diff options
Diffstat (limited to 'block/blk-iolatency.c')
| -rw-r--r-- | block/blk-iolatency.c | 1065 |
1 files changed, 1065 insertions, 0 deletions
diff --git a/block/blk-iolatency.c b/block/blk-iolatency.c new file mode 100644 index 000000000..571fa95aa --- /dev/null +++ b/block/blk-iolatency.c @@ -0,0 +1,1065 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Block rq-qos base io controller + * + * This works similar to wbt with a few exceptions + * + * - It's bio based, so the latency covers the whole block layer in addition to + * the actual io. + * - We will throttle all IO that comes in here if we need to. + * - We use the mean latency over the 100ms window. This is because writes can + * be particularly fast, which could give us a false sense of the impact of + * other workloads on our protected workload. + * - By default there's no throttling, we set the queue_depth to UINT_MAX so + * that we can have as many outstanding bio's as we're allowed to. Only at + * throttle time do we pay attention to the actual queue depth. + * + * The hierarchy works like the cpu controller does, we track the latency at + * every configured node, and each configured node has it's own independent + * queue depth. This means that we only care about our latency targets at the + * peer level. Some group at the bottom of the hierarchy isn't going to affect + * a group at the end of some other path if we're only configred at leaf level. + * + * Consider the following + * + * root blkg + * / \ + * fast (target=5ms) slow (target=10ms) + * / \ / \ + * a b normal(15ms) unloved + * + * "a" and "b" have no target, but their combined io under "fast" cannot exceed + * an average latency of 5ms. If it does then we will throttle the "slow" + * group. In the case of "normal", if it exceeds its 15ms target, we will + * throttle "unloved", but nobody else. + * + * In this example "fast", "slow", and "normal" will be the only groups actually + * accounting their io latencies. We have to walk up the heirarchy to the root + * on every submit and complete so we can do the appropriate stat recording and + * adjust the queue depth of ourselves if needed. + * + * There are 2 ways we throttle IO. + * + * 1) Queue depth throttling. As we throttle down we will adjust the maximum + * number of IO's we're allowed to have in flight. This starts at (u64)-1 down + * to 1. If the group is only ever submitting IO for itself then this is the + * only way we throttle. + * + * 2) Induced delay throttling. This is for the case that a group is generating + * IO that has to be issued by the root cg to avoid priority inversion. So think + * REQ_META or REQ_SWAP. If we are already at qd == 1 and we're getting a lot + * of work done for us on behalf of the root cg and are being asked to scale + * down more then we induce a latency at userspace return. We accumulate the + * total amount of time we need to be punished by doing + * + * total_time += min_lat_nsec - actual_io_completion + * + * and then at throttle time will do + * + * throttle_time = min(total_time, NSEC_PER_SEC) + * + * This induced delay will throttle back the activity that is generating the + * root cg issued io's, wethere that's some metadata intensive operation or the + * group is using so much memory that it is pushing us into swap. + * + * Copyright (C) 2018 Josef Bacik + */ +#include <linux/kernel.h> +#include <linux/blk_types.h> +#include <linux/backing-dev.h> +#include <linux/module.h> +#include <linux/timer.h> +#include <linux/memcontrol.h> +#include <linux/sched/loadavg.h> +#include <linux/sched/signal.h> +#include <trace/events/block.h> +#include <linux/blk-mq.h> +#include "blk-rq-qos.h" +#include "blk-stat.h" +#include "blk-cgroup.h" +#include "blk.h" + +#define DEFAULT_SCALE_COOKIE 1000000U + +static struct blkcg_policy