Isolation-Safe Speculative Access Control for Hardware Transactional Memory

On shared-memory systems such as multi-core processors, lock-based mechanisms have been used in parallel programs to exclude conflicting accesses on shared variables. Transactional memory (TM) is a new paradigm to arbitrate conflicting accesses and is expected to be an alternative to the traditional lock-based mechanisms. Transactional memory speculatively executes transactions in parallel and cancels the execution when access conflicts are detected between them. Because canceling the speculative execution has an impact on TM performance, it is advisable to reduce conflicts. We found that some of the accesses, that are judged as conflicting accesses by TM, need not be denied and can be granted. In this paper, we propose a novel execution control for TMs for speculatively granting a certain type of access requests. The result of the evaluation shows that the execution cycles can be reduced by 63.6% at a maximum and 38.8% on average.