Very large multithreaded programs with lots of diverse uses of locks, including:

- uncontended, mildly contended, and horrifically contended

- short and long critical sections

- contention among small numbers of threads and large numbers of threads

- contention that happens when other locks are held recursively and those are also contended on (like, thread A wants a lock held by thread B, but thread B is trying to get a lock held by thread C)

Different lock algos work well or badly depending on how the locks are used, so it’s important to pick real programs as your benchmark rather than trying to cook a synthetic benchmark.