From: Peter Zijlstra <peterz@infradead.org>
To: Qais Yousef <qyousef@layalina.io>
Cc: Christian Loehle <christian.loehle@arm.com>,
Ingo Molnar <mingo@kernel.org>,
Vincent Guittot <vincent.guittot@linaro.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Steven Rostedt <rostedt@goodmis.org>,
John Stultz <jstultz@google.com>,
linux-kernel@vger.kernel.org, Wei Wang <wvw@google.com>
Subject: Re: [PATCH v4 1/2] sched/uclamp: Fix race condition leading to imbalanced uclamp_rq
Date: Fri, 30 Oct 2026 13:15:18 +0100 [thread overview]
Message-ID: <20261030121518.GE1813469@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <20261030112825.z7k57twgua27p2vu@airbuntu>
On Fri, Oct 30, 2026 at 11:28:25AM +0000, Qais Yousef wrote:
> Peter/Vincent, what do you think? It seems we have a schrodenger task that is
> both enqueued and dequeued simultaneously in these throttling paths. Shouldn't
> this be fixed? If yes, any thoughts on the right approach? Should we throttle
> if there are no other tasks on the rq too? I didn't realize the semantics are
> that strong for enforcing the quota.
Urgh, nothing is ever straight forward is it ...
Bah, so this is because the core does uclamp (for classes that have it
on) but then the class does the throttle without going through the core
{en,de}queue.
Does it make sense to have throttle_Cfs_rq_work() and tg_unthrottle_up()
do uclamp_rq_{dec,inc}() respectively, along with the
{de,en}queue_task_fair() they're already doing?
next prev parent reply other threads:[~2026-10-30 12:15 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-29 13:13 [PATCH v4 0/2] Fix uclamp race against non atomic static key enable Qais Yousef
2026-10-29 13:13 ` [PATCH v4 1/2] sched/uclamp: Fix race condition leading to imbalanced uclamp_rq Qais Yousef
2026-10-29 15:58 ` Christian Loehle
2026-10-29 23:43 ` Qais Yousef
2026-10-30 10:50 ` Christian Loehle
2026-10-30 11:28 ` Qais Yousef
2026-10-30 12:15 ` Peter Zijlstra [this message]
2026-10-30 12:41 ` Qais Yousef
2026-10-30 13:21 ` Christian Loehle
2026-10-30 14:13 ` Peter Zijlstra
2026-10-29 13:13 ` [PATCH v4 2/2] sched/uclamp: Use wrappers instead of open coding UCLAMP_FLAG_IDLE Qais Yousef
2026-10-30 14:57 ` Kayra Cizmeci
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