Remote Transaction Commit: Centralizing Software Transactional Memory Commits

Abstract

Software Transactional Memory (STM) has recently emerged as a promising synchronization abstraction for multicore architectures. State-of-the-art STM algorithms, however, suffer from performance challenges due to contention and spinning on locks during the transaction commit phase. In this paper, we introduce Remote Transaction Commit (or RTC), a mechanism for executing commit phases of STM transactions. RTC dedicates server cores to execute transactional commit phases on behalf of application threads. This approach has two major benefits. First, it decreases the overheads of spinning on locks during commit, such as the number of cache misses, blocking of lock holders, and CAS operations. Second, it enables exploiting the benefits of coarse-grained locking algorithms (simple and fast lock acquisition, reduced false conflicts) and bloom filter-based algorithms (concurrent execution of independent transactions). Our experimental study on a 64-core machine with four sockets shows that RTC solves the problem of performance degradation due to spin locking on both micro-benchmarks (red-black trees), and macro-benchmarks (STAMP), especially when the commit phase is relatively long and when thread contention increases.