Benchmark(3perl) Perl Programmers Reference Guide Benchmark(3perl)
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 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.
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 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.
Benchmark Object
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 = ", $result->cpu_a, "\n";
NOTES
The data is stored as a list of values from the time and times
functions:
($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 noticeably 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
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 from 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::NYTProf - 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 v5.40.1 2026-08-30 Benchmark(3perl)
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