Exploring Selective coherence as a Solution to Self-invalidation in ArgoDSM

Maintaining coherency in a distributed system can prove challenging, this is especially true for distributed shared memory systems. The problem with remote synchronization in the distributed shared memory software ArgoDSM occurs when a lock operation has to cross the boundaries of a node, this causes a large number of self-invalidations (SI) or self-downgrades (SD) which is costly. The performance of the coherency protocol can be improved if the SI/SD situations can be avoided by using a suitable alternative. This work explores if the use of selective coherence operations and non-synchronizing locking can help alleviate the issue of SI and SD in ArgoDSM in order to improve performance compared to the cache-wide coherence operations that are triggered by the default locking mechanism in ArgoDSM. An implementation of the concept is done by replacing the standard coherence protocol used in locking operations with selective operations which is then used to analyze the performance compared to the baseline software. The selective coherence operations are more powerful than the default protocol when applied to synchronization-heavy benchmarks, while the baseline software performs better when there is a lower amount of parallel work being done