The effects of virtually addressed caches on virtual memory design and performance

Abstract

Recent times have witnessed rapid advances in microprocessor technology resulting in an order of magnitude performance improvement every few years. These developments in hardware have been paralleled by several prominent trends in operating system design, the most notable being a move towards message-passing micro-kernels. However, operating system performance has not kept pace with that of the underlying hardware. It has become apparent that design changes to enhance processor performance can have adverse effects on operating system performance. This problem arises when the architectural assumptions implicit in an operating system's design are inappropriate for the architectures on which it executes.This paper examines one specific area in which operating system design assumptions appear to be in conflict with trends in modern processor architecture. We focus on the performance effects of virtually addressed caches on two contemporary operating systems (Mach and Chorus). We present experimental results to illustrate the impact of virtually addressed caches on the performance of primitive virtual memory operations, and higher-level operations, such as inter-process communication, that utilize these primitive operations. The main goal of the paper is to encourage operating system designers to revisit some of the basic architectural assumptions implicit in modern operating system designs.