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 dependancy 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_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);