This was the best I found: https://docs.managarm.org/handbook/sys-arch/thoreir/index.ht...

So as I suspected, posix-subsystem is a single process that provides the POSIX support for all other process, so it's a single point of failure: https://docs.managarm.org/handbook/sys-arch/posix/index.html

It's interesting that they have some kind of subsystem to run code in kernel space too, very against typical microkernel thinking for isolation/safety reasons.

from the documentation, it is not clear to me what shape the posix subsystem has. It might be a library.

thor seems to be an actual "bottleneck".