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Avoid 64bit division in multilist index functions

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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 <mahrens@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> 
Reviewed-by: Mark Maybee <mark.maybee@delphix.com>
Signed-off-by: Alexander Motin <mav@FreeBSD.org>
Sponsored-By: iXsystems, Inc.
Closes #12288
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Alexander Motin 2021-06-29 08:59:14 -04:00 committed by GitHub
parent f20fb199e6
commit 5b7053a9a5
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4 changed files with 21 additions and 6 deletions
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5
module/zfs/arc.c
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@ -7454,9 +7454,10 @@ arc_state_multilist_index_func(multilist_t *ml, void *obj)
* Also, the low order bits of the hash value are thought to be * Also, the low order bits of the hash value are thought to be
* distributed evenly. Otherwise, in the case that the multilist * distributed evenly. Otherwise, in the case that the multilist
* has a power of two number of sublists, each sublists' usage * 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)); multilist_get_num_sublists(ml));
} }

5
module/zfs/dbuf.c
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@ -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 * Also, the low order bits of the hash value are thought to be
* distributed evenly. Otherwise, in the case that the multilist * distributed evenly. Otherwise, in the case that the multilist
* has a power of two number of sublists, each sublists' usage * 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) % db->db_level, db->db_blkid) %
multilist_get_num_sublists(ml)); multilist_get_num_sublists(ml));
} }

10
module/zfs/dmu_objset.c
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@ -399,7 +399,15 @@ static unsigned int
dnode_multilist_index_func(multilist_t *ml, void *obj) dnode_multilist_index_func(multilist_t *ml, void *obj)
{ {
dnode_t *dn = 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)); multilist_get_num_sublists(ml));
} }

7
module/zfs/metaslab.c
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@ -1874,7 +1874,12 @@ static unsigned int
metaslab_idx_func(multilist_t *ml, void *arg) metaslab_idx_func(multilist_t *ml, void *arg)
{ {
metaslab_t *msp = 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 uint64_t