[workspace-user] kvm: better network performance through virtio

Kyle Fransham fransham at uvic.ca
Wed Mar 9 15:59:06 CST 2011

Hi Nimbus devs,

We've configured a nimbus cloud using kvm, and I noticed that the
network performance of the VMs was very poor.  A couple of iperfs
between two VMs on the same physical host shows a bandwidth of
~200Mbits/sec, even though they're connected to a gigE nic.   

Google tells me that the network performance of kvm VMs can be improved
by using the virtio network driver, and that's as simple as editing one
line in the xml.  To test if this works in my case, I hacked the file:


and added the following two lines to the Interface class:

        x.write(L(3, "<model type='%s'/>" % self.model_type))

When I boot VMs on the same physical host, I get iperfs between the two
of >4 GBits/sec, and iperfs between VMs on different physical hosts run
at wirespeed (~900 MBits/sec):

    [root at bbr-ltda-vm001 fransham]# iperf -s
    Server listening on TCP port 5001
    TCP window size: 85.3 KByte (default)
    [  4] local port 5001 connected with
    port 38026
    [ ID] Interval       Transfer     Bandwidth
    [  4]  0.0-10.0 sec  4.96 GBytes  4.25 Gbits/sec
    [  5] local port 5001 connected with
    port 53461
    [  5]  0.0-10.0 sec  1.07 GBytes   914 Mbits/sec

Now obviously what I've done to our setup is a hack, but this seems to
me like a really easy feature for you guys to implement that will
greatly improve the network performance of kvm workspaces.  I'll leave
this info in your capable hands.


*  Kyle Fransham                                      *
*  National Research Council / University of Victoria *
*  Rm 2156, 100 Sussex Dr.                            *
*  Ottawa, Canada, K1A 0R6                            *
*  613-990-1537     fax: 613-993-3127                 *

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