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

     /*-
      * Copyright (c) 2001 Matthew Dillon.  All Rights Reserved.  Copyright
      * terms are as specified in the COPYRIGHT file at the base of the source
      * tree.
      *
      * Mutex pool routines.  These routines are designed to be used as short
      * term leaf mutexes (e.g. the last mutex you might aquire other then
      * calling msleep()).  They operate using a shared pool.  A mutex is chosen
      * from the pool based on the supplied pointer (which may or may not be
     * valid).
     *
     * Advantages:
     *      - no structural overhead.  Mutexes can be associated with structures
     *        without adding bloat to the structures.
     *      - mutexes can be obtained for invalid pointers, useful when uses
     *        mutexes to interlock destructor ops.
     *      - no initialization/destructor overhead.
     *      - can be used with msleep.
     *
     * Disadvantages:
     *      - should generally only be used as leaf mutexes.
     *      - pool/pool dependancy ordering cannot be depended on.
     *      - possible L1 cache mastersip contention between cpus.
     */
    
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD: releng/5.2/sys/kern/kern_mtxpool.c 117660 2003-07-16 01:00:39Z truckman $");
    
    #include <sys/param.h>
    #include <sys/proc.h>
    #include <sys/kernel.h>
    #include <sys/ktr.h>
    #include <sys/lock.h>
    #include <sys/malloc.h>
    #include <sys/mutex.h>
    #include <sys/systm.h>
    
    
    MALLOC_DEFINE(M_MTXPOOL, "mtx_pool", "mutex pool");
    
    /* Pool sizes must be a power of two */
    #ifndef MTX_POOL_LOCKBUILDER_SIZE
    #define MTX_POOL_LOCKBUILDER_SIZE       128
    #endif
    #ifndef MTX_POOL_SLEEP_SIZE
    #define MTX_POOL_SLEEP_SIZE             128
    #endif
    
    struct mtxpool_header {
            int             mtxpool_size;
            int             mtxpool_mask;
            int             mtxpool_shift;
            int             mtxpool_next;
    };
    
    struct mtx_pool {
            struct mtxpool_header mtx_pool_header;
            struct mtx      mtx_pool_ary[1];
    };
    
    static struct mtx_pool_lockbuilder {
            struct mtxpool_header mtx_pool_header;
            struct mtx      mtx_pool_ary[MTX_POOL_LOCKBUILDER_SIZE];
    } lockbuilder_pool;
    
    #define mtx_pool_size   mtx_pool_header.mtxpool_size
    #define mtx_pool_mask   mtx_pool_header.mtxpool_mask
    #define mtx_pool_shift  mtx_pool_header.mtxpool_shift
    #define mtx_pool_next   mtx_pool_header.mtxpool_next
    
    struct mtx_pool *mtxpool_sleep;
    struct mtx_pool *mtxpool_lockbuilder;
    
    #if UINTPTR_MAX == UINT64_MAX   /* 64 bits */
    # define POINTER_BITS           64
    # define HASH_MULTIPLIER        11400714819323198485u /* (2^64)*(sqrt(5)-1)/2 */
    #else                           /* assume 32 bits */
    # define POINTER_BITS           32
    # define HASH_MULTIPLIER        2654435769u           /* (2^32)*(sqrt(5)-1)/2 */
    #endif
    
    /*
     * Return the (shared) pool mutex associated with the specified address.
     * The returned mutex is a leaf level mutex, meaning that if you obtain it
     * you cannot obtain any other mutexes until you release it.  You can
     * legally msleep() on the mutex.
     */
    struct mtx *
    mtx_pool_find(struct mtx_pool *pool, void *ptr)
    {
            int p;
    
