ProPS: A Progressively Pessimistic Scheduler for Software Transactional Memory.

Software Transactional Memory (STM) is one promising abstraction to simplify the task of writing highly parallel applications. Nonetheless, in workloads lacking enough parallelism, STM's optimistic approach to concurrency control can adversely degrade performance as transactions abort and restart often. In this paper, we describe a new scheduling-based solution to improve STM's performance in high-contention scenarios. Our Progressively Pessimistic Scheduler (ProPS) uses a fine-grained scheduling mechanism that controls the amount of concurrency in the system gradually as transactions abort and commit with success. Experimental results with the STMBench7 benchmark and the STAMP benchmark suite showed that current coarse-grained, conservative transaction schedulers are not suitable for workloads with long transactions, whereas ProPS is up to 40% faster than all other scheduling alternatives.