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Merge pull request #220 from arutk/metadata_offset_hash

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New hash function formula
This commit is contained in:
Kamil Łepek
2019-07-29 13:03:04 +02:00
committed by GitHub
parent fa14d6a4b5 9b8815935a
commit 05be67a72b
6 changed files with 90 additions and 26 deletions
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3
src/metadata/metadata_hash.c
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@@ -83,8 +83,7 @@ static ocf_cache_line_t ocf_metadata_hash_get_entries(
return cache_lines;
case metadata_segment_hash:
return OCF_DIV_ROUND_UP(cache_lines / 4, OCF_HASH_PRIME) *
OCF_HASH_PRIME - 1;
return OCF_DIV_ROUND_UP(cache_lines, 4);
case metadata_segment_sb_config:
return OCF_DIV_ROUND_UP(sizeof(struct ocf_superblock_config),

20
src/metadata/metadata_misc.h
View File

@@ -6,21 +6,19 @@
#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).
/* Hash function intentionally returns consecutive (modulo @hash_table_entries)
* values for consecutive @core_line_num. This way it is trivial to sort all
* core lines within a single request in ascending hash value order. This kind
* of sorting is required to assure that (future) hash bucket metadata locks are
* always acquired in fixed order, eliminating the risk of dead locks.
*/
#define OCF_HASH_PRIME 4099
static inline ocf_cache_line_t ocf_metadata_hash_func(ocf_cache_t cache,
uint64_t core_line_num, ocf_core_id_t core_id)
{
return (ocf_cache_line_t) ((core_line_num * OCF_HASH_PRIME + core_id) %
cache->device->hash_table_entries);
const unsigned int entries = cache->device->hash_table_entries;
return (ocf_cache_line_t) ((core_line_num + (core_id * (entries / 32)))
% entries);
}
void ocf_metadata_sparse_cache_line(struct ocf_cache *cache,