Adaptive Transaction Scheduling for Transactional Memory Systems

Transactional memory systems are expected to enable parallel programming at lower programming complexity, while delivering improved performance over traditional lock-based systems. Nonetheless, the authors observed that there are situations where transactional memory systems could actually perform worse, and that these situations will actually become dominant in future workloads as more and larger-scale transactional memory systems are available. Transactional memory systems can excel locks only when the executing workloads contain sufficient parallelism. When the workload lacks the inherent parallelism, blindly launching excessive transactions can adversely result in performance degradation. To quantitatively demonstrate the issues, they introduced the concept of effective transactions in this paper. They show that the effectiveness of a transaction is closely related to a dynamic quantity they call contention intensity.