On Tue, Nov 10, 2009 at 01:52:36PM -0500, Scott McClanahan wrote: > > > Yeah.. Xen paravirtualized mmu is fast, and in some (many) cases beats > > CPU hardware virtualized mmu. > > > > KVM has 'pvmmu' aswell, but it's not as good, so KVM is faster with CPU > > hardware virtualization. But that's a problem of KVM only, they haven't > > managed to optimize the pvmmu. And they're going to drop it altogether. > > > > KVM people tend to say 'paravirtualized mmu is slow', but they just mean > > KVM implementation of it sucks :) > > > > -- Pasi > > I haven't tested or seen any benchmarks but I wonder how much the > addition of a page table for virtualized guests will help. Not to > mention newer features like a virtualized task priority register and > ASID could continue to require less paravirt code in the guest. I get > my two new 5500 series servers in a few weeks so I'm pretty excited to > see some of the second gen hardware virtualization assist features in > action. > I don't know. Of course hardware will add features and get more optimized in the future. Some benchmarks from IBM guys, Xen vs. KVM: http://www.spinics.net/lists/kvm/msg13910.html http://www.spinics.net/lists/kvm/msg14068.html http://www.spinics.net/lists/kvm/msg21913.html Quotes: "So, KVM requires 66.93/52.85 = 26.6% more CPU to do the same amount of work." "If we normalize to CPU utilization, Xen is doing 20% more throughput." "KVM running Windows VMs uses 46% more CPU than the Other-Hypervisor" "A different hypervisor was compared; KVM used about 60% more CPU cycles to complete the same amount of work." I bet KVM will catch up at some point.. at the moment it seems to not perform as good as Xen. Then again it's a much younger product. -- Pasi