1Benchmark(3pm)         Perl Programmers Reference Guide         Benchmark(3pm)
2
3
4

NAME

6       Benchmark - benchmark running times of Perl code
7

SYNOPSIS

9           use Benchmark qw(:all) ;
10
11           timethis ($count, "code");
12
13           # Use Perl code in strings...
14           timethese($count, {
15               'Name1' => '...code1...',
16               'Name2' => '...code2...',
17           });
18
19           # ... or use subroutine references.
20           timethese($count, {
21               'Name1' => sub { ...code1... },
22               'Name2' => sub { ...code2... },
23           });
24
25           # cmpthese can be used both ways as well
26           cmpthese($count, {
27               'Name1' => '...code1...',
28               'Name2' => '...code2...',
29           });
30
31           cmpthese($count, {
32               'Name1' => sub { ...code1... },
33               'Name2' => sub { ...code2... },
34           });
35
36           # ...or in two stages
37           $results = timethese($count,
38               {
39                   'Name1' => sub { ...code1... },
40                   'Name2' => sub { ...code2... },
41               },
42               'none'
43           );
44           cmpthese( $results ) ;
45
46           $t = timeit($count, '...other code...')
47           print "$count loops of other code took:",timestr($t),"\n";
48
49           $t = countit($time, '...other code...')
50           $count = $t->iters ;
51           print "$count loops of other code took:",timestr($t),"\n";
52
53           # enable hires wallclock timing if possible
54           use Benchmark ':hireswallclock';
55

