linux-kernel - Re: [PATCH v5 11/11] sched: introduce cgroup file stat

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Message-Id: <20130109131705.4156ba5c.akpm@linux-foundation.org>
Date:	Wed, 9 Jan 2013 13:17:05 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Glauber Costa <glommer@...allels.com>
Cc:	<cgroups@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	Tejun Heo <tj@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Turner <pjt@...gle.com>
Subject: Re: [PATCH v5 11/11] sched: introduce cgroup file stat_percpu

On Thu, 10 Jan 2013 01:10:02 +0400
Glauber Costa <glommer@...allels.com> wrote:

> The main advantage I see in this approach, is that there is way less
> data to be written using a header. Although your way works, it means we
> will write the strings "nice", "system", etc. #cpu times. Quite a waste.

Yes, overhead can be a significant issue with this type of interface. 
But we already incurred a massive overhead by using a human-readable
ascii interface.  If performance is an issue, perhaps the whole thing
should be grafted onto taskstats instead.  Or create a new
taskstats-like thing.

btw, a more typical interface would be

cat /.../cpu0
nice:nn
system:nn
irq:nn

- the traditional one-per-line name:value tuples.  But I'd assumed that
having a file per CPU would be aawkward.
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