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From: Quentin Perret <qperret@google.com>
To: mingo@redhat.com, peterz@infradead.org,
	vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
	qais.yousef@arm.com, rickyiu@google.com, wvw@google.com,
	patrick.bellasi@matbug.net
Cc: linux-kernel@vger.kernel.org, kernel-team@android.com
Subject: Re: [PATCH] sched: Fix UCLAMP_FLAG_IDLE setting
Date: Wed, 9 Jun 2021 14:37:04 +0000	[thread overview]
Message-ID: <YMDSEHB5+zlajb4x@google.com> (raw)
In-Reply-To: <20210609143339.1194238-1-qperret@google.com>

On Wednesday 09 Jun 2021 at 14:33:39 (+0000), Quentin Perret wrote:
> The UCLAMP_FLAG_IDLE flag is set on a runqueue when dequeueing the last
> active task to maintain the last uclamp.max and prevent blocked util
> from suddenly becoming visible.
> 
> However, there is an asymmetry in how the flag is set and cleared which
> can lead to having the flag set whilst there are active task on the rq.
> Specifically, the flag is set in the uclamp_rq_inc() path, which is
> called at enqueue time, but cleared in the uclamp_rq_dec_id() which is
> called both when dequeueing and task _and_ during cgroup migrations.
> 
> Fix this by setting the flag in the uclamp_rq_inc_id() path to ensure
> things remain symmetrical.
> 
> Reported-by: Rick Yiu <rickyiu@google.com>
> Signed-off-by: Quentin Perret <qperret@google.com>

Argh, and I think this wants

Fixes: e496187da710 ("sched/uclamp: Enforce last task's UCLAMP_MAX")

  reply	other threads:[~2021-06-09 14:37 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-09 14:33 [PATCH] sched: Fix UCLAMP_FLAG_IDLE setting Quentin Perret
2021-06-09 14:37 ` Quentin Perret [this message]
2021-06-10 10:00 ` Qais Yousef
2021-06-10 10:27   ` Quentin Perret

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