linux-kernel - Re: [RFC PATCH 03/19] sched/fair: Use rq->nohz_tick_stopped in update_nohz

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Message-ID: <7f8db11e-35f5-430d-93a7-35c0e9ec8dc7@amd.com>
Date: Thu, 25 Sep 2025 07:18:48 +0530
From: K Prateek Nayak <kprateek.nayak@....com>
To: Shrikanth Hegde <sshegde@...ux.ibm.com>
CC: 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>, "Gautham R.
 Shenoy" <gautham.shenoy@....com>, Swapnil Sapkal <swapnil.sapkal@....com>,
	Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>, "Juri
 Lelli" <juri.lelli@...hat.com>, Vincent Guittot <vincent.guittot@...aro.org>,
	Anna-Maria Behnsen <anna-maria@...utronix.de>, Frederic Weisbecker
	<frederic@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 03/19] sched/fair: Use rq->nohz_tick_stopped in
 update_nohz_stats()

Hello Shrikanth,

On 9/25/2025 1:47 AM, Shrikanth Hegde wrote:
> 
> 
> On 9/4/25 9:44 AM, K Prateek Nayak wrote:
>> "rq->nohz_tick_stopped" always follows the state of CPU on
>> "nohz.idle_cpus_mask". Use the local rq indicator instead of checking
>> for the CPU on the "idle_cpus_mask".
>>
>> Use READ_ONCE() and WRITE_ONCE() for "rq->nohz_tick_stopped" to ensure
>> update_nohz_stats() always sees the latest value.
>>
> 
> Is this ever called by remote CPU? If not, is READ/WRITE ONCE is necessary?

Patch 6 looks at "rq->nohz_tick_stopped" to correct the idle mask in the
sched domain rebuild path which is done from a remote CPU.

-- 
Thanks and Regards,
Prateek