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Message-ID: <20231003100602.GF27267@noisy.programming.kicks-ass.net>
Date: Tue, 3 Oct 2023 12:06:02 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Waiman Long <longman@...hat.com>
Cc: Ingo Molnar <mingo@...hat.com>, Juri Lelli <juri.lelli@...hat.com>,
Vincent Guittot <vincent.guittot@...aro.org>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Steven Rostedt <rostedt@...dmis.org>,
Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
Daniel Bristot de Oliveira <bristot@...hat.com>,
Valentin Schneider <vschneid@...hat.com>,
linux-kernel@...r.kernel.org, Phil Auld <pauld@...hat.com>,
Brent Rowsell <browsell@...hat.com>,
Peter Hunt <pehunt@...hat.com>
Subject: Re: [PATCH v3] sched/core: Use empty mask to reset cpumasks in
sched_setaffinity()
On Thu, Aug 03, 2023 at 10:32:18PM -0400, Waiman Long wrote:
> Since commit 8f9ea86fdf99 ("sched: Always preserve the user requested
> cpumask"), user provided CPU affinity via sched_setaffinity(2) is
> perserved even if the task is being moved to a different cpuset. However,
> that affinity is also being inherited by any subsequently created child
> processes which may not want or be aware of that affinity.
>
> One way to solve this problem is to provide a way to back off from
> that user provided CPU affinity. This patch implements such a scheme
> by using an empty cpumask to signal a reset of the cpumasks to the
> default as allowed by the current cpuset.
So I still don't like this much, the normal state is all bits set:
$ grep allowed /proc/self/status
Cpus_allowed: ff,ffffffff
The all clear bitmask just feels weird for this.
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