Xen 4.0.x 3,000 second time skew problem

[Andy Smith <andy@strugglers.net>]

Hi,

I have two installs of Xen 4.0.1 on Debian squeeze dom0s that
occasionally skew the time by 3000 seconds. It is always 3000
seconds and it always affects all guests.

Depending on the kernels in the guests they will say:

    tp0 kernel: [9339489.266542] Clocksource tsc unstable (delta = -2999660317697 ns)

or perhaps the kernel doesn't notice but ntpd does:

    ls0 ntpd[15009]: time reset -2999.683517 s

the point is it does affect all guests.

Back in February 2011 there was a thread started by Olivier Hanesse
which appears to be exactly the same issue:

    http://old-list-archives.xen.org/archives/html/xen-users/2011-02/msg00609.html

Like Olivier, one of my hosts used to run Xen 3.x and did not
experience this issue until after it was upgraded to Xen 4. The
other has only ever run 4.0.x so I don't know.

The above thread ends with Olivier using clocksource=pit on his Xen
command line and waiting to see if it fixed things. If you are
reading, Olivier, did it fix things for you?

These are Debian squeeze installs so using packaged versions of xen
and kernel:

ii  linux-image-2.6.32-5-xen-amd64 2.6.32-45 Linux 2.6.32 for 64-bit PCs, Xen dom0 support
ii  xen-hypervisor-4.0-amd64       4.0.1-4   The Xen Hypervisor on AMD64

One of the hosts affected is:

CPU: Xeon 5410
Motherboard: Supermicro X7DCL-i

The other is:

CPU: Xeon E5606
Motherboard: SUpermicro X8DTN+

but I do have other servers with same hardware as both of these that
aren't affected.

Cheers,
Andy