Re: CPUID emulation

[Stephane Eranian <eranian-sDzT885Ts8HQT0dZR+AlfA@public.gmane.org>]

Avi,

On Thu, May 31, 2007 at 02:52:05PM +0300, Avi Kivity wrote:
> Stephane Eranian wrote:
> >>
> >>If the guest cpuid is set to a least common denominator, it should work.
> >>
> >>    
> >There is no common denominator between a P4 and Intel Core 2 Duo for the
> >performance counters. So you cannot simply use a generic member of family
> >15 to fake the guest cpuid runnning on Intel Core 2 Duo host.
> >
> >  
> 
> So, the performance counter functionality will not be available if you 
> have a mixed server farm with these processors.
> 
That's like what is going to happen.

> If applications use model version to detect performance counters, and 
> not cpuid bits, then there is no way to prevent guests using performance 
> counters.  Fortunately this is limited to specialized applications.
> 
They use cpuid. I expect more and more applications/OS will rely on
performance counters to boost performance at runtime.

-- 
-Stephane

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