linux-kernel - Re: [PATCH 2/2] sched/fair: Always propagate runnable_load

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Date:   Thu, 4 May 2017 10:19:46 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Tejun Heo <tj@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Mike Galbraith <efault@....de>, Paul Turner <pjt@...gle.com>,
        Chris Mason <clm@...com>, kernel-team@...com
Subject: Re: [PATCH 2/2] sched/fair: Always propagate runnable_load_avg

On 3 May 2017 at 23:49, Tejun Heo <tj@...nel.org> wrote:
> On Wed, May 03, 2017 at 03:09:38PM +0200, Peter Zijlstra wrote:
>> On Wed, May 03, 2017 at 12:37:37PM +0200, Vincent Guittot wrote:
>> > On 3 May 2017 at 11:37, Peter Zijlstra <peterz@...radead.org> wrote:
>>
>> > > Of course, it could be I overlooked something, in which case, please
>> > > tell :-)
>> >
>> > That's mainly based on the regression i see on my platform. I haven't
>> > find the root cause of the regression but it's there which means that
>> > using group_entity's load_avg to propagate child cfs_rq
>> > runnable_load_avg breaks something
>>
>> (as mentioned on IRC)
>>
>> Right.. so looking through the code, (group) se->avg.load_avg is used in
>> effective_load() (and thereby wake_affine()) and update_cfs_rq_h_load()
>> (and therefore task_h_load()).
>>
>> So changing it will affect those two functions, which could well lead to
>> your regression.
>
> Ah, okay, that makes sense.  I'll try to finish the patch to propagate
> runnable without affecting group se->avg.load_avg.  BTW, Vincent, did
> you boost the weight of the cgroup when you were testing?  If you put

I use default group weight

> schbench inside a cgroup and have some base load, it is actually
> expected to show worse latency.  You need to give higher weight to the
> cgroup matching the number of active threads (to be accruate, scaled
> by duty cycle but shouldn't matter too much in practice).

I don't have to change anything cgroup weight with mainline to get
good number which means that the base load which is quite close to
null, is probably not the problem

>
> Thanks.
>
> --
> tejun