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

NAME
       Benchmark - benchmark running times of Perl code

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... },
	   });

	   # 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";

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 = 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 fol
		 lowed 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 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.

       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 ( COUT, CODEHASHREF, [ STYLE ] )
       cmpthese ( RESULTSHASHREF )
		 Optionally calls timethese(), then outputs com
		 parison chart.	 This chart is sorted from slow
		 est to fastest, and shows the percent speed dif
		 ference between each pair of tests.  Can also be
		 passed the data structure that timethese()
		 returns:

		     $results = timethese( .... );
		     cmpthese( $results );

		 Returns the data structure returned by
		 timethese() (or passed in).

       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.
		 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().

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.

EXAMPLES
       For example,

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

       outputs something like this:

	  Benchmark: running a, b, each for at least 5 CPU seconds...
		   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%   --

       while

	  use Benchmark;
	  $x=3;
	  $r=timethese(-5,{a=>sub{$x*$x},b=>sub{$x**2}},'none');
	  cmpthese($r);

       outputs something like this:

		 Rate	 b    a
	  b 1559428/s	-- -62%
	  a 4152037/s 166%   --


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');

       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
       the Devel::DProf manpage - 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()).

2001-02-22		   perl v5.6.1		     Benchmark(3)
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