1 /*- 2 * Copyright (c) 1982, 1986, 1990, 1991, 1993 3 * The Regents of the University of California. All rights reserved. 4 * (c) UNIX System Laboratories, Inc. 5 * All or some portions of this file are derived from material licensed 6 * to the University of California by American Telephone and Telegraph 7 * Co. or Unix System Laboratories, Inc. and are reproduced herein with 8 * the permission of UNIX System Laboratories, Inc. 9 * 10 * Redistribution and use in source and binary forms, with or without 11 * modification, are permitted provided that the following conditions 12 * are met: 13 * 1. Redistributions of source code must retain the above copyright 14 * notice, this list of conditions and the following disclaimer. 15 * 2. Redistributions in binary form must reproduce the above copyright 16 * notice, this list of conditions and the following disclaimer in the 17 * documentation and/or other materials provided with the distribution. 18 * 4. Neither the name of the University nor the names of its contributors 19 * may be used to endorse or promote products derived from this software 20 * without specific prior written permission. 21 * 22 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32 * SUCH DAMAGE. 33 * 34 * @(#)kern_synch.c 8.9 (Berkeley) 5/19/95 35 */ 36 37 #include <sys/cdefs.h> 38 __FBSDID("$FreeBSD$"); 39 40 #include "opt_ktrace.h" 41 #include "opt_sched.h" 42 43 #include <sys/param.h> 44 #include <sys/systm.h> 45 #include <sys/condvar.h> 46 #include <sys/kdb.h> 47 #include <sys/kernel.h> 48 #include <sys/ktr.h> 49 #include <sys/lock.h> 50 #include <sys/mutex.h> 51 #include <sys/proc.h> 52 #include <sys/resourcevar.h> 53 #include <sys/sched.h> 54 #include <sys/sdt.h> 55 #include <sys/signalvar.h> 56 #include <sys/sleepqueue.h> 57 #include <sys/smp.h> 58 #include <sys/sx.h> 59 #include <sys/sysctl.h> 60 #include <sys/sysproto.h> 61 #include <sys/vmmeter.h> 62 #ifdef KTRACE 63 #include <sys/uio.h> 64 #include <sys/ktrace.h> 65 #endif 66 67 #include <machine/cpu.h> 68 69 #ifdef XEN 70 #include <vm/vm.h> 71 #include <vm/vm_param.h> 72 #include <vm/pmap.h> 73 #endif 74 75 #define KTDSTATE(td) \ 76 (((td)->td_inhibitors & TDI_SLEEPING) != 0 ? "sleep" : \ 77 ((td)->td_inhibitors & TDI_SUSPENDED) != 0 ? "suspended" : \ 78 ((td)->td_inhibitors & TDI_SWAPPED) != 0 ? "swapped" : \ 79 ((td)->td_inhibitors & TDI_LOCK) != 0 ? "blocked" : \ 80 ((td)->td_inhibitors & TDI_IWAIT) != 0 ? "iwait" : "yielding") 81 82 static void synch_setup(void *dummy); 83 SYSINIT(synch_setup, SI_SUB_KICK_SCHEDULER, SI_ORDER_FIRST, synch_setup, 84 NULL); 85 86 int hogticks; 87 static uint8_t pause_wchan[MAXCPU]; 88 89 static struct callout loadav_callout; 90 91 struct loadavg averunnable = 92 { {0, 0, 0}, FSCALE }; /* load average, of runnable procs */ 93 /* 94 * Constants for averages over 1, 5, and 15 minutes 95 * when sampling at 5 second intervals. 