Re: [Xen-users] time synchronization problem (using NTP)

["Ulrich Windl" <ulrich.windl@xxxxxxxxxxxxxxxxxxxx>]

On 11 Oct 2006 at 5:55, Thomas Harold wrote:

> Ulrich Windl wrote:
> > Hi,
> > 
> > using SLES10 I'm unable to synchronize the time of DomU with that of Dom0. 
> > There 
> > is a persistent offset of about 3 seconds!
> 
> (laughs) I just happen to be working on this myself.  All of my DomUs 
> are about 15 seconds fast compared to the Dom0 and I've been searching 
> the archives to figure out why this happens.

Hi!

I've dumped VMware server because it was unable to keep the time. XEN looked 
much 
better, but now I'm puzzled: Each DomU has it's own kernel with a software 
clock: 
Why shouldn't it be possible to tune that software clock?

Using Dom0's clock (IMHO) takes away some of the freedoms DomU offers: Testing 
new 
kernels with probably different time settings.

OK, normally you want to have "just the correct time".

> 
> -------------------------------------------
> 
> According to the wiki:
> 
> http://wiki.xensource.com/xenwiki/InstallationNotes
> 
> xenU services
> 
> The following services are not needed anymore:
> 
> * ntpd
> 
> the xenU uses the dom0 time

Are there any statements how close both times (Dom0 and DomU) are together? 
Three 
seconds seems way too far apart for me. (It seems another DomU has a different 
constant offset)

> 
> If you want to run ntp in the domU, try: echo 1 > 
> /proc/sys/xen/independent_wallclock

OK, trying that. So far ntpd could sync at least. I'll have to monitor offset 
and 
stability however before I make any conclusion. Thanks for the hint!

> 
> -------------------------------------------
> 
> But if I look through news.gmane.org's archive of xen-users 
> (gmane.comp.emulators.xen.user), there's conflicting advice given back 
> in April 2006 (and Nov 2005... and May 2005).
> 
> One camp says that we should run ntpd in Dom0, leave 
> independent_wallclock set to zero and the DomUs should take their time 
> from Dom0 and stay in sync.

It's probably simpler and needs less resources IF IT WORKS.

> 
> The other camp says that we should set independent_wallclock to 1 and 
> run ntpd within the DomUs.

This will add more flexibility (e.g. testing different versions or 
configurations 
of NTP) IF IT WORKS.

Now I'm looking for a version that simply works.

Regards,
Ulrich


_______________________________________________
Xen-users mailing list
Xen-users@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-users