Re: [Xen-devel] domU time drifting

[Keir Fraser <keir@xxxxxxx>]

If the domU kernels are pv_ops kernels, they don't keep their time in sync
with dom0 after boot. You have to run ntpd in every domU.

 -- Keir

On 13/12/2010 00:12, "Carl Jones" <carl@xxxxxxxxxxxxx> wrote:

> Hi,
> 
> I am trying to track down the cause of time drifting on our domUs.
> We're using various versions of Xen, and various domU kernels.
> 
> dom0s all run ntpd and are in sync. No issues there.
> 
> dom0s are all running CentOS 5 64bit. domUs run various distributions
> (the examples below happen to be Debian and Ubuntu only).
> 
> domUs that do not run ntpd tend to drift (both forwards and
> backwards). domUs are using clocksource=xen. dom0s are using
> clocksource=jiffies.
> 
> Some example setups:
> 
> Xen: 3.4.3
> dom0: 2.6.18.8 x86_64 based on el5 sources
> domU: 2.6.30.5 i386
> domU uptime: 68 days
> 
> dom0: Sun Dec 12 23:45:59 UTC 2010
> domU: Sun Dec 12 23:44:48 UTC 2010
> 
> Xen: 3.3.1
> dom0 2.6.18.8 x86_64 from xen.org
> domU: 2.6.33.3 i386
> domU uptime: 34 days
> 
> dom0: Sun Dec 12 23:51:20 UTC 2010
> domU: Sun Dec 12 23:50:39 UTC 2010
> 
> Xen: 3.4.3
> dom0: 2.6.18.8 x86_64 based on el5 sources
> domU: 2.6.30.5 i386
> domU uptime: #1 28 days #2 26 days
> 
> dom0: Sun Dec 12 23:58:23 UTC 2010
> domU #1: Sun Dec 12 23:58:03 UTC 2010
> domU #2: Sun Dec 12 23:58:04 UTC 2010
> 
> The last example is interesting. Two domUs on the same host have the
> same (incorrect) time. Same domU kernel. Different uptime.
> 
> I've tried suggestions in bug reports like these:
> 
> http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=534978
> http://wiki.debian.org/Xen#A.27clocksource.2BAC8-0.3ATimewentbackwards.27
> http://my.opera.com/marcomarongiu/blog/2010/08/18/debugging-ntp-again-part-4-a
> nd-last
> 
> But so far the problem persists.
> 
> Is there anything we can do on the host side of things to prevent
> domUs from drifting? With clocksource=xen shouldn't the domUs stay in
> sync provided the host keeps the correct time?
> 
> Please let me know if I can provide further details.
> 
> Regards,
> Carl
> 
> _______________________________________________
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> Xen-devel@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-devel



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