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dmu_objset: replace dnode_hash impl with cityhash4

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As mentioned in PR #16131, replacing CRC-based hash with cityhash4
could slightly improve the performance by eliminating memory access.
Replacing algorightm is safe since the hash result is not persisted.

Reviewed by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Tino Reichardt <milky-zfs@mcmilk.de>
Signed-off-by: Shengqi Chen <harry-chen@outlook.com>
Closes #16131
Closes #16483
This commit is contained in:
Shengqi Chen 2024-08-27 15:52:33 +08:00 committed by Brian Behlendorf
parent 4d469acd17
commit 1c35206124
1 changed files with 3 additions and 16 deletions
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19
module/zfs/dmu_objset.c
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@ -66,6 +66,7 @@
#include "zfs_namecheck.h" #include "zfs_namecheck.h"
#include <sys/vdev_impl.h> #include <sys/vdev_impl.h>
#include <sys/arc.h> #include <sys/arc.h>
#include <cityhash.h>
/* /*
* Needed to close a window in dnode_move() that allows the objset to be freed * Needed to close a window in dnode_move() that allows the objset to be freed
@ -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 cityhash4 on the objset_t pointer and the object number.
*/ */
static uint64_t static uint64_t
dnode_hash(const objset_t *os, uint64_t obj) dnode_hash(const objset_t *os, uint64_t obj)
{ {
uintptr_t osv = (uintptr_t)os; uintptr_t osv = (uintptr_t)os;
uint64_t crc = -1ULL; return (cityhash4((uint64_t)osv, obj, 0, 0));
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);
} }
static unsigned int static unsigned int