linux-kernel - Re: [PATCH 0/6] Optimize the cpu hotplug locking -v2

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Date:	Thu, 10 Oct 2013 19:39:37 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...nel.org>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/6] Optimize the cpu hotplug locking -v2

On 10/10, Peter Zijlstra wrote:
>
> The freeze suggestion from Ingo would actually work because we freeze
> tasks at known good points

Not really known/good, we have more and more freezable_schedule's.
But probably this is fine, nobody should do this under get_online_cpus().

> (userspace and kthread_freeze() points) where
> we know they're not fiddling with per-cpu state.

We should also take care of PF_NOFREEZE kthreads.

Oleg.

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