Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)
[ source navigation ] [ diff markup ] [ identifier search ] [ freetext search ] [ file search ] [ list types ] [ track identifier ]
FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_switch.c
Version:
- FREEBSD - FREEBSD-13-STABLE - FREEBSD-13-0 - FREEBSD-12-STABLE - FREEBSD-12-0 - FREEBSD-11-STABLE - FREEBSD-11-0 - FREEBSD-10-STABLE - FREEBSD-10-0 - FREEBSD-9-STABLE - FREEBSD-9-0 - FREEBSD-8-STABLE - FREEBSD-8-0 - FREEBSD-7-STABLE - FREEBSD-7-0 - FREEBSD-6-STABLE - FREEBSD-6-0 - FREEBSD-5-STABLE - FREEBSD-5-0 - FREEBSD-4-STABLE - FREEBSD-3-STABLE - FREEBSD22 - l41 - OPENBSD - linux-2.6 - MK84 - PLAN9 - xnu-8792
SearchContext: - none - 3 - 10
SearchContext: - none - 3 - 10
1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD 3 * 4 * Copyright (c) 2001 Jake Burkholder <jake@FreeBSD.org> 5 * All rights reserved. 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 * 16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 17 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 20 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26 * SUCH DAMAGE. 27 */ 28 29 30 #include <sys/cdefs.h> 31 __FBSDID("$FreeBSD$"); 32 33 #include "opt_sched.h" 34 35 #include <sys/param.h> 36 #include <sys/systm.h> 37 #include <sys/kdb.h> 38 #include <sys/kernel.h> 39 #include <sys/ktr.h> 40 #include <sys/lock.h> 41 #include <sys/mutex.h> 42 #include <sys/proc.h> 43 #include <sys/queue.h> 44 #include <sys/sched.h> 45 #include <sys/smp.h> 46 #include <sys/sysctl.h> 47 48 #include <machine/cpu.h> 49 50 /* Uncomment this to enable logging of critical_enter/exit. */ 51 #if 0 52 #define KTR_CRITICAL KTR_SCHED 53 #else 54 #define KTR_CRITICAL 0 55 #endif 56 57 #ifdef FULL_PREEMPTION 58 #ifndef PREEMPTION 59 #error "The FULL_PREEMPTION option requires the PREEMPTION option" 60 #endif 61 #endif 62 63 CTASSERT((RQB_BPW * RQB_LEN) == RQ_NQS); 64 65 /* 66 * kern.sched.preemption allows user space to determine if preemption support 67 * is compiled in or not. It is not currently a boot or runtime flag that 68 * can be changed. 69 */ 70 #ifdef PREEMPTION 71 static int kern_sched_preemption = 1; 72 #else 73 static int kern_sched_preemption = 0; 74 #endif 75 SYSCTL_INT(_kern_sched, OID_AUTO, preemption, CTLFLAG_RD, 76 &kern_sched_preemption, 0, "Kernel preemption enabled"); 77 78 /* 79 * Support for scheduler stats exported via kern.sched.stats. All stats may 80 * be reset with kern.sched.stats.reset = 1. Stats may be defined elsewhere 81 * with SCHED_STAT_DEFINE(). 82 */ 83 #ifdef SCHED_STATS 84 SYSCTL_NODE(_kern_sched, OID_AUTO, stats, CTLFLAG_RW, 0, "switch stats"); 85 86 /* Switch reasons from mi_switch(). */ 87 DPCPU_DEFINE(long, sched_switch_stats[SWT_COUNT]); 88 SCHED_STAT_DEFINE_VAR(uncategorized, 89 &DPCPU_NAME(sched_switch_stats[SWT_NONE]), ""); 90 SCHED_STAT_DEFINE_VAR(preempt, 91 &DPCPU_NAME(sched_switch_stats[SWT_PREEMPT]), ""); 92 SCHED_STAT_DEFINE_VAR(owepreempt, 93 &DPCPU_NAME(sched_switch_stats[SWT_OWEPREEMPT]), ""); 94 SCHED_STAT_DEFINE_VAR(turnstile, 