Context switching doesn't need to be as expensive as it is in these cases, it's just that Linux doesn't provide the mechanisms needed to make it more efficient.

Context switching doesn't need to be as expensive as it is in these cases, it's just that Linux doesn't provide the mechanisms needed to make it more efficient. See, e.g., https://blog.linuxplumbersconf.org/2013/ocw/system/presentations/1653/original/LPC%20-%20User%20Threading.pdf https://blog.linuxplumbersconf.org/2013/ocw/system/presentat... which implemented a syscall for a process-directed context switch directly to another thread.