linux-kernel - Re: CFS review

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Date:	Wed, 01 Aug 2007 09:36:02 +0200
From:	Mike Galbraith <efault@....de>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Roman Zippel <zippel@...ux-m68k.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: CFS review

On Wed, 2007-08-01 at 09:30 +0200, Ingo Molnar wrote:
> * Mike Galbraith <efault@....de> wrote:

> > I haven't been able to reproduce this with any combination of 
> > features, and massive_intr tweaked to his work/sleep cycle.  I notice 
> > he's collecting stats though, and they look funky.  Recompiling.
> 
> yeah, the posted numbers look most weird, but there's a complete lack of 
> any identification of test environment - so we'll need some more word 
> >from Roman. Perhaps this was run on some really old box that does not 
> have a high-accuracy sched_clock()? The patch below should simulate that 
> scenario on 32-bit x86.
> 
> 	Ingo
> 
> Index: linux/arch/i386/kernel/tsc.c
> ===================================================================
> --- linux.orig/arch/i386/kernel/tsc.c
> +++ linux/arch/i386/kernel/tsc.c
> @@ -110,7 +110,7 @@ unsigned long long native_sched_clock(vo
>  	 *   very important for it to be as fast as the platform
>  	 *   can achive it. )
>  	 */
> -	if (unlikely(!tsc_enabled && !tsc_unstable))
> +//	if (unlikely(!tsc_enabled && !tsc_unstable))
>  		/* No locking but a rare wrong value is not a big deal: */
>  		return (jiffies_64 - INITIAL_JIFFIES) * (1000000000 / HZ);
>  

Ah, thanks.  I noticed that clocksource= went away.  I'll test with
stats, with and without jiffies resolution.

	-Mike

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