Re: about vEOI optimization

[Avi Kivity <avi@redhat.com>]

On 08/23/2011 11:09 AM, Tian, Kevin wrote:
> Hi, Avi,
>
> Both Eddie and Marcello once suggested vEOI optimization by skipping
> heavy-weight instruction decode, which reduces vEOI overhead greatly:
>
> http://www.mail-archive.com/kvm@vger.kernel.org/msg18619.html
> http://www.spinics.net/lists/kvm/msg36691.html
>
> Though virtual x2apic serves similar purpose, it depends on guest OS
> to support x2apic. Many Windows versions don't support x2apic though,
> including Win7, Windows server before 2008 R2, etc. Given that virtualization
> need support various OS versions, any chance to incorporate above vEOI
> optimization in KVM as an alternative to boost performance when guest
> doesn't support x2apic?
>

Yes.  There was a problem with the guest using MOVSD or STOSD to write 
the EOI; if we don't emulate, then registers don't get updated.  I guess 
we can ignore it since no sane guest will use those instructions for EOI.

Another option is the hyper-V EOI support, which can also eliminate the 
EOI exit when no additional interrupt is pending.  This can improve EOI 
performance even more.


-- 
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