Re: [patch v4 02/18] sched: select_task_rq_fair clean up

From: Alex Shi
Date: Wed Feb 13 2013 - 09:44:22 EST

On 02/12/2013 06:14 PM, Peter Zijlstra wrote:
> On Thu, 2013-01-24 at 11:06 +0800, Alex Shi wrote:
>> It is impossible to miss a task allowed cpu in a eligible group.
> I suppose your reasoning goes like: tsk->cpus_allowed is protected by
> ->pi_lock, we hold this, therefore it cannot change and
> find_idlest_group() dtrt?

> We can then state that this is due to adding proper serialization to
> tsk->cpus_allowed.
>> And since find_idlest_group only return a different group which
>> excludes old cpu, it's also impossible to find a new cpu same as old
>> cpu.
> Sounds plausible, but I'm not convinced, do we have hard serialization
> against hotplug?

Any caller of select_task_rq will check if returned dst_cpu is still
working. So there is nothing need worry about.

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