// SPDX-License-Identifier: GPL-2.0 /* * buffered writeback throttling. loosely based on CoDel. We can't drop * packets for IO scheduling, so the logic is something like this: * * - Monitor latencies in a defined window of time. * - If the minimum latency in the above window exceeds some target, increment * scaling step and scale down queue depth by a factor of 2x. The monitoring * window is then shrunk to 100 / sqrt(scaling step + 1). * - For any window where we don't have solid data on what the latencies * look like, retain status quo. * - If latencies look good, decrement scaling step. * - If we're only doing writes, allow the scaling step to go negative. This * will temporarily boost write performance, snapping back to a stable * scaling step of 0 if reads show up or the heavy writers finish. Unlike * positive scaling steps where we shrink the monitoring window, a negative * scaling step retains the default step==0 window size. * * Copyright (C) 2016 Jens Axboe * */ #include <linux/kernel.h> #include <linux/blk_types.h> #include <linux/slab.h> #include <linux/backing-dev.h> #include <linux/swap.h> #include "blk-wbt.h" #include "blk-rq-qos.h" #define CREATE_TRACE_POINTS #include <trace/events/wbt.h> static inline void wbt_clear_state(struct request *rq) { rq->wbt_flags = 0; } static inline enum wbt_flags wbt_flags(struct request *rq) { return rq->wbt_flags; } static inline bool wbt_is_tracked(struct request *rq) { return rq->wbt_flags & WBT_TRACKED; } static inline bool wbt_is_read(struct request *rq) { return rq->wbt_flags & WBT_READ; } enum { /* * Default setting, we'll scale up (to 75% of QD max) or down (min 1) * from here depending on device stats */ RWB_DEF_DEPTH = 16, /* * 100msec window */ RWB_WINDOW_NSEC = 100 * 1000 * 1000ULL, /* * Disregard stats, if we don't meet this minimum */ RWB_MIN_WRITE_SAMPLES = 3, /* * If we have this number of consecutive windows with not enough * information to scale up or down, scale up. */ RWB_UNKNOWN_BUMP = 5, }; static inline bool rwb_enabled(struct rq_wb *rwb) { return rwb && rwb->wb_normal != 0; } static void wb_timestamp(struct rq_wb *rwb, unsigned long *var) { if (rwb_enabled(rwb)) { const unsigned long cur = jiffies; if (cur != *var) *var = cur; } } /* * If a task was rate throttled in balance_dirty_pages() within the last * second or so, use that to indicate a higher cleaning rate. */ static bool wb_recent_wait(struct rq_wb *rwb) { struct bdi_writeback *wb = &rwb->rqos.q->backing_dev_info->wb; return time_before(jiffies, wb->dirty_sleep + HZ); } static inline struct rq_wait *get_rq_wait(struct rq_wb *rwb, enum wbt_flags wb_acct) { if (wb_acct & WBT_KSWAPD) return &rwb->rq_wait[WBT_RWQ_KSWAPD]; else if (wb_acct & WBT_DISCARD) return &rwb->rq_wait[WBT_RWQ_DISCARD]; return &rwb->rq_wait[WBT_RWQ_BG]; } static void rwb_wake_all(struct rq_wb *rwb) { int i; for (i = 0; i < WBT_NUM_RWQ; i++) { struct rq_wait *rqw = &rwb->rq_wait[i]; if (wq_has_sleeper(&rqw->wait)) wake_up_all(&rqw->wait); } } static void wbt_rqw_done(struct rq_wb *rwb, struct rq_wait *rqw, enum wbt_flags wb_acct) { int inflight, limit; inflight = atomic_dec_return(&rqw->inflight); /* * wbt got disabled with IO in flight. Wake up any potential * waiters, we