1 /*- 2 * Copyright (c) 2001 Jake Burkholder <jake@FreeBSD.org> 3 * All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * 1. Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * 2. Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in the 12 * documentation and/or other materials provided with the distribution. 13 * 14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 15 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 17 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 18 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 19 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 20 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 21 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 22 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 23 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 24 * SUCH DAMAGE. 25 */ 26 27 28 #include <sys/cdefs.h> 29 __FBSDID("$FreeBSD$"); 30 31 #include "opt_sched.h" 32 33 #include <sys/param.h> 34 #include <sys/systm.h> 35 #include <sys/kdb.h> 36 #include <sys/kernel.h> 37 #include <sys/ktr.h> 38 #include <sys/lock.h> 39 #include <sys/mutex.h> 40 #include <sys/proc.h> 41 #include <sys/queue.h> 42 #include <sys/sched.h> 43 #include <sys/smp.h> 44 #include <sys/sysctl.h> 45 46 #include <machine/cpu.h> 47 48 /* Uncomment this to enable logging of critical_enter/exit. */ 49 #if 0 50 #define KTR_CRITICAL KTR_SCHED 51 #else 52 #define KTR_CRITICAL 0 53 #endif 54 55 #ifdef FULL_PREEMPTION 56 #ifndef PREEMPTION 57 #error "The FULL_PREEMPTION option requires the PREEMPTION option" 58 #endif 59 #endif 60 61 CTASSERT((RQB_BPW * RQB_LEN) == RQ_NQS); 62 63 /* 64 * kern.sched.preemption allows user space to determine if preemption support 65 * is compiled in or not. It is not currently a boot or runtime flag that 66 * can be changed. 67 */ 68 #ifdef PREEMPTION 69 static int kern_sched_preemption = 1; 70 #else 71 static int kern_sched_preemption = 0; 72 #endif 73 SYSCTL_INT(_kern_sched, OID_AUTO, preemption, CTLFLAG_RD, 74 &kern_sched_preemption, 0, "Kernel preemption enabled"); 75 76 /* 77 * Support for scheduler stats exported via kern.sched.stats. All stats may 78 * be reset with kern.sched.stats.reset = 1. Stats may be defined elsewhere 79 * with SCHED_STAT_DEFINE(). 80 */ 81 #ifdef SCHED_STATS 82 SYSCTL_NODE(_kern_sched, OID_AUTO, stats, CTLFLAG_RW, 0, "switch stats"); 83 84 /* Switch reasons from mi_switch(). */ 85 DPCPU_DEFINE(long, sched_switch_stats[SWT_COUNT]); 86 SCHED_STAT_DEFINE_VAR(uncategorized, 87 &DPCPU_NAME(sched_switch_stats[SWT_NONE]), ""); 88 SCHED_STAT_DEFINE_VAR(preempt, 89 &DPCPU_NAME(sched_switch_stats[SWT_PREEMPT]), ""); 90 SCHED_STAT_DEFINE_VAR(owepreempt, 91 &DPCPU_NAME(sched_switch_stats[SWT_OWEPREEMPT]), ""); 92 SCHED_STAT_DEFINE_VAR(turnstile, 93 &DPCPU_NAME(sched_switch_stats[SWT_TURNSTILE]), ""); 94 SCHED_STAT_DEFINE_VAR(sleepq, 95 &DPCPU_NAME(sched_switch_stats[SWT_SLEEPQ]), ""); 96 SCHED_STAT_DEFINE_VAR(sleepqtimo, 97 &DPCPU_NAME(sched_switch_stats[SWT_SLEEPQTIMO]), ""); 98 SCHED_STAT_DEFINE_VAR(relinquish, 99 &DPCPU_NAME(sched_switch_stats[SWT_RELINQUISH]), ""); 100 SCHED_STAT_DEFINE_VAR(needresched, 101 &DPCPU_NAME(sched_switch_stats[SWT_NEEDRESCHED]), ""); 102 SCHED_STAT_DEFINE_VAR(idle, 103 &DPCPU_NAME(sched_switch_stats[SWT_IDLE]), ""); 104 SCHED_STAT_DEFINE_VAR(iwait, 105 &DPCPU_NAME(sched_switch_stats[SWT_IWAIT]), ""); 106 SCHED_STAT_DEFINE_VAR(suspend, 107 &DPCPU_NAME(sched_switch_stats[SWT_SUSPEND]), ""); 108 