linux-kernel - Re: [PATCH v2 2/2] sched/fair: leverage the idle state info when choosing the "idlest" cpu

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Message-ID: <alpine.LFD.2.11.1409301904150.5311@knanqh.ubzr>
Date:	Tue, 30 Sep 2014 19:15:00 -0400 (EDT)
From:	Nicolas Pitre <nicolas.pitre@...aro.org>
To:	Rik van Riel <riel@...hat.com>
cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, linaro-kernel@...ts.linaro.org
Subject: Re: [PATCH v2 2/2] sched/fair: leverage the idle state info when
 choosing the "idlest" cpu

On Tue, 30 Sep 2014, Rik van Riel wrote:

> On 09/04/2014 11:32 AM, Nicolas Pitre wrote:
> > The code in find_idlest_cpu() looks for the CPU with the smallest
> > load. However, if multiple CPUs are idle, the first idle CPU is
> > selected irrespective of the depth of its idle state.
> > 
> > Among the idle CPUs we should pick the one with with the shallowest
> > idle state, or the latest to have gone idle if all idle CPUs are in
> > the same state.  The later applies even when cpuidle is configured
> > out.
> > 
> > This patch doesn't cover the following issues:
> 
> The main thing it does not cover is already running tasks that
> get woken up again, since select_idle_sibling() covers everything
> except for newly forked and newly executed tasks.

True. Now that you bring this up, I remember that Peter mentioned it as 
well.

> I am looking at adding similar logic to select_idle_sibling()

OK thanks.


Nicolas
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