From: Andi Kleen <ak@suse.de>
Organization: SUSE Linux Products GmbH, Nuernberg, GF: Markus Rex, HRB 16746 (AG Nuernberg)
To: john stultz <johnstul@us.ibm.com>
Subject: Re: [PATCH] Blacklist Dell Optiplex 320 from using the HPET
Date: Sat, 5 May 2007 01:18:34 +0200
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Cc: Andrew Morton <akpm@linux-foundation.org>,
       "Guilherme M. Schroeder" <guilherme@centralinf.com.br>,
       lkml <linux-kernel@vger.kernel.org>,
       Thomas Gleixner <tglx@linutronix.de>
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On Friday 04 May 2007 23:29:04 john stultz wrote:
> One of the 2.6.21 regressions was Guilherme's problem seeing his box
> lock up when the system detected an unstable TSC and dropped back to
> using the HPET.
> 
> In digging deeper, we found the HPET is not actually incrementing on
> this system. And in fact, the reason why this issue just cropped up was
> because of Thomas's clocksource watchdog code was comparing the TSC to
> the HPET (which wasn't moving) and thought the TSC was broken.
> 
> Anyway, Guliherme checked for a BIOS update and did not find one, so
> I've added a DMI blacklist against his system so the HPET is not used.
> 
> Many thanks to Guilherme for the slow and laborious testing that finally
> narrowed down this issue.

Before going to hard to maintain DMI black lists we should first check 
if it's a more general problem and can't it be solved better? Most likely
that system isn't the one with this issue and I don't want to apply
DMI patches forever.

In particular: what lspci chipset does it have?  If it's Intel it might be
worth checking the datasheet if there is some "HPET stop" bit -- perhaps it 
could be fixed up.

We seem to have a couple of Intel systems recently with HPET trouble.

-Andi
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