FASTM: A Log-based Hardware Transactional Memory with Fast Abort Recovery

• Published in: 2009 18th International Conference on Parallel Architectures and Compilation Techniques pp. 293 - 302
• Main Authors: Lupon, M., Magklis, G., Gonzalez, A.
• Format: Conference Proceeding Publication
• Language: English
• Published: IEEE 01.09.2009; IEEE Computer Society
• Subjects: Application software; Arquitectura de computadors; Birth disorders; Cache memory; Conference management; Degradation; Delay; Fast abort recovery; FASTM; Hardware; Harwdare transactional memory; Informàtica; Memory management; Memòria ràpida de treball (Informàtica); Parallel architectures; Parallel processing (Electronic computers); Processament en paral·lel (Ordinadors); Protocols; Software management; Software performance; System recovery; transactional coherence protocols; Transactional coherence protocols cache storage; Àrees temàtiques de la UPC
• ISBN: 9780769537719; 0769537715
• ISSN: 1089-795X; 2641-7944
• DOI: 10.1109/PACT.2009.19

Version management, one of the key design dimensions of hardware transactional memory (HTM) systems, defines where and how transactional modifications are stored. Current HTM systems use either eager or lazy version management. Eager systems that keep new values in-place while they hold old values in a software log, suffer long delays when aborts are frequent because the pre-transactional state is recovered by software. Lazy systems that buffer new values in specialized hardware offer complex and inefficient solutions to handle hardware overflows, which are common in applications with coarse-grain transactions. In this paper, we present FASTM, an eager log-based HTM that takes advantage of the processorpsilas cache hierarchy to provide fast abort recovery. FASTM uses a novel coherence protocol to buffer the transactional modifications in the first level cache and to keep the non-speculative values in the higher levels of the memory hierarchy. This mechanism allows fast abort recovery of transactions that do not overflow the first level cache resources. Contrary to lazy HTM systems, committing transactions do not have to perform any actions in order to make their results visible to the rest of the system. FASTM keeps the pre-transactional state in a software-managed log as well, which permits the eviction of speculative values and enables transparent execution even in the case of cache overflow. This approach simplifies eviction policies without degrading performance, because it only falls back to a software abort recovery for transactions whose modified state has overflowed the cache. Simulation results show that FASTM achieves a speed-up of 43% compared to LogTM-SE, improving the scalability of applications with coarse-grain transactions and obtaining similar performance to an ideal eager HTM with zero-cost abort recovery.