Towards an Adaptive Distributed Shared Memory 1 ( Preliminary

The focus of this report is on software implementations of Distributed Shared Memory (DSM). In the recent years, many protocols for implementing DSM have been proposed. The protocols can be broadly divided into two classes: invalidation-based schemes and update-based schemes. Performance of these protocols depends on the memory access behavior of the applications. Some researchers have proposed DSMs that provide a family of consistency protocols or application speciic protocols, and the programmer is allowed to choose any one of them for each shared memory object (or page) or each stage of an application. While such implementations have a potential for achieving optimal performance, they impose undue burden on the programmer. An adaptive implementation that automatically chooses the appropriate protocol for each shared memory page (at run-time) will ease the task of programming for DSM. This report presents a simple approach for implementing adaptive DSMs. The approach is illustrated with the example of an adaptive DSM based on the competitive update protocol. The objective of the adaptive scheme is to minimize a pre-deened \cost" function. The cost functions considered here are number of messages and size of messages. (Other cost functions can also be used similarly.) The proposed scheme allows each node to independently choose (at run-time) a diierent protocol for each page. The report presents preliminary evaluation of the adaptive DSM. Preliminary results shows that the performance is improved by dynamically selecting the appropriate protocol. 2 This report will be revised to include more discussion, generalizations of the proposed approach, and further experimental results. This preliminary version presents the basic adaptive scheme and evaluation of a synthetic application.