[TriLUG] Xen HVM guest has severe clock drift

[Igor Partola]

Wow, Justis that is some thorough research. Yes, those last two are
the other two questions where I asked about this problem. Sounds like
I should just move to a PV VPS, but I will let the provider know about
what they can do on their end since they seemed receptive to it in the
past.

Thanks everyone for the useful info.

Igor

On Thu, Mar 10, 2011 at 1:48 PM, Justis Peters <jtrilug at indythinker.com> wrote:
> 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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