linux-kernel - Re: [patch 06/19] sched/mmcid: Prevent pointless work in mm_update_cpus

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Message-ID: <87y0p9zo9y.ffs@tglx>
Date: Fri, 17 Oct 2025 14:49:29 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: Peter Zijlstra <peterz@...radead.org>
Cc: LKML <linux-kernel@...r.kernel.org>, Gabriele Monaco
 <gmonaco@...hat.com>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Michael Jeanson <mjeanson@...icios.com>, Jens Axboe <axboe@...nel.dk>,
 "Paul E. McKenney" <paulmck@...nel.org>, "Gautham R. Shenoy"
 <gautham.shenoy@....com>, Florian Weimer <fweimer@...hat.com>, Tim Chen
 <tim.c.chen@...el.com>, TCMalloc Team <tcmalloc-eng@...gle.com>
Subject: Re: [patch 06/19] sched/mmcid: Prevent pointless work in
 mm_update_cpus_allowed()

On Fri, Oct 17 2025 at 13:12, Peter Zijlstra wrote:
> On Wed, Oct 15, 2025 at 07:29:34PM +0200, Thomas Gleixner wrote:
>
>> +	if (!mm || READ_ONCE(mm->mm_cid.nr_cpus_allowed) == nr_cpu_ids)
>>  		return;
>
> FWIW this doesn't work on architectures that change their
> cpu_possible_mask around (eg. Power).

No. Power does not change it after boot either. Half of the kernel would
explode if that'd be the case.

Thanks,

        tglx