which entails that the array can be + * initialized only in a function. + */ +static int ref_wr_duration[2]; + +/* + * BFQ uses the above-detailed, time-based weight-raising mechanism to + * privilege interactive tasks. This mechanism is vulnerable to the + * following false positives: I/O-bound applications that will go on + * doing I/O for much longer than the duration of weight + * raising. These applications have basically no benefit from being + * weight-raised at the beginning of their I/O. On the opposite end, + * while being weight-raised, these applications + * a) unjustly steal throughput to applications that may actually need + * low latency; + * b) make BFQ uselessly perform device idling; device idling results + * in loss of device throughput with most flash-based storage, and may + * increase latencies when used purposelessly. + * + * BFQ tries to reduce these problems, by adopting the following + * countermeasure. To introduce this countermeasure, we need first to + * finish explaining how the duration of weight-raising for + * interactive tasks is computed. + * + * For a bfq_queue deemed as interactive, the duration of weight + * raising is dynamically adjusted, as a function of the estimated + * peak rate of the device, so as to be equal to the time needed to + * execute the 'largest' interactive task we benchmarked so far. By + * largest task, we mean the task for which each involved process has + * to do more I/O than for any of the other tasks we benchmarked. This + * reference interactive task is the start-up of LibreOffice Writer, + * and in this task each process/bfq_queue needs to have at most ~110K + * sectors transferred. + * + * This last piece of information enables BFQ to reduce the actual + * duration of weight-raising for at least one class of I/O-bound + * applications: those doing sequential or quasi-sequential I/O. An + * example is file copy. In fact, once started, the main I/O-bound + * processes of these applications usually consume the above 110K + * sectors in much less time than the processes of an application that + * is starting, because these I/O-bound processes will greedily devote + * almost all their CPU cycles only to their target, + * throughput-friendly I/O operations. This is even more true if BFQ + * happens to be underestimating the device peak rate, and thus + * overestimating the duration of weight raising. But, according to + * our measurements, once transferred 110K sectors, these processes + * have no right to be weight-raised any longer. + * + * Basing on the last consideration, BFQ ends weight-raising for a + * bfq_queue if the latter happens to have received an amount of + * service at least equal to the following constant. The constant is + * set to slightly more than 110K, to have a minimum safety margin. + * + * This early ending of weight-raising reduces the amount of time + * during which interactive false positives cause the two problems + * described at the beginning of these comments. + */ +static const unsigned long max_service_from_wr = 120000; + +#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) +{ + struct bfq_queue *old_bfqq = bic->bfqq[is_sync]; + + /* Clear bic pointer if bfqq is detached from this bic */ + if (old_bfqq && old_bfqq->bic == bic) + old_bfqq->bic = NULL; + + 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) +{ + lockdep_assert_held(&bfqd->lock); + + 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_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 closer 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; + } +} + +/* + * Async I/O can easily starve sync I/O (both sync reads and sync + * writes), by consuming all tags. Similarly, storms of sync writes, + * such as those that sync(2) may trigger, can starve sync reads. + * Limit depths of async I/O and sync writes so as to counter both + * problems. + */ +static void bfq_limit_depth(unsigned int op, struct blk_mq_alloc_data *data) +{ + struct bfq_data *bfqd = data->q->elevator->elevator_data; + + if (op_is_sync(op) && !op_is_write(op)) + return; + + data->shallow_depth = + bfqd->word_depths[!!bfqd->wr_busy_queues][op_is_sync(op)]; + + bfq_log(bfqd, "[%s] wr_busy %d sync %d depth %u", + __func__, bfqd->wr_busy_queues, op_is_sync(op), + data->shallow_depth); +} + +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; +} + +static bool bfq_too_late_for_merging(struct bfq_queue *bfqq) +{ + return bfqq->service_from_backlogged > 0 && + time_is_before_jiffies(bfqq->first_IO_time + + bfq_merge_time_limit); +} + +/* + * The following function is not marked as __cold because it is + * actually cold, but for the same performance goal described in the + * comments on the likely() at the beginning of + * bfq_setup_cooperator(). Unexpectedly, to reach an even lower + * execution time for the case where this function is not invoked, we + * had to add an unlikely() in each involved if(). + */ +void __cold +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; + } + + /* oom_bfqq does not participate in queue merging */ + if (bfqq == &bfqd->oom_bfqq) + return; + + /* + * bfqq cannot be merged any longer (see comments in + * bfq_setup_cooperator): no point in adding bfqq into the + * position tree. + */ + if (bfq_too_late_for_merging(bfqq)) + return; + + 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; +} + +/* + * The following function returns false either if every active queue + * must receive the same share of the throughput (symmetric scenario), + * or, as a special case, if bfqq must receive a share of the + * throughput lower than or equal to the share that every other active + * queue must receive. If bfqq does sync I/O, then these are the only + * two cases where bfqq happens to be guaranteed its share of the + * throughput even if I/O dispatching is not plugged when bfqq remains + * temporarily empty (for more details, see the comments in the + * function bfq_better_to_idle()). For this reason, the return value + * of this function is used to check whether I/O-dispatch plugging can + * be avoided. + * + * The above first case (symmetric scenario) occurs when: + * 1) all active queues have the same weight, + * 2) all active queues belong to the same I/O-priority class, + * 3) all active groups at the same level in the groups tree have the same + * weight, + * 4) 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 last two symmetry sub-conditions above would be quite complex + * and time consuming. Therefore this function evaluates, instead, + * only the following stronger three sub-conditions, for which it is + * much easier to maintain the needed state: + * 1) all active queues have the same weight, + * 2) all active queues belong to the same I/O-priority class, + * 3) there are no active groups. + * In particular, the last condition is always true if hierarchical + * support or the cgroups interface are not enabled, thus no state + * needs to be maintained in this case. + */ +static bool bfq_asymmetric_scenario(struct bfq_data *bfqd, + struct bfq_queue *bfqq) +{ + bool smallest_weight = bfqq && + bfqq->weight_counter && + bfqq->weight_counter == + container_of( + rb_first_cached(&bfqd->queue_weights_tree), + struct bfq_weight_counter, + weights_node); + + /* + * For queue weights to differ, queue_weights_tree must contain + * at least two nodes. + */ + bool varied_queue_weights = !smallest_weight && + !RB_EMPTY_ROOT(&bfqd->queue_weights_tree.rb_root) && + (bfqd->queue_weights_tree.rb_root.rb_node->rb_left || + bfqd->queue_weights_tree.rb_root.rb_node->rb_right); + + bool multiple_classes_busy = + (bfqd->busy_queues[0] && bfqd->busy_queues[1]) || + (bfqd->busy_queues[0] && bfqd->busy_queues[2]) || + (bfqd->busy_queues[1] && bfqd->busy_queues[2]); + + return varied_queue_weights || multiple_classes_busy +#ifdef CONFIG_BFQ_GROUP_IOSCHED + || bfqd->num_groups_with_pending_reqs > 0 +#endif + ; +} + +/* + * If the weight-counter tree passed as input contains no counter for + * the weight of the input queue, 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_queue *bfqq, + struct rb_root_cached *root) +{ + struct bfq_entity *entity = &bfqq->entity; + struct rb_node **new = &(root->rb_root.rb_node), *parent = NULL; + bool leftmost = true; + + /* + * Do not insert if the queue is already associated with a + * counter, which happens if: + * 1) 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, + * 2) 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 (bfqq->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) { + bfqq->weight_counter = __counter; + goto inc_counter; + } + if (entity->weight < __counter->weight) + new = &((*new)->rb_left); + else { + new = &((*new)->rb_right); + leftmost = false; + } + } + + bfqq->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 queue to not be + * considered in bfq_asymmetric_scenario, which, in its turn, + * causes the scenario to be deemed wrongly symmetric in case + * bfqq's weight would have been the only weight making the + * scenario asymmetric. On the bright side, no unbalance will + * however occur when bfqq becomes inactive again (the + * invocation of this function is triggered by an activation + * of queue). In fact, bfq_weights_tree_remove does nothing + * if !bfqq->weight_counter. + */ + if (unlikely(!bfqq->weight_counter)) + return; + + bfqq->weight_counter->weight = entity->weight; + rb_link_node(&bfqq->weight_counter->weights_node, parent, new); + rb_insert_color_cached(&bfqq->weight_counter->weights_node, root, + leftmost); + +inc_counter: + bfqq->weight_counter->num_active++; + bfqq->ref++; +} + +/* + * Decrement the weight counter associated with the queue, 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_queue *bfqq, + struct rb_root_cached *root) +{ + if (!bfqq->weight_counter) + return; + + bfqq->weight_counter->num_active--; + if (bfqq->weight_counter->num_active > 0) + goto reset_entity_pointer; + + rb_erase_cached(&bfqq->weight_counter->weights_node, root); + kfree(bfqq->weight_counter); + +reset_entity_pointer: + bfqq->weight_counter = NULL; + bfq_put_queue(bfqq); +} + +/* + * Invoke __bfq_weights_tree_remove on bfqq and decrement the number + * of active groups for each queue's inactive parent entity. + */ +void bfq_weights_tree_remove(struct bfq_data *bfqd, + struct bfq_queue *bfqq) +{ + struct bfq_entity *entity = bfqq->entity.parent; + + for_each_entity(entity) { + struct bfq_sched_data *sd = entity->my_sched_data; + + if (sd->next_in_service || sd->in_service_entity) { + /* + * entity is still active, because either + * next_in_service or in_service_entity is not + * NULL (see the comments on the definition of + * next_in_service for details on why + * in_service_entity must be checked too). + * + * As a consequence, its parent entities are + * active as well, and thus this loop must + * stop here. + */ + break; + } + + /* + * The decrement of num_groups_with_pending_reqs is + * not performed immediately upon the deactivation of + * entity, but it is delayed to when it also happens + * that the first leaf descendant bfqq of entity gets + * all its pending requests completed. The following + * instructions perform this delayed decrement, if + * needed. See the comments on + * num_groups_with_pending_reqs for details. + */ + if (entity->in_groups_with_pending_reqs) { + entity->in_groups_with_pending_reqs = false; + bfqd->num_groups_with_pending_reqs--; + } + } + + /* + * Next function is invoked last, because it causes bfqq to be + * freed if the following holds: bfqq is not in service and + * has no dispatched request. DO NOT use bfqq after the next + * function invocation. + */ + __bfq_weights_tree_remove(bfqd, bfqq, + &bfqd->queue_weights_tree); +} + +/* + * 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 || + bfq_asymmetric_scenario(bfqq->bfqd, bfqq)) + return blk_rq_sectors(rq); + + return blk_rq_sectors(rq) * 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, + max_t(unsigned long, bfqq->max_budget, + bfq_serv_to_charge(next_rq, bfqq)), + entity->service); + 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 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->rate_dur_prod; + do_div(dur, bfqd->peak_rate); + + /* + * Limit duration between 3 and 25 seconds. The upper limit + * has been conservatively set after the following worst case: + * on a QEMU/KVM virtual machine + * - running in a slow PC + * - with a virtual disk stacked on a slow low-end 5400rpm HDD + * - serving a heavy I/O workload, such as the sequential reading + * of several files + * mplayer took 23 seconds to start, if constantly weight-raised. + * + * As for higher values than that accommodating the above bad + * scenario, tests show that higher values would often yield + * the opposite of the desired result, i.e., would worsen + * responsiveness by allowing non-interactive applications to + * preserve weight raising for too long. + * + * On the other end, lower values than 3 seconds make it + * difficult for most interactive tasks to complete their jobs + * before weight-raising finishes. + */ + return clamp_val(dur, msecs_to_jiffies(3000), msecs_to_jiffies(25000)); +} + +/* switch back from soft real-time to interactive weight raising */ +static void switch_back_to_interactive_wr(struct bfq_queue *bfqq, + struct bfq_data *bfqd) +{ + bfqq->wr_coeff = bfqd->bfq_wr_coeff; + bfqq->wr_cur_max_time = bfq_wr_duration(bfqd); + bfqq->last_wr_start_finish = bfqq->wr_start_at_switch_to_srt; +} + +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->entity.new_weight = bic->saved_weight; + 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))) { + if (bfqq->wr_cur_max_time == bfqd->bfq_wr_rt_max_time && + !bfq_bfqq_in_large_burst(bfqq) && + time_is_after_eq_jiffies(bfqq->wr_start_at_switch_to_srt + + bfq_wr_duration(bfqd))) { + switch_back_to_interactive_wr(bfqq, bfqd); + } else { + bfqq->wr_coeff = 1; + bfq_log_bfqq(bfqq->bfqd, bfqq, + "resume state: switching off wr"); + } + } + + /* 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_or_in_serv - + (bfqq->weight_counter != NULL); +} + +/* 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); + + /* + * Start the creation of a new burst list only if there is no + * active queue. See comments on the conditional invocation of + * bfq_handle_burst(). + */ + if (bfq_tot_busy_queues(bfqd) == 0) { + hlist_add_head(&bfqq->burst_list_node, &bfqd->burst_list); + bfqd->burst_size = 1; + } else + bfqd->burst_size = 0; + + 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, unless these queues must be + * protected from the I/O flowing through other active 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, unless there are other active queues to isolate + * these new queues from. If there no other active queues, then + * weight-raising these new queues just lowers throughput in most + * cases. + * + * 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 is invoked only if there are + * no active queues (apart from active queues that would belong to the + * same, possible burst bfqq would belong to), and 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, which may in turn cause loss of throughput. Finally, there may + * even be no in-service queue when the next function is invoked (so, + * no queue to compare timestamps with). Because of these facts, the + * next function adopts the following simple scheme to avoid costly + * operations, too frequent preemptions and too many dependencies on + * the state of the scheduler: it requests the expiration of the + * in-service queue (unconditionally) only for queues that need to + * recover a hole. Then it delegates to other parts of the code the + * responsibility of handling the above case 2. + */ +static bool bfq_bfqq_update_budg_for_activation(struct bfq_data *bfqd, + struct bfq_queue *bfqq, + bool arrived_in_time) +{ + struct bfq_entity *entity = &bfqq->entity; + + /* + * In the next compound condition, we check also whether there + * is some budget left, because otherwise there is no point in + * trying to go on serving bfqq with this same budget: bfqq + * would be expired immediately after being selected for + * service. This would only cause useless overhead. + */ + if (bfq_bfqq_non_blocking_wait_rq(bfqq) && arrived_in_time && + bfq_bfqq_budget_left(bfqq) > 0) { + /* + * 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. + */ + entity->budget = min_t(unsigned long, + bfq_bfqq_budget_left(bfqq), + bfqq->max_budget); + + /* + * At this point, we have used entity->service to get + * the budget left (needed for updating + * entity->budget). Thus we finally can, and have to, + * reset entity->service. The latter must be reset + * because bfqq would otherwise be charged again for + * the service it has received during its previous + * service slot(s). + */ + entity->service = 0; + + return true; + } + + /* + * We can finally complete expiration, by setting service to 0. + */ + entity->service = 0; + 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 false; +} + +/* + * Return the farthest past time instant according to jiffies + * macros. + */ +static unsigned long bfq_smallest_from_now(void) +{ + return jiffies - MAX_JIFFY_OFFSET; +} + +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->service_from_wr = 0; + bfqq->wr_coeff = bfqd->bfq_wr_coeff; + bfqq->wr_cur_max_time = bfq_wr_duration(bfqd); + } else { + /* + * No interactive weight raising in progress + * here: assign minus infinity to + * wr_start_at_switch_to_srt, to make sure + * that, at the end of the soft-real-time + * weight raising periods that is starting + * now, no interactive weight-raising period + * may be wrongly considered as still in + * progress (and thus actually started by + * mistake). + */ + bfqq->wr_start_at_switch_to_srt = + bfq_smallest_from_now(); + 