From: Qais Yousef <qyousef@layalina.io>
To: Christian Loehle <christian.loehle@arm.com>,
Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>,
John Stultz <jstultz@google.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Qais Yousef <qyousef@google.com>,
LKML <linux-kernel@vger.kernel.org>,
Hongyan Xia <hongyan.xia2@arm.com>,
Ingo Molnar <mingo@kernel.org>, Wei Wang <wvw@google.com>,
Patrick Bellasi <patrick.bellasi@arm.com>,
Dietmar Eggemann <dietmar.eggemann@arm.com>
Subject: Re: Uclamp races due to non-atomic static_branch_likely updates
Date: Sat, 24 Oct 2026 12:34:41 +0100 [thread overview]
Message-ID: <fca73fed-da43-485e-8a7c-1ddef9515f16@layalina.io> (raw)
In-Reply-To: <005ed941-2737-413c-8436-a9de227d01ca@arm.com>
On 10/22/26 14:18, Christian Loehle wrote:
> So I guess the clear-when-entering-idle taper is sufficient for UCLAMP_MIN.
> UCLAMP_MAX (where on a sufficiently low setting we may just never have that
> idle entry to clear) we expect to be fine because it's max-aggregated, i.e.
> a second task would let us escape the low stale UCLAMP_MAX on the rq?
I am not sure I got you. We should eventually go to idle and reset the
settings. But you made me realize the unconditional reset could break
the saved uclamp max at idle :-/ I could either unconditionally set both
uclamp_{min, max} to 0, or just have some conditions to do_once when
uclamp_is_used(). I prefer setting to 0, but this is a change in behavior.
> I guess we could reevaluate the static branch at every tick too if we really
> care?
It seems you are worried about the temporary corrupt state after boot
(first uclamp use more precisely) where there's no idle time, right? I
think we can live with that.
next prev parent reply other threads:[~2026-10-24 11:34 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-20 18:53 John Stultz
2026-10-20 19:29 ` Steven Rostedt
2026-10-21 11:38 ` Peter Zijlstra
2026-10-21 13:20 ` Qais Yousef
2026-10-21 13:29 ` Peter Zijlstra
2026-10-21 14:02 ` Qais Yousef
2026-10-22 13:18 ` Christian Loehle
2026-10-24 11:34 ` Qais Yousef [this message]
2026-10-21 13:21 ` Steven Rostedt
2026-10-21 13:34 ` Peter Zijlstra
2026-10-21 13:59 ` Steven Rostedt
2026-10-21 17:56 ` John Stultz
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