Directory-based conflict detection in hardware transactional memory

Abstract

One of the key design points of any hardware transactional memory (HTM) system is the conflict detection mechanism, and its efficient implementation becomes critical when conflicts are not a rare event. While many contemporary proposals rely on the coherence protocol to carry out conflict detection at the private cache levels, this approach is not optimal for systems that use a directory to maintain coherence over an unordered, scalable network, such as tiled CMPs. In this paper, we present a new scheme of conflict detection for HTM systems, which moves this key mechanism from the private caches to the directory level. We propose a novel transactional book-keeping method and describe how this detection can be carried out more efficiently at the directory. Simulation results show that our approach obtains reductions in execution time between 25 and 55% for transactional benchmarks with a high number of conflicts, with an average improvement over LogTM-SE of 15%. © 2008 Springer Berlin Heidelberg.