linux-kernel - Re: [PATCH 0/9] Per-cgroup /proc/stat

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Date:	Thu, 15 Sep 2011 10:56:29 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Glauber Costa <glommer@...allels.com>,
	linux-kernel@...r.kernel.org, xemul@...allels.com,
	paul@...lmenage.org, lizf@...fujitsu.com, daniel.lezcano@...e.fr,
	mingo@...e.hu, jbottomley@...allels.com,
	Paul Turner <pjt@...gle.com>
Subject: Re: [PATCH 0/9] Per-cgroup /proc/stat

On Wed, 2011-09-14 at 13:23 -0700, Andi Kleen wrote:
> Peter Zijlstra <a.p.zijlstra@...llo.nl> writes:
> >
> > Guys we should seriously trim back a lot of that code, not grow ever
> > more and more. The sad fact is that if you build a kernel with
> > cpu-cgroup support the context switch cost is more than double that of a
> > kernel without, and then you haven't even started creating cgroups yet.
> 
> That sounds indeed quite bad. Is it known why it is so costly?

Mostly because all data structures grow and all code paths grow, some by
quite a bit, its spread all over the place, lots of little cuts etc..

pjt and I tried trimming some of the code paths with static_branch() but
didn't really get anywhere.. need to get back to looking at this stuff
sometime soon.
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