linux-kernel - Re: [PATCH RFC] select_idle

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Message-ID: <20160409173034.GA85074@clm-mbp.thefacebook.com>
Date:	Sat, 9 Apr 2016 13:30:34 -0400
From:	Chris Mason <clm@...com>
To:	Mike Galbraith <mgalbraith@...e.de>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Matt Fleming <matt@...eblueprint.co.uk>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC] select_idle_sibling experiments

On Wed, Apr 06, 2016 at 09:27:24AM +0200, Mike Galbraith wrote:
> > On Tue, 2016-04-05 at 14:08 -0400, Chris Mason wrote:
> 
> > Now, on to the patch.  I pushed some code around and narrowed the
> > problem down to select_idle_sibling()   We have cores going into and out
> > of idle fast enough that even this cut our latencies in half:
> 
> Are you using NO_HZ?  If so, you may want to try the attached.

[ nohz throttling patch ]

I tested the nohz throttle two different ways, first with schbench's
pipe simulation, it's easily 8% faster with messages bouncing between
cpus.

In production it's hard to pick a single number because the benchmarks
produce latency curves as the workload scales up in RPS.  The benefits
range from 2-9% depending on the metric.  It's a nice win, and I'd love to
see it go in.

-chris