Category Archives: Benchmarking

Doing less work to compute excellent numbers

When I last looked at excellent numbers, I knew there was more work I could do to optimize what I was doing. In particular, I knew there was some upper limit to the range of numbers I had to check. I didn’t take the time to think about until today. I had a brief foray into other languages, such as my attempt with Julia, as I ran out of time to think about it. Read more »

Computing excellent numbers

In the “Benchmarking” chapter of Mastering Perl, I emphasize better algorithms over different syntax. Many of the problems we think we have better solutions if we change how we do things instead of worrying about the efficiency of a particular keyword. In this item, I’ll go through my actual path through a problem rather than hiding all my failed experiments. The negative results are just as valuable. Read more »

Ten numbers on a blackboard

In Ten numbers on a blackboard, someone asks about the largest number you can compute by reducing a set of numbers. I was surprised to see that someone spent quite a bit of time to brute force it and that their Python solution was so slow. So many of the things I write about in the “Benchmarking” and “Profiling” chapters come into play in this conversation. Read more »

A new perlbench

I’ve released a new version of perlbench, which I write about in the Benchmarking chapter. After I posted “New in Benchmarking”, I wrote to Gisle Aas to volunteer to help. He immediately made me a co-maintainer and pointed me at his own GitHub repository for perlbench. I’ve cloned that and now my repo is upstream.

I’ve released version 0.94 and cleared out the RT Queue.

New to “Benchmarking”

Computers are much faster eight years later so my benchmark sample results are much faster. I’m regenerating those results with v5.18. I’ve tweaked many of the programs to be a bit more useful; in the previous edition I hardcoded values, such as the number of iterations. Now I can specify those on the command line.

Several of the benchmarks dealt with listing files with glob. In the first edition, I used a couple of existing directories. This time around, I spent too much time looking for suitable directories with the right numbers of files. After awhile, I gave up on that and had the programs create temporary directories with the number of files I specify:

use File::Temp qw(tempdir);
my $dir = tempdir( CLEANUP => 1 );

chdir( $dir ) or die "Could not change to $dir: $!";
foreach ( 1 .. $files ) {
    open my($fh), '>', "$0.$_.tmp" or die "Could not create a file: $!";
    print { $fh } time();
    }

After I covered Benchmark, I also mentioned Steffen Müller’s Dumbbench (see my earlier post, Playing with Dumbbench).

I updated the section on perlbench, Gisle Aas’s tool to compare benchmarks across different interpreters. Since he hasn’t updated that since I wrote the first edition, I took all of the previous releases and imported them into git so I could fix RT 73642, which recognizes the new way that perl reports its version. That’s now in my perlbench GitHub project.

Most of the other stuff is the same, with minor updates.

Check out this chapter in O’Reilly Atlas.

(Mis)adventures in benchmarking

In Adventures in Benchmarking, Part 1, David Golden ran a benchmark program to compare Path::Tiny‘s slurp against itself several times. He thought he had discovered a problem with the ordering of code in Benchmark, which runs the code in the lexigraphical order of their labels. He created several subroutines that did the same thing:


use v5.10;
use strict;
use warnings;
use Benchmark qw( cmpthese );
use Path::Tiny;
 
my $file = "ascii-large";
 
my $count = -1;
cmpthese(
    $count,
    {
        map { $_ => sub { path($file)->slurp } } ("a" .. "l")
    }
);

His results looked surprising, and I was a bit excited about this because I was working on the “Benchmarking” chapter of Mastering Perl the day that I read this. These numbers would make an excellent story:

