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, "");
88 static int64_t spinlocks_contested2;
89 SYSCTL_QUAD(_debug, OID_AUTO, spinlocks_contested2, CTLFLAG_RD,
90 &spinlocks_contested2, 0, "");
92 static int spinlocks_backoff_limit = BACKOFF_LIMIT;
93 SYSCTL_INT(_debug, OID_AUTO, spinlocks_bolim, CTLFLAG_RW,
94 &spinlocks_backoff_limit, 0, "");
96 struct exponential_backoff {
102 static int exponential_backoff(struct exponential_backoff *bo);
106 exponential_init(struct exponential_backoff *bo, struct spinlock *mtx)
108 bo->backoff = BACKOFF_INITIAL;
111 bo->base = 0; /* silence gcc */
115 * We contested due to another exclusive lock holder. We lose.
118 spin_trylock_wr_contested2(globaldata_t gd)
120 ++spinlocks_contested1;
121 --gd->gd_spinlocks_wr;
122 --gd->gd_curthread->td_critcount;
127 * We were either contested due to another exclusive lock holder,
128 * or due to the presence of shared locks
130 * NOTE: If value indicates an exclusively held mutex, no shared bits
131 * would have been set and we can throw away value.
134 spin_lock_wr_contested2(struct spinlock *mtx)
136 struct exponential_backoff backoff;
140 * Wait until we can gain exclusive access vs another exclusive
143 ++spinlocks_contested1;
144 exponential_init(&backoff, mtx);
146 logspin(beg, mtx, 'w');
148 if (exponential_backoff(&backoff))
150 value = atomic_swap_int(&mtx->lock, SPINLOCK_EXCLUSIVE);
151 } while (value & SPINLOCK_EXCLUSIVE);
152 logspin(end, mtx, 'w');
156 * Handle exponential backoff and indefinite waits.
158 * If the system is handling a panic we hand the spinlock over to the caller
159 * after 1 second. After 10 seconds we attempt to print a debugger
160 * backtrace. We also run pending interrupts in order to allow a console
165 exponential_backoff(struct exponential_backoff *bo)
170 #ifdef _RDTSC_SUPPORTED_
171 if (cpu_feature & CPUID_TSC) {
173 (((u_long)rdtsc() ^ (((u_long)curthread) >> 5)) &
174 (bo->backoff - 1)) + BACKOFF_INITIAL;
177 backoff = bo->backoff;
178 logspin_backoff(bo->mtx, bo->backoff, curthread, backoff);
183 for (; backoff; --backoff)
185 if (bo->backoff < spinlocks_backoff_limit) {
189 bo->backoff = BACKOFF_INITIAL;
192 logspin(bofail, bo->mtx, 'u');
197 ++spinlocks_contested2;
198 cpu_spinlock_contested();
200 bo->base = sys_cputimer->count();
204 count = sys_cputimer->count();
205 if (count - bo->base > sys_cputimer->freq) {
206 kprintf("spin_lock: %p, indefinite wait!\n", bo->mtx);
209 #if defined(INVARIANTS)
210 if (spin_lock_test_mode) {
216 #if defined(INVARIANTS)
221 panic("spin_lock: %p, indefinite wait!\n", bo->mtx);
228 * If INVARIANTS is enabled various spinlock timing tests can be run
229 * by setting debug.spin_lock_test:
231 * 1 Test the indefinite wait code
232 * 2 Time the best-case exclusive lock overhead (spin_test_count)
233 * 3 Time the best-case shared lock overhead (spin_test_count)
238 static int spin_test_count = 10000000;
239 SYSCTL_INT(_debug, OID_AUTO, spin_test_count, CTLFLAG_RW, &spin_test_count, 0, "");
242 sysctl_spin_lock_test(SYSCTL_HANDLER_ARGS)
249 if ((error = priv_check(curthread, PRIV_ROOT)) != 0)
251 if ((error = SYSCTL_IN(req, &value, sizeof(value))) != 0)
255 * Indefinite wait test
259 spin_lock(&mtx); /* force an indefinite wait */
260 spin_lock_test_mode = 1;
262 spin_unlock(&mtx); /* Clean up the spinlock count */
264 spin_lock_test_mode = 0;
268 * Time best-case exclusive spinlocks
271 globaldata_t gd = mycpu;
274 for (i = spin_test_count; i > 0; --i) {
275 spin_lock_wr_quick(gd, &mtx);
276 spin_unlock_wr_quick(gd, &mtx);
283 SYSCTL_PROC(_debug, KERN_PROC_ALL, spin_lock_test, CTLFLAG_RW|CTLTYPE_INT,
284 0, 0, sysctl_spin_lock_test, "I", "Test spinlock wait code");
286 #endif /* INVARIANTS */