[ntp:questions] Flash 400 on all peers; can't get ntpd to be happy

David Woolley david at ex.djwhome.demon.invalid
Mon Mar 7 08:37:42 UTC 2011

Ralph wrote:
>> Can it even be fixed?  
> Well I hope so.  Not to bash on the linux world, but I don't get why this timing thing is so hard...  I mean I understand it from a techinical perspective because I've read all about how the hardware and timers and stuff work, but practically speaking, somebody needs to get with the program and find a solution.  I've done many, many windows installs in Virtual PC, VMWare, Hyper-V, and others and even without the VM tools installed in the guest I've never had a clock problem that was big enough to worry about.

Virtual machines do not normally run in real time. The host speeds up 
and slows down the time seen by the guest so that time appears to flow 
almost normally, but the VM may actually be locked out of the processor 
for longish intervals. If you try and run a network time protocol, it 
sees true time and can't reconcile it with the fiction that is being fed 
to it by the host.

This can also cause very large interrupt latencies.

Run as a real machine, Linux ntpd, out of the box, will outperform 
nearly any Windows machine, but run on a VM, one needs to turn all the 
right knobs and the best option is often to synchronise the host and 
then occasionally run ntpdate, etc., in case the host has got its 
bookkeeping wrong.

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