Computer, tune thyself

Performance engineers are sometimes accused of being obsessed with
performance, to the exclusion of common sense. We tweak and tune
systems for the maximum possible throughput, and frankly some ordinary
users are left behind – people who don’t really care how fast it is so
long as it’s fast enough – people who have their own jobs to
do, and for whom the computer is just another tool.

Verlag Heinz Heise publishing (iX
Magazin, Germany) has long offered constructive criticism to SPEC like this article
on the release of the CPU2000 benchmark suite. Not ones to just heckle
the teams from the sideline, iX runs their own benchmark tests
publishing them in their own magazine and web site and also at SPEC.
This lets them show performance that they consider real world,
tuned according to good application development practice but short of
what they consider heroic benchmark tuning. For example in 2001 they
published this result of 88.3 SPECint_rate_base2000 on our 24 chip 750 MHz
Sun Fire 6800. We tuned the same system to achieve 96.1
SPECint_rate_base2000
and 101 SPECint_rate2000 (peak).

So we could show the user how to get 14% more performance from the
system. However today you can get 78.8
SPECint_rate_base2000
and 89.8 SPECint_rate2000from a 4 chip 3 GHz
Sun Fire V40z. So who’s to blame the user if instead of investing much
effort in performance tuning he would rather just ride Moore’s Law for
a while?

It’s relatively easy for an independent party like Verlag Heinz Heise
to say what they mean by real world optimization, compared to the
difficulty of the members of SPEC agreeing on what we mean by
peak versus baseline optimization. As we described the
baseline metric, it "…uses performance compiler flags that
a compiler vendor would suggest for a given program knowing only its
own language."
(See CPU2000 FAQ.) But of course degree of optimization is a
continuum, and there will be application developers who do not
optimize even as much as SPEC base and there will be those who
optimize more than SPEC peak.

One benefit of SPEC’s full disclosure reports is that they can serve
as examples of good tuning practice to supplement system
documentation. SPEC benchmarks may not use tuning that is not
documented, supported, and recommended for general use. So a visit to
the flags disclosure
pages
may provide a wealth of good tuning ideas for your own
applications.

Tuning for system level benchmarks may be even more complex than
compiler options for the CPU benchmarks. For example, in this
SPECjAppServer2004 result
there are tuning notes for the emulator
software, the database software, the driver software, and the
operating systems, as well as for the J2EE application server:

JVM Options: -server -Xms3g -Xmx3g -Xmn800m -Xss128k -XX:+AggressiveHeap
-XX:+UseParallelGC -XX:ParallelGCThreads=32 -XX:PermSize=128m
-XX:MaxTenuringThreshold=3 -XX:LargePageSizeInBytes=4m -XX:SurvivorRatio=20
-verbose:gc -XX:+PrintGCDetails -XX:+PrintGCTimeStamps -XX:-TraceClassUnloading
-XX:+UseParallelOldGC -Dweblogic.DevPollSocketReaders=2
Java process started in FX class using /usr/bin/priocntl -e -c FX

 

Again the SPEC full disclosure reports may guide the reader in
discovering and using various system tuning parameters. Of course with
system tuning you’ll probably also want to take a course and/or get a
good book like Solaris
Internals
.

For the user without time or inclination to learn system performance
tuning, who wants his system to be just fast enough while he
waits for Moore’s Law to bring next year’s more powerful server, I’m
afraid the computer industry just hasn’t done enough. Directions are
positive though. Suppose you discover, for instance, that it’s good
for your C application to align
branch targets based on execution frequency.
A Java application
may have such an optimization applied automatically by a Java Virtual
Machine with dynamic optimization such as HotSpot.
Operating systems may with your permission automatically apply system
updates including performance updates, such as Microsoft
Update
(Sorry, the corresponding URL on microsoft.com only works with Explorer.)
and Sun Update
Connection.

Computer, tune thyself.

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