In this paper, we describe a multithreaded software distributed shared memory (DSM) system named Orion. It has been developed to provide POSIX-thread (pthread) like interface. We believe this will avoid creating another unique set of application programming interface and ease the porting of pthread programs to a distributed environment. Orion implements home-based consistency model. In this paper, we also present 2 adaptive schemes for home-based DSM systems: home migration and dynamic adaptation between write-invalidation and write-update protocols. The two fully automatic schemes aim to involve minimal user intervention and yet deliver good performances with some speedups ranging from 2% to 79% observed in some 8 benchmarks tested.

1.1 An Efficient Shared Memory Layer for Distributed Memory Machines...... 3 1.2 Fine-grain Access Control for Distributed Shared Memory............. 3 1.2.1 Software look-up................................ 4

This document reports on results obtained from early 1998 through early 1999, and outlines plans for the third and final year of the Cashmere ESS grant.

Cache memories are used extensively in modern computer organizations in order to reduce the performance gap between fast microprocessors and slower main memory. Cache memory hides the main memory access latency by exploiting the data locality present in pre-fetched memory blocks in the cache. Conventional pre-fetching policies used in traditional cache organizations have the potential to waste the available cache bandwidth and space by bringing non-usable data in the cache. Conventional caches cannot meet the different sized storage requirements of data that exhibit spatial or temporal locality characteristics when their address spaces vary and are non-overlapping. Data characterized by spatial or temporal locality could be more efficiently accommodated if caches with different line sizes based on the locality type could be used. The fixed line size of a conventional cache restricts this efficiency. To reduce the performance bottleneck of conventional caches, an alternative cache organization is explored in this research. The SPEC92 benchmarks as well as other standard benchmark programs are used to observe run-time data locality. Based on the locality analysis, a simple locality prediction technique was designed in hardware capable of estimating the data locality bias of the cache-resident data during run-time. This prediction hardware is used to design a split data cache that uses two sub-caches; spatial and temporal cache. This organization stores data in the respective sub-caches based on the dynamic locality estimation during run-time of the executing programs. The split data cache organization showed a considerable performance increase over a conventional unified data cache by iv reducing the overall cache miss rate and bus data traffic. A better utilization of t...

As more and more software DSM systems with their unique APIs surface, it becomes imperative for the industry to come up with a standardized API to facilitate users in using different types of DSM systems. A multithreaded software DSM, Orion, has been developed to provide POSIX-thread ( pthread) like API which avoids creating another unique set of API and helps in porting pthread programs to a distributed environment. Orion implements home-based consistency model, which is a recent development in the DSM field that has open up many areas for further research and development. In this paper, we also present 2 adaptive schemes for home-based DSM systems: home migration and dynamic adaptation between write-invalidation and write-update protocols. The two fully automatic schemes aim to involve minimal user intervention and yet deliver good performances with some speedups ranging from 2% to 79% observed in some 8 benchmarks tested.