EVOLUTION-MANAGER

Edit File: speed_matters.pod

=head1 NAME

Which Coding Technique is Faster

=head1 Description

This document tries to show more efficient coding styles by
benchmarking various styles.

WARNING: This doc is under construction

META: for now these are just unprocessed snippets from the mailing
list. Please help me to make these into useful essays.

=head1 backticks vs XS

META: unprocessed yet.

compare the difference of calling an
xsub that does _nothing_ vs. a backticked program that does _nothing_.

/* file:test.c */
  int main(int argc, char **argv, char **env)
  {
      return 1;
  }

/* file:TickTest.xs */
  #include "EXTERN.h"
  #include "perl.h"
  #include "XSUB.h"
  
  MODULE = TickTest		PACKAGE = TickTest		
  
  void
  foo()
  
  CODE:

# file:test.pl
  use blib;
  use TickTest ();
  
  use Benchmark;
  
  timethese(100_000, {
      backtick => sub { `./test` },
      xs => sub { TickTest::foo() },
  });

Results:

Benchmark: timing 100000 iterations of backtick, xs...
    backtick: 292 wallclock secs (18.68 usr 43.93 sys + 142.43 cusr 84.00 csys = 289.04 CPU) @ 1597.19/s (n=100000)
          xs: -1 wallclock secs ( 0.25 usr +  0.00 sys =  0.25 CPU) @ 400000.00/s (n=100000)
              (warning: too few iterations for a reliable count)

=head1 sv_catpvn vs. fprintf

META: unprocessed yet.

and what i'm trying to say is that if both the xs code and external
program are doing the same thing, xs will be heaps faster than backticking
a program.  your xsub and external program are not doing the same thing.

i'm guessing part of the difference in your code is due to fprintf having
a pre-allocated buffer, whereas the SV's SvPVX has not been pre-allocated
and gets realloc-ed each time you call sv_catpv.  have a look at the code
below, fprintf is faster than sv_catpvn, but if the SvPVX is preallocated,
sv_catpvn becomes faster than fprintf:

timethese(1_000, {
      fprintf   => sub { TickTest::fprintf() },
      svcat     => sub { TickTest::svcat() },
      svcat_pre => sub { TickTest::svcat_pre() },
  });
  
  Benchmark: timing 1000 iterations of fprintf, svcat, svcat_pre...
     fprintf:  9 wallclock secs ( 8.72 usr +  0.00 sys =  8.72 CPU) @ 114.68/s (n=1000)
       svcat: 13 wallclock secs (12.82 usr +  0.00 sys = 12.82 CPU) @ 78.00/s (n=1000)
   svcat_pre:  2 wallclock secs ( 2.75 usr +  0.00 sys =  2.75 CPU) @ 363.64/s (n=1000)
  
  #include "EXTERN.h"
  #include "perl.h"
  #include "XSUB.h"
  
  static FILE *devnull;
  
  MODULE = TickTest		PACKAGE = TickTest		
  
  BOOT:
  devnull = fopen("/dev/null", "w");
  
  void
  fprintf()
  
      CODE:
      {
          int i;
          char buffer[8292];
  
          for (i=0; i<sizeof(buffer); i++) {
              fprintf(devnull, "a");
          }
      }
  
  void
  svcat()
  
      CODE:
      {
          int i;
          char buffer[8292];
          SV *sv = newSV(0);
  
          for (i=0; i<sizeof(buffer); i++) {
              sv_catpvn(sv, "a", 1);
          }
  
          SvREFCNT_dec(sv);
      }
  
  void
  svcat_pre()
  
      CODE:
      {
          int i;
          char buffer[8292];
          SV *sv = newSV(sizeof(buffer)+1);
  
          for (i=0; i<sizeof(buffer); i++) {
              sv_catpvn(sv, "a", 1);
          }
  
          SvREFCNT_dec(sv);
      }

=head1 Maintainers

Maintainer is the person(s) you should contact with updates,
corrections and patches.

Stas Bekman [http://stason.org/]

=head1 Authors

=over

=item *

Stas Bekman [http://stason.org/]

=item *

Doug MacEachern E<lt>dougm (at) covalent.netE<gt>

=back

Only the major authors are listed above. For contributors see the
Changes file.

=cut