1 /*- 2 * SPDX-License-Identifier: BSD-3-Clause 3 * 4 * Copyright (c) 1982, 1986, 1990, 1991, 1993 5 * The Regents of the University of California. All rights reserved. 6 * (c) UNIX System Laboratories, Inc. 7 * All or some portions of this file are derived from material licensed 8 * to the University of California by American Telephone and Telegraph 9 * Co. or Unix System Laboratories, Inc. and are reproduced herein with 10 * the permission of UNIX System Laboratories, Inc. 11 * 12 * Redistribution and use in source and binary forms, with or without 13 * modification, are permitted provided that the following conditions 14 * are met: 15 * 1. Redistributions of source code must retain the above copyright 16 * notice, this list of conditions and the following disclaimer. 17 * 2. Redistributions in binary form must reproduce the above copyright 18 * notice, this list of conditions and the following disclaimer in the 19 * documentation and/or other materials provided with the distribution. 20 * 3. Neither the name of the University nor the names of its contributors 21 * may be used to endorse or promote products derived from this software 22 * without specific prior written permission. 23 * 24 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 25 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 26 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 27 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 28 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 29 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 30 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 31 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 32 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 33 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 34 * SUCH DAMAGE. 35 * 36 * @(#)kern_synch.c 8.9 (Berkeley) 5/19/95 37 */ 38 39 #include <sys/cdefs.h> 40 __FBSDID("$FreeBSD$"); 41 42 #include "opt_ktrace.h" 43 #include "opt_sched.h" 44 45 #include <sys/param.h> 46 #include <sys/systm.h> 47 #include <sys/condvar.h> 48 #include <sys/kdb.h> 49 #include <sys/kernel.h> 50 #include <sys/ktr.h> 51 #include <sys/lock.h> 52 #include <sys/mutex.h> 53 #include <sys/proc.h> 54 #include <sys/resourcevar.h> 55 #include <sys/refcount.h> 56 #include <sys/sched.h> 57 #include <sys/sdt.h> 58 #include <sys/signalvar.h> 59 #include <sys/sleepqueue.h> 60 #include <sys/smp.h> 61 #include <sys/sx.h> 62 #include <sys/sysctl.h> 63 #include <sys/sysproto.h> 64 #include <sys/vmmeter.h> 65 #ifdef KTRACE 66 #include <sys/uio.h> 67 #include <sys/ktrace.h> 68 #endif 69 #ifdef EPOCH_TRACE 70 #include <sys/epoch.h> 71 #endif 72 73 #include <machine/cpu.h> 74 75 static void synch_setup(void *dummy); 76 SYSINIT(synch_setup, SI_SUB_KICK_SCHEDULER, SI_ORDER_FIRST, synch_setup, 77 NULL); 78 79 int hogticks; 80 static uint8_t pause_wchan[MAXCPU]; 81 82 static struct callout loadav_callout; 83 84 struct loadavg averunnable = 85 { {0, 0, 0}, FSCALE }; /* load average, of runnable procs */ 86 /* 87 * Constants for averages over 1, 5, and 15 minutes 88 * when sampling at 5 second intervals. 