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); +} + + +/* + * Return true if bfqq is in a higher priority class, or has a higher + * weight than the in-service queue. + */ +static bool bfq_bfqq_higher_class_or_weight(struct bfq_queue *bfqq, + struct bfq_queue *in_serv_bfqq) +{ + int bfqq_weight, in_serv_weight; + + if (bfqq->ioprio_class < in_serv_bfqq->ioprio_class) + return true; + + if (in_serv_bfqq->entity.parent == bfqq->entity.parent) { + bfqq_weight = bfqq->entity.weight; + in_serv_weight = in_serv_bfqq->entity.weight; + } else { + if (bfqq->entity.parent) + bfqq_weight = bfqq->entity.parent->weight; + else + bfqq_weight = bfqq->entity.weight; + if (in_serv_bfqq->entity.parent) + in_serv_weight = in_serv_bfqq->entity.parent->weight; + else + in_serv_weight = in_serv_bfqq->entity.weight; + } + + return bfqq_weight > in_serv_weight; +} + +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; + + + /* + * 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 && + !BFQQ_TOTALLY_SEEKY(bfqq) && + !in_burst && + time_is_before_jiffies(bfqq->soft_rt_next_start) && + bfqq->dispatched == 0; + *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); + + /* + * 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 particular, we care only about two + * cases. The first is that bfqq has to recover a service + * hole, as explained in the comments on + * bfq_bfqq_update_budg_for_activation(), i.e., that + * bfqq_wants_to_preempt is true. However, if bfqq does not + * carry time-critical I/O, then bfqq's bandwidth is less + * important than that of queues that carry time-critical I/O. + * So, as a further constraint, we consider this case only if + * bfqq is at least as weight-raised, i.e., at least as time + * critical, as the in-service queue. + * + * The second case is that bfqq is in a higher priority class, + * or has a higher weight than the in-service queue. If this + * condition does not hold, we don't care because, even if + * bfqq does not start to be served immediately, the resulting + * delay for bfqq's I/O is however lower or much lower than + * the ideal completion time to be guaranteed to bfqq's I/O. + * + * In both cases, preemption is needed only if, according to + * the timestamps of both bfqq and of the in-service queue, + * bfqq actually is the next queue to serve. So, to reduce + * useless preemptions, the return value of + * next_queue_may_preempt() is considered in the next compound + * condition too. Yet next_queue_may_preempt() just checks a + * simple, necessary condition for bfqq to be the next queue + * to serve. In fact, to evaluate a sufficient condition, the + * timestamps of the in-service queue would need to be + * updated, and this operation is quite costly (see the + * comments on bfq_bfqq_update_budg_for_activation()). + */ + if (bfqd->in_service_queue && + ((bfqq_wants_to_preempt && + bfqq->wr_coeff >= bfqd->in_service_queue->wr_coeff) || + bfq_bfqq_higher_class_or_weight(bfqq, bfqd->in_service_queue)) && + next_queue_may_preempt(bfqd)) + bfq_bfqq_expire(bfqd, bfqd->in_service_queue, + false, BFQQE_PREEMPTED); +} + +static void bfq_reset_inject_limit(struct bfq_data *bfqd, + struct bfq_queue *bfqq) +{ + /* invalidate baseline total service time */ + bfqq->last_serv_time_ns = 0; + + /* + * Reset pointer in case we are waiting for + * some request completion. + */ + bfqd->waited_rq = NULL; + + /* + * If bfqq has a short think time, then start by setting the + * inject limit to 0 prudentially, because the service time of + * an injected I/O request may be higher than the think time + * of bfqq, and therefore, if one request was injected when + * bfqq remains empty, this injected request might delay the + * service of the next I/O request for bfqq significantly. In + * case bfqq can actually tolerate some injection, then the + * adaptive update will however raise the limit soon. This + * lucky circumstance holds exactly because bfqq has a short + * think time, and thus, after remaining empty, is likely to + * get new I/O enqueued---and then completed---before being + * expired. This is the very pattern that gives the + * limit-update algorithm the chance to measure the effect of + * injection on request service times, and then to update the + * limit accordingly. + * + * However, in the following special case, the inject limit is + * left to 1 even if the think time is short: bfqq's I/O is + * synchronized with that of some other queue, i.e., bfqq may + * receive new I/O only after the I/O of the other queue is + * completed. Keeping the inject limit to 1 allows the + * blocking I/O to be served while bfqq is in service. And + * this is very convenient both for bfqq and for overall + * throughput, as explained in detail in the comments in + * bfq_update_has_short_ttime(). + * + * On the opposite end, if bfqq has a long think time, then + * start directly by 1, because: + * a) on the bright side, keeping at most one request in + * service in the drive is unlikely to cause any harm to the + * latency of bfqq's requests, as the service time of a single + * request is likely to be lower than the think time of bfqq; + * b) on the downside, after becoming empty, bfqq is likely to + * expire before getting its next request. With this request + * arrival pattern, it is very hard to sample total service + * times and update the inject limit accordingly (see comments + * on bfq_update_inject_limit()). So the limit is likely to be + * never, or at least seldom, updated. As a consequence, by + * setting the limit to 1, we avoid that no injection ever + * occurs with bfqq. On the downside, this proactive step + * further reduces chances to actually compute the baseline + * total service time. Thus it reduces chances to execute the + * limit-update algorithm and possibly raise the limit to more + * than 1. + */ + if (bfq_bfqq_has_short_ttime(bfqq)) + bfqq->inject_limit = 0; + else + bfqq->inject_limit = 1; + + bfqq->decrease_time_jif = jiffies; +} + +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++; + + if (RB_EMPTY_ROOT(&bfqq->sort_list) && bfq_bfqq_sync(bfqq)) { + /* + * Detect whether bfqq's I/O seems synchronized with + * that of some other queue, i.e., whether bfqq, after + * remaining empty, happens to receive new I/O only + * right after some I/O request of the other queue has + * been completed. We call waker queue the other + * queue, and we assume, for simplicity, that bfqq may + * have at most one waker queue. + * + * A remarkable throughput boost can be reached by + * unconditionally injecting the I/O of the waker + * queue, every time a new bfq_dispatch_request + * happens to be invoked while I/O is being plugged + * for bfqq. In addition to boosting throughput, this + * unblocks bfqq's I/O, thereby improving bandwidth + * and latency for bfqq. Note that these same results + * may be achieved with the general injection + * mechanism, but less effectively. For details on + * this aspect, see the comments on the choice of the + * queue for injection in bfq_select_queue(). + * + * Turning back to the detection of a waker queue, a + * queue Q is deemed as a waker queue for bfqq if, for + * two consecutive times, bfqq happens to become non + * empty right after a request of Q has been + * completed. In particular, on the first time, Q is + * tentatively set as a candidate waker queue, while + * on the second time, the flag + * bfq_bfqq_has_waker(bfqq) is set to confirm that Q + * is a waker queue for bfqq. These detection steps + * are performed only if bfqq has a long think time, + * so as to make it more likely that bfqq's I/O is + * actually being blocked by a synchronization. This + * last filter, plus the above two-times requirement, + * make false positives less likely. + * + * NOTE + * + * The sooner a waker queue is detected, the sooner + * throughput can be boosted by injecting I/O from the + * waker queue. Fortunately, detection is likely to be + * actually fast, for the following reasons. While + * blocked by synchronization, bfqq has a long think + * time. This implies that bfqq's inject limit is at + * least equal to 1 (see the comments in + * bfq_update_inject_limit()). So, thanks to + * injection, the waker queue is likely to be served + * during the very first I/O-plugging time interval + * for bfqq. This triggers the first step of the + * detection mechanism. Thanks again to injection, the + * candidate waker queue is then likely to be + * confirmed no later than during the next + * I/O-plugging interval for bfqq. + */ + if (bfqd->last_completed_rq_bfqq && + !bfq_bfqq_has_short_ttime(bfqq) && + ktime_get_ns() - bfqd->last_completion < + 200 * NSEC_PER_USEC) { + if (bfqd->last_completed_rq_bfqq != bfqq && + bfqd->last_completed_rq_bfqq != + bfqq->waker_bfqq) { + /* + * First synchronization detected with + * a candidate waker queue, or with a + * different candidate waker queue + * from the current one. + */ + bfqq->waker_bfqq = bfqd->last_completed_rq_bfqq; + + /* + * If the waker queue disappears, then + * bfqq->waker_bfqq must be reset. To + * this goal, we maintain in each + * waker queue a list, woken_list, of + * all the queues that reference the + * waker queue through their + * waker_bfqq pointer. When the waker + * queue exits, the waker_bfqq pointer + * of all the queues in the woken_list + * is reset. + * + * In addition, if bfqq is already in + * the woken_list of a waker queue, + * then, before being inserted into + * the woken_list of a new waker + * queue, bfqq must be removed from + * the woken_list of the old waker + * queue. + */ + if (!hlist_unhashed(&bfqq->woken_list_node)) + hlist_del_init(&bfqq->woken_list_node); + hlist_add_head(&bfqq->woken_list_node, + &bfqd->last_completed_rq_bfqq->woken_list); + + bfq_clear_bfqq_has_waker(bfqq); + } else if (bfqd->last_completed_rq_bfqq == + bfqq->waker_bfqq && + !bfq_bfqq_has_waker(bfqq)) { + /* + * synchronization with waker_bfqq + * seen for the second time + */ + bfq_mark_bfqq_has_waker(bfqq); + } + } + + /* + * Periodically reset inject limit, to make sure that + * the latter eventually drops in case workload + * changes, see step (3) in the comments on + * bfq_update_inject_limit(). + */ + if (time_is_before_eq_jiffies(bfqq->decrease_time_jif + + msecs_to_jiffies(1000))) + bfq_reset_inject_limit(bfqd, bfqq); + + /* + * The following conditions must hold to setup a new + * sampling of total service time, and then a new + * update of the inject limit: + * - bfqq is in service, because the total service + * time is evaluated only for the I/O requests of + * the queues in service; + * - this is the right occasion to compute or to + * lower the baseline total service time, because + * there are actually no requests in the drive, + * or + * the baseline total service time is available, and + * this is the right occasion to compute the other + * quantity needed to update the inject limit, i.e., + * the total service time caused by the amount of + * injection allowed by the current value of the + * limit. It is the right occasion because injection + * has actually been performed during the service + * hole, and there are still in-flight requests, + * which are very likely to be exactly the injected + * requests, or part of them; + * - the minimum interval for sampling the total + * service time and updating the inject limit has + * elapsed. + */ + if (bfqq == bfqd->in_service_queue && + (bfqd->rq_in_driver == 0 || + (bfqq->last_serv_time_ns > 0 && + bfqd->rqs_injected && bfqd->rq_in_driver > 0)) && + time_is_before_eq_jiffies(bfqq->decrease_time_jif + + msecs_to_jiffies(10))) { + bfqd->last_empty_occupied_ns = ktime_get_ns(); + /* + * Start the state machine for measuring the + * total service time of rq: setting + * wait_dispatch will cause bfqd->waited_rq to + * be set when rq will be dispatched. + */ + bfqd->wait_dispatch = true; + /* + * If there is no I/O in service in the drive, + * then possible injection occurred before the + * arrival of rq will not affect the total + * service time of rq. So the injection limit + * must not be updated as a function of such + * total service time, unless new injection + * occurs before rq is completed. To have the + * injection limit updated only in the latter + * case, reset rqs_injected here (rqs_injected + * will be set in case injection is performed + * on bfqq before rq is completed). + */ + if (bfqd->rq_in_driver == 0) + bfqd->rqs_injected = false; + } + } + + 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. + * See comments on bfq_pos_tree_add_move() for the unlikely(). + */ + if (unlikely(!bfqd->nonrot_with_queueing && 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; + } + } else { + /* see comments on bfq_pos_tree_add_move() for the unlikely() */ + if (unlikely(!bfqd->nonrot_with_queueing)) + bfq_pos_tree_add_move(bfqd, bfqq); + } + + if (rq->cmd_flags & REQ_META) + bfqq->meta_pending--; + +} + +static bool bfq_bio_merge(struct request_queue *q, struct bio *bio, + unsigned int nr_segs) +{ + 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) { + /* + * Make sure cgroup info is uptodate for current process before + * considering the merge. + */ + bfq_bic_update_cgroup(bic, bio); + + 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, nr_segs, &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; + + if (blk_discard_mergable(__rq)) + return ELEVATOR_DISCARD_MERGE; + 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; + struct request *prev, *next_rq; + + if (!bfqq) + return; + + bfqd = bfqq->bfqd; + + /* 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); + /* + * See comments on bfq_pos_tree_add_move() for + * the unlikely(). + */ + if (unlikely(!bfqd->nonrot_with_queueing)) + bfq_pos_tree_add_move(bfqd, bfqq); + } + } +} + +/* + * This function is called to notify the scheduler that the requests + * rq and 'next' have been merged, with 'next' going away. BFQ + * exploits this hook to address the following issue: if 'next' has a + * fifo_time lower that rq, then the fifo_time of rq must be set to + * the value of 'next', to not forget the greater age of 'next'. + * + * NOTE: in this function we assume that rq is in a bfq_queue, basing + * on that rq is picked from the hash table q->elevator->hash, which, + * in its turn, is filled only with I/O requests present in + * bfq_queues, while BFQ is in use for the request queue q. In fact, + * the function that fills this hash table (elv_rqhash_add) is called + * only by bfq_insert_request. + */ +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 (!bfqq) + return; + + /* + * 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; + + 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; + + /* + * Make sure merged queues belong to the same parent. Parents could + * have changed since the time we decided the two queues are suitable + * for merging. + */ + if (new_bfqq->entity.parent != bfqq->entity.parent) + 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; + /* + * The above assignment schedules the following redirections: + * each time some I/O for bfqq arrives, the process that + * generated that I/O is disassociated from bfqq and + * associated with new_bfqq. Here we increases new_bfqq->ref + * in advance, adding the number of processes that are + * expected to be associated with new_bfqq as they happen to + * issue I/O. + */ + 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_too_late_for_merging(new_bfqq)) + return false; + + 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; +} + +/* + * 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. + * + * 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 a merge has already been setup, then proceed with that first */ + if (bfqq->new_bfqq) + return bfqq->new_bfqq; + + /* + * Do not perform queue merging if the device is non + * rotational and performs internal queueing. In fact, such a + * device reaches a high speed through internal parallelism + * and pipelining. This means that, to reach a high + * throughput, it must have many requests enqueued at the same + * time. But, in this configuration, the internal scheduling + * algorithm of the device does exactly the job of queue + * merging: it reorders requests so as to obtain as much as + * possible a sequential I/O pattern. As a consequence, with + * the workload generated by processes doing interleaved I/O, + * the throughput reached by the device is likely to be the + * same, with and without queue merging. + * + * Disabling merging also provides a remarkable benefit in + * terms of throughput. Merging tends to make many workloads + * artificially more uneven, because of shared queues + * remaining non empty for incomparably more time than + * non-merged queues. This may accentuate workload + * asymmetries. For example, if one of the queues in a set of + * merged queues has a higher weight than a normal queue, then + * the shared queue may inherit such a high weight and, by + * staying almost always active, may force BFQ to perform I/O + * plugging most of the time. This evidently makes it harder + * for BFQ to let the device reach a high throughput. + * + * Finally, the likely() macro below is not used because one + * of the two branches is more likely than the other, but to + * have the code path after the following if() executed as + * fast as possible for the case of a non rotational device + * with queueing. We want it because this is the fastest kind + * of device. On the opposite end, the likely() may lengthen + * the execution time of BFQ for the case of slower devices + * (rotational or at least without queueing). But in this case + * the execution time of BFQ matters very little, if not at + * all. + */ + if (likely(bfqd->nonrot_with_queueing)) + return NULL; + + /* + * Prevent bfqq from being merged if it