bench_lang_intro(3tcl) Benchmarking/Performance tools bench_lang_intro(3tcl)
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NAME
bench_lang_intro - bench language introduction
DESCRIPTION
This document is an informal introduction to version 1 of the bench
language based on a multitude of examples. After reading this a bench-
mark writer should be ready to understand the formal bench language
specification.
FUNDAMENTALS
In the broadest terms possible the bench language is essentially Tcl,
plus a number of commands to support the declaration of benchmarks. A
document written in this language is a Tcl script and has the same syn-
tax.
BASICS
One of the most simplest benchmarks which can be written in bench is
bench -desc LABEL -body {
set a b
}
This code declares a benchmark named LABEL which measures the time it
takes to assign a value to a variable. The Tcl code doing this assign-
ment is the -body of the benchmark.
PRE- AND POSTPROCESSING
Our next example demonstrates how to declare initialization and cleanup
code, i.e. code computing information for the use of the -body, and for
releasing such resources after the measurement is done. They are the
-pre- and the -post-body, respectively.
In our example, directly drawn from the benchmark suite of Tcllib's aes
package, the concrete initialization code constructs the key schedule
used by the encryption command whose speed we measure, and the cleanup
code releases any resources bound to that schedule.
bench -desc "AES-${len} ECB encryption core" -pre {
set key [aes::Init ecb $k $i]
} -body {
aes::Encrypt $key $p
} -post {
aes::Final $key
}
ADVANCED PRE- AND POSTPROCESSING
Our last example again deals with initialization and cleanup code. To
see the difference to the regular initialization and cleanup discussed
in the last section it is necessary to know a bit more about how bench
actually measures the speed of the the -body.
Instead of running the -body just once the system actually executes the
-body several hundred times and then returns the average of the found
execution times. This is done to remove environmental effects like ma-
chine load from the result as much as possible, with outliers canceling
each other out in the average.
The drawback of doing things this way is that when we measure opera-
tions which are not idempotent we will most likely not measure the time
for the operation we want, but of the state(s) the system is in after
the first iteration, a mixture of things we have no interest in.
Should we wish, for example, to measure the time it takes to include an
element into a set, with the element not yet in the set, and the set
having specific properties like being a shared Tcl_Obj, then the first
iteration will measure the time for this. However all subsequent itera-
tions will measure the time to include an element which is already in
the set, and the Tcl_Obj holding the set will not be shared anymore ei-
ther. In the end the timings taken for the several hundred iterations
of this state will overwhelm the time taken from the first iteration,
the only one which actually measured what we wanted.
The advanced initialization and cleanup codes, -ipre- and the -ipost-
body respectively, are present to solve this very problem. While the
regular initialization and cleanup codes are executed before and after
the whole series of iterations the advanced codes are executed before
and after each iteration of the body, without being measured them-
selves. This allows them to bring the system into the exact state the
body wishes to measure.
Our example, directly drawn from the benchmark suite of Tcllib's
struct::set package, is for exactly the example we used above to demon-
strate the necessity for the advanced initialization and cleanup. Its
concrete initialization code constructs a variable refering to a set
with specific properties (The set has a string representation, which is
shared) affecting the speed of the inclusion command, and the cleanup
code releases the temporary variables created by this initialization.
bench -desc "set include, missing <SC> x$times $n" -ipre {
set A $sx($times,$n)
set B $A
} -body {
struct::set include A x
} -ipost {
unset A B
}
FURTHER READING
Now that this document has been digested the reader, assumed to be a
writer of benchmarks, he should be fortified enough to be able to un-
derstand the formal bench language specfication. It will also serve as
the detailed specification and cheat sheet for all available commands
and their syntax.
BUGS, IDEAS, FEEDBACK
This document, and the package it describes, will undoubtedly contain
bugs and other problems. Please report such in the category bench of
the Tcllib Trackers [http://core.tcl.tk/tcllib/reportlist]. Please
also report any ideas for enhancements you may have for either package
and/or documentation.
When proposing code changes, please provide unified diffs, i.e the out-
put of diff -u.
Note further that attachments are strongly preferred over inlined
patches. Attachments can be made by going to the Edit form of the
ticket immediately after its creation, and then using the left-most
button in the secondary navigation bar.
SEE ALSO
bench_intro, bench_lang_spec
KEYWORDS
bench language, benchmark, examples, performance, testing
CATEGORY
Benchmark tools
COPYRIGHT
Copyright (c) 2007 Andreas Kupries <andreas_kupries@users.sourceforge.net>
tcllib 1.0 bench_lang_intro(3tcl)