precalculating hash keys in XS slower?

[patcat88]

I've been thinking of how to speed up XS code, and saw many hv functions take a "hash number". Its 99% of the time zero in every example I've seen. Your supposed to use the "PERL_HASH" macro to calculate the hash number. The only example I have found of PERL_HASH being used anywhere was here http://cpansearch.perl.org/src/DOY/Moose-1.9902-TRIAL/mop.c

I've been having problems figuring out if its faster or SLOWER to use precalculated hashes. I wrote a test library to time the difference. The Time::HiRes time() benchmarking says caching the key hashes is faster (get was 0.95s, getKC was 0.89s). My C profiler (DevPartner 8) says no key caching is faster (get=5.81us per run, getKC=5.89us per run). Nytprof says no key caching is faster (get is 516ms, getKC is 531ms).

I did my tests on Windows XP ActivePerl 5.10 build 1003 compiled with VS2003.

here is XHVKC.xs

#define PERL_NO_GET_CONTEXT
#include "EXTERN.h"
#include "perl.h"
#include "XSUB.h"

#include "ppport.h"

typedef struct {
    const char * key;
    unsigned long hash;
    const signed long klen;
} hvCacheKeyStruct;

typedef struct {
    hvCacheKeyStruct jiugsdh1;
    hvCacheKeyStruct iusidfsd2;
    hvCacheKeyStruct ihfsdgsfg3;
    hvCacheKeyStruct sudfyf4;
    hvCacheKeyStruct sfyuihldfss5;
    hvCacheKeyStruct iuodafohsd6;
    hvCacheKeyStruct kjsdjdfsj7;
    hvCacheKeyStruct layer1;
    hvCacheKeyStruct layer2;
    hvCacheKeyStruct layer3;
} hvCacheStruct;

#define HVCKSINIT(keyname) {#keyname, 0, sizeof(#keyname)-1 }
static hvCacheStruct hvCache = {
    HVCKSINIT(jiugsdh1),
    HVCKSINIT(iusidfsd2),
    HVCKSINIT(ihfsdgsfg3),
    HVCKSINIT(sudfyf4),
    HVCKSINIT(sfyuihldfss5),
    HVCKSINIT(iuodafohsd6),
    HVCKSINIT(kjsdjdfsj7),
    HVCKSINIT(layer1),
    HVCKSINIT(layer2),
    HVCKSINIT(layer3)
};
#undef HVCKSINIT
#define HVKC_KEY(x) (hvCache.x.key)
#define HVKC_KLEN(x) (hvCache.x.klen)
#define HVKC_HASH(x) (hvCache.x.hash)

#define HVKC_ARR_KEY(x)  ((((hvCacheKeyStruct*)&(hvCache))+(x))->key)
#define HVKC_ARR_KLEN(x) ((((hvCacheKeyStruct*)&(hvCache))+(x))->klen)
#define HVKC_ARR_HASH(x) ((((hvCacheKeyStruct*)&(hvCache))+(x))->hash)

#define hvkc_hv_fetch(hv, key, klen, lval, hash)                      
+             \
((SV**) hv_common_key_len((hv), (key), (klen), (lval)               \
? (HV_FETCH_JUST_SV | HV_FETCH_LVALUE)    \
: HV_FETCH_JUST_SV, NULL, (hash)))

#define hvkc_hv_fetch_kc(hv, key, lval)                               
+    \
((SV**) hv_common_key_len((hv), (HVKC_KEY(key)), (HVKC_KLEN(key)), (lv
+al)               \
? (HV_FETCH_JUST_SV | HV_FETCH_LVALUE)    \
: HV_FETCH_JUST_SV, NULL, (HVKC_HASH(key))))

void initializeHVCache(pTHX) {
    unsigned long i;
    const unsigned long arraylength = sizeof(hvCacheStruct)/sizeof(hvC
+acheKeyStruct);
    for(i=0; i<arraylength; i++){
        printf("initializeHVCache b4 %s hash=%u klen=%u\n",
               (((hvCacheKeyStruct*)&(hvCache))+i)->key,
               (((hvCacheKeyStruct*)&(hvCache))+i)->hash,
               (((hvCacheKeyStruct*)&(hvCache))+i)->klen
               );
        PERL_HASH(
                  ((((hvCacheKeyStruct*)&(hvCache))+i)->hash),
                  ((((hvCacheKeyStruct*)&(hvCache))+i)->key),
                  ((((hvCacheKeyStruct*)&(hvCache))+i)->klen)
                );
        printf("initializeHVCache after %s hash=%u klen=%u\n",
       (((hvCacheKeyStruct*)&(hvCache))+i)->key,
       (((hvCacheKeyStruct*)&(hvCache))+i)->hash,
       (((hvCacheKeyStruct*)&(hvCache))+i)->klen
       );
    }
}

