Iperf performance: KVM guest running on CPU with e1000 NICs


We are running following setup and see low iperf performance (around 1.8Gbps between the two VMs) in the following setup where VM1 and VM2 are KVM guests and the NICs are e1000. Same setup using NICs with igb drivers works much better (5.5-6Gbps between the two VMs).

VM1—Host1—NicBond1—8 phy nics===network === 8 phy nics—NicBond2—Host2—VM2

Is this a known issue and are there any tweaks or configuration changes we can apply either in KVM or on e1000 drivers to increase the network performance? Would using driver other than virtio help?