don't have to do more than that. */ if (unlikely(!rwb_enabled(rwb))) { rwb_wake_all(rwb); return; } /* * For discards, our limit is always the background. For writes, if * the device does write back caching, drop further down before we * wake people up. */ if (wb_acct & WBT_DISCARD) limit = rwb->wb_background; else if (rwb->wc && !wb_recent_wait(rwb)) limit = 0; else limit = rwb->wb_normal; /* * Don't wake anyone up if we are above the normal limit. */ if (inflight && inflight >= limit) return; if (wq_has_sleeper(&rqw->wait)) { int diff = limit - inflight; if (!inflight || diff >= rwb->wb_background / 2) wake_up_all(&rqw->wait); } } static void __wbt_done(struct rq_qos *rqos, enum wbt_flags wb_acct) { struct rq_wb *rwb = RQWB(rqos); struct rq_wait *rqw; if (!(wb_acct & WBT_TRACKED)) return; rqw = get_rq_wait(rwb, wb_acct); wbt_rqw_done(rwb, rqw, wb_acct); } /* * Called on completion of a request. Note that it's also called when * a request is merged, when the request gets freed. */ static void wbt_done(struct rq_qos *rqos, struct request *rq) { struct rq_wb *rwb = RQWB(rqos); if (!wbt_is_tracked(rq)) { if (rwb->sync_cookie == rq) { rwb->sync_issue = 0; rwb->sync_cookie = NULL; } if (wbt_is_read(rq)) wb_timestamp(rwb, &rwb->last_comp); } else { WARN_ON_ONCE(rq == rwb->sync_cookie); __wbt_done(rqos, wbt_flags(rq)); } wbt_clear_state(rq); } static inline bool stat_sample_valid(struct blk_rq_stat *stat) { /* * We need at least one read sample, and a minimum of * RWB_MIN_WRITE_SAMPLES. We require some write samples to know * that it's writes impacting us, and not just some sole read on * a device that is in a lower power state. */ return (stat[READ].nr_samples >= 1 && stat[WRITE].nr_samples >= RWB_MIN_WRITE_SAMPLES); } static u64 rwb_sync_issue_lat(struct rq_wb *rwb) { u64 now, issue = READ_ONCE(rwb->sync_issue); if (!issue || !rwb->sync_cookie) return 0; now = ktime_to_ns(ktime_get()); return now - issue; } enum { LAT_OK = 1, LAT_UNKNOWN, LAT_UNKNOWN_WRITES, LAT_EXCEEDED, }; static int latency_exceeded(struct rq_wb *rwb, struct blk_rq_stat *stat) { struct backing_dev_info *bdi = rwb->rqos.q->backing_dev_info; struct rq_depth *rqd = &rwb->rq_depth; u64 thislat; /* * If our stored sync issue exceeds the window size, or it * exceeds our min target AND we haven't logged any entries, * flag the latency as exceeded. wbt works off completion latencies, * but for a flooded device, a single sync IO can take a long time * to complete after being issued. If this time exceeds our * monitoring window AND we didn't see any other completions in that * window, then count that sync IO as a violation of the latency. */ thislat = rwb_sync_issue_lat(rwb); if (thislat > rwb->cur_win_nsec || (thislat > rwb->min_lat_nsec && !stat[READ].nr_samples)) { trace_wbt_lat(bdi, thislat); return LAT_EXCEEDED; } /* * No read/write mix, if stat isn't valid */ if (!stat_sample_valid(stat)) { /* * If we had writes in this stat window and the window is * current, we're only doing writes. If a task recently * waited or still has writes in flights, consider us doing * just writes as well. */ if (stat[WRITE].nr_samples || wb_recent_wait(rwb) || wbt_inflight(rwb)) return LAT_UNKNOWN_WRITES; return