has been created too + * long ago. The idea is that true cooperating processes, and + * thus their associated bfq_queues, are supposed to be + * created shortly after each other. This is the case, e.g., + * for KVM/QEMU and dump I/O threads. Basing on this + * assumption, the following filtering greatly reduces the + * probability that two non-cooperating processes, which just + * happen to do close I/O for some short time interval, have + * their queues merged by mistake. + */ + if (bfq_too_late_for_merging(bfqq)) + return NULL; + + if (!io_struct || unlikely(bfqq == &bfqd->oom_bfqq)) + return NULL; + + /* If there is only one backlogged queue, don't search. */ + if (bfq_tot_busy_queues(bfqd) == 1) + return NULL; + + in_service_bfqq = bfqd->in_service_queue; + + if (in_service_bfqq && in_service_bfqq != bfqq && + likely(in_service_bfqq != &bfqd->oom_bfqq) && + bfq_rq_close_to_sector(io_struct, request, + bfqd->in_serv_last_pos) && + 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. + */ + new_bfqq = bfq_find_close_cooperator(bfqd, bfqq, + bfq_io_struct_pos(io_struct, request)); + + if (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_weight = bfqq->entity.orig_weight; + 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); + if (unlikely(bfq_bfqq_just_created(bfqq) && + !bfq_bfqq_in_large_burst(bfqq) && + bfqq->bfqd->low_latency)) { + /* + * bfqq being merged right after being created: bfqq + * would have deserved interactive weight raising, but + * did not make it to be set in a weight-raised state, + * because of this early merge. Store directly the + * weight-raising state that would have been assigned + * to bfqq, so that to avoid that bfqq unjustly fails + * to enjoy weight raising if split soon. + */ + bic->saved_wr_coeff = bfqq->bfqd->bfq_wr_coeff; + bic->saved_wr_start_at_switch_to_srt = bfq_smallest_from_now(); + bic->saved_wr_cur_max_time = bfq_wr_duration(bfqq->bfqd); + bic->saved_last_wr_start_finish = jiffies; + } else { + 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; + } +} + +void bfq_release_process_ref(struct bfq_data *bfqd, struct bfq_queue *bfqq) +{ + /* + * To prevent bfqq's service guarantees from being violated, + * bfqq may be left busy, i.e., queued for service, even if + * empty (see comments in __bfq_bfqq_expire() for + * details). But, if no process will send requests to bfqq any + * longer, then there is no point in keeping bfqq queued for + * service. In addition, keeping bfqq queued for service, but + * with no process ref any longer, may have caused bfqq to be + * freed when dequeued from service. But this is assumed to + * never happen. + */ + if (bfq_bfqq_busy(bfqq) && RB_EMPTY_ROOT(&bfqq->sort_list) && + bfqq != bfqd->in_service_queue) + bfq_del_bfqq_busy(bfqd, bfqq, false); + + bfq_put_queue(bfqq); +} + +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, true); + 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; + /* + * If the queue is shared, the pid is the pid of one of the associated + * processes. Which pid depends on the exact sequence of merge events + * the queue underwent. So printing such a pid is useless and confusing + * because it reports a random pid between those of the associated + * processes. + * We mark such a queue with a pid -1, and then print SHARED instead of + * a pid in logging messages. + */ + new_bfqq->pid = -1; + bfqq->bic = NULL; + bfq_release_process_ref(bfqd, 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 between bfqq and new_bfqq can be safely + * fulfilled, 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) { + 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; + bfqd->in_serv_last_pos = 0; +} + +/* + * 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_asymmetric_scenario(bfqd, bfqq)) + sl = min_t(u64, sl, BFQ_MIN_TT); + else if (bfqq->wr_coeff > 1) + sl = max_t(u32, sl, 20ULL * NSEC_PER_MSEC); + + bfqd->last_idling_start = ktime_get(); + bfqd->last_idling_start_jiffies = jiffies; + + 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 the ref_wr_duration array. + */ +static void update_thr_responsiveness_params(struct bfq_data *bfqd) +{ + if (bfqd->bfq_user_max_budget == 0) { + bfqd->bfq_max_budget = + bfq_calc_max_budget(bfqd); + bfq_log(bfqd, "new max_budget = %d", bfqd->bfq_max_budget); + } +} + +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; + + /* + * For a very slow device, bfqd->peak_rate can reach 0 (see + * the minimum representable values reported in the comments + * on BFQ_RATE_SHIFT). Push to 1 if this happens, to avoid + * divisions by zero where bfqd->peak_rate is used as a + * divisor. + */ + bfqd->peak_rate = max_t(u32, 1, bfqd->peak_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) + && !BFQ_RQ_SEEKY(bfqd, bfqd->last_position, rq)) + 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); + if (RQ_BFQQ(rq) == bfqd->in_service_queue) + bfqd->in_serv_last_pos = bfqd->last_position; + 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); +} + +/* + * There is a case where idling does not have to be performed for + * throughput concerns, but to preserve the throughput share of + * the process associated with bfqq. + * + * 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 throughput + * distribution only in a completely symmetric, or favorably + * skewed scenario where: + * (i-a) each of these processes must get the same throughput as + * the others, + * (i-b) in case (i-a) does not hold, it holds that the process + * associated with bfqq must receive a lower or equal + * throughput than any of the other processes; + * (ii) the I/O of each process has the same properties, in + * terms of locality (sequential or random), direction + * (reads or writes), request sizes, greediness + * (from I/O-bound to sporadic), and so on; + + * In fact, in such a scenario, the drive tends to treat the requests + * of each process in about the same way as the requests of the + * others, and thus to provide each of these processes with about the + * same throughput. This is exactly the desired throughput + * distribution if (i-a) holds, or, if (i-b) holds instead, this is an + * even more convenient distribution for (the process associated with) + * bfqq. + * + * In contrast, in any asymmetric or unfavorable scenario, device + * idling (I/O-dispatch plugging) is certainly needed to guarantee + * that bfqq receives its assigned fraction of the device throughput + * (see [1] for details). + * + * The problem is that idling may significantly reduce throughput with + * certain combinations of types of I/O and devices. An important + * example is sync random I/O on flash storage with command + * queueing. So, unless bfqq falls in cases where idling also boosts + * throughput, it is important to check conditions (i-a), i(-b) and + * (ii) accurately, so as to avoid idling when not strictly needed for + * service guarantees. + * + * Unfortunately, it is extremely difficult to thoroughly check + * condition (ii). And, in case there are active groups, it becomes + * very difficult to check conditions (i-a) and (i-b) too. In fact, + * if there are active groups, then, for conditions (i-a) or (i-b) to + * become false 'indirectly', it is enough that an active group + * contains more active processes or sub-groups than some other active + * group. More precisely, for conditions (i-a) or (i-b) to become + * false because of such a group, it is not even necessary that the + * group is (still) active: it is sufficient that, even if the group + * has become inactive, some of its descendant processes still have + * some request already dispatched but still waiting for + * completion. In fact, requests have still to be guaranteed their + * share of the throughput even after being dispatched. In this + * respect, it is easy to show that, if a group frequently becomes + * inactive while still having in-flight requests, and if, when this + * happens, the group is not considered in the calculation of whether + * the scenario is asymmetric, then the group may fail to be + * guaranteed its fair share of the throughput (basically because + * idling may not be performed for the descendant processes of the + * group, but it had to be). We address this issue with the following + * bi-modal behavior, implemented in the function + * bfq_asymmetric_scenario(). + * + * If there are groups with requests waiting for completion + * (as commented above, some of these groups may even be + * already inactive), then the scenario is tagged as + * asymmetric, conservatively, without checking any of the + * conditions (i-a), (i-b) or (ii). So the device is idled for bfqq. + * This behavior matches also the fact that groups are created + * exactly if controlling I/O is a primary concern (to + * preserve bandwidth and latency guarantees). + * + * On the opposite end, if there are no groups with requests waiting + * for completion, then only conditions (i-a) and (i-b) are actually + * controlled, i.e., provided that conditions (i-a) or (i-b) holds, + * idling is not performed, regardless of whether condition (ii) + * holds. In other words, only if conditions (i-a) and (i-b) do not + * hold, then idling is allowed, and the device tends to be prevented + * from queueing many requests, possibly of several processes. Since + * there are no groups with requests waiting for completion, then, to + * control conditions (i-a) and (i-b) it is enough to check just + * whether all the queues with requests waiting for completion also + * have the same weight. + * + * Not checking condition (ii) evidently exposes bfqq to the + * risk of getting less throughput than its fair share. + * However, for queues with the same weight, a further + * mechanism, preemption, mitigates or even eliminates this + * problem. And it does so without consequences on overall + * throughput. This mechanism and its benefits are explained + * in the next three 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. + * + * 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. + * + * The motivation for using preemption instead of idling (for + * queues with the same weight) is that, by not idling, + * service guarantees are preserved (completely or at least in + * part) without minimally sacrificing throughput. And, if + * there is no active group, then the primary expectation for + * this device is probably a high throughput. + * + * We are now left only with explaining the two sub-conditions in the + * additional compound condition that is checked below for deciding + * whether the scenario is asymmetric. To explain the first + * sub-condition, we need to add that the function + * bfq_asymmetric_scenario checks the weights of only + * non-weight-raised queues, for efficiency reasons (see comments on + * bfq_weights_tree_add()). Then the fact that bfqq is weight-raised + * is checked explicitly here. More precisely, the compound condition + * below takes into account also the fact that, even if bfqq is being + * weight-raised, the scenario is still symmetric if all queues with + * requests waiting for completion happen to be + * weight-raised. Actually, we should be even more precise here, and + * differentiate between interactive weight raising and soft real-time + * weight raising. + * + * The second sub-condition checked in the compound condition is + * whether there is a fair amount of already in-flight I/O not + * belonging to bfqq. If so, I/O dispatching is to be plugged, for the + * following reason. The drive may decide to serve in-flight + * non-bfqq's I/O requests before bfqq's ones, thereby delaying the + * arrival of new I/O requests for bfqq (recall that bfqq is sync). If + * I/O-dispatching is not plugged, then, while bfqq remains empty, a + * basically uncontrolled amount of I/O from other queues may be + * dispatched too, possibly causing the service of bfqq's I/O to be + * delayed even longer in the drive. This problem gets more and more + * serious as the speed and the queue depth of the drive grow, + * because, as these two quantities grow, the probability to find no + * queue busy but many requests in flight grows too. By contrast, + * plugging I/O dispatching minimizes the delay induced by already + * in-flight I/O, and enables bfqq to recover the bandwidth it may + * lose because of this delay. + * + * As a side note, it is worth considering that the above + * device-idling countermeasures may however fail in the following + * unlucky scenario: if I/O-dispatch plugging is (correctly) disabled + * in a time period during which all symmetry sub-conditions hold, and + * therefore 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 make requests be served in the desired + * order until all the requests already queued in the device have been + * served. The last sub-condition commented above somewhat mitigates + * this problem for weight-raised queues. + */ +static bool idling_needed_for_service_guarantees(struct bfq_data *bfqd, + struct bfq_queue *bfqq) +{ + /* No point in idling for bfqq if it won't get requests any longer */ + if (unlikely(!bfqq_process_refs(bfqq))) + return false; + + return (bfqq->wr_coeff > 1 && + (bfqd->wr_busy_queues < + bfq_tot_busy_queues(bfqd) || + bfqd->rq_in_driver >= + bfqq->dispatched + 4)) || + bfq_asymmetric_scenario(bfqd, bfqq); +} + +static bool __bfq_bfqq_expire(struct bfq_data *bfqd, struct bfq_queue *bfqq, + enum bfqq_expiration reason) +{ + /* + * 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); + + /* + * Consider queues with a higher finish virtual time than + * bfqq. If idling_needed_for_service_guarantees(bfqq) returns + * true, then bfqq's bandwidth would be violated if an + * uncontrolled amount of I/O from these queues were + * dispatched while bfqq is waiting for its new I/O to + * arrive. This is exactly what may happen if this is a forced + * expiration caused by a preemption attempt, and if bfqq is + * not re-scheduled. To prevent this from happening, re-queue + * bfqq if it needs I/O-dispatch plugging, even if it is + * empty. By doing so, bfqq is granted to be served before the + * above queues (provided that bfqq is of course eligible). + */ + if (RB_EMPTY_ROOT(&bfqq->sort_list) && + !(reason == BFQQE_PREEMPTED && + idling_needed_for_service_guarantees(bfqd, bfqq))) { + 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. + * See comments on bfq_pos_tree_add_move() for the unlikely(). + */ + if (unlikely(!bfqd->nonrot_with_queueing && + !RB_EMPTY_ROOT(&bfqq->sort_list))) + 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 entities as no more in service. This + * may cause bfqq to be freed. If this happens, the next + * function returns true. + */ + return __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 (i.e., I/O-bound) application may + * happen to meet, occasionally or systematically, both the above + * bandwidth and isochrony requirements. This may happen at least in + * the following circumstances. First, if the CPU load is high. 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. The other circumstances are related to the storage + * device: the storage device is highly loaded or reaches a low-enough + * throughput with the I/O of the application (e.g., because the I/O + * is random and/or the device is slow). In all these cases, the + * I/O of the application may be simply slowed down enough to meet + * the bandwidth and isochrony requirements. To reduce the probability + * that greedy applications are deemed as soft real-time in these + * corner cases, a further rule is used in the computation of + * soft_rt_next_start: the return value of this function is forced to + * be higher than the maximum between the following two quantities. + * + * (a) Current time plus: (1) the maximum time for which the arrival + * of a request is waited for when a sync queue becomes idle, + * namely bfqd->bfq_slice_idle, and (2) a few extra jiffies. We + * postpone for a moment the reason for adding a few extra + * jiffies; we get back to it after next item (b). Lower-bounding + * the return value of this function with the current time plus + * bfqd->bfq_slice_idle tends to filter out greedy applications, + * because the latter issue their next request as soon as possible + * after the last one has been completed. In contrast, a soft + * real-time application spends some time processing data, after a + * batch of its requests has been completed. + * + * (b) Current value of bfqq->soft_rt_next_start. As pointed out + * above, greedy applications may happen to meet both the + * bandwidth and isochrony requirements under heavy CPU or + * storage-device load. In more detail, in these scenarios, these + * applications happen, only for limited time periods, to do I/O + * slowly enough to meet all the requirements described so far, + * including the filtering in above item (a). These slow-speed + * time intervals are usually interspersed between other time + * intervals during which these applications do I/O at a very high + * speed. Fortunately, exactly because of the high speed of the + * I/O in the high-speed intervals, the values returned by this + * function happen to be so high, near the end of any such + * high-speed interval, to be likely to fall *after* the end of + * the low-speed time interval that follows. These high values are + * stored in bfqq->soft_rt_next_start after each invocation of + * this function. As a consequence, if the last value of + * bfqq->soft_rt_next_start is constantly used to lower-bound the + * next value that this function may return, then, from the very + * beginning of a low-speed interval, bfqq->soft_rt_next_start is + * likely to be constantly kept so high that any I/O request + * issued during the low-speed interval is considered as arriving + * to soon for the application to be deemed as soft + * real-time. Then, in the high-speed interval that follows, the + * application will not be deemed as soft real-time, just because + * it will do I/O at a high speed. And so on. + * + * Getting back to the filtering in item (a), in the following two + * cases this filtering might be easily passed by a greedy + * application, if the reference quantity was just + * bfqd->bfq_slice_idle: + * 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. The time granularity may be so coarse + * that the approximation, in jiffies, of bfqd->bfq_slice_idle + * is rather lower than the exact value. + * 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, in the filtering in (a) 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 max3(bfqq->soft_rt_next_start, + 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); +} + +/** + * 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; + + /* + * Check whether the process is slow (see bfq_bfqq_is_slow). + */ + slow = bfq_bfqq_is_slow(bfqd, bfqq, compensate, reason, &delta); + + /* + * 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. And we do it, unless bfqq is in + * interactive weight raising. We do not do it in the + * latter subcase, for the following reason. bfqq may + * be conveying the I/O needed to load a soft + * real-time application. Such an application will + * actually exhibit a soft real-time I/O pattern after + * it finally starts doing its job. But, if + * soft_rt_next_start is computed here for an + * interactive bfqq, and bfqq had received a lot of + * service before remaining with no outstanding + * request (likely to happen on a fast device), then + * soft_rt_next_start would be assigned such a high + * value that, for a very long time, bfqq would be + * prevented from being possibly considered as soft + * real time. + * + * 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->wr_coeff != bfqd->bfq_wr_coeff) + bfqq->soft_rt_next_start = + bfq_bfqq_softrt_next_start(bfqd, bfqq); + else if (bfqq->dispatched > 0) { + /* + * 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)); + + /* + * bfqq expired, so no total service time needs to be computed + * any longer: reset state machine for measuring total service + * times. + */ + bfqd->rqs_injected = bfqd->wait_dispatch = false; + bfqd->waited_rq = NULL; + + /* + * Increase, decrease or leave budget unchanged according to + * reason. + */ + __bfq_bfqq_recalc_budget(bfqd, bfqq, reason); + if (__bfq_bfqq_expire(bfqd, bfqq, reason)) + /* bfqq is gone, no more actions on it */ + return; + + /* mark bfqq as waiting a request only if a bic still points to it */ + if (!bfq_bfqq_busy(bfqq) && + reason != BFQQE_BUDGET_TIMEOUT && + reason != BFQQE_BUDGET_EXHAUSTED) { + bfq_mark_bfqq_non_blocking_wait_rq(bfqq); + /* + * Not setting service to 0, because, if the next rq + * arrives in time, the queue will go on receiving + * service with this same budget (as if it never expired) + */ + } else + entity->service = 0; + + /* + * Reset the received-service counter for every parent entity. + * Differently from what happens with bfqq->entity.service, + * the resetting of this counter never needs to be postponed + * for parent entities. In fact, in case bfqq may have a + * chance to go on being served using the last, partially + * consumed budget, bfqq->entity.service needs to be kept, + * because if bfqq then actually goes on being served using + * the same budget, the last value of bfqq->entity.service is + * needed to properly decrement bfqq->entity.budget by the + * portion already consumed. In contrast, it is not necessary + * to keep entity->service for parent entities too, because + * the bubble up of the new value of bfqq->entity.budget will + * make sure that the budgets of parent entities are correct, + * even in case bfqq and thus parent entities go on receiving + * service with the same budget. + */ + entity = entity->parent; + for_each_entity(entity) + entity->service = 0; +} + +/* + * 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); +} + +static bool idling_boosts_thr_without_issues(struct bfq_data *bfqd, + struct bfq_queue *bfqq) +{ + bool rot_without_queueing = + !blk_queue_nonrot(bfqd->queue) && !bfqd->hw_tag, + bfqq_sequential_and_IO_bound, + idling_boosts_thr; + + /* No point in idling for bfqq if it won't get requests any longer */ + if (unlikely(!bfqq_process_refs(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 return value of this function 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 return value 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. + */ + return idling_boosts_thr && + bfqd->wr_busy_queues == 0; +} + +/* + * For a queue that becomes empty, device idling is allowed only if + * this function returns true for that queue. As a consequence, since + * device idling plays a critical role for both throughput boosting + * and service guarantees, the return value of this function plays a + * critical role 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. + * + * Most of the issues taken into account to get the return value of + * this function are not trivial. We discuss these issues in the two + * functions providing the main pieces of information needed by this + * function. + */ +static bool bfq_better_to_idle(struct bfq_queue *bfqq) +{ + struct bfq_data *bfqd = bfqq->bfqd; + bool idling_boosts_thr_with_no_issue, idling_needed_for_service_guar; + + /* No point in idling for bfqq if it won't get requests any longer */ + if (unlikely(!bfqq_process_refs(bfqq))) + return false; + + if (unlikely(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; + + idling_boosts_thr_with_no_issue = + idling_boosts_thr_without_issues(bfqd, bfqq); + + idling_needed_for_service_guar = + idling_needed_for_service_guarantees(bfqd, bfqq); + + /* + * We have now the two 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_with_no_issue || + idling_needed_for_service_guar; +} + +/* + * If the in-service queue is empty but the function bfq_better_to_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_better_to_idle for the reasons + * why performing device idling is the best choice to boost the throughput + * and preserve service guarantees when bfq_better_to_idle itself + * returns true. + */ +static bool bfq_bfqq_must_idle(struct bfq_queue *bfqq) +{ + return RB_EMPTY_ROOT(&bfqq->sort_list) && bfq_better_to_idle(bfqq); +} + +/* + * This function chooses the queue from which to pick the next extra + * I/O request to inject, if it finds a compatible queue. See the + * comments on bfq_update_inject_limit() for details on the injection + * mechanism, and for the definitions of the quantities mentioned + * below. + */ +static struct bfq_queue * +bfq_choose_bfqq_for_injection(struct bfq_data *bfqd) +{ + struct bfq_queue *bfqq, *in_serv_bfqq = bfqd->in_service_queue; + unsigned int limit = in_serv_bfqq->inject_limit; + /* + * If + * - bfqq is not weight-raised and therefore does not carry + * time-critical I/O, + * or + * - regardless of whether bfqq is weight-raised, bfqq has + * however a long think time, during which it can absorb the + * effect of an appropriate number of extra I/O requests + * from other queues (see bfq_update_inject_limit for + * details on the computation of this number); + * then injection can be performed without restrictions. + */ + bool in_serv_always_inject = in_serv_bfqq->wr_coeff == 1 || + !bfq_bfqq_has_short_ttime(in_serv_bfqq); + + /* + * If + * - the baseline total service time could not be sampled yet, + * so the inject limit happens to be still 0, and + * - a lot of time has elapsed since the plugging of I/O + * dispatching started, so drive speed is being wasted + * significantly; + * then temporarily raise inject limit to one request. + */ + if (limit == 0 && in_serv_bfqq->last_serv_time_ns == 0 && + bfq_bfqq_wait_request(in_serv_bfqq) && + time_is_before_eq_jiffies(bfqd->last_idling_start_jiffies + + bfqd->bfq_slice_idle) + ) + limit = 1; + + if (bfqd->rq_in_driver >= limit) + return NULL; + + /* + * Linear search of the source queue for injection; but, with + * a high probability, very few steps are needed to find a + * candidate queue, i.e., a queue with enough budget left for + * its next request. In fact: + * - BFQ dynamically updates the budget of every queue so as + * to accommodate the expected backlog of the queue; + * - if a queue gets all its requests dispatched as injected + * service, then the queue is removed from the active list + * (and re-added only if it gets new requests, but then it + * is assigned again enough budget for its new backlog). + */ + list_for_each_entry(bfqq, &bfqd->active_list, bfqq_list) + if (!RB_EMPTY_ROOT(&bfqq->sort_list) && + (in_serv_always_inject || bfqq->wr_coeff > 1) && + bfq_serv_to_charge(bfqq->next_rq, bfqq) <= + bfq_bfqq_budget_left(bfqq)) { + /* + * Allow for only one large in-flight request + * on non-rotational devices, for the + * following reason. On non-rotationl drives, + * large requests take much longer than + * smaller requests to be served. In addition, + * the drive prefers to serve large requests + * w.r.t. to small ones, if it can choose. So, + * having more than one large requests queued + * in the drive may easily make the next first + * request of the in-service queue wait for so + * long to break bfqq's service guarantees. On + * the bright side, large requests let the + * drive reach a very high throughput, even if + * there is only one in-flight large request + * at a time. + */ + if (blk_queue_nonrot(bfqd->queue) && + blk_rq_sectors(bfqq->next_rq) >= + BFQQ_SECT_THR_NONROT) + limit = min_t(unsigned int, 1, limit); + else + limit = in_serv_bfqq->inject_limit; + + if (bfqd->rq_in_driver < limit) { + bfqd->rqs_injected = true; + return bfqq; + } + } + + return NULL; +} + +/* + * 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"); + + /* + * Do not expire bfqq for budget timeout if bfqq may be about + * to enjoy device idling. The reason why, in this case, we + * prevent bfqq from expiring is the same as in the comments + * on the case where bfq_bfqq_must_idle() returns true, in + * bfq_completed_request(). + */ + if (bfq_may_expire_for_budg_timeout(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. + */ + bfq_clear_bfqq_wait_request(bfqq); + hrtimer_try_to_cancel(&bfqd->idle_slice_timer); + } + goto keep_queue; + } + } + + /* + * No requests pending. However, if the in-service queue is idling + * for a new request, or has requests waiting for a completion and + * may idle after their completion, then keep it anyway. + * + * Yet, inject service from other queues if it boosts + * throughput and is possible. + */ + if (bfq_bfqq_wait_request(bfqq) || + (bfqq->dispatched != 0 && bfq_better_to_idle(bfqq))) { + struct bfq_queue *async_bfqq = + bfqq->bic && bfqq->bic->bfqq[0] && + bfq_bfqq_busy(bfqq->bic->bfqq[0]) && + bfqq->bic->bfqq[0]->next_rq ? + bfqq->bic->bfqq[0] : NULL; + + /* + * The next three mutually-exclusive ifs decide + * whether to try injection, and choose the queue to + * pick an I/O request from. + * + * The first if checks whether the process associated + * with bfqq has also async I/O pending. If so, it + * injects such I/O unconditionally. Injecting async + * I/O from the same process can cause no harm to the + * process. On the contrary, it can only increase + * bandwidth and reduce latency for the process. + * + * The second if checks whether there happens to be a + * non-empty waker queue for bfqq, i.e., a queue whose + * I/O needs to be completed for bfqq to receive new + * I/O. This happens, e.g., if bfqq is associated with + * a process that does some sync. A sync generates + * extra blocking I/O, which must be completed before + * the process associated with bfqq can go on with its + * I/O. If the I/O of the waker queue is not served, + * then bfqq remains empty, and no I/O is dispatched, + * until the idle timeout fires for bfqq. This is + * likely to result in lower bandwidth and higher + * latencies for bfqq, and in a severe loss of total + * throughput. The best action to take is therefore to + * serve the waker queue as soon as possible. So do it + * (without relying on the third alternative below for + * eventually serving waker_bfqq's I/O; see the last + * paragraph for further details). This systematic + * injection of I/O from the waker queue does not + * cause any delay to bfqq's I/O. On the contrary, + * next bfqq's I/O is brought forward dramatically, + * for it is not blocked for milliseconds. + * + * The third if checks whether bfqq is a queue for + * which it is better to avoid injection. It is so if + * bfqq delivers more throughput when served without + * any further I/O from other queues in the middle, or + * if the service times of bfqq's I/O requests both + * count more than overall throughput, and may be + * easily increased by injection (this happens if bfqq + * has a short think time). If none of these + * conditions holds, then a candidate queue for + * injection is looked for through + * bfq_choose_bfqq_for_injection(). Note that the + * latter may return NULL (for example if the inject + * limit for bfqq is currently 0). + * + * NOTE: motivation for the second alternative + * + * Thanks to the way the inject limit is updated in + * bfq_update_has_short_ttime(), it is rather likely + * that, if I/O is being plugged for bfqq and the + * waker queue has pending I/O requests that are + * blocking bfqq's I/O, then the third alternative + * above lets the waker queue get served before the + * I/O-plugging timeout fires. So one may deem the + * second alternative superfluous. It is not, because + * the third alternative may be way less effective in + * case of a synchronization. For two main + * reasons. First, throughput may be low because the + * inject limit may be too low to guarantee the same + * amount of injected I/O, from the waker queue or + * other queues, that the second alternative + * guarantees (the second alternative unconditionally + * injects a pending I/O request of the waker queue + * for each bfq_dispatch_request()). Second, with the + * third alternative, the duration of the plugging, + * i.e., the time before bfqq finally receives new I/O, + * may not be minimized, because the waker queue may + * happen to be served only after other queues. + */ + if (async_bfqq && + icq_to_bic(async_bfqq->next_rq->elv.icq) == bfqq->bic && + bfq_serv_to_charge(async_bfqq->next_rq, async_bfqq) <= + bfq_bfqq_budget_left(async_bfqq)) + bfqq = bfqq->bic->bfqq[0]; + else if (bfq_bfqq_has_waker(bfqq) && + bfq_bfqq_busy(bfqq->waker_bfqq) && + bfqq->next_rq && + bfq_serv_to_charge(bfqq->waker_bfqq->next_rq, + bfqq->waker_bfqq) <= + bfq_bfqq_budget_left(bfqq->waker_bfqq) + ) + bfqq = bfqq->waker_bfqq; + else if (!idling_boosts_thr_without_issues(bfqd, bfqq) && + (bfqq->wr_coeff == 1 || bfqd->wr_busy_queues > 1 || + !bfq_bfqq_has_short_ttime(bfqq))) + bfqq = bfq_choose_bfqq_for_injection(bfqd); + else + bfqq = NULL; + + goto keep_queue; + } + + reason = BFQQE_NO_MORE_REQUESTS; +expire: + bfq_bfqq_expire(bfqd, bfqq, false, reason); +new_queue: + bfqq = bfq_set_in_service_queue(bfqd); + if (bfqq) { + bfq_log_bfqq(bfqd, bfqq, "select_queue: checking new queue"); + goto check_queue; + } +keep_queue: + if (bfqq) + bfq_log_bfqq(bfqd, bfqq, "select_queue: returned this queue"); + else + bfq_log(bfqd, "select_queue: no queue returned"); + + return bfqq; +} + +static void bfq_update_wr_data(struct bfq_data *bfqd, struct bfq_queue *bfqq) +{ + struct bfq_entity *entity = &bfqq->entity; + + if (bfqq->wr_coeff > 1) { /* queue is being weight-raised */ + bfq_log_bfqq(bfqd, bfqq, + "raising period dur %u/%u msec, old coeff %u, w %d(%d)", + jiffies_to_msecs(jiffies - bfqq->last_wr_start_finish), + jiffies_to_msecs(bfqq->wr_cur_max_time), + bfqq->wr_coeff, + bfqq->entity.weight, bfqq->entity.orig_weight); + + if (entity->prio_changed) + bfq_log_bfqq(bfqd, bfqq, "WARN: pending prio change"); + + /* + * If the queue was activated in a burst, or too much + * time has elapsed from the beginning of this + * weight-raising period, then end weight raising. + */ + if (bfq_bfqq_in_large_burst(bfqq)) + bfq_bfqq_end_wr(bfqq); + else if (time_is_before_jiffies(bfqq->last_wr_start_finish + + bfqq->wr_cur_max_time)) { + if (bfqq->wr_cur_max_time != bfqd->bfq_wr_rt_max_time || + time_is_before_jiffies(bfqq->wr_start_at_switch_to_srt + + bfq_wr_duration(bfqd))) + bfq_bfqq_end_wr(bfqq); + else { + switch_back_to_interactive_wr(bfqq, bfqd); + bfqq->entity.prio_changed = 1; + } + } + if (bfqq->wr_coeff > 1 && + bfqq->wr_cur_max_time != bfqd->bfq_wr_rt_max_time && + bfqq->service_from_wr > max_service_from_wr) { + /* see comments on max_service_from_wr */ + bfq_bfqq_end_wr(bfqq); + } + } + /* + * To improve latency (for this or other queues), immediately + * update weight both if it must be raised and if it must be + * lowered. Since, entity may be on some active tree here, and + * might have a pending change of its ioprio class, invoke + * next function with the last parameter unset (see the + * comments on the function). + */ + if ((entity->weight > entity->orig_weight) != (bfqq->wr_coeff > 1)) + __bfq_entity_update_weight_prio(bfq_entity_service_tree(entity), + entity, false); +} + +/* + * Dispatch next request from bfqq. + */ +static struct request *bfq_dispatch_rq_from_bfqq(struct bfq_data *bfqd, + struct bfq_queue *bfqq) +{ + struct request *rq = bfqq->next_rq; + unsigned long service_to_charge; + + service_to_charge = bfq_serv_to_charge(rq, bfqq); + + bfq_bfqq_served(bfqq, service_to_charge); + + if (bfqq == bfqd->in_service_queue && bfqd->wait_dispatch) { + bfqd->wait_dispatch = false; + bfqd->waited_rq = rq; + } + + bfq_dispatch_remove(bfqd->queue, rq); + + if (bfqq != bfqd->in_service_queue) + goto return_rq; + + /* + * If weight raising has to terminate for bfqq, then next + * function causes an immediate update of bfqq's weight, + * without waiting for next activation. As a consequence, on + * expiration, bfqq will be timestamped as if has never been + * weight-raised during this service slot, even if it has + * received part or even most of the service as a + * weight-raised queue. This inflates bfqq's timestamps, which + * is beneficial, as bfqq is then more willing to leave the + * device immediately to possible other weight-raised queues. + */ + bfq_update_wr_data(bfqd, bfqq); + + /* + * Expire bfqq, pretending that its budget expired, if bfqq + * belongs to CLASS_IDLE and other queues are waiting for + * service. + */ + if (!