Re: [PATCH 04/40] sched: implement __set_cpus_allowed()

From: Tejun Heo
Date: Mon Jan 18 2010 - 20:02:37 EST


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().


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