[ntp:questions] Need suggestion on compensating clock drift on Xen based VPS

Ulrich Windl Ulrich.Windl at RZ.Uni-Regensburg.DE
Thu Nov 12 13:24:56 UTC 2009


malayter at gmail.com (Ryan Malayter) writes:

> On Mon, Aug 24, 2009 at 5:32 PM, Todd Glassey<tglassey at earthlink.net> wrote:
>
>> Only someone who was trying to sell VM systems would even bother - its way
>> to simple to maintain the VM system as a client and make all of this noise
>> in the wind.
>
> I am not selling anything... where did you get that from? Perhaps I am
> just mis-understanding your comment, which has an interesting
> grammatical structure.
>
> The simple fact is that timekeeping in VMs isn't particularly easy,
> because the guest VMs are in effect "paused" at random intervals, and
> then interrupts are fired more quickly than normal to "catch up".
> Running ntp as a client in a VM without any other compensating
> controls works well for lightly-loaded systems, but not so well for a
> busy host with may VMs.

I agree: We are running ntpd on XEN VMs (paravirtualized)
here. Monitoring the reported offset shows "interesting" graphs, but as
long as it works to everybody's satisfaction, it's OK.

Maybe Dave could write an article about "Time in virtual machines" (if
not done already) ;-)

Regards,
Ulrich




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