linux-kernel - [PATCH 1/3 for-5.4/block] iocost: better trace vrate changes

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Message-ID: <20190925230207.GI2233839@devbig004.ftw2.facebook.com>
Date:   Wed, 25 Sep 2019 16:02:07 -0700
From:   Tejun Heo <tj@...nel.org>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-team@...com, cgroups@...r.kernel.org
Subject: [PATCH 1/3 for-5.4/block] iocost: better trace vrate changes

vrate_adj tracepoint traces vrate changes; however, it does so only
when busy_level is non-zero.  busy_level turning to zero can sometimes
be as interesting an event.  This patch also enables vrate_adj
tracepoint on other vrate related events - busy_level changes and
non-zero nr_lagging.

Signed-off-by: Tejun Heo <tj@...nel.org>
---
Hello, Jens.

I've encountered vrate regulation issues while testing on a hard disk
machine.  These are three patches to improve vrate adj visibility and
fix the issue.

Thanks.

 block/blk-iocost.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

--- a/block/blk-iocost.c
+++ b/block/blk-iocost.c
@@ -1343,7 +1343,7 @@ static void ioc_timer_fn(struct timer_li
 	u32 ppm_wthr = MILLION - ioc->params.qos[QOS_WPPM];
 	u32 missed_ppm[2], rq_wait_pct;
 	u64 period_vtime;
-	int i;
+	int prev_busy_level, i;
 
 	/* how were the latencies during the period? */
 	ioc_lat_stat(ioc, missed_ppm, &rq_wait_pct);
@@ -1531,6 +1531,7 @@ skip_surplus_transfers:
 	 * and experiencing shortages but not surpluses, we're too stingy
 	 * and should increase vtime rate.
 	 */
+	prev_busy_level = ioc->busy_level;
 	if (rq_wait_pct > RQ_WAIT_BUSY_PCT ||
 	    missed_ppm[READ] > ppm_rthr ||
 	    missed_ppm[WRITE] > ppm_wthr) {
@@ -1592,6 +1593,10 @@ skip_surplus_transfers:
 		atomic64_set(&ioc->vtime_rate, vrate);
 		ioc->inuse_margin_vtime = DIV64_U64_ROUND_UP(
 			ioc->period_us * vrate * INUSE_MARGIN_PCT, 100);
+	} else if (ioc->busy_level != prev_busy_level || nr_lagging) {
+		trace_iocost_ioc_vrate_adj(ioc, atomic64_read(&ioc->vtime_rate),
+					   &missed_ppm, rq_wait_pct, nr_lagging,
+					   nr_shortages, nr_surpluses);
 	}
 
 	ioc_refresh_params(ioc, false);