Re: [Xen-users] Clock skew on domU, no ntpd

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Wed, Jan 20, 2010 at 09:46:43AM -0600, Steven Timm wrote:
>
> Setup: RedHat/Centos/Sci. Linux 5 update 3,
> Dom0: kernel-xen-2.6.18-164.10.1.el5xen 64-bit
> (on Dell Poweredge 2950 dual quad-core).
> DomU: kernel-xen-2.6.18-164.10.1.el5xen 32-bit, 1 vcpu
> 6 domU's per dom0.
>
> We have also seen the same problem with 2.6.18-164.9.1 and 2.6.18-164.6.1
> kernels on this branch.
>
> Symptom: On 32-bit domU only (we have never seen 64-bit domU be affected),
> we observe that the clock gets set forward by a random amount of time,
> between 40-80 minutes.  We originally thought this was due to
> rogue ntp broadcasts because the ntp broadcastclient was disabled,
> but we have now disabled ntpd on all domU and the problem persists.
> During the 40-80 minutes it is possible to log into the domU via
> the Xen console, it appears to be otherwise functional although
> the clock is stuck at the forward time. The daemons
> (which are Axis-based web services) continue to function and service
> requests, the node remains pingable, there is no loss of network.
> Once the clock on the dom0 catches up to the time on the domU,
> then the clock advances normally again on the domU as though nothing
> had happened.
>
> It is happening on any given domU on the average of every 2-3 weeks,
> although they do appear to happen in time clusters.  i.e. 3-4 domU's  
> report the clock skew within the span of a day or two, and then
> nothing for a couple of weeks, and then we get another round and so forth.
>
> Only one of the several domU's on the machine is affected at any
> given time.  We see this on two different pieces of hardware that
> are identically configured.
>
> There is nothing in dmesg, nothing in /var/log/messages or related
> files,nothing in the xend logs.  On the domU /var/log/messages
> and related files have a total gap during this time.  The logs of the
> daemons continue to get written at a constant time stamp, although
> I have seen cases where the system clock is 19:53, a daemon log
> gets rotated at 19:40 and the time stamp on the rotated log shows
> 19:40.
>
> Any help?  Has anyone else seen anything like this?
>

Nope.. I haven't seen that.

Did you search Redhat bugzilla about that? That's good source for 
RHEL5 Xen related problems.

Also does it still happen if you downgrade domU kernel to, say, 2.6.18-128 ?
aka try to figure out if it's a problem in domU or dom0.

-- Pasi


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