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/blockcount.h> 48 #include <sys/condvar.h> 49 #include <sys/kdb.h> 50 #include <sys/kernel.h> 51 #include <sys/ktr.h> 52 #include <sys/lock.h> 53 #include <sys/mutex.h> 54 #include <sys/proc.h> 55 #include <sys/resourcevar.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 const char 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(const 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 if (priority & PDROP) 155 KASSERT(lock != NULL && lock != &Giant.lock_object, 156 ("PDROP requires a non-Giant lock")); 157 if (lock != NULL) 158 class = LOCK_CLASS(lock); 159 else 160 class = NULL; 161 162 if (SCHEDULER_STOPPED_TD(td)) { 163 if (lock != NULL && priority & PDROP) 164 class->lc_unlock(lock); 165 return (0); 166 } 167 catch = priority & PCATCH; 168 pri = priority & PRIMASK; 169 170 KASSERT(!TD_ON_SLEEPQ(td), ("recursive sleep")); 171 172 if ((uintptr_t)ident >= (uintptr_t)&pause_wchan[0] && 173 (uintptr_t)ident <= (uintptr_t)&pause_wchan[MAXCPU - 1]) 174 sleepq_flags = SLEEPQ_PAUSE; 175 else 176 sleepq_flags = SLEEPQ_SLEEP; 177 if (catch) 178 sleepq_flags |= SLEEPQ_INTERRUPTIBLE; 179 180 sleepq_lock(ident); 181 CTR5(KTR_PROC, "sleep: thread %ld (pid %ld, %s) on %s (%p)", 182 td->td_tid, td->td_proc->p_pid, td->td_name, wmesg, ident); 183 184 if (lock == &Giant.lock_object) 185 mtx_assert(&Giant, MA_OWNED); 186 DROP_GIANT(); 187 if (lock != NULL && lock != &Giant.lock_object && 188 !(class->lc_flags & LC_SLEEPABLE)) { 189 WITNESS_SAVE(lock, lock_witness); 190 lock_state = class->lc_unlock(lock); 191 } else 192 /* GCC needs to follow the Yellow Brick Road */ 193 lock_state = -1; 194 195 /* 196 * We put ourselves on the sleep queue and start our timeout 197 * before calling thread_suspend_check, as we could stop there, 198 * and a wakeup or a SIGCONT (or both) could occur while we were 199 * stopped without resuming us. Thus, we must be ready for sleep 200 * when cursig() is called. If the wakeup happens while we're 201 * stopped, then td will no longer be on a sleep queue upon 202 * return from cursig(). 203 */ 204 sleepq_add(ident, lock, wmesg, sleepq_flags, 0); 205 if (sbt != 0) 206 sleepq_set_timeout_sbt(ident, sbt, pr, flags); 207 if (lock != NULL && class->lc_flags & LC_SLEEPABLE) { 208 sleepq_release(ident); 209 WITNESS_SAVE(lock, lock_witness); 210 lock_state = class->lc_unlock(lock); 211 sleepq_lock(ident); 212 } 213 if (sbt != 0 && catch) 214 rval = sleepq_timedwait_sig(ident, pri); 215 else if (sbt != 0) 216 rval = sleepq_timedwait(ident, pri); 217 else if (catch) 218 rval = sleepq_wait_sig(ident, pri); 219 else { 220 sleepq_wait(ident, pri); 221 rval = 0; 222 } 223 #ifdef KTRACE 224 if (KTRPOINT(td, KTR_CSW)) 225 ktrcsw(0, 0, wmesg); 226 #endif 227 PICKUP_GIANT(); 228 if (lock != NULL && lock != &Giant.lock_object && !