Locality and performance of page- and object-based 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 implications of each approach, including the object approach´s advantages in bandwidth consumption and lack of false sharing. Somewhat surprisingly the locality and data aggregation advantages of page-based systems prove to be the dominant factors with typical operating system overheads. We show that large page sizes actually improve the performance of multiwriter protocols, primarily because validating a single object validates all order objects on the same page as well. Since our applications have significant spatial locality, these additional validates reduce the number of remote misses, without significantly 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 techniques that could allow each approach to benefit from the best features of the other