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Message-ID: <20250716133631.GZ905792@noisy.programming.kicks-ass.net>
Date: Wed, 16 Jul 2025 15:36:31 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Andrea Righi <arighi@...dia.com>
Cc: Breno Leitao <leitao@...ian.org>, Tejun Heo <tj@...nel.org>,
	David Vernet <void@...ifault.com>,
	Changwoo Min <changwoo@...lia.com>, Ingo Molnar <mingo@...hat.com>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>, sched-ext@...ts.linux.dev,
	linux-kernel@...r.kernel.org, kernel-team@...a.com,
	jake@...lion.co.uk
Subject: Re: [PATCH] sched/ext: Suppress warning in __this_cpu_write() by
 disabling preemption

On Wed, Jul 16, 2025 at 03:15:12PM +0200, Andrea Righi wrote:

> The idea is to track the scx callbacks that are invoked with a rq lock held
> and, in those cases, store the locked rq. However, some callbacks may also
> be invoked from an unlocked context, where no rq is locked and in this case
> rq should be NULL.
> 
> In the latter case, it's acceptable for preemption to remain enabled, but
> we still want to explicitly set locked_rq = NULL. If during the execution
> of the callback we jump on another CPU, it'd still be in an unlocked state,
> so it's locked_rq is still NULL.

Right; but doing superfluous NULL stores seems pointless. So better to
avoid the store entirely, rather than making it more expensive and no
less pointless, right?

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