A dedicated kernel for multi-threading applications.

Thursday, January 25, 2018

Toro supports Virtio network drivers!

Hello folks! the last three weeks, I have been working on adding support for virtio network drivers in Toro (see VirtIONet.pas). In a virtualisation environment, virtio drivers have many benefits:
- they perform better than e1000 or other emulated network card.
- they abstract away the hardware of the host thus enabling the drivers to work on different hardware.  
- they are an standard way to talk with network cards which is supported by many hypervisors like KVM, QEMU or VirtualBox. 
The way that virtio network cards work is quite simple. They are based on the notion of virtqueue. In the case of networking, network cards have mainly two queues: the reception queue and the transmission queue. Roughly speaking, each queue has two rings of buffers: the available buffers and the used buffers. To provide a buffer to the device, the driver puts buffers in the available ring, then the device consumes and put them in the used ring. For example, in the case of the reception queue, the driver feeds the device by putting buffers in the available queue. Then, when a packet arrives, the device takes buffers from the available queue, writes the content and puts them in the used queue. You can find many bibliography on internet. However, I would recommend this post which also proposes the code C of the drivers. I think testing is the harder part. I found different behaviours depending on where are you testing, e.g., KVM, QEMU. For example, in KVM, if you don't set the model=virtio-net, the driver just does not work. To test, I basically have my own version of QEMU which prints all the logs straight to stdout. Also, Wireshark helps to trace the traffic and find duplicate packets or other kind of misbehaviour. The good part: when you are done with one virtio network driver, you can easily use it as a template because all virtio driver are very similar. I had no time yet to compare with e1000 but I am expecting good numbers :)

Cheers, Matias. 

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