[TriLUG] Xen HVM guest has severe clock drift
Justis Peters
jtrilug at indythinker.com
Thu Mar 10 13:48:25 EST 2011
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
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