Re: Re: [PATCH] [PVOPS] dom0 sync xen wallclock

[Jeremy Fitzhardinge <jeremy@goop.org>]

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
> world.

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).

     J