TSC calibration in virtual machines

[Jung-uk Kim]

On 06/27/2018 03:14, Andriy Gapon wrote:
> 
> It seems that TSC calibration in virtual machines sometimes can do more harm
> than good.  Should we default to trusting the information provided by a hypervisor?
> 
> Specifically, I am observing a problem on GCE instances where calibrated TSC
> frequency is about 10% lower than advertised frequency.  And apparently the
> advertised frequency is the right one.
> 
> I found this thread with similar reports and a variety of workarounds from
> administratively disabling the calibration to switching to a different timecounter:
> https://lists.freebsd.org/pipermail/freebsd-cloud/2017-January/000080.html

We already do that for VMware hosts since r221214.

https://svnweb.freebsd.org/changeset/base/221214

We should do the same for each hypervisor.

Jung-uk Kim

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