Re: (tye)Re: A better non-existant string...

I was going to disagree, but continue reading to see why I'm not. My code is below, have I done something wrong?

#!/usr/bin/perl

use Benchmark;

sub double {
    $teststring = '';
    if( $teststring ne "" ) {
        return 1;
    } else {
        return 0;
    }
}

sub single {
    $teststring = '';
    if( $teststring ne '' ) {
        return 1;
    } else {
        return 0;
    }
}

timethese( 1000000, { double => 'double( )',
                  single => 'single( )' } );
[download]

Which gave these results on 3 consecutive trials

Benchmark: timing 1000000 iterations of double, single...
    double:  3 wallclock secs ( 2.14 usr +  0.00 sys =  2.14 CPU)
    single:  1 wallclock secs ( 1.86 usr +  0.00 sys =  1.86 CPU)

Benchmark: timing 1000000 iterations of double, single...
    double:  1 wallclock secs ( 1.86 usr +  0.00 sys =  1.86 CPU)
    single:  2 wallclock secs ( 1.92 usr +  0.00 sys =  1.92 CPU)

Benchmark: timing 1000000 iterations of double, single...
    double:  1 wallclock secs ( 1.89 usr +  0.00 sys =  1.89 CPU)
    single:  1 wallclock secs ( 1.86 usr +  0.00 sys =  1.86 CPU)
[download]

The way I understand the Benchmark module, system load at the time of benchmarking doesn't
influence the numbers. Is that statement correct? Does anybody know what's going on?

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(tye)Re2: A better non-existant string...
by tye (Sage) on Jan 23, 2001 at 11:44 UTC

It isn't the start-up time. It is probably an effect of the working set "settling in" or any number of other things that can affect benchmark numbers. In general, a 5% or less difference isn't something I would consider "real" as running it an hour later could certainly swing the answer that much. Here is the code I used:

use Benchmark qw(cmpthese);

my $str= "This is a test, " x 200;
my $single= "'".$str."'";
my $double= '"'.$str.'"';
cmpthese( -3, {
    a_double => sub { eval $double },
    b_single => sub { eval $single },
    c_double => sub { eval $double },
    d_single => sub { eval $single },
} );
[download]

           Rate a_double c_double b_single d_single
a_double 4773/s       --      -1%     -23%     -23%
c_double 4830/s       1%       --     -22%     -22%
b_single 6170/s      29%      28%       --      -0%
d_single 6172/s      29%      28%       0%       --
[download]

tye

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