


Benchmark(3p)    Perl Programmers Reference Guide   Benchmark(3p)


NAME
       Benchmark - benchmark running times of code

       timethis - run a chunk of code several times

       timethese - run several chunks of code several times

       timeit - run a chunk of code and see how long it goes

SYNOPSIS
           timethis ($count, "code");

           # Use Perl code in strings...
           timethese($count, {
               'Name1' => '...code1...',
               'Name2' => '...code2...',
           });

           # ... or use subroutine references.
           timethese($count, {
               'Name1' => sub { ...code1... },
               'Name2' => sub { ...code2... },
           });

           $t = timeit($count, '...other code...')
           print "$count loops of other code took:",timestr($t),"\n";


DESCRIPTION
       The Benchmark module encapsulates a number of routines to
       help you figure out how long it takes to execute some
       code.

       Methods


       new       Returns the current time.   Example:

                     use Benchmark;
                     $t0 = new Benchmark;
                     # ... your code here ...
                     $t1 = new Benchmark;
                     $td = timediff($t1, $t0);
                     print "the code took:",timestr($td),"\n";


       debug     Enables or disable debugging by setting the
                 $Benchmark::Debug flag:

                     debug Benchmark 1;
                     $t = timeit(10, ' 5 ** $Global ');
                     debug Benchmark 0;





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Benchmark(3p)    Perl Programmers Reference Guide   Benchmark(3p)


       Standard Exports

       The following routines will be exported into your
       namespace if you use the Benchmark module:

       timeit(COUNT, CODE)
                 Arguments: COUNT is the number of times to run
                 the loop, and CODE is the code to run.  CODE may
                 be either a code reference or a string to be
                 eval'd; either way it will be run in the
                 caller's package.

                 Returns: a Benchmark object.

       timethis ( COUNT, CODE, [ TITLE, [ STYLE ]] )
                 Time COUNT iterations of CODE. CODE may be a
                 string to eval or a code reference; either way
                 the CODE will run in the caller's package.
                 Results will be printed to STDOUT as TITLE
                 followed by the times.  TITLE defaults to
                 "timethis COUNT" if none is provided. STYLE
                 determines the format of the output, as
                 described for timestr() below.

                 The COUNT can be zero or negative: this means
                 the minimum number of CPU seconds to run.  A
                 zero signifies the default of 3 seconds.  For
                 example to run at least for 10 seconds:

                         timethis(-10, $code)

                 or to run two pieces of code tests for at least
                 3 seconds:

                         timethese(0, { test1 => '...', test2 => '...'})

                 CPU seconds is, in UNIX terms, the user time
                 plus the system time of the process itself, as
                 opposed to the real (wallclock) time and the
                 time spent by the child processes.  Less than
                 0.1 seconds is not accepted (-0.01 as the count,
                 for example, will cause a fatal runtime
                 exception).

                 Note that the CPU seconds is the minimum time:
                 CPU scheduling and other operating system
                 factors may complicate the attempt so that a
                 little bit more time is spent.  The benchmark
                 output will, however, also tell the number of
                 $code runs/second, which should be a more
                 interesting number than the actually spent
                 seconds.

                 Returns a Benchmark object.



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Benchmark(3p)    Perl Programmers Reference Guide   Benchmark(3p)


       timethese ( COUNT, CODEHASHREF, [ STYLE ] )
                 The CODEHASHREF is a reference to a hash
                 containing names as keys and either a string to
                 eval or a code reference for each value.  For
                 each (KEY, VALUE) pair in the CODEHASHREF, this
                 routine will call

                         timethis(COUNT, VALUE, KEY, STYLE)

                 The routines are called in string comparison
                 order of KEY.

                 The COUNT can be zero or negative, see
                 timethis().

       timediff ( T1, T2 )
                 Returns the difference between two Benchmark
                 times as a Benchmark object suitable for passing
                 to timestr().

       timesum ( T1, T2 )
                 Returns the sum of two Benchmark times as a
                 Benchmark object suitable for passing to
                 timestr().

       timestr ( TIMEDIFF, [ STYLE, [ FORMAT ] ] )
                 Returns a string that formats the times in the
                 TIMEDIFF object in the requested STYLE. TIMEDIFF
                 is expected to be a Benchmark object similar to
                 that returned by timediff().

                 STYLE can be any of 'all', 'noc', 'nop' or
                 'auto'. 'all' shows each of the 5 times
                 available ('wallclock' time, user time, system
                 time, user time of children, and system time of
                 children). 'noc' shows all except the two
                 children times. 'nop' shows only wallclock and
                 the two children times. 'auto' (the default)
                 will act as 'all' unless the children times are
                 both zero, in which case it acts as 'noc'.

                 FORMAT is the the printf(3) manpage-style format
                 specifier (without the leading '%') to use to
                 print the times. It defaults to '5.2f'.

       Optional Exports

       The following routines will be exported into your
       namespace if you specifically ask that they be imported:

       clearcache ( COUNT )
                 Clear the cached time for COUNT rounds of the
                 null loop.




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Benchmark(3p)    Perl Programmers Reference Guide   Benchmark(3p)


       clearallcache ( )
                 Clear all cached times.

       disablecache ( )
                 Disable caching of timings for the null loop.
                 This will force Benchmark to recalculate these
                 timings for each new piece of code timed.

       enablecache ( )
                 Enable caching of timings for the null loop. The
                 time taken for COUNT rounds of the null loop
                 will be calculated only once for each different
                 COUNT used.

NOTES
       The data is stored as a list of values from the time and
       times functions:

             ($real, $user, $system, $children_user, $children_system)

       in seconds for the whole loop (not divided by the number
       of rounds).

       The timing is done using time(3) and times(3).

       Code is executed in the caller's package.

       The time of the null loop (a loop with the same number of
       rounds but empty loop body) is subtracted from the time of
       the real loop.

       The null loop times are cached, the key being the number
       of rounds. The caching can be controlled using calls like
       these:

           clearcache($key);
           clearallcache();

           disablecache();
           enablecache();


INHERITANCE
       Benchmark inherits from no other class, except of course
       for Exporter.

CAVEATS
       Comparing eval'd strings with code references will give
       you inaccurate results: a code reference will show a
       slower execution time than the equivalent eval'd string.

       The real time timing is done using time(2) and the
       granularity is therefore only one second.




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Benchmark(3p)    Perl Programmers Reference Guide   Benchmark(3p)


       Short tests may produce negative figures because perl can
       appear to take longer to execute the empty loop than a
       short test; try:

           timethis(100,'1');

       The system time of the null loop might be slightly more
       than the system time of the loop with the actual code and
       therefore the difference might end up being < 0.

AUTHORS
       Jarkko Hietaniemi <jhi@iki.fi>, Tim Bunce
       <Tim.Bunce@ig.co.uk>

MODIFICATION HISTORY
       September 8th, 1994; by Tim Bunce.

       March 28th, 1997; by Hugo van der Sanden: added support
       for code references and the already documented 'debug'
       method; revamped documentation.

       April 04-07th, 1997: by Jarkko Hietaniemi, added the run-
       for-some-time functionality.


































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