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From: peterz@infradead.org
To: Valentin Schneider <valentin.schneider@arm.com>
Cc: mingo@kernel.org, vincent.guittot@linaro.org, tglx@linutronix.de,
	linux-kernel@vger.kernel.org, dietmar.eggemann@arm.com,
	rostedt@goodmis.org, bristot@redhat.com, swood@redhat.com,
	Vincent Donnefort <Vincent.Donnefort@arm.com>
Subject: Re: [PATCH 2/2] sched/hotplug: Ensure only per-cpu kthreads run during hotplug
Date: Fri, 11 Sep 2020 14:29:22 +0200	[thread overview]
Message-ID: <20200911122922.GJ1362448@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <jhjr1r85wye.mognet@arm.com>

On Fri, Sep 11, 2020 at 01:17:45PM +0100, Valentin Schneider wrote:

> > @@ -6968,6 +7064,8 @@ int sched_cpu_deactivate(unsigned int cp
> >        */
> >       synchronize_rcu();
> >
> > +	balance_push_set(cpu, true);
> > +
> 
> IIUC this is going to make every subsequent finish_lock_switch()
> migrate the switched-to task if it isn't a pcpu kthread. So this is going
> to lead to a dance of
> 
> switch_to(<task0>) -> switch_to(<stopper>) -> switch_to(<task1>) -> switch_to(<stopper>) ...
> 
> Wouldn't it be better to batch all those in a migrate_tasks() sibling that
> skips pcpu kthreads?

That's 'difficult', this is hotplug, performance is not a consideration.

Basically we don't have an iterator for the runqueues, so finding these
tasks is hard.

  reply	other threads:[~2020-09-11 17:46 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-11  8:17 [PATCH 0/2] sched: migrate_disable() preparations Peter Zijlstra
2020-09-11  8:17 ` [PATCH 1/2] sched: Fix balance_callback() Peter Zijlstra
2020-09-11 12:17   ` Valentin Schneider
2020-09-11 12:25     ` peterz
2020-09-11 13:27       ` Valentin Schneider
2020-09-11  8:17 ` [PATCH 2/2] sched/hotplug: Ensure only per-cpu kthreads run during hotplug Peter Zijlstra
2020-09-11 12:17   ` Valentin Schneider
2020-09-11 12:29     ` peterz [this message]
2020-09-11 13:48       ` Valentin Schneider
2020-09-16 10:18   ` Sebastian Andrzej Siewior
2020-09-16 12:10     ` peterz
2020-09-16 13:58       ` Sebastian Andrzej Siewior
2020-09-16 14:07         ` peterz

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