(priority & PDROP)) { 229 class->lc_lock(lock, lock_state); 230 WITNESS_RESTORE(lock, lock_witness); 231 } 232 return (rval); 233 } 234 235 int 236 msleep_spin_sbt(const void *ident, struct mtx *mtx, const char *wmesg, 237 sbintime_t sbt, sbintime_t pr, int flags) 238 { 239 struct thread *td; 240 int rval; 241 WITNESS_SAVE_DECL(mtx); 242 243 td = curthread; 244 KASSERT(mtx != NULL, ("sleeping without a mutex")); 245 KASSERT(ident != NULL, ("msleep_spin_sbt: NULL ident")); 246 KASSERT(TD_IS_RUNNING(td), ("msleep_spin_sbt: curthread not running")); 247 248 if (SCHEDULER_STOPPED_TD(td)) 249 return (0); 250 251 sleepq_lock(ident); 252 CTR5(KTR_PROC, "msleep_spin: thread %ld (pid %ld, %s) on %s (%p)", 253 td->td_tid, td->td_proc->p_pid, td->td_name, wmesg, ident); 254 255 DROP_GIANT(); 256 mtx_assert(mtx, MA_OWNED | MA_NOTRECURSED); 257 WITNESS_SAVE(&mtx->lock_object, mtx); 258 mtx_unlock_spin(mtx); 259 260 /* 261 * We put ourselves on the sleep queue and start our timeout. 262 */ 263 sleepq_add(ident, &mtx->lock_object, wmesg, SLEEPQ_SLEEP, 0); 264 if (sbt != 0) 265 sleepq_set_timeout_sbt(ident, sbt, pr, flags); 266 267 /* 268 * Can't call ktrace with any spin locks held so it can lock the 269 * ktrace_mtx lock, and WITNESS_WARN considers it an error to hold 270 * any spin lock. Thus, we have to drop the sleepq spin lock while 271 * we handle those requests. This is safe since we have placed our 272 * thread on the sleep queue already. 273 */ 274 #ifdef KTRACE 275 if (KTRPOINT(td, KTR_CSW)) { 276 sleepq_release(ident); 277 ktrcsw(1, 0, wmesg); 278 sleepq_lock(ident); 279 } 280 #endif 281 #ifdef WITNESS 282 sleepq_release(ident); 283 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, "Sleeping on \"%s\"", 284 wmesg); 285 sleepq_lock(ident); 286 #endif 287 if (sbt != 0) 288 rval = sleepq_timedwait(ident, 0); 289 else { 290 sleepq_wait(ident, 0); 291 rval = 0; 292 } 293 #ifdef KTRACE 294 if (KTRPOINT(td, KTR_CSW)) 295 ktrcsw(0, 0, wmesg); 296 #endif 297 PICKUP_GIANT(); 298 mtx_lock_spin(mtx); 299 WITNESS_RESTORE(&mtx->lock_object, mtx); 300 return (rval); 301 } 302 303 /* 304 * pause_sbt() delays the calling thread by the given signed binary 305 * time. During cold bootup, pause_sbt() uses the DELAY() function 306 * instead of the _sleep() function to do the waiting. The "sbt" 307 * argument must be greater than or equal to zero. A "sbt" value of 308 * zero is equivalent to a "sbt" value of one tick. 309 */ 310 int 311 pause_sbt(const char *wmesg, sbintime_t sbt, sbintime_t pr, int flags) 312 { 313 KASSERT(sbt >= 0, ("pause_sbt: timeout must be >= 0")); 314 315 /* silently convert invalid timeouts */ 316 if (sbt == 0) 317 sbt = tick_sbt; 318 319 if ((cold && curthread == &thread0) || kdb_active || 320 SCHEDULER_STOPPED()) { 321 /* 322 * We delay one second at a time to avoid overflowing the 323 * system specific DELAY() function(s): 324 */ 325 while (sbt >= SBT_1S) { 326 DELAY(1000000); 327 sbt -= SBT_1S; 328 } 329 /* Do the delay remainder, if any */ 330 sbt = howmany(sbt, SBT_1US); 331 if (sbt > 0) 332 DELAY(sbt); 333 return (EWOULDBLOCK); 334 } 335 return (_sleep(&pause_wchan[curcpu], NULL, 336 (flags & C_CATCH) ? PCATCH : 0, wmesg, sbt, pr, flags)); 337 } 338 339 /* 340 * Make all threads sleeping on the specified identifier runnable. 