diff options
| author | Alexander Motin <[email protected]> | 2021-06-29 08:59:14 -0400 |
|---|---|---|
| committer | Brian Behlendorf <[email protected]> | 2021-06-29 13:15:04 -0700 |
| commit | ea478570908b57f9c141c0082cb6b6815938ea17 (patch) | |
| tree | b1cf0c6b90a5fe70432e1693be2faad4db6a4147 | |
| parent | 4ebda5d4d32dd641ded589f336de4ac4964b92fb (diff) | |
Avoid 64bit division in multilist index functions
The number of sublists in a multilist is relatively small. We dont need
64 bits to calculate an index. 32 bits is sufficient and makes the
code more efficient.
Reviewed-by: Matthew Ahrens <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Reviewed-by: Mark Maybee <[email protected]>
Signed-off-by: Alexander Motin <[email protected]>
Sponsored-By: iXsystems, Inc.
Closes #12288
| -rw-r--r-- | module/zfs/arc.c | 5 | ||||
| -rw-r--r-- | module/zfs/dbuf.c | 5 | ||||
| -rw-r--r-- | module/zfs/dmu_objset.c | 10 | ||||
| -rw-r--r-- | module/zfs/metaslab.c | 7 |
4 files changed, 21 insertions, 6 deletions
diff --git a/module/zfs/arc.c b/module/zfs/arc.c index 7d892f4c7..2226539a1 100644 --- a/module/zfs/arc.c +++ b/module/zfs/arc.c @@ -7459,9 +7459,10 @@ arc_state_multilist_index_func(multilist_t *ml, void *obj) * Also, the low order bits of the hash value are thought to be * distributed evenly. Otherwise, in the case that the multilist * has a power of two number of sublists, each sublists' usage - * would not be evenly distributed. + * would not be evenly distributed. In this context full 64bit + * division would be a waste of time, so limit it to 32 bits. */ - return (buf_hash(hdr->b_spa, &hdr->b_dva, hdr->b_birth) % + return ((unsigned int)buf_hash(hdr->b_spa, &hdr->b_dva, hdr->b_birth) % multilist_get_num_sublists(ml)); } diff --git a/module/zfs/dbuf.c b/module/zfs/dbuf.c index 8e55a613b..45886e573 100644 --- a/module/zfs/dbuf.c +++ b/module/zfs/dbuf.c @@ -622,9 +622,10 @@ dbuf_cache_multilist_index_func(multilist_t *ml, void *obj) * Also, the low order bits of the hash value are thought to be * distributed evenly. Otherwise, in the case that the multilist * has a power of two number of sublists, each sublists' usage - * would not be evenly distributed. + * would not be evenly distributed. In this context full 64bit + * division would be a waste of time, so limit it to 32 bits. */ - return (dbuf_hash(db->db_objset, db->db.db_object, + return ((unsigned int)dbuf_hash(db->db_objset, db->db.db_object, db->db_level, db->db_blkid) % multilist_get_num_sublists(ml)); } diff --git a/module/zfs/dmu_objset.c b/module/zfs/dmu_objset.c index 22deee7f3..af107fb8a 100644 --- a/module/zfs/dmu_objset.c +++ b/module/zfs/dmu_objset.c @@ -399,7 +399,15 @@ static unsigned int dnode_multilist_index_func(multilist_t *ml, void *obj) { dnode_t *dn = obj; - return (dnode_hash(dn->dn_objset, dn->dn_object) % + + /* + * The low order bits of the hash value are thought to be + * distributed evenly. Otherwise, in the case that the multilist + * has a power of two number of sublists, each sublists' usage + * would not be evenly distributed. In this context full 64bit + * division would be a waste of time, so limit it to 32 bits. + */ + return ((unsigned int)dnode_hash(dn->dn_objset, dn->dn_object) % multilist_get_num_sublists(ml)); } diff --git a/module/zfs/metaslab.c b/module/zfs/metaslab.c index 0ddad5b02..08d7a5635 100644 --- a/module/zfs/metaslab.c +++ b/module/zfs/metaslab.c @@ -1874,7 +1874,12 @@ static unsigned int metaslab_idx_func(multilist_t *ml, void *arg) { metaslab_t *msp = arg; - return (msp->ms_id % multilist_get_num_sublists(ml)); + + /* + * ms_id values are allocated sequentially, so full 64bit + * division would be a waste of time, so limit it to 32 bits. + */ + return ((unsigned int)msp->ms_id % multilist_get_num_sublists(ml)); } uint64_t |