linux-kernel - Re: [PATCH] Restore deterministic CPU accounting on powerpc

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Date:	Sat, 3 Nov 2007 09:54:20 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Paul Mackerras <paulus@...ba.org>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	linux-kernel@...r.kernel.org, linuxppc-dev@...abs.org
Subject: Re: [PATCH] Restore deterministic CPU accounting on powerpc


* Paul Mackerras <paulus@...ba.org> wrote:

> Since powerpc started using CONFIG_GENERIC_CLOCKEVENTS, the 
> deterministic CPU accounting (CONFIG_VIRT_CPU_ACCOUNTING) has been 
> broken on powerpc, because we end up counting user time twice: once in 
> timer_interrupt() and once in update_process_times().
> 
> This fixes the problem by pulling the code in update_process_times 
> that updates utime and stime into a separate function called 
> account_process_tick.  If CONFIG_VIRT_CPU_ACCOUNTING is not defined, 
> there is a version of account_process_tick in kernel/timer.c that 
> simply accounts a whole tick to either utime or stime as before.  If 
> CONFIG_VIRT_CPU_ACCOUNTING is defined, then arch code gets to 
> implement account_process_tick.
> 
> This also lets us simplify the s390 code a bit; it means that the s390 
> timer interrupt can now call update_process_times even when 
> CONFIG_VIRT_CPU_ACCOUNTING is turned on, and can just implement a 
> suitable account_process_tick().
> 
> Signed-off-by: Paul Mackerras <paulus@...ba.org>

lets push this towards Linus via the scheduler tree, ok?

	Ingo
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