89 */ 90 static fixpt_t cexp[3] = { 91 0.9200444146293232 * FSCALE, /* exp(-1/12) */ 92 0.9834714538216174 * FSCALE, /* exp(-1/60) */ 93 0.9944598480048967 * FSCALE, /* exp(-1/180) */ 94 }; 95 96 /* kernel uses `FSCALE', userland (SHOULD) use kern.fscale */ 97 SYSCTL_INT(_kern, OID_AUTO, fscale, CTLFLAG_RD, SYSCTL_NULL_INT_PTR, FSCALE, ""); 98 99 static void loadav(void *arg); 100 101 SDT_PROVIDER_DECLARE(sched); 102 SDT_PROBE_DEFINE(sched, , , preempt); 103 104 static void 105 sleepinit(void *unused) 106 { 107 108 hogticks = (hz / 10) * 2; /* Default only. */ 109 init_sleepqueues(); 110 } 111 112 /* 113 * vmem tries to lock the sleepq mutexes when free'ing kva, so make sure 114 * it is available. 115 */ 116 SYSINIT(sleepinit, SI_SUB_KMEM, SI_ORDER_ANY, sleepinit, NULL); 117 118 /* 119 * General sleep call. Suspends the current thread until a wakeup is 120 * performed on the specified identifier. The thread will then be made 121 * runnable with the specified priority. Sleeps at most sbt units of time 122 * (0 means no timeout). If pri includes the PCATCH flag, let signals 123 * interrupt the sleep, otherwise ignore them while sleeping. Returns 0 if 124 * awakened, EWOULDBLOCK if the timeout expires. If PCATCH is set and a 125 * signal becomes pending, ERESTART is returned if the current system 126 * call should be restarted if possible, and EINTR is returned if the system 127 * call should be interrupted by the signal (return EINTR). 128 * 129 * The lock argument is unlocked before the caller is suspended, and 130 * re-locked before _sleep() returns. If priority includes the PDROP 131 * flag the lock is not re-locked before returning. 132 */ 133 int 134 _sleep(void *ident, struct lock_object *lock, int priority, 135 const char *wmesg, sbintime_t sbt, sbintime_t pr, int flags) 136 { 137 struct thread *td; 138 struct lock_class *class; 139 uintptr_t lock_state; 140 int catch, pri, rval, sleepq_flags; 141 WITNESS_SAVE_DECL(lock_witness); 142 143 td = curthread; 144 #ifdef KTRACE 145 if (KTRPOINT(td, KTR_CSW)) 146 ktrcsw(1, 0, wmesg); 147 #endif 148 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock, 149 "Sleeping on \"%s\"", wmesg); 150 KASSERT(sbt != 0 || mtx_owned(&Giant) || lock != NULL, 151 ("sleeping without a lock")); 152 KASSERT(ident != NULL, ("_sleep: NULL ident")); 153 KASSERT(TD_IS_RUNNING(td), ("_sleep: curthread not running")); 154 #ifdef EPOCH_TRACE 155 if (__predict_false(curthread->td_epochnest > 0)) 156 epoch_trace_list(curthread); 157 #endif 158 KASSERT(td->td_epochnest == 0, ("sleeping in an epoch section")); 159 if (priority & PDROP) 160 KASSERT(lock != NULL && lock != &Giant.lock_object, 161 ("PDROP requires a non-Giant lock")); 162 if (lock != NULL) 163 class = LOCK_CLASS(lock); 164 else 165 class = NULL; 166 167 if (SCHEDULER_STOPPED_TD(td)) { 168 if (lock != NULL && priority & PDROP) 169 class->lc_unlock(lock); 170 return (0); 171 } 172 catch = priority & PCATCH; 173 pri = priority & PRIMASK; 174 175 KASSERT(!TD_ON_SLEEPQ(td), ("recursive sleep")); 176 177 if ((uint8_t *)ident >= &pause_wchan[0] && 178 (uint8_t *)ident <= &pause_wchan[MAXCPU - 1]) 179 sleepq_flags = SLEEPQ_PAUSE; 180 else 181 sleepq_flags = SLEEPQ_SLEEP; 182 if (catch) 183 sleepq_flags |= SLEEPQ_INTERRUPTIBLE; 184 185 sleepq_lock(ident); 186 CTR5(KTR_PROC, "sleep: thread %ld (pid %ld, %s) on %s (%p)", 187 td->td_tid, td->td_proc->p_pid, td->td_name, wmesg, ident); 188 189 if (lock == &Giant.lock_object) 190 mtx_assert(&Giant, MA_OWNED); 191 DROP_GIANT(); 192 if (lock != NULL && lock != &Giant.lock_object && 193 !