linux-kernel - Re: [PATCH -v3 3/9] sched: Dont run cpu-online with balance

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Message-ID: <jhjft2umlte.mognet@arm.com>
Date:   Thu, 21 Jan 2021 14:00:45 +0000
From:   Valentin Schneider <valentin.schneider@....com>
To:     Peter Zijlstra <peterz@...radead.org>, mingo@...nel.org,
        tglx@...utronix.de
Cc:     linux-kernel@...r.kernel.org, jiangshanlai@...il.com,
        cai@...hat.com, vincent.donnefort@....com, decui@...rosoft.com,
        paulmck@...nel.org, vincent.guittot@...aro.org,
        rostedt@...dmis.org, tj@...nel.org, peterz@...radead.org
Subject: Re: [PATCH -v3 3/9] sched: Dont run cpu-online with balance_push() enabled

On 21/01/21 11:17, Peter Zijlstra wrote:
> @@ -7608,6 +7614,12 @@ int sched_cpu_dying(unsigned int cpu)
>       }
>       rq_unlock_irqrestore(rq, &rf);
>
> +	/*
> +	 * Should really be after we clear cpu_online(), but we're in
> +	 * stop_machine(), so it all works.
> +	 */

I believe you noted yourself in some earlier version that this *is* running
with cpu_online(cpu) == false, __cpu_disable() being invoked before the
_DYING .teardown callbacks are run.

> +	balance_push_set(cpu, false);
> +
>       calc_load_migrate(rq);
>       update_max_interval();
>       nohz_balance_exit_idle(rq);