linux-kernel - Re: [PATCH v2 11/11] sched: replace capacity by activity

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Date:	Thu, 29 May 2014 21:51:12 +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>
Subject: Re: [PATCH v2 11/11] sched: replace capacity by activity

On 29 May 2014 15:55, Peter Zijlstra <peterz@...radead.org> wrote:
> On Fri, May 23, 2014 at 05:53:05PM +0200, Vincent Guittot wrote:
>> The scheduler tries to compute how many tasks a group of CPUs can handle by
>> assuming that a task's load is SCHED_LOAD_SCALE and a CPU capacity is
>> SCHED_POWER_SCALE.
>> We can now have a better idea of the utilization of a group fo CPUs thanks to
>> group_actitvity and deduct how many capacity is still available.
>>
>> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
>> ---
>
> Right, so as Preeti already mentioned, this wrecks SMT. It also seems to
> loose the aggressive spread, where we want to run 1 task on each 'core'
> before we start 'balancing'.
>
> So I think we should be able to fix this by setting PREFER_SIBLING on
> the SMT domain, that way we'll get single tasks running on each SMT
> domain before filling them up until capacity.
>
> Now, its been a while since I looked at PREFER_SIBLING, and I've not yet
> looked at what your patch does to it, but it seems to me that that is
> the first direction we should look for an answer to this.

OK, i'm going to look more deeply in PREFER_SIBLING too
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