(bfq_tot_busy_queues(bfqd) > 1 && bfq_class_idle(bfqq))) + goto return_rq; + + bfq_bfqq_expire(bfqd, bfqq, false, BFQQE_BUDGET_EXHAUSTED); + +return_rq: + return rq; +} + +static bool bfq_has_work(struct blk_mq_hw_ctx *hctx) +{ + struct bfq_data *bfqd = hctx->queue->elevator->elevator_data; + + if (!atomic_read(&hctx->elevator_queued)) + return false; + + /* + * Avoiding lock: a race on bfqd->busy_queues should cause at + * most a call to dispatch for nothing + */ + return !list_empty_careful(&bfqd->dispatch) || + bfq_tot_busy_queues(bfqd) > 0; +} + +static struct request *__bfq_dispatch_request(struct blk_mq_hw_ctx *hctx) +{ + struct bfq_data *bfqd = hctx->queue->elevator->elevator_data; + struct request *rq = NULL; + struct bfq_queue *bfqq = NULL; + + if (!list_empty(&bfqd->dispatch)) { + rq = list_first_entry(&bfqd->dispatch, struct request, + queuelist); + list_del_init(&rq->queuelist); + + bfqq = RQ_BFQQ(rq); + + if (bfqq) { + /* + * Increment counters here, because this + * dispatch does not follow the standard + * dispatch flow (where counters are + * incremented) + */ + bfqq->dispatched++; + + goto inc_in_driver_start_rq; + } + + /* + * We exploit the bfq_finish_requeue_request hook to + * decrement rq_in_driver, but + * bfq_finish_requeue_request will not be invoked on + * this request. So, to avoid unbalance, just start + * this request, without incrementing rq_in_driver. As + * a negative consequence, rq_in_driver is deceptively + * lower than it should be while this request is in + * service. This may cause bfq_schedule_dispatch to be + * invoked uselessly. + * + * As for implementing an exact solution, the + * bfq_finish_requeue_request hook, if defined, is + * probably invoked also on this request. So, by + * exploiting this hook, we could 1) increment + * rq_in_driver here, and 2) decrement it in + * bfq_finish_requeue_request. Such a solution would + * let the value of the counter be always accurate, + * but it would entail using an extra interface + * function. This cost seems higher than the benefit, + * being the frequency of non-elevator-private + * requests very low. + */ + goto start_rq; + } + + bfq_log(bfqd, "dispatch requests: %d busy queues", + bfq_tot_busy_queues(bfqd)); + + if (bfq_tot_busy_queues(bfqd) == 0) + goto exit; + + /* + * Force device to serve one request at a time if + * strict_guarantees is true. Forcing this service scheme is + * currently the ONLY way to guarantee that the request + * service order enforced by the scheduler is respected by a + * queueing device. Otherwise the device is free even to make + * some unlucky request wait for as long as the device + * wishes. + * + * Of course, serving one request at a time may cause loss of + * throughput. + */ + if (bfqd->strict_guarantees && bfqd->rq_in_driver > 0) + goto exit; + + bfqq = bfq_select_queue(bfqd); + if (!bfqq) + goto exit; + + rq = bfq_dispatch_rq_from_bfqq(bfqd, bfqq); + + if (rq) { +inc_in_driver_start_rq: + bfqd->rq_in_driver++; +start_rq: + rq->rq_flags |= RQF_STARTED; + } +exit: + return rq; +} + +#ifdef CONFIG_BFQ_CGROUP_DEBUG +static void bfq_update_dispatch_stats(struct request_queue *q, + struct request *rq, + struct bfq_queue *in_serv_queue, + bool idle_timer_disabled) +{ + struct bfq_queue *bfqq = rq ? RQ_BFQQ(rq) : NULL; + + if (!idle_timer_disabled && !bfqq) + return; + + /* + * rq and bfqq are guaranteed to exist until this function + * ends, for the following reasons. First, rq can be + * dispatched to the device, and then can be completed and + * freed, only after this function ends. Second, rq cannot be + * merged (and thus freed because of a merge) any longer, + * because it has already started. Thus rq cannot be freed + * before this function ends, and, since rq has a reference to + * bfqq, the same guarantee holds for bfqq too. + * + * In addition, the following queue lock guarantees that + * bfqq_group(bfqq) exists as well. + */ + spin_lock_irq(&q->queue_lock); + if (idle_timer_disabled) + /* + * Since the idle timer has been disabled, + * in_serv_queue contained some request when + * __bfq_dispatch_request was invoked above, which + * implies that rq was picked exactly from + * in_serv_queue. Thus in_serv_queue == bfqq, and is + * therefore guaranteed to exist because of the above + * arguments. + */ + bfqg_stats_update_idle_time(bfqq_group(in_serv_queue)); + if (bfqq) { + struct bfq_group *bfqg = bfqq_group(bfqq); + + bfqg_stats_update_avg_queue_size(bfqg); + bfqg_stats_set_start_empty_time(bfqg); + bfqg_stats_update_io_remove(bfqg, rq->cmd_flags); + } + spin_unlock_irq(&q->queue_lock); +} +#else +static inline void bfq_update_dispatch_stats(struct request_queue *q, + struct request *rq, + struct bfq_queue *in_serv_queue, + bool idle_timer_disabled) {} +#endif /* CONFIG_BFQ_CGROUP_DEBUG */ + +static struct request *bfq_dispatch_request(struct blk_mq_hw_ctx *hctx) +{ + struct bfq_data *bfqd = hctx->queue->elevator->elevator_data; + struct request *rq; + struct bfq_queue *in_serv_queue; + bool waiting_rq, idle_timer_disabled = false; + + spin_lock_irq(&bfqd->lock); + + in_serv_queue = bfqd->in_service_queue; + waiting_rq = in_serv_queue && bfq_bfqq_wait_request(in_serv_queue); + + rq = __bfq_dispatch_request(hctx); + if (in_serv_queue == bfqd->in_service_queue) { + idle_timer_disabled = + waiting_rq && !bfq_bfqq_wait_request(in_serv_queue); + } + + spin_unlock_irq(&bfqd->lock); + bfq_update_dispatch_stats(hctx->queue, rq, + idle_timer_disabled ? in_serv_queue : NULL, + idle_timer_disabled); + + return rq; +} + +/* + * Task holds one reference to the queue, dropped when task exits. Each rq + * in-flight on this queue also holds a reference, dropped when rq is freed. + * + * Scheduler lock must be held here. Recall not to use bfqq after calling + * this function on it. + */ +void bfq_put_queue(struct bfq_queue *bfqq) +{ + struct bfq_queue *item; + struct hlist_node *n; + struct bfq_group *bfqg = bfqq_group(bfqq); + + if (bfqq->bfqd) + bfq_log_bfqq(bfqq->bfqd, bfqq, "put_queue: %p %d", + bfqq, bfqq->ref); + + bfqq->ref--; + if (bfqq->ref) + return; + + if (!hlist_unhashed(&bfqq->burst_list_node)) { + hlist_del_init(&bfqq->burst_list_node); + /* + * Decrement also burst size after the removal, if the + * process associated with bfqq is exiting, and thus + * does not contribute to the burst any longer. This + * decrement helps filter out false positives of large + * bursts, when some short-lived process (often due to + * the execution of commands by some service) happens + * to start and exit while a complex application is + * starting, and thus spawning several processes that + * do I/O (and that *must not* be treated as a large + * burst, see comments on bfq_handle_burst). + * + * In particular, the decrement is performed only if: + * 1) bfqq is not a merged queue, because, if it is, + * then this free of bfqq is not triggered by the exit + * of the process bfqq is associated with, but exactly + * by the fact that bfqq has just been merged. + * 2) burst_size is greater than 0, to handle + * unbalanced decrements. Unbalanced decrements may + * happen in te following case: bfqq is inserted into + * the current burst list--without incrementing + * bust_size--because of a split, but the current + * burst list is not the burst list bfqq belonged to + * (see comments on the case of a split in + * bfq_set_request). + */ + if (bfqq->bic && bfqq->bfqd->burst_size > 0) + bfqq->bfqd->burst_size--; + } + + /* + * bfqq does not exist any longer, so it cannot be woken by + * any other queue, and cannot wake any other queue. Then bfqq + * must be removed from the woken list of its possible waker + * queue, and all queues in the woken list of bfqq must stop + * having a waker queue. Strictly speaking, these updates + * should be performed when bfqq remains with no I/O source + * attached to it, which happens before bfqq gets freed. In + * particular, this happens when the last process associated + * with bfqq exits or gets associated with a different + * queue. However, both events lead to bfqq being freed soon, + * and dangling references would come out only after bfqq gets + * freed. So these updates are done here, as a simple and safe + * way to handle all cases. + */ + /* remove bfqq from woken list */ + if (!hlist_unhashed(&bfqq->woken_list_node)) + hlist_del_init(&bfqq->woken_list_node); + + /* reset waker for all queues in woken list */ + hlist_for_each_entry_safe(item, n, &bfqq->woken_list, + woken_list_node) { + item->waker_bfqq = NULL; + bfq_clear_bfqq_has_waker(item); + hlist_del_init(&item->woken_list_node); + } + + if (bfqq->bfqd && bfqq->bfqd->last_completed_rq_bfqq == bfqq) + bfqq->bfqd->last_completed_rq_bfqq = NULL; + + kmem_cache_free(bfq_pool, bfqq); + bfqg_and_blkg_put(bfqg); +} + +void bfq_put_cooperator(struct bfq_queue *bfqq) +{ + struct bfq_queue *__bfqq, *next; + + /* + * If this queue was scheduled to merge with another queue, be + * sure to drop the reference taken on that queue (and others in + * the merge chain). See bfq_setup_merge and bfq_merge_bfqqs. + */ + __bfqq = bfqq->new_bfqq; + while (__bfqq) { + if (__bfqq == bfqq) + break; + next = __bfqq->new_bfqq; + bfq_put_queue(__bfqq); + __bfqq = next; + } +} + +static void bfq_exit_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq) +{ + if (bfqq == bfqd->in_service_queue) { + __bfq_bfqq_expire(bfqd, bfqq, BFQQE_BUDGET_TIMEOUT); + bfq_schedule_dispatch(bfqd); + } + + bfq_log_bfqq(bfqd, bfqq, "exit_bfqq: %p, %d", bfqq, bfqq->ref); + + bfq_put_cooperator(bfqq); + + bfq_release_process_ref(bfqd, bfqq); +} + +static void bfq_exit_icq_bfqq(struct bfq_io_cq *bic, bool is_sync) +{ + struct bfq_queue *bfqq = bic_to_bfqq(bic, is_sync); + struct bfq_data *bfqd; + + if (bfqq) + bfqd = bfqq->bfqd; /* NULL if scheduler already exited */ + + if (bfqq && bfqd) { + unsigned long flags; + + spin_lock_irqsave(&bfqd->lock, flags); + bic_set_bfqq(bic, NULL, is_sync); + bfq_exit_bfqq(bfqd, bfqq); + spin_unlock_irqrestore(&bfqd->lock, flags); + } +} + +static void bfq_exit_icq(struct io_cq *icq) +{ + struct bfq_io_cq *bic = icq_to_bic(icq); + + bfq_exit_icq_bfqq(bic, true); + bfq_exit_icq_bfqq(bic, false); +} + +/* + * Update the entity prio values; note that the new values will not + * be used until the next (re)activation. + */ +static void +bfq_set_next_ioprio_data(struct bfq_queue *bfqq, struct bfq_io_cq *bic) +{ + struct task_struct *tsk = current; + int ioprio_class; + struct bfq_data *bfqd = bfqq->bfqd; + + if (!bfqd) + return; + + ioprio_class = IOPRIO_PRIO_CLASS(bic->ioprio); + switch (ioprio_class) { + default: + pr_err("bdi %s: bfq: bad prio class %d\n", + bdi_dev_name(bfqq->bfqd->queue->backing_dev_info), + ioprio_class); + fallthrough; + case IOPRIO_CLASS_NONE: + /* + * No prio set, inherit CPU scheduling settings. + */ + bfqq->new_ioprio = task_nice_ioprio(tsk); + bfqq->new_ioprio_class = task_nice_ioclass(tsk); + break; + case IOPRIO_CLASS_RT: + bfqq->new_ioprio = IOPRIO_PRIO_DATA(bic->ioprio); + bfqq->new_ioprio_class = IOPRIO_CLASS_RT; + break; + case IOPRIO_CLASS_BE: + bfqq->new_ioprio = IOPRIO_PRIO_DATA(bic->ioprio); + bfqq->new_ioprio_class = IOPRIO_CLASS_BE; + break; + case IOPRIO_CLASS_IDLE: + bfqq->new_ioprio_class = IOPRIO_CLASS_IDLE; + bfqq->new_ioprio = 7; + break; + } + + if (bfqq->new_ioprio >= IOPRIO_BE_NR) { + pr_crit("bfq_set_next_ioprio_data: new_ioprio %d\n", + bfqq->new_ioprio); + bfqq->new_ioprio = IOPRIO_BE_NR - 1; + } + + bfqq->entity.new_weight = bfq_ioprio_to_weight(bfqq->new_ioprio); + bfqq->entity.prio_changed = 1; +} + +static struct bfq_queue *bfq_get_queue(struct bfq_data *bfqd, + struct bio *bio, bool is_sync, + struct bfq_io_cq *bic); + +static void bfq_check_ioprio_change(struct bfq_io_cq *bic, struct bio *bio) +{ + struct bfq_data *bfqd = bic_to_bfqd(bic); + struct bfq_queue *bfqq; + int ioprio = bic->icq.ioc->ioprio; + + /* + * This condition may trigger on a newly created bic, be sure to + * drop the lock before returning. + */ + if (unlikely(!bfqd) || likely(bic->ioprio == ioprio)) + return; + + bic->ioprio = ioprio; + + bfqq = bic_to_bfqq(bic, false); + if (bfqq) { + struct bfq_queue *old_bfqq = bfqq; + + bfqq = bfq_get_queue(bfqd, bio, false, bic); + bic_set_bfqq(bic, bfqq, false); + bfq_release_process_ref(bfqd, old_bfqq); + } + + bfqq = bic_to_bfqq(bic, true); + if (bfqq) + bfq_set_next_ioprio_data(bfqq, bic); +} + +static void bfq_init_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq, + struct bfq_io_cq *bic, pid_t pid, int is_sync) +{ + RB_CLEAR_NODE(&bfqq->entity.rb_node); + INIT_LIST_HEAD(&bfqq->fifo); + INIT_HLIST_NODE(&bfqq->burst_list_node); + INIT_HLIST_NODE(&bfqq->woken_list_node); + INIT_HLIST_HEAD(&bfqq->woken_list); + + bfqq->ref = 0; + bfqq->bfqd = bfqd; + + if (bic) + bfq_set_next_ioprio_data(bfqq, bic); + + if (is_sync) { + /* + * No need to mark as has_short_ttime if in + * idle_class, because no device idling is performed + * for queues in idle class + */ + if (!bfq_class_idle(bfqq)) + /* tentatively mark as has_short_ttime */ + bfq_mark_bfqq_has_short_ttime(bfqq); + bfq_mark_bfqq_sync(bfqq); + bfq_mark_bfqq_just_created(bfqq); + } else + bfq_clear_bfqq_sync(bfqq); + + /* set end request to minus infinity from now */ + bfqq->ttime.last_end_request = ktime_get_ns() + 1; + + bfq_mark_bfqq_IO_bound(bfqq); + + bfqq->pid = pid; + + /* Tentative initial value to trade off between thr and lat */ + bfqq->max_budget = (2 * bfq_max_budget(bfqd)) / 3; + bfqq->budget_timeout = bfq_smallest_from_now(); + + bfqq->wr_coeff = 1; + bfqq->last_wr_start_finish = jiffies; + bfqq->wr_start_at_switch_to_srt = bfq_smallest_from_now(); + bfqq->split_time = bfq_smallest_from_now(); + + /* + * To not forget the possibly high bandwidth consumed by a + * process/queue in the recent past, + * bfq_bfqq_softrt_next_start() returns a value at least equal + * to the current value of bfqq->soft_rt_next_start (see + * comments on bfq_bfqq_softrt_next_start). Set + * soft_rt_next_start to now, to mean that bfqq has consumed + * no bandwidth so far. + */ + bfqq->soft_rt_next_start = jiffies; + + /* first request is almost certainly seeky */ + bfqq->seek_history = 1; +} + +static struct bfq_queue **bfq_async_queue_prio(struct bfq_data *bfqd, + struct bfq_group *bfqg, + int ioprio_class, int ioprio) +{ + switch (ioprio_class) { + case IOPRIO_CLASS_RT: + return &bfqg->async_bfqq[0][ioprio]; + case IOPRIO_CLASS_NONE: + ioprio = IOPRIO_NORM; + fallthrough; + case IOPRIO_CLASS_BE: + return &bfqg->async_bfqq[1][ioprio]; + case IOPRIO_CLASS_IDLE: + return &bfqg->async_idle_bfqq; + default: + return NULL; + } +} + +static struct bfq_queue *bfq_get_queue(struct bfq_data *bfqd, + struct bio *bio, bool is_sync, + struct bfq_io_cq *bic) +{ + const int ioprio = IOPRIO_PRIO_DATA(bic->ioprio); + const int ioprio_class = IOPRIO_PRIO_CLASS(bic->ioprio); + struct bfq_queue **async_bfqq = NULL; + struct bfq_queue *bfqq; + struct bfq_group *bfqg; + + bfqg = bfq_bio_bfqg(bfqd, bio); + if (!is_sync) { + async_bfqq = bfq_async_queue_prio(bfqd, bfqg, ioprio_class, + ioprio); + bfqq = *async_bfqq; + if (bfqq) + goto out; + } + + bfqq = kmem_cache_alloc_node(bfq_pool, + GFP_NOWAIT | __GFP_ZERO | __GFP_NOWARN, + bfqd->queue->node); + + if (bfqq) { + bfq_init_bfqq(bfqd, bfqq, bic, current->pid, + is_sync); + bfq_init_entity(&bfqq->entity, bfqg); + bfq_log_bfqq(bfqd, bfqq, "allocated"); + } else { + bfqq = &bfqd->oom_bfqq; + bfq_log_bfqq(bfqd, bfqq, "using oom bfqq"); + goto out; + } + + /* + * Pin the queue now that it's allocated, scheduler exit will + * prune it. + */ + if (async_bfqq) { + bfqq->ref++; /* + * Extra group reference, w.r.t. sync + * queue. This extra reference is removed + * only if bfqq->bfqg disappears, to + * guarantee that this queue is not freed + * until its group goes away. + */ + bfq_log_bfqq(bfqd, bfqq, "get_queue, bfqq not in async: %p, %d", + bfqq, bfqq->ref); + *async_bfqq = bfqq; + } + +out: + bfqq->ref++; /* get a process reference to this queue */ + bfq_log_bfqq(bfqd, bfqq, "get_queue, at end: %p, %d", bfqq, bfqq->ref); + return bfqq; +} + +static void bfq_update_io_thinktime(struct bfq_data *bfqd, + struct bfq_queue *bfqq) +{ + struct bfq_ttime *ttime = &bfqq->ttime; + u64 elapsed = ktime_get_ns() - bfqq->ttime.last_end_request; + + elapsed = min_t(u64, elapsed, 2ULL * bfqd->bfq_slice_idle); + + ttime->ttime_samples = (7*bfqq->ttime.ttime_samples + 256) / 8; + ttime->ttime_total = div_u64(7*ttime->ttime_total + 256*elapsed, 8); + ttime->ttime_mean = div64_ul(ttime->ttime_total + 128, + ttime->ttime_samples); +} + +static void +bfq_update_io_seektime(struct bfq_data *bfqd, struct bfq_queue *bfqq, + struct request *rq) +{ + bfqq->seek_history <<= 1; + bfqq->seek_history |= BFQ_RQ_SEEKY(bfqd, bfqq->last_request_pos, rq); + + if (bfqq->wr_coeff > 1 && + bfqq->wr_cur_max_time == bfqd->bfq_wr_rt_max_time && + BFQQ_TOTALLY_SEEKY(bfqq)) + bfq_bfqq_end_wr(bfqq); +} + +static void bfq_update_has_short_ttime(struct bfq_data *bfqd, + struct bfq_queue *bfqq, + struct bfq_io_cq *bic) +{ + bool has_short_ttime = true, state_changed; + + /* + * No need to