Losing time like crazy (1s short per 10s) - how to investigate?

[Martin S. Weber]

This is on FreeBSD 10.3-RELEASE-p7. I've only noticed this today,
so I'd suspect this is post the p7 update (although I haven't
investigated in that direction yet). I'm losing roughly a second
per 10 seconds wall time.  Look at this crazy guy:

# ntpd -q ; sleep 10; ntpd -q                                                                
16 Aug 13:12:52 ntpd[48425]: ntpd 4.2.8p8-a (1): Starting
16 Aug 13:12:52 ntpd[48425]: Command line: ntpd -q
16 Aug 13:12:52 ntpd[48425]: proto: precision = 0.230 usec (-22)
16 Aug 13:12:52 ntpd[48425]: leapsecond file ('/var/db/ntpd.leap-seconds.list'): good hash signature
16 Aug 13:12:52 ntpd[48425]: leapsecond file ('/var/db/ntpd.leap-seconds.list'): loaded, expire=2016-12-28T00:00:00Z last=2015-07-01T00:00:00Z ofs=36
16 Aug 13:12:52 ntpd[48425]: Listen and drop on 0 v6wildcard [::]:123
16 Aug 13:12:52 ntpd[48425]: Listen and drop on 1 v4wildcard 0.0.0.0:123
16 Aug 13:12:52 ntpd[48425]: Listen normally on 2 em0 10.10.1.79:123
16 Aug 13:12:52 ntpd[48425]: Listen normally on 3 lo0 [::1]:123
16 Aug 13:12:52 ntpd[48425]: Listen normally on 4 lo0 [fe80::1%2]:123
16 Aug 13:12:52 ntpd[48425]: Listen normally on 5 lo0 127.0.0.1:123
16 Aug 13:12:52 ntpd[48425]: Listening on routing socket on fd #26 for interface updates
16 Aug 13:12:54 ntpd[48425]: ntpd: time set +0.891676 s
ntpd: time set +0.891676s
16 Aug 13:13:04 ntpd[48426]: ntpd 4.2.8p8-a (1): Starting
16 Aug 13:13:04 ntpd[48426]: Command line: ntpd -q
16 Aug 13:13:04 ntpd[48426]: proto: precision = 0.229 usec (-22)
16 Aug 13:13:04 ntpd[48426]: leapsecond file ('/var/db/ntpd.leap-seconds.list'): good hash signature
16 Aug 13:13:04 ntpd[48426]: leapsecond file ('/var/db/ntpd.leap-seconds.list'): loaded, expire=2016-12-28T00:00:00Z last=2015-07-01T00:00:00Z ofs=36
16 Aug 13:13:04 ntpd[48426]: Listen and drop on 0 v6wildcard [::]:123
16 Aug 13:13:04 ntpd[48426]: Listen and drop on 1 v4wildcard 0.0.0.0:123
16 Aug 13:13:04 ntpd[48426]: Listen normally on 2 em0 10.10.1.79:123
16 Aug 13:13:04 ntpd[48426]: Listen normally on 3 lo0 [::1]:123
16 Aug 13:13:04 ntpd[48426]: Listen normally on 4 lo0 [fe80::1%2]:123
16 Aug 13:13:04 ntpd[48426]: Listen normally on 5 lo0 127.0.0.1:123
16 Aug 13:13:04 ntpd[48426]: Listening on routing socket on fd #26 for interface updates
16 Aug 13:13:06 ntpd[48426]: ntpd: time set +1.218972 s
ntpd: time set +1.218972s

This is a CRAZY amount of skew. I've never noticed this before --
and I have tmux with a clock running on various servers I'm logged
in; And a chiming wall clock whose skew I check vs. my system clock.
This is a new "feature" - I suspect an unfortunate interaction with
FreeBSD-EN-16:13.vmbus. Running ntpd or not doesn't make a difference,
interestingly, I'm still losing time even with ntpd on (above example
is with ntpd not running).

How can I investigate what might be the source of the problem? What
info can I give that might help more informed people jump to the
correct conclusion what's off?

Here's what I've lost since starting to write this email:

16 Aug 13:17:58 ntpd[48461]: Listening on routing socket on fd #26 for interface updates
16 Aug 13:18:31 ntpd[48461]: ntpd: time set +32.207535 s
ntpd: time set +32.207535s

This can't be right.

TIA,
-Martin