Re: about vEOI optimization
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. -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain. -- To unsubscribe from this list: send the line unsubscribe kvm in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
RE: about vEOI optimization
From: Avi Kivity [mailto:a...@redhat.com] 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@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. 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 majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: about vEOI optimization
On 08/25/2011 05:24 AM, Tian, Kevin wrote: 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. -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain. -- To unsubscribe from this list: send the line unsubscribe kvm in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
about vEOI optimization
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? Thanks Kevin -- To unsubscribe from this list: send the line unsubscribe kvm in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
