linux-kernel - Re: [RFC][PATCH 09/10] taskstats: Fix exit CPU time accounting

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Message-ID: <20100928110828.54e1cf25@mschwide.boeblingen.de.ibm.com>
Date:	Tue, 28 Sep 2010 11:08:28 +0200
From:	Martin Schwidefsky <schwidefsky@...ibm.com>
To:	balbir@...ux.vnet.ibm.com
Cc:	Oleg Nesterov <oleg@...hat.com>,
	Michael Holzheu <holzheu@...ux.vnet.ibm.com>,
	Shailabh Nagar <nagar1234@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Venkatesh Pallipadi <venki@...gle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	John stultz <johnstul@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH 09/10] taskstats: Fix exit CPU time accounting

On Tue, 28 Sep 2010 14:06:02 +0530
Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:

> * Martin Schwidefsky <schwidefsky@...ibm.com> [2010-09-27 15:42:57]:
> > Got the part about self-reaping processes. But there is another issue:
> > consider an exiting thread where the group leader is still active.
> > The time for the thread will be added to the utime/stime fields in
> > the signal structure. Taskstats will happily ignore that time while
> > the group leader is still running.
> >
> 
> Why do you say that? Not sure your comment is very clean, in
> fill_tgid, we do
> 
> 1. Accumulate signal stats (contains stats for dead threads)
> 2. Accumulate stats for current threads
> 
> fill_tgid_exit does something similar

Hmm, I can't find anything in the code where the tsk->signal->{utime,stime}
gets transferred to the taskstats record. There is a loop in fill_tgid over
the threads of the process but all it does is to call delayacct_add_tsk.
And that function does nothing with the cpu time of dead threads which is
stored in the signal structure. In addition which taskstats field is
supposed to contain the cpu time of the dead thread, ac_utime/ac_stime?

-- 
blue skies,
   Martin.

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

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