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XSConfig.pod

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NAME

XSConfig - Fast XS drop-in replacement for Config.pm with perfect hashing.

VERSION

Version 6.27

SYNOPSIS

The Config.pm included by default with Perl is pure Perl. Nearly all Perl apps will load Config.pm. For a number of reasons, of speed and memory space, reimplement the P5P shipped Config.pm as an XS library, shareable between processes as read-only memory, and with a hash that is better optimized than Perl hashes, courtesy of gperf tool which generates collision-free perfect hashes.

This module is a drop-in replacement for Config.pm. All code that does

use Config;

will use the XS implementation after installing this module. To revert to the original pure perl Config.pm, go and delete the following 3 files that will be next to each other in /site, Config.pm, Config_mini.pl, Config_xs_heavy.pl, and the Config shared library in /auto, after deleting the /site files, the original pure perl Config.pm in /lib will be loaded.

Since XS Config is a compiled C shared library, it can not be edited with a text editor after it is built. To change the values in the XS Config module, edit the pure perl Config_heavy.pl file with a text editor and rebuild XS Config.

IT IS HIGHLY RECOMMENDED THAT YOU HAVE GPERF TOOL INSTALLED AND RUNNABLE FROM YOUR PATH BEFORE INSTALLING XS CONFIG.

BENCHMARKS

perl -MXSLoader -MConfig -E"say $Config{ccflags}; sleep 1000"

Memory Usage KB Total   Image Committed Image Private   Heap Private
With PP Config  34,468  8,020           204             1120
With XS Config  33,564  8,120           212             652

Using XSConfig 6.13, with a VC 2013 32 bit threaded perl, you save 468 KB of per process memory, in exchange for 92 KB of shared between process, memory mapped (Config.dll) memory. Even if you have just a single perl process ever running on the machine at a time, you will still save 376 KB.

The total size of Config.dll in memory is 100 KB, with 8 KB of unshareable memory, the rest is shared. The smallest (no XSUBs except boot) Win32 XS DLL without taking special measures is 24 KB, with 8 KB of unshareable memory. So around ~24 KB is the overhead of a Visual C 2013 DLL with all the C compiler specific hidden static linked functions inside the DLL (these can be removed, but it is "special measures" that aren't typical on Win32 Perls).

Onto performance, to slurp the entire tied %Config hash into a non-tied hash, with XS Config is %36 faster than with PP Config. To read 1 key in the tied %Config hash is 15% faster than with PP Config.

Raw data with XS Config

C:\sources>timeit -f t.dat perl -MXSLoader -MConfig -e"print
$Config::VERSION.\"\n\";my %h; %h = %Config for 0..1000"
6.13

Version Number:   Windows NT 6.1 (Build 7601)
Exit Time:        2:32 pm, Tuesday, February 2 2016
Elapsed Time:     0:00:06.285
Process Time:     0:00:06.271
System Calls:     19974
Context Switches: 4317
Page Faults:      2334
Bytes Read:       73084
Bytes Written:    0
Bytes Other:      8528

C:\sources>timeit -f t.dat perl -MXSLoader -MConfig -e"print
$Config::VERSION.\"\n\";my $v; $v = $Config{'ccflags'} for 0..1000000;print
$v"
6.13
-nologo -GF -W3 -O1 -MD -Zi -DNDEBUG -GL -DWIN32 -D_CONSOLE -DNO_STRICT -D_CRT_S
ECURE_NO_DEPRECATE -D_CRT_NONSTDC_NO_DEPRECATE  -DPERL_TEXTMODE_SCRIPTS -DPERL_I
MPLICIT_CONTEXT -DPERL_IMPLICIT_SYS -DWIN32_NO_REGISTRY
Version Number:   Windows NT 6.1 (Build 7601)
Exit Time:        2:33 pm, Tuesday, February 2 2016
Elapsed Time:     0:00:03.168
Process Time:     0:00:03.151
System Calls:     11223
Context Switches: 2482
Page Faults:      2070
Bytes Read:       77180
Bytes Written:    0
Bytes Other:      7318

With PP Config

C:\sources>timeit -f t.dat perl -MXSLoader -MConfig -e"print
$Config::VERSION.\"\n\";my %h; %h = %Config for 0..1000"
5.023008

Version Number:   Windows NT 6.1 (Build 7601)
Exit Time:        2:34 pm, Tuesday, February 2 2016
Elapsed Time:     0:00:09.907
Process Time:     0:00:09.843
System Calls:     39114
Context Switches: 7145
Page Faults:      3426
Bytes Read:       118536
Bytes Written:    0
Bytes Other:      13446

C:\sources>timeit -f t.dat perl -MXSLoader -MConfig -e"print
$Config::VERSION.\"\n\";my $v; $v = $Config{'ccflags'} for 0..1000000;print
$v"
5.023008
-nologo -GF -W3 -O1 -MD -Zi -DNDEBUG -GL -DWIN32 -D_CONSOLE -DNO_STRICT -D_CRT_S
ECURE_NO_DEPRECATE -D_CRT_NONSTDC_NO_DEPRECATE  -DPERL_TEXTMODE_SCRIPTS -DPERL_I
MPLICIT_CONTEXT -DPERL_IMPLICIT_SYS -DWIN32_NO_REGISTRY
Version Number:   Windows NT 6.1 (Build 7601)
Exit Time:        2:35 pm, Tuesday, February 2 2016
Elapsed Time:     0:00:03.755
Process Time:     0:00:03.744
System Calls:     12721
Context Switches: 3152
Page Faults:      1392
Bytes Read:       113612
Bytes Written:    0
Bytes Other:      6674

AUTHOR

Daniel Dragan <BULKDD at cpan.org> Reini Urban <rurban at cpanel.net>

LICENSE AND COPYRIGHT

Copyright (C) 2015, Daniel Dragan Copyright (C) 2015, cPanel Inc

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.