[rrss]

> is that it's rarely called due to elision.

Calling this 'elision' is a bit confusing, since the glibc developers use the term 'lock elision' to refer to hardware lock elision via Intel TSX extensions.

What eliminates the syscall cost is optimistic spinning in userspace, so that locking only does futex_wait in cases of contention when the lock isn't released 'soon' after the thread starts trying to acquire it.