l 1599/s   -- -14% -15% -19% -20% -20% -21% -21% -21% -23% -23% -23%
h 1866/s  17%   --  -1%  -6%  -6%  -7%  -8%  -8%  -8% -10% -10% -10%
i 1879/s  17%   1%   --  -5%  -6%  -6%  -8%  -8%  -8%  -9%  -9%  -9%
j 1981/s  24%   6%   5%   --  -1%  -1%  -3%  -3%  -3%  -4%  -4%  -4%
f 1995/s  25%   7%   6%   1%   --  -0%  -2%  -2%  -2%  -3%  -4%  -4%
b 1999/s  25%   7%   6%   1%   0%   --  -2%  -2%  -2%  -3%  -3%  -4%
g 2033/s  27%   9%   8%   3%   2%   2%   --  -0%  -0%  -2%  -2%  -2%
c 2035/s  27%   9%   8%   3%   2%   2%   0%   --  -0%  -2%  -2%  -2%
a 2036/s  27%   9%   8%   3%   2%   2%   0%   0%   --  -1%  -2%  -2%
e 2067/s  29%  11%  10%   4%   4%   3%   2%   2%   2%   --  -0%  -0%
k 2070/s  29%  11%  10%   4%   4%   4%   2%   2%   2%   0%   --  -0%
d 2074/s  30%  11%  10%   5%   4%   4%   2%   2%   2%   0%   0%   --

I tried it myself on my Mac Pro running OS X.8 with a Perl v5.14.2 compiled with the defaults. I didn’t get the same dramatic results:

macpro> perl5.14.2 path-tiny.pl /Volumes/Perl/BackPAN/modules/06perms.txt.gz
     Rate   l   j   g   k   a   b   i   e   d   f   c   h
l 1382/s  -- -1% -1% -1% -1% -1% -1% -1% -1% -2% -3% -3%
j 1395/s  1%  --  0% -0% -0% -0% -0% -0% -0% -1% -2% -2%
g 1395/s  1%  0%  -- -0% -0% -0% -0% -0% -0% -1% -2% -2%
k 1395/s  1%  0%  0%  -- -0% -0% -0% -0% -0% -1% -2% -2%
a 1395/s  1%  0%  0%  0%  -- -0% -0% -0% -0% -1% -2% -2%
b 1395/s  1%  0%  0%  0%  0%  -- -0% -0% -0% -1% -2% -2%
i 1395/s  1%  0%  0%  0%  0%  0%  -- -0% -0% -1% -2% -2%
e 1399/s  1%  0%  0%  0%  0%  0%  0%  -- -0% -1% -2% -2%
d 1400/s  1%  0%  0%  0%  0%  0%  0%  0%  -- -1% -2% -2%
f 1408/s  2%  1%  1%  1%  1%  1%  1%  1%  1%  -- -1% -1%
c 1422/s  3%  2%  2%  2%  2%  2%  2%  2%  2%  1%  -- -0%
h 1422/s  3%  2%  2%  2%  2%  2%  2%  2%  2%  1%  0%  --

macpro> perl5.14.2 path-tiny.pl /Volumes/Perl/BackPAN/modules/06perms.txt.gz 
    Rate   a   b   l   k   i   c   e   d   j   h   f   g
a 1370/s  -- -1% -2% -2% -2% -2% -2% -2% -2% -2% -3% -3%
b 1382/s  1%  -- -1% -1% -1% -1% -1% -1% -1% -1% -2% -2%
l 1395/s  2%  1%  --  0%  0% -0% -0% -0% -0% -0% -1% -1%
k 1395/s  2%  1%  0%  --  0% -0% -0% -0% -0% -0% -1% -1%
i 1395/s  2%  1%  0%  0%  -- -0% -0% -0% -0% -0% -1% -1%
c 1395/s  2%  1%  0%  0%  0%  -- -0% -0% -0% -0% -1% -1%
e 1395/s  2%  1%  0%  0%  0%  0%  -- -0% -0% -0% -1% -1%
d 1395/s  2%  1%  0%  0%  0%  0% -0%  -- -0% -0% -1% -1%
j 1399/s  2%  1%  0%  0%  0%  0%  0%  0%  --  0% -1% -1%
h 1399/s  2%  1%  0%  0%  0%  0%  0%  0%  0%  -- -1% -1%
f 1408/s  3%  2%  1%  1%  1%  1%  1%  1%  1%  1%  -- -0%
g 1408/s  3%  2%  1%  1%  1%  1%  1%  1%  1%  1%  0%  --

More interestingly, my results seem to disprove his assertion that there are internal ordering effects at play. That is, Benchmark::Forking doesn’t matter. I was curious about that in his results too, but with modern filesystems doing what they do, the side effects are likely outside of his program. The ordering of the tests relative to each other is unrepeatable, even when I switch to Benchmark::Forking, which only isolates effects inside the program.

