kernel - Provide descriptions for lwkt.* and debug.* sysctl's
[dragonfly.git] / sys / kern / kern_spinlock.c
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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
d666840a 5 * by Jeffrey M. Hsu. and Matthew Dillon
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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 *
1541028a 32 * $DragonFly: src/sys/kern/kern_spinlock.c,v 1.16 2008/09/11 01:11:42 y0netan1 Exp $
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33 */
34
35#include <sys/param.h>
b02926de 36#include <sys/systm.h>
b1af91cb 37#include <sys/types.h>
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38#include <sys/kernel.h>
39#include <sys/sysctl.h>
40#ifdef INVARIANTS
41#include <sys/proc.h>
42#endif
895c1f85 43#include <sys/priv.h>
b1af91cb 44#include <machine/atomic.h>
b02926de 45#include <machine/cpufunc.h>
10c66d57 46#include <machine/specialreg.h>
b02926de 47#include <machine/clock.h>
b1af91cb 48#include <sys/spinlock.h>
35a832df 49#include <sys/spinlock2.h>
57aa743c 50#include <sys/ktr.h>
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51
52#define BACKOFF_INITIAL 1
53#define BACKOFF_LIMIT 256
54
55#ifdef SMP
56
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57/*
58 * Kernal Trace
59 */
60#if !defined(KTR_SPIN_CONTENTION)
61#define KTR_SPIN_CONTENTION KTR_ALL
62#endif
63#define SPIN_STRING "spin=%p type=%c"
64#define SPIN_ARG_SIZE (sizeof(void *) + sizeof(int))
65
66KTR_INFO_MASTER(spin);
67KTR_INFO(KTR_SPIN_CONTENTION, spin, beg, 0, SPIN_STRING, SPIN_ARG_SIZE);
68KTR_INFO(KTR_SPIN_CONTENTION, spin, end, 1, SPIN_STRING, SPIN_ARG_SIZE);
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69KTR_INFO(KTR_SPIN_CONTENTION, spin, backoff, 2,
70 "spin=%p bo1=%d thr=%p bo=%d",
71 ((2 * sizeof(void *)) + (2 * sizeof(int))));
72KTR_INFO(KTR_SPIN_CONTENTION, spin, bofail, 3, SPIN_STRING, SPIN_ARG_SIZE);
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73
74#define logspin(name, mtx, type) \
75 KTR_LOG(spin_ ## name, mtx, type)
76
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77#define logspin_backoff(mtx, bo1, thr, bo) \
78 KTR_LOG(spin_backoff, mtx, bo1, thr, bo)
79
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80#ifdef INVARIANTS
81static int spin_lock_test_mode;
82#endif
83
84static int64_t spinlocks_contested1;
10c66d57 85SYSCTL_QUAD(_debug, OID_AUTO, spinlocks_contested1, CTLFLAG_RD,
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86 &spinlocks_contested1, 0,
87 "Spinlock contention count due to collisions with exclusive lock holders");
10c66d57 88
b02926de 89static int64_t spinlocks_contested2;
10c66d57 90SYSCTL_QUAD(_debug, OID_AUTO, spinlocks_contested2, CTLFLAG_RD,
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91 &spinlocks_contested2, 0,
92 "Serious spinlock contention count");
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93
94static int spinlocks_backoff_limit = BACKOFF_LIMIT;
95SYSCTL_INT(_debug, OID_AUTO, spinlocks_bolim, CTLFLAG_RW,
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96 &spinlocks_backoff_limit, 0,
97 "Contested spinlock backoff limit");
b02926de 98
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99struct exponential_backoff {
100 int backoff;
101 int nsec;
102 struct spinlock *mtx;
103 sysclock_t base;
104};
105static int exponential_backoff(struct exponential_backoff *bo);
106
107static __inline
b1af91cb 108void
d666840a 109exponential_init(struct exponential_backoff *bo, struct spinlock *mtx)
b1af91cb 110{
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111 bo->backoff = BACKOFF_INITIAL;
112 bo->nsec = 0;
113 bo->mtx = mtx;
8f165b8c 114 bo->base = 0; /* silence gcc */
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115}
116
117/*
8f165b8c 118 * We contested due to another exclusive lock holder. We lose.
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119 */
120int
8f165b8c 121spin_trylock_wr_contested2(globaldata_t gd)
d666840a 122{
b02926de 123 ++spinlocks_contested1;
74af985e 124 --gd->gd_spinlocks_wr;
77912481 125 --gd->gd_curthread->td_critcount;
d666840a 126 return (FALSE);
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127}
128
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129/*
130 * We were either contested due to another exclusive lock holder,
131 * or due to the presence of shared locks
132 *
133 * NOTE: If value indicates an exclusively held mutex, no shared bits
134 * would have been set and we can throw away value.
135 */
136void
8f165b8c 137spin_lock_wr_contested2(struct spinlock *mtx)
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138{
139 struct exponential_backoff backoff;
8f165b8c 140 int value;
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141
142 /*
143 * Wait until we can gain exclusive access vs another exclusive
144 * holder.
