| Benchmark - benchmark running times of Perl code |
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';
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
use Benchmark;
$t0 = Benchmark->new;
# ... your code here ...
$t1 = Benchmark->new;
$td = timediff($t1, $t0);
print "the code took:",timestr($td),"\n";
$Benchmark::Debug flag:
Benchmark->debug(1);
$t = timeit(10, ' 5 ** $Global ');
Benchmark->debug(0);
The following routines will be exported into your namespace if you use the Benchmark module:
Returns: a Benchmark object.
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.
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.
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'.
The following routines will be exported into your namespace if you specifically ask that they be imported:
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.
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.
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.
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:
The following illustrates use of the Benchmark object:
$result = timethis(100000, sub { ... });
print "total CPU = ", $result->cpu_a, "\n";
The data is stored as a list of values from the time and times functions:
($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.
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 from 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 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.
the Devel::NYTProf manpage - 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 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.
| Benchmark - benchmark running times of Perl code |