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


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



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


       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 = 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;

       iters     Returns the number of iterations.

       Standard Exports

       The following routines will be exported into your names-
       pace 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



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


                 followed by the times.  TITLE defaults to "time-
                 this COUNT" if none is provided. STYLE deter-
                 mines 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 excep-
                 tion).

                 Note that the CPU seconds is the minimum time:
                 CPU scheduling and other operating system fac-
                 tors 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 con-
                 taining 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 time-
                 this().

                 Returns a hash of Benchmark objects, keyed by
                 name.





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


       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 chil-
                 dren 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 names-
       pace 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 com-
                 parison 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 chart is sorted from slowest to fastest,
                 and shows the percent speed difference between
                 each pair of tests.



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


                 c<cmpthese> can also be passed the data struc-
                 ture that timethese() returns:

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

                 in case you want to see both sets of results.

                 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 val-
                 ues between the two examples; this is typical of
                 benchmarking.  If this were a real benchmark,
                 you would probably want to run a lot more itera-
                 tions.

       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 itera-
                 tions.

                 Returns: a Benchmark object.

       disablecache ( )
                 Disable caching of timings for the null loop.



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


                 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 con-
       ducted 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 num-
       ber 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.



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


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

           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
       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 granu-
       larity 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');



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


       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 accu-
       racy and efficiency tweaks.  Added cmpthese().  A result
       is now returned from timethese().  Exposed countit() (was
       runfor()).

       December, 2001; by Nicholas Clark: make timestr() recog-
       nise 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 regres-
       sion test.

       September, 2002; by Jarkko Hietaniemi: add ':hireswall-
       clock' 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'.

















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