On Mon, May 4, 2009 at 9:49 AM, howard chen <howachen@xxxxxxxxx> wrote: > On Mon, May 4, 2009 at 10:44 PM, Pasi Kärkkäinen <pasik@xxxxxx> wrote: >> On Mon, May 04, 2009 at 10:40:00PM +0800, howard chen wrote: >> Yes, paravirtualization is good. If running KVM, use paravirtualized network >> and disk/block drivers for better performance. > > So does it mean generally Xen is more optimized than KVM for speed? no Xen started as paravirtualization-only, and later got full virtualization capabilities, mainly to run windows guests. KVM is full-virtualization-only. if things stopped there, then yes, Xen would be much faster than kvm. but on almost all cases, biggest bottleneck (by far) isn't the CPU, it's I/O. adding paravirtualization drivers to a fully virtualized guest brings it roughly to the same speed level as a PV guest. that makes kvm comparable to Xen in most workloads. there some real advantages of kvm: - less context switches needed to make a block or packet go from guest to hardware and viceversa - paravirtualized drivers widely available both for Linux and Windows (Xen's drivers on windows can be hard and/or expensive to get) - tight work with the qemu/kernel guys make big advances in througput. i recall that virtio-net can go near 2Gbit with little tuning, almost twice as the best Xen numbers. of course, there are also several hard, real advantages of Xen: - the hypervisor's scheduler is more appropriate for dataserver managers that sell VMs - wider recognition from supporting companies (changing quickly) several more for each side that i don't remember right now, i'm sure -- Javier -- 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
