Il 11/11/2013 17:43, Michael S. Tsirkin ha scritto: > On Thu, Nov 07, 2013 at 06:29:40PM +0100, Paolo Bonzini wrote: >> Il 07/11/2013 17:47, Michael S. Tsirkin ha scritto: >>> That's on kvm with 52 bit address. >>> But where I would be concerned is systems with e.g. 36 bit address >>> space where we are doubling the cost of the lookup. >>> E.g. try i386 and not x86_64. >> >> Tried now... >> >> P_L2_LEVELS pre-patch post-patch >> i386 3 6 >> x86_64 4 6 >> >> I timed the inl_from_qemu test of vmexit.flat with both KVM and TCG. With >> TCG there's indeed a visible penalty of 20 cycles for i386 and 10 for x86_64 >> (you can extrapolate to 30 cycles for TARGET_PHYS_ADDR_SPACE_BITS=32 >> targets). > > So how did you measure this exactly?
I mention extrapolation because x86 is TARGET_PHYS_ADDR_SPACE_BITS=36, not 32. Paolo
