Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)
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FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_switch.c
Version:
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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: releng/11.2/sys/kern/kern_switch.c 327481 2018-01-02 00:14:46Z mjg $"); 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 */ 153 154 static __noinline struct thread * 155 choosethread_panic(struct thread *td) 156 { 157 158 /* 159 * If we are in panic, only allow system threads, 160 * plus the one we are running in, to be run. 161 */ 162 retry: 163 if (((td->td_proc->p_flag & P_SYSTEM) == 0 && 164 (td->td_flags & TDF_INPANIC) == 0)) { 165 /* note that it is no longer on the run queue */ 166 TD_SET_CAN_RUN(td); 167 td = sched_choose(); 168 goto retry; 169 } 170 171 TD_SET_RUNNING(td); 172 return (td); 173 } 174 175 struct thread * 176 choosethread(void) 177 { 178 struct thread *td; 179 180 td = sched_choose(); 181 182 if (__predict_false(panicstr != NULL)) 183 return (choosethread_panic(td)); 184 185 TD_SET_RUNNING(td); 186 return (td); 187 } 188 189 /* 190 * Kernel thread preemption implementation. Critical sections mark 191 * regions of code in which preemptions are not allowed. 192 * 193 * It might seem a good idea to inline critical_enter() but, in order 194 * to prevent instructions reordering by the compiler, a __compiler_membar() 195 * would have to be used here (the same as sched_pin()). The performance 196 * penalty imposed by the membar could, then, produce slower code than 197 * the function call itself, for most cases. 198 */ 199 void 200 critical_enter(void) 201 { 202 struct thread *td; 203 204 td = curthread; 205 td->td_critnest++; 206 CTR4(KTR_CRITICAL, "critical_enter by thread %p (%ld, %s) to %d", td, 207 (long)td->td_proc->p_pid, td->td_name, td->td_critnest); 208 } 209 210 void 211 critical_exit(void) 212 { 213 struct thread *td; 214 int flags; 215 216 td = curthread; 217 KASSERT(td->td_critnest != 0, 218 ("critical_exit: td_critnest == 0")); 219 220 if (td->td_critnest == 1) { 221 td->td_critnest = 0; 222 223 /* 224 * Interrupt handlers execute critical_exit() on 225 * leave, and td_owepreempt may be left set by an 226 * interrupt handler only when td_critnest > 0. If we 227 * are decrementing td_critnest from 1 to 0, read 228 * td_owepreempt after decrementing, to not miss the 229 * preempt. Disallow compiler to reorder operations. 230 */ 231 __compiler_membar(); 232 if (td->td_owepreempt && !kdb_active) { 233 /* 234 * Microoptimization: we committed to switch, 235 * disable preemption in interrupt handlers 236 * while spinning for the thread lock. 237 */ 238 td->td_critnest = 1; 239 thread_lock(td); 240 td->td_critnest--; 241 flags = SW_INVOL | SW_PREEMPT; 242 if (TD_IS_IDLETHREAD(td)) 243 flags |= SWT_IDLE; 244 else 245 flags |= SWT_OWEPREEMPT; 246 mi_switch(flags, NULL); 247 thread_unlock(td); 248 } 249 } else 250 td->td_critnest--; 251 252 CTR4(KTR_CRITICAL, "critical_exit by thread %p (%ld, %s) to %d", td, 253 (long)td->td_proc->p_pid, td->td_name, td->td_critnest); 254 } 255 256 /************************************************************************ 257 * SYSTEM RUN QUEUE manipulations and tests * 258 ************************************************************************/ 259 /* 260 * Initialize a run structure. 261 */ 262 void 263 runq_init(struct runq *rq) 264 { 265 int i; 266 267 bzero(rq, sizeof *rq); 268 for (i = 0; i < RQ_NQS; i++) 269 TAILQ_INIT(&rq->rq_queues[i]); 270 } 271 272 /* 273 * Clear the status bit of the queue corresponding to priority level pri, 274 * indicating that it is empty. 