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Reply-To: "Hillf Danton" <hillf.zj@alibaba-inc.com>
From: "Hillf Danton" <hillf.zj@alibaba-inc.com>
To: "'Vincent Guittot'" <vincent.guittot@linaro.org>
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Subject: RE: [PATCH v8 03/10] sched: move cfs task on a CPU with higher capacity
Date: Tue, 04 Nov 2014 20:54:29 +0800
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> 
> On 4 November 2014 13:07, Hillf Danton <hillf.zj@alibaba-inc.com> wrote:
> >> >>   +     /*
> >> >> +        * The dst_cpu is idle and the src_cpu CPU has only 1 CFS task.
> >> >
> >> >
> >> > Why specify one task instead of not less than one?
> >>
> >> if cfs.h_nr_running = 0 (which should not occurs at that point), we
> >> don't need to do more test to check if it's worth moving the task
> >> because there is no task to move.
> >>
> > I wonder if you can please shed light on the case that
> > the dst_cpu is newly idle.
> 
> The main problem if we do the test only for newly idle case, is that
> we are not sure to move the task because we must rely on the
> wakeup/sleep sequence of other tasks on an idle CPU in order to trig
> the migration (periodic background task as an example). So we might
> never move the task whereas idle CPUs are available
> 
So no task is migrated in the newly idle case, if I understand the
above correctly.

Hillf