Re: [Xen-devel] [PATCH 0/2] Viridian MSRs

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 15.10.13 at 20:12, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
> This set of two patches advertises 3 constant, read-only MSRs of timing
> information to a viridian capable VM.
> 
> There is an as-yet-unidentified issue when running Windows 8.1 / Server 2012r2
> under Xen where it will periodically (1 in 10 attempt) appear to fall into 
> an
> idle loop rather than schedule userspace processes (such as failing to run a
> login session).
> 
> I am still investigating the underlying cause.  One possibility is an
> interaction of TSC time calibration interacting poorly with the Xen 
> scheduler.
> 
> Unfortunately, attempting to divine what windows is unhappy about with its
> environment is rather tricky (even a BSOD would be more useful than the
> current symptoms), but providing these MSRs causes Windows to prefer rdtsc
> over the HPET main counter as a source of time, and 'fixes' the above issue.

So even now reading it again after a couple of weeks I'm still
uncertain whether the issue you describe is with or without these
patches applied, or independent of them.

Jan


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