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 * 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 Here is the logic.. 29 30 If there are N processors, then there are at most N KSEs (kernel 31 schedulable entities) working to process threads that belong to a 32 KSEGROUP (kg). If there are X of these KSEs actually running at the 33 moment in question, then there are at most M (N-X) of these KSEs on 34 the run queue, as running KSEs are not on the queue. 35 36 Runnable threads are queued off the KSEGROUP in priority order. 37 If there are M or more threads runnable, the top M threads 38 (by priority) are 'preassigned' to the M KSEs not running. The KSEs take 39 their priority from those threads and are put on the run queue. 40 41 The last thread that had a priority high enough to have a KSE associated 42 with it, AND IS ON THE RUN QUEUE is pointed to by 43 kg->kg_last_assigned. If no threads queued off the KSEGROUP have KSEs 44 assigned as all the available KSEs are activly running, or because there 45 are no threads queued, that pointer is NULL. 46 47 When a KSE is removed from the run queue to become runnable, we know 48 it was associated with the highest priority thread in the queue (at the head 49 of the queue). If it is also the last assigned we know M was 1 and must 50 now be 0. Since the thread is no longer queued that pointer must be 51 removed from it. Since we know there were no more KSEs available, 52 (M was 1 and is now 0) and since we are not FREEING our KSE 53 but using it, we know there are STILL no more KSEs available, we can prove 54 that the next thread in the ksegrp list will not have a KSE to assign to 55 it, so we can show that the pointer must be made 'invalid' (NULL). 56 57 The pointer exists so that when a new thread is made runnable, it can 58 have its priority compared with the last assigned thread to see if 59 it should 'steal' its KSE or not.. i.e. is it 'earlier' 60 on the list than that thread or later.. If it's earlier, then the KSE is 61 removed from the last assigned (which is now not assigned a KSE) 62 and reassigned to the new thread, which is placed earlier in the list. 63 The pointer is then backed up to the previous thread (which may or may not 64 be the new thread). 65 66 When a thread sleeps or is removed, the KSE becomes available and if there 67 are queued threads that are not assigned KSEs, the highest priority one of 68 them is assigned the KSE, which is then placed back on the run queue at 69 the approipriate place, and the kg->kg_last_assigned pointer is adjusted down 70 to point to it. 71 72 The following diagram shows 2 KSEs and 3 threads from a single process. 73 74 RUNQ: --->KSE---KSE--... (KSEs queued at priorities from threads) 75 \ \____ 76 \ \ 77 KSEGROUP---thread--thread--thread (queued in priority order) 78 \ / 79 \_______________/ 80 (last_assigned) 81 82 The result of this scheme is that the M available KSEs are always 83 queued at the priorities they have inherrited from the M highest priority 84 threads for that KSEGROUP. If this situation changes, the KSEs are 85 reassigned to keep this true. 86 ***/ 87 88 #include <sys/cdefs.h> 89 __FBSDID("$FreeBSD: releng/5.3/sys/kern/kern_switch.c 136789 2004-10-22 19:13:07Z scottl $"); 90 91 #include "opt_sched.h" 92 93 #ifndef KERN_SWITCH_INCLUDE 94 #include <sys/param.h> 95 #include <sys/systm.h> 96 #include <sys/kdb.h> 97 #include <sys/kernel.h> 98 #include <sys/ktr.h> 99 #include <sys/lock.h> 100 #include <sys/mutex.h> 101 #include <sys/proc.h> 102 #include <sys/queue.h> 103 #include <sys/sched.h> 104 #else /* KERN_SWITCH_INCLUDE */ 105 #if defined(SMP) && (defined(__i386__) || defined(__amd64__)) 106 #include <sys/smp.h> 107 #endif 108 #include <machine/critical.h> 109 #if defined(SMP) && defined(SCHED_4BSD) 110 #include <sys/sysctl.h> 111 #endif 112 113 #ifdef FULL_PREEMPTION 114 #ifndef PREEMPTION 115 #error "The FULL_PREEMPTION option requires the PREEMPTION option" 116 #endif 117 #endif 118 119 CTASSERT((RQB_BPW * RQB_LEN) == RQ_NQS); 120 121 #define td_kse td_sched 122 123 /************************************************************************ 124 * Functions that manipulate runnability from a thread perspective. * 125 ************************************************************************/ 126 /* 127 * Select the KSE that will be run next. From that find the thread, and 128 * remove it from the KSEGRP's run queue. If there is thread clustering, 129 * this will be what does it. 130 */ 131 struct thread * 132 choosethread(void) 133 { 134 struct kse *ke; 135 struct thread *td; 136 struct ksegrp *kg; 137 138 #if defined(SMP) && (defined(__i386__) || defined(__amd64__)) 139 if (smp_active == 0 && PCPU_GET(cpuid) != 0) { 140 /* Shutting down, run idlethread on AP's */ 141 td = PCPU_GET(idlethread); 142 ke = td->td_kse; 143 CTR1(KTR_RUNQ, "choosethread: td=%p (idle)", td); 144 ke->ke_flags |= KEF_DIDRUN; 145 TD_SET_RUNNING(td); 146 return (td); 147 } 148 #endif 149 150 retry: 151 ke = sched_choose(); 152 if (ke) { 153 td = ke->ke_thread; 154 KASSERT((td->td_kse == ke), ("kse/thread mismatch")); 155 kg = ke->ke_ksegrp; 156 if (td->td_proc->p_flag & P_HADTHREADS) { 157 if (kg->kg_last_assigned == td) { 158 kg->kg_last_assigned = TAILQ_PREV(td, 159 threadqueue, td_runq); 160 } 161 TAILQ_REMOVE(&kg->kg_runq, td, td_runq); 162 kg->kg_runnable--; 163 } 164 CTR2(KTR_RUNQ, "choosethread: td=%p pri=%d", 165 td, td->td_priority); 166 } else { 167 /* Simulate runq_choose() having returned the idle thread */ 168 td = PCPU_GET(idlethread); 169 ke = td->td_kse; 170 CTR1(KTR_RUNQ, "choosethread: td=%p (idle)", td); 171 } 172 ke->ke_flags |= KEF_DIDRUN; 173 174 /* 175 * If we are in panic, only allow system threads, 176 * plus the one we are running in, to be run. 177 */ 178 if (panicstr && ((td->td_proc->p_flag & P_SYSTEM) == 0 && 179 (td->td_flags & TDF_INPANIC) == 0)) { 180 /* note that it is no longer on the run queue */ 181 TD_SET_CAN_RUN(td); 182 goto retry; 183 } 184 185 TD_SET_RUNNING(td); 186 return (td); 187 } 188 189 /* 190 * Given a surplus system slot, try assign a new runnable thread to it. 191 * Called from: 192 * sched_thread_exit() (local) 193 * sched_switch() (local) 194 * sched_thread_exit() (local) 195 * remrunqueue() (local) (not at the moment) 196 */ 197 static void 198 slot_fill(struct ksegrp *kg) 199 { 200 struct thread *td; 201 202 mtx_assert(&sched_lock, MA_OWNED); 203 while (kg->kg_avail_opennings > 0) { 204 /* 205 * Find the first unassigned thread 206 */ 207 if ((td = kg->kg_last_assigned) != NULL) 208 td = TAILQ_NEXT(td, td_runq); 209 else 210 td = TAILQ_FIRST(&kg->kg_runq); 211 212 /* 213 * If we found one, send it to the system scheduler. 214 */ 215 if (td) { 216 kg->kg_last_assigned = td; 217 sched_add(td, SRQ_YIELDING); 218 CTR2(KTR_RUNQ, "slot_fill: td%p -> kg%p", td, kg); 219 } else { 220 /* no threads to use up the slots. quit now */ 221 break; 222 } 223 } 224 } 225 226 #ifdef SCHED_4BSD 227 /* 228 * Remove a thread from its KSEGRP's run queue. 229 * This in turn may remove it from a KSE if it was already assigned 230 * to one, possibly causing a new thread to be assigned to the KSE 231 * and the KSE getting a new priority. 232 */ 233 static void 234 remrunqueue(struct thread *td) 235 { 236 struct thread *td2, *td3; 237 struct ksegrp *kg; 238 struct kse *ke; 239 240 mtx_assert(&sched_lock, MA_OWNED); 241 KASSERT((TD_ON_RUNQ(td)), ("remrunqueue: Bad state on run queue")); 242 kg = td->td_ksegrp; 243 ke = td->td_kse; 244 CTR1(KTR_RUNQ, "remrunqueue: td%p", td); 245 TD_SET_CAN_RUN(td); 246 /* 247 * If it is not a threaded process, take the shortcut. 