bhyve clock problem, solved by kern.timecounter.hardware="TSC-low" in /etc/sysctl.conf

Paul Vixie paul at
Fri Apr 10 17:35:58 UTC 2015

here is a representative one-hour sample of ntp messages from
/var/log/messages on a freebsd 10.1 bhyve guest:

> Apr 10 12:00:46 family ntpd[634]: time reset -0.613057 s
> Apr 10 12:17:02 family ntpd[634]: time reset -0.604933 s
> Apr 10 12:33:51 family ntpd[634]: time reset -0.650622 s
> Apr 10 12:55:06 family ntpd[634]: time reset -0.743930 s

that's with kern.timecounter.hardware: HPET, which is the default.

a "time reset" from ntpd means the clock either won't slew at all or
can't slew fast enough. in other words a normal freebsd 10.1 server can
run for months or even years without ever outputting one of these messages.

google reports that some folks have had good luck with
kern.timecounter.hardware: TSC-low. so i tried that on another freebsd
10.1 bhyve guest on the same bhyve server, with dramatic results -- no
more ntpd messages.

can we make TSC-low the default?


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