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

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Date:	Tue, 24 Aug 2010 14:06:19 +0200
From:	Martin Schwidefsky <schwidefsky@...ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	balbir@...ux.vnet.ibm.com, Venkatesh Pallipadi <venki@...gle.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, 24 Aug 2010 13:53:55 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> 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?

Well, I have sent a patch back in 2006 that stops adding the hardirq /
softirq time to the currently running process. See
http://lkml.org/lkml/2006/8/24/139
It did not get very far, so that answer to the question if we need
accounting madness seems to be yes ..

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.

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