2016-09-15 14:29 GMT+08:00 Paolo Bonzini <pbonzini@xxxxxxxxxx>: > > > On 15/09/2016 03:19, Wanpeng Li wrote: >> 2016-09-14 20:03 GMT+08:00 Radim Krčmář <rkrcmar@xxxxxxxxxx>: >>> 2016-09-14 11:40+0200, Paolo Bonzini: >>>> On 14/09/2016 09:58, Wanpeng Li wrote: >>>>> From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx> >>>>> >>>>> I observed that kvmvapic(to optimize flexpriority=N or AMD) is used >>>>> to boost TPR access when testing kvm-unit-test/eventinj.flat tpr case >>>>> on my haswell desktop (w/ flexpriority, w/o APICv). Commit (8d14695f9542 >>>>> x86, apicv: add virtual x2apic support) disable virtual x2apic mode >>>>> completely if w/o APICv, and the author also told me that windows guest >>>>> can't enter into x2apic mode when he developed the APICv feature several >>>>> years ago. However, it is not truth currently, Interrupt Remapping and >>>>> vIOMMU is added to qemu and the developers from Intel test windows 8 can >>>>> work in x2apic mode w/ Interrupt Remapping enabled recently. >>>>> >>>>> This patch enables TPR shadow for virtual x2apic mode to boost >>>>> windows guest in x2apic mode even if w/o APICv. >>>>> >>>>> Can pass the kvm-unit-test. >>>> >>>> Ok, now I see what you meant; this actually makes sense. I don't expect >>>> much speedup though, because Linux doesn't touch the TPR and Windows is >>>> likely going to use the Hyper-V APIC MSRs when APICv is disabled. For >>>> this reason I'm not sure if the patch is useful in practice. >>> >>> I agree with Paolo on the use case -- what configurations benefit from >>> this change? >> >> Old windows guest w/o Hyper-V synthetic interrupt support. > > ... but with Hyper-V synthetic interrupt support enabled in the QEMU > command line. Right? I think so. :) Regards, Wanpeng Li -- 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
