> From: Avi Kivity [mailto:avi@xxxxxxxxxx] > Sent: Wednesday, August 24, 2011 6:00 PM > > 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@xxxxxxxxxxxxxxx/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. yes, sane guests all use MOV for EOI. btw, Xen has integrated a similar acceleration for several releases. When we're measuring 10G SR-IOV network performance, vEOI access overhead may be up to 6%-8% based on interrupt rate which is one factor for KVM to lag behind. > > 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. > yes, and this is an orthogonal option. So if you agree, I'll send out an updated patch atop their work. Thanks Kevin -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
