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![Jens Axboe](/assets/img/avatar_default.png)
No point in providing and exporting this helper. There's just one (real) user of it, just use rq_data_dir(). Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Jens Axboe <axboe@fb.com>
758 lines
18 KiB
C
758 lines
18 KiB
C
/*
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* buffered writeback throttling. loosely based on CoDel. We can't drop
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* packets for IO scheduling, so the logic is something like this:
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*
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* - Monitor latencies in a defined window of time.
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* - If the minimum latency in the above window exceeds some target, increment
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* scaling step and scale down queue depth by a factor of 2x. The monitoring
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* window is then shrunk to 100 / sqrt(scaling step + 1).
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* - For any window where we don't have solid data on what the latencies
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* look like, retain status quo.
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* - If latencies look good, decrement scaling step.
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* - If we're only doing writes, allow the scaling step to go negative. This
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* will temporarily boost write performance, snapping back to a stable
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* scaling step of 0 if reads show up or the heavy writers finish. Unlike
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* positive scaling steps where we shrink the monitoring window, a negative
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* scaling step retains the default step==0 window size.
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*
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* Copyright (C) 2016 Jens Axboe
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*
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*/
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#include <linux/kernel.h>
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#include <linux/blk_types.h>
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#include <linux/slab.h>
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#include <linux/backing-dev.h>
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#include <linux/swap.h>
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#include "blk-wbt.h"
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#define CREATE_TRACE_POINTS
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#include <trace/events/wbt.h>
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enum {
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/*
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* Default setting, we'll scale up (to 75% of QD max) or down (min 1)
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* from here depending on device stats
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*/
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RWB_DEF_DEPTH = 16,
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/*
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* 100msec window
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*/
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RWB_WINDOW_NSEC = 100 * 1000 * 1000ULL,
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/*
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* Disregard stats, if we don't meet this minimum
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*/
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RWB_MIN_WRITE_SAMPLES = 3,
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/*
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* If we have this number of consecutive windows with not enough
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* information to scale up or down, scale up.
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*/
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RWB_UNKNOWN_BUMP = 5,
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};
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static inline bool rwb_enabled(struct rq_wb *rwb)
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{
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return rwb && rwb->wb_normal != 0;
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}
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/*
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* Increment 'v', if 'v' is below 'below'. Returns true if we succeeded,
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* false if 'v' + 1 would be bigger than 'below'.
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*/
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static bool atomic_inc_below(atomic_t *v, int below)
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{
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int cur = atomic_read(v);
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for (;;) {
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int old;
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if (cur >= below)
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return false;
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old = atomic_cmpxchg(v, cur, cur + 1);
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if (old == cur)
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break;
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cur = old;
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}
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return true;
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}
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static void wb_timestamp(struct rq_wb *rwb, unsigned long *var)
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{
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if (rwb_enabled(rwb)) {
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const unsigned long cur = jiffies;
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if (cur != *var)
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*var = cur;
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}
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}
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/*
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* If a task was rate throttled in balance_dirty_pages() within the last
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* second or so, use that to indicate a higher cleaning rate.
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*/
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static bool wb_recent_wait(struct rq_wb *rwb)
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{
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struct bdi_writeback *wb = &rwb->queue->backing_dev_info->wb;
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return time_before(jiffies, wb->dirty_sleep + HZ);
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}
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static inline struct rq_wait *get_rq_wait(struct rq_wb *rwb, bool is_kswapd)
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{
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return &rwb->rq_wait[is_kswapd];
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}
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static void rwb_wake_all(struct rq_wb *rwb)
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{
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int i;
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for (i = 0; i < WBT_NUM_RWQ; i++) {
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struct rq_wait *rqw = &rwb->rq_wait[i];
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if (waitqueue_active(&rqw->wait))
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wake_up_all(&rqw->wait);
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}
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}
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void __wbt_done(struct rq_wb *rwb, enum wbt_flags wb_acct)
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{
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struct rq_wait *rqw;
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int inflight, limit;
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if (!(wb_acct & WBT_TRACKED))
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return;
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rqw = get_rq_wait(rwb, wb_acct & WBT_KSWAPD);
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inflight = atomic_dec_return(&rqw->inflight);
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/*
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* wbt got disabled with IO in flight. Wake up any potential
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* waiters, we don't have to do more than that.
