linux-kernel - Re: [patch 13/19] GTOD: Mark TSC unusable for highres timers

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Date:	Sat, 11 Nov 2006 14:58:08 +0100
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Andi Kleen <ak@...e.de>
Cc:	Andrew Morton <akpm@...l.org>, Ingo Molnar <mingo@...e.hu>,
	john stultz <johnstul@...ibm.com>,
	LKML <linux-kernel@...r.kernel.org>, Len Brown <lenb@...nel.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Roman Zippel <zippel@...ux-m68k.org>
Subject: Re: [patch 13/19] GTOD: Mark TSC unusable for highres timers

On Sat, 2006-11-11 at 14:51 +0100, Andi Kleen wrote:
> > > > And afaict the reason for that is that we're using jiffies to determine if
> > > > the TSC has gone bad, and that test is getting false positives.
> > > 
> > > The i386 clocksource had always trouble with that. e.g.  I have a box
> > > where the TSC works perfectly fine on a 64bit kernel, but since the new i386
> > > clocksource code is in it always insists on disabling it shortly after boot.
> 
> shortly after boot means in user space here, not during the first idling.
> 
> > > My guess is that some of the checks in there are just broken and need
> > > to be fixed.
> > 
> > It's the unconditional mark_unstable call in ACPI C2 state. /me looks.
> 
> The system doesn't support C2 states. It's an older single socket Athlon 64 
> with VIA chipset. I haven't looked in detail on why it fails.

Does it have cpu freqency changing ?

	tglx


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