Merge branch 'vendor/TCPDUMP' and update build for the update.
[dragonfly.git] / sys / sys / spinlock2.h
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1/*
2 * Copyright (c) 2005 Jeffrey M. Hsu. All rights reserved.
3 *
4 * This code is derived from software contributed to The DragonFly Project
5 * by Jeffrey M. Hsu.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 * notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 * notice, this list of conditions and the following disclaimer in the
14 * documentation and/or other materials provided with the distribution.
15 * 3. Neither the name of The DragonFly Project nor the names of its
16 * contributors may be used to endorse or promote products derived
17 * from this software without specific, prior written permission.
18 *
19 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
20 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
21 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
22 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
23 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
24 * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
25 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
26 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
27 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
28 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
29 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
30 * SUCH DAMAGE.
31 *
74af985e 32 * $DragonFly: src/sys/sys/spinlock2.h,v 1.12 2008/06/04 04:34:54 nth Exp $
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33 */
34
35#ifndef _SYS_SPINLOCK2_H_
36#define _SYS_SPINLOCK2_H_
37
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38#ifndef _KERNEL
39
40#error "This file should not be included by userland programs."
41
42#else
43
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44#ifndef _SYS_SYSTM_H_
45#include <sys/systm.h>
46#endif
03d6a592 47#ifndef _SYS_THREAD2_H_
35a832df 48#include <sys/thread2.h>
03d6a592 49#endif
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50#ifndef _SYS_GLOBALDATA_H_
51#include <sys/globaldata.h>
52#endif
03d6a592 53#ifndef _MACHINE_ATOMIC_H_
35a832df 54#include <machine/atomic.h>
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55#endif
56#ifndef _MACHINE_CPUFUNC_H_
35a832df 57#include <machine/cpufunc.h>
03d6a592 58#endif
35a832df 59
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60/*
61 * SPECIAL NOTE! Obtaining a spinlock does not enter a critical section
62 * or protect against FAST interrupts but it will prevent thread preemption.
63 * Because the spinlock code path is ultra critical, we do not check for
64 * LWKT reschedule requests (due to an interrupt thread not being able to
65 * preempt).
66 */
67
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68#ifdef SMP
69
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70extern int spin_trylock_wr_contested(globaldata_t gd, struct spinlock *mtx,
71 int value);
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72extern void spin_lock_wr_contested(struct spinlock *mtx, int value);
73extern void spin_lock_rd_contested(struct spinlock *mtx);
9d265729 74
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75#endif
76
77#ifdef SMP
78
79/*
80 * Attempt to obtain an exclusive spinlock. Returns FALSE on failure,
81 * TRUE on success. Since the caller assumes that spinlocks must actually
82 * work when using this function, it is only made available to SMP builds.
83 */
84static __inline boolean_t
85spin_trylock_wr(struct spinlock *mtx)
69d78e99 86{
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87 globaldata_t gd = mycpu;
88 int value;
89
90 ++gd->gd_spinlocks_wr;
91 if ((value = atomic_swap_int(&mtx->lock, SPINLOCK_EXCLUSIVE)) != 0)
74af985e 92 return (spin_trylock_wr_contested(gd, mtx, value));
d666840a 93 return (TRUE);
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94}
95
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96#endif
97
98/*
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99 * Obtain an exclusive spinlock and return. Shortcut the case where the only
100 * cached read lock was from our own cpu (it can just be cleared).
9d265729 101 */
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102static __inline void
103spin_lock_wr_quick(globaldata_t gd, struct spinlock *mtx)
35a832df 104{
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105#ifdef SMP
106 int value;
9d265729 107#endif
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108
109 ++gd->gd_spinlocks_wr;
110#ifdef SMP
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111 if ((value = atomic_swap_int(&mtx->lock, SPINLOCK_EXCLUSIVE)) != 0) {
112 value &= ~gd->gd_cpumask;
113 if (value)
114 spin_lock_wr_contested(mtx, value);
115 }
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116#endif
117}
118
119static __inline void
120spin_lock_wr(struct spinlock *mtx)
121{
122 spin_lock_wr_quick(mycpu, mtx);
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123}
124
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125#if 0
126
9d265729 127/*
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128 * Upgrade a shared spinlock to exclusive. Return TRUE if we were
129 * able to upgrade without another exclusive holder getting in before
130 * us, FALSE otherwise.
