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: stable/10/sys/kern/kern_mtxpool.c 302234 2016-06-27 21:50:30Z bdrewery $");
   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         pool = malloc(sizeof (struct mtx_pool) +
  150             ((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);

Cache object: 9c1737248da72fd6dfd6d69c9376ad17


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