linux-kernel - Re: [PATCH v3 1/3] sched/fair: Move checking for nohz cpus after time check

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Message-ID: <20260108124443.GA2490257@noisy.programming.kicks-ass.net>
Date: Thu, 8 Jan 2026 13:44:43 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Shrikanth Hegde <sshegde@...ux.ibm.com>
Cc: mingo@...nel.org, vincent.guittot@...aro.org,
	linux-kernel@...r.kernel.org, kprateek.nayak@....com,
	juri.lelli@...hat.com, vschneid@...hat.com, tglx@...utronix.de,
	dietmar.eggemann@....com, anna-maria@...utronix.de,
	frederic@...nel.org, wangyang.guo@...el.com
Subject: Re: [PATCH v3 1/3] sched/fair: Move checking for nohz cpus after
 time check

On Wed, Jan 07, 2026 at 12:21:23PM +0530, Shrikanth Hegde wrote:
> NOHZ idle load balancer is kicked off only after time check. So move
> the atomic read after the time check to access it only when needed.
> 
> When there are no idle CPUs(100% busy), even if the flag gets set to
> NOHZ_STATS_KICK | NOHZ_NEXT_KICK, find_new_ilb will fail and
> there will be no NOHZ idle balance. The current behaviour is retained.
> 
> Note: This patch doesn't solve any cacheline overheads. No improvement
> in performance apart from saving a few cycles of atomic_read.

Note that atomic_read() == READ_ONCE() is just a regular load, but sure.