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 home 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 skewed in the same way as that of the application. This paper presents a comparative evaluation of invalidation-based homeless and home-based software DSM protocols, We pay particular attention to those performance differences caused by symmetric and asymmetric features of the protocols. We then show how the picture changes when update protocols are targeted. We show that a modified home-based protocol can significantly outperform more general protocols in this application domain because of reduced protocol complexity. We further optimize our protocol by completely eliminating such memory manipulation calls from the steady-stale execution. Our resulting protocol improves average application performance by a further 34%, on top of the 19% improvement gained by our initial modification of the home-based protocol. (C) 2000 Academic Press.