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>
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)
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)
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