linux-kernel - Re: CFS review

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Date:	Wed, 1 Aug 2007 19:50:04 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Roman Zippel <zippel@...ux-m68k.org>,
	Mike Galbraith <efault@....de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: CFS review


* Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> On Wed, 1 Aug 2007, Andi Kleen wrote:
> 
> > Ingo Molnar <mingo@...e.hu> writes:
> > 
> > > thanks. Just to make sure, while you said that your TSC was off on that 
> > > laptop, the bootup log of yours suggests a working TSC:
> > > 
> > >   Time: tsc clocksource has been installed.
> > 
> > Standard kernels often disable the TSC later after running a bit 
> > with it (e.g. on any cpufreq change without p state invariant TSC) 
> 
> I assume that what Roman hit was that he had explicitly disabled the 
> TSC because of TSC instability with the "notsc" kernel command line. 
> Which disabled is *entirely*.

but that does not appear to be the case, the debug info i got from Roman 
includes the following boot options:

  Kernel command line: auto BOOT_IMAGE=2.6.23-rc1-git9 ro root=306

there's no "notsc" option there.

Andi's theory cannot be true either, Roman's debug info also shows this 
/proc/<PID>/sched data:

  clock-delta              :                  95

that means that sched_clock() is in high-res mode, the TSC is alive and 
kicking and a sched_clock() call took 95 nanoseconds.

Roman, could you please help us with this mystery?

	Ingo
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