OCTOBER 1989 WRL Technical Note TN 11 Why Aren t Operating Systems Getting Faster As Fast As Hardware John Ousterhout digi tal Western Research Laboratory 100 Hamilton Avenue Palo Alto California 94301 USA The Western Research Laboratory WRL is a computer systems research group that was founded by Digital Equipment Corporation in 1982 Our focus is computer science research relevant to the design and application of high performance scientific computers We test our ideas by designing building and using real systems The systems we build are research prototypes they are not intended to become products There is a second research laboratory located in Palo Alto the Systems Research Center SRC Other Digital research groups are located in Paris PRL and in Cambridge Massachusetts CRL Our research is directed towards mainstream high performance computer systems Our prototypes are intended to foreshadow the future computing environments used by many Digital customers The long term goal of WRL is to aid and accelerate the development of high performance uni and multi processors The research projects within WRL will address various aspects of high performance computing We believe that significant advances in computer systems do not come from any single technological advance Technologies both hardware and software do not all advance at the same pace System design is the art of composing systems which use each level of technology in an appropriate balance A major advance in overall system performance will require reexamination of all aspects of the system We do work in the design fabrication and packaging of hardware language processing and scaling issues in system software design and the exploration of new applications areas that are opening up with the advent of higher performance systems Researchers at WRL cooperate closely and move freely among the various levels of system design This allows us to explore a wide range of tradeoffs to meet system goals We publish the results of our work in a variety of journals conferences research reports and technical notes This document is a technical note We use this form for rapid distribution of technical material Usually this represents research in progress Research reports are normally accounts of completed research and may include material from earlier technical notes Research reports and technical notes may be ordered from us You may mail your order to Technical Report Distribution DEC Western Research Laboratory UCO 4 100 Hamilton Avenue Palo Alto California 94301 USA Reports and notes may also be ordered by electronic mail Use one of the following addresses Digital E net DECWRL WRL TECHREPORTS DARPA Internet WRL Techreports decwrl dec com CSnet WRL Techreports decwrl dec com UUCP decwrl wrl techreports To obtain more details on ordering by electronic mail send a message to one of these addresses with the word help in the Subject line you will receive detailed instructions Why Aren t Operating Systems Getting Faster As Fast As Hardware John Ousterhout October 1989 Abstract This note evaluates several hardware platforms and operating systems using a set of benchmarks that test memory bandwidth and various operating system features such as kernel entry exit and file systems The overall conclusion is that operating system performance does not seem to be improving at the same rate as the base speed of the underlying hardware Copyright 1989 Digital Equipment Corporation digi tal Western Research Laboratory 100 Hamilton Avenue Palo Alto California 94301 USA 1 Introduction This technical note contains results from several benchmark programs that I ran recently on machines at DEC s Western Research Laboratory and at the University of California at Berkeley The benchmarks are mostly micro benchmarks meaning that each one measures a particular hardware or operating system feature such as memory to memory copy speed or kernel entry exit Micro benchmarks like these can identify particular strengths and weaknesses of systems but they may not give a good indication of overall system performance The benchmarks also include one macro benchmark which exercises a variety of file system features and gives a better idea of overall operating system speed My goal in running the benchmarks was partly to compare different hardware platforms and operating systems but mostly to understand whether or not operating system performance will scale with the base performance of hardware platforms The answer for today s RISC workstations and RISC mainframes including machines from DEC Sun and MIPS Computer seems to be no when comparing slower older machines to newer RISC machines the speedup in most of the benchmarks is much less than the difference in raw hardware speed The benchmarks suggest at least two possible factors that contribute to non scalability of operating systems The first is memory bandwidth which has not scaled to match processor speed in faster machines The second factor is file systems some of which require synchronous disk I Os in common situations The synchronous I O requirements limit the performance of operating systems when processors get faster but disks don t 2 Hardware I used five hardware platforms for the benchmarks which are listed in Table 1 Table 1 also includes an abbreviation for each platform which is used in the rest of this note an approximate MIPS rating and an indication of whether the machine is based on a RISC processor or a CISC processor The MIPS ratings are my own estimates and are intended to give a rough idea of the base integer performance provided by each platform The main use of the MIPS ratings is to establish an expectation level for benchmarks For example if operating system performance scales with base system performance then a DS3100 should run the various benchmarks about 1 5 times as fast as a Sun4 and about seven times as fast as a Sun3 Hardware Abbreviation RISC CISC MIPS M2000 RISC 20 DS3100 RISC 13 Sun 4 280 Sun4 RISC 9 VAX 8800 8800 CISC 6 Sun 3 75 Sun3 CISC 1 8 MVAX2 CISC 0 9 MIPS M2000 DECstation 3100 Microvax II Table 1 Hardware Platforms 1 OPERATING SYSTEM BENCHMARKS All of the machines were generously endowed with memory As far as I know no significant paging occurred in any of the benchmarks In the file related benchmarks the relevant files all fit in the main memory buffer caches maintained by the operating systems 3 Operating Systems I used four operating systems for the benchmarks Ultrix SunOS RISC os and
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