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Re: [Xen-users] Clock (time) issue

To: Mark Adams <mark@xxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-users] Clock (time) issue
From: Steven Timm <timm@xxxxxxxx>
Date: Mon, 04 Oct 2010 09:08:07 -0500 (CDT)
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Mark, are your domU's 32-bit or 64-bit, likewise with dom0?
We have seen the domU clock on a 32-bit instance jump forward
by 40-80 minutes for no good reason and stay stuck there until
the outside world catches up (and any time set commands fail).
But never saw dom0 clock jump.


On Mon, 4 Oct 2010, Mark Adams wrote:

Hi All,

Im running Xen 4.0.1-rc6 Debian squeeze with pvops 2.6.32-21 kernel.
Today I noticed (when kerberos to the domain controllers stopped
working..) that the clock was 50 minutes out in dom0 -- This caused the
HVM windows domain controllers to have the wrong time.

I'm not sure if this is a kernel issue or a xen issue, but the only
thing related is I can see the following in the kernel log:

Oct  2 18:50:33 havhost1 kernel: [623480.977748] Clocksource tsc unstable 
(delta = -2999660303788 ns)

But I also see in the dmesg log that xen is using it's own clock.

[    7.676563] Switching to clocksource xen

I can't identify anything else in the logs to indicate when the time
might have changed. I have a few other dom0 at the same level that
haven't decided to change the time.

Can anyone confirm whether xen controls the time or the kernel? Also
when I corrected the time in dom0 it was still wrong in HVM domU -- How
long does it take for this to propogate? (I rebooted the VM's to correct
it immediately).

Any other pointers on how to ensure stability of clocks from dom0 to
domU HVM hosts (and pv for that matter..) would be appreciated.


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Steven C. Timm, Ph.D  (630) 840-8525
timm@xxxxxxxx  http://home.fnal.gov/~timm/
Fermilab Computing Division, Scientific Computing Facilities,
Grid Facilities Department, FermiGrid Services Group, Assistant Group Leader.

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