linux-kernel - Re: CFS review

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Date:	Wed, 1 Aug 2007 09:30:42 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Mike Galbraith <efault@....de>
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


* Mike Galbraith <efault@....de> wrote:

> > Thanks for the testing and the feedback, it's much appreciated! :-) 
> > On what platform did you do your tests, and what .config did you use 
> > (and could you please send me your .config)?
> > 
> > Please also send me the output of this script:
> > 
> >   http://people.redhat.com/mingo/cfs-scheduler/tools/cfs-debug-info.sh
> > 
> > (if the output is too large send it to me privately, or bzip2 -9 
> > it.)
> > 
> > Could you also please send the source code for the "l.c" and "lt.c" 
> > apps you used for your testing so i can have a look. Thanks!
> 
> 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);
 
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