145 */
d666840a 146 ++spinlocks_contested1;
8f165b8c 147 exponential_init(&backoff, mtx);
d666840a 148
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149 logspin(beg, mtx, 'w');
150 do {
151 if (exponential_backoff(&backoff))
d666840a 152 break;
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153 value = atomic_swap_int(&mtx->lock, SPINLOCK_EXCLUSIVE);
154 } while (value & SPINLOCK_EXCLUSIVE);
57aa743c 155 logspin(end, mtx, 'w');
d666840a 156}
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157
158/*
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159 * Handle exponential backoff and indefinite waits.
160 *
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
164 * break into DDB.
165 */
166static
167int
168exponential_backoff(struct exponential_backoff *bo)
b02926de 169{
b02926de 170 sysclock_t count;
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171 int backoff;
172
173#ifdef _RDTSC_SUPPORTED_
174 if (cpu_feature & CPUID_TSC) {
175 backoff =
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176 (((u_long)rdtsc() ^ (((u_long)curthread) >> 5)) &
177 (bo->backoff - 1)) + BACKOFF_INITIAL;
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178 } else
179#endif
180 backoff = bo->backoff;
181 logspin_backoff(bo->mtx, bo->backoff, curthread, backoff);
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182
183 /*
184 * Quick backoff
185 */
10c66d57 186 for (; backoff; --backoff)
14dd663d 187 cpu_pause();
10c66d57 188 if (bo->backoff < spinlocks_backoff_limit) {
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189 bo->backoff <<= 1;
190 return (FALSE);
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191 } else {
192 bo->backoff = BACKOFF_INITIAL;
d666840a 193 }
b02926de 194
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195 logspin(bofail, bo->mtx, 'u');
196
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197 /*
198 * Indefinite
199 */
b02926de 200 ++spinlocks_contested2;
06615ccb 201 cpu_spinlock_contested();
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202 if (bo->nsec == 0) {
203 bo->base = sys_cputimer->count();
204 bo->nsec = 1;
205 }
206
207 count = sys_cputimer->count();
208 if (count - bo->base > sys_cputimer->freq) {
6ea70f76 209 kprintf("spin_lock: %p, indefinite wait!\n", bo->mtx);
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210 if (panicstr)
211 return (TRUE);
1e5fb84b 212#if defined(INVARIANTS)
d666840a 213 if (spin_lock_test_mode) {
7ce2998e 214 print_backtrace(-1);
d666840a 215 return (TRUE);
b02926de 216 }
d666840a 217#endif
b526356c 218 ++bo->nsec;
1e5fb84b 219#if defined(INVARIANTS)
b526356c 220 if (bo->nsec == 11)
7ce2998e 221 print_backtrace(-1);
b526356c 222#endif
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223 if (bo->nsec == 60)
224 panic("spin_lock: %p, indefinite wait!\n", bo->mtx);
d666840a 225 bo->base = count;
b02926de 226 }
d666840a 227 return (FALSE);
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228}
229
230/*
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231 * If INVARIANTS is enabled various spinlock timing tests can be run
232 * by setting debug.spin_lock_test:
233 *
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)
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237 */
238
239#ifdef INVARIANTS
240
d666840a 241static int spin_test_count = 10000000;
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242SYSCTL_INT(_debug, OID_AUTO, spin_test_count, CTLFLAG_RW, &spin_test_count, 0,
243 "Number of iterations to use for spinlock wait code test");
d666840a 244
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245static int
246sysctl_spin_lock_test(SYSCTL_HANDLER_ARGS)
247{
248 struct spinlock mtx;
249 int error;
250 int value = 0;
d666840a 251 int i;
b02926de 252
895c1f85 253 if ((error = priv_check(curthread, PRIV_ROOT)) != 0)
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254 return (error);
255 if ((error = SYSCTL_IN(req, &value, sizeof(value))) != 0)
256 return (error);
257
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258 /*
259 * Indefinite wait test
260 */
b02926de 261 if (value == 1) {
d666840a 262 spin_init(&mtx);
287a8577 263 spin_lock(&mtx); /* force an indefinite wait */
b02926de 264 spin_lock_test_mode = 1;
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265 spin_lock(&mtx);
266 spin_unlock(&mtx); /* Clean up the spinlock count */
267 spin_unlock(&mtx);
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268 spin_lock_test_mode = 0;
269 }
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270
271 /*
272 * Time best-case exclusive spinlocks
273 */
274 if (value == 2) {
275 globaldata_t gd = mycpu;
276
277 spin_init(&mtx);
278 for (i = spin_test_count; i > 0; --i) {
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279 spin_lock_quick(gd, &mtx);
280 spin_unlock_quick(gd, &mtx);
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281 }
282 }
283
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284 return (0);
285}
286
287SYSCTL_PROC(_debug, KERN_PROC_ALL, spin_lock_test, CTLFLAG_RW|CTLTYPE_INT,
288 0, 0, sysctl_spin_lock_test, "I", "Test spinlock wait code");
289
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290#endif /* INVARIANTS */
291#endif /* SMP */