Benchmark::Timer - Benchmarking with statistical confidence

Author

       The original code (written before April 20, 2001) was written by Andrew Ho <andrew@zeuscat.com>,  and  is
       copyright (c) 2000-2001 Andrew Ho.  Versions up to 0.5 are distributed under the same terms as Perl.

       Maintenance of this module is now being done by David Coppit <david@coppit.org>.

Bugs

       Benchmarking is  an  inherently  futile  activity,  fraught  with  uncertainty  not  dissimilar  to  that
       experienced in quantum mechanics. But things are a little better if you apply statistics.

Description

       The Benchmark::Timer class allows you to time portions of code conveniently, as well as benchmark code by
       allowing timings of repeated trials. It is perfect for when you need more precise information about the
       running time of portions of your code than the Benchmark module will give you, but don't want to go all
       out and profile your code.

       The methodology is simple; create a Benchmark::Timer object, and wrap portions of code that you want to
       benchmark with "start()" and "stop()" method calls.  You can supply a tag to those methods if you plan to
       time multiple portions of code.  If you provide error and confidence values, you can also use
       "need_more_samples()" to determine, statistically, whether you need to collect more data.

       After you have run your code, you can obtain information about the running time by calling the
       "results()" method, or get a descriptive benchmark report by calling "report()".  If you run your code
       over multiple trials, the average time is reported.  This is wonderful for benchmarking time-critical
       portions of code in a rigorous way. You can also optionally choose to skip any number of initial trials
       to cut down on initial case irregularities.

License

       This  code  is distributed under the GNU General Public License (GPL) Version 2.  See the file LICENSE in
       the distribution for details.

Methods

In all of the following methods, $tag refers to the user-supplied name of the code being timed. Unless
otherwise specified, $tag defaults to the tag of the last call to "start()", or "_default" if "start()"
was not previously called with a tag.

$t = Benchmark::Timer->new( [options] );
Constructor for the Benchmark::Timer object; returns a reference to a timer object. Takes the
following named arguments:

skip
The number of trials (if any) to skip before recording timing information.

minimum
The minimum number of trials to run.

error
A percentage between 0 and 100 which indicates how much error you are willing to tolerate in the
average time measured by the benchmark. For example, a value of 1 means that you want the
reported average time to be within 1% of the real average time. "need_more_samples()" will use
this value to determine when it is okay to stop collecting data.

If you specify an error you must also specify a confidence.

confidence
A percentage between 0 and 100 which indicates how confident you want to be in the error measured
by the benchmark. For example, a value of 97.5 means that you want to be 97.5% confident that the
real average time is within the error margin you have specified. "need_more_samples()" will use
this value to compute the estimated error for the collected data, so that it can determine when
it is okay to stop.

If you specify a confidence you must also specify an error.

$t->reset;
Reset the timer object to the pristine state it started in. Erase all memory of tags and any
previously accumulated timings. Returns a reference to the timer object. It takes the same arguments
the constructor takes.

$t->start($tag);
Record the current time so that when "stop()" is called, we can calculate an elapsed time.

$t->stop($tag);
Record timing information. If $tag is supplied, it must correspond to one given to a previously
called "start()" call. It returns the elapsed time in milliseconds. "stop()" croaks if the timer
gets out of sync (e.g. the number of "start()"s does not match the number of "stop()"s.)

$t->need_more_samples($tag);
Compute the estimated error in the average of the data collected thus far, and return true if that
error exceeds the user-specified error. If a $tag is supplied, it must correspond to one given to a
previously called "start()" call.

This routine assumes that the data are normally distributed.

$t->report($tag);
Returns a string containing a simple report on the collected timings for $tag. This report contains
the number of trials run, the total time taken, and, if more than one trial was run, the average time
needed to run one trial and error information. "report()" will complain (via a warning) if a tag is
still active.

$t->reports;
In a scalar context, returns a string containing a simple report on the collected timings for all
tags. The report is a concatenation of the individual tag reports, in the original tag order. In an
list context, returns a hash keyed by tag and containing reports for each tag. The return value is
actually an array, so that the original tag order is preserved if you assign to an array instead of a
hash. "reports()" will complain (via a warning) if a tag is still active.

$t->result($tag);
Return the time it took for $tag to elapse, or the mean time it took for $tag to elapse once, if $tag
was used to time code more than once. "result()" will complain (via a warning) if a tag is still
active.

$t->results;
Returns the timing data as a hash keyed on tags where each value is the time it took to run that
code, or the average time it took, if that code ran more than once. In scalar context it returns a
reference to that hash. The return value is actually an array, so that the original tag order is
preserved if you assign to an array instead of a hash.

$t->data($tag), $t->data;
These methods are useful if you want to recover the full internal timing data to roll your own
reports.

If called with a $tag, returns the raw timing data for that $tag as an array (or a reference to an
array if called in scalar context). This is useful for feeding to something like the
Statistics::Descriptive package.

If called with no arguments, returns the raw timing data as a hash keyed on tags, where the values of
the hash are lists of timings for that code. In scalar context, it returns a reference to that hash.
As with "results()", the data is internally represented as an array so you can recover the original
tag order by assigning to an array instead of a hash.

Name

       Benchmark::Timer - Benchmarking with statistical confidence

Synopsis

         # Non-statistical usage
         use Benchmark::Timer;
         $t = Benchmark::Timer->new(skip => 1);

         for(1 .. 1000) {
             $t->start('tag');
             &long_running_operation();
             $t->stop('tag');
         }
         print $t->report;

         # --------------------------------------------------------------------

         # Statistical usage
         use Benchmark::Timer;
         $t = Benchmark::Timer->new(skip => 1, confidence => 97.5, error => 2);

         while($t->need_more_samples('tag')) {
             $t->start('tag');
             &long_running_operation();
             $t->stop('tag');
         }
         print $t->report;