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

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Message-ID: <20170503130938.44rftdivrlpz4p3b@hirez.programming.kicks-ass.net>
Date:   Wed, 3 May 2017 15:09:38 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Tejun Heo <tj@...nel.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 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.