248 */ 249 if ((td->td_proc->p_flag & P_HADTHREADS) == 0) { 250 /* remve from sys run queue and free up a slot */ 251 sched_rem(td); 252 ke->ke_state = KES_THREAD; 253 return; 254 } 255 td3 = TAILQ_PREV(td, threadqueue, td_runq); 256 TAILQ_REMOVE(&kg->kg_runq, td, td_runq); 257 kg->kg_runnable--; 258 if (ke->ke_state == KES_ONRUNQ) { 259 /* 260 * This thread has been assigned to the system run queue. 261 * We need to dissociate it and try assign the 262 * KSE to the next available thread. Then, we should 263 * see if we need to move the KSE in the run queues. 264 */ 265 sched_rem(td); 266 ke->ke_state = KES_THREAD; 267 td2 = kg->kg_last_assigned; 268 KASSERT((td2 != NULL), ("last assigned has wrong value")); 269 if (td2 == td) 270 kg->kg_last_assigned = td3; 271 /* slot_fill(kg); */ /* will replace it with another */ 272 } 273 } 274 #endif 275 276 /* 277 * Change the priority of a thread that is on the run queue. 278 */ 279 void 280 adjustrunqueue( struct thread *td, int newpri) 281 { 282 struct ksegrp *kg; 283 struct kse *ke; 284 285 mtx_assert(&sched_lock, MA_OWNED); 286 KASSERT((TD_ON_RUNQ(td)), ("adjustrunqueue: Bad state on run queue")); 287 288 ke = td->td_kse; 289 CTR1(KTR_RUNQ, "adjustrunqueue: td%p", td); 290 /* 291 * If it is not a threaded process, take the shortcut. 292 */ 293 if ((td->td_proc->p_flag & P_HADTHREADS) == 0) { 294 /* We only care about the kse in the run queue. */ 295 td->td_priority = newpri; 296 if (ke->ke_rqindex != (newpri / RQ_PPQ)) { 297 sched_rem(td); 298 sched_add(td, SRQ_BORING); 299 } 300 return; 301 } 302 303 /* It is a threaded process */ 304 kg = td->td_ksegrp; 305 if (ke->ke_state == KES_ONRUNQ) { 306 if (kg->kg_last_assigned == td) { 307 kg->kg_last_assigned = 308 TAILQ_PREV(td, threadqueue, td_runq); 309 } 310 sched_rem(td); 311 } 312 TAILQ_REMOVE(&kg->kg_runq, td, td_runq); 313 kg->kg_runnable--; 314 TD_SET_CAN_RUN(td); 315 td->td_priority = newpri; 316 setrunqueue(td, SRQ_BORING); 317 } 318 319 /* 320 * This function is called when a thread is about to be put on a 321 * ksegrp run queue because it has been made runnable or its 322 * priority has been adjusted and the ksegrp does not have a 323 * free kse slot. It determines if a thread from the same ksegrp 324 * should be preempted. If so, it tries to switch threads 325 * if the thread is on the same cpu or notifies another cpu that 326 * it should switch threads. 327 */ 328 329 static void 330 maybe_preempt_in_ksegrp(struct thread *td) 331 #if !defined(SMP) 332 { 333 struct thread *running_thread; 334 335 #ifndef FULL_PREEMPTION 336 int pri; 337 pri = td->td_priority; 338 if (!(pri >= PRI_MIN_ITHD && pri <= PRI_MAX_ITHD)) 339 return; 340 #endif 341 mtx_assert(&sched_lock, MA_OWNED); 342 running_thread = curthread; 343 344 if (running_thread->td_ksegrp != td->td_ksegrp) 345 return; 346 347 if (td->td_priority > running_thread->td_priority) 348 return; 349 #ifdef PREEMPTION 350 if (running_thread->td_critnest > 1) 351 running_thread->td_pflags |= TDP_OWEPREEMPT; 352 else 353 mi_switch(SW_INVOL, NULL); 354 355 #else 356 running_thread->td_flags |= TDF_NEEDRESCHED; 357 #endif 358 return; 359 } 360 361 #else /* SMP */ 362 { 363 struct thread *running_thread; 364 int worst_pri; 365 struct ksegrp *kg; 366 cpumask_t cpumask,dontuse; 367 struct pcpu *pc; 368 struct pcpu *best_pcpu; 369 struct thread *cputhread; 370 371 #ifndef FULL_PREEMPTION 372 int pri; 373 pri = td->td_priority; 374 if (!