update has_short_ttime if bfqq is async or in + * idle io prio class, or if bfq_slice_idle is zero, because + * no device idling is performed for bfqq in this case. + */ + if (!bfq_bfqq_sync(bfqq) || bfq_class_idle(bfqq) || + bfqd->bfq_slice_idle == 0) + return; + + /* Idle window just restored, statistics are meaningless. */ + if (time_is_after_eq_jiffies(bfqq->split_time + + bfqd->bfq_wr_min_idle_time)) + return; + + /* Think time is infinite if no process is linked to + * bfqq. Otherwise check average think time to + * decide whether to mark as has_short_ttime + */ + if (atomic_read(&bic->icq.ioc->active_ref) == 0 || + (bfq_sample_valid(bfqq->ttime.ttime_samples) && + bfqq->ttime.ttime_mean > bfqd->bfq_slice_idle)) + has_short_ttime = false; + + state_changed = has_short_ttime != bfq_bfqq_has_short_ttime(bfqq); + + if (has_short_ttime) + bfq_mark_bfqq_has_short_ttime(bfqq); + else + bfq_clear_bfqq_has_short_ttime(bfqq); + + /* + * Until the base value for the total service time gets + * finally computed for bfqq, the inject limit does depend on + * the think-time state (short|long). In particular, the limit + * is 0 or 1 if the think time is deemed, respectively, as + * short or long (details in the comments in + * bfq_update_inject_limit()). Accordingly, the next + * instructions reset the inject limit if the think-time state + * has changed and the above base value is still to be + * computed. + * + * However, the reset is performed only if more than 100 ms + * have elapsed since the last update of the inject limit, or + * (inclusive) if the change is from short to long think + * time. The reason for this waiting is as follows. + * + * bfqq may have a long think time because of a + * synchronization with some other queue, i.e., because the + * I/O of some other queue may need to be completed for bfqq + * to receive new I/O. Details in the comments on the choice + * of the queue for injection in bfq_select_queue(). + * + * As stressed in those comments, if such a synchronization is + * actually in place, then, without injection on bfqq, the + * blocking I/O cannot happen to served while bfqq is in + * service. As a consequence, if bfqq is granted + * I/O-dispatch-plugging, then bfqq remains empty, and no I/O + * is dispatched, until the idle timeout fires. This is likely + * to result in lower bandwidth and higher latencies for bfqq, + * and in a severe loss of total throughput. + * + * On the opposite end, a non-zero inject limit may allow the + * I/O that blocks bfqq to be executed soon, and therefore + * bfqq to receive new I/O soon. + * + * But, if the blocking gets actually eliminated, then the + * next think-time sample for bfqq may be very low. This in + * turn may cause bfqq's think time to be deemed + * short. Without the 100 ms barrier, this new state change + * would cause the body of the next if to be executed + * immediately. But this would set to 0 the inject + * limit. Without injection, the blocking I/O would cause the + * think time of bfqq to become long again, and therefore the + * inject limit to be raised again, and so on. The only effect + * of such a steady oscillation between the two think-time + * states would be to prevent effective injection on bfqq. + * + * In contrast, if the inject limit is not reset during such a + * long time interval as 100 ms, then the number of short + * think time samples can grow significantly before the reset + * is performed. As a consequence, the think time state can + * become stable before the reset. Therefore there will be no + * state change when the 100 ms elapse, and no reset of the + * inject limit. The inject limit remains steadily equal to 1 + * both during and after the 100 ms. So injection can be + * performed at all times, and throughput gets boosted. + * + * An inject limit equal to 1 is however in conflict, in + * general, with the fact that the think time of bfqq is + * short, because injection may be likely to delay bfqq's I/O + * (as explained in the comments in + * bfq_update_inject_limit()). But this does not happen in + * this special case, because bfqq's low think time is due to + * an effective handling of a synchronization, through + * injection. In this special case, bfqq's I/O does not get + * delayed by injection; on the contrary, bfqq's I/O is + * brought forward, because it is not blocked for + * milliseconds. + * + * In addition, serving the blocking I/O much sooner, and much + * more frequently than once per I/O-plugging timeout, makes + * it much quicker to detect a waker queue (the concept of + * waker queue is defined in the comments in + * bfq_add_request()). This makes it possible to start sooner + * to boost throughput more effectively, by injecting the I/O + * of the waker queue unconditionally on every + * bfq_dispatch_request(). + * + * One last, important benefit of not resetting the inject + * limit before 100 ms is that, during this time interval, the + * base value for the total service time is likely to get + * finally computed for bfqq, freeing the inject limit from + * its relation with the think time. + */ + if (state_changed && bfqq->last_serv_time_ns == 0 && + (time_is_before_eq_jiffies(bfqq->decrease_time_jif + + msecs_to_jiffies(100)) || + !has_short_ttime)) + bfq_reset_inject_limit(bfqd, bfqq); +} + +/* + * Called when a new fs request (rq) is added to bfqq. Check if there's + * something we should do about it. + */ +static void bfq_rq_enqueued(struct bfq_data *bfqd, struct bfq_queue *bfqq, + struct request *rq) +{ + if (rq->cmd_flags & REQ_META) + bfqq->meta_pending++; + + bfqq->last_request_pos = blk_rq_pos(rq) + blk_rq_sectors(rq); + + if (bfqq == bfqd->in_service_queue && bfq_bfqq_wait_request(bfqq)) { + bool small_req = bfqq->queued[rq_is_sync(rq)] == 1 && + blk_rq_sectors(rq) < 32; + bool budget_timeout = bfq_bfqq_budget_timeout(bfqq); + + /* + * There is just this request queued: if + * - the request is small, and + * - we are idling to boost throughput, and + * - the queue is not to be expired, + * then just exit. + * + * In this way, if the device is being idled to wait + * for a new request from the in-service queue, we + * avoid unplugging the device and committing the + * device to serve just a small request. In contrast + * we wait for the block layer to decide when to + * unplug the device: hopefully, new requests will be + * merged to this one quickly, then the device will be + * unplugged and larger requests will be dispatched. + */ + if (small_req && idling_boosts_thr_without_issues(bfqd, bfqq) && + !budget_timeout) + return; + + /* + * A large enough request arrived, or idling is being + * performed to preserve service guarantees, or + * finally the queue is to be expired: in all these + * cases disk idling is to be stopped, so clear + * wait_request flag and reset timer. + */ + bfq_clear_bfqq_wait_request(bfqq); + hrtimer_try_to_cancel(&bfqd->idle_slice_timer); + + /* + * The queue is not empty, because a new request just + * arrived. Hence we can safely expire the queue, in + * case of budget timeout, without risking that the + * timestamps of the queue are not updated correctly. + * See [1] for more details. + */ + if (budget_timeout) + bfq_bfqq_expire(bfqd, bfqq, false, + BFQQE_BUDGET_TIMEOUT); + } +} + +/* returns true if it causes the idle timer to be disabled */ +static bool __bfq_insert_request(struct bfq_data *bfqd, struct request *rq) +{ + struct bfq_queue *bfqq = RQ_BFQQ(rq), + *new_bfqq = bfq_setup_cooperator(bfqd, bfqq, rq, true); + bool waiting, idle_timer_disabled = false; + + if (new_bfqq) { + /* + * Release the request's reference to the old bfqq + * and make sure one is taken to the shared queue. + */ + new_bfqq->allocated++; + bfqq->allocated--; + new_bfqq->ref++; + /* + * If the bic associated with the process + * issuing this request still points to bfqq + * (and thus has not been already redirected + * to new_bfqq or even some other bfq_queue), + * then complete the merge and redirect it to + * new_bfqq. + */ + if (bic_to_bfqq(RQ_BIC(rq), 1) == bfqq) + bfq_merge_bfqqs(bfqd, RQ_BIC(rq), + bfqq, new_bfqq); + + bfq_clear_bfqq_just_created(bfqq); + /* + * rq is about to be enqueued into new_bfqq, + * release rq reference on bfqq + */ + bfq_put_queue(bfqq); + rq->elv.priv[1] = new_bfqq; + bfqq = new_bfqq; + } + + bfq_update_io_thinktime(bfqd, bfqq); + bfq_update_has_short_ttime(bfqd, bfqq, RQ_BIC(rq)); + bfq_update_io_seektime(bfqd, bfqq, rq); + + waiting = bfqq && bfq_bfqq_wait_request(bfqq); + bfq_add_request(rq); + idle_timer_disabled = waiting && !bfq_bfqq_wait_request(bfqq); + + rq->fifo_time = ktime_get_ns() + bfqd->bfq_fifo_expire[rq_is_sync(rq)]; + list_add_tail(&rq->queuelist, &bfqq->fifo); + + bfq_rq_enqueued(bfqd, bfqq, rq); + + return idle_timer_disabled; +} + +#ifdef CONFIG_BFQ_CGROUP_DEBUG +static void bfq_update_insert_stats(struct request_queue *q, + struct bfq_queue *bfqq, + bool idle_timer_disabled, + unsigned int cmd_flags) +{ + if (!bfqq) + return; + + /* + * bfqq still exists, because it can disappear only after + * either it is merged with another queue, or the process it + * is associated with exits. But both actions must be taken by + * the same process currently executing this flow of + * instructions. + * + * In addition, the following queue lock guarantees that + * bfqq_group(bfqq) exists as well. + */ + spin_lock_irq(&q->queue_lock); + bfqg_stats_update_io_add(bfqq_group(bfqq), bfqq, cmd_flags); + if (idle_timer_disabled) + bfqg_stats_update_idle_time(bfqq_group(bfqq)); + spin_unlock_irq(&q->queue_lock); +} +#else +static inline void bfq_update_insert_stats(struct request_queue *q, + struct bfq_queue *bfqq, + bool idle_timer_disabled, + unsigned int cmd_flags) {} +#endif /* CONFIG_BFQ_CGROUP_DEBUG */ + +static struct bfq_queue *bfq_init_rq(struct request *rq); + +static void bfq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq, + bool at_head) +{ + struct request_queue *q = hctx->queue; + struct bfq_data *bfqd = q->elevator->elevator_data; + struct bfq_queue *bfqq; + bool idle_timer_disabled = false; + unsigned int cmd_flags; + +#ifdef CONFIG_BFQ_GROUP_IOSCHED + if (!cgroup_subsys_on_dfl(io_cgrp_subsys) && rq->bio) + bfqg_stats_update_legacy_io(q, rq); +#endif + spin_lock_irq(&bfqd->lock); + bfqq = bfq_init_rq(rq); + if (blk_mq_sched_try_insert_merge(q, rq)) { + spin_unlock_irq(&bfqd->lock); + return; + } + + blk_mq_sched_request_inserted(rq); + + if (!bfqq || at_head || blk_rq_is_passthrough(rq)) { + if (at_head) + list_add(&rq->queuelist, &bfqd->dispatch); + else + list_add_tail(&rq->queuelist, &bfqd->dispatch); + } else { + idle_timer_disabled = __bfq_insert_request(bfqd, rq); + /* + * Update bfqq, because, if a queue merge has occurred + * in __bfq_insert_request, then rq has been + * redirected into a new queue. + */ + bfqq = RQ_BFQQ(rq); + + if (rq_mergeable(rq)) { + elv_rqhash_add(q, rq); + if (!q->last_merge) + q->last_merge = rq; + } + } + + /* + * Cache cmd_flags before releasing scheduler lock, because rq + * may disappear afterwards (for example, because of a request + * merge). + */ + cmd_flags = rq->cmd_flags; + + spin_unlock_irq(&bfqd->lock); + + bfq_update_insert_stats(q, bfqq, idle_timer_disabled, + cmd_flags); +} + +static void bfq_insert_requests(struct blk_mq_hw_ctx *hctx, + struct list_head *list, bool at_head) +{ + while (!list_empty(list)) { + struct request *rq; + + rq = list_first_entry(list, struct request, queuelist); + list_del_init(&rq->queuelist); + bfq_insert_request(hctx, rq, at_head); + atomic_inc(&hctx->elevator_queued); + } +} + +static void bfq_update_hw_tag(struct bfq_data *bfqd) +{ + struct bfq_queue *bfqq = bfqd->in_service_queue; + + bfqd->max_rq_in_driver = max_t(int, bfqd->max_rq_in_driver, + bfqd->rq_in_driver); + + if (bfqd->hw_tag == 1) + return; + + /* + * This sample is valid if the number of outstanding requests + * is large enough to allow a queueing behavior. Note that the + * sum is not exact, as it's not taking into account deactivated + * requests. + */ + if (bfqd->rq_in_driver + bfqd->queued <= BFQ_HW_QUEUE_THRESHOLD) + return; + + /* + * If active queue hasn't enough requests and can idle, bfq might not + * dispatch sufficient requests to hardware. Don't zero hw_tag in this + * case + */ + if (bfqq && bfq_bfqq_has_short_ttime(bfqq) && + bfqq->dispatched + bfqq->queued[0] + bfqq->queued[1] < + BFQ_HW_QUEUE_THRESHOLD && + bfqd->rq_in_driver < BFQ_HW_QUEUE_THRESHOLD) + return; + + if (bfqd->hw_tag_samples++ < BFQ_HW_QUEUE_SAMPLES) + return; + + bfqd->hw_tag = bfqd->max_rq_in_driver > BFQ_HW_QUEUE_THRESHOLD; + bfqd->max_rq_in_driver = 0; + bfqd->hw_tag_samples = 0; + + bfqd->nonrot_with_queueing = + blk_queue_nonrot(bfqd->queue) && bfqd->hw_tag; +} + +static void bfq_completed_request(struct bfq_queue *bfqq, struct bfq_data *bfqd) +{ + u64 now_ns; + u32 delta_us; + + bfq_update_hw_tag(bfqd); + + bfqd->rq_in_driver--; + bfqq->dispatched--; + + if (!bfqq->dispatched && !bfq_bfqq_busy(bfqq)) { + /* + * Set budget_timeout (which we overload 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_weights_tree_remove(bfqd, bfqq); + } + + now_ns = ktime_get_ns(); + + bfqq->ttime.last_end_request = now_ns; + + /* + * Using us instead of ns, to get a reasonable precision in + * computing rate in next check. + */ + delta_us = div_u64(now_ns - bfqd->last_completion, NSEC_PER_USEC); + + /* + * If the request took rather long to complete, and, according + * to the maximum request size recorded, this completion latency + * implies that the request was certainly served at a very low + * rate (less than 1M sectors/sec), then the whole observation + * interval that lasts up to this time instant cannot be a + * valid time interval for computing a new peak rate. Invoke + * bfq_update_rate_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 + * - reset to zero samples, which will trigger a proper + * re-initialization of the observation interval on next + * dispatch + */ + if (delta_us > BFQ_MIN_TT/NSEC_PER_USEC && + (bfqd->last_rq_max_size<<BFQ_RATE_SHIFT)/delta_us < + 1UL<<(BFQ_RATE_SHIFT - 10)) + bfq_update_rate_reset(bfqd, NULL); + bfqd->last_completion = now_ns; + bfqd->last_completed_rq_bfqq = bfqq; + + /* + * If we are waiting to discover whether the request pattern + * of the task associated with the queue is actually + * isochronous, and both requisites for this condition to hold + * are now satisfied, then compute soft_rt_next_start (see the + * comments on the function bfq_bfqq_softrt_next_start()). We + * do not compute soft_rt_next_start if bfqq is in interactive + * weight raising (see the comments in bfq_bfqq_expire() for + * an explanation). We schedule this delayed update when bfqq + * expires, if it still has in-flight requests. + */ + if (bfq_bfqq_softrt_update(bfqq) && bfqq->dispatched == 0 && + RB_EMPTY_ROOT(&bfqq->sort_list) && + bfqq->wr_coeff != bfqd->bfq_wr_coeff) + bfqq->soft_rt_next_start = + bfq_bfqq_softrt_next_start(bfqd, bfqq); + + /* + * If this is the in-service queue, check if it needs to be expired, + * or if we want to idle in case it has no pending requests. + */ + if (bfqd->in_service_queue == bfqq) { + if (bfq_bfqq_must_idle(bfqq)) { + if (bfqq->dispatched == 0) + bfq_arm_slice_timer(bfqd); + /* + * If we get here, we do not expire bfqq, even + * if bfqq was in budget timeout or had no + * more requests (as controlled in the next + * conditional instructions). The reason for + * not expiring bfqq is as follows. + * + * Here bfqq->dispatched > 0 holds, but + * bfq_bfqq_must_idle() returned true. This + * implies that, even if no request arrives + * for bfqq before bfqq->dispatched reaches 0, + * bfqq will, however, not be expired on the + * completion event that causes bfqq->dispatch + * to reach zero. In contrast, on this event, + * bfqq will start enjoying device idling + * (I/O-dispatch plugging). + * + * But, if we expired bfqq here, bfqq would + * not have the chance to enjoy device idling + * when bfqq->dispatched finally reaches + * zero. This would expose bfqq to violation + * of its reserved service guarantees. + */ + return; + } else if (bfq_may_expire_for_budg_timeout(bfqq)) + bfq_bfqq_expire(bfqd, bfqq, false, + BFQQE_BUDGET_TIMEOUT); + else if (RB_EMPTY_ROOT(&bfqq->sort_list) && + (bfqq->dispatched == 0 || + !bfq_better_to_idle(bfqq))) + bfq_bfqq_expire(bfqd, bfqq, false, + BFQQE_NO_MORE_REQUESTS); + } + + if (!bfqd->rq_in_driver) + bfq_schedule_dispatch(bfqd); +} + +static void bfq_finish_requeue_request_body(struct bfq_queue *bfqq) +{ + bfqq->allocated--; + + bfq_put_queue(bfqq); +} + +/* + * The processes associated with bfqq may happen to generate their + * cumulative I/O at a lower rate than the rate at which the device + * could serve the same I/O. This is rather probable, e.g., if only + * one process is associated with bfqq and the device is an SSD. It + * results in bfqq becoming often empty while in service. In this + * respect, if BFQ is allowed to switch to another queue when bfqq + * remains empty, then the device goes on being fed with I/O requests, + * and the throughput is not affected. In contrast, if BFQ is not + * allowed to switch to another queue---because bfqq is sync and + * I/O-dispatch needs to be plugged while bfqq is temporarily + * empty---then, during the service of bfqq, there will be frequent + * "service holes", i.e., time intervals during which bfqq gets empty + * and the device can only consume the I/O already queued in its + * hardware queues. During service holes, the device may even get to + * remaining idle. In the end, during the service of bfqq, the device + * is driven at a lower speed than the one it can reach with the kind + * of I/O flowing through bfqq. + * + * To counter this loss of throughput, BFQ implements a "request + * injection mechanism", which tries