1 /* 2 * Copyright (c) 2005 Jeffrey M. Hsu. All rights reserved. 3 * 4 * This code is derived from software contributed to The DragonFly Project 5 * by Jeffrey M. Hsu. and Matthew Dillon 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 * 32 * $DragonFly: src/sys/kern/kern_spinlock.c,v 1.16 2008/09/11 01:11:42 y0netan1 Exp $ 33 */ 34 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> 40 #ifdef INVARIANTS 41 #include <sys/proc.h> 42 #endif 43 #include <sys/priv.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> 50 #include <sys/ktr.h> 51 52 #define BACKOFF_INITIAL 1 53 #define BACKOFF_LIMIT 256 54 55 #ifdef SMP 56 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 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); 73 74 #define logspin(name, mtx, type) \ 75 KTR_LOG(spin_ ## name, mtx, type) 76 77 #define logspin_backoff(mtx, bo1, thr, bo) \ 78 KTR_LOG(spin_backoff, mtx, bo1, thr, bo) 79 80 #ifdef INVARIANTS 81 static int spin_lock_test_mode; 82 #endif 83 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"); 88 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"); 93 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"); 98 99 struct exponential_backoff { 100 int backoff; 101 int nsec; 102 struct spinlock *mtx; 103 sysclock_t base; 104 }; 105 static int exponential_backoff(struct exponential_backoff *bo); 106 107 static __inline 108 void 109 exponential_init(struct exponential_backoff *bo, struct spinlock *mtx) 110 { 111 bo->backoff = BACKOFF_INITIAL; 112 bo->nsec = 0; 113 bo->mtx = mtx; 114 bo->base = 0; /* silence gcc */ 115 } 116 117 /* 118 * We contested due to another exclusive lock holder. We lose. 119 */ 120 int 121 spin_trylock_wr_contested2(globaldata_t gd) 122 { 123 ++spinlocks_contested1; 124 --gd->gd_spinlocks_wr; 125 --gd->gd_curthread->td_critcount; 126 return (FALSE); 127 } 128 129 /* 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 */ 136 void 137 spin_lock_wr_contested2(struct spinlock *mtx) 138 { 139 struct exponential_backoff backoff; 140 int value; 141 142 /* 143 * Wait until we can gain exclusive access vs another exclusive 144 * holder. 145 */ 146 ++spinlocks_contested1; 147 exponential_init(&backoff, mtx); 148 149 logspin(beg, mtx, 'w'); 150 do { 151 if (exponential_backoff(&backoff)) 152 break; 153 value = atomic_swap_int(&mtx->lock, SPINLOCK_EXCLUSIVE); 154 } while (value & SPINLOCK_EXCLUSIVE); 155 logspin(end, mtx, 'w'); 156 } 157 158 /* 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 */ 166 static 167 int 168 exponential_backoff(struct exponential_backoff *bo) 169 { 170 sysclock_t count; 171 int backoff; 172 173 #ifdef _RDTSC_SUPPORTED_ 174 if (cpu_feature & CPUID_TSC) { 175 backoff = 176 (((u_long)rdtsc() ^ (((u_long)curthread) >> 5)) & 177 (bo->backoff - 1)) + BACKOFF_INITIAL; 178 } else 179 #endif 180 backoff = bo->backoff; 181 logspin_backoff(bo->mtx, bo->backoff, curthread, backoff); 182 183 /* 184 * Quick backoff 185 */ 186 for (; backoff; --backoff) 187 cpu_pause(); 188 if (bo->backoff < spinlocks_backoff_limit) { 189 bo->backoff <<= 1; 190 return (FALSE); 191 } else { 192 bo->backoff = BACKOFF_INITIAL; 193 } 194 195 logspin(bofail, bo->mtx, 'u'); 196 197 /* 198 * Indefinite 199 */ 200 ++spinlocks_contested2; 201 cpu_spinlock_contested(); 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) { 209 kprintf("spin_lock: %p, indefinite wait!\n", bo->mtx); 210 if (panicstr) 211 return (TRUE); 212 #if defined(INVARIANTS) 213 if (spin_lock_test_mode) { 214 print_backtrace(-1); 215 return (TRUE); 216 } 217 #endif 218 ++bo->nsec; 219 #if defined(INVARIANTS) 220 if (bo->nsec == 11) 221 print_backtrace(-1); 222 #endif 223 if (bo->nsec == 60) 224 panic("spin_lock: %p, indefinite wait!\n", bo->mtx); 225 bo->base = count; 226 } 227 return (FALSE); 228 } 229 230 /* 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) 237 */ 238 239 #ifdef INVARIANTS 240 241 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"); 244 245 static int 246 sysctl_spin_lock_test(SYSCTL_HANDLER_ARGS) 247 { 248 struct spinlock mtx; 249 int error; 250 int value = 0; 251 int i; 252 253 if ((error = priv_check(curthread, PRIV_ROOT)) != 0) 254 return (error); 255 if ((error = SYSCTL_IN(req, &value, sizeof(value))) != 0) 256 return (error); 257 258 /* 259 * Indefinite wait test 260 */ 261 if (value == 1) { 262 spin_init(&mtx); 263 spin_lock(&mtx); /* force an indefinite wait */ 264 spin_lock_test_mode = 1; 265 spin_lock(&mtx); 266 spin_unlock(&mtx); /* Clean up the spinlock count */ 267 spin_unlock(&mtx); 268 spin_lock_test_mode = 0; 269 } 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) { 279 spin_lock_quick(gd, &mtx); 280 spin_unlock_quick(gd, &mtx); 281 } 282 } 283 284 return (0); 285 } 286 287 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"); 289 290 #endif /* INVARIANTS */ 291 #endif /* SMP */ 292