I figured this might not be an issue with my particular operating system and setup, so I also tried it on a FreeBSD machine. I got the same non-results. There’s no consistent ordering of tests relative to each other with Benchmark or Benchmark::Forking, and there’s no consistent range of values.

freebsd> perl5.10.1 path-tiny.pl dp-dump.mysql
    Rate    b    h    j    i    a    l    k    g    f    d    e    c
b 1137/s   --  -7% -11% -11% -11% -11% -12% -12% -12% -12% -13% -13%
h 1218/s   7%   --  -4%  -4%  -5%  -5%  -5%  -5%  -5%  -6%  -6%  -6%
j 1273/s  12%   4%   --   0%  -1%  -1%  -1%  -1%  -1%  -2%  -2%  -2%
i 1273/s  12%   4%   0%   --  -1%  -1%  -1%  -1%  -1%  -2%  -2%  -2%
a 1283/s  13%   5%   1%   1%   --  -0%  -0%  -0%  -0%  -1%  -2%  -2%
l 1283/s  13%   5%   1%   1%   0%   --  -0%  -0%  -0%  -1%  -2%  -2%
k 1286/s  13%   6%   1%   1%   0%   0%   --   0%   0%  -1%  -1%  -1%
g 1286/s  13%   6%   1%   1%   0%   0%   0%   --   0%  -1%  -1%  -1%
f 1286/s  13%   6%   1%   1%   0%   0%   0%   0%   --  -1%  -1%  -1%
d 1295/s  14%   6%   2%   2%   1%   1%   1%   1%   1%   --  -1%  -1%
e 1303/s  15%   7%   2%   2%   2%   2%   1%   1%   1%   1%   --   0%
c 1303/s  15%   7%   2%   2%   2%   2%   1%   1%   1%   1%   0%   --

freebsd> perl5.10.1 path-tiny.pl dp-dump.mysql
    Rate   g   h   f   i   d   j   e   l   k   c   b   a
g 1168/s  -- -1% -2% -2% -4% -4% -5% -5% -5% -6% -7% -8%
h 1184/s  1%  -- -1% -1% -3% -3% -3% -3% -3% -4% -6% -6%
f 1193/s  2%  1%  --  0% -2% -2% -3% -3% -3% -4% -5% -6%
i 1193/s  2%  1%  0%  -- -2% -2% -3% -3% -3% -4% -5% -6%
d 1218/s  4%  3%  2%  2%  --  0% -1% -1% -1% -1% -3% -4%
j 1218/s  4%  3%  2%  2%  0%  -- -1% -1% -1% -1% -3% -4%
e 1227/s  5%  4%  3%  3%  1%  1%  --  0%  0% -1% -2% -3%
l 1227/s  5%  4%  3%  3%  1%  1%  0%  --  0% -1% -2% -3%
k 1227/s  5%  4%  3%  3%  1%  1%  0%  0%  -- -1% -2% -3%
c 1236/s  6%  4%  4%  4%  1%  1%  1%  1%  1%  -- -1% -2%
b 1254/s  7%  6%  5%  5%  3%  3%  2%  2%  2%  1%  -- -1%
a 1264/s  8%  7%  6%  6%  4%  4%  3%  3%  3%  2%  1%  --

I suspect that there are a couple of runs of the target code that take abnormally long and skew the results. These happen at certain times regardless of the code being run. A cache adjusts itself, another program is asking for the I/O channels, a disk has to wake up, or something else. In short, these numbers are useless because they treat every run the same despite what happened.

