Subject: Re: [PATCH] Blacklist Dell Optiplex 320 from using the HPET
From: john stultz <johnstul@us.ibm.com>
To: Andi Kleen <ak@suse.de>
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>
In-Reply-To: <200705050118.34711.ak@suse.de>
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	 <200705050118.34711.ak@suse.de>
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Date: Fri, 04 May 2007 16:27:08 -0700
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On Sat, 2007-05-05 at 01:18 +0200, Andi Kleen wrote:
> 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.

We can give it a whirl, I just didn't want to add yet another "compare
with some other counter that may or may not work" check. In this case,
probably reading three times in a row and getting the same result would
be a clearly broken box. 


> 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.

Guilherme: Could you provide lspci output? 


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

Ok, I wasn't aware it was a common issue.

thanks
-john

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