SCHED_STAT_DEFINE_VAR(remotepreempt, 109 &DPCPU_NAME(sched_switch_stats[SWT_REMOTEPREEMPT]), ""); 110 SCHED_STAT_DEFINE_VAR(remotewakeidle, 111 &DPCPU_NAME(sched_switch_stats[SWT_REMOTEWAKEIDLE]), ""); 112 113 static int 114 sysctl_stats_reset(SYSCTL_HANDLER_ARGS) 115 { 116 struct sysctl_oid *p; 117 uintptr_t counter; 118 int error; 119 int val; 120 int i; 121 122 val = 0; 123 error = sysctl_handle_int(oidp, &val, 0, req); 124 if (error != 0 || req->newptr == NULL) 125 return (error); 126 if (val == 0) 127 return (0); 128 /* 129 * Traverse the list of children of _kern_sched_stats and reset each 130 * to 0. Skip the reset entry. 131 */ 132 SLIST_FOREACH(p, oidp->oid_parent, oid_link) { 133 if (p == oidp || p->oid_arg1 == NULL) 134 continue; 135 counter = (uintptr_t)p->oid_arg1; 136 CPU_FOREACH(i) { 137 *(long *)(dpcpu_off[i] + counter) = 0; 138 } 139 } 140 return (0); 141 } 142 143 SYSCTL_PROC(_kern_sched_stats, OID_AUTO, reset, CTLTYPE_INT | CTLFLAG_WR, NULL, 144 0, sysctl_stats_reset, "I", "Reset scheduler statistics"); 145 #endif 146 147 /************************************************************************ 148 * Functions that manipulate runnability from a thread perspective. * 149 ************************************************************************/ 150 /* 151 * Select the thread that will be run next. 152 */ 153 struct thread * 154 choosethread(void) 155 { 156 struct thread *td; 157 158 retry: 159 td = sched_choose(); 160 161 /* 162 * If we are in panic, only allow system threads, 163 * plus the one we are running in, to be run. 164 */ 165 if (panicstr && ((td->td_proc->p_flag & P_SYSTEM) == 0 && 166 (td->td_flags & TDF_INPANIC) == 0)) { 167 /* note that it is no longer on the run queue */ 168 TD_SET_CAN_RUN(td); 169 goto retry; 170 } 171 172 TD_SET_RUNNING(td); 173 return (td); 174 } 175 176 /* 177 * Kernel thread preemption implementation. Critical sections mark 178 * regions of code in which preemptions are not allowed. 179 */ 180 void 181 critical_enter(void) 182 { 183 struct thread *td; 184 185 td = curthread; 186 td->td_critnest++; 187 CTR4(KTR_CRITICAL, "critical_enter by thread %p (%ld, %s) to %d", td, 188 (long)td->td_proc->p_pid, td->td_name, td->td_critnest); 189 } 190 191 void 192 critical_exit(void) 193 { 194 struct thread *td; 195 int flags; 196 197 td = curthread; 198 KASSERT(td->td_critnest != 0, 199 ("critical_exit: td_critnest == 0")); 200 201 if (td->td_critnest == 1) { 202 td->td_critnest = 0; 203 if (td->td_owepreempt) { 204 td->td_critnest = 1; 205 thread_lock(td); 206 td->td_critnest--; 207 flags = SW_INVOL | SW_PREEMPT; 208 if (TD_IS_IDLETHREAD(td)) 209 flags |= SWT_IDLE; 210 else 211 flags |= SWT_OWEPREEMPT; 212 mi_switch(flags, NULL); 213 thread_unlock(td); 214 } 215 } else 216 td->td_critnest--; 217 218 CTR4(KTR_CRITICAL, "critical_exit by thread %p (%ld, %s) to %d", td, 219 (long)td->td_proc->p_pid, td->td_name, td->td_critnest); 220 } 221 222 /************************************************************************ 223 * SYSTEM RUN QUEUE manipulations and tests * 224 ************************************************************************/ 225 /* 226 * Initialize a run structure. 227 */ 228 void 229 runq_init(struct runq *rq) 230 { 231 int i; 232 233 bzero(rq, sizeof *rq); 234 for (i = 0; i < RQ_NQS; i++) 235 TAILQ_INIT(&rq->rq_queues[i]); 236 } 237 238 /* 239 * Clear the status bit of the queue corresponding to priority level pri, 240 * indicating that it is empty. 