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From: Thomas Gleixner <tglx@linutronix.de>
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To: Peter Zijlstra <peterz@infradead.org>
Cc: LKML <linux-kernel@vger.kernel.org>, Gabriele Monaco
 <gmonaco@redhat.com>, Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
 Michael Jeanson <mjeanson@efficios.com>, Jens Axboe <axboe@kernel.dk>,
 "Paul E. McKenney" <paulmck@kernel.org>, "Gautham R. Shenoy"
 <gautham.shenoy@amd.com>, Florian Weimer <fweimer@redhat.com>, Tim Chen
 <tim.c.chen@intel.com>, TCMalloc Team <tcmalloc-eng@google.com>
Subject: Re: [patch 06/19] sched/mmcid: Prevent pointless work in
 mm_update_cpus_allowed()
In-Reply-To: <20251017111223.GD4067720@noisy.programming.kicks-ass.net>
References: <20251015164952.694882104@linutronix.de>
 <20251015172834.694547089@linutronix.de>
 <20251017111223.GD4067720@noisy.programming.kicks-ass.net>
Date: Fri, 17 Oct 2025 14:49:29 +0200
Message-ID: <87y0p9zo9y.ffs@tglx>
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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