(class->lc_flags & LC_SLEEPABLE)) { 194 WITNESS_SAVE(lock, lock_witness); 195 lock_state = class->lc_unlock(lock); 196 } else 197 /* GCC needs to follow the Yellow Brick Road */ 198 lock_state = -1; 199 200 /* 201 * We put ourselves on the sleep queue and start our timeout 202 * before calling thread_suspend_check, as we could stop there, 203 * and a wakeup or a SIGCONT (or both) could occur while we were 204 * stopped without resuming us. Thus, we must be ready for sleep 205 * when cursig() is called. If the wakeup happens while we're 206 * stopped, then td will no longer be on a sleep queue upon 207 * return from cursig(). 208 */ 209 sleepq_add(ident, lock, wmesg, sleepq_flags, 0); 210 if (sbt != 0) 211 sleepq_set_timeout_sbt(ident, sbt, pr, flags); 212 if (lock != NULL && class->lc_flags & LC_SLEEPABLE) { 213 sleepq_release(ident); 214 WITNESS_SAVE(lock, lock_witness); 215 lock_state = class->lc_unlock(lock); 216 sleepq_lock(ident); 217 } 218 if (sbt != 0 && catch) 219 rval = sleepq_timedwait_sig(ident, pri); 220 else if (sbt != 0) 221 rval = sleepq_timedwait(ident, pri); 222 else if (catch) 223 rval = sleepq_wait_sig(ident, pri); 224 else { 225 sleepq_wait(ident, pri); 226 rval = 0; 227 } 228 #ifdef KTRACE 229 if (KTRPOINT(td, KTR_CSW)) 230 ktrcsw(0, 0, wmesg); 231 #endif 232 PICKUP_GIANT(); 233 if (lock != NULL && lock != &Giant.lock_object && !(priority & PDROP)) { 234 class->lc_lock(lock, lock_state); 235 WITNESS_RESTORE(lock, lock_witness); 236 } 237 return (rval); 238 } 239 240 int 241 msleep_spin_sbt(void *ident, struct mtx *mtx, const char *wmesg, 242 sbintime_t sbt, sbintime_t pr, int flags) 243 { 244 struct thread *td; 245 int rval; 246 WITNESS_SAVE_DECL(mtx); 247 248 td = curthread; 249 KASSERT(mtx != NULL, ("sleeping without a mutex")); 250 KASSERT(ident != NULL, ("msleep_spin_sbt: NULL ident")); 251 KASSERT(TD_IS_RUNNING(td), ("msleep_spin_sbt: curthread not running")); 252 253 if (SCHEDULER_STOPPED_TD(td)) 254 return (0); 255 256 sleepq_lock(ident); 257 CTR5(KTR_PROC, "msleep_spin: thread %ld (pid %ld, %s) on %s (%p)", 258 td->td_tid, td->td_proc->p_pid, td->td_name, wmesg, ident); 259 260 DROP_GIANT(); 261 mtx_assert(mtx, MA_OWNED | MA_NOTRECURSED); 262 WITNESS_SAVE(&mtx->lock_object, mtx); 263 mtx_unlock_spin(mtx); 264 265 /* 266 * We put ourselves on the sleep queue and start our timeout. 267 */ 268 sleepq_add(ident, &mtx->lock_object, wmesg, SLEEPQ_SLEEP, 0); 269 if (sbt != 0) 270 sleepq_set_timeout_sbt(ident, sbt, pr, flags); 271 272 /* 273 * Can't call ktrace with any spin locks held so it can lock the 274 * ktrace_mtx lock, and WITNESS_WARN considers it an error to hold 275 * any spin lock. Thus, we have to drop the sleepq spin lock while 276 * we handle those requests. This is safe since we have placed our 277 * thread on the sleep queue already. 