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 "Fixed-point scale factor used for calculating load average values"); 99 100 static void loadav(void *arg); 101 102 SDT_PROVIDER_DECLARE(sched); 103 SDT_PROBE_DEFINE(sched, , , preempt); 104 105 static void 106 sleepinit(void *unused) 107 { 108 109 hogticks = (hz / 10) * 2; /* Default only. */ 110 init_sleepqueues(); 111 } 112 113 /* 114 * vmem tries to lock the sleepq mutexes when free'ing kva, so make sure 115 * it is available. 116 */ 117 SYSINIT(sleepinit, SI_SUB_KMEM, SI_ORDER_ANY, sleepinit, NULL); 118 119 /* 120 * General sleep call. Suspends the current thread until a wakeup is 121 * performed on the specified identifier. The thread will then be made 122 * runnable with the specified priority. Sleeps at most sbt units of time 123 * (0 means no timeout). If pri includes the PCATCH flag, let signals 124 * interrupt the sleep, otherwise ignore them while sleeping. Returns 0 if 125 * awakened, EWOULDBLOCK if the timeout expires. If PCATCH is set and a 126 * signal becomes pending, ERESTART is returned if the current system 127 * call should be restarted if possible, and EINTR is returned if the system 128 * call should be interrupted by the signal (return EINTR). 129 * 130 * The lock argument is unlocked before the caller is suspended, and 131 * re-locked before _sleep() returns. If priority includes the PDROP 132 * flag the lock is not re-locked before returning. 133 */ 134 int 135 _sleep(const void *ident, struct lock_object *lock, int priority, 136 const char *wmesg, sbintime_t sbt, sbintime_t pr, int flags) 137 { 138 struct thread *td; 139 struct lock_class *class; 140 uintptr_t lock_state; 141 int catch, pri, rval, sleepq_flags; 142 WITNESS_SAVE_DECL(lock_witness); 143 144 td = curthread; 145 #ifdef KTRACE 146 if (KTRPOINT(td, KTR_CSW)) 147 ktrcsw(1, 0, wmesg); 148 #endif 149 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock, 150 "Sleeping on \"%s\"", wmesg); 151 KASSERT(sbt != 0 || mtx_owned(&Giant) || lock != NULL || 152 (priority & PNOLOCK) != 0, 153 ("sleeping without a lock")); 154 KASSERT(ident != NULL, ("_sleep: NULL ident")); 155 KASSERT(TD_IS_RUNNING(td), ("_sleep: curthread not running")); 156 if (priority & PDROP) 157 KASSERT(lock != NULL && lock != &Giant.lock_object, 158 ("PDROP requires a non-Giant lock")); 159 if (lock != NULL) 160 class = LOCK_CLASS(lock); 161 else 162 class = NULL; 163 164 if (SCHEDULER_STOPPED_TD(td)) { 165 if (lock != NULL && priority & PDROP) 166 class->lc_unlock(lock); 167 return (0); 168 } 169 catch = priority & PCATCH; 170 pri = priority & PRIMASK; 171 172 KASSERT(!TD_ON_SLEEPQ(td), ("recursive sleep")); 173 174 if ((uintptr_t)ident >= (uintptr_t)&pause_wchan[0] && 175 (uintptr_t)ident <= (uintptr_t)&pause_wchan[MAXCPU - 1]) 176 sleepq_flags = SLEEPQ_PAUSE; 177 else 178 sleepq_flags = SLEEPQ_SLEEP; 179 if (catch) 180 sleepq_flags |= SLEEPQ_INTERRUPTIBLE; 181 182 sleepq_lock(ident); 183 CTR5(KTR_PROC, "sleep: thread %ld (pid %ld, %s) on %s (%p)", 184 td->td_tid, td->td_proc->p_pid, td->td_name, wmesg, ident); 185 186 if (lock == &Giant.lock_object) 187 mtx_assert(&Giant, MA_OWNED); 188 DROP_GIANT(); 189 if (lock != NULL && lock != &Giant.lock_object && 190 !(class->lc_flags & LC_SLEEPABLE)) { 191 KASSERT(!