After migrating a standalone windows udt-application from physical to virtual, the virtual machine only delivers about 10% bandwidth in comparison to the physical machine. The TCP-bandwidth of the VM is equal to the physical machine. The VM lives within a 11-node KVM-cluster, based on ubuntu 12.04. Two operating systems (Windows7 and Windows2003) perform in the same way. Both VMs use the actual Red Hat virtio-win-0.1-52 driver.
Any idea, where to start debugging (UDT,KVM,Virt-IO)?