278 */ 279 #ifdef KTRACE 280 if (KTRPOINT(td, KTR_CSW)) { 281 sleepq_release(ident); 282 ktrcsw(1, 0, wmesg); 283 sleepq_lock(ident); 284 } 285 #endif 286 #ifdef WITNESS 287 sleepq_release(ident); 288 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, "Sleeping on \"%s\"", 289 wmesg); 290 sleepq_lock(ident); 291 #endif 292 if (sbt != 0) 293 rval = sleepq_timedwait(ident, 0); 294 else { 295 sleepq_wait(ident, 0); 296 rval = 0; 297 } 298 #ifdef KTRACE 299 if (KTRPOINT(td, KTR_CSW)) 300 ktrcsw(0, 0, wmesg); 301 #endif 302 PICKUP_GIANT(); 303 mtx_lock_spin(mtx); 304 WITNESS_RESTORE(&mtx->lock_object, mtx); 305 return (rval); 306 } 307 308 /* 309 * pause_sbt() delays the calling thread by the given signed binary 310 * time. During cold bootup, pause_sbt() uses the DELAY() function 311 * instead of the _sleep() function to do the waiting. The "sbt" 312 * argument must be greater than or equal to zero. A "sbt" value of 313 * zero is equivalent to a "sbt" value of one tick. 314 */ 315 int 316 pause_sbt(const char *wmesg, sbintime_t sbt, sbintime_t pr, int flags) 317 { 318 KASSERT(sbt >= 0, ("pause_sbt: timeout must be >= 0")); 319 320 /* silently convert invalid timeouts */ 321 if (sbt == 0) 322 sbt = tick_sbt; 323 324 if ((cold && curthread == &thread0) || kdb_active || 325 SCHEDULER_STOPPED()) { 326 /* 327 * We delay one second at a time to avoid overflowing the 328 * system specific DELAY() function(s): 329 */ 330 while (sbt >= SBT_1S) { 331 DELAY(1000000); 332 sbt -= SBT_1S; 333 } 334 /* Do the delay remainder, if any */ 335 sbt = howmany(sbt, SBT_1US); 336 if (sbt > 0) 337 DELAY(sbt); 338 return (EWOULDBLOCK); 339 } 340 return (_sleep(&pause_wchan[curcpu], NULL, 341 (flags & C_CATCH) ? PCATCH : 0, wmesg, sbt, pr, flags)); 342 } 343 344 /* 345 * Potentially release the last reference for refcount. Check for 346 * unlikely conditions and signal the caller as to whether it was 347 * the final ref. 348 */ 349 bool 350 refcount_release_last(volatile u_int *count, u_int n, u_int old) 351 { 352 u_int waiter; 353 354 waiter = old & REFCOUNT_WAITER; 355 old = REFCOUNT_COUNT(old); 356 if (__predict_false(n > old || REFCOUNT_SATURATED(old))) { 357 /* 358 * Avoid multiple destructor invocations if underflow occurred. 359 * This is not perfect since the memory backing the containing 360 * object may already have been reallocated. 361 */ 362 _refcount_update_saturated(count); 363 return (false); 364 } 365 366 /* 367 * Attempt to atomically clear the waiter bit. Wakeup waiters 368 * if we are successful. 369 */ 370 if (waiter != 0 && atomic_cmpset_int(count, REFCOUNT_WAITER, 0)) 371 wakeup(__DEVOLATILE(u_int *, count)); 372 373 /* 374 * Last reference. Signal the user to call the destructor. 375 * 376 * Ensure that the destructor sees all updates. The fence_rel 377 * at the start of refcount_releasen synchronizes with this fence. 378 */ 379 atomic_thread_fence_acq(); 380 return (true); 381 } 382 383 /* 384 * Wait for a refcount wakeup. This does not guarantee that the ref is still 385 * zero on return and may be subject to transient wakeups. Callers wanting 386 * a precise answer should use refcount_wait(). 387 */ 388 void 389 refcount_sleep(volatile u_int *count, const char *wmesg, int pri) 390 { 391 void *wchan; 392 u_int old; 393 394 if (REFCOUNT_COUNT(*count) == 0) 395 return; 396 wchan = __DEVOLATILE(void *, count); 397 sleepq_lock(wchan); 398 old = *count; 399 for (;;) { 400 if (REFCOUNT_COUNT(old) == 0) { 401 sleepq_release(wchan); 402 return; 403 } 404 if (old & REFCOUNT_WAITER) 405 break; 406 if (atomic_fcmpset_int(count, &old, old | REFCOUNT_WAITER)) 407 break; 408 } 409 sleepq_add(wchan, NULL, wmesg, 0, 0); 410 sleepq_wait(wchan, pri); 411 } 412 413 /* 414 * Make all threads sleeping on the specified identifier runnable. 