(pri >= PRI_MIN_ITHD && pri <= PRI_MAX_ITHD)) 375 return; 376 #endif 377 378 mtx_assert(&sched_lock, MA_OWNED); 379 380 running_thread = curthread; 381 382 #if !defined(KSEG_PEEMPT_BEST_CPU) 383 if (running_thread->td_ksegrp != td->td_ksegrp) { 384 #endif 385 kg = td->td_ksegrp; 386 387 /* if someone is ahead of this thread, wait our turn */ 388 if (td != TAILQ_FIRST(&kg->kg_runq)) 389 return; 390 391 worst_pri = td->td_priority; 392 best_pcpu = NULL; 393 dontuse = stopped_cpus | idle_cpus_mask; 394 395 /* 396 * Find a cpu with the worst priority that runs at thread from 397 * the same ksegrp - if multiple exist give first the last run 398 * cpu and then the current cpu priority 399 */ 400 401 SLIST_FOREACH(pc, &cpuhead, pc_allcpu) { 402 cpumask = pc->pc_cpumask; 403 cputhread = pc->pc_curthread; 404 405 if ((cpumask & dontuse) || 406 cputhread->td_ksegrp != kg) 407 continue; 408 409 if (cputhread->td_priority > worst_pri) { 410 worst_pri = cputhread->td_priority; 411 best_pcpu = pc; 412 continue; 413 } 414 415 if (cputhread->td_priority == worst_pri && 416 best_pcpu != NULL && 417 (td->td_lastcpu == pc->pc_cpuid || 418 (PCPU_GET(cpumask) == cpumask && 419 td->td_lastcpu != best_pcpu->pc_cpuid))) 420 best_pcpu = pc; 421 } 422 423 /* Check if we need to preempt someone */ 424 if (best_pcpu == NULL) 425 return; 426 427 if (PCPU_GET(cpuid) != best_pcpu->pc_cpuid) { 428 best_pcpu->pc_curthread->td_flags |= TDF_NEEDRESCHED; 429 ipi_selected(best_pcpu->pc_cpumask, IPI_AST); 430 return; 431 } 432 #if !defined(KSEG_PEEMPT_BEST_CPU) 433 } 434 #endif 435 436 if (td->td_priority > running_thread->td_priority) 437 return; 438 #ifdef PREEMPTION 439 if (running_thread->td_critnest > 1) 440 running_thread->td_pflags |= TDP_OWEPREEMPT; 441 else 442 mi_switch(SW_INVOL, NULL); 443 444 #else 445 running_thread->td_flags |= TDF_NEEDRESCHED; 446 #endif 447 return; 448 } 449 #endif /* !SMP */ 450 451 452 int limitcount; 453 void 454 setrunqueue(struct thread *td, int flags) 455 { 456 struct ksegrp *kg; 457 struct thread *td2; 458 struct thread *tda; 459 460 CTR3(KTR_RUNQ, "setrunqueue: td:%p kg:%p pid:%d", 461 td, td->td_ksegrp, td->td_proc->p_pid); 462 mtx_assert(&sched_lock, MA_OWNED); 463 KASSERT((td->td_inhibitors == 0), 464 ("setrunqueue: trying to run inhibitted thread")); 465 KASSERT((TD_CAN_RUN(td) || TD_IS_RUNNING(td)), 466 ("setrunqueue: bad thread state")); 467 TD_SET_RUNQ(td); 468 kg = td->td_ksegrp; 469 if ((td->td_proc->p_flag & P_HADTHREADS) == 0) { 470 /* 471 * Common path optimisation: Only one of everything 472 * and the KSE is always already attached. 473 * Totally ignore the ksegrp run queue. 474 */ 475 if (kg->kg_avail_opennings != 1) { 476 if (limitcount < 1) { 477 limitcount++; 478 printf("pid %d: corrected slot count (%d->1)\n", 479 td->td_proc->p_pid, kg->kg_avail_opennings); 480 481 } 482 kg->kg_avail_opennings = 1; 483 } 484 sched_add(td, flags); 485 return; 486 } 487 488 /* 489 * If the concurrency has reduced, and we would go in the 490 * assigned section, then keep removing entries from the 491 * system run queue, until we are not in that section 492 * or there is room for us to be put in that section. 493 * What we MUST avoid is the case where there are threads of less 494 * priority than the new one scheduled, but it can not 495 * be scheduled itself. That would lead to a non contiguous set 496 * of scheduled threads, and everything would break. 497 */ 498 tda = kg->kg_last_assigned; 499 while ((kg->kg_avail_opennings <= 0) && 500 (tda && (tda->td_priority > td->td_priority))) { 501 /* 502 * None free, but there is one we can commandeer. 503 */ 504 CTR2(KTR_RUNQ, 505 "setrunqueue: kg:%p: take slot from td: %p", kg, tda); 506 sched_rem(tda); 507 tda = kg->kg_last_assigned = 508 TAILQ_PREV(tda, threadqueue, td_runq); 509 } 510 511 /* 512 * Add the thread to the ksegrp's run queue at 513 * the appropriate place. 