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
26 #include <sys/cdefs.h>
27 __FBSDID("$FreeBSD: releng/5.2/sys/kern/kern_mtxpool.c 117660 2003-07-16 01:00:39Z truckman $");
28
29 #include <sys/param.h>
30 #include <sys/proc.h>
31 #include <sys/kernel.h>
32 #include <sys/ktr.h>
33 #include <sys/lock.h>
34 #include <sys/malloc.h>
35 #include <sys/mutex.h>
36 #include <sys/systm.h>
37
38
39 MALLOC_DEFINE(M_MTXPOOL, "mtx_pool", "mutex pool");
40
41 /* Pool sizes must be a power of two */
42 #ifndef MTX_POOL_LOCKBUILDER_SIZE
43 #define MTX_POOL_LOCKBUILDER_SIZE 128
44 #endif
45 #ifndef MTX_POOL_SLEEP_SIZE
46 #define MTX_POOL_SLEEP_SIZE 128
47 #endif
48
49 struct mtxpool_header {
50 int mtxpool_size;
51 int mtxpool_mask;
52 int mtxpool_shift;
53 int mtxpool_next;
54 };
55
56 struct mtx_pool {
57 struct mtxpool_header mtx_pool_header;
58 struct mtx mtx_pool_ary[1];
59 };
60
61 static struct mtx_pool_lockbuilder {
62 struct mtxpool_header mtx_pool_header;
63 struct mtx mtx_pool_ary[MTX_POOL_LOCKBUILDER_SIZE];
64 } lockbuilder_pool;
65
66 #define mtx_pool_size mtx_pool_header.mtxpool_size
67 #define mtx_pool_mask mtx_pool_header.mtxpool_mask
68 #define mtx_pool_shift mtx_pool_header.mtxpool_shift
69 #define mtx_pool_next mtx_pool_header.mtxpool_next
70
71 struct mtx_pool *mtxpool_sleep;
72 struct mtx_pool *mtxpool_lockbuilder;
73
74 #if UINTPTR_MAX == UINT64_MAX /* 64 bits */
75 # define POINTER_BITS 64
76 # define HASH_MULTIPLIER 11400714819323198485u /* (2^64)*(sqrt(5)-1)/2 */
77 #else /* assume 32 bits */
78 # define POINTER_BITS 32
79 # define HASH_MULTIPLIER 2654435769u /* (2^32)*(sqrt(5)-1)/2 */
80 #endif
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 */
88 struct mtx *
89 mtx_pool_find(struct mtx_pool *pool, void *ptr)
90 {
91 int p;
92
93 KASSERT(pool != NULL, ("_mtx_pool_find(): null pool"));
94 /*
95 * Fibonacci hash, see Knuth's
96 * _Art of Computer Programming, Volume 3 / Sorting and Searching_
97 */
98 p = ((HASH_MULTIPLIER * (uintptr_t)ptr) >> pool->mtx_pool_shift) &
99 pool->mtx_pool_mask;
100 return (&pool->mtx_pool_ary[p]);
101 }
102
103 static void
104 mtx_pool_initialize(struct mtx_pool *pool, const char *mtx_name, int pool_size,
105 int opts)
106 {
107 int i, maskbits;
108
109 pool->mtx_pool_size = pool_size;
110 pool->mtx_pool_mask = pool_size - 1;
111 for (i = 1, maskbits = 0; (i & pool_size) == 0; i = i << 1)
112 maskbits++;
113 pool->mtx_pool_shift = POINTER_BITS - maskbits;
114 pool->mtx_pool_next = 0;
115 for (i = 0; i < pool_size; ++i)
116 mtx_init(&pool->mtx_pool_ary[i], mtx_name, NULL, opts);
117 }
118
119 struct mtx_pool *
120 mtx_pool_create(const char *mtx_name, int pool_size, int opts)
121 {
122 struct mtx_pool *pool;
123
124 if (pool_size <= 0 || !powerof2(pool_size)) {
125 printf("WARNING: %s pool size is not a power of 2.\n",
126 mtx_name);
127 pool_size = 128;
128 }
129 MALLOC(pool, struct mtx_pool *,
130 sizeof (struct mtx_pool) + ((pool_size - 1) * sizeof (struct mtx)),
131 M_MTXPOOL, M_WAITOK | M_ZERO);
132 mtx_pool_initialize(pool, mtx_name, pool_size, opts);
133 return pool;
134 }
135
136 void
137 mtx_pool_destroy(struct mtx_pool **poolp)
138 {
139 int i;
140 struct mtx_pool *pool = *poolp;
141
142 for (i = pool->mtx_pool_size - 1; i >= 0; --i)
143 mtx_destroy(&pool->mtx_pool_ary[i]);
144 FREE(pool, M_MTXPOOL);
145 *poolp = NULL;
146 }
147
148 static void
149 mtx_pool_setup_static(void *dummy __unused)
150 {
151 mtx_pool_initialize((struct mtx_pool *)&lockbuilder_pool,
152 "lockbuilder mtxpool", MTX_POOL_LOCKBUILDER_SIZE,
153 MTX_DEF | MTX_NOWITNESS | MTX_QUIET);
154 mtxpool_lockbuilder = (struct mtx_pool *)&lockbuilder_pool;
155 }
156
157 static void
158 mtx_pool_setup_dynamic(void *dummy __unused)
159 {
160 mtxpool_sleep = mtx_pool_create("sleep mtxpool",
161 MTX_POOL_SLEEP_SIZE, MTX_DEF);
162 }
163
164 /*
165 * Obtain a (shared) mutex from the pool. The returned mutex is a leaf
166 * level mutex, meaning that if you obtain it you cannot obtain any other
167 * mutexes until you release it. You can legally msleep() on the mutex.
168 */
169 struct mtx *
170 mtx_pool_alloc(struct mtx_pool *pool)
171 {
172 int i;
173
174 KASSERT(pool != NULL, ("mtx_pool_alloc(): null pool"));
175 /*
176 * mtx_pool_next is unprotected against multiple accesses,
177 * but simultaneous access by two CPUs should not be very
178 * harmful.
179 */
180 i = pool->mtx_pool_next;
181 pool->mtx_pool_next = (i + 1) & pool->mtx_pool_mask;
182 return (&pool->mtx_pool_ary[i]);
183 }
184
185 /*
186 * The lockbuilder pool must be initialized early because the lockmgr
187 * and sx locks depend on it. The sx locks are used in the kernel
188 * memory allocator. The lockmgr subsystem is initialized by
189 * SYSINIT(..., SI_SUB_LOCKMGR, ...).
190 *
191 * We can't call MALLOC() to dynamically allocate the sleep pool
192 * until after kmeminit() has been called, which is done by
193 * SYSINIT(..., SI_SUB_KMEM, ...).
194 */
195 SYSINIT(mtxpooli1, SI_SUB_MTX_POOL_STATIC, SI_ORDER_FIRST,
196 mtx_pool_setup_static, NULL);
197 SYSINIT(mtxpooli2, SI_SUB_MTX_POOL_DYNAMIC, SI_ORDER_FIRST,
198 mtx_pool_setup_dynamic, NULL);
Cache object: 7a377bf748aaa1d576107e1c0e162c6c
|