linux-kernel - [PATCH 5.9 180/252] sched/fair: Fix overutilized update in enqueue_task

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Date:   Mon, 23 Nov 2020 13:22:10 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Rick Yiu <rickyiu@...gle.com>,
        Quentin Perret <qperret@...gle.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Valentin Schneider <valentin.schneider@....com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.9 180/252] sched/fair: Fix overutilized update in enqueue_task_fair()

From: Quentin Perret <qperret@...gle.com>

[ Upstream commit 8e1ac4299a6e8726de42310d9c1379f188140c71 ]

enqueue_task_fair() attempts to skip the overutilized update for new
tasks as their util_avg is not accurate yet. However, the flag we check
to do so is overwritten earlier on in the function, which makes the
condition pretty much a nop.

Fix this by saving the flag early on.

Fixes: 2802bf3cd936 ("sched/fair: Add over-utilization/tipping point indicator")
Reported-by: Rick Yiu <rickyiu@...gle.com>
Signed-off-by: Quentin Perret <qperret@...gle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@...aro.org>
Reviewed-by: Valentin Schneider <valentin.schneider@....com>
Link: https://lkml.kernel.org/r/20201112111201.2081902-1-qperret@google.com
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 kernel/sched/fair.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 48a6d442b4443..c0c4d9ad7da8e 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5473,6 +5473,7 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
 	struct cfs_rq *cfs_rq;
 	struct sched_entity *se = &p->se;
 	int idle_h_nr_running = task_has_idle_policy(p);
+	int task_new = !(flags & ENQUEUE_WAKEUP);
 
 	/*
 	 * The code below (indirectly) updates schedutil which looks at
@@ -5545,7 +5546,7 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
 	 * into account, but that is not straightforward to implement,
 	 * and the following generally works well enough in practice.
 	 */
-	if (flags & ENQUEUE_WAKEUP)
+	if (!task_new)
 		update_overutilized_status(rq);
 
 enqueue_throttle:
-- 
2.27.0