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*/
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if (unlikely(!rwb_enabled(rwb))) {
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rwb_wake_all(rwb);
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return;
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}
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/*
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* If the device does write back caching, drop further down
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* before we wake people up.
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*/
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if (rwb->wc && !wb_recent_wait(rwb))
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limit = 0;
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else
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limit = rwb->wb_normal;
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/*
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* Don't wake anyone up if we are above the normal limit.
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*/
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if (inflight && inflight >= limit)
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return;
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if (waitqueue_active(&rqw->wait)) {
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int diff = limit - inflight;
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if (!inflight || diff >= rwb->wb_background / 2)
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wake_up_all(&rqw->wait);
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}
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}
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/*
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* Called on completion of a request. Note that it's also called when
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* a request is merged, when the request gets freed.
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*/
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void wbt_done(struct rq_wb *rwb, struct blk_issue_stat *stat)
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{
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if (!rwb)
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return;
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if (!wbt_is_tracked(stat)) {
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if (rwb->sync_cookie == stat) {
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rwb->sync_issue = 0;
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rwb->sync_cookie = NULL;
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}
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if (wbt_is_read(stat))
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wb_timestamp(rwb, &rwb->last_comp);
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wbt_clear_state(stat);
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} else {
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WARN_ON_ONCE(stat == rwb->sync_cookie);
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__wbt_done(rwb, wbt_stat_to_mask(stat));
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wbt_clear_state(stat);
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}
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}
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/*
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* Return true, if we can't increase the depth further by scaling
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*/
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static bool calc_wb_limits(struct rq_wb *rwb)
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{
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unsigned int depth;
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bool ret = false;
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if (!rwb->min_lat_nsec) {
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rwb->wb_max = rwb->wb_normal = rwb->wb_background = 0;
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return false;
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}
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/*
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* For QD=1 devices, this is a special case. It's important for those
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* to have one request ready when one completes, so force a depth of
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* 2 for those devices. On the backend, it'll be a depth of 1 anyway,
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* since the device can't have more than that in flight. If we're
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* scaling down, then keep a setting of 1/1/1.
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*/
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if (rwb->queue_depth == 1) {
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if (rwb->scale_step > 0)
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rwb->wb_max = rwb->wb_normal = 1;
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else {
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rwb->wb_max = rwb->wb_normal = 2;
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ret = true;
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}
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rwb->wb_background = 1;
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} else {
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/*
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* scale_step == 0 is our default state. If we have suffered
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* latency spikes, step will be > 0, and we shrink the
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* allowed write depths. If step is < 0, we're only doing
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* writes, and we allow a temporarily higher depth to
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* increase performance.
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*/
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depth = min_t(unsigned int, RWB_DEF_DEPTH, rwb->queue_depth);
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if (rwb->scale_step > 0)
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depth = 1 + ((depth - 1) >> min(31, rwb->scale_step));
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else if (rwb->scale_step < 0) {
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unsigned int maxd = 3 * rwb->queue_depth / 4;
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depth = 1 + ((depth - 1) << -rwb->scale_step);
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if (depth > maxd) {
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depth = maxd;
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ret = true;
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}
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}
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/*
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* Set our max/normal/bg queue depths based on how far
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* we have scaled down (->scale_step).
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*/
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rwb->wb_max = depth;
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rwb->wb_normal = (rwb->wb_max + 1) / 2;
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rwb->wb_background = (rwb->wb_max + 3) / 4;
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}
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return ret;
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}
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static inline bool stat_sample_valid(struct blk_rq_stat *stat)
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{
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/*
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* We need at least one read sample, and a minimum of
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* RWB_MIN_WRITE_SAMPLES. We require some write samples to know
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* that it's writes impacting us, and not just some sole read on
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* a device that is in a lower power state.
