linux-kernel - How to draw values for /proc/stat

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Date:	Mon, 5 Dec 2011 07:32:33 -0200
From:	Glauber Costa <glommer@...allels.com>
To:	Paul Turner <pjt@...gle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	<cgroups@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>, <devel@...nvz.org>,
	Linux Containers <containers@...ts.osdl.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Balbir Singh <bsingharora@...il.com>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: How to draw values for /proc/stat

Hi,

Specially Peter and Paul, but all the others:

As you can see in https://lkml.org/lkml/2011/12/4/178, and in my answer 
to that, there is a question - one I've asked before but without that 
much of an audience - of whether /proc files read from process living on 
cgroups should display global or per-cgroup resources.

In the past, I was arguing for a knob to control that, but I recently 
started to believe that a knob here will only overcomplicate matters:
if you live in a cgroup, you should display only the resources you can 
possibly use. Global is for whoever is in the main cgroup.

Now, it comes two questions:
1) Do you agree with that, for files like /proc/stat ? I think the most 
important part is to be consistent inside the system, regardless of what 
is done

2) Will cpuacct stay? I think if it does, that becomes almost mandatory 
(at least the bind mount idea is pretty much over here), because drawing 
value for /proc/stat becomes quite complex.
The cpuacct cgroup can provide user, sys, etc values. But we also have:

* nr_context_switches,
* jiffies since boot,
* total_forks,
* nr_running,
* nr_iowait,

Now I doubt any of us want to see /proc/stat extended to accommodate 
things like nr_context_switches, or even worse, nr_running. The way I 
see it, there are two options here:

  a) moving everything to cpu cgroup so we keep all values being drawn
     from the same place
  b) Collect that info from multiple places in a transparent way. ctx,
     nr_running and nr_iowait will probably come from cpu. jiffies can
     come from wherever, and maybe we can even draw total_forks
     from Frederic's and avoid counting it twice.
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