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

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Date:	Thu, 15 Sep 2011 10:53:09 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Glauber Costa <glommer@...allels.com>
Cc:	linux-kernel@...r.kernel.org, xemul@...allels.com,
	paul@...lmenage.org, lizf@...fujitsu.com, daniel.lezcano@...e.fr,
	mingo@...e.hu, jbottomley@...allels.com
Subject: Re: [PATCH 0/9] Per-cgroup /proc/stat

On Wed, 2011-09-14 at 17:20 -0300, Glauber Costa wrote:


> Answering just a single point here, if you look closely, it does not 
> duplicate  anything from cpuacct. What it does, is to divide it in more
> fine grained groups than just user/system. But it is not even called 
> more than it already used to be. Also, I change the counters to per-cpu 
> variables instead of percpu counters (so we can access per-cpu data). If 
> there is any perf. change wrt the current code, it comes from that, and 
> since percpu variables are cheaper to update (and summing up is much 
> less frequent), it will end up even cheaper.

I just saw the word statistics and 234 lines added to sched.c and went
mental ;-)

> The steal time feature is really trivial once it is in place.
> 
> About your point of the context switch cost, how would you feel if we 
> optimized it out using static_branch() like it was done for kvm steal time?

Both pjt and me tried, but its hard, part of the problem is also data
structure bloat.
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