514 */ 515 TAILQ_FOREACH(td2, &kg->kg_runq, td_runq) { 516 if (td2->td_priority > td->td_priority) { 517 kg->kg_runnable++; 518 TAILQ_INSERT_BEFORE(td2, td, td_runq); 519 break; 520 } 521 } 522 if (td2 == NULL) { 523 /* We ran off the end of the TAILQ or it was empty. */ 524 kg->kg_runnable++; 525 TAILQ_INSERT_TAIL(&kg->kg_runq, td, td_runq); 526 } 527 528 /* 529 * If we have a slot to use, then put the thread on the system 530 * run queue and if needed, readjust the last_assigned pointer. 531 * it may be that we need to schedule something anyhow 532 * even if the availabel slots are -ve so that 533 * all the items < last_assigned are scheduled. 534 */ 535 if (kg->kg_avail_opennings > 0) { 536 if (tda == NULL) { 537 /* 538 * No pre-existing last assigned so whoever is first 539 * gets the slot.. (maybe us) 540 */ 541 td2 = TAILQ_FIRST(&kg->kg_runq); 542 kg->kg_last_assigned = td2; 543 } else if (tda->td_priority > td->td_priority) { 544 td2 = td; 545 } else { 546 /* 547 * We are past last_assigned, so 548 * give the next slot to whatever is next, 549 * which may or may not be us. 550 */ 551 td2 = TAILQ_NEXT(tda, td_runq); 552 kg->kg_last_assigned = td2; 553 } 554 sched_add(td2, flags); 555 } else { 556 CTR3(KTR_RUNQ, "setrunqueue: held: td%p kg%p pid%d", 557 td, td->td_ksegrp, td->td_proc->p_pid); 558 if ((flags & SRQ_YIELDING) == 0) 559 maybe_preempt_in_ksegrp(td); 560 } 561 } 562 563 /* 564 * Kernel thread preemption implementation. Critical sections mark 565 * regions of code in which preemptions are not allowed. 566 */ 567 void 568 critical_enter(void) 569 { 570 struct thread *td; 571 572 td = curthread; 573 if (td->td_critnest == 0) 574 cpu_critical_enter(td); 575 td->td_critnest++; 576 } 577 578 void 579 critical_exit(void) 580 { 581 struct thread *td; 582 583 td = curthread; 584 KASSERT(td->td_critnest != 0, 585 ("critical_exit: td_critnest == 0")); 586 if (td->td_critnest == 1) { 587 if (td->td_pflags & TDP_WAKEPROC0) { 588 td->td_pflags &= ~TDP_WAKEPROC0; 589 wakeup(&proc0); 590 } 591 #ifdef PREEMPTION 592 mtx_assert(&sched_lock, MA_NOTOWNED); 593 if (td->td_pflags & TDP_OWEPREEMPT) { 594 mtx_lock_spin(&sched_lock); 595 mi_switch(SW_INVOL, NULL); 596 mtx_unlock_spin(&sched_lock); 597 } 598 #endif 599 td->td_critnest = 0; 600 cpu_critical_exit(td); 601 } else { 602 td->td_critnest--; 603 } 604 } 605 606 /* 607 * This function is called when a thread is about to be put on run queue 608 * because it has been made runnable or its priority has been adjusted. It 609 * determines if the new thread should be immediately preempted to. If so, 610 * it switches to it and eventually returns true. If not, it returns false 611 * so that the caller may place the thread on an appropriate run queue. 612 */ 613 int 614 maybe_preempt(struct thread *td) 615 { 616 #ifdef PREEMPTION 617 struct thread *ctd; 618 int cpri, pri; 619 #endif 620 621 mtx_assert(&sched_lock, MA_OWNED); 622 #ifdef PREEMPTION 623 /* 624 * The new thread should not preempt the current thread if any of the 625 * following conditions are true: 626 * 627 * - The current thread has a higher (numerically lower) or 628 * equivalent priority. Note that this prevents curthread from 629 * trying to preempt to itself. 630 * - It is too early in the boot for context switches (cold is set). 631 * - The current thread has an inhibitor set or is in the process of 632 * exiting. In this case, the current thread is about to switch 633 * out anyways, so there's no point in preempting. If we did, 634 * the current thread would not be properly resumed as well, so 635 * just avoid that whole landmine. 