linux-kernel - Re: 2.6.25.9: system clocks works normally then speeds up 4x...

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Date:	Wed, 09 Jul 2008 14:21:39 -0700
From:	john stultz <johnstul@...ibm.com>
To:	Philippe Troin <phil@...i.org>
Cc:	linux-kernel@...r.kernel.org, macro@...ux-mips.org
Subject: Re: 2.6.25.9: system clocks works normally then speeds up 4x...


On Wed, 2008-07-09 at 13:53 -0700, Philippe Troin wrote:
> john stultz <johnstul@...ibm.com> writes:
> 
> > On Wed, 2008-07-09 at 13:01 -0700, Philippe Troin wrote:
> > > "john stultz" <johnstul@...ibm.com> writes:
> > > 
> > > > On Wed, Jul 9, 2008 at 12:21 PM, Philippe Troin <phil@...i.org> wrote:
> > > > >
> > > > > Symptoms:
> > > > >
> > > > >  The system boots fine. Clock seems to run normally.
> > > > >
> > > > >  Then after a random amount of time (on the current boot, 3 days),
> > > > >  clock starts to be running 2-4x faster (on the current boot, 4x).
> > > > >
> > > > >  I have tried booting with "nohz=off highres=off" but it does not
> > > > >  help.
> > > > 
> > > > Could you provide the output from the following:
> > > >    sudo cat /sys/devices/system/clocksource/clocksource0/*
> > > 
> > > Sure.
> > > 
> > > It is:
> > > available: jiffies tsc 
> > > current:   jiffies
> > > 
> > > > Did this issue occur with 2.6.24 or earlier kernels?
> > > 
> > > No.  It started with 2.6.25.
> > > 
> > > Interestingly:
> > > 
> > >   I've just modified the current clocksource to tsc and the clock went
> > >   back to its normal speed.
> > > 
> > >   Then I reset the current clocksource to jiffies, and the clock went
> > >   back to its (wrong) 4x speed.
> > > 
> > > So it looks like the kernel is counting jiffies 4x too fast.
> > 
> > When you're seeing the issue, can you do the following:
> >   cat /proc/interrupts > interrupts
> > 
> >   <wait 10 seconds by your wristwatch> 
> > 
> >   cat /proc/interrupts >> interrupts
> > 
> > And send the results?
> 
> There you are:
> 
>            CPU0       CPU1
>   0:        353          0   IO-APIC-edge      timer
> LOC:  546305845   33155722   Local timer interrupts
> Roughly 10 seconds later:
>   0:        353          0   IO-APIC-edge      timer
> LOC:  546361653   33156517   Local timer interrupts

Huh. So that's a diff of:
LOCdiff   55808        795  

So that's 55 seconds worth of ticks on cpu0 and not one on cpu1. So yea,
something seems off with your timer interrupts.

> > Could you also try booting with noapic to see if that changes anything?
> 
> Sure.  This will mean I will lose the "wedged" system.  Is there
> anything else that needs to be checked on it before I lose the broken
> state?
> Also keep in mind that the symptoms take a while to manifest
> themselves (a few days typically).

I can't think of anything right off. But maybe we should give some
others a chance to look.

I would like to see the same /proc/interrupt data when the system is
properly functioning as well. So whenever you do reboot, that would be
interesting to me.

thanks
-john

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