linux-kernel - Re: [PATCH 2/2 v4] sched: Rewrite per entity runnable load average

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Date:	Fri, 1 Aug 2014 11:28:26 +0200
From:	Vincent Guittot <vincent.guittot@...aro.org>
To:	Yuyang Du <yuyang.du@...el.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	"mingo@...hat.com" <mingo@...hat.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Paul Turner <pjt@...gle.com>,
	Benjamin Segall <bsegall@...gle.com>,
	arjan.van.de.ven@...el.com, Len Brown <len.brown@...el.com>,
	rafael.j.wysocki@...el.com, alan.cox@...el.com,
	"Gross, Mark" <mark.gross@...el.com>,
	"fengguang.wu@...el.com" <fengguang.wu@...el.com>,
	Morten Rasmussen <morten.rasmussen@....com>
Subject: Re: [PATCH 2/2 v4] sched: Rewrite per entity runnable load average

On 31 July 2014 21:16, Yuyang Du <yuyang.du@...el.com> wrote:
> Hi Vincent,
>
> On Thu, Jul 31, 2014 at 11:56:13AM +0200, Vincent Guittot wrote:
>>
>> load_sum is now the average runnable time before being weighted
>
> So when weight changes, load_avg will completely use new weight. I have
> some cents:
>
> 1) Task does not change weight much, so it is practically ok
>
> 2) Group entity does change weight much, and very likely back and forth,
>    so I really think keeping the intact history will make everything
>    more predictable/stable, prevent thrashing, etc.
>
> 3) If you do the same for cfs_rq->load.weight, then we simply abandoned
>    blocked entities, and all states won't compute. So we then need to
>    maintain blocked load average again, and we just can't do cfs_rq load
>    average as a whole anymore, but must update at the granularity of an
>    entity...
>
> Anyway, it does not seem to me you really need to change load_sum, no? So
> could you please not change it?
>
>> The sum of usage_sum of the tasks that are on a rq, is used to detect
>> the overload of a rq.
>
> I think you only need usage_sum for task and rq, but not cfs_rq. Others
> are ok.

yes, only usage_sum is useful for my rework of cpu_power

>
>> Does something like the patch below to be applied of top of your patchset, seem
>> reasonable add-on?
>>
>
> If you only add running statistics, I am all good, and indeed reasonable if
> you can make good use of it. I am not at all against adding anything or
> adding running average or unweighted anything...

ok. Thanks

Vincent

>
> Thanks,
> Yuyang
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