1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause 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 #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 static MALLOC_DEFINE(M_MTXPOOL, "mtx_pool", "mutex pool"); 59 60 /* Pool sizes must be a power of two */ 61 #ifndef MTX_POOL_SLEEP_SIZE 62 #define MTX_POOL_SLEEP_SIZE 1024 63 #endif 64 65 struct mtxpool_header { 66 int mtxpool_size; 67 int mtxpool_mask; 68 int mtxpool_shift; 69 int mtxpool_next __aligned(CACHE_LINE_SIZE); 70 }; 71 72 struct mtx_pool { 73 struct mtxpool_header mtx_pool_header; 74 struct mtx mtx_pool_ary[1]; 75 }; 76 77 #define mtx_pool_size mtx_pool_header.mtxpool_size 78 #define mtx_pool_mask mtx_pool_header.mtxpool_mask 79 #define mtx_pool_shift mtx_pool_header.mtxpool_shift 80 #define mtx_pool_next mtx_pool_header.mtxpool_next 81 82 struct mtx_pool __read_mostly *mtxpool_sleep; 83 84 #if UINTPTR_MAX == UINT64_MAX /* 64 bits */ 85 # define POINTER_BITS 64 86 # define HASH_MULTIPLIER 11400714819323198485u /* (2^64)*(sqrt(5)-1)/2 */ 87 #else /* assume 32 bits */ 88 # define POINTER_BITS 32 89 # define HASH_MULTIPLIER 2654435769u /* (2^32)*(sqrt(5)-1)/2 */ 90 #endif 91 92 /* 93 * Return the (shared) pool mutex associated with the specified address. 94 * The returned mutex is a leaf level mutex, meaning that if you obtain it 95 * you cannot obtain any other mutexes until you release it. You can 96 * legally msleep() on the mutex. 97 */ 98 struct mtx * 99 mtx_pool_find(struct mtx_pool *pool, void *ptr) 100 { 101 int p; 102 103 KASSERT(pool != NULL, ("_mtx_pool_find(): null pool")); 104 /* 105 * Fibonacci hash, see Knuth's 106 * _Art of Computer Programming, Volume 3 / Sorting and Searching_ 107 */ 108 p = ((HASH_MULTIPLIER * (uintptr_t)ptr) >> pool->mtx_pool_shift) & 109 pool->mtx_pool_mask; 110 return (&pool->mtx_pool_ary[p]); 111 } 112 113 static void 114 mtx_pool_initialize(struct mtx_pool *pool, const char *mtx_name, int pool_size, 115 int opts) 116 { 117 int i, maskbits; 118 119 pool->mtx_pool_size = pool_size; 120 pool->mtx_pool_mask = pool_size - 1; 121 for (i = 1, maskbits = 0; (i & pool_size) == 0; i = i << 1) 122 maskbits++; 123 pool->mtx_pool_shift = POINTER_BITS - maskbits; 124 pool->mtx_pool_next = 0; 125 for (i = 0; i < pool_size; ++i) 126 mtx_init(&pool->mtx_pool_ary[i], mtx_name, NULL, opts); 127 } 128 129 struct mtx_pool * 130 mtx_pool_create(const char *mtx_name, int pool_size, int opts) 131 { 132 struct mtx_pool *pool; 133 134 if (pool_size <= 0 || !powerof2(pool_size)) { 135 printf("WARNING: %s pool size is not a power of 2.\n", 136 mtx_name); 137 pool_size = 128; 138 } 139 pool = malloc(sizeof (struct mtx_pool) + 140 ((pool_size - 1) * sizeof (struct mtx)), 141 M_MTXPOOL, M_WAITOK | M_ZERO); 142 mtx_pool_initialize(pool, mtx_name, pool_size, opts); 143 return pool; 144 } 145 146 void 147 mtx_pool_destroy(struct mtx_pool **poolp) 148 { 149 int i; 150 struct mtx_pool *pool = *poolp; 151 152 for (i = pool->mtx_pool_size - 1; i >= 0; --i) 153 mtx_destroy(&pool->mtx_pool_ary[i]); 154 free(pool, M_MTXPOOL); 155 *poolp = NULL; 156 } 157 158 static void 159 mtx_pool_setup_dynamic(void *dummy __unused) 160 { 161 mtxpool_sleep = mtx_pool_create("sleep mtxpool", 162 MTX_POOL_SLEEP_SIZE, MTX_DEF); 163 } 164 165 /* 166 * Obtain a (shared) mutex from the pool. The returned mutex is a leaf 167 * level mutex, meaning that if you obtain it you cannot obtain any other 168 * mutexes until you release it. You can legally msleep() on the mutex. 169 */ 170 struct mtx * 171 mtx_pool_alloc(struct mtx_pool *pool) 172 { 173 int i; 174 175 KASSERT(pool != NULL, ("mtx_pool_alloc(): null pool")); 176 /* 177 * mtx_pool_next is unprotected against multiple accesses, 178 * but simultaneous access by two CPUs should not be very 179 * harmful. 180 */ 181 i = pool->mtx_pool_next; 182 pool->mtx_pool_next = (i + 1) & pool->mtx_pool_mask; 183 return (&pool->mtx_pool_ary[i]); 184 } 185 186 SYSINIT(mtxpooli2, SI_SUB_MTX_POOL_DYNAMIC, SI_ORDER_FIRST, 187 mtx_pool_setup_dynamic, NULL); 188