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Re: [Xen-devel] Re: [PATCH] [PVOPS] dom0 sync xen wallclock

On 02/10/2010 04:06 PM, Keir Fraser wrote:
A Xen ABI for adjtime()-alike warping of Xen system time is something we
should add at some point, as that's the logical thing for ntp in dom0 to
affect, keeping the system's 'nanosecond ticker' in sync with the wider

Hm. I think it would be best to keep the ticker unchanged, but perhaps offer a mechanism so that dom0 can set separate offset and drift parameters which other domains can query to may system time to global time. But I don't think even that is a very compelling idea.

  That'd keep all domU clocks in sync, all except for fixed wallclock
offsets. But it doesn't currently exist, so instead it gets bunged in with
Xen's existing settimeofday()-alike interface: hence domUs either can see
discontinuities, or don't get the automatic benefits of ntp sync at all,
because they only read the wallclock offset at boot time.

I suppose. All the domains can already run ntp if you really want to keep them in sync with each other and/or dom0 and/or the outside world. I'm not sure there's much point in making Xen ABI changes in this area; anything we do will come down to being a partial and probably inadequate reimplementation of ntp (esp when you consider how to deal with migration).


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