415 */ 416 void 417 wakeup(void *ident) 418 { 419 int wakeup_swapper; 420 421 sleepq_lock(ident); 422 wakeup_swapper = sleepq_broadcast(ident, SLEEPQ_SLEEP, 0, 0); 423 sleepq_release(ident); 424 if (wakeup_swapper) { 425 KASSERT(ident != &proc0, 426 ("wakeup and wakeup_swapper and proc0")); 427 kick_proc0(); 428 } 429 } 430 431 /* 432 * Make a thread sleeping on the specified identifier runnable. 433 * May wake more than one thread if a target thread is currently 434 * swapped out. 435 */ 436 void 437 wakeup_one(void *ident) 438 { 439 int wakeup_swapper; 440 441 sleepq_lock(ident); 442 wakeup_swapper = sleepq_signal(ident, SLEEPQ_SLEEP, 0, 0); 443 sleepq_release(ident); 444 if (wakeup_swapper) 445 kick_proc0(); 446 } 447 448 void 449 wakeup_any(void *ident) 450 { 451 int wakeup_swapper; 452 453 sleepq_lock(ident); 454 wakeup_swapper = sleepq_signal(ident, SLEEPQ_SLEEP | SLEEPQ_UNFAIR, 455 0, 0); 456 sleepq_release(ident); 457 if (wakeup_swapper) 458 kick_proc0(); 459 } 460 461 static void 462 kdb_switch(void) 463 { 464 thread_unlock(curthread); 465 kdb_backtrace(); 466 kdb_reenter(); 467 panic("%s: did not reenter debugger", __func__); 468 } 469 470 /* 471 * The machine independent parts of context switching. 472 */ 473 void 474 mi_switch(int flags, struct thread *newtd) 475 { 476 uint64_t runtime, new_switchtime; 477 struct thread *td; 478 479 td = curthread; /* XXX */ 480 THREAD_LOCK_ASSERT(td, MA_OWNED | MA_NOTRECURSED); 481 KASSERT(!TD_ON_RUNQ(td), ("mi_switch: called by old code")); 482 #ifdef INVARIANTS 483 if (!TD_ON_LOCK(td) && !TD_IS_RUNNING(td)) 484 mtx_assert(&Giant, MA_NOTOWNED); 485 #endif 486 KASSERT(td->td_critnest == 1 || panicstr, 487 ("mi_switch: switch in a critical section")); 488 KASSERT((flags & (SW_INVOL | SW_VOL)) != 0, 489 ("mi_switch: switch must be voluntary or involuntary")); 490 KASSERT(newtd != curthread, ("mi_switch: preempting back to ourself")); 491 492 /* 493 * Don't perform context switches from the debugger. 494 */ 495 if (kdb_active) 496 kdb_switch(); 497 if (SCHEDULER_STOPPED_TD(td)) 498 return; 499 if (flags & SW_VOL) { 500 td->td_ru.ru_nvcsw++; 501 td->td_swvoltick = ticks; 502 } else { 503 td->td_ru.ru_nivcsw++; 504 td->td_swinvoltick = ticks; 505 } 506 #ifdef SCHED_STATS 507 SCHED_STAT_INC(sched_switch_stats[flags & SW_TYPE_MASK]); 508 #endif 509 /* 510 * Compute the amount of time during which the current 511 * thread was running, and add that to its total so far. 512 */ 513 new_switchtime = cpu_ticks(); 514 runtime = new_switchtime - PCPU_GET(switchtime); 515 td->td_runtime += runtime; 516 td->td_incruntime += runtime; 517 PCPU_SET(switchtime, new_switchtime); 518 td->td_generation++; /* bump preempt-detect counter */ 519 VM_CNT_INC(v_swtch); 520 PCPU_SET(switchticks, ticks); 521 CTR4(KTR_PROC, "mi_switch: old thread %ld (td_sched %p, pid %ld, %s)", 522 td->td_tid, td_get_sched(td), td->td_proc->p_pid, td->td_name); 523 #ifdef KDTRACE_HOOKS 524 if (SDT_PROBES_ENABLED() && 525 ((flags & SW_PREEMPT) != 0 || ((flags & SW_INVOL) != 0 && 526 (flags & SW_TYPE_MASK) == SWT_NEEDRESCHED))) 527 SDT_PROBE0(sched, , , preempt); 