9d265729 131 */
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132static __inline int
133spin_lock_upgrade(struct spinlock *mtx)
9d265729 134{
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135 globaldata_t gd = mycpu;
136#ifdef SMP
137 int value;
9d265729 138#endif
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139
140 ++gd->gd_spinlocks_wr;
141#ifdef SMP
142 value = atomic_swap_int(&mtx->lock, SPINLOCK_EXCLUSIVE);
9d265729 143 cpu_sfence();
d666840a 144#endif
bbb31c5d 145 gd->gd_spinlock_rd = NULL;
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146#ifdef SMP
147 value &= ~gd->gd_cpumask;
148 if (value) {
149 spin_lock_wr_contested(mtx, value);
150 if (value & SPINLOCK_EXCLUSIVE)
151 return (FALSE);
152 XXX regain original shared lock?
153 }
154 return (TRUE);
155#endif
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156}
157
d666840a 158#endif
35a832df 159
69d78e99 160/*
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161 * Obtain a shared spinlock and return. This is a critical code path.
162 *
163 * The vast majority of the overhead is in the cpu_mfence() (5ns vs 1ns for
164 * the entire rest of the procedure). Unfortunately we have to ensure that
bbb31c5d 165 * spinlock pointer is written out before we check the cpumask to interlock
d666840a 166 * against an exclusive spinlock that clears the cpumask and then checks
bbb31c5d 167 * the spinlock pointer.
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168 *
169 * But what is EXTREMELY important here is that we do not have to perform
170 * a locked bus cycle on the spinlock itself if the shared bit for our cpu
171 * is already found to be set. We only need the mfence, and the mfence is
172 * local to the cpu and never conflicts with other cpu's.
9d265729 173 *
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174 * This means that multiple parallel shared acessors (e.g. filedescriptor
175 * table lookups, namecache lookups) run at full speed and incur NO cache
bbb31c5d 176 * contention at all. It is the difference between 10ns and 40-100ns.
69d78e99 177 */
35a832df 178static __inline void
d666840a 179spin_lock_rd_quick(globaldata_t gd, struct spinlock *mtx)
35a832df 180{
bbb31c5d 181 gd->gd_spinlock_rd = mtx;
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182#ifdef SMP
183 cpu_mfence();
184 if ((mtx->lock & gd->gd_cpumask) == 0)
185 spin_lock_rd_contested(mtx);
9d265729 186#endif
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187}
188
189static __inline void
d666840a 190spin_lock_rd(struct spinlock *mtx)
35a832df 191{
d666840a 192 spin_lock_rd_quick(mycpu,mtx);
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193}
194
9d265729 195/*
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196 * Release an exclusive spinlock. We can just do this passively, only
197 * ensuring that our spinlock count is left intact until the mutex is
198 * cleared.
9d265729 199 */
35a832df 200static __inline void
d666840a 201spin_unlock_wr_quick(globaldata_t gd, struct spinlock *mtx)
35a832df 202{
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203#ifdef SMP
204 mtx->lock = 0;
205#endif
4ccaa0da 206 KKASSERT(gd->gd_spinlocks_wr > 0);
d666840a 207 --gd->gd_spinlocks_wr;
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208}
209
503a0d52 210static __inline void
d666840a 211spin_unlock_wr(struct spinlock *mtx)
503a0d52 212{
d666840a 213 spin_unlock_wr_quick(mycpu, mtx);
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214}
215
dd55d707 216/*
d666840a 217 * Release a shared spinlock. We leave the shared bit set in the spinlock
bbb31c5d 218 * as a cache and simply clear the spinlock pointer for the cpu. This
d666840a 219 * fast-paths another shared lock later at the cost of an exclusive lock
bbb31c5d 220 * having to check per-cpu spinlock pointers to determine when there are no
d666840a 221 * shared holders remaining.
dd55d707 222 */
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223static __inline void
224spin_unlock_rd_quick(globaldata_t gd, struct spinlock *mtx)
225{
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226 KKASSERT(gd->gd_spinlock_rd == mtx);
227 gd->gd_spinlock_rd = NULL;
d666840a 228}
35a832df 229
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230static __inline void
231spin_unlock_rd(struct spinlock *mtx)
232{
233 spin_unlock_rd_quick(mycpu, mtx);
234}
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235
236static __inline void
d666840a 237spin_init(struct spinlock *mtx)
35a832df 238{
d666840a 239 mtx->lock = 0;
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240}
241
242static __inline void
d666840a 243spin_uninit(struct spinlock *mtx)
35a832df 244{
d666840a 245 /* unused */
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246}
247
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248#endif /* _KERNEL */
249#endif /* _SYS_SPINLOCK2_H_ */
35a832df 250