Multicore Locks: The Case Is Not Closed Yet

NUMA multicore machines are pervasive and many multithreaded applications are suffering from lock contention. To mitigate this issue, application and library developers can choose from the plethora of optimized mutex lock algorithms that have been designed over the past 25 years. Unfortunately, there is currently no broad study of the behavior of these optimized lock algorithms on realistic applications. In this paper, we attempt to fill this gap. We perform a performance study of 27 state-of-the-art mutex lock algorithms on 35 applications. Our study shows that the case is not yet closed regarding locking on multicore machines. Indeed, our conclusions include the following findings: (i) at its optimized contention level, no single lock is the best for more than 52% of the studied workloads; (ii) every lock is harmful for several applications, even if the application parallelism is properly tuned; (iii) for several applications, the best lock changes when varying the number of threads. These findings call for further research on optimized lock algorithms and dynamic adaptation of contention management.