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Used hashed package name in _alpm_pkg_find

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This results in huge gains to a lot of our codepaths since this is the most
frequent method of random access to packages in a list. The gains are seen
in both profiling and real life.

    $ pacman -Sii zvbi
    real: 0.41 sec -> 0.32 sec
    strcmp: 16,669,760 calls -> 473,942 calls
    _alpm_pkg_find: 52.73% -> 26.31% of time

    $ pacman -Su (no upgrades found)
    real: 0.40 sec -> 0.50 sec
    strcmp: 19,497,226 calls -> 524,097 calls
    _alpm_pkg_find: 52.36% -> 26.15% of time

There is some minor risk with this patch, but most of it should be avoided
by falling back to strcmp() if we encounter a package with a '0' hash value
(which we should not via any existing code path). We also do a strcmp once
hash values match to ensure against hash collisions. The risk left is that a
package name is modified once it was originally set, but the hash value is
left alone. That would probably result in a lot of other problems anyway.

Signed-off-by: Dan McGee <dan@archlinux.org>
This commit is contained in:
Dan McGee 2010-12-14 12:36:02 -06:00
parent c2a73ba989
commit 919bb6c9e0
1 changed files with 13 additions and 2 deletions
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15
lib/libalpm/package.c
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@ -552,6 +552,7 @@ int _alpm_pkg_cmp(const void *p1, const void *p2)
pmpkg_t *_alpm_pkg_find(alpm_list_t *haystack, const char *needle)
{
alpm_list_t *lp;
unsigned long needle_hash;
ALPM_LOG_FUNC;
@ -559,11 +560,21 @@ pmpkg_t *_alpm_pkg_find(alpm_list_t *haystack, const char *needle)
return(NULL);
}
needle_hash = _alpm_hash_sdbm(needle);
for(lp = haystack; lp; lp = lp->next) {
pmpkg_t *info = lp->data;
if(info && strcmp(info->name, needle) == 0) {
return(info);
if(info) {
/* a zero hash will cause a fall-through just in case */
if(info->name_hash && info->name_hash != needle_hash) {
continue;
}
/* finally: we had hash match, verify string match */
if(strcmp(info->name, needle) == 0) {
return(info);
}
}
}
return(NULL);