1 /*-
2 * Copyright (c) 2001 Matthew Dillon. All Rights Reserved.
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
6 * are met:
7 * 1. Redistributions of source code must retain the above copyright
8 * notice, this list of conditions and the following disclaimer.
9 * 2. Redistributions in binary form must reproduce the above copyright
10 * notice, this list of conditions and the following disclaimer in the
11 * documentation and/or other materials provided with the distribution.
12 *
13 * THIS SOFTWARE IS PROVIDED BY AUTHOR AND CONTRIBUTORS ``AS IS'' AND
14 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
15 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
16 * ARE DISCLAIMED. IN NO EVENT SHALL AUTHOR OR CONTRIBUTORS BE LIABLE
17 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
18 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
19 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
20 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
21 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
22 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
23 * SUCH DAMAGE.
24 */
25
26 /* Mutex pool routines. These routines are designed to be used as short
27 * term leaf mutexes (e.g. the last mutex you might acquire other then
28 * calling msleep()). They operate using a shared pool. A mutex is chosen
29 * from the pool based on the supplied pointer (which may or may not be
30 * valid).
31 *
32 * Advantages:
33 * - no structural overhead. Mutexes can be associated with structures
34 * without adding bloat to the structures.
35 * - mutexes can be obtained for invalid pointers, useful when uses
36 * mutexes to interlock destructor ops.
37 * - no initialization/destructor overhead.
38 * - can be used with msleep.
39 *
40 * Disadvantages:
41 * - should generally only be used as leaf mutexes.
42 * - pool/pool dependancy ordering cannot be depended on.
43 * - possible L1 cache mastersip contention between cpus.
44 */
45
46 #include <sys/cdefs.h>
47 __FBSDID("$FreeBSD: src/sys/kern/kern_mtxpool.c,v 1.12 2007/05/27 20:50:23 rwatson Exp $");
48
49 #include <sys/param.h>
50 #include <sys/proc.h>
51 #include <sys/kernel.h>
52 #include <sys/ktr.h>
53 #include <sys/lock.h>
54 #include <sys/malloc.h>
55 #include <sys/mutex.h>
56 #include <sys/systm.h>
57
58
59 static MALLOC_DEFINE(M_MTXPOOL, "mtx_pool", "mutex pool");
60
61 /* Pool sizes must be a power of two */
62 #ifndef MTX_POOL_LOCKBUILDER_SIZE
63 #define MTX_POOL_LOCKBUILDER_SIZE 128
64 #endif
65 #ifndef MTX_POOL_SLEEP_SIZE
66 #define MTX_POOL_SLEEP_SIZE 128
67 #endif
68
69 struct mtxpool_header {
70 int mtxpool_size;
71 int mtxpool_mask;
72 int mtxpool_shift;
73 int mtxpool_next;
74 };
75
76 struct mtx_pool {
77 struct mtxpool_header mtx_pool_header;
78 struct mtx mtx_pool_ary[1];
79 };
80
81 static struct mtx_pool_lockbuilder {
82 struct mtxpool_header mtx_pool_header;
83 struct mtx mtx_pool_ary[MTX_POOL_LOCKBUILDER_SIZE];
84 } lockbuilder_pool;
85
86 #define mtx_pool_size mtx_pool_header.mtxpool_size
87 #define mtx_pool_mask mtx_pool_header.mtxpool_mask
88 #define mtx_pool_shift mtx_pool_header.mtxpool_shift
89 #define mtx_pool_next mtx_pool_header.mtxpool_next
90
91 struct mtx_pool *mtxpool_sleep;
92 struct mtx_pool *mtxpool_lockbuilder;
93
94 #if UINTPTR_MAX == UINT64_MAX /* 64 bits */
95 # define POINTER_BITS 64
96 # define HASH_MULTIPLIER 11400714819323198485u /* (2^64)*(sqrt(5)-1)/2 */
97 #else /* assume 32 bits */
98 # define POINTER_BITS 32
99 # define HASH_MULTIPLIER 2654435769u /* (2^32)*(sqrt(5)-1)/2 */
100 #endif
101
102 /*
103 * Return the (shared) pool mutex associated with the specified address.
104 * The returned mutex is a leaf level mutex, meaning that if you obtain it
105 * you cannot obtain any other mutexes until you release it. You can
106 * legally msleep() on the mutex.