(class->lc_flags & LC_SPINLOCK), 192 ("spin locks can only use msleep_spin")); 193 WITNESS_SAVE(lock, lock_witness); 194 lock_state = class->lc_unlock(lock); 195 } else 196 /* GCC needs to follow the Yellow Brick Road */ 197 lock_state = -1; 198 199 /* 200 * We put ourselves on the sleep queue and start our timeout 201 * before calling thread_suspend_check, as we could stop there, 202 * and a wakeup or a SIGCONT (or both) could occur while we were 203 * stopped without resuming us. Thus, we must be ready for sleep 204 * when cursig() is called. If the wakeup happens while we're 205 * stopped, then td will no longer be on a sleep queue upon 206 * return from cursig(). 207 */ 208 sleepq_add(ident, lock, wmesg, sleepq_flags, 0); 209 if (sbt != 0) 210 sleepq_set_timeout_sbt(ident, sbt, pr, flags); 211 if (lock != NULL && class->lc_flags & LC_SLEEPABLE) { 212 sleepq_release(ident); 213 WITNESS_SAVE(lock, lock_witness); 214 lock_state = class->lc_unlock(lock); 215 sleepq_lock(ident); 216 } 217 if (sbt != 0 && catch) 218 rval = sleepq_timedwait_sig(ident, pri); 219 else if (sbt != 0) 220 rval = sleepq_timedwait(ident, pri); 221 else if (catch) 222 rval = sleepq_wait_sig(ident, pri); 223 else { 224 sleepq_wait(ident, pri); 225 rval = 0; 226 } 227 #ifdef KTRACE 228 if (KTRPOINT(td, KTR_CSW)) 229 ktrcsw(0, 0, wmesg); 230 #endif 231 PICKUP_GIANT(); 232 if (lock != NULL && lock != &Giant.lock_object && !(priority & PDROP)) { 233 class->lc_lock(lock, lock_state); 234 WITNESS_RESTORE(lock, lock_witness); 235 } 236 return (rval); 237 } 238 239 int 240 msleep_spin_sbt(const void *ident, struct mtx *mtx, const char *wmesg, 241 sbintime_t sbt, sbintime_t pr, int flags) 242 { 243 struct thread *td; 244 int rval; 245 WITNESS_SAVE_DECL(mtx); 246 247 td = curthread; 248 KASSERT(mtx != NULL, ("sleeping without a mutex")); 249 KASSERT(ident != NULL, ("msleep_spin_sbt: NULL ident")); 250 KASSERT(TD_IS_RUNNING(td), ("msleep_spin_sbt: curthread not running")); 251 252 if (SCHEDULER_STOPPED_TD(td)) 253 return (0); 254 255 sleepq_lock(ident); 256 CTR5(KTR_PROC, "msleep_spin: thread %ld (pid %ld, %s) on %s (%p)", 257 td->td_tid, td->td_proc->p_pid, td->td_name, wmesg, ident); 258 259 DROP_GIANT(); 260 mtx_assert(mtx, MA_OWNED | MA_NOTRECURSED); 261 WITNESS_SAVE(&mtx->lock_object, mtx); 262 mtx_unlock_spin(mtx); 263 264 /* 265 * We put ourselves on the sleep queue and start our timeout. 266 */ 267 sleepq_add(ident, &mtx->lock_object, wmesg, SLEEPQ_SLEEP, 0); 268 if (sbt != 0) 269 sleepq_set_timeout_sbt(ident, sbt, pr, flags); 270 271 /* 272 * Can't call ktrace with any spin locks held so it can lock the 273 * ktrace_mtx lock, and WITNESS_WARN considers it an error to hold 274 * any spin lock. Thus, we have to drop the sleepq spin lock while 275 * we handle those requests. This is safe since we have placed our 276 * thread on the sleep queue already. 277 */ 278 #ifdef KTRACE 279 if (KTRPOINT(td, KTR_CSW)) { 280 sleepq_release(ident); 281 ktrcsw(1, 0, wmesg); 282 sleepq_lock(ident); 283 } 284 #endif 285 #ifdef WITNESS 286 sleepq_release(ident); 287 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, "Sleeping on \"%s\"", 288 wmesg); 289 sleepq_lock(ident); 290 #endif 291 if (sbt != 0) 292 rval = sleepq_timedwait(ident, 0); 293 else { 294 sleepq_wait(ident, 0); 295 rval = 0; 296 } 297 #ifdef KTRACE 298 if (KTRPOINT(td, KTR_CSW)) 299 ktrcsw(0, 0, wmesg); 300 #endif 301 PICKUP_GIANT(); 302 mtx_lock_spin(mtx); 303 WITNESS_RESTORE(&mtx->lock_object, mtx); 304 return (rval); 305 } 306 307 /* 308 * pause_sbt() delays the calling thread by the given signed binary 309 * time. During cold bootup, pause_sbt() uses the DELAY() function 310 * instead of the _sleep() function to do the waiting. The "sbt" 311 * argument must be greater than or equal to zero. A "sbt" value of 312 * zero is equivalent to a "sbt" value of one tick. 313 */ 314 int 315 pause_sbt(const char *wmesg, sbintime_t sbt, sbintime_t pr, int flags) 316 { 317 KASSERT(sbt >= 0, ("pause_sbt: timeout must be >= 0")); 318 319 /* silently convert invalid timeouts */ 320 if (sbt == 0) 321 sbt = tick_sbt; 322 323 if ((cold && curthread == &thread0) || kdb_active || 324 SCHEDULER_STOPPED()) { 325 /* 326 * We delay one second at a time to avoid overflowing the 327 * system specific DELAY() function(s): 328 */ 329 while (sbt >= SBT_1S) { 330 DELAY(1000000); 331 sbt -= SBT_1S; 332 } 333 /* Do the delay remainder, if any */ 334 sbt = howmany(sbt, SBT_1US); 335 if (sbt > 0) 336 DELAY(sbt); 337 return (EWOULDBLOCK); 338 } 339 return (_sleep(&pause_wchan[curcpu], NULL, 340 (flags & C_CATCH) ? PCATCH : 0, wmesg, sbt, pr, flags)); 341 } 342 343 /* 344 * Make all threads sleeping on the specified identifier runnable. 345 */ 346 void 347 wakeup(const void *ident) 348 { 349 int wakeup_swapper; 350 351 sleepq_lock(ident); 352 wakeup_swapper = sleepq_broadcast(ident, SLEEPQ_SLEEP, 0, 0); 353 sleepq_release(ident); 354 if (wakeup_swapper) { 355 KASSERT(ident != &proc0, 356 ("wakeup and wakeup_swapper and proc0")); 357 kick_proc0(); 358 } 359 } 360 361 /* 362 * Make a thread sleeping on the specified identifier runnable. 363 * May wake more than one thread if a target thread is currently 364 * swapped out. 365 */ 366 void 367 wakeup_one(const void *ident) 368 { 369 int wakeup_swapper; 370 371 sleepq_lock(ident); 372 wakeup_swapper = sleepq_signal(ident, SLEEPQ_SLEEP | SLEEPQ_DROP, 0, 0); 373 if (wakeup_swapper) 374 kick_proc0(); 375 } 376 377 void 378 wakeup_any(const void *ident) 379 { 380 int wakeup_swapper; 381 382 sleepq_lock(ident); 383 wakeup_swapper = sleepq_signal(ident, SLEEPQ_SLEEP | SLEEPQ_UNFAIR | 384 SLEEPQ_DROP, 0, 0); 385 if (wakeup_swapper) 386 kick_proc0(); 387 } 388 389 /* 390 * Signal sleeping waiters after the counter has reached zero. 391 */ 392 void 393 _blockcount_wakeup(blockcount_t *bc, u_int old) 394 { 395 396 KASSERT(_BLOCKCOUNT_WAITERS(old), 397 ("%s: no waiters on %p", __func__, bc)); 398 399 if (atomic_cmpset_int(&bc->__count, _BLOCKCOUNT_WAITERS_FLAG, 0)) 400 wakeup(bc); 401 } 402 403 /* 404 * Wait for a wakeup or a signal. This does not guarantee that the count is 405 * still zero on return. Callers wanting a precise answer should use 406 * blockcount_wait() with an interlock. 407 * 408 * If there is no work to wait for, return 0. If the sleep was interrupted by a 409 * signal, return EINTR or ERESTART, and return EAGAIN otherwise. 410 */ 411 int 412 _blockcount_sleep(blockcount_t *bc, struct lock_object *lock, const char *wmesg, 413 int prio) 414 { 415 void *wchan; 416 uintptr_t lock_state; 417 u_int old; 418 int ret; 419 bool catch, drop; 420 421 KASSERT(lock != &Giant.lock_object, 422 ("%s: cannot use Giant as the interlock", __func__)); 423 424 catch = (prio & PCATCH) != 0; 425 drop = (prio & PDROP) != 0; 426 prio &= PRIMASK; 427 428 /* 429 * Synchronize with the fence in blockcount_release(). If we end up 430 * waiting, the sleepqueue lock acquisition will provide the required 431 * side effects. 