341 */ 342 void 343 wakeup(const void *ident) 344 { 345 int wakeup_swapper; 346 347 sleepq_lock(ident); 348 wakeup_swapper = sleepq_broadcast(ident, SLEEPQ_SLEEP, 0, 0); 349 sleepq_release(ident); 350 if (wakeup_swapper) { 351 KASSERT(ident != &proc0, 352 ("wakeup and wakeup_swapper and proc0")); 353 kick_proc0(); 354 } 355 } 356 357 /* 358 * Make a thread sleeping on the specified identifier runnable. 359 * May wake more than one thread if a target thread is currently 360 * swapped out. 361 */ 362 void 363 wakeup_one(const void *ident) 364 { 365 int wakeup_swapper; 366 367 sleepq_lock(ident); 368 wakeup_swapper = sleepq_signal(ident, SLEEPQ_SLEEP, 0, 0); 369 sleepq_release(ident); 370 if (wakeup_swapper) 371 kick_proc0(); 372 } 373 374 void 375 wakeup_any(const void *ident) 376 { 377 int wakeup_swapper; 378 379 sleepq_lock(ident); 380 wakeup_swapper = sleepq_signal(ident, SLEEPQ_SLEEP | SLEEPQ_UNFAIR, 381 0, 0); 382 sleepq_release(ident); 383 if (wakeup_swapper) 384 kick_proc0(); 385 } 386 387 /* 388 * Signal sleeping waiters after the counter has reached zero. 389 */ 390 void 391 _blockcount_wakeup(blockcount_t *bc, u_int old) 392 { 393 394 KASSERT(_BLOCKCOUNT_WAITERS(old), 395 ("%s: no waiters on %p", __func__, bc)); 396 397 if (atomic_cmpset_int(&bc->__count, _BLOCKCOUNT_WAITERS_FLAG, 0)) 398 wakeup(bc); 399 } 400 401 /* 402 * Wait for a wakeup. This does not guarantee that the count is still zero on 403 * return and may be subject to transient wakeups. Callers wanting a precise 404 * answer should use blockcount_wait() with an interlock. 405 * 406 * Return 0 if there is no work to wait for, and 1 if we slept waiting for work 407 * to complete. In the latter case the counter value must be re-read. 408 */ 409 int 410 _blockcount_sleep(blockcount_t *bc, struct lock_object *lock, const char *wmesg, 411 int prio) 412 { 413 void *wchan; 414 uintptr_t lock_state; 415 u_int old; 416 int ret; 417 418 KASSERT(lock != &Giant.lock_object, 419 ("%s: cannot use Giant as the interlock", __func__)); 420 421 /* 422 * Synchronize with the fence in blockcount_release(). If we end up 423 * waiting, the sleepqueue lock acquisition will provide the required 424 * side effects. 425 * 426 * If there is no work to wait for, but waiters are present, try to put 427 * ourselves to sleep to avoid jumping ahead. 428 */ 429 if (atomic_load_acq_int(&bc->__count) == 0) { 430 if (lock != NULL && (prio & PDROP) != 0) 431 LOCK_CLASS(lock)->lc_unlock(lock); 432 return (0); 433 } 434 lock_state = 0; 435 wchan = bc; 436 sleepq_lock(wchan); 437 DROP_GIANT(); 438 if (lock != NULL) 439 lock_state = LOCK_CLASS(lock)->lc_unlock(lock); 440 old = blockcount_read(bc); 441 do { 442 if (_BLOCKCOUNT_COUNT(old) == 0) { 443 sleepq_release(wchan); 444 ret = 0; 445 goto out; 446 } 447 if (_BLOCKCOUNT_WAITERS(old)) 