636 * - If the new thread's priority is not a realtime priority and 637 * the current thread's priority is not an idle priority and 638 * FULL_PREEMPTION is disabled. 639 * 640 * If all of these conditions are false, but the current thread is in 641 * a nested critical section, then we have to defer the preemption 642 * until we exit the critical section. Otherwise, switch immediately 643 * to the new thread. 644 */ 645 ctd = curthread; 646 KASSERT ((ctd->td_kse != NULL && ctd->td_kse->ke_thread == ctd), 647 ("thread has no (or wrong) sched-private part.")); 648 KASSERT((td->td_inhibitors == 0), 649 ("maybe_preempt: trying to run inhibitted thread")); 650 pri = td->td_priority; 651 cpri = ctd->td_priority; 652 if (pri >= cpri || cold /* || dumping */ || TD_IS_INHIBITED(ctd) || 653 td->td_kse->ke_state != KES_THREAD) 654 return (0); 655 #ifndef FULL_PREEMPTION 656 if (!(pri >= PRI_MIN_ITHD && pri <= PRI_MAX_ITHD) && 657 !(cpri >= PRI_MIN_IDLE)) 658 return (0); 659 #endif 660 if (ctd->td_critnest > 1) { 661 CTR1(KTR_PROC, "maybe_preempt: in critical section %d", 662 ctd->td_critnest); 663 ctd->td_pflags |= TDP_OWEPREEMPT; 664 return (0); 665 } 666 667 /* 668 * Thread is runnable but not yet put on system run queue. 669 */ 670 MPASS(TD_ON_RUNQ(td)); 671 MPASS(td->td_sched->ke_state != KES_ONRUNQ); 672 if (td->td_proc->p_flag & P_HADTHREADS) { 673 /* 674 * If this is a threaded process we actually ARE on the 675 * ksegrp run queue so take it off that first. 676 * Also undo any damage done to the last_assigned pointer. 677 * XXX Fix setrunqueue so this isn't needed 678 */ 679 struct ksegrp *kg; 680 681 kg = td->td_ksegrp; 682 if (kg->kg_last_assigned == td) 683 kg->kg_last_assigned = 684 TAILQ_PREV(td, threadqueue, td_runq); 685 TAILQ_REMOVE(&kg->kg_runq, td, td_runq); 686 } 687 688 TD_SET_RUNNING(td); 689 CTR3(KTR_PROC, "preempting to thread %p (pid %d, %s)\n", td, 690 td->td_proc->p_pid, td->td_proc->p_comm); 691 mi_switch(SW_INVOL|SW_PREEMPT, td); 692 return (1); 693 #else 694 return (0); 695 #endif 696 } 697 698 #if 0 699 #ifndef PREEMPTION 700 /* XXX: There should be a non-static version of this. */ 701 static void 702 printf_caddr_t(void *data) 703 { 704 printf("%s", (char *)data); 705 } 706 static char preempt_warning[] = 707 "WARNING: Kernel preemption is disabled, expect reduced performance.\n"; 708 SYSINIT(preempt_warning, SI_SUB_COPYRIGHT, SI_ORDER_ANY, printf_caddr_t, 709 preempt_warning) 710 #endif 711 #endif 712 713 /************************************************************************ 714 * SYSTEM RUN QUEUE manipulations and tests * 715 ************************************************************************/ 716 /* 717 * Initialize a run structure. 718 */ 719 void 720 runq_init(struct runq *rq) 721 { 722 int i; 723 724 bzero(rq, sizeof *rq); 725 for (i = 0; i < RQ_NQS; i++) 726 TAILQ_INIT(&rq->rq_queues[i]); 727 } 728 729 /* 730 * Clear the status bit of the queue corresponding to priority level pri, 731 * indicating that it is empty. 732 */ 733 static __inline void 734 runq_clrbit(struct runq *rq, int pri) 735 { 736 struct rqbits *rqb; 737 738 rqb = &rq->rq_status; 739 CTR4(KTR_RUNQ, "runq_clrbit: bits=%#x %#x bit=%#x word=%d", 740 rqb->rqb_bits[RQB_WORD(pri)], 741 rqb->rqb_bits[RQB_WORD(pri)] & ~RQB_BIT(pri), 742 RQB_BIT(pri), RQB_WORD(pri)); 743 rqb->rqb_bits[RQB_WORD(pri)] &= ~RQB_BIT(pri); 744 } 745 746 /* 747 * Find the index of the first non-empty run queue. This is done by 748 * scanning the status bits, a set bit indicates a non-empty queue. 