Dumbbench can handle this situation. It times the code, running it enought time to get to a certain precision by ignoring outliers. The Benchmark::Dumb module is a mostly compatible interface, although I specify a number of maximum iterations and a target precision instead of a number of iterations:

#!/usr/bin/perl
# path-tiny.pl

use Benchmark::Dumb qw( cmpthese );
use Path::Tiny;
 
my $file = $ARGV[0];
 
my $count = 1000.01;
cmpthese(
    $count, {
        map { $_ => sub { path($file)->slurp } } ("a" .. "l")
        }
        );

The ordering of tests is still not consistent, but the spread of results seems more reasonable and repeatable. This is all running in the same Perl process. The results can be a bit wide since the module also reports uncertainties if it can, but the widget thing should give you the raw text:

freebsd> perl5.10.1 path-tiny.pl dp-dump.mysql
           Rate           k           d           g           e           f           c           l           h           i           j          b     a
k 1135.1+-1.5/s          --       -0.6%       -0.6%       -0.7%       -0.7%       -1.0%       -2.1%       -3.2%       -3.7%       -3.9%      -4.5% -4.7%
d 1141.5+-1.6/s  0.56+-0.2%          --        0.0%       -0.1%       -0.1%       -0.5%       -1.6%       -2.6%       -3.1%       -3.4%      -4.0% -4.1%
g 1141.9+-1.6/s   0.6+-0.2%  0.03+-0.2%          --       -0.1%       -0.1%       -0.5%       -1.5%       -2.6%       -3.1%       -3.4%      -4.0% -4.1%
e 1142.9+-1.5/s 0.68+-0.19% 0.12+-0.19% 0.09+-0.19%          --        0.0%       -0.4%       -1.4%       -2.5%       -3.0%       -3.3%      -3.9% -4.0%
f 1142.9+-1.5/s 0.69+-0.19%  0.12+-0.2% 0.09+-0.19%    0+-0.19%          --       -0.4%       -1.4%       -2.5%       -3.0%       -3.3%      -3.9% -4.0%
c 1147.1+-1.4/s 1.06+-0.19% 0.49+-0.19% 0.46+-0.19% 0.37+-0.18% 0.37+-0.18%          --       -1.1%       -2.2%       -2.7%       -2.9%      -3.5% -3.6%
l 1159.6+-1.5/s 2.16+-0.19% 1.59+-0.19% 1.55+-0.19% 1.46+-0.18% 1.46+-0.19% 1.09+-0.18%          --       -1.1%       -1.6%       -1.9%      -2.5% -2.6%
h 1172.4+-1.4/s 3.29+-0.19% 2.71+-0.19% 2.68+-0.19% 2.59+-0.18% 2.58+-0.19% 2.21+-0.18% 1.11+-0.18%          --       -0.5%       -0.8%      -1.4% -1.5%
i 1178.6+-1.2/s 3.83+-0.18% 3.25+-0.18% 3.22+-0.18% 3.13+-0.17% 3.12+-0.17% 2.75+-0.17% 1.64+-0.17% 0.53+-0.16%          --       -0.3%      -0.9% -1.0%
j 1181.6+-1.2/s  4.1+-0.18% 3.52+-0.18% 3.48+-0.18% 3.39+-0.17% 3.39+-0.17% 3.01+-0.17%  1.9+-0.17% 0.79+-0.16% 0.26+-0.15%          --      -0.6% -0.7%
b   1189+-1.7/s 4.75+-0.21% 4.16+-0.21% 4.13+-0.21%  4.04+-0.2%  4.03+-0.2%  3.65+-0.2%  2.54+-0.2% 1.41+-0.19% 0.88+-0.18% 0.62+-0.18%         -- -0.1%
a 1190.5+-1.7/s 4.88+-0.21%  4.3+-0.21% 4.26+-0.21%  4.17+-0.2%  4.17+-0.2%  3.79+-0.2%  2.67+-0.2% 1.54+-0.19% 1.01+-0.18% 0.75+-0.18% 0.13+-0.2%    --

