Lies Damn Lies and Benchmarks Are your benchmark

Lies, Damn Lies and Benchmarks Are your benchmark tests reliable? 6. 1 Advanced Operating Systems

Typical Computer Systems Paper Abstract: What this paper contains. – Most readers will be reading just this. Introduction: Present a problem. – The universe cannot go on, if the problem persists. Related Work: Show the work of competitors. – They are stink. Solution: Present the suggested solution. – We are the best. 6. 2 Advanced Operating Systems

Typical Paper (Cont. ) Technique: Go into details. – Many drawings and figures. Experiments: Prove our point, Evaluation Methodology. – Which benchmarks adhere to my assumptions? Results: Show the enhancement is great. – The objective benchmarks agree that we are the best. Conclusions: Highlights of the paper. – Some readers will be reading besides the abstract, also this. 6. 3 Advanced Operating Systems

SPEC is Standard Performance Evaluation Corporation. – Legally, SPEC is a non-profit corporation registered in California. SPEC's mission: To establish, maintain, and endorse a standardized set of relevant benchmarks and metrics for performance evaluation of modern computer systems. "SPEC CPU 2000 is the next-generation industrystandardized CPU-intensive benchmark suite. " – Composed of 12 integer (CINT 2000) and 14 floatingpoint benchmarks (CFP 2000). 6. 4 Advanced Operating Systems

Some Conferences Statistics Number of papers published: 209 Papers that used a version of SPEC: 138 (66%) Earliest conference deadline: December 2000 SPEC CPU 2000 announced: December 1999 6. 5 Advanced Operating Systems

Partial use of CINT 2000 6. 6 Advanced Operating Systems

Why not using it all? It seemed that many papers are not using all benchmarks of the suite. Selected excuses were: – – – “The chosen benchmarks stress the problem …” “Several benchmarks couldn’t be simulated …” “A subset of CINT 2000 was chosen …” “… select benchmarks from CPU 2000 …” “More benchmarks wouldn't fit into our displays …” 6. 7 Advanced Operating Systems

Omission Explanation Roughly a third of the papers (34/108) present any reason at all. Many reasons are not so convincing. – Are the claims in the previous slide persuasive? 6. 8 Advanced Operating Systems

What has been omitted Possible reasons for the omissions: – eon is written in C++. – gap calls ioctl system call, which is a device specific call. – crafty uses a 64 -bit word. – perlbmk has problems with 64 bit processors 6. 9 Advanced Operating Systems

CINT 95 Still widespread even though it retired on June 2000. Smaller suite (8 vs. 12). Over 50% of full use, but around for at least 3 years already. Only 5 papers out of 36 explain the partial use. 6. 10 Advanced Operating Systems

Using of CINT 2000 The using of CINT has been increasing over the years. The benchmarking of new systems is done by old tests 6. 11 Advanced Operating Systems

Amdahl's Law Fenhanced is the percents of the benchmarks that were enhanced. Speedup is: CPU Timeold = = CPU Timenew CPU Timeold (1 - Fenhanced) + CPU Timeold Fenhanced (1/ speedupenhanced) 1 (1 - Fenhanced ) + Fenhanced speedupenhanced Example: if we have a way to improve just the gzip benchmark by a factor of 10, what fraction of usage must be gzip to achieve a 300% speedup? 3= 1 F (1 - Fenhanced ) + enhanced 10 Fenhanced=20/27=74% 6. 12 Advanced Operating Systems

Breaking Amdahl's Law "The performance improvement to be gained from using some faster mode of execution is limited by the fraction of the time the faster mode be used. " Just the full suite can accurately gauge the enhancement. It is possible that other benchmarks : – produce similar results. – degrade performance. – invariant to the enhancement. Even in this case the published results are too high according to Amdahl's Law. 6. 13 Advanced Operating Systems

Tradeoffs What about papers that offer performance tradeoffs? – Performance tradeoff are more than 40% of the papers. – An average paper contains just 8 tests out of the 12. What do we assume about missing results? I shouldn't have left eon out 6. 14 Advanced Operating Systems

Besides SPEC Categories of benchmarks: – Official benchmarks like SPEC; there also official benchmarks by non-vendor source. • They will not always concentrate on the points important for your usage. – Traces – real users whose activities are logged and kept. • An improved (or worsened) system may change the users behavior. 6. 15 Advanced Operating Systems

Besides SPEC (Cont. ) – Microbenchmarks – test just an isolated component of a system. • Using multiple microbenchmarks will not test the interaction between the components. – Ad-hoc benchmarks – run a bunch of programs that seem interesting. • If you suggest a way to compile Linux faster, Linux compilation can be a good benchmark. – Synthetic Benchmarks – write a program to test yourself. • You can stress your point. 6. 16 Advanced Operating Systems

Whetstone Benchmark Historically it is the first synthetic microbenchmark. The original Whetstone benchmark was designed in the 60's. First practical implementation on 1972. – Was named after the small town of Whetstone, where it was designed. Designed to measure the execution speed of a variety of FP instructions (+, *, sin, cos, atan, sqrt, log, exp). Contains small loop of FP instructions. The majority of its variables are global; hence will not show up the RISC advantages, where large number of registers enhance the local variables handling. 6. 17 Advanced Operating Systems

The Andrew benchmark was suggested at 1988. In the early 90's the Andrew benchmark was one of the popular non-vendor benchmark for file system efficiency. The Andrew benchmark: – Copies a directory hierarchy containing a source code of a large program. – "stat"s every file in the hierarchy. – Reads any byte of every copied file. – Compiles the code in the copied hierarchy. Does this reflect the reality? Who does work like this? 6. 18 Advanced Operating Systems

Kernel Compilation Maybe a "real" job can be more representative? Measure the compilation of the Linux kernel. The compilation reads large memory areas only once. This reduces the influence of the cache efficiency. – The influence of the L 2 cache will be drastically reduced. 6. 19 Advanced Operating Systems

Benchmarks' Contribution On 1999 Mogul presented statistics which have shown that while HW is usually measured by SPEC; when it comes to the code of the Operating System, no standard is popular. Distributed Systems are commonly benchmarked by NAS. On 1993, Chen & Patterson wrote: "Benchmarks do not help in understanding system performance". 6. 20 Advanced Operating Systems