For a Microkernel, a Big Lock Is Fine

It is well-established that high-end scalability requires fine-grained locking, and for a system like Linux, a big lock degrades performance even at moderate core counts. Nevertheless, we argue that a big lock may be fine-grained enough for a microkernel designed to run on closely-coupled cores (sharing a cache), as with the short system calls typical for a well-designed microkernel, lock contention remains low under realistic loads.