They might claim that NetBSD scales best, but it took some code changes to get it to do so (which have since been picked up and are included in the base).
The REAL reason for why they picked NetBSD is that Ragge (Anders Magnusson), the person doing a fair chunk of the testing, is heavily involved in the project and knows the code base. It was simply easiest to work with for him.:-)
Actually, we did tests with Linux (both 2.4 and 2.6) and FreeBSD also, but with not as good results.
Linux IP stack eats much more CPU (and memory!) than it should. Basic problem is the network buffer implementation (or the lack of!). This is true for both 2.4 and 2.6. A redesign is needed of the IP stack to make it perform better.
FreeBSD have a lot of linear searches in their IP stack left, fixing that would most likely give the same result as for NetBSD. I may port over some of the NetBSD changes if I get some spare time.
NetBSD had already fixed (most of) those problems, some of them long ago, therefore it was simple to just use it.
Why NetBSD was chosen (Score:3, Interesting)
The REAL reason for why they picked NetBSD is that Ragge (Anders Magnusson), the person doing a fair chunk of the testing, is heavily involved in the project and knows the code base. It was simply easiest to work with for him.
Re:Why NetBSD was chosen (Score:5, Informative)