Maybe this is just a bad example, but I was digging through the timing wheel code of the kernels of all three main BSDs at one point. FreeBSD and NetBSD had nearly the same code. OpenBSD's was rather simpler and did not have a lot of the locking code that the other two had. My guess is that OpenBSD has either a giant lock or its kernel only runs on one core.

Most of the OpenBSD kernel is under a big lock but they are adding more fine grained locking. OpenBSD didn't add kernel threads until 2012. A bit late in comparison to freebsd and linux but it wasn't a priority to them. It also allowed them to benefit from the lessons everybody else learned the hard way.

NetBSD kernel code is not simpler compared to FreeBSD/OpenBSD kernel code. On average, it's probably the same. I can definitely think of some things for which it is more complex.

  > I can definitely think of some things for which it is more complex.

How do you write this in a comment and then click submit? Why would you not include at least one example?

I guess it should be largely the same since OpenBSD originally forked from NetBSD...

A very long time ago and much has changed for both.

It dumbed down the malloc() interface, for example (no tags).