432 * 433 * If there is no work to wait for, but waiters are present, try to put 434 * ourselves to sleep to avoid jumping ahead. 435 */ 436 if (atomic_load_acq_int(&bc->__count) == 0) { 437 if (lock != NULL && drop) 438 LOCK_CLASS(lock)->lc_unlock(lock); 439 return (0); 440 } 441 lock_state = 0; 442 wchan = bc; 443 sleepq_lock(wchan); 444 DROP_GIANT(); 445 if (lock != NULL) 446 lock_state = LOCK_CLASS(lock)->lc_unlock(lock); 447 old = blockcount_read(bc); 448 ret = 0; 449 do { 450 if (_BLOCKCOUNT_COUNT(old) == 0) { 451 sleepq_release(wchan); 452 goto out; 453 } 454 if (_BLOCKCOUNT_WAITERS(old)) 455 break; 456 } while (!atomic_fcmpset_int(&bc->__count, &old, 457 old | _BLOCKCOUNT_WAITERS_FLAG)); 458 sleepq_add(wchan, NULL, wmesg, catch ? SLEEPQ_INTERRUPTIBLE : 0, 0); 459 if (catch) 460 ret = sleepq_wait_sig(wchan, prio); 461 else 462 sleepq_wait(wchan, prio); 463 if (ret == 0) 464 ret = EAGAIN; 465 466 out: 467 PICKUP_GIANT(); 468 if (lock != NULL && !drop) 469 LOCK_CLASS(lock)->lc_lock(lock, lock_state); 470 471 return (ret); 472 } 473 474 static void 475 kdb_switch(void) 476 { 477 thread_unlock(curthread); 478 kdb_backtrace(); 479 kdb_reenter(); 480 panic("%s: did not reenter debugger", __func__); 481 } 482 483 /* 484 * The machine independent parts of context switching. 485 * 486 * The thread lock is required on entry and is no longer held on return. 487 */ 488 void 489 mi_switch(int flags) 490 { 491 uint64_t runtime, new_switchtime; 492 struct thread *td; 493 494 td = curthread; /* XXX */ 495 THREAD_LOCK_ASSERT(td, MA_OWNED | MA_NOTRECURSED); 496 KASSERT(!TD_ON_RUNQ(td), ("mi_switch: called by old code")); 497 #ifdef INVARIANTS 498 if (!TD_ON_LOCK(td) && !TD_IS_RUNNING(td)) 499 mtx_assert(&Giant, MA_NOTOWNED); 500 #endif 501 KASSERT(td->td_critnest == 1 || KERNEL_PANICKED(), 502 ("mi_switch: switch in a critical section")); 503 KASSERT((flags & (SW_INVOL | SW_VOL)) != 0, 504 ("mi_switch: switch must be voluntary or involuntary")); 505 506 /* 507 * Don't perform context switches from the debugger. 508 */ 509 if (kdb_active) 510 kdb_switch(); 511 if (SCHEDULER_STOPPED_TD(td)) 512 return; 513 if (flags & SW_VOL) { 514 td->td_ru.ru_nvcsw++; 515 td->td_swvoltick = ticks; 516 } else { 517 td->td_ru.ru_nivcsw++; 518 td->td_swinvoltick = ticks; 519 } 520 #ifdef SCHED_STATS 521 SCHED_STAT_INC(sched_switch_stats[flags & SW_TYPE_MASK]); 522 #endif 523 /* 524 * Compute the amount of time during which the current 525 * thread was running, and add that to its total so far. 526 */ 527 new_switchtime = cpu_ticks(); 528 runtime = new_switchtime - PCPU_GET(switchtime); 529 td->td_runtime += runtime; 530 td->td_incruntime += runtime; 531 PCPU_SET(switchtime, new_switchtime); 532 td->td_generation++; /* bump preempt-detect counter */ 533 VM_CNT_INC(v_swtch); 534 PCPU_SET(switchticks, ticks); 535 CTR4(KTR_PROC, "mi_switch: old thread %ld (td_sched %p, pid %ld, %s)", 536 td->td_tid, td_get_sched(td), td->td_proc->p_pid, td->td_name); 537 #ifdef KDTRACE_HOOKS 538 if (SDT_PROBES_ENABLED() && 539 ((flags & SW_PREEMPT) != 0 || ((flags & SW_INVOL) != 0 && 540 (flags & SW_TYPE_MASK) == SWT_NEEDRESCHED))) 541 SDT_PROBE0(sched, , , preempt); 542 #endif 543 sched_switch(td, flags); 544 CTR4(KTR_PROC, "mi_switch: new thread %ld (td_sched %p, pid %ld, %s)", 545 td->td_tid, td_get_sched(td), td->td_proc->p_pid, td->td_name); 546 547 /* 548 * If the last thread was exiting, finish cleaning it up. 549 */ 550 if ((td = PCPU_GET(deadthread))) { 551 PCPU_SET(deadthread, NULL); 552 thread_stash(td); 553 } 554 spinlock_exit(); 555 } 556 557 /* 558 * Change thread state to be runnable, placing it on the run queue if 559 * it is in memory. If it is swapped out, return true so our caller 560 * will know to awaken the swapper. 