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radix_trie: eliminate iteration in keydiff

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Use flsll(), instead of a loop, to find where two keys differ, and
then arithmetic to transform that to a trie level.
Approved by:	alc, markj
Differential Revision:	https://reviews.freebsd.org/D40585
This commit is contained in:
Doug Moore 2023-06-20 11:30:29 -05:00
parent afb001df81
commit 05963ea4d1
2 changed files with 16 additions and 12 deletions
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14
sys/kern/subr_pctrie.c
View file

@ -54,6 +54,7 @@ __FBSDID("$FreeBSD$");
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/libkern.h>
#include <sys/pctrie.h>
#include <sys/proc.h> /* smr.h depends on struct thread. */
#include <sys/smr.h>
@ -259,21 +260,22 @@ pctrie_addval(struct pctrie_node *node, uint64_t index, uint16_t clev,
}
/*
* Returns the slot where two keys differ.
* Returns the level where two keys differ.
* It cannot accept 2 equal keys.
*/
static __inline uint16_t
pctrie_keydiff(uint64_t index1, uint64_t index2)
{
uint16_t clev;
KASSERT(index1 != index2, ("%s: passing the same key value %jx",
__func__, (uintmax_t)index1));
CTASSERT(sizeof(long long) >= sizeof(uint64_t));
index1 ^= index2;
for (clev = PCTRIE_LIMIT;; clev--)
if (pctrie_slot(index1, clev) != 0)
return (clev);
/*
* From the highest-order bit where the indexes differ,
* compute the highest level in the trie where they differ.
*/
return ((flsll(index1 ^ index2) - 1) / PCTRIE_WIDTH);
}
/*

14
sys/vm/vm_radix.c
View file

@ -58,6 +58,7 @@ __FBSDID("$FreeBSD$");
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/libkern.h>
#include <sys/proc.h>
#include <sys/vmmeter.h>
#include <sys/smr.h>
@ -285,21 +286,22 @@ vm_radix_addpage(struct vm_radix_node *rnode, vm_pindex_t index, uint16_t clev,
}
/*
* Returns the slot where two keys differ.
* Returns the level where two keys differ.
* It cannot accept 2 equal keys.
*/
static __inline uint16_t
vm_radix_keydiff(vm_pindex_t index1, vm_pindex_t index2)
{
uint16_t clev;
KASSERT(index1 != index2, ("%s: passing the same key value %jx",
__func__, (uintmax_t)index1));
CTASSERT(sizeof(long long) >= sizeof(vm_pindex_t));
index1 ^= index2;
for (clev = VM_RADIX_LIMIT;; clev--)
if (vm_radix_slot(index1, clev) != 0)
return (clev);
/*
* From the highest-order bit where the indexes differ,
* compute the highest level in the trie where they differ.
*/
return ((flsll(index1 ^ index2) - 1) / VM_RADIX_WIDTH);
}
/*