749 */ 750 static __inline int 751 runq_findbit(struct runq *rq) 752 { 753 struct rqbits *rqb; 754 int pri; 755 int i; 756 757 rqb = &rq->rq_status; 758 for (i = 0; i < RQB_LEN; i++) 759 if (rqb->rqb_bits[i]) { 760 pri = RQB_FFS(rqb->rqb_bits[i]) + (i << RQB_L2BPW); 761 CTR3(KTR_RUNQ, "runq_findbit: bits=%#x i=%d pri=%d", 762 rqb->rqb_bits[i], i, pri); 763 return (pri); 764 } 765 766 return (-1); 767 } 768 769 /* 770 * Set the status bit of the queue corresponding to priority level pri, 771 * indicating that it is non-empty. 772 */ 773 static __inline void 774 runq_setbit(struct runq *rq, int pri) 775 { 776 struct rqbits *rqb; 777 778 rqb = &rq->rq_status; 779 CTR4(KTR_RUNQ, "runq_setbit: bits=%#x %#x bit=%#x word=%d", 780 rqb->rqb_bits[RQB_WORD(pri)], 781 rqb->rqb_bits[RQB_WORD(pri)] | RQB_BIT(pri), 782 RQB_BIT(pri), RQB_WORD(pri)); 783 rqb->rqb_bits[RQB_WORD(pri)] |= RQB_BIT(pri); 784 } 785 786 /* 787 * Add the KSE to the queue specified by its priority, and set the 788 * corresponding status bit. 789 */ 790 void 791 runq_add(struct runq *rq, struct kse *ke, int flags) 792 { 793 struct rqhead *rqh; 794 int pri; 795 796 pri = ke->ke_thread->td_priority / RQ_PPQ; 797 ke->ke_rqindex = pri; 798 runq_setbit(rq, pri); 799 rqh = &rq->rq_queues[pri]; 800 CTR5(KTR_RUNQ, "runq_add: td=%p ke=%p pri=%d %d rqh=%p", 801 ke->ke_thread, ke, ke->ke_thread->td_priority, pri, rqh); 802 if (flags & SRQ_PREEMPTED) { 803 TAILQ_INSERT_HEAD(rqh, ke, ke_procq); 804 } else { 805 TAILQ_INSERT_TAIL(rqh, ke, ke_procq); 806 } 807 } 808 809 /* 810 * Return true if there are runnable processes of any priority on the run 811 * queue, false otherwise. Has no side effects, does not modify the run 812 * queue structure. 813 */ 814 int 815 runq_check(struct runq *rq) 816 { 817 struct rqbits *rqb; 818 int i; 819 820 rqb = &rq->rq_status; 821 for (i = 0; i < RQB_LEN; i++) 822 if (rqb->rqb_bits[i]) { 823 CTR2(KTR_RUNQ, "runq_check: bits=%#x i=%d", 824 rqb->rqb_bits[i], i); 825 return (1); 826 } 827 CTR0(KTR_RUNQ, "runq_check: empty"); 828 829 return (0); 830 } 831 832 #if defined(SMP) && defined(SCHED_4BSD) 833 int runq_fuzz = 1; 834 SYSCTL_INT(_kern_sched, OID_AUTO, runq_fuzz, CTLFLAG_RW, &runq_fuzz, 0, ""); 835 #endif 836 837 /* 838 * Find the highest priority process on the run queue. 839 */ 840 struct kse * 841 runq_choose(struct runq *rq) 842 { 843 struct rqhead *rqh; 844 struct kse *ke; 845 int pri; 846 847 mtx_assert(&sched_lock, MA_OWNED); 848 while ((pri = runq_findbit(rq)) != -1) { 849 rqh = &rq->rq_queues[pri]; 850 #if defined(SMP) && defined(SCHED_4BSD) 851 /* fuzz == 1 is normal.. 0 or less are ignored */ 852 if (runq_fuzz > 1) { 853 /* 854 * In the first couple of entries, check if 855 * there is one for our CPU as a preference. 856 */ 857 int count = runq_fuzz; 858 int cpu = PCPU_GET(cpuid); 859 struct kse *ke2; 860 ke2 = ke = TAILQ_FIRST(rqh); 861 862 while (count-- && ke2) { 863 if (ke->ke_thread->td_lastcpu == cpu) { 864 ke = ke2; 865 break; 866 } 867 ke2 = TAILQ_NEXT(ke2, ke_procq); 868 } 869 } else 870 #endif 871 ke = TAILQ_FIRST(rqh); 872 KASSERT(ke != NULL, ("runq_choose: no proc on busy queue")); 873 CTR3(KTR_RUNQ, 874 "runq_choose: pri=%d kse=%p rqh=%p", pri, ke, rqh); 875 return (ke); 876 } 877 CTR1(KTR_RUNQ, "runq_choose: idleproc pri=%d", pri); 878 879 return (NULL); 880 } 881 882 /* 883 * Remove the KSE from the queue specified by its priority, and clear the 884 * corresponding status bit if the queue becomes empty. 885 * Caller must set ke->ke_state afterwards. 