528 #endif 529 sched_switch(td, newtd, flags); 530 CTR4(KTR_PROC, "mi_switch: new thread %ld (td_sched %p, pid %ld, %s)", 531 td->td_tid, td_get_sched(td), td->td_proc->p_pid, td->td_name); 532 533 /* 534 * If the last thread was exiting, finish cleaning it up. 535 */ 536 if ((td = PCPU_GET(deadthread))) { 537 PCPU_SET(deadthread, NULL); 538 thread_stash(td); 539 } 540 } 541 542 /* 543 * Change thread state to be runnable, placing it on the run queue if 544 * it is in memory. If it is swapped out, return true so our caller 545 * will know to awaken the swapper. 546 */ 547 int 548 setrunnable(struct thread *td) 549 { 550 551 THREAD_LOCK_ASSERT(td, MA_OWNED); 552 KASSERT(td->td_proc->p_state != PRS_ZOMBIE, 553 ("setrunnable: pid %d is a zombie", td->td_proc->p_pid)); 554 switch (td->td_state) { 555 case TDS_RUNNING: 556 case TDS_RUNQ: 557 return (0); 558 case TDS_INHIBITED: 559 /* 560 * If we are only inhibited because we are swapped out 561 * then arange to swap in this process. Otherwise just return. 562 */ 563 if (td->td_inhibitors != TDI_SWAPPED) 564 return (0); 565 /* FALLTHROUGH */ 566 case TDS_CAN_RUN: 567 break; 568 default: 569 printf("state is 0x%x", td->td_state); 570 panic("setrunnable(2)"); 571 } 572 if ((td->td_flags & TDF_INMEM) == 0) { 573 if ((td->td_flags & TDF_SWAPINREQ) == 0) { 574 td->td_flags |= TDF_SWAPINREQ; 575 return (1); 576 } 577 } else 578 sched_wakeup(td); 579 return (0); 580 } 581 582 /* 583 * Compute a tenex style load average of a quantity on 584 * 1, 5 and 15 minute intervals. 585 */ 586 static void 587 loadav(void *arg) 588 { 589 int i, nrun; 590 struct loadavg *avg; 591 592 nrun = sched_load(); 593 avg = &averunnable; 594 595 for (i = 0; i < 3; i++) 596 avg->ldavg[i] = (cexp[i] * avg->ldavg[i] + 597 nrun * FSCALE * (FSCALE - cexp[i])) >> FSHIFT; 598 599 /* 600 * Schedule the next update to occur after 5 seconds, but add a 601 * random variation to avoid synchronisation with processes that 602 * run at regular intervals. 603 */ 604 callout_reset_sbt(&loadav_callout, 605 SBT_1US * (4000000 + (int)(random() % 2000001)), SBT_1US, 606 loadav, NULL, C_DIRECT_EXEC | C_PREL(32)); 607 } 608 609 /* ARGSUSED */ 610 static void 611 synch_setup(void *dummy) 612 { 613 callout_init(&loadav_callout, 1); 614 615 /* Kick off timeout driven events by calling first time. */ 616 loadav(NULL); 617 } 618 619 int 620 should_yield(void) 621 { 622 623 return ((u_int)ticks - (u_int)curthread->td_swvoltick >= hogticks); 624 } 625 626 void 627 maybe_yield(void) 628 { 629 630 if (should_yield()) 631 kern_yield(PRI_USER); 632 } 633 634 void 635 kern_yield(int prio) 636 { 637 struct thread *td; 638 639 td = curthread; 640 DROP_GIANT(); 641 thread_lock(td); 642 if (prio == PRI_USER) 643 prio = td->td_user_pri; 644 if (prio >= 0) 645 sched_prio(td, prio); 646 mi_switch(SW_VOL | SWT_RELINQUISH, NULL); 647 thread_unlock(td); 648 PICKUP_GIANT(); 649 } 650 651 /* 652 * General purpose yield system call. 653 */ 654 int 655 sys_yield(struct thread *td, struct yield_args *uap) 656 { 657 658 thread_lock(td); 659 if (PRI_BASE(td->td_pri_class) == PRI_TIMESHARE) 660 sched_prio(td, PRI_MAX_TIMESHARE); 661 mi_switch(SW_VOL | SWT_RELINQUISH, NULL); 662 thread_unlock(td); 663 td->td_retval[0] = 0; 664 return (0); 665 } 666