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man : Benchmark(3p)
Benchmark(3p) Perl Programmers Reference Guide Benchmark(3p)
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
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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 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
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followed by the times. TITLE defaults to "time-
this COUNT" if none is provided. STYLE deter-
mines 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 excep-
tion).
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.
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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 ( 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 struc-
ture 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,
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.
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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 con-
ducted in CPU time, not wallclock time.
NOTES
The data is stored as a list of values from the time and
times functions:
($real, $user, $system, $children_user, $children_system, $iters)
in seconds for the whole loop (not divided by the number
of rounds).
The timing is done using time(3) and times(3).
Code is executed in the caller's package.
The time of the null loop (a loop with the same number of
rounds but empty loop body) is subtracted from the time of
the real loop.
The null loop times can be cached, the key being the num-
ber of rounds. The caching can be controlled using calls
like these:
clearcache($key);
clearallcache();
disablecache();
enablecache();
Caching is off by default, as it can (usually slightly)
decrease accuracy and does not usually noticably affect
runtimes.
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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
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');
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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 <jhiATiki.fi>, Tim Bunce
<Tim.BunceATig.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 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.
September, 2002; by Jarkko Hietaniemi: add ':hireswall-
clock' 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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