On the Performance of Contention Managers for Complex Transactional Memory Benchmarks

In Transactional Memory (TM), contention management is the process of selecting which transaction should be aborted when a data access conflict arises. In this paper, the performance of published contention managers (CMs) is re-investigated using complex benchmarks recently published in the literature. Our results redefine the CM performance hierarchy. Greedy and Priority are found to give the best performance overall. Polka is still competitive, but by no means best performing as previously published, and in some cases degrading performance by orders of magnitude. In the worst example, execution of a benchmark completes in 6.5 seconds with Priority, yet fails to complete even after 20 minutes with Polka. Analysis of the benchmark found it aborted only 22% of all transactions, spread consistently over the duration of its execution. More generally, all delay-based CMs, which pause a transaction for some finite duration upon conflict, are found to be unsuitable for the evaluated benchmarks with even moderate amounts of contention. This has significant implications, given that TM is primarily aimed at easing concurrent programming for mainstream software development, where applications are unlikely to be highly optimised to reduce aborts.