linux-kernel - Re: [PATCH v3 08/12] sched: move cfs task on a CPU with higher capacity

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Message-ID: <CAKfTPtCoBpt5aOe9z2LjvOZBsiNnnC5wCFRyyOS_RPoqshJCxw@mail.gmail.com>
Date:	Tue, 15 Jul 2014 11:21:24 +0200
From:	Vincent Guittot <vincent.guittot@...aro.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...nel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	LAK <linux-arm-kernel@...ts.infradead.org>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Morten Rasmussen <Morten.Rasmussen@....com>,
	Mike Galbraith <efault@....de>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>
Subject: Re: [PATCH v3 08/12] sched: move cfs task on a CPU with higher capacity

On 14 July 2014 15:51, Peter Zijlstra <peterz@...radead.org> wrote:
> On Fri, Jul 11, 2014 at 05:17:44PM +0200, Vincent Guittot wrote:
>> > In any case, its feels rather arbitrary to me. What about machines where
>> > there's no cache sharing at all (the traditional SMP systems). This
>> > thing you're trying to do still seems to make sense there.
>>
>> ok, I thought that traditional SMP systems have this flag set at core
>> level.
>
> Yeah, with 1 core, so its effectively disabled.
>
>> I mean ARM platforms have the flag for CPUs in the same cluster
>> (which include current ARM SMP system) and the corei7 of my laptop has
>> the flag at the cores level.
>
> So I can see 'small' parts reducing shared caches in order to improve
> idle performance.
>
> The point being that LLC seems a somewhat arbitrary measure for this.
>
> Can we try and see what happens if you remove the limit. Its always best
> to try the simpler things first and only make it more complex if we have
> to.

ok. i will remove the condition in the next version
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