linux-kernel - Re: [patch v2 4/4] taskstats: Export "cdata

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Date:	Fri, 10 Dec 2010 14:26:20 +0100
From:	Michael Holzheu <holzheu@...ux.vnet.ibm.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Shailabh Nagar <nagar1234@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	John stultz <johnstul@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Roland McGrath <roland@...hat.com>, Valdis.Kletnieks@...edu,
	linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org
Subject: Re: [patch v2 4/4] taskstats: Export "cdata_wait" CPU times with
 taskstats

Hello Oleg,

On Wed, 2010-12-08 at 21:23 +0100, Oleg Nesterov wrote:
> Oh, sorry for the delay. Again ;)

No problem, I know this can be exhausting ;-)

> On 12/02, Michael Holzheu wrote:
> > When the last thread exits and the process/thread group dies,
> > taskstats_exit() sends an additional taskstats struct to userspace that
> > aggregates the thread accounting data. Currently only the delay
> > accounting data is aggregated (see
> > taskstats_exit->fill_tgid_exit->delayacct_add_tsk). Not sure, why the
> > other information is not aggregated. We perhaps also should include
> > ac_cXtime in the aggregated taskstats.
> 
> Not sure I understand... Do you mean
> 
> 	if (is_thread_group)
> 		fill_tgid_exit(tsk);
> 
> ? Afaics, this is not "When the last thread exits", this is
> "this program is multithreaded, it has (or had) other threads".

fill_tgid_exit() adds the data of the dying thread to the thread group
data (tsk->signal->stats). Currently only for delay accounting.

But the accumulated data is sent to userspace only after the last thread
has died:

        if (!is_thread_group || >>>!group_dead<<<)
                goto send;

        stats = mk_reply(rep_skb, TASKSTATS_TYPE_TGID, tsk->tgid);
        if (!stats)
                goto err;

Michael

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