275 */ 276 static __inline void 277 runq_clrbit(struct runq *rq, int pri) 278 { 279 struct rqbits *rqb; 280 281 rqb = &rq->rq_status; 282 CTR4(KTR_RUNQ, "runq_clrbit: bits=%#x %#x bit=%#x word=%d", 283 rqb->rqb_bits[RQB_WORD(pri)], 284 rqb->rqb_bits[RQB_WORD(pri)] & ~RQB_BIT(pri), 285 RQB_BIT(pri), RQB_WORD(pri)); 286 rqb->rqb_bits[RQB_WORD(pri)] &= ~RQB_BIT(pri); 287 } 288 289 /* 290 * Find the index of the first non-empty run queue. This is done by 291 * scanning the status bits, a set bit indicates a non-empty queue. 292 */ 293 static __inline int 294 runq_findbit(struct runq *rq) 295 { 296 struct rqbits *rqb; 297 int pri; 298 int i; 299 300 rqb = &rq->rq_status; 301 for (i = 0; i < RQB_LEN; i++) 302 if (rqb->rqb_bits[i]) { 303 pri = RQB_FFS(rqb->rqb_bits[i]) + (i << RQB_L2BPW); 304 CTR3(KTR_RUNQ, "runq_findbit: bits=%#x i=%d pri=%d", 305 rqb->rqb_bits[i], i, pri); 306 return (pri); 307 } 308 309 return (-1); 310 } 311 312 static __inline int 313 runq_findbit_from(struct runq *rq, u_char pri) 314 { 315 struct rqbits *rqb; 316 rqb_word_t mask; 317 int i; 318 319 /* 320 * Set the mask for the first word so we ignore priorities before 'pri'. 321 */ 322 mask = (rqb_word_t)-1 << (pri & (RQB_BPW - 1)); 323 rqb = &rq->rq_status; 324 again: 325 for (i = RQB_WORD(pri); i < RQB_LEN; mask = -1, i++) { 326 mask = rqb->rqb_bits[i] & mask; 327 if (mask == 0) 328 continue; 329 pri = RQB_FFS(mask) + (i << RQB_L2BPW); 330 CTR3(KTR_RUNQ, "runq_findbit_from: bits=%#x i=%d pri=%d", 331 mask, i, pri); 332 return (pri); 333 } 334 if (pri == 0) 335 return (-1); 336 /* 337 * Wrap back around to the beginning of the list just once so we 338 * scan the whole thing. 339 */ 340 pri = 0; 341 goto again; 342 } 343 344 /* 345 * Set the status bit of the queue corresponding to priority level pri, 346 * indicating that it is non-empty. 347 */ 348 static __inline void 349 runq_setbit(struct runq *rq, int pri) 350 { 351 struct rqbits *rqb; 352 353 rqb = &rq->rq_status; 354 CTR4(KTR_RUNQ, "runq_setbit: bits=%#x %#x bit=%#x word=%d", 355 rqb->rqb_bits[RQB_WORD(pri)], 356 rqb->rqb_bits[RQB_WORD(pri)] | RQB_BIT(pri), 357 RQB_BIT(pri), RQB_WORD(pri)); 358 rqb->rqb_bits[RQB_WORD(pri)] |= RQB_BIT(pri); 359 } 360 361 /* 362 * Add the thread to the queue specified by its priority, and set the 363 * corresponding status bit. 364 */ 365 void 366 runq_add(struct runq *rq, struct thread *td, int flags) 367 { 368 struct rqhead *rqh; 369 int pri; 370 371 pri = td->td_priority / RQ_PPQ; 372 td->td_rqindex = pri; 373 runq_setbit(rq, pri); 374 rqh = &rq->rq_queues[pri]; 375 CTR4(KTR_RUNQ, "runq_add: td=%p pri=%d %d rqh=%p", 376 td, td->td_priority, pri, rqh); 377 if (flags & SRQ_PREEMPTED) { 378 TAILQ_INSERT_HEAD(rqh, td, td_runq); 379 } else { 380 TAILQ_INSERT_TAIL(rqh, td, td_runq); 381 } 382 } 383 384 void 385 runq_add_pri(struct runq *rq, struct thread *td, u_char pri, int flags) 386 { 387 struct rqhead *rqh; 388 389 KASSERT(pri < RQ_NQS, ("runq_add_pri: %d out of range", pri)); 390 td->td_rqindex = pri; 391 runq_setbit(rq, pri); 392 rqh = &rq->rq_queues[pri]; 393 CTR4(KTR_RUNQ, "runq_add_pri: td=%p pri=%d idx=%d rqh=%p", 394 td, td->td_priority, pri, rqh); 395 if (flags & SRQ_PREEMPTED) { 396 TAILQ_INSERT_HEAD(rqh, td, td_runq); 397 } else { 398 TAILQ_INSERT_TAIL(rqh, td, td_runq); 399 } 400 } 401 /* 402 * Return true if there are runnable processes of any priority on the run 403 * queue, false otherwise. Has no side effects, does not modify the run 404 * queue structure. 