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

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Date:	Thu, 10 Jul 2014 16:03:51 +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 10 July 2014 13:18, Peter Zijlstra <peterz@...radead.org> wrote:
> On Mon, Jun 30, 2014 at 06:05:39PM +0200, Vincent Guittot wrote:
>> +             /*
>> +              * If the CPUs share their cache and the src_cpu's capacity is
>> +              * reduced because of other sched_class or IRQs, we trig an
>> +              * active balance to move the task
>> +              */
>> +             if ((sd->flags & SD_SHARE_PKG_RESOURCES)
>> +              && ((capacity_orig_of(src_cpu) * 100) > (capacity_of(src_cpu) *
>> +                                                     sd->imbalance_pct)))
>>                       return 1;
>
> Why is this tied to shared caches?

It's just to limit the change of the policy to a level that can have
benefit without performance regression. I'm not sure that we can do
that at any level without risk
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