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*/
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return (stat[READ].nr_samples >= 1 &&
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stat[WRITE].nr_samples >= RWB_MIN_WRITE_SAMPLES);
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}
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static u64 rwb_sync_issue_lat(struct rq_wb *rwb)
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{
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u64 now, issue = ACCESS_ONCE(rwb->sync_issue);
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if (!issue || !rwb->sync_cookie)
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return 0;
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now = ktime_to_ns(ktime_get());
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return now - issue;
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}
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enum {
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LAT_OK = 1,
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LAT_UNKNOWN,
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LAT_UNKNOWN_WRITES,
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LAT_EXCEEDED,
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};
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static int latency_exceeded(struct rq_wb *rwb, struct blk_rq_stat *stat)
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{
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struct backing_dev_info *bdi = rwb->queue->backing_dev_info;
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u64 thislat;
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/*
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* If our stored sync issue exceeds the window size, or it
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* exceeds our min target AND we haven't logged any entries,
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* flag the latency as exceeded. wbt works off completion latencies,
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* but for a flooded device, a single sync IO can take a long time
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* to complete after being issued. If this time exceeds our
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* monitoring window AND we didn't see any other completions in that
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* window, then count that sync IO as a violation of the latency.
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*/
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thislat = rwb_sync_issue_lat(rwb);
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if (thislat > rwb->cur_win_nsec ||
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(thislat > rwb->min_lat_nsec && !stat[READ].nr_samples)) {
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trace_wbt_lat(bdi, thislat);
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return LAT_EXCEEDED;
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}
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/*
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* No read/write mix, if stat isn't valid
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*/
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if (!stat_sample_valid(stat)) {
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/*
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* If we had writes in this stat window and the window is
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* current, we're only doing writes. If a task recently
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* waited or still has writes in flights, consider us doing
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* just writes as well.
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*/
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if (stat[WRITE].nr_samples || wb_recent_wait(rwb) ||
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wbt_inflight(rwb))
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return LAT_UNKNOWN_WRITES;
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return LAT_UNKNOWN;
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}
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/*
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* If the 'min' latency exceeds our target, step down.
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*/
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if (stat[READ].min > rwb->min_lat_nsec) {
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trace_wbt_lat(bdi, stat[READ].min);
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trace_wbt_stat(bdi, stat);
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return LAT_EXCEEDED;
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}
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if (rwb->scale_step)
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trace_wbt_stat(bdi, stat);
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return LAT_OK;
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}
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static void rwb_trace_step(struct rq_wb *rwb, const char *msg)
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{
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struct backing_dev_info *bdi = rwb->queue->backing_dev_info;
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trace_wbt_step(bdi, msg, rwb->scale_step, rwb->cur_win_nsec,
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rwb->wb_background, rwb->wb_normal, rwb->wb_max);
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}
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static void scale_up(struct rq_wb *rwb)
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{
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/*
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* Hit max in previous round, stop here
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*/
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if (rwb->scaled_max)
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return;
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rwb->scale_step--;
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rwb->unknown_cnt = 0;
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rwb->scaled_max = calc_wb_limits(rwb);
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rwb_wake_all(rwb);
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rwb_trace_step(rwb, "step up");
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}
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/*
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* Scale rwb down. If 'hard_throttle' is set, do it quicker, since we
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* had a latency violation.
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*/
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static void scale_down(struct rq_wb *rwb, bool hard_throttle)
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{
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/*
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* Stop scaling down when we've hit the limit. This also prevents
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* ->scale_step from going to crazy values, if the device can't
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* keep up.
