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



NAME
       Benchmark - benchmark running times of Perl code

SYNOPSIS
           use Benchmark qw(:all) ;

           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... },
           });

           # cmpthese can be used both ways as well
           cmpthese($count, {
               'Name1' => '...code1...',
               'Name2' => '...code2...',
           });

           cmpthese($count, {
               'Name1' => sub { ...code1... },
               'Name2' => sub { ...code2... },
           });

           # ...or in two stages
           $results = timethese($count,
               {
                   'Name1' => sub { ...code1... },
                   'Name2' => sub { ...code2... },
               },
               'none'
           );
           cmpthese( $results ) ;

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

           $t = countit($time, '...other code...')
           $count = $t->iters ;
           print "$count loops of other code took:",timestr($t),"\n";

           # enable hires wallclock timing if possible
           use Benchmark ':hireswallclock';

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

       timethis - run a chunk of code several times

       timethese - run several chunks of code several times

       cmpthese - print results of timethese as a comparison chart

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

       countit - see how many times a chunk of code runs in a given time

   Methods
       new       Returns the current time.   Example:

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

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

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

       iters     Returns the number of iterations.

   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.

       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().

                 Returns a hash reference of Benchmark objects, keyed by name.

       timediff ( T1, T2 )
                 Returns the difference between 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', 'none', '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'.  'none' prevents output.

                 FORMAT is the printf(3)-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.

       clearallcache ( )
                 Clear all cached times.

       cmpthese ( COUNT, CODEHASHREF, [ STYLE ] )
       cmpthese ( RESULTSHASHREF, [ STYLE ] )
                 Optionally calls timethese(), then outputs comparison chart.  This:

                     cmpthese( -1, { a => "++\$i", b => "\$i *= 2" } ) ;

                 outputs a chart like:

                            Rate    b    a
                     b 2831802/s   -- -61%
                     a 7208959/s 155%   --This -This

                 This chart is sorted from slowest to fastest, and shows the percent speed difference
                 between each pair of tests.

                 "cmpthese" can also be passed the data structure that timethese() returns:

                     $results = timethese( -1, { a => "++\$i", b => "\$i *= 2" } ) ;
                     cmpthese( $results );

                 in case you want to see both sets of results.  If the first argument is an unblessed hash
                 reference, that is RESULTSHASHREF; otherwise that is COUNT.

                 Returns a reference to an ARRAY of rows, each row is an ARRAY of cells from the above
                 chart, including labels. This:

                     my $rows = cmpthese( -1, { a => '++$i', b => '$i *= 2' }, "none" );

                 returns a data structure like:

                     [
                         [ '',       'Rate',   'b',    'a' ],
                         [ 'b', '2885232/s',  '--', '-59%' ],
                         [ 'a', '7099126/s', '146%',  '--' ],
                     ]

                 NOTE: This result value differs from previous versions, which returned the "timethese()"
                 result structure.  If you want that, just use the two statement "timethese"..."cmpthese"
                 idiom shown above.

                 Incidently, note the variance in the result values between the two examples; this is
                 typical of benchmarking.  If this were a real benchmark, you would probably want to run a
                 lot more iterations.

       countit(TIME, CODE)
                 Arguments: TIME is the minimum length of time to run CODE for, 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.

                 TIME is not negative.  countit() will run the loop many times to calculate the speed of
                 CODE before running it for TIME.  The actual time run for will usually be greater than TIME
                 due to system clock resolution, so it's best to look at the number of iterations divided by
                 the times that you are concerned with, not just the iterations.

                 Returns: a Benchmark object.

       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.

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

   :hireswallclock
       If the Time::HiRes module has been installed, you can specify the special tag ":hireswallclock" for
       Benchmark (if Time::HiRes is not available, the tag will be silently ignored).  This tag will cause
       the wallclock time to be measured in microseconds, instead of integer seconds.  Note though that the
       speed computations are still conducted in CPU time, not wallclock time.

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

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

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

           clearcache($key);
           clearallcache();

           disablecache();
           enablecache();

       Caching is off by default, as it can (usually slightly) decrease accuracy and does not usually
       noticably affect runtimes.

EXAMPLES
       For example,

           use Benchmark qw( cmpthese ) ;
           $x = 3;
           cmpthese( -5, {
               a => sub{$x*$x},
               b => sub{$x**2},
           } );

       outputs something like this:

          Benchmark: running a, b, each for at least 5 CPU seconds...
                 Rate    b    a
          b 1559428/s   -- -62%
          a 4152037/s 166%   --while -while

       while

           use Benchmark qw( timethese cmpthese ) ;
           $x = 3;
           $r = timethese( -5, {
               a => sub{$x*$x},
               b => sub{$x**2},
           } );
           cmpthese $r;

       outputs something like this:

           Benchmark: running a, b, each for at least 5 CPU seconds...
                    a: 10 wallclock secs ( 5.14 usr +  0.13 sys =  5.27 CPU) @ 3835055.60/s (n=20210743)
                    b:  5 wallclock secs ( 5.41 usr +  0.00 sys =  5.41 CPU) @ 1574944.92/s (n=8520452)
                  Rate    b    a
           b 1574945/s   -- -59%
           a 3835056/s 144%   --INHERITANCE -INHERITANCE

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 slightly 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.

       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.

SEE ALSO
       Devel::DProf - a Perl code profiler

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.

       September, 1999; by Barrie Slaymaker: math fixes and accuracy and efficiency tweaks.  Added
       cmpthese().  A result is now returned from timethese().  Exposed countit() (was runfor()).

       December, 2001; by Nicholas Clark: make timestr() recognise the style 'none' and return an empty
       string. If cmpthese is calling timethese, make it pass the style in. (so that 'none' will suppress
       output). Make sub new dump its debugging output to STDERR, to be consistent with everything else.
       All bugs found while writing a regression test.

       September, 2002; by Jarkko Hietaniemi: add ':hireswallclock' special tag.

       February, 2004; by Chia-liang Kao: make cmpthese and timestr use time statistics for children instead
       of parent when the style is 'nop'.

       November, 2007; by Christophe Grosjean: make cmpthese and timestr compute time consistently with
       style argument, default is 'all' not 'noc' any more.



perl v5.12.5                                     2012-11-03                                   Benchmark(3pm)