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