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 fill this gap. We perform a performance study of 19 state-of-the-art mutex lock algorithms on 36 realistic applications. Our study shows that regarding locking on multicore machines, the case is not closed yet. Indeed, our conclusions include the following findings: (i) no single lock is the best for more than 50% 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 optimal lock changes when varying the number of applications or the workload. These findings call for further research on optimized lock algorithms and dynamic adaptation of contention management.