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 most promising relaxed memory consistency models that tend to minimize communication costs, which is the important goal of software-based DSM solutions built on the top of networks of workstations. While Midway uses fine-grain, update-based coherence protocol, TreadMarks implements invalidation-based protocol with virtual memory page as a granularity unit. Instead of transferring whole page on a page fault, TreadMarks transfers diffs - lists of modifications to the page during one critical section. According to a previous comparative study of EC and LRC none of them is unconditionally better, and performance advantages of one or the other highly depend on the application. The goal of this paper is to examine performance/complexity trade-offs of entry consistency and lazy release consistency, based on the model that includes storage overhead, as well as communication and computation costs. A proposal for a new hybrid of LRC and EC is also presented.