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

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Message-ID: <20170501155613.plfee2hzfvt3n6j7@hirez.programming.kicks-ass.net>
Date:   Mon, 1 May 2017 17:56:13 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Tejun Heo <tj@...nel.org>
Cc:     Vincent Guittot <vincent.guittot@...aro.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 Fri, Apr 28, 2017 at 04:33:47PM -0400, Tejun Heo wrote:
> I'm attaching the debug patch.  With your change (avg instead of
> runnable_avg), the following trace shows why it's wrong.

Ah, OK. So you really want runnable_avg (and I understand why), which is
rather unfortunate, since we have everything on load_avg.

So for shares, load_avg gives a more stable number. This is important
since tg->load_avg is a global number, so computing it is expensive (and
slow). Therefore more stable numbers are good.

> The thing with cfs_rq se's load_avg is that, it isn't really used
> anywhere else AFAICS, so overriding it to the cfs_rq's
> runnable_load_avg isn't prettiest but doesn't really change anything.

You mean, consistently expressing a group's se->load.weight in terms of
runnable_load_avg? See the above.