linux-kernel - Re: [PATCH 2/2] workqueue: Fix affinity of kworkers attached during late hotplug

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Message-ID: <20201211125101.GX2414@hirez.programming.kicks-ass.net>
Date:   Fri, 11 Dec 2020 13:51:01 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Vincent Donnefort <vincent.donnefort@....com>
Cc:     Valentin Schneider <valentin.schneider@....com>,
        linux-kernel@...r.kernel.org, Qian Cai <cai@...hat.com>,
        tglx@...utronix.de, mingo@...nel.org, bigeasy@...utronix.de,
        qais.yousef@....com, swood@...hat.com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, tj@...nel.org, ouwen210@...mail.com
Subject: Re: [PATCH 2/2] workqueue: Fix affinity of kworkers attached during
 late hotplug

On Fri, Dec 11, 2020 at 11:39:21AM +0000, Vincent Donnefort wrote:
> On Thu, Dec 10, 2020 at 04:38:30PM +0000, Valentin Schneider wrote:
> > +	if (pool->flags & POOL_DISASSOCIATED) {
> >  		worker->flags |= WORKER_UNBOUND;
> > +		set_cpus_allowed_ptr(worker->task, cpu_active_mask);
> > +	} else {
> > +		/*
> > +		 * set_cpus_allowed_ptr() will fail if the cpumask doesn't have any
> > +		 * online CPUs. It'll be re-applied when any of the CPUs come up.
> > +		 */
> 
> Does this comment still stand ? IIUC, we should always be in the
> POOL_DISASSOCIATED case if the CPU from cpumask is offline. Unless a
> pool->attrs->cpumask can have several CPUs. In that case maybe we should check
> for the cpu_active_mask here too ?

IIUC it can be a numa mask, and would still be valid in that case.

> > +		set_cpus_allowed_ptr(worker->task, pool->attrs->cpumask);
> > +	}