to fill the above service holes + * with I/O requests taken from other queues. The hard part in this + * mechanism is finding the right amount of I/O to inject, so as to + * both boost throughput and not break bfqq's bandwidth and latency + * guarantees. In this respect, the mechanism maintains a per-queue + * inject limit, computed as below. While bfqq is empty, the injection + * mechanism dispatches extra I/O requests only until the total number + * of I/O requests in flight---i.e., already dispatched but not yet + * completed---remains lower than this limit. + * + * A first definition comes in handy to introduce the algorithm by + * which the inject limit is computed. We define as first request for + * bfqq, an I/O request for bfqq that arrives while bfqq is in + * service, and causes bfqq to switch from empty to non-empty. The + * algorithm updates the limit as a function of the effect of + * injection on the service times of only the first requests of + * bfqq. The reason for this restriction is that these are the + * requests whose service time is affected most, because they are the + * first to arrive after injection possibly occurred. + * + * To evaluate the effect of injection, the algorithm measures the + * "total service time" of first requests. We define as total service + * time of an I/O request, the time that elapses since when the + * request is enqueued into bfqq, to when it is completed. This + * quantity allows the whole effect of injection to be measured. It is + * easy to see why. Suppose that some requests of other queues are + * actually injected while bfqq is empty, and that a new request R + * then arrives for bfqq. If the device does start to serve all or + * part of the injected requests during the service hole, then, + * because of this extra service, it may delay the next invocation of + * the dispatch hook of BFQ. Then, even after R gets eventually + * dispatched, the device may delay the actual service of R if it is + * still busy serving the extra requests, or if it decides to serve, + * before R, some extra request still present in its queues. As a + * conclusion, the cumulative extra delay caused by injection can be + * easily evaluated by just comparing the total service time of first + * requests with and without injection. + * + * The limit-update algorithm works as follows. On the arrival of a + * first request of bfqq, the algorithm measures the total time of the + * request only if one of the three cases below holds, and, for each + * case, it updates the limit as described below: + * + * (1) If there is no in-flight request. This gives a baseline for the + * total service time of the requests of bfqq. If the baseline has + * not been computed yet, then, after computing it, the limit is + * set to 1, to start boosting throughput, and to prepare the + * ground for the next case. If the baseline has already been + * computed, then it is updated, in case it results to be lower + * than the previous value. + * + * (2) If the limit is higher than 0 and there are in-flight + * requests. By comparing the total service time in this case with + * the above baseline, it is possible to know at which extent the + * current value of the limit is inflating the total service + * time. If the inflation is below a certain threshold, then bfqq + * is assumed to be suffering from no perceivable loss of its + * service guarantees, and the limit is even tentatively + * increased. If the inflation is above the threshold, then the + * limit is decreased. Due to the lack of any hysteresis, this + * logic makes the limit oscillate even in steady workload + * conditions. Yet we opted for it, because it is fast in reaching + * the best value for the limit, as a function of the current I/O + * workload. To reduce oscillations, this step is disabled for a + * short time interval after the limit happens to be decreased. + * + * (3) Periodically, after resetting the limit, to make sure that the + * limit eventually drops in case the workload changes. This is + * needed because, after the limit has gone safely up for a + * certain workload, it is impossible to guess whether the + * baseline total service time may have changed, without measuring + * it again without injection. A more effective version of this + * step might be to just sample the baseline, by interrupting + * injection only once, and then to reset/lower the limit only if + * the total service time with the current limit does happen to be + * too large. + * + * More details on each step are provided in the comments on the + * pieces of code that implement these steps: the branch handling the + * transition from empty to non empty in bfq_add_request(), the branch + * handling injection in bfq_select_queue(), and the function + * bfq_choose_bfqq_for_injection(). These comments also explain some + * exceptions, made by the injection mechanism in some special cases. + */ +static void bfq_update_inject_limit(struct bfq_data *bfqd, + struct bfq_queue *bfqq) +{ + u64 tot_time_ns = ktime_get_ns() - bfqd->last_empty_occupied_ns; + unsigned int old_limit = bfqq->inject_limit; + + if (bfqq->last_serv_time_ns > 0 && bfqd->rqs_injected) { + u64 threshold = (bfqq->last_serv_time_ns * 3)>>1; + + if (tot_time_ns >= threshold && old_limit > 0) { + bfqq->inject_limit--; + bfqq->decrease_time_jif = jiffies; + } else if (tot_time_ns < threshold && + old_limit <= bfqd->max_rq_in_driver) + bfqq->inject_limit++; + } + + /* + * Either we still have to compute the base value for the + * total service time, and there seem to be the right + * conditions to do it, or we can lower the last base value + * computed. + * + * NOTE: (bfqd->rq_in_driver == 1) means that there is no I/O + * request in flight, because this function is in the code + * path that handles the completion of a request of bfqq, and, + * in particular, this function is executed before + * bfqd->rq_in_driver is decremented in such a code path. + */ + if ((bfqq->last_serv_time_ns == 0 && bfqd->rq_in_driver == 1) || + tot_time_ns < bfqq->last_serv_time_ns) { + if (bfqq->last_serv_time_ns == 0) { + /* + * Now we certainly have a base value: make sure we + * start trying injection. + */ + bfqq->inject_limit = max_t(unsigned int, 1, old_limit); + } + bfqq->last_serv_time_ns = tot_time_ns; + } else if (!bfqd->rqs_injected && bfqd->rq_in_driver == 1) + /* + * No I/O injected and no request still in service in + * the drive: these are the exact conditions for + * computing the base value of the total service time + * for bfqq. So let's update this value, because it is + * rather variable. For example, it varies if the size + * or the spatial locality of the I/O requests in bfqq + * change. + */ + bfqq->last_serv_time_ns = tot_time_ns; + + + /* update complete, not waiting for any request completion any longer */ + bfqd->waited_rq = NULL; + bfqd->rqs_injected = false; +} + +/* + * Handle either a requeue or a finish for rq. The things to do are + * the same in both cases: all references to rq are to be dropped. In + * particular, rq is considered completed from the point of view of + * the scheduler. + */ +static void bfq_finish_requeue_request(struct request *rq) +{ + struct bfq_queue *bfqq = RQ_BFQQ(rq); + struct bfq_data *bfqd; + + /* + * rq either is not associated with any icq, or is an already + * requeued request that has not (yet) been re-inserted into + * a bfq_queue. + */ + if (!rq->elv.icq || !bfqq) + return; + + bfqd = bfqq->bfqd; + + if (rq->rq_flags & RQF_STARTED) + bfqg_stats_update_completion(bfqq_group(bfqq), + rq->start_time_ns, + rq->io_start_time_ns, + rq->cmd_flags); + + if (likely(rq->rq_flags & RQF_STARTED)) { + unsigned long flags; + + spin_lock_irqsave(&bfqd->lock, flags); + + if (rq == bfqd->waited_rq) + bfq_update_inject_limit(bfqd, bfqq); + + bfq_completed_request(bfqq, bfqd); + bfq_finish_requeue_request_body(bfqq); + atomic_dec(&rq->mq_hctx->elevator_queued); + + spin_unlock_irqrestore(&bfqd->lock, flags); + } else { + /* + * Request rq may be still/already in the scheduler, + * in which case we need to remove it (this should + * never happen in case of requeue). And we cannot + * defer such a check and removal, to avoid + * inconsistencies in the time interval from the end + * of this function to the start of the deferred work. + * This situation seems to occur only in process + * context, as a consequence of a merge. In the + * current version of the code, this implies that the + * lock is held. + */ + + if (!RB_EMPTY_NODE(&rq->rb_node)) { + bfq_remove_request(rq->q, rq); + bfqg_stats_update_io_remove(bfqq_group(bfqq), + rq->cmd_flags); + } + bfq_finish_requeue_request_body(bfqq); + } + + /* + * Reset private fields. In case of a requeue, this allows + * this function to correctly do nothing if it is spuriously + * invoked again on this same request (see the check at the + * beginning of the function). Probably, a better general + * design would be to prevent blk-mq from invoking the requeue + * or finish hooks of an elevator, for a request that is not + * referred by that elevator. + * + * Resetting the following fields would break the + * request-insertion logic if rq is re-inserted into a bfq + * internal queue, without a re-preparation. Here we assume + * that re-insertions of requeued requests, without + * re-preparation, can happen only for pass_through or at_head + * requests (which are not re-inserted into bfq internal + * queues). + */ + rq->elv.priv[0] = NULL; + rq->elv.priv[1] = NULL; +} + +/* + * Removes the association between the current task and bfqq, assuming + * that bic points to the bfq iocontext of the task. + * Returns NULL if a new bfqq should be allocated, or the old bfqq if this + * was the last process referring to that bfqq. + */ +static struct bfq_queue * +bfq_split_bfqq(struct bfq_io_cq *bic, struct bfq_queue *bfqq) +{ + bfq_log_bfqq(bfqq->bfqd, bfqq, "splitting queue"); + + if (bfqq_process_refs(bfqq) == 1) { + bfqq->pid = current->pid; + bfq_clear_bfqq_coop(bfqq); + bfq_clear_bfqq_split_coop(bfqq); + return bfqq; + } + + bic_set_bfqq(bic, NULL, true); + + bfq_put_cooperator(bfqq); + + bfq_release_process_ref(bfqq->bfqd, bfqq); + return NULL; +} + +static struct bfq_queue *bfq_get_bfqq_handle_split(struct bfq_data *bfqd, + struct bfq_io_cq *bic, + struct bio *bio, + bool split, bool is_sync, + bool *new_queue) +{ + struct bfq_queue *bfqq = bic_to_bfqq(bic, is_sync); + + if (likely(bfqq && bfqq != &bfqd->oom_bfqq)) + return bfqq; + + if (new_queue) + *new_queue = true; + + if (bfqq) + bfq_put_queue(bfqq); + bfqq = bfq_get_queue(bfqd, bio, is_sync, bic); + + bic_set_bfqq(bic, bfqq, is_sync); + if (split && is_sync) { + if ((bic->was_in_burst_list && bfqd->large_burst) || + bic->saved_in_large_burst) + bfq_mark_bfqq_in_large_burst(bfqq); + else { + bfq_clear_bfqq_in_large_burst(bfqq); + if (bic->was_in_burst_list) + /* + * If bfqq was in the current + * burst list before being + * merged, then we have to add + * it back. And we do not need + * to increase burst_size, as + * we did not decrement + * burst_size when we removed + * bfqq from the burst list as + * a consequence of a merge + * (see comments in + * bfq_put_queue). In this + * respect, it would be rather + * costly to know whether the + * current burst list is still + * the same burst list from + * which bfqq was removed on + * the merge. To avoid this + * cost, if bfqq was in a + * burst list, then we add + * bfqq to the current burst + * list without any further + * check. This can cause + * inappropriate insertions, + * but rarely enough to not + * harm the detection of large + * bursts significantly. + */ + hlist_add_head(&bfqq->burst_list_node, + &bfqd->burst_list); + } + bfqq->split_time = jiffies; + } + + return bfqq; +} + +/* + * Only reset private fields. The actual request preparation will be + * performed by bfq_init_rq, when rq is either inserted or merged. See + * comments on bfq_init_rq for the reason behind this delayed + * preparation. + */ +static void bfq_prepare_request(struct request *rq) +{ + /* + * Regardless of whether we have an icq attached, we have to + * clear the scheduler pointers, as they might point to + * previously allocated bic/bfqq structs. + */ + rq->elv.priv[0] = rq->elv.priv[1] = NULL; +} + +/* + * If needed, init rq, allocate bfq data structures associated with + * rq, and increment reference counters in the destination bfq_queue + * for rq. Return the destination bfq_queue for rq, or NULL is rq is + * not associated with any bfq_queue. + * + * This function is invoked by the functions that perform rq insertion + * or merging. One may have expected the above preparation operations + * to be performed in bfq_prepare_request, and not delayed to when rq + * is inserted or merged. The rationale behind this delayed + * preparation is that, after the prepare_request hook is invoked for + * rq, rq may still be transformed into a request with no icq, i.e., a + * request not associated with any queue. No bfq hook is invoked to + * signal this transformation. As a consequence, should these + * preparation operations be performed when the prepare_request hook + * is invoked, and should rq be transformed one moment later, bfq + * would end up in an inconsistent state, because it would have + * incremented some queue counters for an rq destined to + * transformation, without any chance to correctly lower these + * counters back. In contrast, no transformation can still happen for + * rq after rq has been inserted or merged. So, it is safe to execute + * these preparation operations when rq is finally inserted or merged. + */ +static struct bfq_queue *bfq_init_rq(struct request *rq) +{ + struct request_queue *q = rq->q; + struct bio *bio = rq->bio; + struct bfq_data *bfqd = q->elevator->elevator_data; + struct bfq_io_cq *bic; + const int is_sync = rq_is_sync(rq); + struct bfq_queue *bfqq; + bool new_queue = false; + bool bfqq_already_existing = false, split = false; + + if (unlikely(!rq->elv.icq)) + return NULL; + + /* + * Assuming that elv.priv[1] is set only if everything is set + * for this rq. This holds true, because this function is + * invoked only for insertion or merging, and, after such + * events, a request cannot be manipulated any longer before + * being removed from bfq. + */ + if (rq->elv.priv[1]) + return rq->elv.priv[1]; + + bic = icq_to_bic(rq->elv.icq); + + bfq_check_ioprio_change(bic, bio); + + bfq_bic_update_cgroup(bic, bio); + + bfqq = bfq_get_bfqq_handle_split(bfqd, bic, bio, false, is_sync, + &new_queue); + + if (likely(!new_queue)) { + /* If the queue was seeky for too long, break it apart. */ + if (bfq_bfqq_coop(bfqq) && bfq_bfqq_split_coop(bfqq)) { + bfq_log_bfqq(bfqd, bfqq, "breaking apart bfqq"); + + /* Update bic before losing reference to bfqq */ + if (bfq_bfqq_in_large_burst(bfqq)) + bic->saved_in_large_burst = true; + + bfqq = bfq_split_bfqq(bic, bfqq); + split = true; + + if (!bfqq) + bfqq = bfq_get_bfqq_handle_split(bfqd, bic, bio, + true, is_sync, + NULL); + else + bfqq_already_existing = true; + } + } + + bfqq->allocated++; + bfqq->ref++; + bfq_log_bfqq(bfqd, bfqq, "get_request %p: bfqq %p, %d", + rq, bfqq, bfqq->ref); + + rq->elv.priv[0] = bic; + rq->elv.priv[1] = bfqq; + + /* + * If a bfq_queue has only one process reference, it is owned + * by only this bic: we can then set bfqq->bic = bic. in + * addition, if the queue has also just been split, we have to + * resume its state. + */ + if (likely(bfqq != &bfqd->oom_bfqq) && bfqq_process_refs(bfqq) == 1) { + bfqq->bic = bic; + if (split) { + /* + * The queue has just been split from a shared + * queue: restore the idle window and the + * possible weight raising period. + */ + bfq_bfqq_resume_state(bfqq, bfqd, bic, + bfqq_already_existing); + } + } + + /* + * Consider bfqq as possibly belonging to a burst of newly + * created queues only if: + * 1) A burst is actually happening (bfqd->burst_size > 0) + * or + * 2) There is no other active queue. In fact, if, in + * contrast, there are active queues not belonging to the + * possible burst bfqq may belong to, then there is no gain + * in considering bfqq as belonging to a burst, and + * therefore in not weight-raising bfqq. See comments on + * bfq_handle_burst(). + * + * This filtering also helps eliminating false positives, + * occurring when bfqq does not belong to an actual large + * burst, but some background task (e.g., a service) happens + * to trigger the creation of new queues very close to when + * bfqq and its possible companion queues are created. See + * comments on bfq_handle_burst() for further details also on + * this issue. + */ + if (unlikely(bfq_bfqq_just_created(bfqq) && + (bfqd->burst_size > 0 || + bfq_tot_busy_queues(bfqd) == 0))) + bfq_handle_burst(bfqd, bfqq); + + return bfqq; +} + +static void +bfq_idle_slice_timer_body(struct bfq_data *bfqd, struct bfq_queue *bfqq) +{ + enum bfqq_expiration reason; + unsigned long flags; + + spin_lock_irqsave(&bfqd->lock, flags); + + /* + * Considering that bfqq may be in race, we should firstly check + * whether bfqq is in service before doing something on it. If + * the bfqq in race is not in service, it has already been expired + * through __bfq_bfqq_expire func and its wait_request flags has + * been cleared in __bfq_bfqd_reset_in_service func. + */ + if (bfqq != bfqd->in_service_queue) { + spin_unlock_irqrestore(&bfqd->lock, flags); + return; + } + + bfq_clear_bfqq_wait_request(bfqq); + + if (bfq_bfqq_budget_timeout(bfqq)) + /* + * Also here the queue can be safely expired + * for budget timeout without wasting + * guarantees + */ + reason = BFQQE_BUDGET_TIMEOUT; + else if (bfqq->queued[0] == 0 && bfqq->queued[1] == 0) + /* + * The queue may not be empty upon timer expiration, + * because we may not disable the timer when