linux-kernel - Re: [PATCH 0/4] Reduce overhead of menu governor

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Message-ID: <3495244.HqlX2f8Ijd@vostro.rjw.lan>
Date:	Wed, 06 Aug 2014 21:17:45 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Rafael J Wysocki <rafael.j.wysocki@...el.com>,
	Nicolas Pitre <nico@...aro.org>,
	Mike Galbraith <mgalbraith@...e.de>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/4] Reduce overhead of menu governor

On Wednesday, August 06, 2014 02:19:17 PM Mel Gorman wrote:
> The menu_select function is heavy and is very noticable in profiles for
> workloads that enter/leave idle state a lot. This primarily happens
> for scheduler microbenchmarks. The biggest contibution is the standard
> deviation calculations and comparisons but the excessive calls into
> the scheduler core do not help.
> 
> It would be nice to reduce the number of times nr_iowait is checked to
> once per 8 intervals but I was not sure how to measure what the general
> impact of such a change could be.
> 
> Similiarly I looked at different ways the standard deviation could be
> calculated but the standard equivalent calculations potentially overflow.
> It could be done as rolling average and rolling deviation but again
> it was unclear how that could be evaluated. Tips on how the goodness/badness
> of governor changes are evalated would be nice.
> 
> In the meantime, here are patches against some  of the obvious stuff.

They look good, I'm going to apply them.

Rafael

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