linux-kernel - Re: [PATCH -v2 12/17] sched,rt: Use cpumask_any*

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Message-ID: <20201007072258.GA2628@hirez.programming.kicks-ass.net>
Date:   Wed, 7 Oct 2020 09:22:58 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Qais Yousef <qais.yousef@....com>
Cc:     tglx@...utronix.de, mingo@...nel.org, linux-kernel@...r.kernel.org,
        bigeasy@...utronix.de, swood@...hat.com,
        valentin.schneider@....com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, vincent.donnefort@....com, tj@...nel.org
Subject: Re: [PATCH -v2 12/17] sched,rt: Use cpumask_any*_distribute()

On Tue, Oct 06, 2020 at 04:55:27PM +0100, Qais Yousef wrote:
> > +int cpumask_any_distribute(const struct cpumask *srcp)
> > +{
> > +	int next, prev;
> > +
> > +	/* NOTE: our first selection will skip 0. */
> > +	prev = __this_cpu_read(distribute_cpu_mask_prev);
> 
> We had a discussion then that __this_cpu*() variant assumes preemption being
> disabled and it's safer to use this_cpu*() variant instead. Still holds true
> here?

I think we ended up with not caring. We wanted a 'random' value, we get
a 'random' value from a 'random' CPU, still works ;-)