I agree with your analysis. I did try to build my own xnu at one point, and gave up in frustration. In a microkernel architecture like Mach most of the core services are system daemons and most of the drivers communicate with them and not the kernel directly. I suspect the speed advantages of a custom kernel for Mac OS X Mr. Yager describes are minute, if they exist at all.
In my Linux second life I find that taking things out of the kernel mostly improves speed of booting, not using. To achieve notable performance improvements you usually have to try out different patches, and there are several "leading" patched distributions, like Con Kolivas', which give you small but somewhat noticeable improvements.
by Daniel Lyons — May 17
In my Linux second life I find that taking things out of the kernel mostly improves speed of booting, not using. To achieve notable performance improvements you usually have to try out different patches, and there are several "leading" patched distributions, like Con Kolivas', which give you small but somewhat noticeable improvements.