vhost-net module is a kernel-level back end for virtio networking that reduces virtualization overhead by moving virtio packet processing tasks out of user space (the qemu process) and into the kernel (the
vhost-net driver). vhost-net is only available for virtio network interfaces. If the vhost-net kernel module is loaded, it is enabled by default for all virtio interfaces, but can be disabled in the interface configuration in the case that a particular workload experiences a degradation in performance when vhost-net is in use.
Specifically, when UDP traffic is sent from a host machine to a guest virtual machine on that host, performance degradation can occur if the guest virtual machine processes incoming data at a rate slower than the host machine sends it. In this situation, enabling
vhost-net causes the UDP socket's receive buffer to overflow more quickly, which results in greater packet loss. It is therefore better to disable
vhost-net in this situation to slow the traffic, and improve overall performance.
vhost-net, edit the
<interface> sub-element in the guest virtual machine's XML configuration file and define the network as follows:
Setting the driver name to
qemu forces packet processing into qemu user space, effectively disabling vhost-net for that interface.