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  * 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: releng/12.0/sys/kern/kern_mtxpool.c 326271 2017-11-27 15:20:12Z pfg $");
   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);

Cache object: b7f2202a929ba76404cce2e59aeec0e7


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