blkcg_policy_iolatency; +struct iolatency_grp; + +struct blk_iolatency { + struct rq_qos rqos; + struct timer_list timer; + + /* + * ->enabled is the master enable switch gating the throttling logic and + * inflight tracking. The number of cgroups which have iolat enabled is + * tracked in ->enable_cnt, and ->enable is flipped on/off accordingly + * from ->enable_work with the request_queue frozen. For details, See + * blkiolatency_enable_work_fn(). + */ + bool enabled; + atomic_t enable_cnt; + struct work_struct enable_work; +}; + +static inline struct blk_iolatency *BLKIOLATENCY(struct rq_qos *rqos) +{ + return container_of(rqos, struct blk_iolatency, rqos); +} + +struct child_latency_info { + spinlock_t lock; + + /* Last time we adjusted the scale of everybody. */ + u64 last_scale_event; + + /* The latency that we missed. */ + u64 scale_lat; + + /* Total io's from all of our children for the last summation. */ + u64 nr_samples; + + /* The guy who actually changed the latency numbers. */ + struct iolatency_grp *scale_grp; + + /* Cookie to tell if we need to scale up or down. */ + atomic_t scale_cookie; +}; + +struct percentile_stats { + u64 total; + u64 missed; +}; + +struct latency_stat { + union { + struct percentile_stats ps; + struct blk_rq_stat rqs; + }; +}; + +struct iolatency_grp { + struct blkg_policy_data pd; + struct latency_stat __percpu *stats; + struct latency_stat cur_stat; + struct blk_iolatency *blkiolat; + struct rq_depth rq_depth; + struct rq_wait rq_wait; + atomic64_t window_start; + atomic_t scale_cookie; + u64 min_lat_nsec; + u64 cur_win_nsec; + + /* total running average of our io latency. */ + u64 lat_avg; + + /* Our current number of IO's for the last summation. */ + u64 nr_samples; + + bool ssd; + struct child_latency_info child_lat; +}; + +#define BLKIOLATENCY_MIN_WIN_SIZE (100 * NSEC_PER_MSEC) +#define BLKIOLATENCY_MAX_WIN_SIZE NSEC_PER_SEC +/* + * These are the constants used to fake the fixed-point moving average + * calculation just like load average. The call to calc_load() folds + * (FIXED_1 (2048) - exp_factor) * new_sample into lat_avg. The sampling + * window size is bucketed to try to approximately calculate average + * latency such that 1/exp (decay rate) is [1 min, 2.5 min) when windows + * elapse immediately. Note, windows only elapse with IO activity. Idle + * periods extend the most recent window. + */ +#define BLKIOLATENCY_NR_EXP_FACTORS 5 +#define BLKIOLATENCY_EXP_BUCKET_SIZE (BLKIOLATENCY_MAX_WIN_SIZE / \ + (BLKIOLATENCY_NR_EXP_FACTORS - 1)) +static const u64 iolatency_exp_factors[BLKIOLATENCY_NR_EXP_FACTORS] = { + 2045, // exp(1/600) - 600 samples + 2039, // exp(1/240) - 240 samples + 2031, // exp(1/120) - 120 samples + 2023, // exp(1/80) - 80 samples + 2014, // exp(1/60) - 60 samples +}; + +static inline struct iolatency_grp *pd_to_lat(struct blkg_policy_data *pd) +{ + return pd ? container_of(pd, struct iolatency_grp, pd) : NULL; +} + +static inline struct iolatency_grp *blkg_to_lat(struct blkcg_gq *blkg) +{ + return pd_to_lat(blkg_to_pd(blkg, &blkcg_policy_iolatency)); +} + +static inline struct blkcg_gq *lat_to_blkg(struct iolatency_grp *iolat) +{ + return pd_to_blkg(&iolat->pd); +} + +static inline void latency_stat_init(struct iolatency_grp *iolat, + struct latency_stat *stat) +{ + if (iolat->ssd) { + stat->ps.total = 0; + stat->ps.missed = 0; + } else + blk_rq_stat_init(&stat->rqs); +} + +static inline void latency_stat_sum(struct iolatency_grp *iolat, + struct latency_stat *sum, + struct latency_stat *stat) +{ + if (iolat->ssd) { + sum->ps.total += stat->ps.total; + sum->ps.missed += stat->ps.missed; + } else + blk_rq_stat_sum(&sum->rqs, &stat->rqs); +} + +static inline void latency_stat_record_time(struct iolatency_grp *iolat, + u64 req_time) +{ + struct latency_stat *stat = get_cpu_ptr(iolat->stats); + if (iolat->ssd) { + if (req_time >= iolat->min_lat_nsec) + stat->ps.missed++; + stat->ps.total++; + } else + blk_rq_stat_add(&stat->rqs, req_time); + put_cpu_ptr(stat); +} + +static inline bool latency_sum_ok(struct iolatency_grp *iolat, + struct latency_stat *stat) +{ + if (iolat->ssd) { + u64 thresh = div64_u64(stat->ps.total, 10); + thresh = max(thresh, 1ULL); + return stat->ps.missed < thresh; + } + return stat->rqs.mean <= iolat->min_lat_nsec; +} + +static inline u64 latency_stat_samples(struct iolatency_grp *iolat, + struct latency_stat *stat) +{ + if (iolat->ssd) + return stat->ps.total; + return stat->rqs.nr_samples; +} + +static inline void iolat_update_total_lat_avg(struct iolatency_grp *iolat, + struct latency_stat *stat) +{ + int exp_idx; + + if (iolat->ssd) + return; + + /* + * calc_load() takes in a number stored in fixed point representation. + * Because we are using this for IO time in ns, the values stored + * are significantly larger than the FIXED_1 denominator (2048). + * Therefore, rounding errors in the calculation are negligible and + * can be ignored. + */ + exp_idx = min_t(int, BLKIOLATENCY_NR_EXP_FACTORS - 1, + div64_u64(iolat->cur_win_nsec, + BLKIOLATENCY_EXP_BUCKET_SIZE)); + iolat->lat_avg = calc_load(iolat->lat_avg, + iolatency_exp_factors[exp_idx], + stat->rqs.mean); +} + +static void iolat_cleanup_cb(struct rq_wait *rqw, void *private_data) +{ + atomic_dec(&rqw->inflight); + wake_up(&rqw->wait); +} + +static bool iolat_acquire_inflight(struct rq_wait *rqw, void *private_data) +{ + struct iolatency_grp *iolat = private_data; + return rq_wait_inc_below(rqw, iolat->rq_depth.max_depth); +} + +static void __blkcg_iolatency_throttle(struct rq_qos *rqos, + struct iolatency_grp *iolat, + bool issue_as_root, + bool use_memdelay) +{ + struct rq_wait *rqw = &iolat->rq_wait; + unsigned use_delay = atomic_read(&lat_to_blkg(iolat)->use_delay); + + if (use_delay) + blkcg_schedule_throttle(rqos->q->disk, use_memdelay); + + /* + * To avoid priority inversions we want to just take a slot if we are + * issuing as root. If we're being killed off there's no point in + * delaying things, we may have been killed by OOM so throttling may + * make recovery take even longer, so just let the IO's through so the + * task can go away. + */ + if (issue_as_root || fatal_signal_pending(current)) { + atomic_inc(&rqw->inflight); + return; + } + + rq_qos_wait(rqw, iolat, iolat_acquire_inflight, iolat_cleanup_cb); +} + +#define SCALE_DOWN_FACTOR 2 +#define SCALE_UP_FACTOR 4 + +static inline unsigned long scale_amount(unsigned long qd, bool up) +{ + return max(up ? qd >> SCALE_UP_FACTOR : qd >> SCALE_DOWN_FACTOR, 1UL); +} + +/* + * We scale the qd down faster than we scale up, so we need to use this helper + * to adjust the scale_cookie accordingly so we don't prematurely get + * scale_cookie at DEFAULT_SCALE_COOKIE and unthrottle too much. + * + * Each group has their own local copy of the last scale cookie they saw, so if + * the global scale cookie goes up or down they know which way they need to go + * based on their last knowledge of it. + */ +static void scale_cookie_change(struct blk_iolatency *blkiolat, + struct child_latency_info *lat_info, + bool up) +{ + unsigned long qd = blkiolat->rqos.q->nr_requests; + unsigned long scale = scale_amount(qd, up); + unsigned long old = atomic_read(&lat_info->scale_cookie); + unsigned long max_scale = qd << 1; + unsigned long diff = 0; + + if (old < DEFAULT_SCALE_COOKIE) + diff = DEFAULT_SCALE_COOKIE - old; + + if (up) { + if (scale + old > DEFAULT_SCALE_COOKIE) + atomic_set(&lat_info->scale_cookie, + DEFAULT_SCALE_COOKIE); + else if (diff > qd) + atomic_inc(&lat_info->scale_cookie); + else + atomic_add(scale, &lat_info->scale_cookie); + } else { + /* + * We don't want to dig a hole so deep that it takes us hours to + * dig out of