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Merge pull request #9 from robertbaldyga/better-hash-function

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Introduce more uniform hash function
This commit is contained in:
Michał Mielewczyk 2018-12-07 15:24:50 +01:00 committed by GitHub
commit 8be3b88360
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2 changed files with 14 additions and 3 deletions
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3
src/metadata/metadata_hash.c
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@ -81,7 +81,8 @@ static ocf_cache_line_t ocf_metadata_hash_get_entires(
return cache_lines;
case metadata_segment_hash:
return cache_lines / 4;
return DIV_ROUND_UP(cache_lines / 4, OCF_HASH_PRIME) *
OCF_HASH_PRIME - 1;
case metadata_segment_sb_config:
return DIV_ROUND_UP(sizeof(struct ocf_superblock_config),

14
src/metadata/metadata_misc.h
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@ -6,10 +6,20 @@
#ifndef __METADATA_MISC_H__
#define __METADATA_MISC_H__
/*
* Hash function needs number that has no common factors with both number
* of cores and number of entries in metadata hash container (hash lists).
* This can be easily achived by picking prime which is bigger than maximum
* number of cores and ensuring that count of hash table entries is not
* divisible by this number. Let's choose 4099, which is smallest prime
* greater than OCF_CORE_MAX (which is 4096).
*/
#define OCF_HASH_PRIME 4099
static inline ocf_cache_line_t ocf_metadata_hash_func(ocf_cache_t cache,
uint64_t cache_line_num, ocf_core_id_t core_id)
uint64_t core_line_num, ocf_core_id_t core_id)
{
return (ocf_cache_line_t) ((cache_line_num * (core_id + 1)) %
return (ocf_cache_line_t) ((core_line_num * OCF_HASH_PRIME + core_id) %
cache->device->hash_table_entries);
}