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*/
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if (rwb->wb_max == 1)
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return;
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if (rwb->scale_step < 0 && hard_throttle)
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rwb->scale_step = 0;
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else
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rwb->scale_step++;
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rwb->scaled_max = false;
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rwb->unknown_cnt = 0;
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calc_wb_limits(rwb);
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rwb_trace_step(rwb, "step down");
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}
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static void rwb_arm_timer(struct rq_wb *rwb)
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{
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if (rwb->scale_step > 0) {
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/*
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* We should speed this up, using some variant of a fast
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* integer inverse square root calculation. Since we only do
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* this for every window expiration, it's not a huge deal,
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* though.
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*/
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rwb->cur_win_nsec = div_u64(rwb->win_nsec << 4,
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int_sqrt((rwb->scale_step + 1) << 8));
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} else {
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/*
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* For step < 0, we don't want to increase/decrease the
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* window size.
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*/
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rwb->cur_win_nsec = rwb->win_nsec;
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}
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blk_stat_activate_nsecs(rwb->cb, rwb->cur_win_nsec);
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}
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static void wb_timer_fn(struct blk_stat_callback *cb)
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{
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struct rq_wb *rwb = cb->data;
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unsigned int inflight = wbt_inflight(rwb);
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int status;
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status = latency_exceeded(rwb, cb->stat);
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trace_wbt_timer(rwb->queue->backing_dev_info, status, rwb->scale_step,
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inflight);
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/*
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* If we exceeded the latency target, step down. If we did not,
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* step one level up. If we don't know enough to say either exceeded
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* or ok, then don't do anything.
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*/
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switch (status) {
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case LAT_EXCEEDED:
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scale_down(rwb, true);
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break;
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case LAT_OK:
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scale_up(rwb);
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break;
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case LAT_UNKNOWN_WRITES:
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/*
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* We started a the center step, but don't have a valid
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* read/write sample, but we do have writes going on.
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* Allow step to go negative, to increase write perf.
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*/
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scale_up(rwb);
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break;
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case LAT_UNKNOWN:
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if (++rwb->unknown_cnt < RWB_UNKNOWN_BUMP)
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break;
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/*
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* We get here when previously scaled reduced depth, and we
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* currently don't have a valid read/write sample. For that
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* case, slowly return to center state (step == 0).
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*/
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if (rwb->scale_step > 0)
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scale_up(rwb);
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else if (rwb->scale_step < 0)
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scale_down(rwb, false);
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break;
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default:
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break;
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}
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/*
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* Re-arm timer, if we have IO in flight
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*/
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if (rwb->scale_step || inflight)
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rwb_arm_timer(rwb);
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}
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void wbt_update_limits(struct rq_wb *rwb)
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{
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rwb->scale_step = 0;
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rwb->scaled_max = false;
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calc_wb_limits(rwb);
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rwb_wake_all(rwb);
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}
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static bool close_io(struct rq_wb *rwb)
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{
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const unsigned long now = jiffies;
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return time_before(now, rwb->last_issue + HZ / 10) ||
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time_before(now, rwb->last_comp + HZ / 10);
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}
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#define REQ_HIPRIO (REQ_SYNC | REQ_META | REQ_PRIO)
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static inline unsigned int get_limit(struct rq_wb *rwb, unsigned long rw)
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{
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unsigned int limit;
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/*
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* At this point we know it's a buffered write. If this is
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* kswapd trying to free memory, or REQ_SYNC is set, set, then
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* it's WB_SYNC_ALL writeback, and we'll use the max limit for
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* that. If the write is marked as a background write, then use
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* the idle limit, or go to normal if we haven't had competing
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* IO for a bit.
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*/
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if ((rw & REQ_HIPRIO) || wb_recent_wait(rwb) || current_is_kswapd())
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limit = rwb->wb_max;
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else if ((rw & REQ_BACKGROUND) || close_io(rwb)) {
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/*
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* If less than 100ms since we completed unrelated IO,
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* limit us to half the depth for background writeback.
