Comment 1 for bug 1223267

If basic request/response performance between the two VMs on the same compute node remains the same between the two driver types remains the same (eg netperf TCP_RR) , you might look to whether the "stateless offloads" are lost between the two - things like CKO, TSO/GSO and/or GRO.

If the likes of netperf TCP_RR (or its equivalent) is very different between the two driver versions, then there is likely a non-trivial path-length difference, at least some of which may be visible in the results of a "perf" profile of the compute node.