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linux_atomic64.c revision 1.2 
      1 /*	$NetBSD: linux_atomic64.c,v 1.2 2018/08/27 15:10:53 riastradh Exp $	*/
      2 
      3 /*-
      4  * Copyright (c) 2018 The NetBSD Foundation, Inc.
      5  * All rights reserved.
      6  *
      7  * This code is derived from software contributed to The NetBSD Foundation
      8  * by Taylor R. Campbell.
      9  *
     10  * Redistribution and use in source and binary forms, with or without
     11  * modification, are permitted provided that the following conditions
     12  * are met:
     13  * 1. Redistributions of source code must retain the above copyright
     14  *    notice, this list of conditions and the following disclaimer.
     15  * 2. Redistributions in binary form must reproduce the above copyright
     16  *    notice, this list of conditions and the following disclaimer in the
     17  *    documentation and/or other materials provided with the distribution.
     18  *
     19  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
     20  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
     21  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
     22  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
     23  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
     24  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
     25  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
     26  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
     27  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     28  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     29  * POSSIBILITY OF SUCH DAMAGE.
     30  */
     31 
     32 #include <sys/cdefs.h>
     33 __KERNEL_RCSID(0, "$NetBSD: linux_atomic64.c,v 1.2 2018/08/27 15:10:53 riastradh Exp $");
     34 
     35 #include <sys/param.h>
     36 #include <sys/bitops.h>
     37 #include <sys/lock.h>
     38 
     39 #include <linux/atomic.h>
     40 
     41 #ifdef __HAVE_ATOMIC64_OPS
     42 
     43 int
     44 linux_atomic64_init(void)
     45 {
     46 	return 0;
     47 }
     48 
     49 void
     50 linux_atomic64_fini(void)
     51 {
     52 }
     53 
     54 #else
     55 
     56 static struct {
     57 	kmutex_t	lock;
     58 	uint32_t	gen;	/* for unlocked read */
     59 	char		pad[CACHE_LINE_SIZE -
     60 			    sizeof(kmutex_t) - sizeof(uint32_t)];
     61 } atomic64_tab[PAGE_SIZE/CACHE_LINE_SIZE] __cacheline_aligned;
     62 CTASSERT(sizeof(atomic64_tab) == PAGE_SIZE);
     63 CTASSERT(sizeof(atomic64_tab[0]) == CACHE_LINE_SIZE);
     64 
     65 int
     66 linux_atomic64_init(void)
     67 {
     68 	size_t i;
     69 
     70 	for (i = 0; i < __arraycount(atomic64_tab); i++) {
     71 		mutex_init(&atomic64_tab[i].lock, MUTEX_DEFAULT, IPL_HIGH);
     72 		atomic64_tab[i].gen = 0;
     73 	}
     74 
     75 	return 0;
     76 }
     77 
     78 void
     79 linux_atomic64_fini(void)
     80 {
     81 	size_t i;
     82 
     83 	for (i = 0; i < __arraycount(atomic64_tab); i++) {
     84 		KASSERT((atomic64_tab[i].gen & 1) == 0);
     85 		mutex_destroy(&atomic64_tab[i].lock);
     86 	}
     87 }
     88 
     89 static inline size_t
     90 atomic64_hash(const struct atomic64 *a)
     91 {
     92 
     93 	return ((uintptr_t)a >> ilog2(CACHE_LINE_SIZE)) %
     94 	    __arraycount(atomic64_tab);
     95 }
     96 
     97 static void
     98 atomic64_lock(struct atomic64 *a)
     99 {
    100 	size_t i = atomic64_hash(a);
    101 
    102 	mutex_spin_enter(&atomic64_tab[i].lock);
    103 	KASSERT((atomic64_tab[i].gen & 1) == 0);
    104 	atomic64_tab[i].gen |= 1;
    105 	membar_producer();
    106 }
    107 
    108 static void
    109 atomic64_unlock(struct atomic64 *a)
    110 {
    111 	size_t i = atomic64_hash(a);
    112 
    113 	KASSERT(mutex_owned(&atomic64_tab[i].lock));
    114 	KASSERT((atomic64_tab[i].gen & 1) == 1);
    115 
    116 	membar_producer();
    117 	atomic64_tab[i].gen |= 1; /* paranoia */
    118 	atomic64_tab[i].gen++;
    119 	mutex_spin_exit(&atomic64_tab[i].lock);
    120 }
    121 
    122 uint64_t
    123 atomic64_read(const struct atomic64 *a)
    124 {
    125 	size_t i = atomic64_hash(a);
    126 	uint32_t gen;
    127 	uint64_t value;
    128 
    129 	do {
    130 		while (__predict_false((gen = atomic64_tab[i].gen) & 1))
    131 			SPINLOCK_BACKOFF_HOOK;
    132 		membar_consumer();
    133 		value = a->a_v;
    134 		membar_consumer();
    135 	} while (__predict_false(atomic64_tab[i].gen != gen));
    136 
    137 	return value;
    138 }
    139 
    140 void
    141 atomic64_set(struct atomic64 *a, uint64_t value)
    142 {
    143 
    144 	atomic64_lock(a);
    145 	a->a_v = value;
    146 	atomic64_unlock(a);
    147 }
    148 
    149 void
    150 atomic64_add(int64_t delta, struct atomic64 *a)
    151 {
    152 
    153 	atomic64_lock(a);
    154 	a->a_v += delta;
    155 	atomic64_unlock(a);
    156 }
    157 
    158 void
    159 atomic64_sub(int64_t delta, struct atomic64 *a)
    160 {
    161 
    162 	atomic64_lock(a);
    163 	a->a_v -= delta;
    164 	atomic64_unlock(a);
    165 }
    166 
    167 uint64_t
    168 atomic64_xchg(struct atomic64 *a, uint64_t new)
    169 {
    170 	uint64_t old;
    171 
    172 	atomic64_lock(a);
    173 	old = a->a_v;
    174 	a->a_v = new;
    175 	atomic64_unlock(a);
    176 
    177 	return old;
    178 }
    179 
    180 uint64_t
    181 atomic64_cmpxchg(struct atomic64 *a, uint64_t expect, uint64_t new)
    182 {
    183 	uint64_t old;
    184 
    185 	atomic64_lock(a);
    186 	old = a->a_v;
    187 	if (old == expect)
    188 		a->a_v = new;
    189 	atomic64_unlock(a);
    190 
    191 	return old;
    192 }
    193 
    194 #endif
    195