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 #define SPINLOCK_NUM_POOL (1024) 100 static struct spinlock pool_spinlocks[SPINLOCK_NUM_POOL]; 101 102 struct exponential_backoff { 103 int backoff; 104 int nsec; 105 struct spinlock *mtx; 106 sysclock_t base; 107 }; 108 static int exponential_backoff(struct exponential_backoff *bo); 109 110 static __inline 111 void 112 exponential_init(struct exponential_backoff *bo, struct spinlock *mtx) 113 { 114 bo->backoff = BACKOFF_INITIAL; 115 bo->nsec = 0; 116 bo->mtx = mtx; 117 bo->base = 0; /* silence gcc */ 118 } 119 120 /* 121 * We contested due to another exclusive lock holder. We lose. 122 */ 123 int 124 spin_trylock_wr_contested2(globaldata_t gd) 125 { 126 ++spinlocks_contested1; 127 --gd->gd_spinlocks_wr; 128 --gd->gd_curthread->td_critcount; 129 return (FALSE); 130 } 131 132 /* 133 * We were either contested due to another exclusive lock holder, 134 * or due to the presence of shared locks 135 * 136 * NOTE: If value indicates an exclusively held mutex, no shared bits 137 * would have been set and we can throw away value. 138 */ 139 void 140 spin_lock_wr_contested2(struct spinlock *mtx) 141 { 142 struct exponential_backoff backoff; 143 int value; 144 145 /* 146 * Wait until we can gain exclusive access vs another exclusive 147 * holder. 148 */ 149 ++spinlocks_contested1; 150 exponential_init(&backoff, mtx); 151 152 logspin(beg, mtx, 'w'); 153 do { 154 if (exponential_backoff(&backoff)) 155 break; 156 value = atomic_swap_int(&mtx->lock, SPINLOCK_EXCLUSIVE); 157 } while (value & SPINLOCK_EXCLUSIVE); 158 logspin(end, mtx, 'w'); 159 } 160 161 static __inline int 162 _spin_pool_hash(void *ptr) 163 { 164 int i; 165 i = ((int) (uintptr_t) ptr >> 2) ^ ((int) (uintptr_t) ptr >> 12); 166 i &= (SPINLOCK_NUM_POOL - 1); 167 return (i); 168 } 169 170 struct spinlock * 171 spin_pool_lock(void *chan) 172 { 173 struct spinlock *sp; 174 175 sp = &pool_spinlocks[_spin_pool_hash(chan)]; 176 spin_lock(sp); 177 178 return (sp); 179 } 180 181 void 182 spin_pool_unlock(void *chan) 183 { 184 struct spinlock *sp; 185 186 sp = &pool_spinlocks[_spin_pool_hash(chan)]; 187 spin_unlock(sp); 188 } 189 190 /* 191 * Handle exponential backoff and indefinite waits. 192 * 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 196 * break into DDB. 197 */ 198 static 199 int 200 exponential_backoff(struct exponential_backoff *bo) 201 { 202 sysclock_t count; 203 int backoff; 204 205 #ifdef _RDTSC_SUPPORTED_ 206 if (cpu_feature & CPUID_TSC) { 207 backoff = 208 (((u_long)rdtsc() ^ (((u_long)curthread) >> 5)) & 209 (bo->backoff - 1)) + BACKOFF_INITIAL; 210 } else 211 #endif 212 backoff = bo->backoff; 213 logspin_backoff(bo->mtx, bo->backoff, curthread, backoff); 214 215 /* 216 * Quick backoff 217 */ 218 for (; backoff; --backoff) 219 cpu_pause(); 220 if (bo->backoff < spinlocks_backoff_limit) { 221 bo->backoff <<= 1; 222 return (FALSE); 223 } else { 224 bo->backoff = BACKOFF_INITIAL; 225 } 226 227 logspin(bofail, bo->mtx, 'u'); 228 229 /* 230 * Indefinite 231 */ 232 ++spinlocks_contested2; 233 cpu_spinlock_contested(); 234 if (bo->nsec == 0) { 235 bo->base = sys_cputimer->count(); 236 bo->nsec = 1; 237 } 238 239 count = sys_cputimer->count(); 240 if (count - bo->base > sys_cputimer->freq) { 241 kprintf("spin_lock: %p, indefinite wait!\n", bo->mtx); 242 if (panicstr) 243 return (TRUE); 244 #if defined(INVARIANTS) 245 if (spin_lock_test_mode) { 246 print_backtrace(-1); 247 return (TRUE); 248 } 249 #endif 250 ++bo->nsec; 251 #if defined(INVARIANTS) 252 if (bo->nsec == 11) 253 print_backtrace(-1); 254 #endif 255 if (bo->nsec == 60) 256 panic("spin_lock: %p, indefinite wait!\n", bo->mtx); 257 bo->base = count; 258 } 259 return (FALSE); 260 } 261 262 /* 263 * If INVARIANTS is enabled various spinlock timing tests can be run 264 * by setting debug.spin_lock_test: 265 * 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) 269 */ 270 271 #ifdef INVARIANTS 272 273 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"); 276 277 static int 278 sysctl_spin_lock_test(SYSCTL_HANDLER_ARGS) 279 { 280 struct spinlock mtx; 281 int error; 282 int value = 0; 283 int i; 284 285 if ((error = priv_check(curthread, PRIV_ROOT)) != 0) 286 return (error); 287 if ((error = SYSCTL_IN(req, &value, sizeof(value))) != 0) 288 return (error); 289 290 /* 291 * Indefinite wait test 292 */ 293 if (value == 1) { 294 spin_init(&mtx); 295 spin_lock(&mtx); /* force an indefinite wait */ 296 spin_lock_test_mode = 1; 297 spin_lock(&mtx); 298 spin_unlock(&mtx); /* Clean up the spinlock count */ 299 spin_unlock(&mtx); 300 spin_lock_test_mode = 0; 301 } 302 303 /* 304 * Time best-case exclusive spinlocks 305 */ 306 if (value == 2) { 307 globaldata_t gd = mycpu; 308 309 spin_init(&mtx); 310 for (i = spin_test_count; i > 0; --i) { 311 spin_lock_quick(gd, &mtx); 312 spin_unlock_quick(gd, &mtx); 313 } 314 } 315 316 return (0); 317 } 318 319 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"); 321 322 #endif /* INVARIANTS */ 323 #endif /* SMP */ 324