the + * first request of the in-service queue arrives + * during disk idling. + */ + reason = BFQQE_TOO_IDLE; + else + goto schedule_dispatch; + + bfq_bfqq_expire(bfqd, bfqq, true, reason); + +schedule_dispatch: + bfq_schedule_dispatch(bfqd); + spin_unlock_irqrestore(&bfqd->lock, flags); +} + +/* + * Handler of the expiration of the timer running if the in-service queue + * is idling inside its time slice. + */ +static enum hrtimer_restart bfq_idle_slice_timer(struct hrtimer *timer) +{ + struct bfq_data *bfqd = container_of(timer, struct bfq_data, + idle_slice_timer); + struct bfq_queue *bfqq = bfqd->in_service_queue; + + /* + * Theoretical race here: the in-service queue can be NULL or + * different from the queue that was idling if a new request + * arrives for the current queue and there is a full dispatch + * cycle that changes the in-service queue. This can hardly + * happen, but in the worst case we just expire a queue too + * early. + */ + if (bfqq) + bfq_idle_slice_timer_body(bfqd, bfqq); + + return HRTIMER_NORESTART; +} + +static void __bfq_put_async_bfqq(struct bfq_data *bfqd, + struct bfq_queue **bfqq_ptr) +{ + struct bfq_queue *bfqq = *bfqq_ptr; + + bfq_log(bfqd, "put_async_bfqq: %p", bfqq); + if (bfqq) { + bfq_bfqq_move(bfqd, bfqq, bfqd->root_group); + + bfq_log_bfqq(bfqd, bfqq, "put_async_bfqq: putting %p, %d", + bfqq, bfqq->ref); + bfq_put_queue(bfqq); + *bfqq_ptr = NULL; + } +} + +/* + * Release all the bfqg references to its async queues. If we are + * deallocating the group these queues may still contain requests, so + * we reparent them to the root cgroup (i.e., the only one that will + * exist for sure until all the requests on a device are gone). + */ +void bfq_put_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++) + __bfq_put_async_bfqq(bfqd, &bfqg->async_bfqq[i][j]); + + __bfq_put_async_bfqq(bfqd, &bfqg->async_idle_bfqq); +} + +/* + * See the comments on bfq_limit_depth for the purpose of + * the depths set in the function. Return minimum shallow depth we'll use. + */ +static unsigned int bfq_update_depths(struct bfq_data *bfqd, + struct sbitmap_queue *bt) +{ + unsigned int i, j, min_shallow = UINT_MAX; + + /* + * In-word depths if no bfq_queue is being weight-raised: + * leaving 25% of tags only for sync reads. + * + * In next formulas, right-shift the value + * (1U<<bt->sb.shift), instead of computing directly + * (1U<<(bt->sb.shift - something)), to be robust against + * any possible value of bt->sb.shift, without having to + * limit 'something'. + */ + /* no more than 50% of tags for async I/O */ + bfqd->word_depths[0][0] = max((1U << bt->sb.shift) >> 1, 1U); + /* + * no more than 75% of tags for sync writes (25% extra tags + * w.r.t. async I/O, to prevent async I/O from starving sync + * writes) + */ + bfqd->word_depths[0][1] = max(((1U << bt->sb.shift) * 3) >> 2, 1U); + + /* + * In-word depths in case some bfq_queue is being weight- + * raised: leaving ~63% of tags for sync reads. This is the + * highest percentage for which, in our tests, application + * start-up times didn't suffer from any regression due to tag + * shortage. + */ + /* no more than ~18% of tags for async I/O */ + bfqd->word_depths[1][0] = max(((1U << bt->sb.shift) * 3) >> 4, 1U); + /* no more than ~37% of tags for sync writes (~20% extra tags) */ + bfqd->word_depths[1][1] = max(((1U << bt->sb.shift) * 6) >> 4, 1U); + + for (i = 0; i < 2; i++) + for (j = 0; j < 2; j++) + min_shallow = min(min_shallow, bfqd->word_depths[i][j]); + + return min_shallow; +} + +static void bfq_depth_updated(struct blk_mq_hw_ctx *hctx) +{ + struct bfq_data *bfqd = hctx->queue->elevator->elevator_data; + struct blk_mq_tags *tags = hctx->sched_tags; + unsigned int min_shallow; + + min_shallow = bfq_update_depths(bfqd, tags->bitmap_tags); + sbitmap_queue_min_shallow_depth(tags->bitmap_tags, min_shallow); +} + +static int bfq_init_hctx(struct blk_mq_hw_ctx *hctx, unsigned int index) +{ + bfq_depth_updated(hctx); + return 0; +} + +static void bfq_exit_queue(struct elevator_queue *e) +{ + struct bfq_data *bfqd = e->elevator_data; + struct bfq_queue *bfqq, *n; + + hrtimer_cancel(&bfqd->idle_slice_timer); + + spin_lock_irq(&bfqd->lock); + list_for_each_entry_safe(bfqq, n, &bfqd->idle_list, bfqq_list) + bfq_deactivate_bfqq(bfqd, bfqq, false, false); + spin_unlock_irq(&bfqd->lock); + + hrtimer_cancel(&bfqd->idle_slice_timer); + + /* release oom-queue reference to root group */ + bfqg_and_blkg_put(bfqd->root_group); + +#ifdef CONFIG_BFQ_GROUP_IOSCHED + blkcg_deactivate_policy(bfqd->queue, &blkcg_policy_bfq); +#else + spin_lock_irq(&bfqd->lock); + bfq_put_async_queues(bfqd, bfqd->root_group); + kfree(bfqd->root_group); + spin_unlock_irq(&bfqd->lock); +#endif + + wbt_enable_default(bfqd->queue); + + kfree(bfqd); +} + +static void bfq_init_root_group(struct bfq_group *root_group, + struct bfq_data *bfqd) +{ + int i; + +#ifdef CONFIG_BFQ_GROUP_IOSCHED + root_group->entity.parent = NULL; + root_group->my_entity = NULL; + root_group->bfqd = bfqd; +#endif + root_group->rq_pos_tree = RB_ROOT; + for (i = 0; i < BFQ_IOPRIO_CLASSES; i++) + root_group->sched_data.service_tree[i] = BFQ_SERVICE_TREE_INIT; + root_group->sched_data.bfq_class_idle_last_service = jiffies; +} + +static int bfq_init_queue(struct request_queue *q, struct elevator_type *e) +{ + struct bfq_data *bfqd; + struct elevator_queue *eq; + + eq = elevator_alloc(q, e); + if (!eq) + return -ENOMEM; + + bfqd = kzalloc_node(sizeof(*bfqd), GFP_KERNEL, q->node); + if (!bfqd) { + kobject_put(&eq->kobj); + return -ENOMEM; + } + eq->elevator_data = bfqd; + + spin_lock_irq(&q->queue_lock); + q->elevator = eq; + spin_unlock_irq(&q->queue_lock); + + /* + * Our fallback bfqq if bfq_find_alloc_queue() runs into OOM issues. + * Grab a permanent reference to it, so that the normal code flow + * will not attempt to free it. + */ + bfq_init_bfqq(bfqd, &bfqd->oom_bfqq, NULL, 1, 0); + bfqd->oom_bfqq.ref++; + bfqd->oom_bfqq.new_ioprio = BFQ_DEFAULT_QUEUE_IOPRIO; + bfqd->oom_bfqq.new_ioprio_class = IOPRIO_CLASS_BE; + bfqd->oom_bfqq.entity.new_weight = + bfq_ioprio_to_weight(bfqd->oom_bfqq.new_ioprio); + + /* oom_bfqq does not participate to bursts */ + bfq_clear_bfqq_just_created(&bfqd->oom_bfqq); + + /* + * Trigger weight initialization, according to ioprio, at the + * oom_bfqq's first activation. The oom_bfqq's ioprio and ioprio + * class won't be changed any more. + */ + bfqd->oom_bfqq.entity.prio_changed = 1; + + bfqd->queue = q; + + INIT_LIST_HEAD(&bfqd->dispatch); + + hrtimer_init(&bfqd->idle_slice_timer, CLOCK_MONOTONIC, + HRTIMER_MODE_REL); + bfqd->idle_slice_timer.function = bfq_idle_slice_timer; + + bfqd->queue_weights_tree = RB_ROOT_CACHED; + bfqd->num_groups_with_pending_reqs = 0; + + INIT_LIST_HEAD(&bfqd->active_list); + INIT_LIST_HEAD(&bfqd->idle_list); + INIT_HLIST_HEAD(&bfqd->burst_list); + + bfqd->hw_tag = -1; + bfqd->nonrot_with_queueing = blk_queue_nonrot(bfqd->queue); + + bfqd->bfq_max_budget = bfq_default_max_budget; + + bfqd->bfq_fifo_expire[0] = bfq_fifo_expire[0]; + bfqd->bfq_fifo_expire[1] = bfq_fifo_expire[1]; + bfqd->bfq_back_max = bfq_back_max; + bfqd->bfq_back_penalty = bfq_back_penalty; + bfqd->bfq_slice_idle = bfq_slice_idle; + bfqd->bfq_timeout = bfq_timeout; + + bfqd->bfq_requests_within_timer = 120; + + bfqd->bfq_large_burst_thresh = 8; + bfqd->bfq_burst_interval = msecs_to_jiffies(180); + + bfqd->low_latency = true; + + /* + * Trade-off between responsiveness and fairness. + */ + bfqd->bfq_wr_coeff = 30; + bfqd->bfq_wr_rt_max_time = msecs_to_jiffies(300); + bfqd->bfq_wr_max_time = 0; + bfqd->bfq_wr_min_idle_time = msecs_to_jiffies(2000); + bfqd->bfq_wr_min_inter_arr_async = msecs_to_jiffies(500); + bfqd->bfq_wr_max_softrt_rate = 7000; /* + * Approximate rate required + * to playback or record a + * high-definition compressed + * video. + */ + bfqd->wr_busy_queues = 0; + + /* + * Begin by assuming, optimistically, that the device peak + * rate is equal to 2/3 of the highest reference rate. + */ + bfqd->rate_dur_prod = ref_rate[blk_queue_nonrot(bfqd->queue)] * + ref_wr_duration[blk_queue_nonrot(bfqd->queue)]; + bfqd->peak_rate = ref_rate[blk_queue_nonrot(bfqd->queue)] * 2 / 3; + + spin_lock_init(&bfqd->lock); + + /* + * The invocation of the next bfq_create_group_hierarchy + * function is the head of a chain of function calls + * (bfq_create_group_hierarchy->blkcg_activate_policy-> + * blk_mq_freeze_queue) that may lead to the invocation of the + * has_work hook function. For this reason, + * bfq_create_group_hierarchy is invoked only after all + * scheduler data has been initialized, apart from the fields + * that can be initialized only after invoking + * bfq_create_group_hierarchy. This, in particular, enables + * has_work to correctly return false. Of course, to avoid + * other inconsistencies, the blk-mq stack must then refrain + * from invoking further scheduler hooks before this init + * function is finished. + */ + bfqd->root_group = bfq_create_group_hierarchy(bfqd, q->node); + if (!bfqd->root_group) + goto out_free; + bfq_init_root_group(bfqd->root_group, bfqd); + bfq_init_entity(&bfqd->oom_bfqq.entity, bfqd->root_group); + + wbt_disable_default(q); + return 0; + +out_free: + kfree(bfqd); + kobject_put(&eq->kobj); + return -ENOMEM; +} + +static void bfq_slab_kill(void) +{ + kmem_cache_destroy(bfq_pool); +} + +static int __init bfq_slab_setup(void) +{ + bfq_pool = KMEM_CACHE(bfq_queue, 0); + if (!bfq_pool) + return -ENOMEM; + return 0; +} + +static ssize_t bfq_var_show(unsigned int var, char *page) +{ + return sprintf(page, "%u\n", var); +} + +static int bfq_var_store(unsigned long *var, const char *page) +{ + unsigned long new_val; + int ret = kstrtoul(page, 10, &new_val); + + if (ret) + return ret; + *var = new_val; + return 0; +} + +#define SHOW_FUNCTION(__FUNC, __VAR, __CONV) \ +static ssize_t __FUNC(struct elevator_queue *e, char *page) \ +{ \ + struct bfq_data *bfqd = e->elevator_data; \ + u64 __data = __VAR; \ + if (__CONV == 1) \ + __data = jiffies_to_msecs(__data); \ + else if (__CONV == 2) \ + __data = div_u64(__data, NSEC_PER_MSEC); \ + return bfq_var_show(__data, (page)); \ +} +SHOW_FUNCTION(bfq_fifo_expire_sync_show, bfqd->bfq_fifo_expire[1], 2); +SHOW_FUNCTION(bfq_fifo_expire_async_show, bfqd->bfq_fifo_expire[0], 2); +SHOW_FUNCTION(bfq_back_seek_max_show, bfqd->bfq_back_max, 0); +SHOW_FUNCTION(bfq_back_seek_penalty_show, bfqd->bfq_back_penalty, 0); +SHOW_FUNCTION(bfq_slice_idle_show, bfqd->bfq_slice_idle, 2); +SHOW_FUNCTION(bfq_max_budget_show, bfqd->bfq_user_max_budget, 0); +SHOW_FUNCTION(bfq_timeout_sync_show, bfqd->bfq_timeout, 1); +SHOW_FUNCTION(bfq_strict_guarantees_show, bfqd->strict_guarantees, 0); +SHOW_FUNCTION(bfq_low_latency_show, bfqd->low_latency, 0); +#undef SHOW_FUNCTION + +#define USEC_SHOW_FUNCTION(__FUNC, __VAR) \ +static ssize_t __FUNC(struct elevator_queue *e, char *page) \ +{ \ + struct bfq_data *bfqd = e->elevator_data; \ + u64 __data = __VAR; \ + __data = div_u64(__data, NSEC_PER_USEC); \ + return bfq_var_show(__data, (page)); \ +} +USEC_SHOW_FUNCTION(bfq_slice_idle_us_show, bfqd->bfq_slice_idle); +#undef USEC_SHOW_FUNCTION + +#define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV) \ +static ssize_t \ +__FUNC(struct elevator_queue *e, const char *page, size_t count) \ +{ \ + struct bfq_data *bfqd = e->elevator_data; \ + unsigned long __data, __min = (MIN), __max = (MAX); \ + int ret; \ + \ + ret = bfq_var_store(&__data, (page)); \ + if (ret) \ + return ret; \ + if (__data < __min) \ + __data = __min; \ + else if (__data > __max) \ + __data = __max; \ + if (__CONV == 1) \ + *(__PTR) = msecs_to_jiffies(__data); \ + else if (__CONV == 2) \ + *(__PTR) = (u64)__data * NSEC_PER_MSEC; \ + else \ + *(__PTR) = __data; \ + return count; \ +} +STORE_FUNCTION(bfq_fifo_expire_sync_store, &bfqd->bfq_fifo_expire[1], 1, + INT_MAX, 2); +STORE_FUNCTION(bfq_fifo_expire_async_store, &bfqd->bfq_fifo_expire[0], 1, + INT_MAX, 2); +STORE_FUNCTION(bfq_back_seek_max_store, &bfqd->bfq_back_max, 0, INT_MAX, 0); +STORE_FUNCTION(bfq_back_seek_penalty_store, &bfqd->bfq_back_penalty, 1, + INT_MAX, 0); +STORE_FUNCTION(bfq_slice_idle_store, &bfqd->bfq_slice_idle, 0, INT_MAX, 2); +#undef STORE_FUNCTION + +#define USEC_STORE_FUNCTION(__FUNC, __PTR, MIN, MAX) \ +static ssize_t __FUNC(struct elevator_queue *e, const char *page, size_t count)\ +{ \ + struct bfq_data *bfqd = e->elevator_data; \ + unsigned long __data, __min = (MIN), __max = (MAX); \ + int ret; \ + \ + ret = bfq_var_store(&__data, (page)); \ + if (ret) \ + return ret; \ + if (__data < __min) \ + __data = __min; \ + else if (__data > __max) \ + __data = __max; \ + *(__PTR) = (u64)__data * NSEC_PER_USEC; \ + return count; \ +} +USEC_STORE_FUNCTION(bfq_slice_idle_us_store, &bfqd->bfq_slice_idle, 0, + UINT_MAX); +#undef USEC_STORE_FUNCTION + +static ssize_t bfq_max_budget_store(struct elevator_queue *e, + const char *page, size_t count) +{ + struct bfq_data *bfqd = e->elevator_data; + unsigned long __data; + int ret; + + ret = bfq_var_store(&__data, (page)); + if (ret) + return ret; + + if (__data == 0) + bfqd->bfq_max_budget = bfq_calc_max_budget(bfqd); + else { + if (__data > INT_MAX) + __data = INT_MAX; + bfqd->bfq_max_budget = __data; + } + + bfqd->bfq_user_max_budget = __data; + + return count; +} + +/* + * Leaving this name to preserve name compatibility with cfq + * parameters, but this timeout is used for both sync and async. + */ +static ssize_t bfq_timeout_sync_store(struct elevator_queue *e, + const char *page, size_t count) +{ + struct bfq_data *bfqd = e->elevator_data; + unsigned long __data; + int ret; + + ret = bfq_var_store(&__data, (page)); + if (ret) + return ret; + + if (__data < 1) + __data = 1; + else if (__data > INT_MAX) + __data = INT_MAX; + + bfqd->bfq_timeout = msecs_to_jiffies(__data); + if (bfqd->bfq_user_max_budget == 0) + bfqd->bfq_max_budget = bfq_calc_max_budget(bfqd); + + return count; +} + +static ssize_t bfq_strict_guarantees_store(struct elevator_queue *e, + const char *page, size_t count) +{ + struct bfq_data *bfqd = e->elevator_data; + unsigned long __data; + int ret; + + ret = bfq_var_store(&__data, (page)); + if (ret) + return ret; + + if (__data > 1) + __data = 1; + if (!bfqd->strict_guarantees && __data == 1 + && bfqd->bfq_slice_idle < 8 * NSEC_PER_MSEC) + bfqd->bfq_slice_idle = 8 * NSEC_PER_MSEC; + + bfqd->strict_guarantees = __data; + + return count; +} + +static ssize_t bfq_low_latency_store(struct elevator_queue *e, + const char *page, size_t count) +{ + struct bfq_data *bfqd = e->elevator_data; + unsigned long __data; + int ret; + + ret = bfq_var_store(&__data, (page)); + if (ret) + return ret; + + if (__data > 1) + __data = 1; + if (__data == 0 && bfqd->low_latency != 0) + bfq_end_wr(bfqd); + bfqd->low_latency = __data; + + return count; +} + +#define BFQ_ATTR(name) \ + __ATTR(name, 0644, bfq_##name##_show, bfq_##name##_store) + +static struct elv_fs_entry bfq_attrs[] = { + BFQ_ATTR(fifo_expire_sync), + BFQ_ATTR(fifo_expire_async), + BFQ_ATTR(back_seek_max), + BFQ_ATTR(back_seek_penalty), + BFQ_ATTR(slice_idle), + BFQ_ATTR(slice_idle_us), + BFQ_ATTR(max_budget), + BFQ_ATTR(timeout_sync), + BFQ_ATTR(strict_guarantees), + BFQ_ATTR(low_latency), + __ATTR_NULL +}; + +static struct elevator_type iosched_bfq_mq = { + .ops = { + .limit_depth = bfq_limit_depth, + .prepare_request = bfq_prepare_request, + .requeue_request = bfq_finish_requeue_request, + .finish_request = bfq_finish_requeue_request, + .exit_icq = bfq_exit_icq, + .insert_requests = bfq_insert_requests, + .dispatch_request = bfq_dispatch_request, + .next_request = elv_rb_latter_request, + .former_request = elv_rb_former_request, + .allow_merge = bfq_allow_bio_merge, + .bio_merge = bfq_bio_merge, + .request_merge = bfq_request_merge, + .requests_merged = bfq_requests_merged, + .request_merged = bfq_request_merged, + .has_work = bfq_has_work, + .depth_updated = bfq_depth_updated, + .init_hctx = bfq_init_hctx, + .init_sched = bfq_init_queue, + .exit_sched = bfq_exit_queue, + }, + + .icq_size = sizeof(struct bfq_io_cq), + .icq_align = __alignof__(struct bfq_io_cq), + .elevator_attrs = bfq_attrs, + .elevator_name = "bfq", + .elevator_owner = THIS_MODULE, +}; +MODULE_ALIAS("bfq-iosched"); + +static int __init bfq_init(void) +{ + int ret; + +#ifdef CONFIG_BFQ_GROUP_IOSCHED + ret = blkcg_policy_register(&blkcg_policy_bfq); + if (ret) + return ret; +#endif + + ret = -ENOMEM; + if (bfq_slab_setup()) + goto err_pol_unreg; + + /* + * Times to load large popular applications for the typical + * systems installed on the reference devices (see the + * comments before the definition of the next + * array). Actually, we use slightly lower values, as the + * estimated peak rate tends to be smaller than the actual + * peak rate. The reason for this last fact is that estimates + * are computed over much shorter time intervals than the long + * intervals typically used for benchmarking. Why? First, to + * adapt more quickly to variations. Second, because an I/O + * scheduler cannot rely on a peak-rate-evaluation workload to + * be run for a long time. + */ + ref_wr_duration[0] = msecs_to_jiffies(7000); /* actually 8 sec */ + ref_wr_duration[1] = msecs_to_jiffies(2500); /* actually 3 sec */ + + ret = elv_register(&iosched_bfq_mq); + if (ret) + goto slab_kill; + + return 0; + +slab_kill: + bfq_slab_kill(); +err_pol_unreg: +#ifdef CONFIG_BFQ_GROUP_IOSCHED + blkcg_policy_unregister(&blkcg_policy_bfq); +#endif + return ret; +} + +static void __exit bfq_exit(void) +{ + elv_unregister(&iosched_bfq_mq); +#ifdef CONFIG_BFQ_GROUP_IOSCHED + blkcg_policy_unregister(&blkcg_policy_bfq); +#endif + bfq_slab_kill(); +} + +module_init(bfq_init); +module_exit(bfq_exit); + +MODULE_AUTHOR("Paolo Valente"); +MODULE_LICENSE("GPL"); +MODULE_DESCRIPTION("MQ Budget Fair Queueing I/O Scheduler"); |