448 break; 449 } while (!atomic_fcmpset_int(&bc->__count, &old, 450 old | _BLOCKCOUNT_WAITERS_FLAG)); 451 sleepq_add(wchan, NULL, wmesg, 0, 0); 452 sleepq_wait(wchan, prio); 453 ret = 1; 454 455 out: 456 PICKUP_GIANT(); 457 if (lock != NULL && (prio & PDROP) == 0) 458 LOCK_CLASS(lock)->lc_lock(lock, lock_state); 459 460 return (ret); 461 } 462 463 static void 464 kdb_switch(void) 465 { 466 thread_unlock(curthread); 467 kdb_backtrace(); 468 kdb_reenter(); 469 panic("%s: did not reenter debugger", __func__); 470 } 471 472 /* 473 * The machine independent parts of context switching. 474 * 475 * The thread lock is required on entry and is no longer held on return. 476 */ 477 void 478 mi_switch(int flags) 479 { 480 uint64_t runtime, new_switchtime; 481 struct thread *td; 482 483 td = curthread; /* XXX */ 484 THREAD_LOCK_ASSERT(td, MA_OWNED | MA_NOTRECURSED); 485 KASSERT(!TD_ON_RUNQ(td), ("mi_switch: called by old code")); 486 #ifdef INVARIANTS 487 if (!TD_ON_LOCK(td) && !TD_IS_RUNNING(td)) 488 mtx_assert(&Giant, MA_NOTOWNED); 489 #endif 490 KASSERT(td->td_critnest == 1 || KERNEL_PANICKED(), 491 ("mi_switch: switch in a critical section")); 492 KASSERT((flags & (SW_INVOL | SW_VOL)) != 0, 493 ("mi_switch: switch must be voluntary or involuntary")); 494 495 /* 496 * Don't perform context switches from the debugger. 497 */ 498 if (kdb_active) 499 kdb_switch(); 500 if (SCHEDULER_STOPPED_TD(td)) 501 return; 502 if (flags & SW_VOL) { 503 td->td_ru.ru_nvcsw++; 504 td->td_swvoltick = ticks; 505 } else { 506 td->td_ru.ru_nivcsw++; 507 td->td_swinvoltick = ticks; 508 } 509 #ifdef SCHED_STATS 510 SCHED_STAT_INC(sched_switch_stats[flags & SW_TYPE_MASK]); 511 #endif 512 /* 513 * Compute the amount of time during which the current 514 * thread was running, and add that to its total so far. 515 */ 516 new_switchtime = cpu_ticks(); 517 runtime = new_switchtime - PCPU_GET(switchtime); 518 td->td_runtime += runtime; 519 td->td_incruntime += runtime; 520 PCPU_SET(switchtime, new_switchtime); 521 td->td_generation++; /* bump preempt-detect counter */ 522 VM_CNT_INC(v_swtch); 523 PCPU_SET(switchticks, ticks); 524 CTR4(KTR_PROC, "mi_switch: old thread %ld (td_sched %p, pid %ld, %s)", 525 td->td_tid, td_get_sched(td), td->td_proc->p_pid, td->td_name); 526 #ifdef KDTRACE_HOOKS 527 if (SDT_PROBES_ENABLED() && 528 ((flags & SW_PREEMPT) != 0 || ((flags & SW_INVOL) != 0 && 529 (flags & SW_TYPE_MASK) == SWT_NEEDRESCHED))) 530 SDT_PROBE0(sched, , , preempt); 531 #endif 532 sched_switch(td, flags); 533 CTR4(KTR_PROC, "mi_switch: new thread %ld (td_sched %p, pid %ld, %s)", 534 td->td_tid, td_get_sched(td), td->td_proc->p_pid, td->td_name); 535 536 /* 537 * If the last thread was exiting, finish cleaning it up. 538 */ 539 if ((td = PCPU_GET(deadthread))) { 540 PCPU_SET(deadthread, NULL); 541 thread_stash(td); 542 } 543 spinlock_exit(); 544 } 545 546 /* 547 * Change thread state to be runnable, placing it on the run queue if 548 * it is in memory. If it is swapped out, return true so our caller 549 * will know to awaken the swapper. 