Here's a really good article in the Communications of the ACM on reducing network packet processing overhead by redesigning the network stack: Revisiting Network I/O APIs: The Netmap Framework by Luigi Rizzo. As commodity networking performance increases operating systems need to keep up or all those CPUs will go to waste. How do they make this happen?

 

Abstract:

Today 10-gigabit interfaces are used more and more in datacenters and servers. On these links, packets flow as fast as one every 67.2 nanoseconds, yet modern operating systems can take 10-20 times longer just to move one packet between the wire and the application. We can do much better, not with more powerful hardware but by revising architectural decisions made long ago regarding the design of device drivers and network stacks.

The netmap framework is a promising step in this direction. Thanks to a careful design and the engineering of a new packet I/O API, netmap eliminates much unnecessary overhead and moves traffic up to 40 times faster than existing operating systems. Most importantly, netmap is largely compatible with existing applications, so it can be incrementally deployed.