linux-kernel - Re: [patch 0/4] taskstats: Improve cumulative time accounting

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Message-ID: <1290423780.1974.1.camel@holzheu-laptop>
Date:	Mon, 22 Nov 2010 12:03:00 +0100
From:	Michael Holzheu <holzheu@...ux.vnet.ibm.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	Shailabh Nagar <nagar1234@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	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: [patch 0/4] taskstats: Improve cumulative time accounting

On Fri, 2010-11-19 at 21:19 +0100, Peter Zijlstra wrote:
> On Fri, 2010-11-19 at 21:11 +0100, Michael Holzheu wrote:
> > Due to POSIX POSIX.1-2001, the CPU time of processes is not accounted
> > to the cumulative time of the parents, if the parents ignore SIGCHLD
> > or have set SA_NOCLDWAIT. This behaviour has the major drawback that
> > it is not possible to calculate all consumed CPU time of a system by
> > looking at the current tasks. CPU time can be lost.
> > 
> > To solve this problem, this patch set duplicates the cumulative accounting
> > data in the signal_struct. In the second set (cdata_acct) the complete
> > cumulative resource counters are stored. The new cumulative CPU time (utime
> > and stime) is then exported via the taskstats interface. 
> 
> Maybe this has been treated earlier in the threads and I missed it, but
> the obvious solution doesn't get mentioned:
> 
> What would break if we violate this silly POSIX rule and account time of
> childs regardless of SIGCHLD/SA_NOCLDWAIT?

Or maybe we could add a sysctl that allows to switch between the two
semantics.

Michael

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