96 */ 97 static fixpt_t cexp[3] = { 98 0.9200444146293232 * FSCALE, /* exp(-1/12) */ 99 0.9834714538216174 * FSCALE, /* exp(-1/60) */ 100 0.9944598480048967 * FSCALE, /* exp(-1/180) */ 101 }; 102 103 /* kernel uses `FSCALE', userland (SHOULD) use kern.fscale */ 104 SYSCTL_INT(_kern, OID_AUTO, fscale, CTLFLAG_RD, SYSCTL_NULL_INT_PTR, FSCALE, ""); 105 106 static void loadav(void *arg); 107 108 SDT_PROVIDER_DECLARE(sched); 109 SDT_PROBE_DEFINE(sched, , , preempt); 110 111 /* 112 * These probes reference Solaris features that are not implemented in FreeBSD. 113 * Create the probes anyway for compatibility with existing D scripts; they'll 114 * just never fire. 115 */ 116 SDT_PROBE_DEFINE(sched, , , cpucaps__sleep); 117 SDT_PROBE_DEFINE(sched, , , cpucaps__wakeup); 118 SDT_PROBE_DEFINE(sched, , , schedctl__nopreempt); 119 SDT_PROBE_DEFINE(sched, , , schedctl__preempt); 120 SDT_PROBE_DEFINE(sched, , , schedctl__yield); 121 122 static void 123 sleepinit(void *unused) 124 { 125 126 hogticks = (hz / 10) * 2; /* Default only. */ 127 init_sleepqueues(); 128 } 129 130 /* 131 * vmem tries to lock the sleepq mutexes when free'ing kva, so make sure 132 * it is available. 133 */ 134 SYSINIT(sleepinit, SI_SUB_KMEM, SI_ORDER_ANY, sleepinit, 0); 135 136 /* 137 * General sleep call. Suspends the current thread until a wakeup is 138 * performed on the specified identifier. The thread will then be made 139 * runnable with the specified priority. Sleeps at most sbt units of time 140 * (0 means no timeout). If pri includes the PCATCH flag, let signals 141 * interrupt the sleep, otherwise ignore them while sleeping. Returns 0 if 142 * awakened, EWOULDBLOCK if the timeout expires. If PCATCH is set and a 143 * signal becomes pending, ERESTART is returned if the current system 144 * call should be restarted if possible, and EINTR is returned if the system 145 * call should be interrupted by the signal (return EINTR). 146 * 147 * The lock argument is unlocked before the caller is suspended, and 148 * re-locked before _sleep() returns. If priority includes the PDROP 149 * flag the lock is not re-locked before returning. 150 */ 151 int 152 _sleep(void *ident, struct lock_object *lock, int priority, 153 const char *wmesg, sbintime_t sbt, sbintime_t pr, int flags) 154 { 155 struct thread *td; 156 struct proc *p; 157 struct lock_class *class; 158 uintptr_t lock_state; 159 int catch, pri, rval, sleepq_flags; 160 WITNESS_SAVE_DECL(lock_witness); 161 162 td = curthread; 163 p = td->td_proc; 164 #ifdef KTRACE 165 if (KTRPOINT(td, KTR_CSW)) 166 ktrcsw(1, 0, wmesg); 167 #endif 168 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock, 169 "Sleeping on \"%s\"", wmesg); 170 KASSERT(sbt != 0 || mtx_owned(&Giant) || lock != NULL, 171 ("sleeping without a lock")); 172 KASSERT(p != NULL, ("msleep1")); 173 KASSERT(ident != NULL && TD_IS_RUNNING(td), ("msleep")); 174 if (priority & PDROP) 175 KASSERT(lock != NULL && lock != &Giant.lock_object, 176 ("PDROP requires a non-Giant lock")); 177 if (lock != NULL) 178 class = LOCK_CLASS(lock); 179 else 180 class = NULL; 181 182 if (cold || SCHEDULER_STOPPED()) { 183 /* 184 * During autoconfiguration, just return; 185 * don't run any other threads or panic below, 186 * in case this is the idle thread and already asleep. 