linux-kernel - Re: sched: tweak select_idle_sibling to look for idle threads

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Message-ID: <1460559948.11954.41.camel@suse.de>
Date:	Wed, 13 Apr 2016 17:05:48 +0200
From:	Mike Galbraith <mgalbraith@...e.de>
To:	Chris Mason <clm@...com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Matt Fleming <matt@...eblueprint.co.uk>,
	linux-kernel@...r.kernel.org
Subject: Re: sched: tweak select_idle_sibling to look for idle threads

On Wed, 2016-04-13 at 10:36 -0400, Chris Mason wrote:
> On Wed, Apr 13, 2016 at 04:22:58PM +0200, Mike Galbraith wrote:

> > What exactly do you mean by failed affine wakeups?  Failed because
> > wake_wide() said we don't want one, or because wake_affine() said we
> > can't have one?  If the later, my thought bubble may have just burst,
> > but it still "feels" right.
> 
> I mean this number:
> 
> schedstat_inc(p, se.statistics.nr_wakeups_affine_attempts);
> 
> Is much much much higher than this number:
> 
> schedstat_inc(p, se.statistics.nr_wakeups_affine);
> 
> So, wake_affine said we can't have one.  I made a script to sum it up
> across all the threads of the webserver workload.

Hm, ok, that doesn't really tell us more than there's more to the load
than the 1:N bits that wake_wide() apparently did identify fairly well
last go, so targeting them still might help.

	-Mike