Bypass Qemu Network Stack with Virtio-Vhost, for Near Native Performance

For virtualized environments, primary performance bottleneck could happen with below resources:

a. CPU

b. Storage

c. Network

For CPU, direct passthrough option would give a performance near to bare metal. For Storage and Network, deploying VIRTIO drivers (paravirtualization) could provide a descent performance as well. These concepts have been explained here.

With network, one more performance tuning is possible, to completely bypass the Hypervisor (Qemu) network stack, and let the GUEST directly interact with HOST’s network stack. This may give almost similar network performance for guest applications as with application running on the host.

Implementing this requires, enabling ‘vhost_net’ driver on the host, and update the VM Settings to use this driver, which is detailed here.

In an optimal setting, you will also enable the same number of IO-Queues, as with the total number of CPU Cores allotted to the Virtual Machine.

Reference