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

[Peter Zijlstra]

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?



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