2 * Copyright (c) 2005 Jeffrey M. Hsu. All rights reserved.
4 * This code is derived from software contributed to The DragonFly Project
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
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.
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
32 * $DragonFly: src/sys/sys/spinlock2.h,v 1.9 2006/05/21 20:23:27 dillon Exp $
35 #ifndef _SYS_SPINLOCK2_H_
36 #define _SYS_SPINLOCK2_H_
40 #error "This file should not be included by userland programs."
44 #ifndef _SYS_THREAD2_H_
45 #include <sys/thread2.h>
47 #ifndef _SYS_GLOBALDATA_H_
48 #include <sys/globaldata.h>
50 #ifndef _MACHINE_ATOMIC_H_
51 #include <machine/atomic.h>
53 #ifndef _MACHINE_CPUFUNC_H_
54 #include <machine/cpufunc.h>
58 * SPECIAL NOTE! Obtaining a spinlock does not enter a critical section
59 * or protect against FAST interrupts but it will prevent thread preemption.
60 * Because the spinlock code path is ultra critical, we do not check for
61 * LWKT reschedule requests (due to an interrupt thread not being able to
67 extern int spin_trylock_wr_contested(struct spinlock *mtx, int value);
68 extern void spin_lock_wr_contested(struct spinlock *mtx, int value);
69 extern void spin_lock_rd_contested(struct spinlock *mtx);
76 * Attempt to obtain an exclusive spinlock. Returns FALSE on failure,
77 * TRUE on success. Since the caller assumes that spinlocks must actually
78 * work when using this function, it is only made available to SMP builds.
80 static __inline boolean_t
81 spin_trylock_wr(struct spinlock *mtx)
83 globaldata_t gd = mycpu;
86 ++gd->gd_spinlocks_wr;
87 if ((value = atomic_swap_int(&mtx->lock, SPINLOCK_EXCLUSIVE)) != 0)
88 return (spin_trylock_wr_contested(mtx, value));
95 * Obtain an exclusive spinlock and return.
98 spin_lock_wr_quick(globaldata_t gd, struct spinlock *mtx)
104 ++gd->gd_spinlocks_wr;
106 if ((value = atomic_swap_int(&mtx->lock, SPINLOCK_EXCLUSIVE)) != 0)
107 spin_lock_wr_contested(mtx, value);
112 spin_lock_wr(struct spinlock *mtx)
114 spin_lock_wr_quick(mycpu, mtx);
120 * Upgrade a shared spinlock to exclusive. Return TRUE if we were
121 * able to upgrade without another exclusive holder getting in before
122 * us, FALSE otherwise.
125 spin_lock_upgrade(struct spinlock *mtx)
127 globaldata_t gd = mycpu;
132 ++gd->gd_spinlocks_wr;
134 value = atomic_swap_int(&mtx->lock, SPINLOCK_EXCLUSIVE);
137 --gd->gd_spinlocks_rd;
139 value &= ~gd->gd_cpumask;
141 spin_lock_wr_contested(mtx, value);
142 if (value & SPINLOCK_EXCLUSIVE)
144 XXX regain original shared lock?
153 * Obtain a shared spinlock and return. This is a critical code path.
155 * The vast majority of the overhead is in the cpu_mfence() (5ns vs 1ns for
156 * the entire rest of the procedure). Unfortunately we have to ensure that
157 * spinlock count is written out before we check the cpumask to interlock
158 * against an exclusive spinlock that clears the cpumask and then checks
159 * the spinlock count.
161 * But what is EXTREMELY important here is that we do not have to perform
162 * a locked bus cycle on the spinlock itself if the shared bit for our cpu
163 * is already found to be set. We only need the mfence, and the mfence is
164 * local to the cpu and never conflicts with other cpu's.
166 * This means that multiple parallel shared acessors (e.g. filedescriptor
167 * table lookups, namecache lookups) run at full speed and incur NO cache
168 * contention at all. Its the difference between 10ns and 40-100ns.
171 spin_lock_rd_quick(globaldata_t gd, struct spinlock *mtx)
173 ++gd->gd_spinlocks_rd;
176 if ((mtx->lock & gd->gd_cpumask) == 0)
177 spin_lock_rd_contested(mtx);
182 spin_lock_rd(struct spinlock *mtx)
184 spin_lock_rd_quick(mycpu,mtx);
188 * Release an exclusive spinlock. We can just do this passively, only
189 * ensuring that our spinlock count is left intact until the mutex is
193 spin_unlock_wr_quick(globaldata_t gd, struct spinlock *mtx)
198 --gd->gd_spinlocks_wr;
202 spin_unlock_wr(struct spinlock *mtx)
204 spin_unlock_wr_quick(mycpu, mtx);
208 * Release a shared spinlock. We leave the shared bit set in the spinlock
209 * as a cache and simply decrement the spinlock count for the cpu. This
210 * fast-paths another shared lock later at the cost of an exclusive lock
211 * having to check per-cpu spinlock counts to determine when there are no
212 * shared holders remaining.
215 spin_unlock_rd_quick(globaldata_t gd, struct spinlock *mtx)
217 --gd->gd_spinlocks_rd;
221 spin_unlock_rd(struct spinlock *mtx)
223 spin_unlock_rd_quick(mycpu, mtx);
227 spin_init(struct spinlock *mtx)
233 spin_uninit(struct spinlock *mtx)
239 #endif /* _SYS_SPINLOCK2_H_ */