18.7. Optimizing virtual machine network performance

Procedure

• Use any of the following methods and observe if it has a beneficial effect on your VM network performance:

  • Enable the vhost_net module

    On the host, ensure the vhost_net kernel feature is enabled:

    # lsmod | grep vhost
    vhost_net              32768  1
    vhost                  53248  1 vhost_net
    tap                    24576  1 vhost_net
    tun                    57344  6 vhost_net

    If the output of this command is blank, enable the vhost_net kernel module:

    # modprobe vhost_net

• Set up multi-queue virtio-net

  To set up the multi-queue virtio-net feature for a VM, use the virsh edit command to edit to the XML configuration of the VM. In the XML, add the following to the <devices> section, and replace N with the number of vCPUs in the VM, up to 16:

  <interface type='network'>
        <source network='default'/>
        <model type='virtio'/>
        <driver name='vhost' queues='N'/>
  </interface>

  If the VM is running, restart it for the changes to take effect.

  • Batching network packets

    In Linux VM configurations with a long transmission path, batching packets before submitting them to the kernel may improve cache utilization. To set up packet batching, use the following command on the host, and replace tap0 with the name of the network interface that the VMs use:

    # ethtool -C tap0 rx-frames 64

  • SR-IOV

    If your host NIC supports SR-IOV, use SR-IOV device assignment for your vNICs.

    For more information, see Managing SR-IOV devices.