95 &DPCPU_NAME(sched_switch_stats[SWT_TURNSTILE]), ""); 96 SCHED_STAT_DEFINE_VAR(sleepq, 97 &DPCPU_NAME(sched_switch_stats[SWT_SLEEPQ]), ""); 98 SCHED_STAT_DEFINE_VAR(sleepqtimo, 99 &DPCPU_NAME(sched_switch_stats[SWT_SLEEPQTIMO]), ""); 100 SCHED_STAT_DEFINE_VAR(relinquish, 101 &DPCPU_NAME(sched_switch_stats[SWT_RELINQUISH]), ""); 102 SCHED_STAT_DEFINE_VAR(needresched, 103 &DPCPU_NAME(sched_switch_stats[SWT_NEEDRESCHED]), ""); 104 SCHED_STAT_DEFINE_VAR(idle, 105 &DPCPU_NAME(sched_switch_stats[SWT_IDLE]), ""); 106 SCHED_STAT_DEFINE_VAR(iwait, 107 &DPCPU_NAME(sched_switch_stats[SWT_IWAIT]), ""); 108 SCHED_STAT_DEFINE_VAR(suspend, 109 &DPCPU_NAME(sched_switch_stats[SWT_SUSPEND]), ""); 110 SCHED_STAT_DEFINE_VAR(remotepreempt, 111 &DPCPU_NAME(sched_switch_stats[SWT_REMOTEPREEMPT]), ""); 112 SCHED_STAT_DEFINE_VAR(remotewakeidle, 113 &DPCPU_NAME(sched_switch_stats[SWT_REMOTEWAKEIDLE]), ""); 114 115 static int 116 sysctl_stats_reset(SYSCTL_HANDLER_ARGS) 117 { 118 struct sysctl_oid *p; 119 uintptr_t counter; 120 int error; 121 int val; 122 int i; 123 124 val = 0; 125 error = sysctl_handle_int(oidp, &val, 0, req); 126 if (error != 0 || req->newptr == NULL) 127 return (error); 128 if (val == 0) 129 return (0); 130 /* 131 * Traverse the list of children of _kern_sched_stats and reset each 132 * to 0. Skip the reset entry. 133 */ 134 SLIST_FOREACH(p, oidp->oid_parent, oid_link) { 135 if (p == oidp || p->oid_arg1 == NULL) 136 continue; 137 counter = (uintptr_t)p->oid_arg1; 138 CPU_FOREACH(i) { 139 *(long *)(dpcpu_off[i] + counter) = 0; 140 } 141 } 142 return (0); 143 } 144 145 SYSCTL_PROC(_kern_sched_stats, OID_AUTO, reset, CTLTYPE_INT | CTLFLAG_WR, NULL, 146 0, sysctl_stats_reset, "I", "Reset scheduler statistics"); 147 #endif 148 149 /************************************************************************ 150 * Functions that manipulate runnability from a thread perspective. * 151 ************************************************************************/ 152 /* 153 * Select the thread that will be run next. 154 */ 155 156 static __noinline struct thread * 157 choosethread_panic(struct thread *td) 158 { 159 160 /* 161 * If we are in panic, only allow system threads, 162 * plus the one we are running in, to be run. 163 */ 164 retry: 165 if (((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 td = sched_choose(); 170 goto retry; 171 } 172 173 TD_SET_RUNNING(td); 174 return (td); 175 } 176 177 struct thread * 178 choosethread(void) 179 { 180 struct thread *td; 181 182 td = sched_choose(); 183 184 if (__predict_false(panicstr != NULL)) 185 return (choosethread_panic(td)); 186 187 TD_SET_RUNNING(td); 188 return (td); 189 } 190 191 /* 192 * Kernel thread preemption implementation. Critical sections mark 193 * regions of code in which preemptions are not allowed. 194 * 195 * It might seem a good idea to inline critical_enter() but, in order 196 * to prevent instructions reordering by the compiler, a __compiler_membar() 197 * would have to be used here (the same as sched_pin()). The performance 198 * penalty imposed by the membar could, then, produce slower code than 199 * the function call itself, for most cases. 