Perl/Profiling
From charlesreid1
TLDR: Use Devel::NYTProf
Contents
How to profile Perl
Before you begin
Installing cpanm
Start by installing cpanm to take care of all your Perl packages:
brew install cpanm
Installing Perl Profiling Tools
SizeMe
Install SizeMe: http://search.cpan.org/~timb/Devel-SizeMe-0.19/lib/Devel/SizeMe.pm
$ cpanm Devel::SizeMe
Hat tip: https://stackoverflow.com/questions/6645073/profiling-heap-memory-usage-on-perl-programs#6645561
NYTProf
Install the best Perl profiling tool out there, the NYTProf, originally written by Adam Kaplan at the New York Times: https://www.perl.org/about/whitepapers/perl-profiling.html
$ cpanm Devel::NYTProf
This also installs the dependencies, of which there are multiple: https://metacpan.org/pod/Devel::NYTProf
Profiling Code using SizeMe
Official page: http://search.cpan.org/~timb/Devel-SizeMe-0.19/lib/Devel/SizeMe.pm
Hat tip to SO user @TimBunce (author of SizeMe) for pointing out the SizeMe module for profiling Perl heap memory usage: http://stackoverflow.com/a/12821590/463213
Profiling Code using NYTProf
Normally, we can time code using the time function, which gives a really high-level description of how long the code took to do stuff. Like, "this much user time, this much real wall time." Here's an example of output from the time command:
************************************** Running 8 queens problem with Perl... total 92 solutions real 0m0.112s user 0m0.025s sys 0m0.008s ************************************** Running 12 queens problem with Perl... total 14200 solutions real 0m11.726s user 0m11.519s sys 0m0.032s
We want to get a more detailed description of what's going on with the code to find bottlenecks.
Running with NYTProf
After installing it, run a Perl script with the NYTProf module turned on:
perl -d:NYTProf myscript.pl
This results in an incomprehensible nytprof.out file.
Some tools:
- nytprofcsv - export as csv file
- nytprofcfg - generates nytprof.callgraph
- nytprofhtml - generate html version
NYTProf csv format
Now you can run nytprofcsv to turn that output into a CSV file, one line per line of code, with a summary of where all the time was spent:
/usr/local/Cellar/perl/5.24.0_1/bin/nytprofcsv nytprof.out
This puts the CSV file into a nytprof directory. Here's an example output for the N queens problem, N = 11:
# Profile data generated by Devel::NYTProf::Reader
# Version: v6.04
# More information at http://metacpan.org/release/Devel-NYTProf/
# Format: time,calls,time/call,code
0.086191,166926,0.000001,my ($depth, @attacked) = shift;
0.010183,2680,0.000004,push @solutions, "@queens\n";
0.010521,2680,0.000004,return;
0.196345,164246,0.000001,$#attacked = 2 * $board_size;
0.152597,164246,0.000001,for( 0 .. $#queens) {
0.683294,1.26035e+06,0.000001,$attacked[ $ix2 ] = 1;
1.189223,164246,0.000007,for my $row (0 .. $board_size-1) {
0.272883,166925,0.000002,explore($depth+1);
0.116465,166925,0.000001,$occupied[$row] = 0;
0.000001,1,0.000001,$board_size = 11;
0.000019,1,0.000019,explore(0);
0.000080,1,0.000080,print "Found ", scalar(@solutions), " solutions\n";
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From this we can see the bottlenecks are the for loop over each column, and populating the attacked array.
NYTProf html format
/usr/local/Cellar/perl/5.24.0_1/bin/nytprofhtml
Example:
For a recursive backtracking function, you don't get a whole lot of information, but it does tell you the maximum depth of the recursive function and the total call time. It also shows very clearly that the biggest bottlenecks in the code are the population of the array of legal locations to place queens, which makes sense, given that it's a lot of index math and stuffing numbers into arrays.
Here's the relevant portion of the profiler output, which shows that the loop to mark invalid locations on the diagonals of the other queens involves a huge number of calculations - those lines are called 7 million times! Likewise the check of whether the particular square we're considering is a valid square is called 10 million times!
The total number of solutions for the N queens problem, when N is 11, is 2680.
Timing Code
See Perl/Timing
Resources
NYTProf
Official package info (some documentation, but nothing high-level at all): https://metacpan.org/pod/Devel::NYTProf
Slide deck explaining a bit more about how to use NYTProf: http://www.slideshare.net/Tim.Bunce/develnytprof-200907