On Wed, Oct 26, 2022 at 03:23:51PM +0200, Kalabic S. wrote:
> On 26/10/2022 11:33, Scott Cheloha wrote:
> > There might be a second workaround.  Kalabic mentions here in the
> > other thread about this problem:
> > 
> > https://marc.info/?l=openbsd-bugs&m=166664949825616&w=2
> > 
> > ... that changing the ESXi option "Guest OS Version" from "FreeBSD
> > (32-bit)" to "FreeBSD (64-bit)" seemed to fix the problem on his
> > version of ESXi.  Does that work for you?  I don't know what the other
> > consequences of that configuration change are, but it might be worth a
> > try if you prefer to run 7.2-RELEASE or 7.2-STABLE instead of patching
> > -current.
> > 
> > Do you have VMware support?  Is there any way for you to report this
> > problem to them?  It's unlikely they explicitly support running an
> > OpenBSD guest, but it's plausible this issue could affect other
> > operating systems.  I can't imagine OpenBSD is reading the ACPI PM
> > timer differently than Linux or FreeBSD.
> > 
> 
> Maybe related or not, but there's official paper from VMware that describes
> several known timekeeping issues and how to correct or work around them:
> https://www.cse.psu.edu/~buu1/teaching/spring06/papers/vmware-timing.pdf

I did see this, thanks for posting it.  It's not immediately useful here,
though.

> Also pardon my ignorance about TSC counters and related stuff, but just
> looking at FreeBSD related code it seems to take into account the fact it is
> running as a hypervisor guest (ESXi or Xen).
> https://github.com/freebsd/freebsd-src/blob/main/sys/x86/x86/tsc.c
> 
> Is there a detail that makes a difference when different "Guest OS Version"
> is used? Note that I have no idea what is happening there.
> 
> So, just like some AMD related improvements for TSC were introduced into
> OpenBSD recently, maybe this issue can be properly solved only by doing
> something similar for guests on hypervisor?

I would like to derive the TSC and lapic frequency from the hypervisor
CPUID leaves when they are available to avoid calibration.  It's on my
todo list.

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