Home-based Release Consistency in Object-based Software DSM Systems

This paper discusses the application of consistency models in objectbased software distributed shared memory (DSM) systems. In particular, we propose a home-based release consistency protocol as applied to our object-based software DSM system Rthreads (Remote threads). Access to shared data is performed in the Rthreads programs by explicit read/write operations. Global data structures are explicitly distributed over the Rthreads processes by the programmer. The ownership of the data structure, necessary for consistency updates, can also be distributed over different portions. Moreover, ownership can be dynamically rearranged during run-time. In the context of object-based DSM systems, the home-based release consistency protocol proved as superior to a lazy-release consistency protocol. Our consistency protocol is based on a flexible partitioning of the distributed data structures between the parallel Rthreads processes. In particular, by exploiting the data structuring features of Rthreads, consistency updates are restricted to the data that is actually shared between parallel Rthreads processes, thus avoiding false sharing. We have measured several standard benchmarks executed on an IBM RS/6000 SP multiprocessor. Our evaluations show that our home-based consistency protocol yields a performance increase of up to 2.86 over the basic Rthreads system and of up to 2.22 over the page-based CVM [1] system.