I'm employed at Solarflare Communications in the test group, supporting the work of testers and developers by developing test frameworks. (We actually have very few pure testers and a whole lot of automation.). In a major break from my previous jobs, I've been working mostly in Python on applications for use in-house.

More recently I've become involved in maintenance of our network driver for Linux, starting with updating it to use current kernel coding conventions, and submitting for inclusion in the kernel. This has become a bit frustrating because while there are a lot of people prepared to run checkpatch and pick nits, there are not so many who will do a thorough review of a driver that's 20,000-odd lines long. And without someone doing that, it won't go in.

Meanwhile some of my colleagues have done some great work to accelerate Linux networking on Xen by having drivers in dom0 and domU cooperate to expose hardware resources directly to domU. Our hardware architecture supports many virtual NICs with their own packet queues and set of buffers, so this does not compromise the security of the physical machine and dom0. The results are very impressive.

The original motivation for the virtual NIC architecture was as a basis for a user-level networking stack, which can provide very low latency and reduced CPU usage. This software was originally proprietary but has now been released under GPLv2 as OpenOnload. Google invited two of my senior colleagues to talk about this - here's a video of their talk about user-level networking.