linux-kernel - Re: Regression in 2.6.27 caused by commit bfc0f59

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Message-ID: <alpine.LFD.1.10.0809022315090.3243@apollo.tec.linutronix.de>
Date:	Tue, 2 Sep 2008 23:16:20 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Alok Kataria <akataria@...are.com>
cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Larry Finger <Larry.Finger@...inger.net>,
	LKML <linux-kernel@...r.kernel.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Michael Buesch <mb@...sch.de>
Subject: Re: Regression in 2.6.27 caused by commit bfc0f59

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
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