550 * 551 * Requires the thread lock on entry, drops on exit. 552 */ 553 int 554 setrunnable(struct thread *td, int srqflags) 555 { 556 int swapin; 557 558 THREAD_LOCK_ASSERT(td, MA_OWNED); 559 KASSERT(td->td_proc->p_state != PRS_ZOMBIE, 560 ("setrunnable: pid %d is a zombie", td->td_proc->p_pid)); 561 562 swapin = 0; 563 switch (td->td_state) { 564 case TDS_RUNNING: 565 case TDS_RUNQ: 566 break; 567 case TDS_CAN_RUN: 568 KASSERT((td->td_flags & TDF_INMEM) != 0, 569 ("setrunnable: td %p not in mem, flags 0x%X inhibit 0x%X", 570 td, td->td_flags, td->td_inhibitors)); 571 /* unlocks thread lock according to flags */ 572 sched_wakeup(td, srqflags); 573 return (0); 574 case TDS_INHIBITED: 575 /* 576 * If we are only inhibited because we are swapped out 577 * arrange to swap in this process. 578 */ 579 if (td->td_inhibitors == TDI_SWAPPED && 580 (td->td_flags & TDF_SWAPINREQ) == 0) { 581 td->td_flags |= TDF_SWAPINREQ; 582 swapin = 1; 583 } 584 break; 585 default: 586 panic("setrunnable: state 0x%x", td->td_state); 587 } 588 if ((srqflags & (SRQ_HOLD | SRQ_HOLDTD)) == 0) 589 thread_unlock(td); 590 591 return (swapin); 592 } 593 594 /* 595 * Compute a tenex style load average of a quantity on 596 * 1, 5 and 15 minute intervals. 597 */ 598 static void 599 loadav(void *arg) 600 { 601 int i, nrun; 602 struct loadavg *avg; 603 604 nrun = sched_load(); 605 avg = &averunnable; 606 607 for (i = 0; i < 3; i++) 608 avg->ldavg[i] = (cexp[i] * avg->ldavg[i] + 609 nrun * FSCALE * (FSCALE - cexp[i])) >> FSHIFT; 610 611 /* 612 * Schedule the next update to occur after 5 seconds, but add a 613 * random variation to avoid synchronisation with processes that 614 * run at regular intervals. 615 */ 616 callout_reset_sbt(&loadav_callout, 617 SBT_1US * (4000000 + (int)(random() % 2000001)), SBT_1US, 618 loadav, NULL, C_DIRECT_EXEC | C_PREL(32)); 619 } 620 621 /* ARGSUSED */ 622 static void 623 synch_setup(void *dummy) 624 { 625 callout_init(&loadav_callout, 1); 626 627 /* Kick off timeout driven events by calling first time. */ 628 loadav(NULL); 629 } 630 631 int 632 should_yield(void) 633 { 634 635 return ((u_int)ticks - (u_int)curthread->td_swvoltick >= hogticks); 636 } 637 638 void 639 maybe_yield(void) 640 { 641 642 if (should_yield()) 643 kern_yield(PRI_USER); 644 } 645 646 void 647 kern_yield(int prio) 648 { 649 struct thread *td; 650 651 td = curthread; 652 DROP_GIANT(); 653 thread_lock(td); 654 if (prio == PRI_USER) 655 prio = td->td_user_pri; 656 if (prio >= 0) 657 sched_prio(td, prio); 658 mi_switch(SW_VOL | SWT_RELINQUISH); 659 PICKUP_GIANT(); 660 } 661 662 /* 663 * General purpose yield system call. 664 */ 665 int 666 sys_yield(struct thread *td, struct yield_args *uap) 667 { 668 669 thread_lock(td); 670 if (PRI_BASE(td->td_pri_class) == PRI_TIMESHARE) 671 sched_prio(td, PRI_MAX_TIMESHARE); 672 mi_switch(SW_VOL | SWT_RELINQUISH); 673 td->td_retval[0] = 0; 674 return (0); 675 } 676