LAT_UNKNOWN; } /* * If the 'min' latency exceeds our target, step down. */ if (stat[READ].min > rwb->min_lat_nsec) { trace_wbt_lat(bdi, stat[READ].min); trace_wbt_stat(bdi, stat); return LAT_EXCEEDED; } if (rqd->scale_step) trace_wbt_stat(bdi, stat); return LAT_OK; } static void rwb_trace_step(struct rq_wb *rwb, const char *msg) { struct backing_dev_info *bdi = rwb->rqos.q->backing_dev_info; struct rq_depth *rqd = &rwb->rq_depth; trace_wbt_step(bdi, msg, rqd->scale_step, rwb->cur_win_nsec, rwb->wb_background, rwb->wb_normal, rqd->max_depth); } static void calc_wb_limits(struct rq_wb *rwb) { if (rwb->min_lat_nsec == 0) { rwb->wb_normal = rwb->wb_background = 0; } else if (rwb->rq_depth.max_depth <= 2) { rwb->wb_normal = rwb->rq_depth.max_depth; rwb->wb_background = 1; } else { rwb->wb_normal = (rwb->rq_depth.max_depth + 1) / 2; rwb->wb_background = (rwb->rq_depth.max_depth + 3) / 4; } } static void scale_up(struct rq_wb *rwb) { if (!rq_depth_scale_up(&rwb->rq_depth)) return; calc_wb_limits(rwb); rwb->unknown_cnt = 0; rwb_wake_all(rwb); rwb_trace_step(rwb, tracepoint_string("scale up")); } static void scale_down(struct rq_wb *rwb, bool hard_throttle) { if (!rq_depth_scale_down(&rwb->rq_depth, hard_throttle)) return; calc_wb_limits(rwb); rwb->unknown_cnt = 0; rwb_trace_step(rwb, tracepoint_string("scale down")); } static void rwb_arm_timer(struct rq_wb *rwb) { struct rq_depth *rqd = &rwb->rq_depth; if (rqd->scale_step > 0) { /* * We should speed this up, using some variant of a fast * integer inverse square root calculation. Since we only do * this for every window expiration, it's not a huge deal, * though. */ rwb->cur_win_nsec = div_u64(rwb->win_nsec << 4, int_sqrt((rqd->scale_step + 1) << 8)); } else { /* * For step < 0, we don't want to increase/decrease the * window size. */ rwb->cur_win_nsec = rwb->win_nsec; } blk_stat_activate_nsecs(rwb->cb, rwb->cur_win_nsec); } static void wb_timer_fn(struct blk_stat_callback *cb) { struct rq_wb *rwb = cb->data; struct rq_depth *rqd = &rwb->rq_depth; unsigned int inflight = wbt_inflight(rwb); int status; status = latency_exceeded(rwb, cb->stat); trace_wbt_timer(rwb->rqos.q->backing_dev_info, status, rqd->scale_step, inflight); /* * If we exceeded the latency target, step down. If we did not, * step one level up. If we don't know enough to say either exceeded * or ok, then don't do anything. */ switch (status) { case LAT_EXCEEDED: scale_down(rwb, true); break; case LAT_OK: scale_up(rwb); break; case LAT_UNKNOWN_WRITES: /* * We started a the center step, but don't have a valid * read/write sample, but we do have writes going on. * Allow step to go negative, to increase write perf. */ scale_up(rwb); break; case LAT_UNKNOWN: if (++rwb->unknown_cnt < RWB_UNKNOWN_BUMP) break; /* * We get here when previously scaled reduced depth, and we * currently don't have a valid read/write sample. For that * case, slowly return to center state (step == 0). */ if (rqd->scale_step > 0) scale_up(rwb); else if (rqd->scale_step < 0) scale_down(rwb, false); break; default: break; } /* * Re-arm timer, if we have IO in flight */ if (rqd->scale_step || inflight) rwb_arm_timer(rwb); } static void wbt_update_limits(struct rq_wb *rwb) { struct rq_depth *rqd = &rwb->rq_depth; rqd->scale_step = 0; rqd->scaled_max = false; rq_depth_calc_max_depth(rqd); calc_wb_limits(rwb); rwb_wake_all(rwb); } u64 wbt_get_min_lat(struct request_queue *q) { struct rq_qos *rqos = wbt_rq_qos(q); if (!rqos) return 0; return RQWB(rqos)->min_lat_nsec; } void wbt_set_min_lat(struct request_queue *q, u64 val) { struct rq_qos *rqos = wbt_rq_qos(q); if (!rqos) return; RQWB(rqos)->min_lat_nsec = val; RQWB(rqos)->enable_state = WBT_STATE_ON_MANUAL; wbt_update_limits(RQWB(rqos)); } static bool close_io(struct rq_wb *rwb) { const unsigned long now = jiffies; return time_before(now, rwb->last_issue + HZ / 10) || time_before(now, rwb->last_comp + HZ / 10); } #define REQ_HIPRIO (REQ_SYNC | REQ_META | REQ_PRIO) static inline unsigned int get_limit(struct rq_wb *rwb, unsigned long rw) { unsigned int limit; /* * If we got disabled, just return UINT_MAX. This ensures that * we'll properly inc a new IO, and dec+wakeup at the end. */ if (!rwb_enabled(rwb)) return UINT_MAX; if ((rw & REQ_OP_MASK) == REQ_OP_DISCARD) return rwb->wb_background; /* * At this point we know it's a buffered write. If this is * kswapd trying to free memory, or REQ_SYNC is set, then * it's WB_SYNC_ALL writeback, and we'll use the max limit for * that. If the write is marked as a background write, then use * the idle limit, or go to normal if we haven't had competing * IO for a bit. */ if ((rw & REQ_HIPRIO) || wb_recent_wait(rwb) || current_is_kswapd()) limit = rwb->rq_depth.max_depth; else if ((rw & REQ_BACKGROUND) || close_io(rwb)) { /* * If less than 100ms since we completed unrelated IO, * limit us to half the depth for background writeback. */ limit = rwb->wb_background; } else limit = rwb->wb_normal; return limit; } struct wbt_wait_data { struct rq_wb *rwb; enum wbt_flags wb_acct; unsigned long rw; }; static bool wbt_inflight_cb(struct rq_wait *rqw, void *private_data) { struct wbt_wait_data *data = private_data; return rq_wait_inc_below(rqw, get_limit(data->rwb, data->rw)); } static void wbt_cleanup_cb(struct rq_wait *rqw, void *private_data) { struct wbt_wait_data *data = private_data; wbt_rqw_done(data->rwb, rqw, data->wb_acct); } /* * Block if we will exceed our limit, or if we are currently waiting for * the timer to kick off queuing again. */ static void __wbt_wait(struct rq_wb *rwb, enum wbt_flags wb_acct, unsigned long rw) { struct rq_wait *rqw = get_rq_wait(rwb, wb_acct); struct wbt_wait_data data = { .rwb = rwb, .wb_acct = wb_acct, .rw = rw, }; rq_qos_wait(rqw, &data, wbt_inflight_cb, wbt_cleanup_cb); } static inline bool wbt_should_throttle(struct rq_wb *rwb, struct bio *bio) { switch (bio_op(bio)) { case REQ_OP_WRITE: /* * Don't throttle WRITE_ODIRECT */ if ((bio->bi_opf & (REQ_SYNC | REQ_IDLE)) == (REQ_SYNC | REQ_IDLE)) return false; fallthrough; case REQ_OP_DISCARD: return true; default: return false; } } static enum wbt_flags bio_to_wbt_flags(struct rq_wb *rwb, struct bio *bio) { enum wbt_flags flags = 0; if (!rwb_enabled(rwb)) return 0; if (bio_op(bio) == REQ_OP_READ) { flags = WBT_READ; } else if (wbt_should_throttle(rwb, bio)) { if (current_is_kswapd()) flags |= WBT_KSWAPD; if (bio_op(bio) == REQ_OP_DISCARD) flags |= WBT_DISCARD; flags |= WBT_TRACKED; } return flags; } static