Lazy Release Consistency for Software Distributed Shared Memory

Abstract

Relaxed memory consistency models, such a s release consistency, w ere introduced in order to reduce the impact of remote memory access latency in both software and hardware distributed shared memory (DSM). However, in a software DSM, it is also important to reduce the number of messages and the amount o f d a t a e xchanged for remote memory access. Lazy release consistency is a new algorithm for implementing release consistency that lazily pulls modi cations across the interconnect only when necessary. T race-driven simulation using the SPLASH benchmarks indicates that lazy release consistency reduces both the number of messages and the amount of data transferred between processors. These reductions are especially signi cant f o r programs that exhibit false sharing and make extensive use of locks.

Delay tolerant lazy release consistency for distributed shared memory in opportunistic networks

“…Acquiring and releasing locks to the critical section now becomes a "synchronization point" within the program, with other processes in the system receiving their invalidation notifications when the process holding the lock releases it. Figure 2.7 illustrates the exchange of consistency information with eager release consistency [12]. Eager release consistency's ability to let the developer specify exactly when consistency data will be traversing a network is very useful in the context of opportunistic networks as connectivity between nodes operating in an ON is erratic and subject to change without notification.…”

“…Lazy release consistency (LRC), as developed by Keleher [12], is an extension of eager release consistency with a number of enhancements to make the scheme better suited to operating in an environment with a high per-message cost. Keleher divides consistency protocols into two broad groups: eager protocols and lazy protocols.…”

“…In this way, LRC substantially reduces the consistency information needing to be sent over the network. Figure 2.8 shows the exchange of consistency information with lazy release consistency [12]. Steps are also taken to avoid false sharing.…”

“…The memory is uniformly divided into segments, with each segment assigned an index. The arrangement of segments and indices is identical for all participating machines, a scheme derived from [12]. The entire data set necessary for operation is then copied to each machine and stored in the predetermined area of memory.…”

View-Oriented Parallel Programming and View-Based Consistency

“…To improve the performance of the strict SC model, a number of Relaxed Sequential Consistency (RSC) models have been proposed [7,9,14,2,13,11], which perform one or more of the above three selection techniques. RSC models can be also called conditional Sequential Consistency models because they guarantee Sequential Consistency for some class of programs that satisfy the conditions imposed by the models.…”