561 * 562 * Requires the thread lock on entry, drops on exit. 563 */ 564 int 565 setrunnable(struct thread *td, int srqflags) 566 { 567 int swapin; 568 569 THREAD_LOCK_ASSERT(td, MA_OWNED); 570 KASSERT(td->td_proc->p_state != PRS_ZOMBIE, 571 ("setrunnable: pid %d is a zombie", td->td_proc->p_pid)); 572 573 swapin = 0; 574 switch (TD_GET_STATE(td)) { 575 case TDS_RUNNING: 576 case TDS_RUNQ: 577 break; 578 case TDS_CAN_RUN: 579 KASSERT((td->td_flags & TDF_INMEM) != 0, 580 ("setrunnable: td %p not in mem, flags 0x%X inhibit 0x%X", 581 td, td->td_flags, td->td_inhibitors)); 582 /* unlocks thread lock according to flags */ 583 sched_wakeup(td, srqflags); 584 return (0); 585 case TDS_INHIBITED: 586 /* 587 * If we are only inhibited because we are swapped out 588 * arrange to swap in this process. 589 */ 590 if (td->td_inhibitors == TDI_SWAPPED && 591 (td->td_flags & TDF_SWAPINREQ) == 0) { 592 td->td_flags |= TDF_SWAPINREQ; 593 swapin = 1; 594 } 595 break; 596 default: 597 panic("setrunnable: state 0x%x", TD_GET_STATE(td)); 598 } 599 if ((srqflags & (SRQ_HOLD | SRQ_HOLDTD)) == 0) 600 thread_unlock(td); 601 602 return (swapin); 603 } 604 605 /* 606 * Compute a tenex style load average of a quantity on 607 * 1, 5 and 15 minute intervals. 608 */ 609 static void 610 loadav(void *arg) 611 { 612 int i, nrun; 613 struct loadavg *avg; 614 615 nrun = sched_load(); 616 avg = &averunnable; 617 618 for (i = 0; i < 3; i++) 619 avg->ldavg[i] = (cexp[i] * avg->ldavg[i] + 620 nrun * FSCALE * (FSCALE - cexp[i])) >> FSHIFT; 621 622 /* 623 * Schedule the next update to occur after 5 seconds, but add a 624 * random variation to avoid synchronisation with processes that 625 * run at regular intervals. 626 */ 627 callout_reset_sbt(&loadav_callout, 628 SBT_1US * (4000000 + (int)(random() % 2000001)), SBT_1US, 629 loadav, NULL, C_DIRECT_EXEC | C_PREL(32)); 630 } 631 632 /* ARGSUSED */ 633 static void 634 synch_setup(void *dummy) 635 { 636 callout_init(&loadav_callout, 1); 637 638 /* Kick off timeout driven events by calling first time. */ 639 loadav(NULL); 640 } 641 642 int 643 should_yield(void) 644 { 645 646 return ((u_int)ticks - (u_int)curthread->td_swvoltick >= hogticks); 647 } 648 649 void 650 maybe_yield(void) 651 { 652 653 if (should_yield()) 654 kern_yield(PRI_USER); 655 } 656 657 void 658 kern_yield(int prio) 659 { 660 struct thread *td; 661 662 td = curthread; 663 DROP_GIANT(); 664 thread_lock(td); 665 if (prio == PRI_USER) 666 prio = td->td_user_pri; 667 if (prio >= 0) 668 sched_prio(td, prio); 669 mi_switch(SW_VOL | SWT_RELINQUISH); 670 PICKUP_GIANT(); 671 } 672 673 /* 674 * General purpose yield system call. 675 */ 676 int 677 sys_yield(struct thread *td, struct yield_args *uap) 678 { 679 680 thread_lock(td); 681 if (PRI_BASE(td->td_pri_class) == PRI_TIMESHARE) 682 sched_prio(td, PRI_MAX_TIMESHARE); 683 mi_switch(SW_VOL | SWT_RELINQUISH); 684 td->td_retval[0] = 0; 685 return (0); 686 } 687