kern_mtxpool.c revision 116305 
1/*-
2 * Copyright (c) 2001 Matthew Dillon.  All Rights Reserved.  Copyright
3 * terms are as specified in the COPYRIGHT file at the base of the source
4 * tree.
5 *
6 * Mutex pool routines.  These routines are designed to be used as short
7 * term leaf mutexes (e.g. the last mutex you might aquire other then
8 * calling msleep()).  They operate using a shared pool.  A mutex is chosen
9 * from the pool based on the supplied pointer (which may or may not be
10 * valid).
11 *
12 * Advantages:
13 *	- no structural overhead.  Mutexes can be associated with structures
14 *	  without adding bloat to the structures.
15 *	- mutexes can be obtained for invalid pointers, useful when uses
16 *	  mutexes to interlock destructor ops.
17 *	- no initialization/destructor overhead.
18 *	- can be used with msleep.
19 *
20 * Disadvantages:
21 *	- should generally only be used as leaf mutexes.
22 *	- pool/pool dependancy ordering cannot be depended on.
23 *	- possible L1 cache mastersip contention between cpus.
24 */
25
26#include <sys/cdefs.h>
27__FBSDID("$FreeBSD: head/sys/kern/kern_mtxpool.c 116305 2003-06-13 19:39:21Z mux $");
28
29#include <sys/param.h>
30#include <sys/proc.h>
31#include <sys/kernel.h>
32#include <sys/ktr.h>
33#include <sys/lock.h>
34#include <sys/malloc.h>
35#include <sys/mutex.h>
36#include <sys/systm.h>
37
38#ifndef MTX_POOL_SIZE
39#define MTX_POOL_SIZE	128
40#endif
41#define MTX_POOL_MASK	(MTX_POOL_SIZE - 1)
42
43static struct mtx mtx_pool_ary[MTX_POOL_SIZE];
44
45int mtx_pool_valid = 0;
46
47/*
48 * Inline version of mtx_pool_find(), used to streamline our main API
49 * function calls.
50 */
51static __inline struct mtx *
52_mtx_pool_find(void *ptr)
53{
54    int p;
55
56    p = (int)(uintptr_t)ptr;
57    return (&mtx_pool_ary[(p ^ (p >> 6)) & MTX_POOL_MASK]);
58}
59
60static void
61mtx_pool_setup(void *dummy __unused)
62{
63    int i;
64
65    for (i = 0; i < MTX_POOL_SIZE; ++i)
66	mtx_init(&mtx_pool_ary[i], "pool mutex", NULL,
67	    MTX_DEF | MTX_NOWITNESS | MTX_QUIET);
68    mtx_pool_valid = 1;
69}
70
71/*
72 * Obtain a (shared) mutex from the pool.  The returned mutex is a leaf
73 * level mutex, meaning that if you obtain it you cannot obtain any other
74 * mutexes until you release it.  You can legally msleep() on the mutex.
75 */
76struct mtx *
77mtx_pool_alloc(void)
78{
79    static int si;
80
81    return (&mtx_pool_ary[si++ & MTX_POOL_MASK]);
82}
83
84/*
85 * Return the (shared) pool mutex associated with the specified address.
86 * The returned mutex is a leaf level mutex, meaning that if you obtain it
87 * you cannot obtain any other mutexes until you release it.  You can
88 * legally msleep() on the mutex.
89 */
90struct mtx *
91mtx_pool_find(void *ptr)
92{
93
94    return (_mtx_pool_find(ptr));
95}
96
97/*
98 * Combined find/lock operation.  Lock the pool mutex associated with
99 * the specified address.
100 */
101void
102mtx_pool_lock(void *ptr)
103{
104
105    mtx_lock(_mtx_pool_find(ptr));
106}
107
108/*
109 * Combined find/unlock operation.  Unlock the pool mutex associated with
110 * the specified address.
111 */
112void
113mtx_pool_unlock(void *ptr)
114{
115
116    mtx_unlock(_mtx_pool_find(ptr));
117}
118
119SYSINIT(mtxpooli, SI_SUB_MTX_POOL, SI_ORDER_FIRST, mtx_pool_setup, NULL);
120