linux-kernel - Re: [patch-mm 14/33] x86_64: Consolidate tsc calibration

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Date:	Tue, 17 Jul 2007 17:00:43 +0200
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Andi Kleen <ak@...e.de>
Cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Chris Wright <chrisw@...s-sol.org>
Subject: Re: [patch-mm 14/33] x86_64: Consolidate tsc calibration

On Tue, 2007-07-17 at 14:51 +0200, Andi Kleen wrote:
> On Sunday 15 July 2007 18:10:55 Thomas Gleixner wrote:
> > Move the TSC calibration code to tsc.c. Reimplement it so the
> > pm timer can be used as a reference as well.
> 
> Why is the pm timer better than the PIT for this? 
> 
> I've had mixed success with the pmtimer too.

I had more consistent results on i386 with pmtimer than with the PIT

> >
> > Index: linux-2.6.22-rc6-mm/include/asm-i386/tsc.h
> > ===================================================================
> > --- linux-2.6.22-rc6-mm.orig/include/asm-i386/tsc.h	2007-07-15 17:26:45.000000000 +0200
> > +++ linux-2.6.22-rc6-mm/include/asm-i386/tsc.h	2007-07-15 17:34:42.000000000 +0200
> > @@ -71,4 +71,8 @@ extern void init_tsc_clocksource(void);
> >  extern void check_tsc_sync_source(int cpu);
> >  extern void check_tsc_sync_target(void);
> >  
> > +#ifdef CONFIG_X86_64
> > +extern void tsc_calibrate(void);
> > +#endif
> 
> The ifdef shouldn't be needed?

Yep. It can go.

	tglx


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