Dom0 <> DomU clock sync

Dom0 <> DomU clock sync

[Sébastien RICCIO]

Hello !

Just a quick question about time synchronization between xen dom0 and 
domUs...

We're running Xen 3.1 64-bit, with 32 and 64 bits linux guests.

It's up since 89 days and the domU's time is around 5 minutes behind the 
dom0,
which is updated via ntpdate...

Any idea why it doesn't sync the guests even that 
/proc/sys/xen/independent_wallclock is 0 ?

Could it be an option that I missed in dom0/domU kernel ?

Thanks for your help !


-- 
Sébastien Riccio
SwissCenter / OpenBusiness SA
sr@openbusiness.com
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Re: Dom0 <> DomU clock sync

[Keir Fraser]

You're not running ntpd in the domU as well, right? Just worth checking...
Apart from that I don't think you can be doing anything wrong. Any weirdness
after long uptime is of course interesting, as it's something that's hard
for developers to test.

If you create a new domU (doesn't need to be from scratch installation -
e.g., just restarting a domU, or starting an existing dormant domU, would
do) then is its time behind dom0, or in sync?

 -- Keir

On 3/9/07 08:45, "Sébastien RICCIO" <sr@swisscenter.com> wrote:

> Hello !
> 
> Just a quick question about time synchronization between xen dom0 and
> domUs...
> 
> We're running Xen 3.1 64-bit, with 32 and 64 bits linux guests.
> 
> It's up since 89 days and the domU's time is around 5 minutes behind the
> dom0,
> which is updated via ntpdate...
> 
> Any idea why it doesn't sync the guests even that
> /proc/sys/xen/independent_wallclock is 0 ?
> 
> Could it be an option that I missed in dom0/domU kernel ?
> 
> Thanks for your help !
> 

Re: Dom0 <> DomU clock sync

[Sébastien RICCIO]

Hi Keir,

Thank you for your answer.

Ntpd is not running in dom0. I am updating the dom0 time with ntpdate 
(crontab every hour).
Should ntpd be running on dom0 ?

Dom0
[root@xen01 /]# date
Mon Sep  3 15:59:37 CEST 2007

DomU (started 5 hours ago)
ns1 bin # date
Mon Sep  3 15:58:05 CEST 2007

ns1 bin # uptime
 15:58:10 up  5:21,  3 users,  load average: 0.00, 0.00, 0.11


But this is strange... I just rebooted the vm:

Dom0:
[root@xen01 /]# date
Mon Sep  3 16:04:13 CEST 2007

DomU:
ns1 ~ # date
Mon Sep  3 16:02:41 CEST 2007

There is already a difference when the vm is freshly rebooted.
Same after a shutdown/xm create....

Weird... Any idea ?

Thanks again!

-- 
Sébastien Riccio
SwissCenter / OpenBusiness SA
sr@openbusiness.com






Keir Fraser a écrit :
> You're not running ntpd in the domU as well, right? Just worth checking...
> Apart from that I don't think you can be doing anything wrong. Any weirdness
> after long uptime is of course interesting, as it's something that's hard
> for developers to test.
>
> If you create a new domU (doesn't need to be from scratch installation -
> e.g., just restarting a domU, or starting an existing dormant domU, would
> do) then is its time behind dom0, or in sync?
>
>  -- Keir
>
> On 3/9/07 08:45, "Sébastien RICCIO" <sr@swisscenter.com> wrote:
>
>   
>> Hello !
>>
>> Just a quick question about time synchronization between xen dom0 and
>> domUs...
>>
>> We're running Xen 3.1 64-bit, with 32 and 64 bits linux guests.
>>
>> It's up since 89 days and the domU's time is around 5 minutes behind the
>> dom0,
>> which is updated via ntpdate...
>>
>> Any idea why it doesn't sync the guests even that
>> /proc/sys/xen/independent_wallclock is 0 ?
>>
>> Could it be an option that I missed in dom0/domU kernel ?
>>
>> Thanks for your help !
>>
>>     
>
>
>
>
>   

Re: Dom0 <> DomU clock sync

[Keir Fraser]

On 3/9/07 15:07, "Sébastien RICCIO" <sr@swisscenter.com> wrote:

> Ntpd is not running in dom0. I am updating the dom0 time with ntpdate
> (crontab every hour).
> Should ntpd be running on dom0 ?

