linux-kernel - Re: [PATCH v4] sched/core: Use zero length to reset cpumasks in sched

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Message-ID: <20231004135236.GB19999@noisy.programming.kicks-ass.net>
Date:   Wed, 4 Oct 2023 15:52:36 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Florian Weimer <fweimer@...hat.com>
Cc:     Waiman Long <longman@...hat.com>, 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 v4] sched/core: Use zero length to reset cpumasks in
 sched_setaffinity()

On Wed, Oct 04, 2023 at 02:34:15PM +0200, Florian Weimer wrote:
> * Peter Zijlstra:
> 
> > Subject: sched: Add CPU_FILL()
> >
> > Add the CPU_FILL() macros to easily create an all-set cpumask.
> >
> > FreeBSD also provides this macro with this semantic.
> >
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> 
> My main concer is that obtaining the size of the mask, or at least an
> approximiation is not exactly easy.  If there's an expectation that
> applications reset the mask more often than they do today (I don't have
> the full context here), then we'd some decent interface to get the
> approriate size.

Isn't sysconf(_SC_NPROCESSORS_CONF) the right number ?