iocost: improve nr_lagging handling (7cd806a9) · Commits · 戴 / test

Some IOs may span multiple periods. As latencies are collected on completion, the inbetween periods won't register them and may incorrectly decide to increase vrate. nr_lagging tracks these IOs to avoid those situations. Currently, whenever there are IOs which are spanning from the previous period, busy_level is reset to 0 if negative thus suppressing vrate increase. This has the following two problems. * When latency target percentiles aren't set, vrate adjustment should only be governed by queue depth depletion; however, the current code keeps nr_lagging active which pulls in latency results and can keep down vrate unexpectedly. * When lagging condition is detected, it resets the entire negative busy_level. This turned out to be way too aggressive on some devices which sometimes experience extended latencies on a small subset of commands. In addition, a lagging IO will be accounted as latency target miss on completion anyway and resetting busy_level amplifies its impact unnecessarily. This patch fixes the above two problems by disabling nr_lagging counting when latency target percentiles aren't set and blocking vrate increases when there are lagging IOs while leaving busy_level as-is. Signed-off-by:

Tejun Heo <tj@kernel.org> Signed-off-by:

Jens Axboe <axboe@kernel.dk>

block/blk-iocost.c

+11 −8

Original line number	Diff line number	Diff line
		@@ -1407,7 +1407,8 @@ static void ioc_timer_fn(struct timer_list *timer)
		* comparing vdone against period start. If lagging behind
		* IOs from past periods, don't increase vrate.
		*/
		if (!atomic_read(&iocg_to_blkg(iocg)->use_delay) &&
		if ((ppm_rthr != MILLION \|\| ppm_wthr != MILLION) &&
		!atomic_read(&iocg_to_blkg(iocg)->use_delay) &&
		time_after64(vtime, vdone) &&
		time_after64(vtime, now.vnow -
		MAX_LAGGING_PERIODS * period_vtime) &&
		@@ -1537,21 +1538,23 @@ skip_surplus_transfers:
		missed_ppm[WRITE] > ppm_wthr) {
		ioc->busy_level = max(ioc->busy_level, 0);
		ioc->busy_level++;
		} else if (nr_lagging) {
		ioc->busy_level = max(ioc->busy_level, 0);
		} else if (nr_shortages && !nr_surpluses &&
		rq_wait_pct <= RQ_WAIT_BUSY_PCT * UNBUSY_THR_PCT / 100 &&
		} else if (rq_wait_pct <= RQ_WAIT_BUSY_PCT * UNBUSY_THR_PCT / 100 &&
		missed_ppm[READ] <= ppm_rthr * UNBUSY_THR_PCT / 100 &&
		missed_ppm[WRITE] <= ppm_wthr * UNBUSY_THR_PCT / 100) {
		/* take action iff there is contention */
		if (nr_shortages && !nr_lagging) {
		ioc->busy_level = min(ioc->busy_level, 0);
		/* redistribute surpluses first */
		if (!nr_surpluses)
		ioc->busy_level--;
		}
		} else {
		ioc->busy_level = 0;
		}

		ioc->busy_level = clamp(ioc->busy_level, -1000, 1000);

		if (ioc->busy_level) {
		if (ioc->busy_level > 0 \|\| (ioc->busy_level < 0 && !nr_lagging)) {
		u64 vrate = atomic64_read(&ioc->vtime_rate);
		u64 vrate_min = ioc->vrate_min, vrate_max = ioc->vrate_max;

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