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Subject: Re: [PATCH 2/4] sched: implement __set_cpus_allowed()
From: Peter Zijlstra <peterz@infradead.org>
To: Tejun Heo <tj@kernel.org>
Cc: mingo@elte.hu, linux-kernel@vger.kernel.org,
       Rusty Russell <rusty@rustcorp.com.au>, Mike Galbraith <efault@gmx.de>
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Date: Mon, 31 May 2010 12:46:36 +0200
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On Mon, 2010-05-31 at 12:19 +0200, Tejun Heo wrote:
> Hello,
> 
> On 05/31/2010 12:15 PM, Peter Zijlstra wrote:
> > On Mon, 2010-05-31 at 12:06 +0200, Tejun Heo wrote:
> >>  I meant CPU_ONLINE not CPU_UP_PREPARE.  So,
> >> we can mark a cpu active before other CPU_ONLINE callbacks are run.
> > 
> > OK, that should work.
> 
> The only remaining problemw is PF_THREAD_BOUND.  It needs to be set
> for wq workers (including rescuers).  Would it be okay to add an
> interface which only ignores PF_THREAD_BOUND?

So workers _are_ thread bound and don't migrate, so for those I don't
see the problem, that is of course until we have to break affinity when
their CPU goes down, at which point we should clear PF_THREAD_BOUND I
think.

For the rescue thread, why not set PF_THREAD_BOUND when its running
worklets and clear it when done? That way we get extra checking that
people won't migrate it when its not allowed.

Does that work, or did I miss something?