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dm: improve hash_locks sizing and hash function 

Both bufio and bio-prison-v1 use the identical model for splitting
their respective locks and rbtrees. Improve dm_num_hash_locks() to
distribute across more rbtrees to improve overall performance -- but
the maximum number of locks/rbtrees is still 64.

Also factor out a common hash function named dm_hash_locks_index(),
the magic numbers used were determined to be best using this program:
 https://gist.github.com/jthornber/e05c47daa7b500c56dc339269c5467fc

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
This commit is contained in:
Joe Thornber 2023-03-29 10:29:34 -04:00 committed by Mike Snitzer
parent b6279f82eb
commit 363b7fd76c
3 changed files with 17 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
drivers/md/dm-bio-prison-v1.c
View File

@ -117,9 +117,10 @@ static int cmp_keys(struct dm_cell_key *lhs,
return 0;
}
static unsigned lock_nr(struct dm_cell_key *key, unsigned int num_locks)
static inline unsigned int lock_nr(struct dm_cell_key *key, unsigned int num_locks)
{
return (key->block_begin >> BIO_PRISON_MAX_RANGE_SHIFT) & (num_locks - 1);
return dm_hash_locks_index((key->block_begin >> BIO_PRISON_MAX_RANGE_SHIFT),
num_locks);
}
bool dm_cell_key_has_valid_range(struct dm_cell_key *key)

2
drivers/md/dm-bufio.c
View File

@ -398,7 +398,7 @@ struct dm_buffer_cache {
static inline unsigned int cache_index(sector_t block, unsigned int num_locks)
{
return block & (num_locks - 1);
return dm_hash_locks_index(block, num_locks);
}
static inline void cache_read_lock(struct dm_buffer_cache *bc, sector_t block)

14
drivers/md/dm.h
View File

@ -233,9 +233,21 @@ unsigned int dm_get_reserved_bio_based_ios(void);
static inline unsigned int dm_num_hash_locks(void)
{
unsigned int num_locks = roundup_pow_of_two(num_online_cpus());
unsigned int num_locks = roundup_pow_of_two(num_online_cpus()) << 1;
return min_t(unsigned int, num_locks, DM_HASH_LOCKS_MAX);
}
#define DM_HASH_LOCKS_MULT 4294967291ULL
#define DM_HASH_LOCKS_SHIFT 6
static inline unsigned int dm_hash_locks_index(sector_t block,
unsigned int num_locks)
{
sector_t h1 = (block * DM_HASH_LOCKS_MULT) >> DM_HASH_LOCKS_SHIFT;
sector_t h2 = h1 >> DM_HASH_LOCKS_SHIFT;
return (h1 ^ h2) & (num_locks - 1);
}
#endif