200 */ 201 void 202 critical_enter_KBI(void) 203 { 204 #ifdef KTR 205 struct thread *td = curthread; 206 #endif 207 critical_enter(); 208 CTR4(KTR_CRITICAL, "critical_enter by thread %p (%ld, %s) to %d", td, 209 (long)td->td_proc->p_pid, td->td_name, td->td_critnest); 210 } 211 212 void __noinline 213 critical_exit_preempt(void) 214 { 215 struct thread *td; 216 int flags; 217 218 /* 219 * If td_critnest is 0, it is possible that we are going to get 220 * preempted again before reaching the code below. This happens 221 * rarely and is harmless. However, this means td_owepreempt may 222 * now be unset. 223 */ 224 td = curthread; 225 if (td->td_critnest != 0) 226 return; 227 if (kdb_active) 228 return; 229 230 /* 231 * Microoptimization: we committed to switch, 232 * disable preemption in interrupt handlers 233 * while spinning for the thread lock. 234 */ 235 td->td_critnest = 1; 236 thread_lock(td); 237 td->td_critnest--; 238 flags = SW_INVOL | SW_PREEMPT; 239 if (TD_IS_IDLETHREAD(td)) 240 flags |= SWT_IDLE; 241 else 242 flags |= SWT_OWEPREEMPT; 243 mi_switch(flags, NULL); 244 thread_unlock(td); 245 } 246 247 void 248 critical_exit_KBI(void) 249 { 250 #ifdef KTR 251 struct thread *td = curthread; 252 #endif 253 critical_exit(); 254 CTR4(KTR_CRITICAL, "critical_exit by thread %p (%ld, %s) to %d", td, 255 (long)td->td_proc->p_pid, td->td_name, td->td_critnest); 256 } 257 258 /************************************************************************ 259 * SYSTEM RUN QUEUE manipulations and tests * 260 ************************************************************************/ 261 /* 262 * Initialize a run structure. 263 */ 264 void 265 runq_init(struct runq *rq) 266 { 267 int i; 268 269 bzero(rq, sizeof *rq); 270 for (i = 0; i < RQ_NQS; i++) 271 TAILQ_INIT(&rq->rq_queues[i]); 272 } 273 274 /* 275 * Clear the status bit of the queue corresponding to priority level pri, 276 * indicating that it is empty. 277 */ 278 static __inline void 279 runq_clrbit(struct runq *rq, int pri) 280 { 281 struct rqbits *rqb; 282 283 rqb = &rq->rq_status; 284 CTR4(KTR_RUNQ, "runq_clrbit: bits=%#x %#x bit=%#x word=%d", 285 rqb->rqb_bits[RQB_WORD(pri)], 286 rqb->rqb_bits[RQB_WORD(pri)] & ~RQB_BIT(pri), 287 RQB_BIT(pri), RQB_WORD(pri)); 288 rqb->rqb_bits[RQB_WORD(pri)] &= ~RQB_BIT(pri); 289 } 290 291 /* 292 * Find the index of the first non-empty run queue. This is done by 293 * scanning the status bits, a set bit indicates a non-empty queue. 294 */ 295 static __inline int 296 runq_findbit(struct runq *rq) 297 { 298 struct rqbits *rqb; 299 int pri; 300 int i; 301 302 rqb = &rq->rq_status; 303 for (i = 0; i < RQB_LEN; i++) 304 if (rqb->rqb_bits[i]) { 305 pri = RQB_FFS(rqb->rqb_bits[i]) + (i << RQB_L2BPW); 306 CTR3(KTR_RUNQ, "runq_findbit: bits=%#x i=%d pri=%d", 307 rqb->rqb_bits[i], i, pri); 308 return (pri); 309 } 310 311 return (-1); 312 } 313 314 static __inline int 315 runq_findbit_from(struct runq *rq, u_char pri) 316 { 317 struct rqbits *rqb; 318 rqb_word_t mask; 319 int i; 320 321 /* 322 * Set the mask for the first word so we ignore priorities before 'pri'. 