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
- 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.
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'.
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().
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:
- 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 = ", $result->cpu_a, "\n";
The data is stored as a list of values from the time and times functions:
($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.
Devel::NYTProf - a Perl code profiler
Jarkko Hietaniemi <
[email protected]>, Tim Bunce
<
[email protected]>
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.