Speculation-Based Conflict Resolution in Hardware Transactional Memory

Conflict management is a key design dimension of hard-ware transactional memory (HTM) systems, and the imple-mentation of efficient mechanisms for detection and resolu-tion becomes critical when conflicts are not a rare event. Current designs address this problem from two opposite perspectives, namely, lazy and eager schemes. While the former approach is based on an purely optimistic view that is not well-suited when conflicts become frequent, the latter results too pessimistic because resolves conflicts too conservatively, often limiting concurrency unnecessarily. In this paper, we present a hybrid, pseudo-optimistic scheme of conflict resolution for HTM systems that recaptures the concept of speculation to allow transactions to continue their execution past conflicting accesses. Simulation results show that our proposal is capable of combining the advantages of both classical approaches. For the STAMP transactional benchmarks, our hybrid scheme outperforms both eager and lazy systems with average reductions in execution time of 8 and 17%, respectively, and it decreases network traffic by another 17 % compared to the eager policy. 1