[ntp:questions] Win7: ntpd adjusting time backwards

Jeroen Mostert jmostert at xs4all.nl
Thu Dec 13 20:30:52 UTC 2012


On 2012-12-13 09:08, David Woolley wrote:
> Jeroen Mostert wrote:
>
>> negatively affect performance of the host (which makes sense, since driving
>> all virtuals with 1000 interrupts/sec can't be easy). Even so,
>
> You wouldn't expect 1ms ticks. You might get 20 ticks back to back, and then a
> gap of 20ms, or even larger numbers. VMs generally only get a virtual 1 second
> per second as a long term average.
>
If your virtualization is that poor, get a refund. :-) However, it's certainly 
true that you cannot count on high-frequency ticks in a VM. There's simply not 
enough horsepower on the guest to achieve that, unless you've got a one-to-one 
mapping between actual and virtual hardware (and then there's not much point to 
virtualizing).

> There has been conflicting advice on running ntpd on VMs, but I suspect the
> current advice to run it is an easy way of getting coarse timing right. Fine
> timing should use the host timing and any special VM support for the OS.

I agree. In the case of Windows on VMWare, however, there doesn't seem to be any.

-- 
J.



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