Re: the clock stopped in F7 ?!

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On 8/27/07, Lonni J Friedman <netllama@xxxxxxxxx> wrote:
> On 8/27/07, Mike <azmr@xxxxxxxxxxxxx> wrote:
> > On Mon, 27 Aug 2007, Lonni J Friedman wrote:
> >
> > >
> > > The timer in /proc/interrupts was not changing, and neither was the
> > > timestamp in /proc/schedstat.  ugh.
> > >
> >
> > Sorry for the confusion.  Andy Green's posts clear this up and hopefully
> > this will clarify somewhat too.
> >
> > For aeon's, well maybe centuries, ok really just decades the majority of
> > OS'es that run on PC's used IRQ0 to update the real time clock.  What this
> > means is that 100 times a second (100 Hz) the kernel (in the case of
> > linux) is interrupted and the real time clock is updated among other
> > things then the kernel goes about it's business.  To get better resolution
> > the 100 Hz parameter is changeable at compile time to 100, 250 or 1000 (I
> > believe).  I think it defaulted to 1000Hz recently.  In any case as Andy
> > Green pointed out modern kernels have gone "tickless".  This is a very
> > good thing for laptops and saving power etc.
> >
> > >From what I have read HPET or High Precision Event Timer is what is used
> > now (in the 2.6.21 or so kernel timeframe and beyond).  HPET is a device
> > that is part of the chipsets on modern motherboards.  From what I've been
> > told the HPET code is broken in some kernel versions (I mean hey it's
> > brand new code, sure could be buggy).
> >
> > So to the original poster (Lonni J Friedman?) I'd suggest (as Andy
> > mentioned) check to see what your clocksource is:
> >
> > cat /sys/devices/system/clocksource/clocksource0/current_clocksource
> >
> > If it says 'hpet' reboot your machine and pass 'hpet=disable' to the
> > kernal via grub.  I don't have a machine that I can reboot at the moment,
> > but IIRC at the grub prompt you press 'e' to edit the command before
> > booting.  From there I forget but google should help find the syntax.  Or
> > perhaps it's even self explanatory.
> >
> > In any case this should force your machine to keep time the old fashioned
> > way which unless you're on a laptop should be just fine.  And if this
> > works you can edit grub.conf (I believe) and 'hpet=disable' to make this
> > permanent.
>
> My system doesn't have HPET.  Also, to clarify, the problem only
> happens after some unknown period of uptime.  The system had been up
> for like 100 days prior to the first occurance, and was up for just 3
> days after the 2nd occurance.  Its not always present.  So clearly
> something is very broken somewhere, and isn't going to be fixed just
> by disabling hpet at boot.  My best guess is flaky hardware.  I'll be
> running memtest86+ tonight.  If that checks out, then I can only
> assume that the CPU (Athlon64X2) is dying.

Just to close the loop, this turned out to be a kernel bug.  Booting
with nohz=off completely eliminated the problem.  This is a tickless
kernel bug.


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