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?
-- Ian
Index: sys/amd64/vmm/io/vhpet.c
===================================================================
--- sys/amd64/vmm/io/vhpet.c (revision 324176)
+++ sys/amd64/vmm/io/vhpet.c (working copy)
@@ -51,7 +51,7 @@ __FBSDID("$FreeBSD$");
static MALLOC_DEFINE(M_VHPET, "vhpet", "bhyve virtual hpet");
-#define HPET_FREQ 10000000 /* 10.0 Mhz */
+#define HPET_FREQ 16777216 /* 16.7 (2^24) Mhz */
#define FS_PER_S 1000000000000000ul
/* Timer N Configuration and Capabilities Register */
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