sys/kern/kern_mtxpool.c

   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("$FreeBSD$");
  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);