Distributed shared memory on IBM SP2

Distributed Shared Memory (DSM) approach provides the illusion of a global shared address space by implementing a layer of shared memory abstraction on a physically distributed memory system. In this paper, we present DSM-SP2, a software distributed shared memory system built on IBM SP2, a distributed memory machine. DSM-SP2 is implemented completely in software as a set of user-level library routines on top of the AIX operating system without requiring any modifications to the operating system or any additional compiler support. The salient features of DSM-SP2 are: (i) it implements lazy release consistency model with hybrid coherence protocol to reduce the communication overheads; (ii) it allows multiple concurrent writers to minimize the effects of false-sharing; (iii) to reduce the DSM overheads and the idling time of processes, the DSM-SP2 implementation allows multiple processes per node; and (iv) it implements a new synchronization primitive called conditional lock acquire/release for effective simple producer-consumer type of synchronization. Detailed performance measurements for three benchmark programs namely, Water, Jacobi and Tomcatv are reported