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*/
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limit = rwb->wb_background;
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} else
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limit = rwb->wb_normal;
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return limit;
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}
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static inline bool may_queue(struct rq_wb *rwb, struct rq_wait *rqw,
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wait_queue_t *wait, unsigned long rw)
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{
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/*
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* inc it here even if disabled, since we'll dec it at completion.
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* this only happens if the task was sleeping in __wbt_wait(),
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* and someone turned it off at the same time.
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*/
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if (!rwb_enabled(rwb)) {
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atomic_inc(&rqw->inflight);
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return true;
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}
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/*
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* If the waitqueue is already active and we are not the next
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* in line to be woken up, wait for our turn.
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*/
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if (waitqueue_active(&rqw->wait) &&
|
|
rqw->wait.task_list.next != &wait->task_list)
|
|
return false;
|
|
|
|
return atomic_inc_below(&rqw->inflight, get_limit(rwb, rw));
|
|
}
|
|
|
|
/*
|
|
* 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, unsigned long rw, spinlock_t *lock)
|
|
__releases(lock)
|
|
__acquires(lock)
|
|
{
|
|
struct rq_wait *rqw = get_rq_wait(rwb, current_is_kswapd());
|
|
DEFINE_WAIT(wait);
|
|
|
|
if (may_queue(rwb, rqw, &wait, rw))
|
|
return;
|
|
|
|
do {
|
|
prepare_to_wait_exclusive(&rqw->wait, &wait,
|
|
TASK_UNINTERRUPTIBLE);
|
|
|
|
if (may_queue(rwb, rqw, &wait, rw))
|
|
break;
|
|
|
|
if (lock) {
|
|
spin_unlock_irq(lock);
|
|
io_schedule();
|
|
spin_lock_irq(lock);
|
|
} else
|
|
io_schedule();
|
|
} while (1);
|
|
|
|
finish_wait(&rqw->wait, &wait);
|
|
}
|
|
|
|
static inline bool wbt_should_throttle(struct rq_wb *rwb, struct bio *bio)
|
|
{
|
|
const int op = bio_op(bio);
|
|
|
|
/*
|
|
* If not a WRITE, do nothing
|
|
*/
|
|
if (op != REQ_OP_WRITE)
|
|
return false;
|
|
|
|
/*
|
|
* Don't throttle WRITE_ODIRECT
|
|
*/
|
|
if ((bio->bi_opf & (REQ_SYNC | REQ_IDLE)) == (REQ_SYNC | REQ_IDLE))
|
|
return false;
|
|
|
|
return true;
|
|
}
|
|
|
|
/*
|
|
* 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.
|
|
*/
|
|
enum wbt_flags wbt_wait(struct rq_wb *rwb, struct bio *bio, spinlock_t *lock)
|
|
{
|
|
unsigned int ret = 0;
|
|
|
|
if (!rwb_enabled(rwb))
|
|
return 0;
|
|
|
|
if (bio_op(bio) == REQ_OP_READ)
|
|
ret = WBT_READ;
|
|
|
|
if (!wbt_should_throttle(rwb, bio)) {
|
|
if (ret & WBT_READ)
|
|
wb_timestamp(rwb, &rwb->last_issue);
|
|
return ret;
|
|
}
|
|
|
|
__wbt_wait(rwb, bio->bi_opf, lock);
|
|
|
|
if (!blk_stat_is_active(rwb->cb))
|
|
rwb_arm_timer(rwb);
|
|
|
|
if (current_is_kswapd())
|
|
ret |= WBT_KSWAPD;
|
|
|
|
return ret | WBT_TRACKED;
|
|
}
|
|
|
|
void wbt_issue(struct rq_wb *rwb, struct blk_issue_stat *stat)
|
|
{
|
|
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. 'stat' can go away when the
|
|
* request 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(stat) && !rwb->sync_issue) {
|
|
rwb->sync_cookie = stat;
|
|
rwb->sync_issue = blk_stat_time(stat);
|
|
}
|
|
}
|
|
|
|
void wbt_requeue(struct rq_wb *rwb, struct blk_issue_stat *stat)
|
|
{
|
|
if (!rwb_enabled(rwb))
|
|
return;
|
|
if (stat == rwb->sync_cookie) {
|
|
rwb->sync_issue = 0;
|
|
rwb->sync_cookie = NULL;
|
|
}
|
|
}
|
|
|
|
void wbt_set_queue_depth(struct rq_wb *rwb, unsigned int depth)
|
|
{
|
|
if (rwb) {
|
|
rwb->queue_depth = depth;
|
|
wbt_update_limits(rwb);
|
|
}
|
|
}
|
|
|
|
void wbt_set_write_cache(struct rq_wb *rwb, bool write_cache_on)
|
|
{
|
|
if (rwb)
|
|
rwb->wc = write_cache_on;
|
|
}
|
|
|
|
/*
|
|
* Disable wbt, if enabled by default. Only called from CFQ.