187 * XXX: this used to do "s = splhigh(); splx(safepri); 188 * splx(s);" to give interrupts a chance, but there is 189 * no way to give interrupts a chance now. 190 */ 191 if (lock != NULL && priority & PDROP) 192 class->lc_unlock(lock); 193 return (0); 194 } 195 catch = priority & PCATCH; 196 pri = priority & PRIMASK; 197 198 /* 199 * If we are already on a sleep queue, then remove us from that 200 * sleep queue first. We have to do this to handle recursive 201 * sleeps. 202 */ 203 if (TD_ON_SLEEPQ(td)) 204 sleepq_remove(td, td->td_wchan); 205 206 if ((uint8_t *)ident >= &pause_wchan[0] && 207 (uint8_t *)ident <= &pause_wchan[MAXCPU - 1]) 208 sleepq_flags = SLEEPQ_PAUSE; 209 else 210 sleepq_flags = SLEEPQ_SLEEP; 211 if (catch) 212 sleepq_flags |= SLEEPQ_INTERRUPTIBLE; 213 214 sleepq_lock(ident); 215 CTR5(KTR_PROC, "sleep: thread %ld (pid %ld, %s) on %s (%p)", 216 td->td_tid, p->p_pid, td->td_name, wmesg, ident); 217 218 if (lock == &Giant.lock_object) 219 mtx_assert(&Giant, MA_OWNED); 220 DROP_GIANT(); 221 if (lock != NULL && lock != &Giant.lock_object && 222 !(class->lc_flags & LC_SLEEPABLE)) { 223 WITNESS_SAVE(lock, lock_witness); 224 lock_state = class->lc_unlock(lock); 225 } else 226 /* GCC needs to follow the Yellow Brick Road */ 227 lock_state = -1; 228 229 /* 230 * We put ourselves on the sleep queue and start our timeout 231 * before calling thread_suspend_check, as we could stop there, 232 * and a wakeup or a SIGCONT (or both) could occur while we were 233 * stopped without resuming us. Thus, we must be ready for sleep 234 * when cursig() is called. If the wakeup happens while we're 235 * stopped, then td will no longer be on a sleep queue upon 236 * return from cursig(). 237 */ 238 sleepq_add(ident, lock, wmesg, sleepq_flags, 0); 239 if (lock != NULL && class->lc_flags & LC_SLEEPABLE) { 240 sleepq_release(ident); 241 WITNESS_SAVE(lock, lock_witness); 242 lock_state = class->lc_unlock(lock); 243 if (sbt != 0) 244 sleepq_set_timeout_sbt(ident, sbt, pr, flags); 245 sleepq_lock(ident); 246 } else if (sbt != 0) { 247 sleepq_release(ident); 248 sleepq_set_timeout_sbt(ident, sbt, pr, flags); 249 sleepq_lock(ident); 250 } 251 if (sbt != 0 && catch) 252 rval = sleepq_timedwait_sig(ident, pri); 253 else if (sbt != 0) 254 rval = sleepq_timedwait(ident, pri); 255 else if (catch) 256 rval = sleepq_wait_sig(ident, pri); 257 else { 258 sleepq_wait(ident, pri); 259 rval = 0; 260 } 261 #ifdef KTRACE 262 if (KTRPOINT(td, KTR_CSW)) 263 ktrcsw(0, 0, wmesg); 264 #endif 265 PICKUP_GIANT(); 266 if (lock != NULL && lock != &Giant.lock_object && !(priority & PDROP)) { 267 class->lc_lock(lock, lock_state); 268 WITNESS_RESTORE(lock, lock_witness); 269 } 270 return (rval); 271 } 272 273 int 274 msleep_spin_sbt(void *ident, struct mtx *mtx, const char *wmesg, 275 sbintime_t sbt, sbintime_t pr, int flags) 276 { 277 struct thread *td; 278 struct proc *p; 279 int rval; 280 WITNESS_SAVE_DECL(mtx); 281 282 td = curthread; 283 p = td->td_proc; 284 KASSERT(mtx != NULL, ("sleeping without a mutex")); 285 KASSERT(p != NULL, ("msleep1")); 286 KASSERT(ident != NULL && TD_IS_RUNNING(td), ("msleep")); 287 288 if (cold || SCHEDULER_STOPPED()) { 289 /* 290 * During autoconfiguration, just return; 291 * don't run any other threads or panic below, 292 * in case this is the idle thread and already asleep. 