On Wed, 2017-10-25 at 00:43 +0300, Boris Samorodov wrote:
> Hi Ian, All!
> 
> 22.10.2017 01:15, Ian Lepore пишет:
> > 
> > On Sat, 2017-10-21 at 17:07 -0400, Michael Voorhis wrote:
> > > 
> > > Ian Lepore writes:
> > > > 
> > > > 
> > > > Beyond that, I'm not sure what else to try.  It might be necessary to
> > > > get some bhyve developers involved (I know almost nothing about it).
> > > NTPD behaves more normally on uniprocessor VMs.
> > > 
> > > A FreeBSD bhyve-guest running on a freebsd host will select a
> > > different timecounter depending on whether it is a multiprocessor or a
> > > uniprocessor.  My uniprocessor bhyve-vm selected TSC-low as the best
> > > timecounter in a uniprocessor.  NTP functions there as expected.
> > > 
> > > kern.timecounter.choice: TSC-low(1000) ACPI-fast(900) HPET(950) i8254(0) 
> > > dummy(-1000000)
> > > kern.timecounter.hardware: TSC-low
> > > 
> > > The very same VM, when given two total CPUs, selected HPET (if I
> > > recall) and the timekeeping with NTPD was unreliable, with many
> > > step-resets to the clock.
> > > 
> > Hmm, I just had glance at the code in sys/amd64/vmm/io/vhpet.c and it
> > looks right.  I wonder if this is just a simple roundoff error in
> > converting between 10.0MHz and SBT units?  If so, that could be wished
> > away easily by using a power-of-2 frequency for the virtual HPET.  I
> > wonder if the attached patch is all that's needed?
> I suppose the answer is "yes", the patch helped. Here are two samples
> (host for bhyve VM without your patch and after patching):
> ---
> https://poudriere.passap.ru/misc/ntpd.jot.log-HPET.frequency.10000000.txt
> https://poudriere.passap.ru/misc/ntpd.jot.log-HPET.frequency.16777216.txt
> ---
> 
> The command was:
> % for t in `jot 1000`; do ntpq -pn; sleep 64; done
> 
> The patch made the system to stabilize the process.
> Ian, thank you!
> 

Hmmm.  The startup behavior wasn't great, it took a long time and
several clock steps for it to figure out the frequency error and get
the clock under control.  But, as you say, it did eventually stabilize
this time.

Can you show the /var/db/ntpd.drift file contents of the host and
guest?  Ideally, now that it's stable, the two values should be very
close.  If they're not, maybe this isn't the right fix.

-- Ian
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