DESCRIPTION

57       The Benchmark module encapsulates a number of routines to help you
58       figure out how long it takes to execute some code.
59
60       timethis - run a chunk of code several times
61
62       timethese - run several chunks of code several times
63
64       cmpthese - print results of timethese as a comparison chart
65
66       timeit - run a chunk of code and see how long it goes
67
68       countit - see how many times a chunk of code runs in a given time
69
70   Methods
71       new       Returns the current time.   Example:
72
73                     use Benchmark;
74                     $t0 = Benchmark->new;
75                     # ... your code here ...
76                     $t1 = Benchmark->new;
77                     $td = timediff($t1, $t0);
78                     print "the code took:",timestr($td),"\n";
79
80       debug     Enables or disable debugging by setting the $Benchmark::Debug
81                 flag:
82
83                     Benchmark->debug(1);
84                     $t = timeit(10, ' 5 ** $Global ');
85                     Benchmark->debug(0);
86
87       iters     Returns the number of iterations.
88
89   Standard Exports
90       The following routines will be exported into your namespace if you use
91       the Benchmark module:
92
93       timeit(COUNT, CODE)
94                 Arguments: COUNT is the number of times to run the loop, and
95                 CODE is the code to run.  CODE may be either a code reference
96                 or a string to be eval'd; either way it will be run in the
97                 caller's package.
98
99                 Returns: a Benchmark object.
100
101       timethis ( COUNT, CODE, [ TITLE, [ STYLE ]] )
102                 Time COUNT iterations of CODE. CODE may be a string to eval
103                 or a code reference; either way the CODE will run in the
104                 caller's package.  Results will be printed to STDOUT as TITLE
105                 followed by the times.  TITLE defaults to "timethis COUNT" if
106                 none is provided. STYLE determines the format of the output,
107                 as described for timestr() below.
108
109                 The COUNT can be zero or negative: this means the minimum
110                 number of CPU seconds to run.  A zero signifies the default
111                 of 3 seconds.  For example to run at least for 10 seconds:
112
113                         timethis(-10, $code)
114
115                 or to run two pieces of code tests for at least 3 seconds:
116
117                         timethese(0, { test1 => '...', test2 => '...'})
118
119                 CPU seconds is, in UNIX terms, the user time plus the system
120                 time of the process itself, as opposed to the real
121                 (wallclock) time and the time spent by the child processes.
122                 Less than 0.1 seconds is not accepted (-0.01 as the count,
123                 for example, will cause a fatal runtime exception).
124
125                 Note that the CPU seconds is the minimum time: CPU scheduling
126                 and other operating system factors may complicate the attempt
127                 so that a little bit more time is spent.  The benchmark
128                 output will, however, also tell the number of $code
129                 runs/second, which should be a more interesting number than
130                 the actually spent seconds.
131
132                 Returns a Benchmark object.
133
134       timethese ( COUNT, CODEHASHREF, [ STYLE ] )
135                 The CODEHASHREF is a reference to a hash containing names as
136                 keys and either a string to eval or a code reference for each
137                 value.  For each (KEY, VALUE) pair in the CODEHASHREF, this
138                 routine will call
139
140                         timethis(COUNT, VALUE, KEY, STYLE)
141
142                 The routines are called in string comparison order of KEY.
143
144                 The COUNT can be zero or negative, see timethis().
145
146                 Returns a hash reference of Benchmark objects, keyed by name.
147
148       timediff ( T1, T2 )
149                 Returns the difference between two Benchmark times as a
150                 Benchmark object suitable for passing to timestr().
151
152       timestr ( TIMEDIFF, [ STYLE, [ FORMAT ] ] )
153                 Returns a string that formats the times in the TIMEDIFF
154                 object in the requested STYLE. TIMEDIFF is expected to be a
155                 Benchmark object similar to that returned by timediff().
156
157                 STYLE can be any of 'all', 'none', 'noc', 'nop' or 'auto'.
158                 'all' shows each of the 5 times available ('wallclock' time,
159                 user time, system time, user time of children, and system
160                 time of children). 'noc' shows all except the two children
161                 times. 'nop' shows only wallclock and the two children times.
162                 'auto' (the default) will act as 'all' unless the children
163                 times are both zero, in which case it acts as 'noc'.  'none'
164                 prevents output.
165
166                 FORMAT is the printf(3)-style format specifier (without the
167                 leading '%') to use to print the times. It defaults to
168                 '5.2f'.
169
170   Optional Exports
171       The following routines will be exported into your namespace if you
172       specifically ask that they be imported:
173
174       clearcache ( COUNT )
175                 Clear the cached time for COUNT rounds of the null loop.
176
177       clearallcache ( )
178                 Clear all cached times.
179
180       cmpthese ( COUNT, CODEHASHREF, [ STYLE ] )
181       cmpthese ( RESULTSHASHREF, [ STYLE ] )
182                 Optionally calls timethese(), then outputs comparison chart.
183                 This:
184
185                     cmpthese( -1, { a => "++\$i", b => "\$i *= 2" } ) ;
186
187                 outputs a chart like:
188
189                            Rate    b    a
190                     b 2831802/s   -- -61%
191                     a 7208959/s 155%   --
192
193                 This chart is sorted from slowest to fastest, and shows the
194                 percent speed difference between each pair of tests.
195
196                 "cmpthese" can also be passed the data structure that
197                 timethese() returns:
198
199                     $results = timethese( -1,
200                         { a => "++\$i", b => "\$i *= 2" } ) ;
201                     cmpthese( $results );
202
203                 in case you want to see both sets of results.  If the first
204                 argument is an unblessed hash reference, that is
205                 RESULTSHASHREF; otherwise that is COUNT.
206
207                 Returns a reference to an ARRAY of rows, each row is an ARRAY
208                 of cells from the above chart, including labels. This:
209
210                     my $rows = cmpthese( -1,
211                         { a => '++$i', b => '$i *= 2' }, "none" );
212
213                 returns a data structure like:
214
215                     [
216                         [ '',       'Rate',   'b',    'a' ],
217                         [ 'b', '2885232/s',  '--', '-59%' ],
218                         [ 'a', '7099126/s', '146%',  '--' ],
219                     ]
220
221                 NOTE: This result value differs from previous versions, which
222                 returned the "timethese()" result structure.  If you want
223                 that, just use the two statement "timethese"..."cmpthese"
224                 idiom shown above.
225
226                 Incidentally, note the variance in the result values between
227                 the two examples; this is typical of benchmarking.  If this
228                 were a real benchmark, you would probably want to run a lot
229                 more iterations.
230
231       countit(TIME, CODE)
232                 Arguments: TIME is the minimum length of time to run CODE
233                 for, and CODE is the code to run.  CODE may be either a code
234                 reference or a string to be eval'd; either way it will be run
235                 in the caller's package.
236
237                 TIME is not negative.  countit() will run the loop many times
238                 to calculate the speed of CODE before running it for TIME.
239                 The actual time run for will usually be greater than TIME due
240                 to system clock resolution, so it's best to look at the
241                 number of iterations divided by the times that you are
242                 concerned with, not just the iterations.
243
244                 Returns: a Benchmark object.
245
246       disablecache ( )
247                 Disable caching of timings for the null loop. This will force
248                 Benchmark to recalculate these timings for each new piece of
249                 code timed.
250
251       enablecache ( )
252                 Enable caching of timings for the null loop. The time taken
253                 for COUNT rounds of the null loop will be calculated only
254                 once for each different COUNT used.
255
256       timesum ( T1, T2 )
257                 Returns the sum of two Benchmark times as a Benchmark object
258                 suitable for passing to timestr().
259
260   :hireswallclock
261       If the Time::HiRes module has been installed, you can specify the
262       special tag ":hireswallclock" for Benchmark (if Time::HiRes is not
263       available, the tag will be silently ignored).  This tag will cause the
264       wallclock time to be measured in microseconds, instead of integer
265       seconds.  Note though that the speed computations are still conducted
266       in CPU time, not wallclock time.
267