MODULE = XHVKC        PACKAGE = XHVKC        

BOOT:
    initializeHVCache(aTHX);


void
get(self, num)
SV * self
unsigned long num
PREINIT:
    void * voidPtr = 0;
    char * finalKeyName;
    unsigned long finalKeyNameLen;
CODE:
    if (SvROK((HV*)self) && SvTYPE(SvRV((HV*)self))==SVt_PVHV)
        self = SvRV((HV*)self);
    else
        Perl_croak(aTHX_ "%s: %s is not a hash reference",
            "XHVKC::get",
            "self");
#define SWITCHMACRO(num,key) case (num): finalKeyName = #key; finalKey
+NameLen = sizeof(#key)-1; break;
    switch(num){
    SWITCHMACRO(1,jiugsdh1)
    SWITCHMACRO(2,iusidfsd2)
    SWITCHMACRO(3,ihfsdgsfg3)
    SWITCHMACRO(4,sudfyf4)
    SWITCHMACRO(5,sfyuihldfss5)
    SWITCHMACRO(6,iuodafohsd6)
    SWITCHMACRO(7,kjsdjdfsj7)
#undef SWITCHMACRO
    default:
        printf("huh?"); exit(1);
    }
    (SV **)voidPtr = hvkc_hv_fetch((HV *)self, "layer1", sizeof("layer
+1")-1, 0,0);
    if(voidPtr){
        (SV *)voidPtr = *(SV **)voidPtr;
        if (SvROK((SV *)voidPtr)){
            (SV *)voidPtr = SvRV((SV *)voidPtr);
            if (SvTYPE((SV *)voidPtr)==SVt_PVHV) {
                (SV **)voidPtr = hvkc_hv_fetch((HV *)voidPtr, "layer2"
+, sizeof("layer2")-1,0,0);
                if(voidPtr) {
                    (SV *)voidPtr = *(SV **)voidPtr;
                    if (SvROK((SV *)voidPtr)){
                        (SV *)voidPtr = SvRV((SV *)voidPtr);
                        if (SvTYPE((SV *)voidPtr)==SVt_PVHV) {
                            (SV **)voidPtr = hvkc_hv_fetch((HV *)voidP
+tr, "layer3", sizeof("layer3")-1,0,0);
                            if(voidPtr) {
                                (SV *)voidPtr = *(SV **)voidPtr;
                                if (SvROK((SV *)voidPtr)){
                                    (SV *)voidPtr = SvRV((SV *)voidPtr
+);
                                    if (SvTYPE((SV *)voidPtr)==SVt_PVH
+V) {
                                        (SV **)voidPtr = hvkc_hv_fetch
+((HV *)voidPtr, finalKeyName, finalKeyNameLen,0,0);
                                        if(voidPtr) {
                                            voidPtr = (void *)SvIV(*(S
+V **)voidPtr);
                                        }
                                        //else stays null
                                    }
                                    else {voidPtr = NULL;}
                                }
                                else {voidPtr = NULL;}
                            }
                            //else stays null
                        }
                        else {voidPtr = NULL;}
                    }
                    else {voidPtr = NULL;}
                }
                //else stays null
            }
            else {voidPtr = NULL;}
        }
        else {voidPtr = NULL;}
    }
    //else stays null
    if(voidPtr != (void *)999) {
        printf("wrong number at end of hash tree");
        exit(1);
    }