241 */ 242 static __inline void 243 runq_clrbit(struct runq *rq, int pri) 244 { 245 struct rqbits *rqb; 246 247 rqb = &rq->rq_status; 248 CTR4(KTR_RUNQ, "runq_clrbit: bits=%#x %#x bit=%#x word=%d", 249 rqb->rqb_bits[RQB_WORD(pri)], 250 rqb->rqb_bits[RQB_WORD(pri)] & ~RQB_BIT(pri), 251 RQB_BIT(pri), RQB_WORD(pri)); 252 rqb->rqb_bits[RQB_WORD(pri)] &= ~RQB_BIT(pri); 253 } 254 255 /* 256 * Find the index of the first non-empty run queue. This is done by 257 * scanning the status bits, a set bit indicates a non-empty queue. 258 */ 259 static __inline int 260 runq_findbit(struct runq *rq) 261 { 262 struct rqbits *rqb; 263 int pri; 264 int i; 265 266 rqb = &rq->rq_status; 267 for (i = 0; i < RQB_LEN; i++) 268 if (rqb->rqb_bits[i]) { 269 pri = RQB_FFS(rqb->rqb_bits[i]) + (i << RQB_L2BPW); 270 CTR3(KTR_RUNQ, "runq_findbit: bits=%#x i=%d pri=%d", 271 rqb->rqb_bits[i], i, pri); 272 return (pri); 273 } 274 275 return (-1); 276 } 277 278 static __inline int 279 runq_findbit_from(struct runq *rq, u_char pri) 280 { 281 struct rqbits *rqb; 282 rqb_word_t mask; 283 int i; 284 285 /* 286 * Set the mask for the first word so we ignore priorities before 'pri'. 287 */ 288 mask = (rqb_word_t)-1 << (pri & (RQB_BPW - 1)); 289 rqb = &rq->rq_status; 290 again: 291 for (i = RQB_WORD(pri); i < RQB_LEN; mask = -1, i++) { 292 mask = rqb->rqb_bits[i] & mask; 293 if (mask == 0) 294 continue; 295 pri = RQB_FFS(mask) + (i << RQB_L2BPW); 296 CTR3(KTR_RUNQ, "runq_findbit_from: bits=%#x i=%d pri=%d", 297 mask, i, pri); 298 return (pri); 299 } 300 if (pri == 0) 301 return (-1); 302 /* 303 * Wrap back around to the beginning of the list just once so we 304 * scan the whole thing. 305 */ 306 pri = 0; 307 goto again; 308 } 309 310 /* 311 * Set the status bit of the queue corresponding to priority level pri, 312 * indicating that it is non-empty. 313 */ 314 static __inline void 315 runq_setbit(struct runq *rq, int pri) 316 { 317 struct rqbits *rqb; 318 319 rqb = &rq->rq_status; 320 CTR4(KTR_RUNQ, "runq_setbit: bits=%#x %#x bit=%#x word=%d", 321 rqb->rqb_bits[RQB_WORD(pri)], 322 rqb->rqb_bits[RQB_WORD(pri)] | RQB_BIT(pri), 323 RQB_BIT(pri), RQB_WORD(pri)); 324 rqb->rqb_bits[RQB_WORD(pri)] |= RQB_BIT(pri); 325 } 326 327 /* 328 * Add the thread to the queue specified by its priority, and set the 329 * corresponding status bit. 330 */ 331 void 332 runq_add(struct runq *rq, struct thread *td, int flags) 333 { 334 struct rqhead *rqh; 335 int pri; 336 337 pri = td->td_priority / RQ_PPQ; 338 td->td_rqindex = pri; 339 runq_setbit(rq, pri); 340 rqh = &rq->rq_queues[pri]; 341 CTR4(KTR_RUNQ, "runq_add: td=%p pri=%d %d rqh=%p", 342 td, td->td_priority, pri, rqh); 343 if (flags & SRQ_PREEMPTED) { 344 TAILQ_INSERT_HEAD(rqh, td, td_runq); 345 } else { 346 TAILQ_INSERT_TAIL(rqh, td, td_runq); 347 } 348 } 349 350 void 351 runq_add_pri(struct runq *rq, struct thread *td, u_char pri, int flags) 352 { 353 struct rqhead *rqh; 354 355 KASSERT(pri < RQ_NQS, ("runq_add_pri: %d out of range", pri)); 356 td->td_rqindex = pri; 357 runq_setbit(rq, pri); 358 rqh = &rq->rq_queues[pri]; 359 CTR4(KTR_RUNQ, "runq_add_pri: td=%p pri=%d idx=%d rqh=%p", 360 td, td->td_priority, pri, rqh); 361 if (flags & SRQ_PREEMPTED) { 362 TAILQ_INSERT_HEAD(rqh, td, td_runq); 363 } else { 364 TAILQ_INSERT_TAIL(rqh, td, td_runq); 365 } 366 } 367 /* 368 * Return true if there are runnable processes of any priority on the run 369 * queue, false otherwise. Has no side effects, does not modify the run 370 * queue structure. 