Benchmark Object

269       Many of the functions in this module return a Benchmark object, or in
270       the case of "timethese()", a reference to a hash, the values of which
271       are Benchmark objects.  This is useful if you want to store or further
272       process results from Benchmark functions.
273
274       Internally the Benchmark object holds timing values, described in
275       "NOTES" below.  The following methods can be used to access them:
276
277       cpu_p
278           Total CPU (User + System) of the main (parent) process.
279
280       cpu_c
281           Total CPU (User + System) of any children processes.
282
283       cpu_a
284           Total CPU of parent and any children processes.
285
286       real
287           Real elapsed time "wallclock seconds".
288
289       iters
290           Number of iterations run.
291
292       The following illustrates use of the Benchmark object:
293
294           $result = timethis(100000, sub { ... });
295           print "total CPU = ", $result->cpu_a, "\n";
296

NOTES

298       The data is stored as a list of values from the time and times
299       functions:
300
301             ($real, $user, $system, $children_user, $children_system, $iters)
302
303       in seconds for the whole loop (not divided by the number of rounds).
304
305       The timing is done using time(3) and times(3).
306
307       Code is executed in the caller's package.
308
309       The time of the null loop (a loop with the same number of rounds but
310       empty loop body) is subtracted from the time of the real loop.
311
312       The null loop times can be cached, the key being the number of rounds.
313       The caching can be controlled using calls like these:
314
315           clearcache($key);
316           clearallcache();
317
318           disablecache();
319           enablecache();
320
321       Caching is off by default, as it can (usually slightly) decrease
322       accuracy and does not usually noticeably affect runtimes.
323

EXAMPLES

325       For example,
326
327           use Benchmark qw( cmpthese ) ;
328           $x = 3;
329           cmpthese( -5, {
330               a => sub{$x*$x},
331               b => sub{$x**2},
332           } );
333
334       outputs something like this:
335
336          Benchmark: running a, b, each for at least 5 CPU seconds...
337                 Rate    b    a
338          b 1559428/s   -- -62%
339          a 4152037/s 166%   --
340
341       while
342
343           use Benchmark qw( timethese cmpthese ) ;
344           $x = 3;
345           $r = timethese( -5, {
346               a => sub{$x*$x},
347               b => sub{$x**2},
348           } );
349           cmpthese $r;
350
351       outputs something like this:
352
353           Benchmark: running a, b, each for at least 5 CPU seconds...
354                    a: 10 wallclock secs ( 5.14 usr +  0.13 sys =  5.27 CPU) @ 3835055.60/s (n=20210743)
355                    b:  5 wallclock secs ( 5.41 usr +  0.00 sys =  5.41 CPU) @ 1574944.92/s (n=8520452)
356                  Rate    b    a
357           b 1574945/s   -- -59%
358           a 3835056/s 144%   --
359

INHERITANCE

361       Benchmark inherits from no other class, except of course from Exporter.
362

CAVEATS

364       Comparing eval'd strings with code references will give you inaccurate
365       results: a code reference will show a slightly slower execution time
366       than the equivalent eval'd string.
367
368       The real time timing is done using time(2) and the granularity is
369       therefore only one second.
370
371       Short tests may produce negative figures because perl can appear to
372       take longer to execute the empty loop than a short test; try:
373
374           timethis(100,'1');
375
376       The system time of the null loop might be slightly more than the system
377       time of the loop with the actual code and therefore the difference
378       might end up being < 0.
379

SEE ALSO

381       Devel::NYTProf - a Perl code profiler
382

AUTHORS

384       Jarkko Hietaniemi <jhi@iki.fi>, Tim Bunce <Tim.Bunce@ig.co.uk>
385

MODIFICATION HISTORY

387       September 8th, 1994; by Tim Bunce.
388
389       March 28th, 1997; by Hugo van der Sanden: added support for code
390       references and the already documented 'debug' method; revamped
391       documentation.
392
393       April 04-07th, 1997: by Jarkko Hietaniemi, added the run-for-some-time
394       functionality.
395
396       September, 1999; by Barrie Slaymaker: math fixes and accuracy and
397       efficiency tweaks.  Added cmpthese().  A result is now returned from
398       timethese().  Exposed countit() (was runfor()).
399
400       December, 2001; by Nicholas Clark: make timestr() recognise the style
401       'none' and return an empty string. If cmpthese is calling timethese,
402       make it pass the style in. (so that 'none' will suppress output). Make
403       sub new dump its debugging output to STDERR, to be consistent with
404       everything else.  All bugs found while writing a regression test.
405
406       September, 2002; by Jarkko Hietaniemi: add ':hireswallclock' special
407       tag.
408
409       February, 2004; by Chia-liang Kao: make cmpthese and timestr use time
410       statistics for children instead of parent when the style is 'nop'.
411
412       November, 2007; by Christophe Grosjean: make cmpthese and timestr
413       compute time consistently with style argument, default is 'all' not
414       'noc' any more.
415
416
417
418perl v5.34.0                      2021-10-18                    Benchmark(3pm)
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