linux-kernel - [PATCH] sched/fair: don't restart enqueued cfs quota slack timer

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Date:   Mon,  3 Jun 2019 12:43:09 +0800
From:   Liangyan <liangyan.peng@...ux.alibaba.com>
To:     mingo@...hat.com, peterz@...radead.org,
        linux-kernel@...r.kernel.org
Cc:     yun.wang@...ux.alibaba.com, shanpeic@...ux.alibaba.com,
        xlpang@...ux.alibaba.com,
        "liangyan.ply" <liangyan.ply@...ux.alibaba.com>,
        Liangyan <liangyan.peng@...ux.alibaba.com>
Subject: [PATCH] sched/fair: don't restart enqueued cfs quota slack timer

From: "liangyan.ply" <liangyan.ply@...ux.alibaba.com>

start_cfs_slack_bandwidth() will restart the quota slack timer,
if it is called frequently, this timer will be restarted continuously
and may have no chance to expire to unthrottle cfs tasks.
This will cause that the throttled tasks can't be unthrottled in time
although they have remaining quota.

Signed-off-by: Liangyan <liangyan.peng@...ux.alibaba.com>
---
 kernel/sched/fair.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index d90a64620072..fdb03c752f97 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4411,9 +4411,11 @@ static void start_cfs_slack_bandwidth(struct cfs_bandwidth *cfs_b)
 	if (runtime_refresh_within(cfs_b, min_left))
 		return;
 
-	hrtimer_start(&cfs_b->slack_timer,
+	if (!hrtimer_active(&cfs_b->slack_timer)) {
+		hrtimer_start(&cfs_b->slack_timer,
 			ns_to_ktime(cfs_bandwidth_slack_period),
 			HRTIMER_MODE_REL);
+	}
 }
 
 /* we know any runtime found here is valid as update_curr() precedes return */
-- 
2.14.4.44.g2045bb6