But you don't get the choice, given the applications. It's not clear to me how Plan9 would help with relevant problems; it was tried on Blue Gene at one stage. If I got the choice of something different, it would likely be capability-, microkernel-based, which might actually help with the jitter problem.
there is an L4 based effort for HPC at TU Dresden called FFMK. the reality is that for HPC you still need high-performance implementation of fast-path system calls (e.g., memory and process management) and the traditional micro-kernel architecture is not suitable for that. as for POSIX, you don't have a choice, people who write apps are used to POSIX and Linux.
