From: Quentin Perret <qperret@google.com>
To: Qais Yousef <qais.yousef@arm.com>
Cc: mingo@redhat.com, peterz@infradead.org,
vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
rickyiu@google.com, wvw@google.com, patrick.bellasi@matbug.net,
linux-kernel@vger.kernel.org, kernel-team@android.com
Subject: Re: [PATCH] sched: Fix UCLAMP_FLAG_IDLE setting
Date: Thu, 10 Jun 2021 10:27:32 +0000 [thread overview]
Message-ID: <YMHpFObpW/VzrTW3@google.com> (raw)
In-Reply-To: <20210610100039.2gvnl3lu6o2hu5yj@e107158-lin.cambridge.arm.com>
On Thursday 10 Jun 2021 at 11:00:39 (+0100), Qais Yousef wrote:
> On 06/09/21 14:33, 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
>
> It is actually the other way around. It is cleared in uclamp_rq_inc() and
> set in uclamp_rq_dec_id().
>
> > called both when dequeueing and task _and_ during cgroup migrations.
>
> Is it cgroup migrations or when cgroup uclamp values are updated you mean?
>
> It is worth being direct and mention that uclamp_update_active() will perform
> uclamp_rq_dec/inc_id() when the cgroup uclamp values are updated, which would
> end up with the flag set but not cleared in this path.
Yep, that's the problematic path.
> >
> > 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>
> > ---
>
> With the commit message fixed.
Ack, this commit message is a mess, I'll rewrite.
> Reviewed-by: Qais Yousef <qais.yousef@arm.com>
Thanks!
Quentin
prev parent reply other threads:[~2021-06-10 10:27 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
2021-06-10 10:00 ` Qais Yousef
2021-06-10 10:27 ` Quentin Perret [this message]
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