From f63e7224d00965ed79fe84a2323ad8dde7f989be Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Wed, 25 Sep 2019 16:03:09 -0700 Subject: [PATCH] iocost: improve nr_lagging handling commit 7cd806a9a953f234b9865c30028f47fd738ce375 upstream. 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 Signed-off-by: Jens Axboe Signed-off-by: Jiufei Xue Reviewed-by: Joseph Qi --- block/blk-iocost.c | 19 +++++++++++-------- 1 file changed, 11 insertions(+), 8 deletions(-) diff --git a/block/blk-iocost.c b/block/blk-iocost.c index 511cf825d60f..9435310e250c 100644 --- a/block/blk-iocost.c +++ b/block/blk-iocost.c @@ -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 @@ static void ioc_timer_fn(struct timer_list *timer) 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) { - ioc->busy_level = min(ioc->busy_level, 0); - ioc->busy_level--; + /* 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; -- GitLab