[TriLUG] Xen HVM guest has severe clock drift

[Justis Peters]

On 03/10/2011 10:52 AM, Igor Partola wrote:
> It's with ThrustVPS. They are a budget provider, so I guess you get
> what you pay for. They do offer a PV option, and otherwise their
> performance seems fine so I am wondering if switching to that would
> work.
Theoretically, your Ubuntu VM will get the best performance by running 
paravirtualized. Xen performs very well with PV guests, as this is what 
the hypervisor was primarily designed to manage.

Chances are that ThrustVPS runs their PV and HVM domUs on different 
dom0s. So, the actual performance you see will have more to do with how 
much your new dom0 is taxed on resources. That said, Xen does an 
excellent job of sharing resources between lots of paravirt domUs.

Also, if you move to paravirt, you could probably set " 
/proc/sys/xen/independent_wallclock" to "0" and allow the dom0 to manage 
your time. Hopefully, the time is slightly more stable on the dom0.

The link below seems to be a fix for HVM mode. It would, unfortunately, 
require action from ThrustVPS that is probably outside their normal path:
http://not403.blogspot.com/2010/12/changing-clock-source-for-xen-hvm-domu.html

Here are some other things that ThrustVPS could look into:
http://serverfault.com/questions/116637/weird-fluctuating-time-on-a-xen-linux-guest
http://wiki.xensource.com/xenwiki/xenpm#head-253cbbe6cf12fa31e10022610cd7090aa980921f

This seems to be a local (domU) workaround:
https://www.hosthop.com/hop/knowledgebase/25/Xen-HVM-Guest-Clock-Drift.html

Here are some other workarounds that may or may not apply in your case:
http://wiki.debian.org/Xen#A.27clocksource.2BAC8-0.3ATimewentbackwards.27

AFAICT, these are some of the other places you've asked the question:
http://serverfault.com/questions/245401/xen-hvm-guest-has-severe-clock-drift
http://www.lowendtalk.com/questions/4335/thrustvps-xen-hvm-clock-drift

Best of luck and let us know what solution you find.

Kind regards,
Justis