371 */ 372 int 373 runq_check(struct runq *rq) 374 { 375 struct rqbits *rqb; 376 int i; 377 378 rqb = &rq->rq_status; 379 for (i = 0; i < RQB_LEN; i++) 380 if (rqb->rqb_bits[i]) { 381 CTR2(KTR_RUNQ, "runq_check: bits=%#x i=%d", 382 rqb->rqb_bits[i], i); 383 return (1); 384 } 385 CTR0(KTR_RUNQ, "runq_check: empty"); 386 387 return (0); 388 } 389 390 /* 391 * Find the highest priority process on the run queue. 392 */ 393 struct thread * 394 runq_choose_fuzz(struct runq *rq, int fuzz) 395 { 396 struct rqhead *rqh; 397 struct thread *td; 398 int pri; 399 400 while ((pri = runq_findbit(rq)) != -1) { 401 rqh = &rq->rq_queues[pri]; 402 /* fuzz == 1 is normal.. 0 or less are ignored */ 403 if (fuzz > 1) { 404 /* 405 * In the first couple of entries, check if 406 * there is one for our CPU as a preference. 407 */ 408 int count = fuzz; 409 int cpu = PCPU_GET(cpuid); 410 struct thread *td2; 411 td2 = td = TAILQ_FIRST(rqh); 412 413 while (count-- && td2) { 414 if (td2->td_lastcpu == cpu) { 415 td = td2; 416 break; 417 } 418 td2 = TAILQ_NEXT(td2, td_runq); 419 } 420 } else 421 td = TAILQ_FIRST(rqh); 422 KASSERT(td != NULL, ("runq_choose_fuzz: no proc on busy queue")); 423 CTR3(KTR_RUNQ, 424 "runq_choose_fuzz: pri=%d thread=%p rqh=%p", pri, td, rqh); 425 return (td); 426 } 427 CTR1(KTR_RUNQ, "runq_choose_fuzz: idleproc pri=%d", pri); 428 429 return (NULL); 430 } 431 432 /* 433 * Find the highest priority process on the run queue. 434 */ 435 struct thread * 436 runq_choose(struct runq *rq) 437 { 438 struct rqhead *rqh; 439 struct thread *td; 440 int pri; 441 442 while ((pri = runq_findbit(rq)) != -1) { 443 rqh = &rq->rq_queues[pri]; 444 td = TAILQ_FIRST(rqh); 445 KASSERT(td != NULL, ("runq_choose: no thread on busy queue")); 446 CTR3(KTR_RUNQ, 447 "runq_choose: pri=%d thread=%p rqh=%p", pri, td, rqh); 448 return (td); 449 } 450 CTR1(KTR_RUNQ, "runq_choose: idlethread pri=%d", pri); 451 452 return (NULL); 453 } 454 455 struct thread * 456 runq_choose_from(struct runq *rq, u_char idx) 457 { 458 struct rqhead *rqh; 459 struct thread *td; 460 int pri; 461 462 if ((pri = runq_findbit_from(rq, idx)) != -1) { 463 rqh = &rq->rq_queues[pri]; 464 td = TAILQ_FIRST(rqh); 465 KASSERT(td != NULL, ("runq_choose: no thread on busy queue")); 466 CTR4(KTR_RUNQ, 467 "runq_choose_from: pri=%d thread=%p idx=%d rqh=%p", 468 pri, td, td->td_rqindex, rqh); 469 return (td); 470 } 471 CTR1(KTR_RUNQ, "runq_choose_from: idlethread pri=%d", pri); 472 473 return (NULL); 474 } 475 /* 476 * Remove the thread from the queue specified by its priority, and clear the 477 * corresponding status bit if the queue becomes empty. 478 * Caller must set state afterwards. 479 */ 480 void 481 runq_remove(struct runq *rq, struct thread *td) 482 { 483 484 runq_remove_idx(rq, td, NULL); 485 } 486 487 void 488 runq_remove_idx(struct runq *rq, struct thread *td, u_char *idx) 489 { 490 struct rqhead *rqh; 491 u_char pri; 492 493 KASSERT(td->td_flags & TDF_INMEM, 494 ("runq_remove_idx: thread swapped out")); 495 pri = td->td_rqindex; 496 KASSERT(pri < RQ_NQS, ("runq_remove_idx: Invalid index %d\n", pri)); 497 rqh = &rq->rq_queues[pri]; 498 CTR4(KTR_RUNQ, "runq_remove_idx: td=%p, pri=%d %d rqh=%p", 499 td, td->td_priority, pri, rqh); 500 TAILQ_REMOVE(rqh, td, td_runq); 501 if (TAILQ_EMPTY(rqh)) { 502 CTR0(KTR_RUNQ, "runq_remove_idx: empty"); 503 runq_clrbit(rq, pri); 504 if (idx != NULL && *idx == pri) 505 *idx = (pri + 1) % RQ_NQS; 506 } 507 } 508