Post on 06-Jan-2018
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6.1 Advanced Operating Systems
Lies, Damn Lies and Benchmarks
Are your benchmark tests reliable?
6.2 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.
6.3 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 how 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.
6.4 Advanced Operating Systems
SPECSPEC 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 CPU2000 is the next-generation industry-standardized CPU-intensive benchmark suite."– Composed of 12 integer (CINT2000) and 14 floating-point
benchmarks (CFP2000).
6.5 Advanced Operating Systems
Some Conferences Statistics
Number of papers published:209Papers that used a version of SPEC: 138 (66%)Earliest conference deadline: December 2000SPEC CPU2000 announced: December 1999
6.6 Advanced Operating Systems
Partial use of CINT2000
0%
20%
40%
60%
80%
100%
perc
ents
of p
aper
s
ISCA2001
Micro2001
HPCA2002
ISCA2002
Micro2002
HPCA2003
ISCA2003
Total
number of benchmarks used per paper
0 1-6 7-11 12
6.7 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 CINT2000 was chosen …”– “… select benchmarks from CPU2000 …”– “More benchmarks wouldn't fit into our displays …”
6.8 Advanced Operating Systems
Omission ExplanationRoughly a third of the papers (34/108) presentany reason at all.Many reasons are not so convincing.– Are the claims in the
previous slide persuasive?
6.9 Advanced Operating Systems
What has been omittedPossible 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
0102030405060708090100
gzip
vpr
parser
gcc
mcf
vortex
twolf
bzip2
perlbmk
crafty
gap
eon
percents of usage
6.10 Advanced Operating Systems
CINT95Still 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.
0%10%20%30%40%50%60%70%80%90%
100%
perc
ents
of p
aper
sCINT95
(1999-2000)CINT2000
(2001-2002)
0 1-6 (1-4) 7-11 (5-7) 12 (8)
6.11 Advanced Operating Systems
Using of CINT2000
The using of CINT has been increasing over the years.The benchmarking of new systems is done by old tests
6.12 Advanced Operating Systems
Amdahl's LawFenhanced is the percents of the benchmarks that were enhanced. Speedup is:
= =
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= Fenhanced=20/27=74%
Fenhanced
speedupenhanced
(1 - Fenhanced ) +
1
CPU Timeold
CPU Timenew
CPU Timeold
CPU Timeold (1 - Fenhanced) + CPU Timeold Fenhanced (1/ speedupenhanced)
Fenhanced
10 (1 - Fenhanced ) +
1
6.13 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.
6.14 Advanced Operating Systems
TradeoffsWhat 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
6.15 Advanced Operating Systems
Besides SPEC
Categories of benchmarks:– Official benchmarks like SPEC; there are
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.
6.16 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.
6.17 Advanced Operating Systems
Whetstone BenchmarkHistorically 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.
6.18 Advanced Operating Systems
The Andrew benchmarkAndrew 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?
6.19 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 L2 cache will be
drastically reduced.
6.20 Advanced Operating Systems
Benchmarks' ContributionOn 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".