freebsd> perl5.10.1 path-tiny.pl dp-dump.mysql
             Rate    g     l     k     j     i     h     f     a     b     c     d     e
g 1240.26+-0.72/s   -- -0.5% -0.9% -1.0% -1.0% -1.1% -1.4% -1.6% -1.7% -1.7% -1.7% -1.8%
l 1246.11+-0.44/s 0.5%    -- -0.4% -0.5% -0.5% -0.6% -0.9% -1.1% -1.2% -1.2% -1.3% -1.4%
k 1251.06+-0.33/s 0.9%  0.4%    -- -0.1% -0.1% -0.2% -0.5% -0.7% -0.8% -0.8% -0.9% -1.0%
j 1252.18+-0.31/s 1.0%  0.5%  0.1%    --  0.0% -0.1% -0.4% -0.6% -0.7% -0.8% -0.8% -0.9%
i 1252.33+-0.38/s 1.0%  0.5%  0.1%  0.0%    -- -0.1% -0.4% -0.6% -0.7% -0.7% -0.8% -0.9%
h 1253.57+-0.28/s 1.1%  0.6%  0.2%  0.1%  0.1%    -- -0.3% -0.5% -0.6% -0.6% -0.7% -0.8%
f 1257.46+-0.21/s 1.4%  0.9%  0.5%  0.4%  0.4%  0.3%    -- -0.2% -0.3% -0.3% -0.4% -0.5%
a 1260.16+-0.23/s 1.6%  1.1%  0.7%  0.6%  0.6%  0.5%  0.2%    -- -0.1% -0.1% -0.2% -0.3%
b 1261.46+-0.15/s 1.7%  1.2%  0.8%  0.7%  0.7%  0.6%  0.3%  0.1%    --  0.0% -0.1% -0.2%
c 1261.75+-0.15/s 1.7%  1.3%  0.9%  0.8%  0.8%  0.7%  0.3%  0.1%  0.0%    --  0.0% -0.1%
d 1262.23+-0.19/s 1.8%  1.3%  0.9%  0.8%  0.8%  0.7%  0.4%  0.2%  0.1%  0.0%    -- -0.1%
e 1263.52+-0.14/s 1.9%  1.4%  1.0%  0.9%  0.9%  0.8%  0.5%  0.3%  0.2%  0.1%  0.1%    --

freebsd> perl5.10.1 path-tiny.pl dp-dump.mysql
           Rate           f           i           e           h           g           l           k           j           d           c           b     a
f 1186.1+-1.8/s          --       -0.2%       -0.2%       -0.2%       -0.3%       -0.6%       -0.9%       -1.6%       -2.3%       -3.2%       -3.2% -3.4%
i 1188.1+-1.6/s 0.17+-0.21%          --        0.0%       -0.1%       -0.1%       -0.4%       -0.7%       -1.4%       -2.1%       -3.0%       -3.0% -3.3%
e 1188.2+-1.8/s 0.17+-0.21%     0+-0.2%          --       -0.1%       -0.1%       -0.4%       -0.7%       -1.4%       -2.1%       -3.0%       -3.0% -3.3%
h   1189+-1.6/s 0.24+-0.21%  0.07+-0.2%  0.07+-0.2%          --       -0.1%       -0.3%       -0.7%       -1.4%       -2.0%       -3.0%       -3.0% -3.2%
g 1189.8+-1.8/s 0.31+-0.22% 0.14+-0.21% 0.14+-0.22% 0.07+-0.21%          --       -0.3%       -0.6%       -1.3%       -2.0%       -2.9%       -2.9% -3.1%
l 1192.8+-1.8/s 0.57+-0.21%  0.4+-0.21% 0.39+-0.21%  0.32+-0.2% 0.26+-0.22%          --       -0.3%       -1.1%       -1.7%       -2.6%       -2.7% -2.9%
k 1196.8+-1.7/s  0.9+-0.21%  0.73+-0.2% 0.73+-0.21%  0.66+-0.2% 0.59+-0.21% 0.33+-0.21%          --       -0.7%       -1.4%       -2.3%       -2.3% -2.6%
j 1205.5+-1.6/s  1.63+-0.2% 1.46+-0.19%  1.46+-0.2% 1.39+-0.19% 1.32+-0.21%  1.06+-0.2% 0.72+-0.19%          --       -0.7%       -1.6%       -1.6% -1.9%
d 1213.8+-1.4/s 2.34+-0.19% 2.16+-0.18% 2.16+-0.19% 2.09+-0.18%  2.02+-0.2% 1.76+-0.19% 1.42+-0.19% 0.69+-0.18%          --       -0.9%       -0.9% -1.2%
c 1225.3+-1.3/s  3.3+-0.19% 3.13+-0.18% 3.12+-0.19% 3.05+-0.18% 2.98+-0.19% 2.72+-0.19% 2.38+-0.18% 1.64+-0.17% 0.94+-0.16%          --        0.0% -0.2%
b 1225.4+-1.1/s 3.31+-0.18% 3.14+-0.17% 3.13+-0.18% 3.06+-0.17% 2.99+-0.19% 2.73+-0.18% 2.39+-0.17% 1.65+-0.16% 0.95+-0.15% 0.01+-0.14%          -- -0.2%
a 1228.3+-1.3/s 3.56+-0.19% 3.38+-0.18% 3.38+-0.19% 3.31+-0.18% 3.24+-0.19% 2.97+-0.19% 2.63+-0.18% 1.89+-0.17% 1.19+-0.16% 0.25+-0.15% 0.24+-0.14%    --

