linux-kernel - Re: [PATCH v3 09/12] Revert "sched: Put rq's sched_avg under CONFIG_FAIR_GROUP

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Date:	Tue, 15 Jul 2014 11:20:21 +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 09/12] Revert "sched: Put rq's sched_avg under CONFIG_FAIR_GROUP_SCHED"

On 11 July 2014 22:12, Peter Zijlstra <peterz@...radead.org> wrote:
> On Fri, Jul 11, 2014 at 07:39:29PM +0200, Vincent Guittot wrote:
>> In my mind, arch_scale_cpu_freq was intend to scale the capacity of
>> the CPU according to the current dvfs operating point.
>> As it's no more use anywhere now that we have arch_scale_cpu, we could
>> probably remove it .. and see when it will become used.
>
> I probably should have written comments when I wrote that code, but it
> was meant to be used only where, as described above, we limit things.
> Ondemand and such, which will temporarily decrease freq, will ramp it up
> again at demand, and therefore lowering the capacity will skew things.
>
> You'll put less load on because its run slower, and then you'll run it
> slower because there's less load on -> cyclic FAIL.
>
>> > In that same discussion ISTR a suggestion about adding avg_running time,
>> > as opposed to the current avg_runnable. The sum of avg_running should be
>> > much more accurate, and still react correctly to migrations.
>>
>> I haven't look in details but I agree that avg_running would be much
>> more accurate than avg_runnable and should probably fit the
>> requirement. Does it means that we could re-add the avg_running (or
>> something similar) that has disappeared during the review of load avg
>> tracking patchset ?
>
> Sure, I think we killed it there because there wasn't an actual use for
> it and I'm always in favour of stripping everything to their bare bones,
> esp big and complex things.
>
> And then later, add things back once we have need for it.

Ok, i'm going to look how to add it back taking nto account current
Yuyang's rework of load_avg

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