            KASSERT(pool != NULL, ("_mtx_pool_find(): null pool"));
            /*
             * Fibonacci hash, see Knuth's
             * _Art of Computer Programming, Volume 3 / Sorting and Searching_
             */
            p = ((HASH_MULTIPLIER * (uintptr_t)ptr) >> pool->mtx_pool_shift) &
                pool->mtx_pool_mask;
           return (&pool->mtx_pool_ary[p]);
   }
   
   static void
   mtx_pool_initialize(struct mtx_pool *pool, const char *mtx_name, int pool_size,
       int opts)
   {
           int i, maskbits;
   
           pool->mtx_pool_size = pool_size;
           pool->mtx_pool_mask = pool_size - 1;
           for (i = 1, maskbits = 0; (i & pool_size) == 0; i = i << 1)
                   maskbits++;
           pool->mtx_pool_shift = POINTER_BITS - maskbits;
           pool->mtx_pool_next = 0;
           for (i = 0; i < pool_size; ++i)
                   mtx_init(&pool->mtx_pool_ary[i], mtx_name, NULL, opts);
   }
   
   struct mtx_pool *
   mtx_pool_create(const char *mtx_name, int pool_size, int opts)
   {
           struct mtx_pool *pool;
   
           if (pool_size <= 0 || !powerof2(pool_size)) {
                   printf("WARNING: %s pool size is not a power of 2.\n",
                       mtx_name);
                   pool_size = 128;
           }
           MALLOC(pool, struct mtx_pool *,
               sizeof (struct mtx_pool) + ((pool_size - 1) * sizeof (struct mtx)),
               M_MTXPOOL, M_WAITOK | M_ZERO);
           mtx_pool_initialize(pool, mtx_name, pool_size, opts);
           return pool;
   }
   
   void
   mtx_pool_destroy(struct mtx_pool **poolp)
   {
           int i;
           struct mtx_pool *pool = *poolp;
   
           for (i = pool->mtx_pool_size - 1; i >= 0; --i)
                   mtx_destroy(&pool->mtx_pool_ary[i]);
           FREE(pool, M_MTXPOOL);
           *poolp = NULL;
   }
   
   static void
   mtx_pool_setup_static(void *dummy __unused)
   {
           mtx_pool_initialize((struct mtx_pool *)&lockbuilder_pool,
               "lockbuilder mtxpool", MTX_POOL_LOCKBUILDER_SIZE,
               MTX_DEF | MTX_NOWITNESS | MTX_QUIET);
           mtxpool_lockbuilder = (struct mtx_pool *)&lockbuilder_pool;
   }
   
   static void
   mtx_pool_setup_dynamic(void *dummy __unused)
   {
           mtxpool_sleep = mtx_pool_create("sleep mtxpool",
               MTX_POOL_SLEEP_SIZE, MTX_DEF);
   }
   
   /*
    * Obtain a (shared) mutex from the pool.  The returned mutex is a leaf
    * level mutex, meaning that if you obtain it you cannot obtain any other
    * mutexes until you release it.  You can legally msleep() on the mutex.
    */
   struct mtx *
   mtx_pool_alloc(struct mtx_pool *pool)
   {
           int i;
   
           KASSERT(pool != NULL, ("mtx_pool_alloc(): null pool"));
           /*
            * mtx_pool_next is unprotected against multiple accesses,
            * but simultaneous access by two CPUs should not be very
            * harmful.
            */
           i = pool->mtx_pool_next;
           pool->mtx_pool_next = (i + 1) & pool->mtx_pool_mask;
           return (&pool->mtx_pool_ary[i]);
   }
   
   /*
    * The lockbuilder pool must be initialized early because the lockmgr
    * and sx locks depend on it.  The sx locks are used in the kernel
    * memory allocator.  The lockmgr subsystem is initialized by
    * SYSINIT(..., SI_SUB_LOCKMGR, ...).
    *
    * We can't call MALLOC() to dynamically allocate the sleep pool
    * until after kmeminit() has been called, which is done by
    * SYSINIT(..., SI_SUB_KMEM, ...).
    */
   SYSINIT(mtxpooli1, SI_SUB_MTX_POOL_STATIC, SI_ORDER_FIRST,
       mtx_pool_setup_static, NULL);
   SYSINIT(mtxpooli2, SI_SUB_MTX_POOL_DYNAMIC, SI_ORDER_FIRST,
       mtx_pool_setup_dynamic, NULL);

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