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

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Message-ID: <20100928092355.GA4261@balbir.in.ibm.com>
Date:	Tue, 28 Sep 2010 14:53:55 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Martin Schwidefsky <schwidefsky@...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

* Martin Schwidefsky <schwidefsky@...ibm.com> [2010-09-28 11:08:28]:

> 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}

That is left to the actual subsystem (I should have been clearer in
stating that the limitation is not with the taskstats infrastructure
itself). Yes, your observation is indeed correct.

taskstats code is expected to contain the callback for the subsystems
it supports. delayacct() already does the right thing today, AFAICS

> 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?
>

I've not focused much on ac_*, The changes that need to occur are we
need to get the tsacct.c callbacks into taskstats.

-- 
	Three Cheers,
	Balbir
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