Benchmark(3p) Perl Programmers Reference Guide Benchmark(3p)
Benchmark - benchmark running times of Perl code
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';
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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 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
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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 sig-
nifies 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, how-
ever, 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 contain-
ing 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 of Benchmark objects, keyed by
name.
timediff ( T1, T2 )
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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 com-
parison 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.
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c<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.
Returns a reference to an ARRAY of rows, each row
is an ARRAY of cells from the above chart, includ-
ing 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 ver-
sions, 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 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 con-
cerned with, not just the iterations.
Returns: a Benchmark object.
disablecache ( )
Disable caching of timings for the null loop. This
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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 Bench-
mark 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.
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 noticably affect
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runtimes.
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% --
Benchmark inherits from no other class, except of course for
Exporter.
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 granular-
ity 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
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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 there-
fore the difference might end up being < 0.
Devel::DProf - a Perl code profiler
Jarkko Hietaniemi <jhi@iki.fi>, Tim Bunce
<Tim.Bunce@ig.co.uk>
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 run-
for()).
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 debug-
ging 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'.
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