Re: [RFC PATCH 1/2] Hyper-H reference counter

Gleb Natapov
2013-05-20T09:41:29Z

On Mon, May 20, 2013 at 11:32:27AM +0200, Paolo Bonzini wrote:
> Il 20/05/2013 11:25, Gleb Natapov ha scritto:
> > So in Hyper-V spec they
> > say:
> >
> > Special value of 0xFFFFFFFF is used to indicate that this facility is no
> > longer a reliable source of reference time and the virtual machine must
> > fall back to a different source (for example, the virtual PM timer).
> >
> > May be they really mean "virtual PM timer" here and reference counter is
> > not considered as a fall back source, but this is not what we want.
> >
> > On the other hand in API specification [1] they have:
> >
> > #define HV_REFERENCE_TSC_SEQUENCE_INVALID (0x00000000)
> >
> > which is not even documented in hyper-v spec. Actually 0 is specified as
> > valid value there. Go figure.
> >
> > [1] http://msdn.microsoft.com/en-us/library/windows/hardware/ff540244%28v=vs.85%29.aspx
>
> Ok, if the API document is right then we should use
> HV_REFERENCE_TSC_SEQUENCE_INVALID instead of 0, with a comment
> explaining why we use 0 and not 0xFFFFFFFF.
>
Using define is always a good idea no matter if API doc is right or
hyper-v spec is, it's just the "decent documentation" part that got me :)
Definitely better than nothing and thanks them for that.

--
Gleb.