323 */ 324 mask = (rqb_word_t)-1 << (pri & (RQB_BPW - 1)); 325 rqb = &rq->rq_status; 326 again: 327 for (i = RQB_WORD(pri); i < RQB_LEN; mask = -1, i++) { 328 mask = rqb->rqb_bits[i] & mask; 329 if (mask == 0) 330 continue; 331 pri = RQB_FFS(mask) + (i << RQB_L2BPW); 332 CTR3(KTR_RUNQ, "runq_findbit_from: bits=%#x i=%d pri=%d", 333 mask, i, pri); 334 return (pri); 335 } 336 if (pri == 0) 337 return (-1); 338 /* 339 * Wrap back around to the beginning of the list just once so we 340 * scan the whole thing. 341 */ 342 pri = 0; 343 goto again; 344 } 345 346 /* 347 * Set the status bit of the queue corresponding to priority level pri, 348 * indicating that it is non-empty. 349 */ 350 static __inline void 351 runq_setbit(struct runq *rq, int pri) 352 { 353 struct rqbits *rqb; 354 355 rqb = &rq->rq_status; 356 CTR4(KTR_RUNQ, "runq_setbit: bits=%#x %#x bit=%#x word=%d", 357 rqb->rqb_bits[RQB_WORD(pri)], 358 rqb->rqb_bits[RQB_WORD(pri)] | RQB_BIT(pri), 359 RQB_BIT(pri), RQB_WORD(pri)); 360 rqb->rqb_bits[RQB_WORD(pri)] |= RQB_BIT(pri); 361 } 362 363 /* 364 * Add the thread to the queue specified by its priority, and set the 365 * corresponding status bit. 366 */ 367 void 368 runq_add(struct runq *rq, struct thread *td, int flags) 369 { 370 struct rqhead *rqh; 371 int pri; 372 373 pri = td->td_priority / RQ_PPQ; 374 td->td_rqindex = pri; 375 runq_setbit(rq, pri); 376 rqh = &rq->rq_queues[pri]; 377 CTR4(KTR_RUNQ, "runq_add: td=%p pri=%d %d rqh=%p", 378 td, td->td_priority, pri, rqh); 379 if (flags & SRQ_PREEMPTED) { 380 TAILQ_INSERT_HEAD(rqh, td, td_runq); 381 } else { 382 TAILQ_INSERT_TAIL(rqh, td, td_runq); 383 } 384 } 385 386 void 387 runq_add_pri(struct runq *rq, struct thread *td, u_char pri, int flags) 388 { 389 struct rqhead *rqh; 390 391 KASSERT(pri < RQ_NQS, ("runq_add_pri: %d out of range", pri)); 392 td->td_rqindex = pri; 393 runq_setbit(rq, pri); 394 rqh = &rq->rq_queues[pri]; 395 CTR4(KTR_RUNQ, "runq_add_pri: td=%p pri=%d idx=%d rqh=%p", 396 td, td->td_priority, pri, rqh); 397 if (flags & SRQ_PREEMPTED) { 398 TAILQ_INSERT_HEAD(rqh, td, td_runq); 399 } else { 400 TAILQ_INSERT_TAIL(rqh, td, td_runq); 401 } 402 } 403 /* 404 * Return true if there are runnable processes of any priority on the run 405 * queue, false otherwise. Has no side effects, does not modify the run 406 * queue structure. 407 */ 408 int 409 runq_check(struct runq *rq) 410 { 411 struct rqbits *rqb; 412 int i; 413 414 rqb = &rq->rq_status; 415 for (i = 0; i < RQB_LEN; i++) 416 if (rqb->rqb_bits[i]) { 417 CTR2(KTR_RUNQ, "runq_check: bits=%#x i=%d", 418 rqb->rqb_bits[i], i); 419 return (1); 420 } 421 CTR0(KTR_RUNQ, "runq_check: empty"); 422 423 return (0); 424 } 425 426 /* 427 * Find the highest priority process on the run queue. 428 */ 429 struct thread * 430 runq_choose_fuzz(struct runq *rq, int fuzz) 431 { 432 struct rqhead *rqh; 433 struct thread *td; 434 int pri; 435 436 while ((pri = runq_findbit(rq)) != -1) { 437 rqh = &rq->rq_queues[pri]; 438 /* fuzz == 1 is normal.. 