Entry consistency versus lazy release consistency in DSM systems: analytical comparison and a new hybrid solution

Entry consistency (EC), implemented in Midway, and lazy release consistency (LRC), implemented in TreadMarks, are two promising relaxed memory consistency models which tend to minimize communication costs. This is an important goal of software-based distributed shared memory (DSM) solutions built on workstation networks. While Midway uses a fine-grain update-based coherence protocol, TreadMarks implements an invalidation-based protocol with virtual memory page as the granularity unit. Instead of transferring the whole page on a page fault, TreadMarks transfers diffs-lists of modifications to the page during a critical section. According to a previous comparative study of EC and LRC neither is unconditionally better than the other and the performance advantages depend highly on the application. This paper examines the performance/complexity trade-offs of EC and LRC, based on a model that includes storage overhead, as well as the communication and computation costs. A proposal for a new hybrid of LRC and EC is also presented