Re: [PATCH 0/1] x2apic implementation for kvm

[Sheng Yang <sheng@linux.intel.com>]

On Monday 25 May 2009 17:22:34 Avi Kivity wrote:
> Sheng Yang wrote:
> > I think that means the PV interface for lapic. And yes, we can support it
> > follow MS's interface, but x2apic still seems another story as you
> > noted... I still don't think support x2apic here would bring us more
> > benefits.
>
> x2apic has the following benefit:
>
> - msr exits are faster than mmio (no page table walk, emulation)

Need PV(at least part of). I don't think Hyper-V considered this, and not sure 
the community's aptitude.

> - no need to read back ICR to look at the busy bit
> - one ICR write instead of two

Maybe the key issue.

> - potential to support large guests once we add interrupt remapping

Then it can be added before we have it. Compared to the workload, x2apic is 
not the problem, interrupt remapping/VT-d is. 

> - shared code with the Hyper-V paravirt interface

So I think the key thing are ICR related(and seems no data available 
currently). Compare the benefit of ICR improve(can it improved in another way? 
Does Hyper-V interface has related things?), and the workload of x2apic 
virtualization as well as guest OS support, well, I don't know, but not 
optimistic.

-- 
regards
Yang, Sheng