linux-kernel - Re: [RFC][PATCH 12/13] stop

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Message-ID: <20150623172416.GA27505@redhat.com>
Date:	Tue, 23 Jun 2015 19:24:16 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	paulmck@...ux.vnet.ibm.com, tj@...nel.org, mingo@...hat.com,
	linux-kernel@...r.kernel.org, der.herr@...r.at, dave@...olabs.net,
	riel@...hat.com, viro@...IV.linux.org.uk,
	torvalds@...ux-foundation.org
Subject: Re: [RFC][PATCH 12/13] stop_machine: Remove lglock

On 06/23, Oleg Nesterov wrote:
>
>
> It would be nice to remove stop_cpus_mutex, it actually protects
> stop_cpus_work... Then probably stop_two_cpus() can just use
> stop_cpus(). We could simply make stop_cpus_mutex per-cpu too,
> but this doesn't look nice.

IOW. Suppose we add ->work_mutex into struct cpu_stopper. Btw,
I think we should move all per-cpu variables there...

Now,

	lock_stop_cpus_works(cpumask)
	{
		for_each_cpu(cpu, cpumask)
			mutex_lock(per_cpu(cpu_stopper_task, cpu).work_mutex);
	}

	unlock_stop_cpus_works(cpumask)
	{
		for_each_cpu(cpu, cpumask)
			mutex_lock(...);
	}

which should be used instead of stop_cpus_mutex. After this change
stop_two_cpus() can just use stop_cpus().


Off-topic. Can't we make __stop_machine() static? The only caller,
_cpu_down() can safely call stop_machine(), get_online_cpus() is
fine under cpu_hotplug_begin().

Oleg.

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