poor network performance with KVM virtualisation (CentOS with virtio)

Mihai Cristea cristea at liacs.nl
Sun Jul 10 03:50:40 CDT 2011


we noticed that our Dell R815 is pretty slow in handling multiple VMs when using Linux/KVM. In our setup we used CentOS 5.6 in host, and CentOS in guests, too.
The slowness we noticed especially on the network traffic between VMs (iperf reports 20Mbps udp traffic!!! between 2 VMs). Again, we instantiated only 2 VMs on this 48cores machine, and that's the performance we get with UDP; TCP gets better, something around 1.2Gbps - but still bad for this powerful & expensive machine.
We tried on latest CentOS 5.6 kernels and also we did update to the latest linux kernels (2.6.38), using latest virtIO drivers, etc. We tried most of tips we've found on Internet/KVM-forums regarding this topic.

What should I do to improve the NIC performance? What do we do wrong?
I'd like to know if we need specific drivers for linux kernel for this machine (especially on the motherboard chipset that handles I/Os, or on the Broadcom NICs)?

Thank you,

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