linux-kernel - [PATCH 5.4 158/158] sched/fair: Fix overutilized update in enqueue_task

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Message-Id: <20201123121827.556725409@linuxfoundation.org>
Date:   Mon, 23 Nov 2020 13:23:06 +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>
Subject: [PATCH 5.4 158/158] sched/fair: Fix overutilized update in enqueue_task_fair()

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

commit 8e1ac4299a6e8726de42310d9c1379f188140c71 upstream.

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: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 kernel/sched/fair.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5228,6 +5228,7 @@ enqueue_task_fair(struct rq *rq, struct
 	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
@@ -5299,7 +5300,7 @@ enqueue_throttle:
 		 * 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);
 
 	}