Mixed CPU / Memory performance data
To shown the aggregate CPU / memory performances, I used a number of synthetic and semi-synthetic benchmarks. The first is SuperPI:
Apart Xen, which is considerably slower, all other virtualizers run neck to neck.
Then, I run some cryptographic related benchmark using OpenSSL. Let's begin with AES-256 encryption benchmark:
Same story here: Xen is slower, while the others are quite on par.
It is RSA-2048 turn now. Key signing speed first...
...and verify speed then:
The results are clear: while VMware, VirtualBox and KVM offer very similar speed, Xen is noticeably slower.
UPDATE: a recent article comparing KVM vs VirtualBox can be found here: http://www.ilsistemista.net/index.php/virtualization/12-kvm-vs-virtualbox-40-on-rhel-6.html