293 * XXX: this used to do "s = splhigh(); splx(safepri); 294 * splx(s);" to give interrupts a chance, but there is 295 * no way to give interrupts a chance now. 296 */ 297 return (0); 298 } 299 300 sleepq_lock(ident); 301 CTR5(KTR_PROC, "msleep_spin: thread %ld (pid %ld, %s) on %s (%p)", 302 td->td_tid, p->p_pid, td->td_name, wmesg, ident); 303 304 DROP_GIANT(); 305 mtx_assert(mtx, MA_OWNED | MA_NOTRECURSED); 306 WITNESS_SAVE(&mtx->lock_object, mtx); 307 mtx_unlock_spin(mtx); 308 309 /* 310 * We put ourselves on the sleep queue and start our timeout. 311 */ 312 sleepq_add(ident, &mtx->lock_object, wmesg, SLEEPQ_SLEEP, 0); 313 if (sbt != 0) { 314 sleepq_release(ident); 315 sleepq_set_timeout_sbt(ident, sbt, pr, flags); 316 sleepq_lock(ident); 317 } 318 319 /* 320 * Can't call ktrace with any spin locks held so it can lock the 321 * ktrace_mtx lock, and WITNESS_WARN considers it an error to hold 322 * any spin lock. Thus, we have to drop the sleepq spin lock while 323 * we handle those requests. This is safe since we have placed our 324 * thread on the sleep queue already. 325 */ 326 #ifdef KTRACE 327 if (KTRPOINT(td, KTR_CSW)) { 328 sleepq_release(ident); 329 ktrcsw(1, 0, wmesg); 330 sleepq_lock(ident); 331 } 332 #endif 333 #ifdef WITNESS 334 sleepq_release(ident); 335 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, "Sleeping on \"%s\"", 336 wmesg); 337 sleepq_lock(ident); 338 #endif 339 if (sbt != 0) 340 rval = sleepq_timedwait(ident, 0); 341 else { 342 sleepq_wait(ident, 0); 343 rval = 0; 344 } 345 #ifdef KTRACE 346 if (KTRPOINT(td, KTR_CSW)) 347 ktrcsw(0, 0, wmesg); 348 #endif 349 PICKUP_GIANT(); 350 mtx_lock_spin(mtx); 351 WITNESS_RESTORE(&mtx->lock_object, mtx); 352 return (rval); 353 } 354 355 /* 356 * pause() delays the calling thread by the given number of system ticks. 357 * During cold bootup, pause() uses the DELAY() function instead of 358 * the tsleep() function to do the waiting. The "timo" argument must be 359 * greater than or equal to zero. A "timo" value of zero is equivalent 360 * to a "timo" value of one. 361 */ 362 int 363 pause_sbt(const char *wmesg, sbintime_t sbt, sbintime_t pr, int flags) 364 { 365 KASSERT(sbt >= 0, ("pause: timeout must be >= 0")); 366 367 /* silently convert invalid timeouts */ 368 if (sbt == 0) 369 sbt = tick_sbt; 370 371 if (cold || kdb_active) { 372 /* 373 * We delay one second at a time to avoid overflowing the 374 * system specific DELAY() function(s): 375 */ 376 while (sbt >= SBT_1S) { 377 DELAY(1000000); 378 sbt -= SBT_1S; 379 } 380 /* Do the delay remainder, if any */ 381 sbt = (sbt + SBT_1US - 1) / SBT_1US; 382 if (sbt > 0) 383 DELAY(sbt); 384 return (0); 385 } 386 return (_sleep(&pause_wchan[curcpu], NULL, 0, wmesg, sbt, pr, flags)); 387 } 388 389 /* 390 * Make all threads sleeping on the specified identifier runnable. 391 */ 392 void 393 wakeup(void *ident) 394 { 395 int wakeup_swapper; 396 397 sleepq_lock(ident); 398 wakeup_swapper = sleepq_broadcast(ident, SLEEPQ_SLEEP, 0, 0); 399 sleepq_release(ident); 400 if (wakeup_swapper) { 401 KASSERT(ident != &proc0, 402 ("wakeup and wakeup_swapper and proc0")); 403 kick_proc0(); 404 } 405 } 406 407 /* 408 * Make a thread sleeping on the specified identifier runnable. 