linux-kernel - Re: [RFC][PATCH v2 5/7] taskstats: Improve cumulative CPU time accounting

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Message-ID: <20101118171001.GB3249@redhat.com>
Date:	Thu, 18 Nov 2010 18:10:01 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Michael Holzheu <holzheu@...ux.vnet.ibm.com>
Cc:	Shailabh Nagar <nagar1234@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Venkatesh Pallipadi <venki@...gle.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>, 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>,
	linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org
Subject: Re: [RFC][PATCH v2 5/7] taskstats: Improve cumulative CPU time
	accounting

Sorry for delay.

On 11/16, Michael Holzheu wrote:
>
> On Sat, 2010-11-13 at 19:38 +0100, Oleg Nesterov wrote:
> > First of all, let me repeat, I am not going to discuss whether we need
> > these changes or not, I do not know even if I understand your motivation.
>
> Sorry, if I was not clear enough with my descriptions. Let me try to
> describe my motivation again:

Yes, more or less I see what this patch does (I hope ;).

> 2. Because of reparent to init, there are situations where it is
>    not clear to which tasks the CPU time of dead tasks between
>    two snapshots has been accounted. This is a problem for example 2.

Yes, I see.

But I must admit, _personally_ I am not sure this problem worth the
trouble. And, I already mentioned daemonize() case, IOW I am not sure
it is _always_ right to choose exiting_parent->parent for accounting.
To me, this can be equally confusing. A user sees the running deamon
with ppid = 1, then this daemon exits and top reports the "unrelated"
process as cpu consumer.


But once again. I am _not_ against this patch. I never know when it
comes to new features. Certainly you know better if this suits top.

What I actually meant is: dear CC list, please look at this change
and comment ;)

Oleg.

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