Report Number: CSL-TR-75-95
Institution: Stanford University, Computer Systems Laboratory
Title: The stack working set: a characterization of spatial locality
Author: Rau, B. Ramakrishna
Date: July 1975
Abstract: Multilevel memory hierarchies are attractive from the point of view of cost-performance. However, they present far greater problems than two-level hierarchies when it comes to analytic performance evaluation. This may be attributed to two factors: firstly, the page size (or the unit of information transfer between two levels) varies with the level in the hierarchy; secondly, the request streams that the lower (slower) levels see are the fault streams out of the immediately higher levels. Therefore, the request stream seen by each level is not necessarily the same as the one generated by the processor. Since the performance depends directly upon the properties of the request stream, this poses a problem. A model for program behavior, which explicitly characterizes the spatial locality of the program, is proposed and validated. It is shown that the spatial locality of a program is an invariant of the hierarchy when characterized in this manner. This invariance is used to solve the first problem stated - that of the varying page sizes. An approximate technique is advanced for the characterization of the fault stream as a function of the request stream and the capacity of the level. A procedure is then outlined for evaluating the performance of a multilevel hierarchy analytically.