linux-kernel - Re: Linux 2.6.29-rc6

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Message-ID: <alpine.LFD.2.00.0902262249390.9135@localhost.localdomain>
Date:	Thu, 26 Feb 2009 22:54:46 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	john stultz <johnstul@...ibm.com>
cc:	Jesper Krogh <jesper@...gh.cc>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Linux 2.6.29-rc6

On Thu, 26 Feb 2009, john stultz wrote:
> On Thu, 2009-02-26 at 22:35 +0100, Jesper Krogh wrote:
> > john stultz wrote:
> > > On Thu, Feb 26, 2009 at 12:43 PM, Jesper Krogh <jesper@...gh.cc> wrote:
> > >> Linus Torvalds wrote:
> > >>> On Thu, 26 Feb 2009, Jesper Krogh wrote:
> > >>>> 2.6.26.8 doesnt have this problem.
> > >>>>
> > >>>> The "current_clocsource" is the same on both systems.
> > >>>>
> > >>>> $ cat /sys/devices/system/clocksource/clocksource0/current_clocksource
> > >>>> tsc
> > >>> What does the frequency calibrate to? It should be in the dmesg. Does it
> > >>> differ by a big amount?
> > >> Non-working:
> > >> $ dmesg | grep -i freq
> > >> [    0.004007] Calibrating delay loop (skipped), value calculated using
> > >> timer frequency.. 4620.05 BogoMIPS (lpj=9240104)
> > >>
> > >> 2.6.26.8 doesn't have that information.
> > > 
> > > I'm surprised the clocksource watchdog isn't catching it.
> > > 
> > > What's the output from:
> > > cat /sys/devices/system/clocksource/clocksource0/available_clocksource
> > 
> > $ cat /sys/devices/system/clocksource/clocksource0/available_clocksource
> > tsc acpi_pm jiffies
> 
> Hmm. Does booting w/ "clocksourc=acpi_pm" also show the severe (~550ppm,
> which NTP can't handle) drift?
> 
> >From the dmesg, I don't see any major calibration difference right off. 
> 
> So I'd suspect something like TSC halting in idle could be causing
> problems, but the watchdog should catch that as well. My only guess at
> this point is that the ACPI PM is halting in idle along with the TSC. 

But why would it do that on 29-rc6 and not on 2.6.28.8 ? I'm not aware
of changes which might cause that.

Thanks,

	tglx
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