One of the papers presented at the recently held Linux Symposium compared Linux Virtualization technologies including KVM, Xen, Linux-Vserver, Vmware ESX, OpenVZ among others. The technologies were a mix of full virtualization, para-virtualization and OS containers.

The conclusions from this paper were that KVM performed very well at cpu intensive tasks but horribly at I/O intensive tasks and should be avoided for network intensive applications. I would strongly disagree with this conclusion. For these tests, KVM-58 running on host kernel 2.6.22-14 and guest kernel 2.6.15-26 were used. Nowhere was it mentioned whether userspace networking or tap mode of networking was used but I will assume from the results that they probably used userspace networking which is default and also poorest performing mode of networking for KVM.

There are many ways to optimize KVM’s networking performance eg. tap networking, paravirtual drivers and pci passthrough that bring KVM’s I/O performance close to native. Apart from that, a lot of development has happened since KVM-58 ; KVM is now at release 72 at the time of this writing. I hope that future benchmarks show KVM’s true I/O performance by considering these more efficient ways handling networking I/O.

The event carried lots of interesting Linux topics apart from this comparison and makes for very good reading so you should check them out. I’ve included the two pdf documents below. The comparison paper can be found within the first document (V1). Happy reading!

Linux Symposium 2008 V1

Linux Symposium 2008 V2