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Date: Tue, 2 Sep 2008 23:16:20 +0200 (CEST)
From: Thomas Gleixner <tglx@linutronix.de>
To: Alok Kataria <akataria@vmware.com>
cc: Linus Torvalds <torvalds@linux-foundation.org>,
       Larry Finger <Larry.Finger@lwfinger.net>,
       LKML <linux-kernel@vger.kernel.org>, "Rafael J. Wysocki" <rjw@sisk.pl>,
       Michael Buesch <mb@bu3sch.de>
Subject: Re: Regression in 2.6.27 caused by commit bfc0f59
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On Tue, 2 Sep 2008, Alok Kataria wrote:
> On Tue, 2008-09-02 at 11:14 -0700, Thomas Gleixner wrote:
> > I think that information is enough to give us a pretty precice idea
> > when to discard the result. I'm currently looking at the hpet/pmtimer
> > values for comparison and I should have a patch for testing ready
> > later tonight.
> > 
> Sorry for joining the party this late...am still going through all my
> mails.
> 
> Ok, so from what I understand until now, we will calibrate TSC against
> PIT as was done in 32bit code and use that as default. If that fails to
> give any sane results we will fall back to calibrating against PM_timer
> or HPET ?
> Thomas has already explained the problem with 32bit calibration ( i.e.
> just against PIT and no checks for SMI's and all) but would like to
> point that this problem is lot more worse in virtualized environment,
> because we may fail to get sane values even from multiple loops of
> calibrating against PIT. 
> If we have a fall back mechanism to detect this SMI event, and then try
> calibrating against PM timer or HPET we should be good. 

I still keep the fallback against pmtimer/hpet alive.

Thanks,

	tglx