it. Just enough that we don't throttle/unthrottle + * with jagged workloads but can still unthrottle once pressure + * has sufficiently dissipated. + */ + if (diff > qd) { + if (diff < max_scale) + atomic_dec(&lat_info->scale_cookie); + } else { + atomic_sub(scale, &lat_info->scale_cookie); + } + } +} + +/* + * Change the queue depth of the iolatency_grp. We add/subtract 1/16th of the + * queue depth at a time so we don't get wild swings and hopefully dial in to + * fairer distribution of the overall queue depth. + */ +static void scale_change(struct iolatency_grp *iolat, bool up) +{ + unsigned long qd = iolat->blkiolat->rqos.q->nr_requests; + unsigned long scale = scale_amount(qd, up); + unsigned long old = iolat->rq_depth.max_depth; + + if (old > qd) + old = qd; + + if (up) { + if (old == 1 && blkcg_unuse_delay(lat_to_blkg(iolat))) + return; + + if (old < qd) { + old += scale; + old = min(old, qd); + iolat->rq_depth.max_depth = old; + wake_up_all(&iolat->rq_wait.wait); + } + } else { + old >>= 1; + iolat->rq_depth.max_depth = max(old, 1UL); + } +} + +/* Check our parent and see if the scale cookie has changed. */ +static void check_scale_change(struct iolatency_grp *iolat) +{ + struct iolatency_grp *parent; + struct child_latency_info *lat_info; + unsigned int cur_cookie; + unsigned int our_cookie = atomic_read(&iolat->scale_cookie); + u64 scale_lat; + int direction = 0; + + if (lat_to_blkg(iolat)->parent == NULL) + return; + + parent = blkg_to_lat(lat_to_blkg(iolat)->parent); + if (!parent) + return; + + lat_info = &parent->child_lat; + cur_cookie = atomic_read(&lat_info->scale_cookie); + scale_lat = READ_ONCE(lat_info->scale_lat); + + if (cur_cookie < our_cookie) + direction = -1; + else if (cur_cookie > our_cookie) + direction = 1; + else + return; + + if (!atomic_try_cmpxchg(&iolat->scale_cookie, &our_cookie, cur_cookie)) { + /* Somebody beat us to the punch, just bail. */ + return; + } + + if (direction < 0 && iolat->min_lat_nsec) { + u64 samples_thresh; + + if (!scale_lat || iolat->min_lat_nsec <= scale_lat) + return; + + /* + * Sometimes high priority groups are their own worst enemy, so + * instead of taking it out on some poor other group that did 5% + * or less of the IO's for the last summation just skip this + * scale down event. + */ + samples_thresh = lat_info->nr_samples * 5; + samples_thresh = max(1ULL, div64_u64(samples_thresh, 100)); + if (iolat->nr_samples <= samples_thresh) + return; + } + + /* We're as low as we can go. */ + if (iolat->rq_depth.max_depth == 1 && direction < 0) { + blkcg_use_delay(lat_to_blkg(iolat)); + return; + } + + /* We're back to the default cookie, unthrottle all the things. */ + if (cur_cookie == DEFAULT_SCALE_COOKIE) { + blkcg_clear_delay(lat_to_blkg(iolat)); + iolat->rq_depth.max_depth = UINT_MAX; + wake_up_all(&iolat->rq_wait.wait); + return; + } + + scale_change(iolat, direction > 0); +} + +static void blkcg_iolatency_throttle(struct rq_qos *rqos, struct bio *bio) +{ + struct blk_iolatency *blkiolat = BLKIOLATENCY(rqos); + struct blkcg_gq *blkg = bio->bi_blkg; + bool issue_as_root = bio_issue_as_root_blkg(bio); + + if (!blkiolat->enabled) + return; + + while (blkg && blkg->parent) { + struct iolatency_grp *iolat = blkg_to_lat(blkg); + if (!iolat) { + blkg = blkg->parent; + continue; + } + + check_scale_change(iolat); + __blkcg_iolatency_throttle(rqos, iolat, issue_as_root, + (bio->bi_opf & REQ_SWAP) == REQ_SWAP); + blkg = blkg->parent; + } + if (!timer_pending(&blkiolat->timer)) + mod_timer(&blkiolat->timer, jiffies + HZ); +} + +static void iolatency_record_time(struct iolatency_grp *iolat, + struct bio_issue *issue, u64 now, + bool issue_as_root) +{ + u64 start = bio_issue_time(issue); + u64 req_time; + + /* + * Have to do this so we are truncated to the correct time that our + * issue is truncated to. + */ + now = __bio_issue_time(now); + + if (now <= start) + return; + + req_time = now - start; + + /* + * We don't want to count issue_as_root bio's in the cgroups latency + * statistics as it could skew the numbers downwards. + */ + if (unlikely(issue_as_root && iolat->rq_depth.max_depth != UINT_MAX)) { + u64 sub = iolat->min_lat_nsec; + if (req_time < sub) + blkcg_add_delay(lat_to_blkg(iolat), now, sub - req_time); + return; + } + + latency_stat_record_time(iolat, req_time); +} + +#define BLKIOLATENCY_MIN_ADJUST_TIME (500 * NSEC_PER_MSEC) +#define BLKIOLATENCY_MIN_GOOD_SAMPLES 5 + +static void iolatency_check_latencies(struct iolatency_grp *iolat, u64 now) +{ + struct blkcg_gq *blkg = lat_to_blkg(iolat); + struct iolatency_grp *parent; + struct child_latency_info *lat_info; + struct latency_stat stat; + unsigned long flags; + int cpu; + + latency_stat_init(iolat, &stat); + preempt_disable(); + for_each_online_cpu(cpu) { + struct latency_stat *s; + s = per_cpu_ptr(iolat->stats, cpu); + latency_stat_sum(iolat, &stat, s); + latency_stat_init(iolat, s); + } + preempt_enable(); + + parent = blkg_to_lat(blkg->parent); + if (!parent) + return; + + lat_info = &parent->child_lat; + + iolat_update_total_lat_avg(iolat, &stat); + + /* Everything is ok and we don't need to adjust the scale. */ + if (latency_sum_ok(iolat, &stat) && + atomic_read(&lat_info->scale_cookie) == DEFAULT_SCALE_COOKIE) + return; + + /* Somebody beat us to the punch, just bail. */ + spin_lock_irqsave(&lat_info->lock, flags); + + latency_stat_sum(iolat, &iolat->cur_stat, &stat); + lat_info->nr_samples -= iolat->nr_samples; + lat_info->nr_samples += latency_stat_samples(iolat, &iolat->cur_stat); + iolat->nr_samples = latency_stat_samples(iolat, &iolat->cur_stat); + + if ((lat_info->last_scale_event >= now || + now - lat_info->last_scale_event < BLKIOLATENCY_MIN_ADJUST_TIME)) + goto out; + + if (latency_sum_ok(iolat, &iolat->cur_stat) && + latency_sum_ok(iolat, &stat)) { + if (latency_stat_samples(iolat, &iolat->cur_stat) < + BLKIOLATENCY_MIN_GOOD_SAMPLES) + goto out; + if (lat_info->scale_grp == iolat) { + lat_info->last_scale_event = now; + scale_cookie_change(iolat->blkiolat, lat_info, true); + } + } else if (lat_info->scale_lat == 0 || + lat_info->scale_lat >= iolat->min_lat_nsec) { + lat_info->last_scale_event = now; + if (!lat_info->scale_grp || + lat_info->scale_lat > iolat->min_lat_nsec) { + WRITE_ONCE(lat_info->scale_lat, iolat->min_lat_nsec); + lat_info->scale_grp = iolat; + } + scale_cookie_change(iolat->blkiolat, lat_info, false); + } + latency_stat_init(iolat, &iolat->cur_stat); +out: + spin_unlock_irqrestore(&lat_info->lock, flags); +} + +static void blkcg_iolatency_done_bio(struct rq_qos *rqos, struct bio *bio) +{ + struct blkcg_gq *blkg; + struct rq_wait *rqw; + struct iolatency_grp *iolat; + u64 window_start; + u64 now; + bool issue_as_root = bio_issue_as_root_blkg(bio); + int inflight = 0; + + blkg = bio->bi_blkg; + if (!blkg || !bio_flagged(bio, BIO_QOS_THROTTLED)) + return; + + iolat = blkg_to_lat(bio->bi_blkg); + if (!iolat) + return; + + if (!iolat->blkiolat->enabled) + return; + + now = ktime_to_ns(ktime_get()); + while (blkg && blkg->parent) { + iolat = blkg_to_lat(blkg); + if (!iolat) { + blkg = blkg->parent; + continue; + } + rqw = &iolat->rq_wait; + + inflight = atomic_dec_return(&rqw->inflight); + WARN_ON_ONCE(inflight < 0); + /* + * If bi_status is BLK_STS_AGAIN, the bio wasn't actually + * submitted, so do not account for it. + */ + if (iolat->min_lat_nsec && bio->bi_status != BLK_STS_AGAIN) { + iolatency_record_time(iolat, &bio->bi_issue, now, + issue_as_root); + window_start = atomic64_read(&iolat->window_start); + if (now > window_start && + (now - window_start) >= iolat->cur_win_nsec) { + if (atomic64_try_cmpxchg(&iolat->window_start, + &window_start, now)) + iolatency_check_latencies(iolat, now); + } + } + wake_up(&rqw->wait); + blkg = blkg->parent; + } +} + +static void blkcg_iolatency_exit(struct rq_qos *rqos) +{ + struct blk_iolatency *blkiolat = BLKIOLATENCY(rqos); + + del_timer_sync(&blkiolat->timer); + flush_work(&blkiolat->enable_work); + blkcg_deactivate_policy(rqos->q, &blkcg_policy_iolatency); + kfree(blkiolat); +} + +static struct rq_qos_ops blkcg_iolatency_ops = { + .throttle = blkcg_iolatency_throttle, + .done_bio = blkcg_iolatency_done_bio, + .exit = blkcg_iolatency_exit, +}; + +static void blkiolatency_timer_fn(struct timer_list *t) +{ + struct blk_iolatency *blkiolat = from_timer(blkiolat, t, timer); + struct blkcg_gq *blkg; + struct cgroup_subsys_state *pos_css; + u64 now = ktime_to_ns(ktime_get()); + + rcu_read_lock(); + blkg_for_each_descendant_pre(blkg, pos_css, + blkiolat->rqos.q->root_blkg) { + struct iolatency_grp *iolat; + struct child_latency_info *lat_info; + unsigned long flags; + u64 cookie; + + /* + * We could be exiting, don't access the pd unless we have a + * ref on the blkg. + */ + if (!blkg_tryget(blkg)) + continue; + + iolat = blkg_to_lat(blkg); + if (!iolat) + goto next; + + lat_info = &iolat->child_lat; + cookie = atomic_read(&lat_info->scale_cookie); + + if (cookie >= DEFAULT_SCALE_COOKIE) + goto next; + + spin_lock_irqsave(&lat_info->lock, flags); + if (lat_info->last_scale_event >= now) + goto next_lock; + + /* + * We scaled down but don't have a scale_grp, scale up and carry + * on. + */ + if (lat_info->scale_grp == NULL) { + scale_cookie_change(iolat->blkiolat, lat_info, true); + goto next_lock; + } + + /* + * It's been 5 seconds since our last scale event, clear the + * scale grp in case the group that needed the scale down isn't + * doing any IO currently. + */ + if (now - lat_info->last_scale_event >= + ((u64)NSEC_PER_SEC * 5)) + lat_info->scale_grp = NULL; +next_lock: + spin_unlock_irqrestore(&lat_info->lock, flags); +next: + blkg_put(blkg); + } + rcu_read_unlock(); +} + +/** + * blkiolatency_enable_work_fn - Enable or disable iolatency on the device + * @work: enable_work of the blk_iolatency of interest + * + * iolatency needs to keep track of the number of in-flight IOs per cgroup. This + * is relatively expensive as it involves walking up the hierarchy twice for + * every IO. Thus, if iolatency is not enabled in any cgroup for the device, we + * want to disable the in-flight tracking. + * + * We have to make sure that the counting is balanced - we don't want to leak + * the in-flight counts by disabling accounting in the completion path while IOs + * are in flight. This is achieved by ensuring that no IO is in flight by + * freezing the queue while flipping ->enabled. As this requires a sleepable + * context, ->enabled flipping is punted to this work function. + */ +static void blkiolatency_enable_work_fn(struct work_struct *work) +{ + struct blk_iolatency *blkiolat = container_of(work, struct blk_iolatency, + enable_work); + bool enabled; + + /* + * There can only be one instance of this function running for @blkiolat + * and it's guaranteed to be executed at least once after the latest + * ->enabled_cnt modification. Acting on the latest ->enable_cnt is + * sufficient. + * + * Also, we know @blkiolat is safe to access as ->enable_work is flushed + * in blkcg_iolatency_exit(). + */ + enabled = atomic_read(&blkiolat->enable_cnt); + if (enabled != blkiolat->enabled) { + blk_mq_freeze_queue(blkiolat->rqos.q); + blkiolat->enabled = enabled; + blk_mq_unfreeze_queue(blkiolat->rqos.q); + } +} + +int blk_iolatency_init(struct gendisk *disk) +{ + struct request_queue *q = disk->queue; + struct blk_iolatency *blkiolat; + struct rq_qos *rqos; + int ret; + + blkiolat = kzalloc(sizeof(*blkiolat), GFP_KERNEL); + if (!blkiolat) + return -ENOMEM; + + rqos = &blkiolat->rqos; + rqos->id = RQ_QOS_LATENCY; + rqos->ops = &blkcg_iolatency_ops; + rqos->q = q; + + ret = rq_qos_add(q, rqos); + if (ret) + goto err_free; + ret = blkcg_activate_policy(q, &blkcg_policy_iolatency); + if (ret) + goto err_qos_del; + + timer_setup(&blkiolat->timer, blkiolatency_timer_fn, 0); + INIT_WORK(&blkiolat->enable_work, blkiolatency_enable_work_fn); + + return 0; + +err_qos_del: + rq_qos_del(q, rqos); +err_free: + kfree(blkiolat); + return ret; +} + +static void iolatency_set_min_lat_nsec(struct blkcg_gq *blkg, u64 val) +{ + struct iolatency_grp *iolat = blkg_to_lat(blkg); + struct blk_iolatency *blkiolat = iolat->blkiolat; + u64 oldval = iolat->min_lat_nsec; + + iolat->min_lat_nsec = val; + iolat->cur_win_nsec = max_t(u64, val << 4, BLKIOLATENCY_MIN_WIN_SIZE); + iolat->cur_win_nsec = min_t(u64, iolat->cur_win_nsec, + BLKIOLATENCY_MAX_WIN_SIZE); + + if (!oldval && val) { + if (atomic_inc_return(&blkiolat->enable_cnt) == 1) + schedule_work(&blkiolat->enable_work); + } + if (oldval && !val) { + blkcg_clear_delay(blkg); + if (atomic_dec_return(&blkiolat->enable_cnt) == 0) + schedule_work(&blkiolat->enable_work); + } +} + +static void iolatency_clear_scaling(struct blkcg_gq *blkg) +{ + if (blkg->parent) { + struct iolatency_grp *iolat = blkg_to_lat(blkg->parent); + struct child_latency_info *lat_info; + if (!iolat) + return; + + lat_info = &iolat->child_lat; + spin_lock(&lat_info->lock); + atomic_set(&lat_info->scale_cookie, DEFAULT_SCALE_COOKIE); + lat_info->last_scale_event = 0; + lat_info->scale_grp = NULL; + lat_info->scale_lat = 0; + spin_unlock(&lat_info->lock); + } +} + +static ssize_t iolatency_set_limit(struct kernfs_open_file *of, char *buf, + size_t nbytes, loff_t off) +{ + struct blkcg *blkcg = css_to_blkcg(of_css(of)); + struct blkcg_gq *blkg; + struct blkg_conf_ctx ctx; + struct iolatency_grp *iolat; + char *p, *tok; + u64 lat_val = 0; + u64 oldval; + int ret; + + ret = blkg_conf_prep(blkcg, &blkcg_policy_iolatency, buf, &ctx); + if (ret) + return ret; + + iolat = blkg_to_lat(ctx.blkg); + p = ctx.body; + + ret = -EINVAL; + while ((tok = strsep(&p, " "))) { + char key[16]; + char val[21]; /* 18446744073709551616 */ + + if (sscanf(tok, "%15[^=]=%20s", key, val) != 2) + goto out; + + if (!strcmp(key, "target")) { + u64 v; + + if (!strcmp(val, "max")) + lat_val = 0; + else if (sscanf(val, "%llu", &v) == 1) + lat_val = v * NSEC_PER_USEC; + else + goto out; + } else { + goto out; + } + } + + /* Walk up the tree to see if our new val is lower than it should be. */ + blkg = ctx.blkg; + oldval = iolat->min_lat_nsec; + + iolatency_set_min_lat_nsec(blkg, lat_val); + if (oldval != iolat->min_lat_nsec) + iolatency_clear_scaling(blkg); + ret = 0; +out: + blkg_conf_finish(&ctx); + return ret ?: nbytes; +} + +static u64 iolatency_prfill_limit(struct seq_file *sf, + struct blkg_policy_data *pd, int off) +{ + struct iolatency_grp *iolat = pd_to_lat(pd); + const char *dname = blkg_dev_name(pd->blkg); + + if (!dname || !iolat->min_lat_nsec) + return 0; + seq_printf(sf, "%s target=%llu\n", + dname, div_u64(iolat->min_lat_nsec, NSEC_PER_USEC)); + return 0; +} + +static int iolatency_print_limit(struct seq_file *sf, void *v) +{ + blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)), + iolatency_prfill_limit, + &blkcg_policy_iolatency, seq_cft(sf)->private, false); + return 0; +} + +static void iolatency_ssd_stat(struct iolatency_grp *iolat, struct seq_file *s) +{ + struct latency_stat stat; + int cpu; + + latency_stat_init(iolat, &stat); + preempt_disable(); + for_each_online_cpu(cpu) { + struct latency_stat *s; + s = per_cpu_ptr(iolat->stats, cpu); + latency_stat_sum(iolat, &stat, s); + } + preempt_enable(); + + if (iolat->rq_depth.max_depth == UINT_MAX) + seq_printf(s, " missed=%llu total=%llu depth=max", + (unsigned long long)stat.ps.missed, + (unsigned long