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dmu_objset: replace dnode_hash impl with cityhash4 #16483

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dmu_objset: replace dnode_hash impl with cityhash4 #16483

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66a53bd
dmu_objset: replace dnode_hash impl with cityhash4
Harry-Chen Aug 27, 2024
f14d9d6
zcommon: add specialized versions of cityhash4
Harry-Chen Sep 7, 2024
e958069
cityhash: replace invocations with specialized versions when possible
Harry-Chen Sep 7, 2024
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4 changes: 2 additions & 2 deletions cmd/zstream/zstream_redup.c
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Original file line number Diff line number Diff line change
Expand Up @@ -132,7 +132,7 @@ static void
rdt_insert(redup_table_t *rdt,
uint64_t guid, uint64_t object, uint64_t offset, uint64_t stream_offset)
{
uint64_t ch = cityhash4(guid, object, offset, 0);
uint64_t ch = cityhash3(guid, object, offset);
uint64_t hashcode = BF64_GET(ch, 0, rdt->numhashbits);
redup_entry_t **rdepp;

Expand All @@ -152,7 +152,7 @@ rdt_lookup(redup_table_t *rdt,
uint64_t guid, uint64_t object, uint64_t offset,
uint64_t *stream_offsetp)
{
uint64_t ch = cityhash4(guid, object, offset, 0);
uint64_t ch = cityhash3(guid, object, offset);
uint64_t hashcode = BF64_GET(ch, 0, rdt->numhashbits);

for (redup_entry_t *rde = rdt->redup_hash_array[hashcode];
Expand Down
7 changes: 7 additions & 0 deletions include/cityhash.h
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Expand Up @@ -32,6 +32,13 @@
extern "C" {
#endif

/*
* Define 1/2/3-argument specialized versions of cityhash4, which can reduce
* instruction count (especially multiplication) on some 32-bit arches.
*/
_SYS_CITYHASH_H uint64_t cityhash1(uint64_t);
_SYS_CITYHASH_H uint64_t cityhash2(uint64_t, uint64_t);
_SYS_CITYHASH_H uint64_t cityhash3(uint64_t, uint64_t, uint64_t);
_SYS_CITYHASH_H uint64_t cityhash4(uint64_t, uint64_t, uint64_t, uint64_t);

#ifdef __cplusplus
Expand Down
18 changes: 18 additions & 0 deletions lib/libzfs/libzfs.abi
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Expand Up @@ -154,6 +154,9 @@
<elf-symbol name='avl_update_lt' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/>
<elf-symbol name='avl_walk' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/>
<elf-symbol name='bookmark_namecheck' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/>
<elf-symbol name='cityhash1' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/>
<elf-symbol name='cityhash2' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/>
<elf-symbol name='cityhash3' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/>
<elf-symbol name='cityhash4' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/>
<elf-symbol name='color_end' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/>
<elf-symbol name='color_start' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/>
Expand Down Expand Up @@ -9241,6 +9244,21 @@
</function-decl>
</abi-instr>
<abi-instr address-size='64' path='module/zcommon/cityhash.c' language='LANG_C99'>
<function-decl name='cityhash1' mangled-name='cityhash1' visibility='default' binding='global' size-in-bits='64' elf-symbol-id='cityhash1'>
<parameter type-id='9c313c2d' name='w'/>
<return type-id='9c313c2d'/>
</function-decl>
<function-decl name='cityhash2' mangled-name='cityhash2' visibility='default' binding='global' size-in-bits='64' elf-symbol-id='cityhash2'>
<parameter type-id='9c313c2d' name='w1'/>
<parameter type-id='9c313c2d' name='w2'/>
<return type-id='9c313c2d'/>
</function-decl>
<function-decl name='cityhash3' mangled-name='cityhash3' visibility='default' binding='global' size-in-bits='64' elf-symbol-id='cityhash3'>
<parameter type-id='9c313c2d' name='w1'/>
<parameter type-id='9c313c2d' name='w2'/>
<parameter type-id='9c313c2d' name='w3'/>
<return type-id='9c313c2d'/>
</function-decl>
<function-decl name='cityhash4' mangled-name='cityhash4' visibility='default' binding='global' size-in-bits='64' elf-symbol-id='cityhash4'>
<parameter type-id='9c313c2d' name='w1'/>
<parameter type-id='9c313c2d' name='w2'/>
Expand Down
4 changes: 2 additions & 2 deletions module/os/linux/zfs/zvol_os.c
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Expand Up @@ -551,8 +551,8 @@ zvol_request_impl(zvol_state_t *zv, struct bio *bio, struct request *rq,
blk_mq_hw_queue =
rq->q->queue_hw_ctx[rq->q->mq_map[rq->cpu]]->queue_num;
#endif
taskq_hash = cityhash4((uintptr_t)zv, offset >> ZVOL_TASKQ_OFFSET_SHIFT,
blk_mq_hw_queue, 0);
taskq_hash = cityhash3((uintptr_t)zv, offset >> ZVOL_TASKQ_OFFSET_SHIFT,
blk_mq_hw_queue);
tq_idx = taskq_hash % ztqs->tqs_cnt;

