Ask HN: What kinds of kernel designs are best for multicore processors?

I think the first question to ask is, what is the definition of a multicore processor? Is it something like the current crop of cache-coherent designs? There are concerns about scaling this design to lots of cores. Or is it something like a network of machines on a chip? In that case, the OS might look more like Mach.

Maybe this question would fit in better at StackOverflow.