Paolo Bonzini wrote on 2015-04-24: > > > On 24/04/2015 09:46, Zhang, Yang Z wrote: >>> On the other hand vmexit is lighter and lighter on newer >>> processors; a Sandy Bridge has less than half the vmexit cost of a >>> Core 2 (IIRC >>> 1000 vs. 2500 clock cycles approximately). >> >> 1000 cycles? I remember it takes about 4000 cycle even in HSW server. > > I was going from memory, but I now measured it with the vmexit test of > kvm-unit-tests. With both SNB Xeon E5 and IVB Core i7, returns about > 1400 clock cycles for a vmcall exit. This includes the overhead of > doing the cpuid itself. > > Thus the vmexit cost is around 1300 cycles. Of this the vmresume > instruction is probably around 800 cycles, and the rest is introduced > by KVM. There are at least 4-5 memory barriers and locked instructions. Yes, that's make sense. The average vmexit/vmentry handle cost is around 4000 cycles. But I guess xsaveopt doesn't take so many cycles. Does anyone have the xsaveopt cost data? > > Paolo Best regards, Yang -- 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
