'Live' Migrate messes up NTP on FreeBSD domU - any suggestions?

[Karl Pielorz]

Hi,

Ok, I've done some proper research into this now...

When Migrating a domU FreeBSD (10.1-R p6) between hosts, it "more often 
than not" gains time.

This breaks NTP on the domU.

I setup a script on the domU being migrated that read out it's clock - and 
called out to an external machine to read it's clock - i.e.

"
  Me: Tue Nov  3 09:55:51 GMT 2015
Them: Tue Nov  3 09:55:51 GMT 2015

  Me: Tue Nov  3 09:55:52 GMT 2015
Them: Tue Nov  3 09:55:52 GMT 2015
"

As you can see 'Me' and 'Them' is in sync.

At this point I live migrated the FreeBSD box from one XenServer (6.5-SP1 
w/hotfixes) to another in the pool (same hardware spec / XenServer etc.)

The domU's clock got advanced by a number of seconds:

"
  Me: Tue Nov  3 09:55:52 GMT 2015
Them: Tue Nov  3 09:55:52 GMT 2015

 [Migrate 'Me' Happens Now]

  Me: Tue Nov  3 09:56:02 GMT 2015
Them: Tue Nov  3 09:55:58 GMT 2015

  Me: Tue Nov  3 09:56:06 GMT 2015
Them: Tue Nov  3 09:55:59 GMT 2015

  Me: Tue Nov  3 09:56:07 GMT 2015
Them: Tue Nov  3 09:56:00 GMT 2015

  Me: Tue Nov  3 09:56:08 GMT 2015
Them: Tue Nov  3 09:56:01 GMT 2015
"

So you can see during the migrate the 'Me' (domU being moved) clock picks 
up 3 seconds, then another 4 seconds to make it 'ahead' 7 seconds in total 
- at which point it stabilises).

It stays this way then - which is enough to cause NTP to "give up" trying 
to bring that back into alignment.

> http://xenbits.xen.org/gitweb/?p=xen.git;a=commit;h=f8e8fd56bd7d5675e8331
> b4ec74bae76c9dbf24e
> http://xenbits.xen.org/gitweb/?p=xen.git;a=commit;h=32c864a35ece2c24a336d
> 183869a546798a4b241

Are either of those fixes likely to cure this?

Thanks,

-Karl