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 struct exponential_backoff {
102 struct spinlock *mtx;
105 static int exponential_backoff(struct exponential_backoff *bo);
109 exponential_init(struct exponential_backoff *bo, struct spinlock *mtx)
111 bo->backoff = BACKOFF_INITIAL;
114 bo->base = 0; /* silence gcc */
118 * We contested due to another exclusive lock holder. We lose.
121 spin_trylock_wr_contested2(globaldata_t gd)
123 ++spinlocks_contested1;
124 --gd->gd_spinlocks_wr;
125 --gd->gd_curthread->td_critcount;
130 * We were either contested due to another exclusive lock holder,
131 * or due to the presence of shared locks
133 * NOTE: If value indicates an exclusively held mutex, no shared bits
134 * would have been set and we can throw away value.
137 spin_lock_wr_contested2(struct spinlock *mtx)
139 struct exponential_backoff backoff;
143 * Wait until we can gain exclusive access vs another exclusive
146 ++spinlocks_contested1;
147 exponential_init(&backoff, mtx);
149 logspin(beg, mtx, 'w');
151 if (exponential_backoff(&backoff))
153 value = atomic_swap_int(&mtx->lock, SPINLOCK_EXCLUSIVE);
154 } while (value & SPINLOCK_EXCLUSIVE);
155 logspin(end, mtx, 'w');
159 * Handle exponential backoff and indefinite waits.
161 * If the system is handling a panic we hand the spinlock over to the caller
162 * after 1 second. After 10 seconds we attempt to print a debugger
163 * backtrace. We also run pending interrupts in order to allow a console
168 exponential_backoff(struct exponential_backoff *bo)
173 #ifdef _RDTSC_SUPPORTED_
174 if (cpu_feature & CPUID_TSC) {
176 (((u_long)rdtsc() ^ (((u_long)curthread) >> 5)) &
177 (bo->backoff - 1)) + BACKOFF_INITIAL;
180 backoff = bo->backoff;
181 logspin_backoff(bo->mtx, bo->backoff, curthread, backoff);
186 for (; backoff; --backoff)
188 if (bo->backoff < spinlocks_backoff_limit) {
192 bo->backoff = BACKOFF_INITIAL;
195 logspin(bofail, bo->mtx, 'u');
200 ++spinlocks_contested2;
201 cpu_spinlock_contested();
203 bo->base = sys_cputimer->count();
207 count = sys_cputimer->count();
208 if (count - bo->base > sys_cputimer->freq) {
209 kprintf("spin_lock: %p, indefinite wait!\n", bo->mtx);
212 #if defined(INVARIANTS)
213 if (spin_lock_test_mode) {
219 #if defined(INVARIANTS)
224 panic("spin_lock: %p, indefinite wait!\n", bo->mtx);
231 * If INVARIANTS is enabled various spinlock timing tests can be run
232 * by setting debug.spin_lock_test:
234 * 1 Test the indefinite wait code
235 * 2 Time the best-case exclusive lock overhead (spin_test_count)
236 * 3 Time the best-case shared lock overhead (spin_test_count)
241 static int spin_test_count = 10000000;
242 SYSCTL_INT(_debug, OID_AUTO, spin_test_count, CTLFLAG_RW, &spin_test_count, 0,
243 "Number of iterations to use for spinlock wait code test");
246 sysctl_spin_lock_test(SYSCTL_HANDLER_ARGS)
253 if ((error = priv_check(curthread, PRIV_ROOT)) != 0)
255 if ((error = SYSCTL_IN(req, &value, sizeof(value))) != 0)
259 * Indefinite wait test
263 spin_lock(&mtx); /* force an indefinite wait */
264 spin_lock_test_mode = 1;
266 spin_unlock(&mtx); /* Clean up the spinlock count */
268 spin_lock_test_mode = 0;
272 * Time best-case exclusive spinlocks
275 globaldata_t gd = mycpu;
278 for (i = spin_test_count; i > 0; --i) {
279 spin_lock_quick(gd, &mtx);
280 spin_unlock_quick(gd, &mtx);
287 SYSCTL_PROC(_debug, KERN_PROC_ALL, spin_lock_test, CTLFLAG_RW|CTLTYPE_INT,
288 0, 0, sysctl_spin_lock_test, "I", "Test spinlock wait code");
290 #endif /* INVARIANTS */