Early Experience on Transactional Execution of JavaTM Programs Using Intel R© Transactional Synchronization Extensions

This paper applies Intel R © Transactional Synchronization Exten-sions (Intel R © TSX) to elide JavaTM monitor locks. By utilizing the transactional execution capability inside a Java Virtual Machine (JVM), applications running on top of the JVM transparently ben-efit without source or bytecode modifications. While others have previously examined transactional execution of Java programs, we find that the absence of a guarantee on even-tual transactional commit requires a software fallback, and present a novel design where the fallback code harmoniously coexists with the JVM locking mechanism. We also find that if not used judi-ciously, a real implementation of hardware transactional memory can significantly degrade application performance. Therefore, we propose an adaptive algorithm that selectively deoptimizes transac-tional lock elision where necessary. Evaluation of the Intel TSX-enabled JVM with various Java workloads shows promising results. For workloads that utilize a significant number of coarse-grained monitors, transactional lock elision provides a substantial performance improvement: up to 1.18x on a standard Java benchmark suite. In contrast, on work-loads with monitor locks that are hard to elide, our adaptive deop-timization approach prevents significant performance degradation from lock elision overheads. 1