RE: [Xen-devel] [PATCH] linux-2.6.18-xen.hg: fix interaction of NTP and dom0->xen time updates

[Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>]

Hi Tim --

Cool!

Just checking... this provides improvement when:

1) the patch is applied to dom0
2) dom0 is running NTP
3) pv domU has independent_wallclock=0
4) pv domU is NOT running NTP

Correct?  Does it also help when:

1) the patch is applied to pv domU
2) pv domU has independent_wallclock=1
3) pv domU IS running NTP

Are there any other configurations where it will
help?  Are there any configurations where it might
cause problems?

Thanks,
Dan

> -----Original Message-----
> From: Tim Deegan [mailto:Tim.Deegan@xxxxxxxxxx]
> Sent: Wednesday, March 18, 2009 5:14 AM
> To: xen-devel@xxxxxxxxxxxxxxxxxxx
> Subject: [Xen-devel] [PATCH] linux-2.6.18-xen.hg: fix 
> interaction of NTP
> and dom0->xen time updates
> 
> 
> Don't discard NTP sync when updating Xen wallclock time from dom0,
> as that's almost the first thing we do when we become synced.
> Move the call to ntp_clear() into do_settimeofday(), which is the
> only caller of __update_wallclock() that looks like it should break
> NTP sync.  
> 
> This fixes the timer chain that sets Xen's wallclock every minute when
> dom0 is NTP synced, which in turn greatly improves wallclock 
> accuracy in
> PV domU.
> 
> Signed-off-by: Tim Deegan <Tim.Deegan@xxxxxxxxxx>
> 
> -- 
> Tim Deegan <Tim.Deegan@xxxxxxxxxx>
> Principal Software Engineer, Citrix Systems (R&D) Ltd.
> [Company #02300071, SL9 0DZ, UK.]
>

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