409 * May wake more than one thread if a target thread is currently 410 * swapped out. 411 */ 412 void 413 wakeup_one(void *ident) 414 { 415 int wakeup_swapper; 416 417 sleepq_lock(ident); 418 wakeup_swapper = sleepq_signal(ident, SLEEPQ_SLEEP, 0, 0); 419 sleepq_release(ident); 420 if (wakeup_swapper) 421 kick_proc0(); 422 } 423 424 static void 425 kdb_switch(void) 426 { 427 thread_unlock(curthread); 428 kdb_backtrace(); 429 kdb_reenter(); 430 panic("%s: did not reenter debugger", __func__); 431 } 432 433 /* 434 * The machine independent parts of context switching. 435 */ 436 void 437 mi_switch(int flags, struct thread *newtd) 438 { 439 uint64_t runtime, new_switchtime; 440 struct thread *td; 441 struct proc *p; 442 443 td = curthread; /* XXX */ 444 THREAD_LOCK_ASSERT(td, MA_OWNED | MA_NOTRECURSED); 445 p = td->td_proc; /* XXX */ 446 KASSERT(!TD_ON_RUNQ(td), ("mi_switch: called by old code")); 447 #ifdef INVARIANTS 448 if (!TD_ON_LOCK(td) && !TD_IS_RUNNING(td)) 449 mtx_assert(&Giant, MA_NOTOWNED); 450 #endif 451 KASSERT(td->td_critnest == 1 || panicstr, 452 ("mi_switch: switch in a critical section")); 453 KASSERT((flags & (SW_INVOL | SW_VOL)) != 0, 454 ("mi_switch: switch must be voluntary or involuntary")); 455 KASSERT(newtd != curthread, ("mi_switch: preempting back to ourself")); 456 457 /* 458 * Don't perform context switches from the debugger. 459 */ 460 if (kdb_active) 461 kdb_switch(); 462 if (SCHEDULER_STOPPED()) 463 return; 464 if (flags & SW_VOL) { 465 td->td_ru.ru_nvcsw++; 466 td->td_swvoltick = ticks; 467 } else 468 td->td_ru.ru_nivcsw++; 469 #ifdef SCHED_STATS 470 SCHED_STAT_INC(sched_switch_stats[flags & SW_TYPE_MASK]); 471 #endif 472 /* 473 * Compute the amount of time during which the current 474 * thread was running, and add that to its total so far. 475 */ 476 new_switchtime = cpu_ticks(); 477 runtime = new_switchtime - PCPU_GET(switchtime); 478 td->td_runtime += runtime; 479 td->td_incruntime += runtime; 480 PCPU_SET(switchtime, new_switchtime); 481 td->td_generation++; /* bump preempt-detect counter */ 482 PCPU_INC(cnt.v_swtch); 483 PCPU_SET(switchticks, ticks); 484 CTR4(KTR_PROC, "mi_switch: old thread %ld (td_sched %p, pid %ld, %s)", 485 td->td_tid, td->td_sched, p->p_pid, td->td_name); 486 #if (KTR_COMPILE & KTR_SCHED) != 0 487 if (TD_IS_IDLETHREAD(td)) 488 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(td), "idle", 489 "prio:%d", td->td_priority); 490 else 491 KTR_STATE3(KTR_SCHED, "thread", sched_tdname(td), KTDSTATE(td), 492 "prio:%d", td->td_priority, "wmesg:\"%s\"", td->td_wmesg, 493 "lockname:\"%s\"", td->td_lockname); 494 #endif 495 SDT_PROBE0(sched, , , preempt); 496 #ifdef XEN 497 PT_UPDATES_FLUSH(); 498 #endif 499 sched_switch(td, newtd, flags); 500 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(td), "running", 501 "prio:%d", td->td_priority); 502 503 CTR4(KTR_PROC, "mi_switch: new thread %ld (td_sched %p, pid %ld, %s)", 504 td->td_tid, td->td_sched, p->p_pid, td->td_name); 505 506 /* 507 * If the last thread was exiting, finish cleaning it up. 508 */ 509 if ((td = PCPU_GET(deadthread))) { 510 PCPU_SET(deadthread, NULL); 511 thread_stash(td); 512 } 513 } 514 515 /* 516 * Change thread state to be runnable, placing it on the run queue if 517 * it is in memory. If it is swapped out, return true so our caller 518 * will know to awaken the swapper. 