void wbt_cleanup(struct rq_qos *rqos, struct bio *bio) { struct rq_wb *rwb = RQWB(rqos); enum wbt_flags flags = bio_to_wbt_flags(rwb, bio); __wbt_done(rqos, flags); } /* * Returns true if the IO request should be accounted, false if not. * May sleep, if we have exceeded the writeback limits. Caller can pass * in an irq held spinlock, if it holds one when calling this function. * If we do sleep, we'll release and re-grab it. */ static void wbt_wait(struct rq_qos *rqos, struct bio *bio) { struct rq_wb *rwb = RQWB(rqos); enum wbt_flags flags; flags = bio_to_wbt_flags(rwb, bio); if (!(flags & WBT_TRACKED)) { if (flags & WBT_READ) wb_timestamp(rwb, &rwb->last_issue); return; } __wbt_wait(rwb, flags, bio->bi_opf); if (!blk_stat_is_active(rwb->cb)) rwb_arm_timer(rwb); } static void wbt_track(struct rq_qos *rqos, struct request *rq, struct bio *bio) { struct rq_wb *rwb = RQWB(rqos); rq->wbt_flags |= bio_to_wbt_flags(rwb, bio); } static void wbt_issue(struct rq_qos *rqos, struct request *rq) { struct rq_wb *rwb = RQWB(rqos); if (!rwb_enabled(rwb)) return; /* * Track sync issue, in case it takes a long time to complete. Allows us * to react quicker, if a sync IO takes a long time to complete. Note * that this is just a hint. The request can go away when it completes, * so it's important we never dereference it. We only use the address to * compare with, which is why we store the sync_issue time locally. */ if (wbt_is_read(rq) && !rwb->sync_issue) { rwb->sync_cookie = rq; rwb->sync_issue = rq->io_start_time_ns; } } static void wbt_requeue(struct rq_qos *rqos, struct request *rq) { struct rq_wb *rwb = RQWB(rqos); if (!rwb_enabled(rwb)) return; if (rq == rwb->sync_cookie) { rwb->sync_issue = 0; rwb->sync_cookie = NULL; } } void wbt_set_write_cache(struct request_queue *q, bool write_cache_on) { struct rq_qos *rqos = wbt_rq_qos(q); if (rqos) RQWB(rqos)->wc = write_cache_on; } /* * Enable wbt if defaults are configured that way */ void wbt_enable_default(struct request_queue *q) { struct rq_qos *rqos = wbt_rq_qos(q); /* Throttling already enabled? */ if (rqos) return; /* Queue not registered? Maybe shutting down... */ if (!blk_queue_registered(q)) return; if (queue_is_mq(q) && IS_ENABLED(CONFIG_BLK_WBT_MQ)) wbt_init(q); } EXPORT_SYMBOL_GPL(wbt_enable_default); u64 wbt_default_latency_nsec(struct request_queue *q) { /* * We default to 2msec for non-rotational storage, and 75msec * for rotational storage. */ if (blk_queue_nonrot(q)) return 2000000ULL; else return 75000000ULL; } static int wbt_data_dir(const struct request *rq) { const int op = req_op(rq); if (op == REQ_OP_READ) return READ; else if (op_is_write(op)) return WRITE; /* don't account */ return -1; } static void wbt_queue_depth_changed(struct rq_qos *rqos) { RQWB(rqos)->rq_depth.queue_depth = blk_queue_depth(rqos->q); wbt_update_limits(RQWB(rqos)); } static void wbt_exit(struct rq_qos *rqos) { struct rq_wb *rwb = RQWB(rqos); struct request_queue *q = rqos->q; blk_stat_remove_callback(q, rwb->cb); blk_stat_free_callback(rwb->cb); kfree(rwb); } /* * Disable wbt, if enabled by default. */ void wbt_disable_default(struct request_queue *q) { struct rq_qos *rqos = wbt_rq_qos(q); struct rq_wb *rwb; if (!rqos) return; rwb = RQWB(rqos); if (rwb->enable_state == WBT_STATE_ON_DEFAULT) { blk_stat_deactivate(rwb->cb); rwb->wb_normal = 0; } } EXPORT_SYMBOL_GPL(wbt_disable_default); #ifdef CONFIG_BLK_DEBUG_FS static int wbt_curr_win_nsec_show(void *data, struct seq_file *m) { struct rq_qos *rqos = data; struct rq_wb *rwb = RQWB(rqos); seq_printf(m, "%llu\n", rwb->cur_win_nsec); return 0; } static int wbt_enabled_show(void *data, struct seq_file *m) { struct rq_qos *rqos = data; struct rq_wb *rwb = RQWB(rqos); seq_printf(m, "%d\n", rwb->enable_state); return 0; } static int wbt_id_show(void *data, struct seq_file *m) { struct rq_qos *rqos = data; seq_printf(m, "%u\n", rqos->id); return 0; } static int wbt_inflight_show(void *data, struct seq_file *m) { struct rq_qos *rqos = data; struct rq_wb *rwb = RQWB(rqos); int i; for (i = 0; i < WBT_NUM_RWQ; i++) seq_printf(m, "%d: inflight %d\n", i, atomic_read(&rwb->rq_wait[i].inflight)); return 0; } static int wbt_min_lat_nsec_show(void *data, struct seq_file *m) { struct rq_qos *rqos = data; struct rq_wb *rwb = RQWB(rqos); seq_printf(m, "%lu\n", rwb->min_lat_nsec); return 0; } static int wbt_unknown_cnt_show(void *data, struct seq_file *m) { struct rq_qos *rqos = data; struct rq_wb *rwb = RQWB(rqos); seq_printf(m, "%u\n", rwb->unknown_cnt); return 0; } static int wbt_normal_show(void *data, struct seq_file *m) { struct rq_qos *rqos = data; struct rq_wb *rwb = RQWB(rqos); seq_printf(m, "%u\n", rwb->wb_normal); return 0; } static int wbt_background_show(void *data, struct seq_file *m) { struct rq_qos *rqos = data; struct rq_wb *rwb = RQWB(rqos); seq_printf(m, "%u\n", rwb->wb_background); return 0; } static const struct blk_mq_debugfs_attr wbt_debugfs_attrs[] = { {"curr_win_nsec", 0400, wbt_curr_win_nsec_show}, {"enabled", 0400, wbt_enabled_show}, {"id", 0400, wbt_id_show}, {"inflight", 0400, wbt_inflight_show}, {"min_lat_nsec", 0400, wbt_min_lat_nsec_show}, {"unknown_cnt", 0400, wbt_unknown_cnt_show}, {"wb_normal", 0400, wbt_normal_show}, {"wb_background", 0400, wbt_background_show}, {}, }; #endif static struct rq_qos_ops wbt_rqos_ops = { .throttle = wbt_wait, .issue = wbt_issue, .track = wbt_track, .requeue = wbt_requeue, .done = wbt_done, .cleanup = wbt_cleanup, .queue_depth_changed = wbt_queue_depth_changed, .exit = wbt_exit, #ifdef CONFIG_BLK_DEBUG_FS .debugfs_attrs = wbt_debugfs_attrs, #endif }; int wbt_init(struct request_queue *q) { struct rq_wb *rwb; int i; rwb = kzalloc(sizeof(*rwb), GFP_KERNEL); if (!rwb) return -ENOMEM; rwb->cb = blk_stat_alloc_callback(wb_timer_fn, wbt_data_dir, 2, rwb); if (!rwb->cb) { kfree(rwb); return -ENOMEM; } for (i = 0; i < WBT_NUM_RWQ; i++) rq_wait_init(&rwb->rq_wait[i]); rwb->rqos.id = RQ_QOS_WBT; rwb->rqos.ops = &wbt_rqos_ops; rwb->rqos.q = q; rwb->last_comp = rwb->last_issue = jiffies; rwb->win_nsec = RWB_WINDOW_NSEC; rwb->enable_state = WBT_STATE_ON_DEFAULT; rwb->wc = 1; rwb->rq_depth.default_depth = RWB_DEF_DEPTH; wbt_update_limits(rwb); /* * Assign rwb and add the stats callback. */ rq_qos_add(q, &rwb->rqos); blk_stat_add_callback(q, rwb->cb); rwb->min_lat_nsec = wbt_default_latency_nsec(q); wbt_queue_depth_changed(&rwb->rqos); wbt_set_write_cache(q, test_bit(QUEUE_FLAG_WC, &q->queue_flags)); return 0; }