405 */ 406 int 407 runq_check(struct runq *rq) 408 { 409 struct rqbits *rqb; 410 int i; 411 412 rqb = &rq->rq_status; 413 for (i = 0; i < RQB_LEN; i++) 414 if (rqb->rqb_bits[i]) { 415 CTR2(KTR_RUNQ, "runq_check: bits=%#x i=%d", 416 rqb->rqb_bits[i], i); 417 return (1); 418 } 419 CTR0(KTR_RUNQ, "runq_check: empty"); 420 421 return (0); 422 } 423 424 /* 425 * Find the highest priority process on the run queue. 426 */ 427 struct thread * 428 runq_choose_fuzz(struct runq *rq, int fuzz) 429 { 430 struct rqhead *rqh; 431 struct thread *td; 432 int pri; 433 434 while ((pri = runq_findbit(rq)) != -1) { 435 rqh = &rq->rq_queues[pri]; 436 /* fuzz == 1 is normal.. 0 or less are ignored */ 437 if (fuzz > 1) { 438 /* 439 * In the first couple of entries, check if 440 * there is one for our CPU as a preference. 441 */ 442 int count = fuzz; 443 int cpu = PCPU_GET(cpuid); 444 struct thread *td2; 445 td2 = td = TAILQ_FIRST(rqh); 446 447 while (count-- && td2) { 448 if (td2->td_lastcpu == cpu) { 449 td = td2; 450 break; 451 } 452 td2 = TAILQ_NEXT(td2, td_runq); 453 } 454 } else 455 td = TAILQ_FIRST(rqh); 456 KASSERT(td != NULL, ("runq_choose_fuzz: no proc on busy queue")); 457 CTR3(KTR_RUNQ, 458 "runq_choose_fuzz: pri=%d thread=%p rqh=%p", pri, td, rqh); 459 return (td); 460 } 461 CTR1(KTR_RUNQ, "runq_choose_fuzz: idleproc pri=%d", pri); 462 463 return (NULL); 464 } 465 466 /* 467 * Find the highest priority process on the run queue. 468 */ 469 struct thread * 470 runq_choose(struct runq *rq) 471 { 472 struct rqhead *rqh; 473 struct thread *td; 474 int pri; 475 476 while ((pri = runq_findbit(rq)) != -1) { 477 rqh = &rq->rq_queues[pri]; 478 td = TAILQ_FIRST(rqh); 479 KASSERT(td != NULL, ("runq_choose: no thread on busy queue")); 480 CTR3(KTR_RUNQ, 481 "runq_choose: pri=%d thread=%p rqh=%p", pri, td, rqh); 482 return (td); 483 } 484 CTR1(KTR_RUNQ, "runq_choose: idlethread pri=%d", pri); 485 486 return (NULL); 487 } 488 489 struct thread * 490 runq_choose_from(struct runq *rq, u_char idx) 491 { 492 struct rqhead *rqh; 493 struct thread *td; 494 int pri; 495 496 if ((pri = runq_findbit_from(rq, idx)) != -1) { 497 rqh = &rq->rq_queues[pri]; 498 td = TAILQ_FIRST(rqh); 499 KASSERT(td != NULL, ("runq_choose: no thread on busy queue")); 500 CTR4(KTR_RUNQ, 501 "runq_choose_from: pri=%d thread=%p idx=%d rqh=%p", 502 pri, td, td->td_rqindex, rqh); 503 return (td); 504 } 505 CTR1(KTR_RUNQ, "runq_choose_from: idlethread pri=%d", pri); 506 507 return (NULL); 508 } 509 /* 510 * Remove the thread from the queue specified by its priority, and clear the 511 * corresponding status bit if the queue becomes empty. 512 * Caller must set state afterwards. 513 */ 514 void 515 runq_remove(struct runq *rq, struct thread *td) 516 { 517 518 runq_remove_idx(rq, td, NULL); 519 } 520 521 void 522 runq_remove_idx(struct runq *rq, struct thread *td, u_char *idx) 523 { 524 struct rqhead *rqh; 525 u_char pri; 526 527 KASSERT(td->td_flags & TDF_INMEM, 528 ("runq_remove_idx: thread swapped out")); 529 pri = td->td_rqindex; 530 KASSERT(pri < RQ_NQS, ("runq_remove_idx: Invalid index %d\n", pri)); 531 rqh = &rq->rq_queues[pri]; 532 CTR4(KTR_RUNQ, "runq_remove_idx: td=%p, pri=%d %d rqh=%p", 533 td, td->td_priority, pri, rqh); 534 TAILQ_REMOVE(rqh, td, td_runq); 535 if (TAILQ_EMPTY(rqh)) { 536 CTR0(KTR_RUNQ, "runq_remove_idx: empty"); 537 runq_clrbit(rq, pri); 538 if (idx != NULL && *idx == pri) 539 *idx = (pri + 1) % RQ_NQS; 540 } 541 }
Cache object: 0586bdb4f5eab3632c5a23622b25df05
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