The impact of symmetry on software distributed shared memory

A homeless protocol is one in which all nodes are treated identically when they access common resources. By contrast, home-based protocols assign a ho me or manager to each resource. Use of the resource by the home incurs less overhead than use by other processors. The key to good performance in such systems is to ensure that the asymmetry of the underlying protocol is skew ed in the same way as that of the application. This paper presents a compar ative evaluation of invalidation-based homeless and home-based software DSM protocols, We pay particular attention to those performance differences ca used by symmetric and asymmetric features of the protocols. We then show ho w the picture changes when update protocols are targeted. We show that a mo dified home-based protocol can significantly outperform more general protoc ols in this application domain because of reduced protocol complexity. We f urther optimize our protocol by completely eliminating such memory manipula tion calls from the steady-stale execution. Our resulting protocol improves average application performance by a further 34%, on top of the 19% improv ement gained by our initial modification of the home-based protocol. (C) 20 00 Academic Press.