1/*-
2 * SPDX-License-Identifier: BSD-2-Clause
3 *
4 * Copyright (c) 2001 Matthew Dillon.  All Rights Reserved.
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
8 * are met:
9 * 1. Redistributions of source code must retain the above copyright
10 *    notice, this list of conditions and the following disclaimer.
11 * 2. Redistributions in binary form must reproduce the above copyright
12 *    notice, this list of conditions and the following disclaimer in the
13 *    documentation and/or other materials provided with the distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY AUTHOR AND CONTRIBUTORS ``AS IS'' AND
16 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
17 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
18 * ARE DISCLAIMED.  IN NO EVENT SHALL AUTHOR OR CONTRIBUTORS BE LIABLE
19 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
20 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
21 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
22 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
23 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
24 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
25 * SUCH DAMAGE.
26 */
27
28/* Mutex pool routines.  These routines are designed to be used as short
29 * term leaf mutexes (e.g. the last mutex you might acquire other then
30 * calling msleep()).  They operate using a shared pool.  A mutex is chosen
31 * from the pool based on the supplied pointer (which may or may not be
32 * valid).
33 *
34 * Advantages:
35 *	- no structural overhead.  Mutexes can be associated with structures
36 *	  without adding bloat to the structures.
37 *	- mutexes can be obtained for invalid pointers, useful when uses
38 *	  mutexes to interlock destructor ops.
39 *	- no initialization/destructor overhead.
40 *	- can be used with msleep.
41 *
42 * Disadvantages:
43 *	- should generally only be used as leaf mutexes.
44 *	- pool/pool dependency ordering cannot be depended on.
45 *	- possible L1 cache mastersip contention between cpus.
46 */
47
48#include <sys/param.h>
49#include <sys/proc.h>
50#include <sys/kernel.h>
51#include <sys/ktr.h>
52#include <sys/lock.h>
53#include <sys/malloc.h>
54#include <sys/mutex.h>
55#include <sys/systm.h>
56
57static MALLOC_DEFINE(M_MTXPOOL, "mtx_pool", "mutex pool");
58
59/* Pool sizes must be a power of two */
60#ifndef MTX_POOL_SLEEP_SIZE
61#define MTX_POOL_SLEEP_SIZE		1024
62#endif
63
64struct mtxpool_header {
65	int		mtxpool_size;
66	int		mtxpool_mask;
67	int		mtxpool_shift;
68	int		mtxpool_next __aligned(CACHE_LINE_SIZE);
69};
70
71struct mtx_pool {
72	struct mtxpool_header mtx_pool_header;
73	struct mtx	mtx_pool_ary[1];
74};
75
76#define mtx_pool_size	mtx_pool_header.mtxpool_size
77#define mtx_pool_mask	mtx_pool_header.mtxpool_mask
78#define mtx_pool_shift	mtx_pool_header.mtxpool_shift
79#define mtx_pool_next	mtx_pool_header.mtxpool_next
80
81struct mtx_pool __read_mostly *mtxpool_sleep;
82
83#if UINTPTR_MAX == UINT64_MAX	/* 64 bits */
84# define POINTER_BITS		64
85# define HASH_MULTIPLIER	11400714819323198485u /* (2^64)*(sqrt(5)-1)/2 */
86#else				/* assume 32 bits */
87# define POINTER_BITS		32
88# define HASH_MULTIPLIER	2654435769u	      /* (2^32)*(sqrt(5)-1)/2 */
89#endif
90
91/*
92 * Return the (shared) pool mutex associated with the specified address.
93 * The returned mutex is a leaf level mutex, meaning that if you obtain it
94 * you cannot obtain any other mutexes until you release it.  You can
95 * legally msleep() on the mutex.
96 */
97struct mtx *
98mtx_pool_find(struct mtx_pool *pool, void *ptr)
99{
100	int p;
101
102	KASSERT(pool != NULL, ("_mtx_pool_find(): null pool"));
103	/*
104	 * Fibonacci hash, see Knuth's
105	 * _Art of Computer Programming, Volume 3 / Sorting and Searching_
106	 */
107	p = ((HASH_MULTIPLIER * (uintptr_t)ptr) >> pool->mtx_pool_shift) &
108	    pool->mtx_pool_mask;
109	return (&pool->mtx_pool_ary[p]);
110}
111
112static void
113mtx_pool_initialize(struct mtx_pool *pool, const char *mtx_name, int pool_size,
114    int opts)
115{
116	int i, maskbits;
117
118	pool->mtx_pool_size = pool_size;
119	pool->mtx_pool_mask = pool_size - 1;
120	for (i = 1, maskbits = 0; (i & pool_size) == 0; i = i << 1)
121		maskbits++;
122	pool->mtx_pool_shift = POINTER_BITS - maskbits;
123	pool->mtx_pool_next = 0;
124	for (i = 0; i < pool_size; ++i)
125		mtx_init(&pool->mtx_pool_ary[i], mtx_name, NULL, opts);
126}
127
128struct mtx_pool *
129mtx_pool_create(const char *mtx_name, int pool_size, int opts)
130{
131	struct mtx_pool *pool;
132
133	if (pool_size <= 0 || !powerof2(pool_size)) {
134		printf("WARNING: %s pool size is not a power of 2.\n",
135		    mtx_name);
136		pool_size = 128;
137	}
138	pool = malloc(sizeof (struct mtx_pool) +
139	    ((pool_size - 1) * sizeof (struct mtx)),
140	    M_MTXPOOL, M_WAITOK | M_ZERO);
141	mtx_pool_initialize(pool, mtx_name, pool_size, opts);
142	return pool;
143}
144
145void
146mtx_pool_destroy(struct mtx_pool **poolp)
147{
148	int i;
149	struct mtx_pool *pool = *poolp;
150
151	for (i = pool->mtx_pool_size - 1; i >= 0; --i)
152		mtx_destroy(&pool->mtx_pool_ary[i]);
153	free(pool, M_MTXPOOL);
154	*poolp = NULL;
155}
156
157static void
158mtx_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 */
169struct mtx *
170mtx_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
185SYSINIT(mtxpooli2, SI_SUB_MTX_POOL_DYNAMIC, SI_ORDER_FIRST,
186    mtx_pool_setup_dynamic, NULL);
187