linux-kernel - [PATCH] sched: refill quota for current period when refilling timer activates

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Date:   Mon, 14 May 2018 13:58:23 +0300
From:   Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Cc:     Ben Segall <bsegall@...gle.com>
Subject: [PATCH] sched: refill quota for current period when refilling timer
 activates

Period timer deactivates if task group has no activity during past period,
i.e. if were no throttle and runtime from global pool weren't consumed.
When timer activates back global pool contains unpredictable amount of
expired runtime allocated long ago. In some cases this works fine and
task could use it until next refill. But series short execution slices
could drain all that leftovers because each switch expires local poll.
In this case task group will be throttled until quota refill.

This patch refills quota right at the moment of timer's activation.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
---
 kernel/sched/fair.c |    2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 79f574dba096..b8d73ed17ff6 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5165,6 +5165,8 @@ void start_cfs_bandwidth(struct cfs_bandwidth *cfs_b)

 	if (!cfs_b->period_active) {
 		cfs_b->period_active = 1;
+		/* refill quota for current period after inactivity */
+		__refill_cfs_bandwidth_runtime(cfs_b);
 		hrtimer_forward_now(&cfs_b->period_timer, cfs_b->period);
 		hrtimer_start_expires(&cfs_b->period_timer, HRTIMER_MODE_ABS_PINNED);
 	}