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 dependency ordering cannot be depended on.
43 * - possible L1 cache mastersip contention between cpus.
44 */
45
46 #include <sys/cdefs.h>
47 __FBSDID("$FreeBSD: releng/11.1/sys/kern/kern_mtxpool.c 298819 2016-04-29 22:15:33Z pfg $");
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_SLEEP_SIZE
63 #define MTX_POOL_SLEEP_SIZE 128
64 #endif
65
66 struct mtxpool_header {
67 int mtxpool_size;
68 int mtxpool_mask;
69 int mtxpool_shift;
70 int mtxpool_next;
71 };
72
73 struct mtx_pool {
74 struct mtxpool_header mtx_pool_header;
75 struct mtx mtx_pool_ary[1];
76 };
77
78 #define mtx_pool_size mtx_pool_header.mtxpool_size
79 #define mtx_pool_mask mtx_pool_header.mtxpool_mask
80 #define mtx_pool_shift mtx_pool_header.mtxpool_shift
81 #define mtx_pool_next mtx_pool_header.mtxpool_next
82
83 struct mtx_pool *mtxpool_sleep;
84
85 #if UINTPTR_MAX == UINT64_MAX /* 64 bits */
86 # define POINTER_BITS 64
87 # define HASH_MULTIPLIER 11400714819323198485u /* (2^64)*(sqrt(5)-1)/2 */
88 #else /* assume 32 bits */
89 # define POINTER_BITS 32
90 # define HASH_MULTIPLIER 2654435769u /* (2^32)*(sqrt(5)-1)/2 */
91 #endif
92
93 /*
94 * Return the (shared) pool mutex associated with the specified address.
95 * The returned mutex is a leaf level mutex, meaning that if you obtain it
96 * you cannot obtain any other mutexes until you release it. You can
97 * legally msleep() on the mutex.
98 */
99 struct mtx *
100 mtx_pool_find(struct mtx_pool *pool, void *ptr)
101 {
102 int p;
103
104 KASSERT(pool != NULL, ("_mtx_pool_find(): null pool"));
105 /*
106 * Fibonacci hash, see Knuth's
107 * _Art of Computer Programming, Volume 3 / Sorting and Searching_
108 */
109 p = ((HASH_MULTIPLIER * (uintptr_t)ptr) >> pool->mtx_pool_shift) &
110 pool->mtx_pool_mask;
111 return (&pool->mtx_pool_ary[p]);
112 }
113
114 static void
115 mtx_pool_initialize(struct mtx_pool *pool, const char *mtx_name, int pool_size,
116 int opts)
117 {
118 int i, maskbits;
119
120 pool->mtx_pool_size = pool_size;
121 pool->mtx_pool_mask = pool_size - 1;
122 for (i = 1, maskbits = 0; (i & pool_size) == 0; i = i << 1)
123 maskbits++;
124 pool->mtx_pool_shift = POINTER_BITS - maskbits;
125 pool->mtx_pool_next = 0;
126 for (i = 0; i < pool_size; ++i)
127 mtx_init(&pool->mtx_pool_ary[i], mtx_name, NULL, opts);
128 }
129
130 struct mtx_pool *
131 mtx_pool_create(const char *mtx_name, int pool_size, int opts)
132 {
133 struct mtx_pool *pool;
134
135 if (pool_size <= 0 || !powerof2(pool_size)) {
136 printf("WARNING: %s pool size is not a power of 2.\n",
137 mtx_name);
138 pool_size = 128;
139 }
140 pool = malloc(sizeof (struct mtx_pool) +
141 ((pool_size - 1) * sizeof (struct mtx)),
142 M_MTXPOOL, M_WAITOK | M_ZERO);
143 mtx_pool_initialize(pool, mtx_name, pool_size, opts);
144 return pool;
145 }
146
147 void
148 mtx_pool_destroy(struct mtx_pool **poolp)
149 {
150 int i;
151 struct mtx_pool *pool = *poolp;
152
153 for (i = pool->mtx_pool_size - 1; i >= 0; --i)
154 mtx_destroy(&pool->mtx_pool_ary[i]);
155 free(pool, M_MTXPOOL);
156 *poolp = NULL;
157 }
158
159 static void
160 mtx_pool_setup_dynamic(void *dummy __unused)
161 {
162 mtxpool_sleep = mtx_pool_create("sleep mtxpool",
163 MTX_POOL_SLEEP_SIZE, MTX_DEF);
164 }
165
166 /*
167 * Obtain a (shared) mutex from the pool. The returned mutex is a leaf
168 * level mutex, meaning that if you obtain it you cannot obtain any other
169 * mutexes until you release it. You can legally msleep() on the mutex.
170 */
171 struct mtx *
172 mtx_pool_alloc(struct mtx_pool *pool)
173 {
174 int i;
175
176 KASSERT(pool != NULL, ("mtx_pool_alloc(): null pool"));
177 /*
178 * mtx_pool_next is unprotected against multiple accesses,
179 * but simultaneous access by two CPUs should not be very
180 * harmful.
181 */
182 i = pool->mtx_pool_next;
183 pool->mtx_pool_next = (i + 1) & pool->mtx_pool_mask;
184 return (&pool->mtx_pool_ary[i]);
185 }
186
187 SYSINIT(mtxpooli2, SI_SUB_MTX_POOL_DYNAMIC, SI_ORDER_FIRST,
188 mtx_pool_setup_dynamic, NULL);
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