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

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