A good part of contention's cost can be the time you wait for the thread scheduler. When the lock-holding thread releases, your thread is moved from 'sleeping'

A good part of contention's cost can be the time you wait for the thread scheduler. When the lock-holding thread releases, your thread is moved from 'sleeping' to 'ready', and then it's gotta wait for a CPU. This is usually fast, but the tail can be awful.