benchmark(3)

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),"0;
$t = countit($time, '...other code...')
$count = $t->iters ;
print      "$count     loops     of     other     code
took:",timestr($t),"0;

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),"0;

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
exception).

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, [ STYLE ] )

Optionally calls timethese(), then outputs com parison chart. This:

cmpthese( -1, { a => "++", b => " *= 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.

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

$results = timethese( -1, { a => "++", b =>

" *= 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.
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, $chil

dren_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 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 sec

onds...

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 sec

onds...

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');

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 runfor-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.

perl v5.8.0 2002-06-01 Benchmark(3)