- NAME
- Description
- backticks vs XS
- sv_catpvn vs. fprintf
- Maintainers
- Authors

# NAME

Which Coding Technique is Faster

# 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.

# 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)

# 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);
         }

# Maintainers

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

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

# Authors

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

- Doug MacEachern <dougm (at) covalent.net>

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