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/*-
* Copyright (c) 2001 Matthew Dillon. All Rights Reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY AUTHOR AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL AUTHOR OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
/* Mutex pool routines. These routines are designed to be used as short
* term leaf mutexes (e.g. the last mutex you might acquire 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 dependency ordering cannot be depended on.
* - possible L1 cache mastersip contention between cpus.
*/
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
#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>
static 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;
}
pool = malloc(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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