This paper describes a method for improving the performance of a large direct-mapped cache by reducing the number of conflict misses. Our solution consists of two components: an inexpensive hardware device called a Cache Miss Lookaside (CML) buffer that detects conflicts by recording and summarizing a history of cache misses, and a software policy within the operating system's virtual memory system that removes conflicts by dynamically remapping pages whenever large numbers of conflict misses are detected. Using trace-driven simulation of applications and the operating system, we show that a CML buffer enables a large direct-mapped cache to perform nearly as well as a two-way set associative cache of equivalent size and speed, although with lower hardware cost and complexity.

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In this paper we evaluate the memory system behavior of two distinctly different implementations of the UNIX operating system: DEC's Ultrix, a monolithic system, and Mach 3.0 with CMU's UNIX server, a microkernel-based system. In our evaluation we use combined system and user memory reference traces of thirteen industry-standard workloads.We show that the microkernel-based system executes substantially more non-idle system instructions for an equivalent workload than the monolithic system. Furthermore, the average instruction for programs running on Mach has a higher cost, in terms of memory cycles per instruction, than on Ultrix. In the context of our traces, we explore a number of popular assertions about the memory system behavior of modern operating systems, paying special attention to the effect that Mach's microkernel architecture has on system performance. Our results indicate that many, but not all of the assertions are true, and that a few, while true, have only negligible impact on real system performance.

This paper describes a method for improving the performance of a large direct-mapped cache by reducing the number of conflict misses. Our solution consists of two components: an inexpensive hardware device called a Cache Miss Lookaside (CML) buffer that detects conflicts by recording and summarizing a history of cache misses, and a software policy within the operating system's virtual memory system that removes conflicts by dynamically remapping pages whenever large numbers of conflict misses are detected. Using trace-driven simulation of applications and the operating system, we show that a CML buffer enables a large direct-mapped cache to perform nearly as well as a two-way set associative cache of equivalent size and speed, although with lower hardware cost and complexity.

No abstract