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

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Date:	Tue, 19 Jan 2010 10:07:46 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Peter Zijlstra <peterz@...radead.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()

Hello,

On 01/18/2010 08:41 PM, Peter Zijlstra wrote:
> On Mon, 2010-01-18 at 20:22 +0900, Tejun Heo wrote:
>> These part haven't changed at all since the last posting so if you
>> disliked it before it's kind of expected you still do so.
> 
> You could at least have augmented the changelog with the why.. my memory
> thinks it had to so with that silly move back on up story.
>
>> Anyways, I'm not the greatest fan of this patch either.  Let's see how
>> the whole series fares out first and try to make this better.  What do
>> you think about doing what's described in the NOTE?
> 
> I'm still not sure we need any of this. For new threads we have the
> stopped state and kthread_bind() should work in its current form (except
> you need patch 1 in your series when you're creating new threads when
> the cpu is currently going down).

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().

Thanks.

-- 
tejun
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