0 or less are ignored */ 439 if (fuzz > 1) { 440 /* 441 * In the first couple of entries, check if 442 * there is one for our CPU as a preference. 443 */ 444 int count = fuzz; 445 int cpu = PCPU_GET(cpuid); 446 struct thread *td2; 447 td2 = td = TAILQ_FIRST(rqh); 448 449 while (count-- && td2) { 450 if (td2->td_lastcpu == cpu) { 451 td = td2; 452 break; 453 } 454 td2 = TAILQ_NEXT(td2, td_runq); 455 } 456 } else 457 td = TAILQ_FIRST(rqh); 458 KASSERT(td != NULL, ("runq_choose_fuzz: no proc on busy queue")); 459 CTR3(KTR_RUNQ, 460 "runq_choose_fuzz: pri=%d thread=%p rqh=%p", pri, td, rqh); 461 return (td); 462 } 463 CTR1(KTR_RUNQ, "runq_choose_fuzz: idleproc pri=%d", pri); 464 465 return (NULL); 466 } 467 468 /* 469 * Find the highest priority process on the run queue. 470 */ 471 struct thread * 472 runq_choose(struct runq *rq) 473 { 474 struct rqhead *rqh; 475 struct thread *td; 476 int pri; 477 478 while ((pri = runq_findbit(rq)) != -1) { 479 rqh = &rq->rq_queues[pri]; 480 td = TAILQ_FIRST(rqh); 481 KASSERT(td != NULL, ("runq_choose: no thread on busy queue")); 482 CTR3(KTR_RUNQ, 483 "runq_choose: pri=%d thread=%p rqh=%p", pri, td, rqh); 484 return (td); 485 } 486 CTR1(KTR_RUNQ, "runq_choose: idlethread pri=%d", pri); 487 488 return (NULL); 489 } 490 491 struct thread * 492 runq_choose_from(struct runq *rq, u_char idx) 493 { 494 struct rqhead *rqh; 495 struct thread *td; 496 int pri; 497 498 if ((pri = runq_findbit_from(rq, idx)) != -1) { 499 rqh = &rq->rq_queues[pri]; 500 td = TAILQ_FIRST(rqh); 501 KASSERT(td != NULL, ("runq_choose: no thread on busy queue")); 502 CTR4(KTR_RUNQ, 503 "runq_choose_from: pri=%d thread=%p idx=%d rqh=%p", 504 pri, td, td->td_rqindex, rqh); 505 return (td); 506 } 507 CTR1(KTR_RUNQ, "runq_choose_from: idlethread pri=%d", pri); 508 509 return (NULL); 510 } 511 /* 512 * Remove the thread from the queue specified by its priority, and clear the 513 * corresponding status bit if the queue becomes empty. 514 * Caller must set state afterwards. 515 */ 516 void 517 runq_remove(struct runq *rq, struct thread *td) 518 { 519 520 runq_remove_idx(rq, td, NULL); 521 } 522 523 void 524 runq_remove_idx(struct runq *rq, struct thread *td, u_char *idx) 525 { 526 struct rqhead *rqh; 527 u_char pri; 528 529 KASSERT(td->td_flags & TDF_INMEM, 530 ("runq_remove_idx: thread swapped out")); 531 pri = td->td_rqindex; 532 KASSERT(pri < RQ_NQS, ("runq_remove_idx: Invalid index %d\n", pri)); 533 rqh = &rq->rq_queues[pri]; 534 CTR4(KTR_RUNQ, "runq_remove_idx: td=%p, pri=%d %d rqh=%p", 535 td, td->td_priority, pri, rqh); 536 TAILQ_REMOVE(rqh, td, td_runq); 537 if (TAILQ_EMPTY(rqh)) { 538 CTR0(KTR_RUNQ, "runq_remove_idx: empty"); 539 runq_clrbit(rq, pri); 540 if (idx != NULL && *idx == pri) 541 *idx = (pri + 1) % RQ_NQS; 542 } 543 }
Cache object: acaad67907366516cb0e5f079e0e1071
[ source navigation ] [ diff markup ] [ identifier search ] [ freetext search ] [ file search ] [ list types ] [ track identifier ]