long)stat.ps.total); + else + seq_printf(s, " missed=%llu total=%llu depth=%u", + (unsigned long long)stat.ps.missed, + (unsigned long long)stat.ps.total, + iolat->rq_depth.max_depth); +} + +static void iolatency_pd_stat(struct blkg_policy_data *pd, struct seq_file *s) +{ + struct iolatency_grp *iolat = pd_to_lat(pd); + unsigned long long avg_lat; + unsigned long long cur_win; + + if (!blkcg_debug_stats) + return; + + if (iolat->ssd) + return iolatency_ssd_stat(iolat, s); + + avg_lat = div64_u64(iolat->lat_avg, NSEC_PER_USEC); + cur_win = div64_u64(iolat->cur_win_nsec, NSEC_PER_MSEC); + if (iolat->rq_depth.max_depth == UINT_MAX) + seq_printf(s, " depth=max avg_lat=%llu win=%llu", + avg_lat, cur_win); + else + seq_printf(s, " depth=%u avg_lat=%llu win=%llu", + iolat->rq_depth.max_depth, avg_lat, cur_win); +} + +static struct blkg_policy_data *iolatency_pd_alloc(gfp_t gfp, + struct request_queue *q, + struct blkcg *blkcg) +{ + struct iolatency_grp *iolat; + + iolat = kzalloc_node(sizeof(*iolat), gfp, q->node); + if (!iolat) + return NULL; + iolat->stats = __alloc_percpu_gfp(sizeof(struct latency_stat), + __alignof__(struct latency_stat), gfp); + if (!iolat->stats) { + kfree(iolat); + return NULL; + } + return &iolat->pd; +} + +static void iolatency_pd_init(struct blkg_policy_data *pd) +{ + struct iolatency_grp *iolat = pd_to_lat(pd); + struct blkcg_gq *blkg = lat_to_blkg(iolat); + struct rq_qos *rqos = blkcg_rq_qos(blkg->q); + struct blk_iolatency *blkiolat = BLKIOLATENCY(rqos); + u64 now = ktime_to_ns(ktime_get()); + int cpu; + + if (blk_queue_nonrot(blkg->q)) + iolat->ssd = true; + else + iolat->ssd = false; + + for_each_possible_cpu(cpu) { + struct latency_stat *stat; + stat = per_cpu_ptr(iolat->stats, cpu); + latency_stat_init(iolat, stat); + } + + latency_stat_init(iolat, &iolat->cur_stat); + rq_wait_init(&iolat->rq_wait); + spin_lock_init(&iolat->child_lat.lock); + iolat->rq_depth.queue_depth = blkg->q->nr_requests; + iolat->rq_depth.max_depth = UINT_MAX; + iolat->rq_depth.default_depth = iolat->rq_depth.queue_depth; + iolat->blkiolat = blkiolat; + iolat->cur_win_nsec = 100 * NSEC_PER_MSEC; + atomic64_set(&iolat->window_start, now); + + /* + * We init things in list order, so the pd for the parent may not be + * init'ed yet for whatever reason. + */ + if (blkg->parent && blkg_to_pd(blkg->parent, &blkcg_policy_iolatency)) { + struct iolatency_grp *parent = blkg_to_lat(blkg->parent); + atomic_set(&iolat->scale_cookie, + atomic_read(&parent->child_lat.scale_cookie)); + } else { + atomic_set(&iolat->scale_cookie, DEFAULT_SCALE_COOKIE); + } + + atomic_set(&iolat->child_lat.scale_cookie, DEFAULT_SCALE_COOKIE); +} + +static void iolatency_pd_offline(struct blkg_policy_data *pd) +{ + struct iolatency_grp *iolat = pd_to_lat(pd); + struct blkcg_gq *blkg = lat_to_blkg(iolat); + + iolatency_set_min_lat_nsec(blkg, 0); + iolatency_clear_scaling(blkg); +} + +static void iolatency_pd_free(struct blkg_policy_data *pd) +{ + struct iolatency_grp *iolat = pd_to_lat(pd); + free_percpu(iolat->stats); + kfree(iolat); +} + +static struct cftype iolatency_files[] = { + { + .name = "latency", + .flags = CFTYPE_NOT_ON_ROOT, + .seq_show = iolatency_print_limit, + .write = iolatency_set_limit, + }, + {} +}; + +static struct blkcg_policy blkcg_policy_iolatency = { + .dfl_cftypes = iolatency_files, + .pd_alloc_fn = iolatency_pd_alloc, + .pd_init_fn = iolatency_pd_init, + .pd_offline_fn = iolatency_pd_offline, + .pd_free_fn = iolatency_pd_free, + .pd_stat_fn = iolatency_pd_stat, +}; + +static int __init iolatency_init(void) +{ + return blkcg_policy_register(&blkcg_policy_iolatency); +} + +static void __exit iolatency_exit(void) +{ + blkcg_policy_unregister(&blkcg_policy_iolatency); +} + +module_init(iolatency_init); +module_exit(iolatency_exit); 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