This paper evaluates several hardware platforms and operating systems using a set of benchmarks that stress kernel entry/exit, file systems, and other things related to operating systems. The overall conclusion is that operating system performance is not improving at the same rate as the base speed of the underlying hardware. The most obvious ways to remedy this situation are to improve memory bandwidth and reduce operating systems' tendency to wait for disk operations to complete. 1. Introduction In the summer and fall of 1989 I assembled a collection of operating system benchmarks. My original intent was to compare the performance of Sprite, a UNIXcompatible research operating system developed at the University of California at Berkeley [4,5], with vendorsupported versions of UNIX running on similar hardware. After running the benchmarks on several configurations I noticed that the "fast" machines didn't seem to be running the benchmarks as quickly as I would have guessed from what...

Superscalar machines can issue several instructions per cycle. Superpipelined machines can issue only one instruction per cycle, but they have cycle times shorter than the latency of any functional unit. In this paper these two techniques are shown to be roughly equivalent ways of exploiting instruction-level parallelism. A parameterizable code reorganization and simulation system was developed and used to measure instruction-level parallelism for a series of benchmarks. Results of these simulations in the presence of various compiler optimizations are presented. The average degree of superpipelining metric is introduced. Our simulations suggest that this metric is already high for many machines. These machines already exploit all of the instruction-level parallelism available in many non-numeric applications, even without parallel instruction issue or higher degrees of pipelining. This is a preprint of a paper that will be presented at the 3rd International Conference on Architectur...

This paper investigates issues involving writes and caches. First, tradeoffs between write-through and write-back caching when writes hit in a cache are considered. A mixture of these two alternatives, called write caching is proposed. Write caching places a small fully-associative cache behind a write-through cache. A write cache can eliminate almost as much write traffic as a write-back cache. Second, tradeoffs on writes that miss in the cache are investigated. In particular, whether the missed cache block is fetched on a write miss, whether the missed cache block is allocated in the cache, and whether the cache line accessed is invalidated are considered. Depending on the combination of these polices chosen, the entire cache miss rate can vary by a factor of two on some applications. Furthermore, the combination of no-fetch-on-write and write-allocate can provide better performance than cache line allocation instructions. Finally, the traffic at the back side of write-through and wr...

The behavior of the TCP protocol in simple situations is well-understood, but when multiple connections share a set of network resources the protocol can exhibit surprising phenomena. Earlier studies have identified several such phenomena, and have analyzed them using simulation or observation of contrived situations. This paper shows how, by analyzing traces of a busy segment of the Internet, it is possible to observe these phenomena in "real life" and measure both their frequency and their effects on performance. A TCP implementation might use similar techniques to support rate-based congestion control.

The performance of two-level on-chip caching is investigated for a range of technology and architecture assumptions. The area and access time of each level of cache is modeled in detail. The results indicate that for most workloads, twolevel cache configurations (with a set-associative second level) perform marginally better than single-level cache configurations that require the same chip area once the first-level cache sizes are 64KB or larger. Two-level configurations become even more important in systems with no off-chip cache and in systems in which the memory cells in the first-level caches are multiported and hence larger than those in the second-level cache. Finally, a new replacement policy called two-level exclusive caching is introduced. Two-level exclusive caching improves the performance of two-level caching organizations by increasing the effective associativity and capacity. d i g i t a l Western Research Laboratory 250 University Avenue Palo Alto, California 94301 USA...

The results of an experimental investigation of pool boiling of water at subatmospheric pressures from small horizontal heat sources are reported. The heat sources are upward-facing copper surfaces submerged in a laterally-confined, finite pool of liquid. The saturated pool boiling heat transfer characteristics and the critical heat flux (CHF) condition were determined in the experiments. Low pressure boiling of saturated water provides a means of removing heat at high heat flux levels while maintaining low surface temperatures. However, at heat flux levels up to about 60 2 W/cm the frequency of bubble departure at low pressure is much less than the frequency of bubble departure at higher pressure (atmospheric). With low pressure boiling, only one or two very large bubbles form cyclically on the small heated surface, during the boiling process. This intermittent process may result in large, undesirable temperature oscillations at the heated surface for low pressure boiling. High-frequ...

This study considers boiling binary mixtures of water with methanol or 2-propanol at subatmospheric pressures. Liquid-phase equilibrium vapor pressures, binary phase equilibrium thermodynamic properties, heat transfer characteristics, and the critical heat flux (CHF) condition are determined for saturated pool boiling from a localized heat source while varying the concentrations of methanol and 2-propanol in water. The heat source is an upward-facing copper surface submerged in a laterally-confined, finite pool. Low pressure boiling of aqueous mixtures provides a means of removing high heat fluxes while maintaining low surface temperatures. Small additions of alcohol to water increase the CHF condition above that of pure water. Higher concentrations of alcohol begin decreasing the CHF condition to that of the pure alcohol. While single-component correlations using mole weighted binary liquid thermodynamic properties have been shown to predict ideal binary mixture boiling behavior, they...

The "mostly-copying" garbage collection algorithm provides a way to perform compacting garbage collection in spite of the presence of ambiguous pointers in the root set. As originally defined, each collection required almost all accessible objects to be moved. While adequate for many applications, programs that retained a large amount of storage spent a significant amount of time garbage collecting. To improve performance of these applications, a generational version of the algorithm has been designed. This note reports on this extension of the algorithm, and its application in collectors for Scheme and C++. Copyright 1989 Digital Equipment Corporation d i g i t a l Western Research Laboratory 100 Hamilton Avenue Palo Alto, California 94301 USA 1. Introduction The "mostly-copying" garbage collection algorithm [1] [2] was developed to allow compacting garbage collection in environments hostile to classical copying collection algorithms. Unlike classical copying collectors, it is ...