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Date:   Fri, 11 Dec 2020 13:16:38 +0000
From:   Vincent Donnefort <vincent.donnefort@arm.com>
To:     Valentin Schneider <valentin.schneider@arm.com>
Cc:     linux-kernel@vger.kernel.org, Qian Cai <cai@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>, tglx@linutronix.de,
        mingo@kernel.org, bigeasy@linutronix.de, qais.yousef@arm.com,
        swood@redhat.com, juri.lelli@redhat.com,
        vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
        rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de,
        bristot@redhat.com, tj@kernel.org, ouwen210@hotmail.com
Subject: Re: [PATCH 2/2] workqueue: Fix affinity of kworkers attached during
 late hotplug
Message-ID: <20201211131638.GA142813@e120877-lin.cambridge.arm.com>
References: <20201210163830.21514-1-valentin.schneider@arm.com>
 <20201210163830.21514-3-valentin.schneider@arm.com>
 <20201211113920.GA75974@e120877-lin.cambridge.arm.com>
 <jhjo8j0tsia.mognet@arm.com>
 <jhjmtyktri8.mognet@arm.com>
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On Fri, Dec 11, 2020 at 01:13:35PM +0000, Valentin Schneider wrote:
> On 11/12/20 12:51, Valentin Schneider wrote:
> >> In that case maybe we should check for the cpu_active_mask here too ?
> >
> > Looking at it again, I think we might need to.
> >
> > IIUC you can end up with pools bound to a single NUMA node (?). In that
> > case, say the last CPU of a node is going down, then:
> >
> >   workqueue_offline_cpu()
> >     wq_update_unbound_numa()
> >       alloc_unbound_pwq()
> >         get_unbound_pool()
> >
> > would still pick that node, because it doesn't look at the online / active
> > mask. And at this point, we would affine the
> > kworkers to that node, and we're back to having kworkers enqueued on a
> > (!active, online) CPU that is going down...
> 
> Assuming a node covers at least 2 CPUs, that can't actually happen per
> is_cpu_allowed().

Yes indeed, my bad, no problem here.