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

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Date:	Tue, 19 Jan 2010 09:37:02 +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 Tue, 2010-01-19 at 10:07 +0900, Tejun Heo wrote:
> 
> It's also necessary to guarantee forward progress during CPU_DOWN.
> The problem with kthread_bind() is that it's not synchronized against
> CPU hotplug operations.  It needs outer synchronization like calling
> it directly from CPU_DOWN_PREP.  I guess it's doable but I think it
> would be better to simply share the backend implementation between
> set_cpus_allowed_ptr() and kthread_bind().

OK, so you're saying you need to migrate the rescue thread during
cpu-down. That thread is guaranteed sleeping right, if it were not it'd
not be elegible to run on our dying cpu. Hence kthread_bind() ought to
just work, no?

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