Date: Tue, 24 Aug 2010 14:06:19 +0200
From: Martin Schwidefsky <schwidefsky@de.ibm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: balbir@linux.vnet.ibm.com, Venkatesh Pallipadi <venki@google.com>,
        Ingo Molnar <mingo@elte.hu>, "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>, Paul Menage <menage@google.com>,
        linux-kernel@vger.kernel.org, Paul Turner <pjt@google.com>,
        Heiko Carstens <heiko.carstens@de.ibm.com>,
        Paul Mackerras <paulus@samba.org>, Tony Luck <tony.luck@intel.com>
Subject: Re: [PATCH 0/4] Finer granularity and task/cgroup irq time
 accounting
Message-ID: <20100824140619.35850ae9@mschwide.boeblingen.de.ibm.com>
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On Tue, 24 Aug 2010 13:53:55 +0200
Peter Zijlstra <peterz@infradead.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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