Neel Natu wrote:
> Hi Paul,
> On Fri, Apr 10, 2015 at 10:35 AM, Paul Vixie <> wrote:
>> ...
>> can we make TSC-low the default?
> The choice of using the TSC is not without issues:
> - As rstone@ points out the TSCs need to be synchronized across physical cpus.

ok, then the reason i'm not seeing this is i have a single 6-core CPU.
(ntpd would complain about clocks going backward.)

> - Depending on system load the guest's estimate of the TSC frequency
> might be way off the mark.

i see what you mean.

> So, in a way the HPET or the ACPI time counters are better since both
> the host and guest agree on the frequency. But it seems there is
> either an issue with the emulation or an artifact due to the
> guest-to-host round trip time.

to be fair, some of my bhyve's ran fast (so, positive adjustments by
ntpd), some ran slow (negative adjustments). i did not try every
possible timecounter hardware; TSC-low fixed it, so i stopped.

> I have been doing experiments but don't have anything conclusive yet.

thanks for looking into it. paravirtualization (kvm-clock or some
equivalent) seems desirable.

Paul Vixie
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