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

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 05/11/13 15:17, Jan Beulich wrote:
>>>> 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
>

It turns out that the problem appears to be independent, and appears to
be in the USB stack.

~Andrew


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