RE: [Xen-devel] Windows SMP

["James Harper" <james.harper@xxxxxxxxxxxxxxxx>]

> > I had to disable both, and PAE. Only APIC=0 would not make any
> difference. I
> > will some further testing with Citrix Xenserver 5, using the same
> virtual
> > machine and another copy with their vmpd drivers. I bet that there
is no
> > difference in performance. It seems to be a Xen architectural issue.
Any
> > ideas?
> 
> The problem is almost certainly APIC related. APIC=0 actually has no
> effect
> for a multi-processor HVM guest, since APICs are architecturally
> absolutely
> required in x86 multi-processor systems.
> 
> The problem is most likely lots of emulated APIC TPR writes slowing
things
> down. Possible fixes:
>  1. Run a Windows guest with the 'lazy TPR' optimisation -- w2k3sp2+,
> w2k8,
> vista. Or run 64-bit Windows which will write TPR in a different way
which
> most Intel/AMD CPUs can virtualise efficiently.
>  2. Run a new enough Intel processor which has automatic TPR handling
even
> for 32-bit Windows guests.
>  3. Run Citrix drivers which patch Windows to avoid TPR writes.
> 

Can you elaborate on that last point? Does that pass WHQL?

I think that 'venefax' is running Windows 2003sp2... does that exclude
'lazy TPR' fix as an option or does it need enabling somehow?

Thanks

James

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