Location Consistency Model Revisited: Problem, Solution and Prospects

Location consistency (LC) is a weak memory consistency model which is defined entirely on partial order execution semantics of parallel programs. Compared with sequential consistency (SC), LC is scalable and provides ample theoretical parallelism. This makes LC an interesting memory model in the upcoming many-core parallel processing era. Previous work has pointed out that LC does not guarantee SC execution behavior for all data race free programs. In this paper, we compare the semantics of LC with PRAM consistency and memory coherence, and prove that LC is strictly weaker than PRAM consistency. For data race free programs, we prove that the semantics of LC is equivalent to memory coherence. In addition, by introducing memory ordering semantics into LC judiciously, we prove that the enhanced model is equivalent to SC for data race free programs. Finally, we discuss possible solutions for adding reasoning rules for LC-like weak memory models.