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

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Message-ID: <20071103093240.GA22932@elte.hu>
Date:	Sat, 3 Nov 2007 10:32:40 +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


* Ingo Molnar <mingo@...e.hu> wrote:

> * 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?

hm, i've removed it for now because it doesnt even build due toj:

+#ifndef CONFIG_VIRT_CPU_ACCOUNTING
+void account_process_tick(int user_tick)
+{
+       if (user_tick) {
+               account_user_time(p, jiffies_to_cputime(1));
+               account_user_time_scaled(p, jiffies_to_cputime(1));

	Ingo
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