freebsd> perl5.10.1 path-tiny.pl dp-dump.mysql
             Rate           b           a     h     i     g     e     c     j     f     d     l     k
b   1177.9+-1.2/s          --       -1.1% -2.5% -2.8% -2.8% -2.8% -2.9% -2.9% -3.1% -3.1% -3.1% -3.2%
a   1191.1+-1.1/s 1.12+-0.14%          -- -1.5% -1.7% -1.7% -1.7% -1.8% -1.9% -2.0% -2.0% -2.0% -2.1%
h 1208.64+-0.64/s 2.61+-0.12% 1.48+-0.11%    -- -0.2% -0.2% -0.3% -0.4% -0.4% -0.5% -0.6% -0.6% -0.7%
i 1211.27+-0.69/s 2.83+-0.12%  1.7+-0.11%  0.2%    --  0.0%  0.0% -0.2% -0.2% -0.3% -0.4% -0.4% -0.5%
g  1211.54+-0.5/s 2.86+-0.12%  1.72+-0.1%  0.2%  0.0%    --  0.0% -0.2% -0.2% -0.3% -0.3% -0.4% -0.4%
e 1211.67+-0.55/s 2.87+-0.12% 1.73+-0.11%  0.3%  0.0%  0.0%    -- -0.1% -0.2% -0.3% -0.3% -0.4% -0.4%
c 1213.44+-0.42/s 3.02+-0.11%  1.88+-0.1%  0.4%  0.2%  0.2%  0.1%    --  0.0% -0.1% -0.2% -0.2% -0.3%
j   1213.6+-0.5/s 3.03+-0.12%  1.89+-0.1%  0.4%  0.2%  0.2%  0.2%  0.0%    -- -0.1% -0.2% -0.2% -0.3%
f  1215.2+-0.38/s 3.17+-0.11%  2.03+-0.1%  0.5%  0.3%  0.3%  0.3%  0.1%  0.1%    --  0.0% -0.1% -0.1%
d 1215.57+-0.36/s  3.2+-0.11%        2.1%  0.6%  0.4%  0.3%  0.3%  0.2%  0.2%  0.0%    --  0.0% -0.1%
l 1215.96+-0.36/s 3.23+-0.11%  2.09+-0.1%  0.6%  0.4%  0.4%  0.4%  0.2%  0.2%  0.1%  0.0%    -- -0.1%
k 1216.84+-0.31/s 3.31+-0.11%        2.2%  0.7%  0.5%  0.4%  0.4%  0.3%  0.3%  0.1%  0.1%  0.1%    --

It’s more interesting to use the dumbbench program because I can get the data as a table instead of as a summary. I create a package that I could pass to dumbbench:

package PathTinyTest;

use v5.10;
use strict;
use warnings;
use Benchmark qw( cmpthese );
use Path::Tiny;

my $file = '/Volumes/Perl/BackPAN/modules/06perms.txt.gz';

