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

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Message-ID: <1282650835.2605.2629.camel@laptop>
Date:	Tue, 24 Aug 2010 13:53:55 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	balbir@...ux.vnet.ibm.com
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

On Tue, 2010-08-24 at 17:08 +0530, Balbir Singh wrote:
> 
> The point is for containers it is more likely to give the right answer
> and so on. Yes, the results are not 100% accurate. 

Consider one group heavily dirtying pages, it stuffs the IO queues full
and gets blocked on IO completion. Since the CPU is then free to
schedule something else we start running things from another group,
those IO completions will come in while we run other group and get
accounted to other group -- FAIL.

s/group/task/ etc..

That just really doesn't work, accounting async work, esp stuff that is
not under software control it very tricky indeed.

So what are you wanting to do, and why. Do you really need accounting
madness?
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