Locality and performance of page- and objectbased DSMs

This paper presents simulated results comparing representatives of two approaches to software DSM: an object-based protocol and a page-based protocol. We explore the performance impli-cations of each approach, including the object approach’s ad-vantages in bandwidth consumption and lack of false sharing. Somewhat surprisingly, the locality and data aggregation ad-vantages of page-based systems prove to be the dominant fac-tors with typical operating system overheads. We show that large page sizes actually improve the performance of multi-writer protocols, primarily because validating a single object validates all other objects on the same page as well. Since our applications have significant spatial locality, these additional validations reduce the number of remote misses, without signifi-cantly increasing bandwidth requirements. For three out of the four applications we tested, our page-based protocol matched or outperformed our object-based protocol under typical operating systems costs. We quantify this effect, and conclude with a discussion of tech-niques that could allow each approach to benefit from the best features of the other. 1