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

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Message-ID: <20160502154725.ckiewczbdubudyc7@floor.masoncoding.com>
Date:	Mon, 2 May 2016 11:47:25 -0400
From:	Chris Mason <clm@...com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Mike Galbraith <mgalbraith@...e.de>,
	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 Mon, May 02, 2016 at 04:58:17PM +0200, Peter Zijlstra wrote:
> On Mon, May 02, 2016 at 04:50:04PM +0200, Mike Galbraith wrote:
> > Oh btw, did you know single socket boxen have no sd_busy?  That doesn't
> > look right.
> 
> I suspected; didn't bother looking at yet. The 'problem' is that the LLC
> domain is the top-most, so it doesn't have a parent domain. I'm sure we
> can come up with something if we can get this all working right.
> 
> And yes, I can get gains on various workloads with various options, I
> can even break all workloads, but I've so far completely failed on
> getting a win for everyone :/

Adding in the task_hot() check to decide if scanning idle was a good
idea ended up being really important.  I'm happy to try a few variations
here as well, do you have a more recent patch?

-chris