Re: [Xen-devel] Xen 4.0.x 3,000 second time skew problem

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 08.06.12 at 16:18, Andy Smith <andy@xxxxxxxxxxxxxx> wrote:
> 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.

So it ought to come from Dom0 (you didn't say whether there
was anything in its logs, or anything interesting going on on it
at the point where the time change happens), or would have
to be "invented" strait in the hypervisor (you didn't say
anything about its log either).

Also you didn't clarify how frequent "occasionally" is, and
whether this is e.g. always happening after a certain amount
of uptime, at some specific time during the day, etc.

> 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

Clearly we'd want to know if this also occurs with current -unstable.

> 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.

Which hints towards something specific to the configurations of
the two affected hosts, suggesting that it would be a good idea
to narrow down the differences between affected and non-
affected, physically identical machines...

Jan


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