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

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

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

NNAAMMEE #

 Benchmark - benchmark running times of Perl code

SSYYNNOOPPSSIISS #

     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';

DDEESSCCRRIIPPTTIIOONN #

 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

MMeetthhooddss 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.

SSttaannddaarrdd EExxppoorrttss 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 ttiimmeessttrr(()) below.

           The COUNT can be zero or negative: this means the _m_i_n_i_m_u_m
           _n_u_m_b_e_r _o_f _C_P_U _s_e_c_o_n_d_s 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 mmiinniimmuumm 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 ttiimmeetthhiiss(()).

           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 ttiimmeessttrr(()).

 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 ttiimmeeddiiffff(()).

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

OOppttiioonnaall EExxppoorrttss 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 ttiimmeetthheessee(()), 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 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
           ttiimmeetthheessee(()) 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%',  '--' ],
               ]

           NNOOTTEE: 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.

           Incidentally, 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 _n_o_t negative.  ccoouunnttiitt(()) 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 ttiimmeessttrr(()).

::hhiirreesswwaallllcclloocckk 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.

BBeenncchhmmaarrkk OObbjjeecctt Many of the functions in this module return a Benchmark object, or in the case of “timethese()”, a reference to a hash, the values of which are Benchmark objects. This is useful if you want to store or further process results from Benchmark functions.

 Internally the Benchmark object holds timing values, described in "NOTES"
 below.  The following methods can be used to access them:

 cpu_p
     Total CPU (User + System) of the main (parent) process.

 cpu_c
     Total CPU (User + System) of any children processes.

 cpu_a
     Total CPU of parent and any children processes.

 real
     Real elapsed time "wallclock seconds".

 iters
     Number of iterations run.

 The following illustrates use of the Benchmark object:

     $result = timethis(100000, sub { ... });
     print "total CPU = ", $result->cpu_a, "\n";

NNOOTTEESS #

 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 ttiimmee(3) and ttiimmeess(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 noticeably affect runtimes.

EEXXAAMMPPLLEESS #

 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%   --

IINNHHEERRIITTAANNCCEE #

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

CCAAVVEEAATTSS #

 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 ttiimmee(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.

SSEEEE AALLSSOO #

 Devel::NYTProf - a Perl code profiler

AAUUTTHHOORRSS #

 Jarkko Hietaniemi <_j_h_i_@_i_k_i_._f_i>, Tim Bunce <_T_i_m_._B_u_n_c_e_@_i_g_._c_o_._u_k>

MMOODDIIFFIICCAATTIIOONN HHIISSTTOORRYY #

 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 ccmmpptthheessee(()).  A result is now returned from
 ttiimmeetthheessee(()).  Exposed ccoouunnttiitt(()) (was rruunnffoorr(())).

 December, 2001; by Nicholas Clark: make ttiimmeessttrr(()) 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 v5.36.3 2021-03-02 Benchmark(3p)