886 */ 887 void 888 runq_remove(struct runq *rq, struct kse *ke) 889 { 890 struct rqhead *rqh; 891 int pri; 892 893 KASSERT(ke->ke_proc->p_sflag & PS_INMEM, 894 ("runq_remove: process swapped out")); 895 pri = ke->ke_rqindex; 896 rqh = &rq->rq_queues[pri]; 897 CTR5(KTR_RUNQ, "runq_remove: td=%p, ke=%p pri=%d %d rqh=%p", 898 ke->ke_thread, ke, ke->ke_thread->td_priority, pri, rqh); 899 KASSERT(ke != NULL, ("runq_remove: no proc on busy queue")); 900 TAILQ_REMOVE(rqh, ke, ke_procq); 901 if (TAILQ_EMPTY(rqh)) { 902 CTR0(KTR_RUNQ, "runq_remove: empty"); 903 runq_clrbit(rq, pri); 904 } 905 } 906 907 /****** functions that are temporarily here ***********/ 908 #include <vm/uma.h> 909 #define RANGEOF(type, start, end) (offsetof(type, end) - offsetof(type, start)) 910 extern struct mtx kse_zombie_lock; 911 912 /* 913 * Allocate scheduler specific per-process resources. 914 * The thread and ksegrp have already been linked in. 915 * In this case just set the default concurrency value. 916 * 917 * Called from: 918 * proc_init() (UMA init method) 919 */ 920 void 921 sched_newproc(struct proc *p, struct ksegrp *kg, struct thread *td) 922 { 923 924 /* This can go in sched_fork */ 925 sched_init_concurrency(kg); 926 } 927 928 /* 929 * Called by the uma process fini routine.. 930 * undo anything we may have done in the uma_init method. 931 * Panic if it's not all 1:1:1:1 932 * Called from: 933 * proc_fini() (UMA method) 934 */ 935 void 936 sched_destroyproc(struct proc *p) 937 { 938 939 /* this function slated for destruction */ 940 KASSERT((p->p_numthreads == 1), ("Cached proc with > 1 thread ")); 941 KASSERT((p->p_numksegrps == 1), ("Cached proc with > 1 ksegrp ")); 942 } 943 944 #define RANGEOF(type, start, end) (offsetof(type, end) - offsetof(type, start)) 945 /* 946 * thread is being either created or recycled. 947 * Fix up the per-scheduler resources associated with it. 948 * Called from: 949 * sched_fork_thread() 950 * thread_dtor() (*may go away) 951 * thread_init() (*may go away) 952 */ 953 void 954 sched_newthread(struct thread *td) 955 { 956 struct td_sched *ke; 957 958 ke = (struct td_sched *) (td + 1); 959 bzero(ke, sizeof(*ke)); 960 td->td_sched = ke; 961 ke->ke_thread = td; 962 ke->ke_oncpu = NOCPU; 963 ke->ke_state = KES_THREAD; 964 } 965 966 /* 967 * Set up an initial concurrency of 1 968 * and set the given thread (if given) to be using that 969 * concurrency slot. 970 * May be used "offline"..before the ksegrp is attached to the world 971 * and thus wouldn't need schedlock in that case. 972 * Called from: 973 * thr_create() 974 * proc_init() (UMA) via sched_newproc() 975 */ 976 void 977 sched_init_concurrency(struct ksegrp *kg) 978 { 979 980 CTR1(KTR_RUNQ,"kg %p init slots and concurrency to 1", kg); 981 kg->kg_concurrency = 1; 982 kg->kg_avail_opennings = 1; 983 } 984 985 /* 986 * Change the concurrency of an existing ksegrp to N 987 * Called from: 988 * kse_create() 989 * kse_exit() 990 * thread_exit() 991 * thread_single() 992 */ 993 void 994 sched_set_concurrency(struct ksegrp *kg, int concurrency) 995 { 996 997 CTR4(KTR_RUNQ,"kg %p set concurrency to %d, slots %d -> %d", 998 kg, 999 concurrency, 1000 kg->kg_avail_opennings, 1001 kg->kg_avail_opennings + (concurrency - kg->kg_concurrency)); 1002 kg->kg_avail_opennings += (concurrency - kg->kg_concurrency); 1003 kg->kg_concurrency = concurrency; 1004 } 1005 1006 /* 1007 * Called from thread_exit() for all exiting thread 1008 * 1009 * Not to be confused with sched_exit_thread() 1010 * that is only called from thread_exit() for threads exiting 1011 * without the rest of the process exiting because it is also called from 1012 * sched_exit() and we wouldn't want to call it twice. 1013 * XXX This can probably be fixed. 1014 */ 1015 void 1016 sched_thread_exit(struct thread *td) 1017 { 1018 1019 SLOT_RELEASE(td->td_ksegrp); 1020 slot_fill(td->td_ksegrp); 1021 } 1022 1023 #endif /* KERN_SWITCH_INCLUDE */
Cache object: 21bf68a9b64b7c8e3e6d1657122b4e38
[ source navigation ] [ diff markup ] [ identifier search ] [ freetext search ] [ file search ] [ list types ] [ track identifier ]