2 * Copyright (c) 2005 Jeffrey M. Hsu. All rights reserved.
4 * This code is derived from software contributed to The DragonFly Project
5 * by Jeffrey M. Hsu. and Matthew Dillon
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/kern/kern_spinlock.c,v 1.16 2008/09/11 01:11:42 y0netan1 Exp $
35 #include <sys/param.h>
36 #include <sys/systm.h>
37 #include <sys/types.h>
38 #include <sys/kernel.h>
39 #include <sys/sysctl.h>
44 #include <machine/atomic.h>
45 #include <machine/cpufunc.h>
46 #include <machine/specialreg.h>
47 #include <machine/clock.h>
48 #include <sys/spinlock.h>
49 #include <sys/spinlock2.h>
52 #define BACKOFF_INITIAL 1
53 #define BACKOFF_LIMIT 256
60 #if !defined(KTR_SPIN_CONTENTION)
61 #define KTR_SPIN_CONTENTION KTR_ALL
63 #define SPIN_STRING "spin=%p type=%c"
64 #define SPIN_ARG_SIZE (sizeof(void *) + sizeof(int))
66 KTR_INFO_MASTER(spin);
67 KTR_INFO(KTR_SPIN_CONTENTION, spin, beg, 0, SPIN_STRING, SPIN_ARG_SIZE);
68 KTR_INFO(KTR_SPIN_CONTENTION, spin, end, 1, SPIN_STRING, SPIN_ARG_SIZE);
69 KTR_INFO(KTR_SPIN_CONTENTION, spin, backoff, 2,
70 "spin=%p bo1=%d thr=%p bo=%d",
71 ((2 * sizeof(void *)) + (2 * sizeof(int))));
72 KTR_INFO(KTR_SPIN_CONTENTION, spin, bofail, 3, SPIN_STRING, SPIN_ARG_SIZE);
74 #define logspin(name, mtx, type) \
75 KTR_LOG(spin_ ## name, mtx, type)
77 #define logspin_backoff(mtx, bo1, thr, bo) \
78 KTR_LOG(spin_backoff, mtx, bo1, thr, bo)
81 static int spin_lock_test_mode;
84 static int64_t spinlocks_contested1;
85 SYSCTL_QUAD(_debug, OID_AUTO, spinlocks_contested1, CTLFLAG_RD,
86 &spinlocks_contested1, 0,
87 "Spinlock contention count due to collisions with exclusive lock holders");
89 static int64_t spinlocks_contested2;
90 SYSCTL_QUAD(_debug, OID_AUTO, spinlocks_contested2, CTLFLAG_RD,
91 &spinlocks_contested2, 0,
92 "Serious spinlock contention count");
94 static int spinlocks_backoff_limit = BACKOFF_LIMIT;
95 SYSCTL_INT(_debug, OID_AUTO, spinlocks_bolim, CTLFLAG_RW,
96 &spinlocks_backoff_limit, 0,
97 "Contested spinlock backoff limit");
99 #define SPINLOCK_NUM_POOL (1024)
100 static struct spinlock pool_spinlocks[SPINLOCK_NUM_POOL];
102 struct exponential_backoff {
105 struct spinlock *mtx;
108 static int exponential_backoff(struct exponential_backoff *bo);
112 exponential_init(struct exponential_backoff *bo, struct spinlock *mtx)
114 bo->backoff = BACKOFF_INITIAL;
117 bo->base = 0; /* silence gcc */
121 * We contested due to another exclusive lock holder. We lose.
124 spin_trylock_wr_contested2(globaldata_t gd)
126 ++spinlocks_contested1;
127 --gd->gd_spinlocks_wr;
128 --gd->gd_curthread->td_critcount;
133 * We were either contested due to another exclusive lock holder,
134 * or due to the presence of shared locks
136 * NOTE: If value indicates an exclusively held mutex, no shared bits
137 * would have been set and we can throw away value.
