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 dependancy ordering cannot be depended on.
43 *	- possible L1 cache mastersip contention between cpus.
44 */
45
46#include <sys/cdefs.h>
47__FBSDID("$FreeBSD$");
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
59static 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
69struct mtxpool_header {
70	int		mtxpool_size;
71	int		mtxpool_mask;
72	int		mtxpool_shift;
73	int		mtxpool_next;
74};
75
76struct mtx_pool {
77	struct mtxpool_header mtx_pool_header;
78	struct mtx	mtx_pool_ary[1];
79};
80
81static 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
91struct mtx_pool *mtxpool_sleep;
92struct 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 */
108struct mtx *
109mtx_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
123static void
124mtx_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
139struct mtx_pool *
140mtx_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
156void
157mtx_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
168static void
169mtx_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
177static void
178mtx_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 */
189struct mtx *
190mtx_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 */
215SYSINIT(mtxpooli1, SI_SUB_MTX_POOL_STATIC, SI_ORDER_FIRST,
216    mtx_pool_setup_static, NULL);
217SYSINIT(mtxpooli2, SI_SUB_MTX_POOL_DYNAMIC, SI_ORDER_FIRST,
218    mtx_pool_setup_dynamic, NULL);
219