Cohesion: An efficient distributed shared memory system supporting multiple memory consistency models

This paper describes a prototype of DSM called Cohesion which supports two memory consistency models, namely Sequential consistency and Release consistency, within a single program to improve the performance and supports wide-variety of parallel programs for the system. Memory that is sequentially consistent is further divided into object-based and conventional (page-based) memory; where they are constructed in user-level and kernel-level, respectively. In object-based memory, the shared data are kept consistent at the granularity of an object; it is provided to improve the performance of the fine-grained parallel applications that may incur a significant overhead in conventional or release memory, as well as to eliminate unnecessary movement of the pages which are protected in a critical section. On the other hand, the Release consistency model is supported in Cohesion to attack the problem of excessive network traffic and false sharing. Cohesion programs are written in C++, and the annotation of shared objects for release and object-based memory is accomplished by inheriting a system-provided base class. Finally, three application programs including Matrix Multiplication, SOR, and Nbody have been employed to evaluate the efficiency of Cohesion. In addition, a Producer-Consumer program is tested to show that the object-based memory will benefit us in a critical section.