Yes, your considerations do make sense, Didi.

My main concern at the beginning was that there could be some limitation "at the wire" with the virtio drivers in Windows.

But I think that the iperf2 test has removed this doubt, correct?

Possibly there are other "inefficiencies" in the virtio driver, like what experimented with the iperf3, so that the application works better with vSphere than with oVirt.

Do you or other ones have any suggestions to dig into that eventually?

Does it make sense to set the VM as a high performance one and test the application again?

One thing I noticed is that at source the VM was configured as 4 vcpus with 4 sockets, besides the hypervisors (both vSphere and oVirt) having 2 sockets. Do you think it can have any performance impact? What could be the best vcpu configuration: 2 sockets and 2 cores each or 1 socket and 4 cores? I can try to tweak also this config parameters and see

Gianluca