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From: Vincent Guittot <vincent.guittot@linaro.org>
Date: Thu, 4 May 2017 21:02:39 +0200
Message-ID: <CAKfTPtAEwFMbobPDXTShBezZhwvxkNPTMWfb3BUfiExaCaq9pg@mail.gmail.com>
Subject: Re: [PATCH 2/2] sched/fair: Always propagate runnable_load_avg
To: Tejun Heo <tj@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@redhat.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Mike Galbraith <efault@gmx.de>, Paul Turner <pjt@google.com>,
        Chris Mason <clm@fb.com>, kernel-team@fb.com
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Hi Tejun,

On 4 May 2017 at 19:43, Tejun Heo <tj@kernel.org> wrote:
> Hello,
>
> On Thu, May 04, 2017 at 10:19:46AM +0200, Vincent Guittot wrote:
>> > 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
>
> So, while that *could* be the case, it could also be the baseline
> incorrectly favoring the nested cfs_rqs over other tasks because of
> the nested runnables being inflated with blocked load avgs.  I think
> it'd be a good idea to test with matching weight to put things on the
> even ground.

In the trace i have uploaded, you will see that regressions happen
whereas there is no other runnable threads around so it's not a matter
of background activities that disturbs schbench

Thanks
Vincent

>
> Thanks.
>
> --
> tejun