void
getKC(self, num)
SV * self
unsigned long num
PREINIT:
    void * voidPtr = 0;
CODE:
    if (SvROK((HV*)self) && SvTYPE(SvRV((HV*)self))==SVt_PVHV)
        self = SvRV((HV*)self);
    else
        Perl_croak(aTHX_ "%s: %s is not a hash reference",
            "XHVKC::get",
            "self");
    (SV **)voidPtr = hvkc_hv_fetch_kc((HV *)self, layer1,0);
    if(voidPtr){
        (SV *)voidPtr = *(SV **)voidPtr;
        if (SvROK((SV *)voidPtr)){
            (SV *)voidPtr = SvRV((SV *)voidPtr);
            if (SvTYPE((SV *)voidPtr)==SVt_PVHV) {
                (SV **)voidPtr = hvkc_hv_fetch_kc((HV *)voidPtr, layer
+2,0);
                if(voidPtr) {
                    (SV *)voidPtr = *(SV **)voidPtr;
                    if (SvROK((SV *)voidPtr)){
                        (SV *)voidPtr = SvRV((SV *)voidPtr);
                        if (SvTYPE((SV *)voidPtr)==SVt_PVHV) {
                            (SV **)voidPtr = hvkc_hv_fetch_kc((HV *)vo
+idPtr, layer3,0);
                            if(voidPtr) {
                                (SV *)voidPtr = *(SV **)voidPtr;
                                if (SvROK((SV *)voidPtr)){
                                    (SV *)voidPtr = SvRV((SV *)voidPtr
+);
                                    if (SvTYPE((SV *)voidPtr)==SVt_PVH
+V) {
                                        num -= 1;
                                        (SV **)voidPtr = hvkc_hv_fetch
+((HV *)voidPtr, HVKC_ARR_KEY(num), HVKC_ARR_KLEN(num), 0, HVKC_ARR_HA
+SH(num));
                                        if(voidPtr) {
                                            voidPtr = (void *)SvIV(*(S
+V **)voidPtr);
                                        }
                                        //else stays null
                                    }
                                    else {voidPtr = NULL;}
                                }
                                else {voidPtr = NULL;}
                            }
                            //else stays null
                        }
                        else {voidPtr = NULL;}
                    }
                    else {voidPtr = NULL;}
                }
                //else stays null
            }
            else {voidPtr = NULL;}
        }
        else {voidPtr = NULL;}
    }
    //else stays null
    if(voidPtr != (void *)999) {
        printf("wrong number at end of hash tree");
        exit(1);
    }

here is XHVKC.pm

package XHVKC;

use strict;
use warnings;

require Exporter;

our @ISA = qw(Exporter);

# Items to export into callers namespace by default. Note: do not expo
+rt
# names by default without a very good reason. Use EXPORT_OK instead.
# Do not simply export all your public functions/methods/constants.

# This allows declaration    use XHVKC ':all';
# If you do not need this, moving things directly into @EXPORT or @EXP
+ORT_OK
# will save memory.
our %EXPORT_TAGS = ( 'all' => [ qw(
    
) ] );

our @EXPORT_OK = ( @{ $EXPORT_TAGS{'all'} } );

our @EXPORT = qw(
    
);

our $VERSION = '0.01';

require XSLoader;
XSLoader::load('XHVKC', $VERSION);

sub new {
     my $href = {
          'layer1' => {
               'layer2' => {
                    'layer3' => {
                         'jiugsdh1' => 999,
                         'iusidfsd2' => 999,
                         'ihfsdgsfg3' => 999,
                         'sudfyf4' => 999,
                         'sfyuihldfss5' => 999,
                         'iuodafohsd6' => 999,
                         'kjsdjdfsj7' => 999
                    }
               }
          }
     };
     bless $href ;
     return $href ;
}
# Preloaded methods go here.

1;
__END__

here is the makefile.pl, it may or may not apply to you, I've disabled a few compiler optimizations to enable step through debugging in VS

use 5.010000;
use ExtUtils::MakeMaker;
# See lib/ExtUtils/MakeMaker.pm for details of how to influence
# the contents of the Makefile that is written.
use Config qw(%Config);

 my $ccflags = $Config{'ccflags'};
warn $ccflags."\n";
$ccflags =~ s/O1/Od/;
$ccflags =~ s/-DNDEBUG//;
warn $ccflags."\n";
WriteMakefile(
    NAME              => 'XHVKC',
    VERSION_FROM      => 'lib/XHVKC.pm', # finds $VERSION
    PREREQ_PM         => {}, # e.g., Module::Name => 1.1
    ($] >= 5.005 ?     ## Add these new keywords supported since 5.005
      (ABSTRACT_FROM  => 'lib/XHVKC.pm', # retrieve abstract from modu
+le
       AUTHOR         => 'A. U. Thor <[e-mail]>'
+) : ()),
    LIBS              => [''], # e.g., '-lm'
    DEFINE            => '', # e.g., '-DHAVE_SOMETHING'
    INC               => '-I.', # e.g., '-I. -I/usr/include/other'
    CCFLAGS           => $ccflags,
    OPTIMIZE          => ' ',
    XSOPT             => ' -nolinenumbers '
    # Un-comment this if you add C files to link with later:
    # OBJECT            => '$(O_FILES)', # link all the C files too
);

the test script

#!/usr/bin/perl -w
use XHVKC;
use Time::HiRes qw( time );
$o = new XHVKC;
$time = time;
for(0..300000){
     for (int(rand 6)+1) {$o->get($_);}
}
print "time was ".(time-$time)."\n";
$time = time;

for(0..300000){
     for (int(rand 6)+1) {$o->getKC($_);}
}
print "time was ".(time-$time)."\n";