# special subroutine for dumbbench --package
sub get_subs_to_benchmark { 'a' .. 'l' }

foreach ( get_subs_to_benchmark() ) {
	no strict 'refs';
	*{"$_"} = sub { path($file)->slurp };
	}

1;

I give that package to dumbbench:

% dumbbench --package PathTinyTest --t pathtiny.dat

Once I the table data, I can pass that to R to plot. It’s much easier to use a proper statistical package than fool with Perl modules. This boxplot.r script comes in the Dumbbench distribution:

file <- commandArgs(trailingOnly=T)[1]
print( file )
t <- read.table(
        file, 
        sep="\t",
        header=T,
        fill=T
        )

base <- sub( "(^[^.]+).*", "\\1", file )
image <- paste( base, "png", sep="." )
png( image )

p <- list(
        boxwex = 0.1,
        ylab   = "Times, s"
        )
boxplot( t, pars=p )

I invoke it:

% Rscript --vanilla --slave boxplot.r pathtiny.dat

And I get a plot:

This box plot shows just what I suspected. Most of the interesting data are pretty much the same. Each circle is something far off the mean, and there's one of h that's really far off. The box for h is also very tall while the others are very short. There's a lot of variability in that particular set of runs.

As with all benchmarks, I try again (and again). The box itself represents the middle 50%, or 1 σ, and the whiskers represent 2 σ. Eventhing else is shown as a circle. The black bar is the mean. Steffen gives some gory details about the distribution in The physicist's way out. Imagine his plots as if you are looking down their Y axes and lining them up next to each other.

So, I think David gets it wrong in that particular benchmark. If there was something odd going on, I'd expect the means to be much different from each other. They aren't.

This is the danger I talk about in the "Benchmarking" chapter. The numbers are only good if they let you understand something. Once you think you understand it, you need to come up with a way to poke that particular thing in a way that demonstrates you know why it does what it does. Here we don't know why the numbers and spread come out as they do or how they relate to each other. Getting numbers that you like better doesn't make them more real.

But, as a true scientist, I also can't say that David is wrong. The most I can say is that he hasn't adequately supported his claim about forking. Or, I should say, that his results might only matter for him, which is another thing I stress in the "Benchmarking" chapter. That no one else can reproduce them on different setups might not matter. He isn't trying to prove a new law of the universe. He just needs to show that when he makes that one change, things work out better for him. Everyone else can run his benchmarks to see if it works out better for them.

This is unrelated to his conclusions about Path::Tiny, which probably is faster than the other modules that do similar things.

Benchmarking HTML entity encoding

I benchmark HTML entity encoding with Surveyor::Benchmark::HTMLEntities using the system I describe in Distribute benchmarks. Already Surveyor::App is making things easier for me.

Tokuhirom shipped HTML::Escape, which implements it encoder in XS, as he describes in his blog post about it. It can be a lot faster than the pure Perl HTML::Entities:

% env survey -p Surveyor::Benchmark::HTMLEntities http://www.perl.org/
Fetching http://www.perl.org/
HTML is 14983 bytes
> (418)
< (418)
& (7)
' (103)
Benchmark: timing 10000 iterations of html_entities, html_escape...
html_entities: 13 wallclock secs (13.75 usr +  0.01 sys = 13.76 CPU) @ 726.74/s (n=10000)
html_escape:  1 wallclock secs ( 0.64 usr +  0.00 sys =  0.64 CPU) @ 15625.00/s (n=10000)

The pure Perl fair fight is also much faster in HTML::Escape:

% env PERL_ONLY=1 survey -p Surveyor::Benchmark::HTMLEntities http://www.perl.org/
Fetching http://www.perl.org/
HTML is 14857 bytes
> (416)
< (416)
& (7)
' (103)
Benchmark: timing 10000 iterations of html_entities, html_escape...
html_entities: 14 wallclock secs (13.74 usr +  0.01 sys = 13.75 CPU) @ 727.27/s (n=10000)
html_escape:  7 wallclock secs ( 7.32 usr +  0.01 sys =  7.33 CPU) @ 1364.26/s (n=10000)

There’s a reason for though: HTML::Escape only handles the characters <, >, &, ‘, and “, while HTML::Entities lets me configure the characters to escape and by default also escapes wide characters.