140 spin_lock_wr_contested2(struct spinlock *mtx)
142 struct exponential_backoff backoff;
146 * Wait until we can gain exclusive access vs another exclusive
149 ++spinlocks_contested1;
150 exponential_init(&backoff, mtx);
152 logspin(beg, mtx, 'w');
154 if (exponential_backoff(&backoff))
156 value = atomic_swap_int(&mtx->lock, SPINLOCK_EXCLUSIVE);
157 } while (value & SPINLOCK_EXCLUSIVE);
158 logspin(end, mtx, 'w');
162 _spin_pool_hash(void *ptr)
165 i = ((int) (uintptr_t) ptr >> 2) ^ ((int) (uintptr_t) ptr >> 12);
166 i &= (SPINLOCK_NUM_POOL - 1);
171 spin_pool_lock(void *chan)
175 sp = &pool_spinlocks[_spin_pool_hash(chan)];
182 spin_pool_unlock(void *chan)
186 sp = &pool_spinlocks[_spin_pool_hash(chan)];
191 * Handle exponential backoff and indefinite waits.
193 * If the system is handling a panic we hand the spinlock over to the caller
194 * after 1 second. After 10 seconds we attempt to print a debugger
195 * backtrace. We also run pending interrupts in order to allow a console
200 exponential_backoff(struct exponential_backoff *bo)
205 #ifdef _RDTSC_SUPPORTED_
206 if (cpu_feature & CPUID_TSC) {
208 (((u_long)rdtsc() ^ (((u_long)curthread) >> 5)) &
209 (bo->backoff - 1)) + BACKOFF_INITIAL;
212 backoff = bo->backoff;
213 logspin_backoff(bo->mtx, bo->backoff, curthread, backoff);
218 for (; backoff; --backoff)
220 if (bo->backoff < spinlocks_backoff_limit) {
224 bo->backoff = BACKOFF_INITIAL;
227 logspin(bofail, bo->mtx, 'u');
232 ++spinlocks_contested2;
233 cpu_spinlock_contested();
235 bo->base = sys_cputimer->count();
239 count = sys_cputimer->count();
240 if (count - bo->base > sys_cputimer->freq) {
241 kprintf("spin_lock: %p, indefinite wait!\n", bo->mtx);
244 #if defined(INVARIANTS)
245 if (spin_lock_test_mode) {
251 #if defined(INVARIANTS)
256 panic("spin_lock: %p, indefinite wait!\n", bo->mtx);
263 * If INVARIANTS is enabled various spinlock timing tests can be run
264 * by setting debug.spin_lock_test:
266 * 1 Test the indefinite wait code
267 * 2 Time the best-case exclusive lock overhead (spin_test_count)
268 * 3 Time the best-case shared lock overhead (spin_test_count)
273 static int spin_test_count = 10000000;
274 SYSCTL_INT(_debug, OID_AUTO, spin_test_count, CTLFLAG_RW, &spin_test_count, 0,
275 "Number of iterations to use for spinlock wait code test");
278 sysctl_spin_lock_test(SYSCTL_HANDLER_ARGS)
285 if ((error = priv_check(curthread, PRIV_ROOT)) != 0)
287 if ((error = SYSCTL_IN(req, &value, sizeof(value))) != 0)
291 * Indefinite wait test
295 spin_lock(&mtx); /* force an indefinite wait */
296 spin_lock_test_mode = 1;
298 spin_unlock(&mtx); /* Clean up the spinlock count */
300 spin_lock_test_mode = 0;
304 * Time best-case exclusive spinlocks
307 globaldata_t gd = mycpu;
310 for (i = spin_test_count; i > 0; --i) {
311 spin_lock_quick(gd, &mtx);
312 spin_unlock_quick(gd, &mtx);
319 SYSCTL_PROC(_debug, KERN_PROC_ALL, spin_lock_test, CTLFLAG_RW|CTLTYPE_INT,
320 0, 0, sysctl_spin_lock_test, "I", "Test spinlock wait code");
322 #endif /* INVARIANTS */