Re: [PATCH 2/2] sched/fair: Always propagate runnable_load_avg

From: Peter Zijlstra
Date: Mon May 01 2017 - 11:56:31 EST

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.