linux-kernel - Re: [PATCH 3/5] sched: Change rcu_dereference_check_sched

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Message-ID: <20251128105723.GZ4067720@noisy.programming.kicks-ass.net>
Date: Fri, 28 Nov 2025 11:57:23 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: mingo@...nel.org, vincent.guittot@...aro.org
Cc: linux-kernel@...r.kernel.org, juri.lelli@...hat.com,
	dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
	mgorman@...e.de, vschneid@...hat.com, tj@...nel.org,
	void@...ifault.com, arighi@...dia.com, changwoo@...lia.com,
	sched-ext@...ts.linux.dev
Subject: Re: [PATCH 3/5] sched: Change rcu_dereference_check_sched_domain()
 to rcu-sched

On Thu, Nov 27, 2025 at 04:39:46PM +0100, Peter Zijlstra wrote:
> By changing rcu_dereference_check_sched_domain() to use
> rcu_dereference_sched_check() it also considers preempt_disable() to
> be equivalent to rcu_read_lock().
> 
> Since rcu fully implies rcu_sched this has absolutely no change in
> behaviour, but it does allow removing a bunch of otherwise redundant
> rcu_read_lock() noise.

This goes sideways with NUMABALANCING=y, it needs a little more. I'll
have a poke.