My Surveyor::App made this simple for me. I created the benchmark, but also ran the target code tests to ensure that I’m returning the same thing. Through that I was able to adjust the target code of HTML::Entities to only escape the same things as HTML::Escape. I might have skipped that step otherwise.

And, now knowing this, I updated the Stackoverflow answer for How can I encode a string for HTML?.

Distribute benchmarks

I want to make it easier for people to share benchmarks. It’s not that hard now: you should be able to post the program you wrote, but not many people do that. That might be partly because those programs are ugly, or they are specific to a set-up, or that we don’t have a good way to distribute programs (although we do!).

Last night I created Surveyor::App. I give it a package name and it loads that module, finds all of the subroutines that start with bench_ then benchmarks them.

I started thinking about this after I added a similar feature to Dumbbench. As I messed around with that idea, I worked on a way to also test all of those subroutines at the same time to ensure that they all returned the same thing. I need to ensure that I’m comparing the same thing and the subroutines are doing the same thing.

I took all the boring bits out and reduced my benchmark code to something like this extract of Surveyor::Benchmark::GetDirectoryListing:

package Surveyor::Benchmark::GetDirectoryListing;

sub set_up {
	my( $class, $directory ) = @_;
	unless( defined $directory ) {
		require Cwd;
		$directory = Cwd::cwd();
		}
	die "Directory [$directory] does not exist!\n" unless -e $directory;
	die "[$directory] does not exist!\n" unless -e $directory;
	chdir( $directory ) or die "Could not change to $ARGV[0]: $!\n";
	my @files = glob( '.* *' );
	printf "$directory has %d files\n", scalar @files;
	}

sub tear_down { 1 }

sub bench_opendir {
	opendir my( $dh ), "."; 
	my @f = readdir( $dh );
	}

sub bench_glob {
	my @f = glob(".* *")
	}

__PACKAGE__;

Nothing in that code cares what’s handling the particular benchmark since I’ve moved all of that into controller module called by the survey program:

% survey -p Surveyor::Benchmark::GetDirectoryListing /etc

From there, the normal benchmarking happens for me. If I want to change the backend, the target code shouldn’t have to change.

My intent it that people will write their benchmarks as a module which they can upload to Github or CPAN or wherever, allowing other people to easily run and improve them.

The next step, which I’m not particularly interested in right now, if outputing the run data. I’ve already provided that feature in I added a similar feature to Dumbbench

Playing with Dumbbench

I’ve been playing with Steffen Müller’s Dumbbench module, which applies some statistical analysis to benchmarking. He explains it all in a couple of blog posts:

The benchmarking part is interesting, but the more interesting part is that Dumbbench can make pictures, unlike the boring, old, ASCII-reporting Benchmark.

Steffen used an interface to ROOT, a huge toolkit out of CERN. I couldn’t compile it on my Mac, so I started playing with R to make my plots. Instead of using ROOT, I added a feature to write the data to a table so I could feed that table to Rscript:

$ dumbbench --code='++$i' --code='$i++' --code='$i+=1' --table=code.dat --maxiter 10000
$ Rscript --vanilla --slave r/boxplot.r code.dat

From that I get an impressive picture that looks as good as the one from ROOT:

I don’t want to supply code on the command line, though. Dumbbench has three sources (or, instances). There’s that --code switch and there’s a final command line argument. The module can take subroutines too, so I added a --package switch. I can put my code to benchmark in a file that I can save and edit and reüse.

$ dumbbench --package=SomePackage --table=some_package.dat --maxiter 10000

There are still some things I want to do. I’d love to figure out how R’s read_table can take its data from standard input so I can get rid of the intermediate file and pipe directly to R.

More interesting than that, however, is fancy stuff I might be able to do in that package. Every subroutine should accomplish the same task, and perhaps return the same thing. The package would be able to automatically test each of the subroutines to verify that. I haven’t thought too much about that yet.