linux-kernel - Re: [PATCH 0/4] Finer granularity and task/cgroup irq time accounting

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Date:	Tue, 24 Aug 2010 17:08:01 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Venkatesh Pallipadi <venki@...gle.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Paul Menage <menage@...gle.com>, linux-kernel@...r.kernel.org,
	Paul Turner <pjt@...gle.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Paul Mackerras <paulus@...ba.org>,
	Tony Luck <tony.luck@...el.com>
Subject: Re: [PATCH 0/4] Finer granularity and task/cgroup irq time accounting

* Peter Zijlstra <peterz@...radead.org> [2010-08-24 11:09:13]:

> > 
> > cgroup level info does make sense, assuming that tasks that share the
> > costs being mentioned here belong to the same cgroup. 
> 
> I don't think that's a valid assumption.
> 
> If its not true for tasks, then its not true for groups of tasks either.
> It might be slightly less wrong due to the larger number of entities
> reducing the error bounds, but its still wrong in principle.
>

The point is for containers it is more likely to give the right answer
and so on. Yes, the results are not 100% accurate.
 
> The whole attribution mess can only be solved by actually splitting out
> the entries that do work, like per-cgroup workqueue threads and similar
> things.
> 
> System wide entities like IRQs are very hard to attribute correctly like
> Martin already argued, and I don't think its worth doing.

I see Martin's view point, is the suggestion then that we amortize
these costs across all tasks?


-- 
	Three Cheers,
	Balbir
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