linux-kernel - Re: [PATCH v3 3/6] expose fine-grained per-cpu data for cpuacct stats

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Message-ID: <4FC6180F.9020009@parallels.com>
Date:	Wed, 30 May 2012 16:52:31 +0400
From:	Glauber Costa <glommer@...allels.com>
To:	Paul Turner <pjt@...gle.com>
CC:	<linux-kernel@...r.kernel.org>, <cgroups@...r.kernel.org>,
	<devel@...nvz.org>, Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Tejun Heo <tj@...nel.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	<handai.szj@...il.com>, <Andrew.Phillips@...x.com>,
	Serge Hallyn <serge.hallyn@...onical.com>
Subject: Re: [PATCH v3 3/6] expose fine-grained per-cpu data for cpuacct stats

On 05/30/2012 04:48 PM, Paul Turner wrote:
> a) the information in /proc/stat is actually much denser since it's
> "cpu VAL VAL VAL VAL" as opposed to "cpuX.FIELD VAL"

easily fixable here. Less descriptive, but we can use a header line
with the description much like how /proc/slabinfo does, and we still
have an extensible interface that is dense, at the same time.

> b) If it became a problem the /proc/stat case is actually fairly
> trivially fixable by defining each cpu as a record and "everything
> else" as a magic im-out-of-cpus value.
>
>> >
>> >  Now, if you guys are okay with a file per-cpu, I can do it as well.
>> >  It pollutes the filesystem, but at least protects against the fact that this
>> >  is kmalloc-backed.
>> >
> As I prefaced, I'm not sure there's much that can be trivially done
> about it.  This is really a fundamental limitation of how read_map()
> works.
>
> What we really need is a proper seq_file exposed through cftypes.
That can be done.

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