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 <stas (at) stason.org>

Authors

• Stas Bekman <stas (at) stason.org>

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

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