if (rw == WRITE) {
Expand Down
33 changes: 31 additions & 2 deletions module/zcommon/cityhash.c
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Expand Up @@ -49,8 +49,8 @@ cityhash_helper(uint64_t u, uint64_t v, uint64_t mul)
return (b);
}

uint64_t
cityhash4(uint64_t w1, uint64_t w2, uint64_t w3, uint64_t w4)
static inline uint64_t
cityhash_impl(uint64_t w1, uint64_t w2, uint64_t w3, uint64_t w4)
{
uint64_t mul = HASH_K2 + 64;
uint64_t a = w1 * HASH_K1;
Expand All @@ -59,9 +59,38 @@ cityhash4(uint64_t w1, uint64_t w2, uint64_t w3, uint64_t w4)
uint64_t d = w3 * HASH_K2;
return (cityhash_helper(rotate(a + b, 43) + rotate(c, 30) + d,
a + rotate(b + HASH_K2, 18) + c, mul));
}

/*
* Passing w as the 2nd argument could save one 64-bit multiplication.
*/
uint64_t
cityhash1(uint64_t w)
{
return (cityhash_impl(0, w, 0, 0));
}

uint64_t
cityhash2(uint64_t w1, uint64_t w2)
{
return (cityhash_impl(w1, w2, 0, 0));
}

uint64_t
cityhash3(uint64_t w1, uint64_t w2, uint64_t w3)
{
return (cityhash_impl(w1, w2, w3, 0));
}

uint64_t
cityhash4(uint64_t w1, uint64_t w2, uint64_t w3, uint64_t w4)
{
return (cityhash_impl(w1, w2, w3, w4));
}

#if defined(_KERNEL)
EXPORT_SYMBOL(cityhash1);
EXPORT_SYMBOL(cityhash2);
EXPORT_SYMBOL(cityhash3);
EXPORT_SYMBOL(cityhash4);
#endif
19 changes: 3 additions & 16 deletions module/zfs/dmu_objset.c
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Expand Up @@ -66,6 +66,7 @@
#include "zfs_namecheck.h"
#include <sys/vdev_impl.h>
#include <sys/arc.h>
#include <cityhash.h>

/*
* Needed to close a window in dnode_move() that allows the objset to be freed
Expand Down Expand Up @@ -404,27 +405,13 @@ dmu_objset_byteswap(void *buf, size_t size)
}

/*
* The hash is a CRC-based hash of the objset_t pointer and the object number.
* Runs cityhash on the objset_t pointer and the object number.
*/
static uint64_t
dnode_hash(const objset_t *os, uint64_t obj)
{
uintptr_t osv = (uintptr_t)os;
uint64_t crc = -1ULL;

ASSERT(zfs_crc64_table[128] == ZFS_CRC64_POLY);
/*
* The lower 11 bits of the pointer don't have much entropy, because
* the objset_t is more than 1KB long and so likely aligned to 2KB.
*/
crc = (crc >> 8) ^ zfs_crc64_table[(crc ^ (osv >> 11)) & 0xFF];
crc = (crc >> 8) ^ zfs_crc64_table[(crc ^ (obj >> 0)) & 0xFF];
crc = (crc >> 8) ^ zfs_crc64_table[(crc ^ (obj >> 8)) & 0xFF];
crc = (crc >> 8) ^ zfs_crc64_table[(crc ^ (obj >> 16)) & 0xFF];

crc ^= (osv>>14) ^ (obj>>24);

return (crc);
return (cityhash2((uint64_t)osv, obj));
}

static unsigned int
Expand Down
4 changes: 2 additions & 2 deletions module/zfs/zio.c
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Expand Up @@ -4182,8 +4182,8 @@ zio_alloc_zil(spa_t *spa, objset_t *os, uint64_t txg, blkptr_t *new_bp,
* some parallelism.
*/
int flags = METASLAB_ZIL;
int allocator = (uint_t)cityhash4(0, 0, 0,
os->os_dsl_dataset->ds_object) % spa->spa_alloc_count;
int allocator = (uint_t)cityhash1(os->os_dsl_dataset->ds_object)
% spa->spa_alloc_count;
error = metaslab_alloc(spa, spa_log_class(spa), size, new_bp, 1,
txg, NULL, flags, &io_alloc_list, NULL, allocator);
*slog = (error == 0);
Expand Down
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