519 */ 520 int 521 setrunnable(struct thread *td) 522 { 523 524 THREAD_LOCK_ASSERT(td, MA_OWNED); 525 KASSERT(td->td_proc->p_state != PRS_ZOMBIE, 526 ("setrunnable: pid %d is a zombie", td->td_proc->p_pid)); 527 switch (td->td_state) { 528 case TDS_RUNNING: 529 case TDS_RUNQ: 530 return (0); 531 case TDS_INHIBITED: 532 /* 533 * If we are only inhibited because we are swapped out 534 * then arange to swap in this process. Otherwise just return. 535 */ 536 if (td->td_inhibitors != TDI_SWAPPED) 537 return (0); 538 /* FALLTHROUGH */ 539 case TDS_CAN_RUN: 540 break; 541 default: 542 printf("state is 0x%x", td->td_state); 543 panic("setrunnable(2)"); 544 } 545 if ((td->td_flags & TDF_INMEM) == 0) { 546 if ((td->td_flags & TDF_SWAPINREQ) == 0) { 547 td->td_flags |= TDF_SWAPINREQ; 548 return (1); 549 } 550 } else 551 sched_wakeup(td); 552 return (0); 553 } 554 555 /* 556 * Compute a tenex style load average of a quantity on 557 * 1, 5 and 15 minute intervals. 558 */ 559 static void 560 loadav(void *arg) 561 { 562 int i, nrun; 563 struct loadavg *avg; 564 565 nrun = sched_load(); 566 avg = &averunnable; 567 568 for (i = 0; i < 3; i++) 569 avg->ldavg[i] = (cexp[i] * avg->ldavg[i] + 570 nrun * FSCALE * (FSCALE - cexp[i])) >> FSHIFT; 571 572 /* 573 * Schedule the next update to occur after 5 seconds, but add a 574 * random variation to avoid synchronisation with processes that 575 * run at regular intervals. 576 */ 577 callout_reset_sbt(&loadav_callout, 578 SBT_1US * (4000000 + (int)(random() % 2000001)), SBT_1US, 579 loadav, NULL, C_DIRECT_EXEC | C_PREL(32)); 580 } 581 582 /* ARGSUSED */ 583 static void 584 synch_setup(void *dummy) 585 { 586 callout_init(&loadav_callout, CALLOUT_MPSAFE); 587 588 /* Kick off timeout driven events by calling first time. */ 589 loadav(NULL); 590 } 591 592 int 593 should_yield(void) 594 { 595 596 return ((u_int)ticks - (u_int)curthread->td_swvoltick >= hogticks); 597 } 598 599 void 600 maybe_yield(void) 601 { 602 603 if (should_yield()) 604 kern_yield(PRI_USER); 605 } 606 607 void 608 kern_yield(int prio) 609 { 610 struct thread *td; 611 612 td = curthread; 613 DROP_GIANT(); 614 thread_lock(td); 615 if (prio == PRI_USER) 616 prio = td->td_user_pri; 617 if (prio >= 0) 618 sched_prio(td, prio); 619 mi_switch(SW_VOL | SWT_RELINQUISH, NULL); 620 thread_unlock(td); 621 PICKUP_GIANT(); 622 } 623 624 /* 625 * General purpose yield system call. 626 */ 627 int 628 sys_yield(struct thread *td, struct yield_args *uap) 629 { 630 631 thread_lock(td); 632 if (PRI_BASE(td->td_pri_class) == PRI_TIMESHARE) 633 sched_prio(td, PRI_MAX_TIMESHARE); 634 mi_switch(SW_VOL | SWT_RELINQUISH, NULL); 635 thread_unlock(td); 636 td->td_retval[0] = 0; 637 return (0); 638 } 639