107 */
108 struct mtx *
109 mtx_pool_find(struct mtx_pool *pool, void *ptr)
110 {
111 int p;
112
113 KASSERT(pool != NULL, ("_mtx_pool_find(): null pool"));
114 /*
115 * Fibonacci hash, see Knuth's
116 * _Art of Computer Programming, Volume 3 / Sorting and Searching_
117 */
118 p = ((HASH_MULTIPLIER * (uintptr_t)ptr) >> pool->mtx_pool_shift) &
119 pool->mtx_pool_mask;
120 return (&pool->mtx_pool_ary[p]);
121 }
122
123 static void
124 mtx_pool_initialize(struct mtx_pool *pool, const char *mtx_name, int pool_size,
125 int opts)
126 {
127 int i, maskbits;
128
129 pool->mtx_pool_size = pool_size;
130 pool->mtx_pool_mask = pool_size - 1;
131 for (i = 1, maskbits = 0; (i & pool_size) == 0; i = i << 1)
132 maskbits++;
133 pool->mtx_pool_shift = POINTER_BITS - maskbits;
134 pool->mtx_pool_next = 0;
135 for (i = 0; i < pool_size; ++i)
136 mtx_init(&pool->mtx_pool_ary[i], mtx_name, NULL, opts);
137 }
138
139 struct mtx_pool *
140 mtx_pool_create(const char *mtx_name, int pool_size, int opts)
141 {
142 struct mtx_pool *pool;
143
144 if (pool_size <= 0 || !powerof2(pool_size)) {
145 printf("WARNING: %s pool size is not a power of 2.\n",
146 mtx_name);
147 pool_size = 128;
148 }
149 MALLOC(pool, struct mtx_pool *,
150 sizeof (struct mtx_pool) + ((pool_size - 1) * sizeof (struct mtx)),
151 M_MTXPOOL, M_WAITOK | M_ZERO);
152 mtx_pool_initialize(pool, mtx_name, pool_size, opts);
153 return pool;
154 }
155
156 void
157 mtx_pool_destroy(struct mtx_pool **poolp)
158 {
159 int i;
160 struct mtx_pool *pool = *poolp;
161
162 for (i = pool->mtx_pool_size - 1; i >= 0; --i)
163 mtx_destroy(&pool->mtx_pool_ary[i]);
164 FREE(pool, M_MTXPOOL);
165 *poolp = NULL;
166 }
167
168 static void
169 mtx_pool_setup_static(void *dummy __unused)
170 {
171 mtx_pool_initialize((struct mtx_pool *)&lockbuilder_pool,
172 "lockbuilder mtxpool", MTX_POOL_LOCKBUILDER_SIZE,
173 MTX_DEF | MTX_NOWITNESS | MTX_QUIET);
174 mtxpool_lockbuilder = (struct mtx_pool *)&lockbuilder_pool;
175 }
176
177 static void
178 mtx_pool_setup_dynamic(void *dummy __unused)
179 {
180 mtxpool_sleep = mtx_pool_create("sleep mtxpool",
181 MTX_POOL_SLEEP_SIZE, MTX_DEF);
182 }
183
184 /*
185 * Obtain a (shared) mutex from the pool. The returned mutex is a leaf
186 * level mutex, meaning that if you obtain it you cannot obtain any other
187 * mutexes until you release it. You can legally msleep() on the mutex.
188 */
189 struct mtx *
190 mtx_pool_alloc(struct mtx_pool *pool)
191 {
192 int i;
193
194 KASSERT(pool != NULL, ("mtx_pool_alloc(): null pool"));
195 /*
196 * mtx_pool_next is unprotected against multiple accesses,
197 * but simultaneous access by two CPUs should not be very
198 * harmful.
199 */
200 i = pool->mtx_pool_next;
201 pool->mtx_pool_next = (i + 1) & pool->mtx_pool_mask;
202 return (&pool->mtx_pool_ary[i]);
203 }
204
205 /*
206 * The lockbuilder pool must be initialized early because the lockmgr
207 * and sx locks depend on it. The sx locks are used in the kernel
208 * memory allocator. The lockmgr subsystem is initialized by
209 * SYSINIT(..., SI_SUB_LOCKMGR, ...).
210 *
211 * We can't call MALLOC() to dynamically allocate the sleep pool
212 * until after kmeminit() has been called, which is done by
213 * SYSINIT(..., SI_SUB_KMEM, ...).
214 */
215 SYSINIT(mtxpooli1, SI_SUB_MTX_POOL_STATIC, SI_ORDER_FIRST,
216 mtx_pool_setup_static, NULL);
217 SYSINIT(mtxpooli2, SI_SUB_MTX_POOL_DYNAMIC, SI_ORDER_FIRST,
218 mtx_pool_setup_dynamic, NULL);
219
|