kern_mtxpool.c revision 86563 
1/*-
2 * Copyright (c) 2001 Matthew Dillon.  All Rights Reserved.  Copyright
3 * terms are as specified in the COPYRIGHT file at the base of the source
4 * tree.
5 *
6 * Mutex pool routines.  These routines are designed to be used as short
7 * term leaf mutexes (e.g. the last mutex you might aquire other then
8 * calling msleep()).  They operate using a shared pool.  A mutex is chosen
9 * from the pool based on the supplied pointer (which may or may not be
10 * valid).
11 *
12 * Advantages:
13 *	- no structural overhead.  Mutexes can be associated with structures
14 *	  without adding bloat to the structures.
15 *	- mutexes can be obtained for invalid pointers, useful when uses
16 *	  mutexes to interlock destructor ops.
17 *	- no initialization/destructor overhead
18 *	- can be used with msleep.
19 *
20 * Disadvantages:
21 *	- should generally only be used as leaf mutexes
22 *	- pool/pool dependancy ordering cannot be depended on.
23 *	- possible L1 cache mastersip contention between cpus
24 *
25 * $FreeBSD: head/sys/kern/kern_mtxpool.c 86563 2001-11-19 00:20:36Z dillon $
26 */
27
28#include <sys/param.h>
29#include <sys/proc.h>
30#include <sys/kernel.h>
31#include <sys/ktr.h>
32#include <sys/lock.h>
33#include <sys/malloc.h>
34#include <sys/mutex.h>
35#include <sys/systm.h>
36
37#ifndef MTX_POOL_SIZE
38#define MTX_POOL_SIZE	128
39#endif
40#define MTX_POOL_MASK	(MTX_POOL_SIZE-1)
41
42static struct mtx mtx_pool_ary[MTX_POOL_SIZE];
43
44int mtx_pool_valid = 0;
45
46/*
47 * Inline version of mtx_pool_find(), used to streamline our main API
48 * function calls.
49 */
50static __inline
51struct mtx *
52_mtx_pool_find(void *ptr)
53{
54    int p;
55
56    p = (int)(uintptr_t)ptr;
57    return(&mtx_pool_ary[(p ^ (p >> 6)) & MTX_POOL_MASK]);
58}
59
60static void
61mtx_pool_setup(void *dummy __unused)
62{
63    int i;
64
65    for (i = 0; i < MTX_POOL_SIZE; ++i)
66	mtx_init(&mtx_pool_ary[i], "pool mutex", MTX_DEF | MTX_NOWITNESS | MTX_QUIET);
67    mtx_pool_valid = 1;
68}
69
70/*
71 * Obtain a (shared) mutex from the pool.  The returned mutex is a leaf
72 * level mutex, meaning that if you obtain it you cannot obtain any other
73 * mutexes until you release it.  You can legally msleep() on the mutex.
74 */
75struct mtx *
76mtx_pool_alloc(void)
77{
78    static int si;
79    return(&mtx_pool_ary[si++ & MTX_POOL_MASK]);
80}
81
82/*
83 * Return the (shared) pool mutex associated with the specified address.
84 * The returned mutex is a leaf level mutex, meaning that if you obtain it
85 * you cannot obtain any other mutexes until you release it.  You can
86 * legally msleep() on the mutex.
87 */
88struct mtx *
89mtx_pool_find(void *ptr)
90{
91    return(_mtx_pool_find(ptr));
92}
93
94/*
95 * Combined find/lock operation.  Lock the pool mutex associated with
96 * the specified address.
97 */
98void
99mtx_pool_lock(void *ptr)
100{
101    mtx_lock(_mtx_pool_find(ptr));
102}
103
104/*
105 * Combined find/unlock operation.  Unlock the pool mutex associated with
106 * the specified address.
107 */
108void
109mtx_pool_unlock(void *ptr)
110{
111    mtx_unlock(_mtx_pool_find(ptr));
112}
113
114SYSINIT(mtxpooli, SI_SUB_MUTEX, SI_ORDER_FIRST, mtx_pool_setup, NULL)
115
116