The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_mtxpool.c

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    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/11.2/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);

Cache object: 0088ab595db9ddf29bc2f5b4057f16d4


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