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Re: [Xen-users] Xen time drift issues



Priya,

What test are you using to  measure  the drift?
Are your VMs HVM or PVM?
What kernel version is your DomUs?

Do you have acpi enabled on any HVM DomUs?


On Jul 8, 2009, at 9:53 AM, Priya wrote:

@tanuj: Thanks! I am not using NTP for syncing. The reason for that is
that I want to get an idea of the fidelity of the time returned by
domU and dom0 w.r.t. the actual real time. I expected to see a
difference, but what is puzzling me is that the difference increases
in such a linear fashion.

@peter: As I mentioned in my previous email, the drift is ~50
microseconds/second on domU and slightly less on dom0

I have been trying to find some documentation pertaining to how Xen
virtualizes the different hardware timers. If anyone has a link to
such a technical report, please send me a link.

Thanks!

Priya


On Wed, Jul 8, 2009 at 9:37 AM, Peter Booth<peter_booth@xxxxxx> wrote:
How are you measuring this drift?

Sent from my iPhone

On Jul 8, 2009, at 7:59 AM, Tanuj Bansal <bansal.tanuj83@xxxxxxxxx> wrote:

Hi Priya:

If you are using NTP, then shutdown the NTP service on all DomU and
restart
it on Dom0 only.



Regards,

Tanuj Bansal

-----Original Message-----
From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx
[mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Priya
Sent: Wednesday, July 01, 2009 8:55 PM
To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-users] Xen time drift issues

Hello everyone!

I been observing some peculiar time drift on my Xen domains (dom0 and
domUs).  The time (as returned by timeofday) on my domains drifts at
an almost steady rate from the real time ( as read from the time stamp
counter ).

The drift is so constant that it makes me think there should be some
simple explanation for it in the way Xen keeps time.

Some info about my set up:
guest OS: ubuntu
independent_wallclock is set to default 0 on all domains
no NTP synchronization

The drift is around 50 microseconds / second on all the domains. Has
anyone else observed this? If anyone can point me to some
documentation that explains this behavior, that would be great!

Good day!

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