Re: [Xen-users] xen time sync problem

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

On 21 Feb 2007 at 17:11, Tim Post wrote:

> On Wed, 2007-02-21 at 09:31 +0100, Ulrich Windl wrote:
> > On 20 Feb 2007 at 21:07, Nadeem Shahbaz wrote:
> > 
> > > Hi,
> > > I am facing problem in sync time within DomU with Dom0. After gone
> > > through mailing lists, I have set /proc/sys/xen/independent_wallclock
> > > to 0. But still DomU are not syncing their time :-S Machine using
> > 
> > Then you missed my messages on how it actually did work. I think 0 is the 
> > default. 
> > So if the default is bad four you, try a change!
> 
> 0 is the default, meaning ! independent wall clocks. I don't see how
> altering this value to 1 can help solve his issue? While I do appreciate
> and employ your problem solving method frequently I don't think it
> applies here... 

XEN (as of SLES10 x86_64) seemed to fail to sync the DomU clocks, so I started 
to 
sync them with NTP. This works, and I'm quite satisfied with it (even though 
our 
primary server has failed):

# ntpq -p
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
 LOCAL(0)        LOCAL(0)        10 l   44   64  377    0.000    0.000   0.001
-rkdvmso5.dvm.kl 192.168.0.11     4 u  536 1024  377    0.153    6.311   0.149
-rksapas01.dvm.k 192.168.0.48     6 u  991 1024  377    0.001   -1.038   0.812
-rksapas02.dvm.k 192.168.0.44     7 u  865 1024  376    0.001   -5.087   0.809
-rksapas03.dvm.k 192.168.0.44     7 u  976 1024  377    0.209   -3.898   1.396
+rksapas04.dvm.k 192.168.0.48     6 u  682 1024  377    0.323    0.278   0.802
+rksapas05.dvm.k 192.168.0.48     6 u  667 1024  377    0.351    0.564   0.782
*rksapas06.dvm.k 192.168.0.63     5 u  544 1024  376    4.418    0.667   0.038
-rksapas07.dvm.k 192.168.0.48     6 u  897 1024  377    0.001   -0.751   0.829
-rksapas08.dvm.k 192.168.0.64     5 u  140 1024  376    0.317    3.123   0.810
-rksapas10.dvm.k 192.168.0.44     7 u  789 1024  376    0.001   -3.955   0.768

(Every server is a XEN para-virtual host)

> 
> Unless of course the poster just gives up sets them independently and
> maintains an ntp time sync across the guests to dom-0.
> 
> That means its still broken, just not annoying anymore. Not sure about
> the poster, but that would bug me relentlessly until I determined the
> issue.

Maybe some /proc/xen/clock_stats would be helpful to find out more on the XEN 
built-in clock synchronisation not working to everybody's satisfaction. 
Personally 
I believe that independent clocks keep up the illusion that a virtual server is 
a 
real server.

Regards,
Ulrich


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