|
|
*/
|
|
void wbt_disable_default(struct request_queue *q)
|
|
{
|
|
struct rq_wb *rwb = q->rq_wb;
|
|
|
|
if (rwb && rwb->enable_state == WBT_STATE_ON_DEFAULT)
|
|
wbt_exit(q);
|
|
}
|
|
EXPORT_SYMBOL_GPL(wbt_disable_default);
|
|
|
|
/*
|
|
* Enable wbt if defaults are configured that way
|
|
*/
|
|
void wbt_enable_default(struct request_queue *q)
|
|
{
|
|
/* Throttling already enabled? */
|
|
if (q->rq_wb)
|
|
return;
|
|
|
|
/* Queue not registered? Maybe shutting down... */
|
|
if (!test_bit(QUEUE_FLAG_REGISTERED, &q->queue_flags))
|
|
return;
|
|
|
|
if ((q->mq_ops && IS_ENABLED(CONFIG_BLK_WBT_MQ)) ||
|
|
(q->request_fn && IS_ENABLED(CONFIG_BLK_WBT_SQ)))
|
|
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)
|
|
{
|
|
return rq_data_dir(rq);
|
|
}
|
|
|
|
int wbt_init(struct request_queue *q)
|
|
{
|
|
struct rq_wb *rwb;
|
|
int i;
|
|
|
|
BUILD_BUG_ON(WBT_NR_BITS > BLK_STAT_RES_BITS);
|
|
|
|
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++) {
|
|
atomic_set(&rwb->rq_wait[i].inflight, 0);
|
|
init_waitqueue_head(&rwb->rq_wait[i].wait);
|
|
}
|
|
|
|
rwb->wc = 1;
|
|
rwb->queue_depth = RWB_DEF_DEPTH;
|
|
rwb->last_comp = rwb->last_issue = jiffies;
|
|
rwb->queue = q;
|
|
rwb->win_nsec = RWB_WINDOW_NSEC;
|
|
rwb->enable_state = WBT_STATE_ON_DEFAULT;
|
|
wbt_update_limits(rwb);
|
|
|
|
/*
|
|
* Assign rwb and add the stats callback.
|
|
*/
|
|
q->rq_wb = rwb;
|
|
blk_stat_add_callback(q, rwb->cb);
|
|
|
|
rwb->min_lat_nsec = wbt_default_latency_nsec(q);
|
|
|
|
wbt_set_queue_depth(rwb, blk_queue_depth(q));
|
|
wbt_set_write_cache(rwb, test_bit(QUEUE_FLAG_WC, &q->queue_flags));
|
|
|
|
return 0;
|
|
}
|
|
|
|
void wbt_exit(struct request_queue *q)
|
|
{
|
|
struct rq_wb *rwb = q->rq_wb;
|
|
|
|
if (rwb) {
|
|
blk_stat_remove_callback(q, rwb->cb);
|
|
blk_stat_free_callback(rwb->cb);
|
|
q->rq_wb = NULL;
|
|
kfree(rwb);
|
|
}
|
|
}
|