linux-kernel - Re: [PATCH 04/40] sched: implement __set_cpus

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Date:	Wed, 20 Jan 2010 09:59:00 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	torvalds@...ux-foundation.org, mingo@...e.hu, awalls@...ix.net,
	linux-kernel@...r.kernel.org, jeff@...zik.org,
	akpm@...ux-foundation.org, jens.axboe@...cle.com,
	rusty@...tcorp.com.au, cl@...ux-foundation.org,
	dhowells@...hat.com, arjan@...ux.intel.com, avi@...hat.com,
	johannes@...solutions.net, andi@...stfloor.org,
	Mike Galbraith <efault@....de>
Subject: Re: [PATCH 04/40] sched: implement __set_cpus_allowed()

On Wed, 2010-01-20 at 18:00 +0900, Tejun Heo wrote:
> Hello,
> 
> On 01/20/2010 05:50 PM, Peter Zijlstra wrote:
> > OK, so maybe I'm confused, but in general the workqueue thing needs to
> > ensure work affinity, right? So why can we move the rescue thread while
> > its processing another CPU's works?
> 
> It doesn't get moved directly.  The CPU requests rescuer and rescuer
> will move itself to the CPU when it becomes idle.  We can of course
> make the rescuer wake up some other thread and then go to sleep and
> the other thread can kthread_bind() the rescuer to the dying CPU but
> that exactly is what the set_cpus_allowed_ptr() does.

Ah, ok I thought it was all mitigated through the management thread.

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