So long as ntpdate calls settimeofday(), this should be sufficient to update
Xen's notion of time too. It seems that isn't happening for some reason.

Do all guests (including dom0) have independent_wallclock equal to 0?

What kernel are you using in dom0 (e.g., vendor kernel?).

Ntpd in dom0 would be an interesting thing to try. That should cause dom0 to
periodically (every few minutes) push its time down to Xen to be picked up
by all domUs. But really ntpdate should be doing the right thing...

In our kernels it should be *impossible* for dom0 and domU time to diverge
when independent_wallclock is set to zero everywhere...

 -- Keir

Re: Dom0 <> DomU clock sync

[Sébastien RICCIO]

Hi again,

I just tried to use ntpd in dom0. So far nothing changed.
The guests are still a couple of minutes behind the dom0.

Dom0 and DomU's are set to independent_wallclock 0.

Kernels are compiled from the sources included in Xen 3.1.

I don't know where to head next :))

Thanks for your help.

-- 
Sébastien Riccio
SwissCenter / OpenBusiness SA
sr@openbusiness.com



Keir Fraser a écrit :
> On 3/9/07 15:07, "Sébastien RICCIO" <sr@swisscenter.com> wrote:
>
>   
>> Ntpd is not running in dom0. I am updating the dom0 time with ntpdate
>> (crontab every hour).
>> Should ntpd be running on dom0 ?
>>     
>
> So long as ntpdate calls settimeofday(), this should be sufficient to update
> Xen's notion of time too. It seems that isn't happening for some reason.
>
> Do all guests (including dom0) have independent_wallclock equal to 0?
>
> What kernel are you using in dom0 (e.g., vendor kernel?).
>
> Ntpd in dom0 would be an interesting thing to try. That should cause dom0 to
> periodically (every few minutes) push its time down to Xen to be picked up
> by all domUs. But really ntpdate should be doing the right thing...
>
> In our kernels it should be *impossible* for dom0 and domU time to diverge
> when independent_wallclock is set to zero everywhere...
>
>  -- Keir
>
>
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel
>
>
>   

Re: Dom0 <> DomU clock sync

[Alex Tomkins]

On 03/09/07, Keir Fraser <Keir.Fraser@cl.cam.ac.uk> wrote:
> So long as ntpdate calls settimeofday(), this should be sufficient to update
> Xen's notion of time too. It seems that isn't happening for some reason.
>
> Do all guests (including dom0) have independent_wallclock equal to 0?
>
> What kernel are you using in dom0 (e.g., vendor kernel?).
>
> Ntpd in dom0 would be an interesting thing to try. That should cause dom0 to
> periodically (every few minutes) push its time down to Xen to be picked up
> by all domUs. But really ntpdate should be doing the right thing...
>
> In our kernels it should be *impossible* for dom0 and domU time to diverge
> when independent_wallclock is set to zero everywhere...
>
>  -- Keir

It occurs with ntpd in dom0 as well:

tomkins@host1 ~ $ date
Mon Sep  3 14:42:04 UTC 2007
testdomu:~# date
Mon Sep  3 14:43:11 UTC 2007

dom0 runs ntpd, the only thing which causes the domUs to correct
themselves is hwclock in dom0.  It's a fairly old machine though and
would need to be updated for testing:

Linux host1 2.6.16.29-xen-host1-1 #1 Sat Nov 25 19:57:50 Local time
zone must be set--see zic manu x86_64 AMD Athlon(tm) 64 Processor
3700+ AuthenticAMD GNU/Linux

However I've been moving all Xen servers away from Gentoo and
switching them to CentOS which doesn't seem to have the same problem.
I remember someone else having similar problems:

<http://lists.xensource.com/archives/html/xen-users/2006-11/msg00861.html>

I've still got a couple of servers which haven't been updated to
CentOS yet.  I could upgrade them to a more recent Xen release as well
as a more recent kernel to test it.


-- 
Alex Tomkins <tomkins@darkzone.net>