kern_synch.c revision 247787
1343835Sdes/*- 2343835Sdes * Copyright (c) 1982, 1986, 1990, 1991, 1993 3343835Sdes * The Regents of the University of California. All rights reserved. 4343835Sdes * (c) UNIX System Laboratories, Inc. 5343835Sdes * All or some portions of this file are derived from material licensed 6343835Sdes * to the University of California by American Telephone and Telegraph 7343835Sdes * Co. or Unix System Laboratories, Inc. and are reproduced herein with 8343835Sdes * the permission of UNIX System Laboratories, Inc. 9343835Sdes * 10343835Sdes * Redistribution and use in source and binary forms, with or without 11343835Sdes * modification, are permitted provided that the following conditions 12343835Sdes * are met: 13343835Sdes * 1. Redistributions of source code must retain the above copyright 14343835Sdes * notice, this list of conditions and the following disclaimer. 15343835Sdes * 2. Redistributions in binary form must reproduce the above copyright 16343835Sdes * notice, this list of conditions and the following disclaimer in the 17343835Sdes * documentation and/or other materials provided with the distribution. 18343835Sdes * 4. Neither the name of the University nor the names of its contributors 19343835Sdes * may be used to endorse or promote products derived from this software 20343835Sdes * without specific prior written permission. 21343835Sdes * 22343835Sdes * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23343835Sdes * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24343835Sdes * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25343835Sdes * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26343835Sdes * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27343835Sdes * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28343835Sdes * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29343835Sdes * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30343835Sdes * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31343835Sdes * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32343835Sdes * SUCH DAMAGE. 33343835Sdes * 34343835Sdes * @(#)kern_synch.c 8.9 (Berkeley) 5/19/95 35343835Sdes */ 36343835Sdes 37343835Sdes#include <sys/cdefs.h> 38343835Sdes__FBSDID("$FreeBSD: head/sys/kern/kern_synch.c 247787 2013-03-04 12:48:41Z davide $"); 39343835Sdes 40343835Sdes#include "opt_kdtrace.h" 41343835Sdes#include "opt_ktrace.h" 42343835Sdes#include "opt_sched.h" 43343835Sdes 44343835Sdes#include <sys/param.h> 45343835Sdes#include <sys/systm.h> 46343835Sdes#include <sys/condvar.h> 47343835Sdes#include <sys/kdb.h> 48343835Sdes#include <sys/kernel.h> 49343835Sdes#include <sys/ktr.h> 50343835Sdes#include <sys/lock.h> 51343835Sdes#include <sys/mutex.h> 52343835Sdes#include <sys/proc.h> 53343835Sdes#include <sys/resourcevar.h> 54343835Sdes#include <sys/sched.h> 55343835Sdes#include <sys/sdt.h> 56343835Sdes#include <sys/signalvar.h> 57343835Sdes#include <sys/sleepqueue.h> 58343835Sdes#include <sys/smp.h> 59343835Sdes#include <sys/sx.h> 60343835Sdes#include <sys/sysctl.h> 61343835Sdes#include <sys/sysproto.h> 62343835Sdes#include <sys/vmmeter.h> 63343835Sdes#ifdef KTRACE 64343835Sdes#include <sys/uio.h> 65343835Sdes#include <sys/ktrace.h> 66343835Sdes#endif 67343835Sdes 68343835Sdes#include <machine/cpu.h> 69343835Sdes 70343835Sdes#ifdef XEN 71343835Sdes#include <vm/vm.h> 72343835Sdes#include <vm/vm_param.h> 73343835Sdes#include <vm/pmap.h> 74343835Sdes#endif 75343835Sdes 76343835Sdes#define KTDSTATE(td) \ 77343835Sdes (((td)->td_inhibitors & TDI_SLEEPING) != 0 ? "sleep" : \ 78343835Sdes ((td)->td_inhibitors & TDI_SUSPENDED) != 0 ? "suspended" : \ 79343835Sdes ((td)->td_inhibitors & TDI_SWAPPED) != 0 ? "swapped" : \ 80343835Sdes ((td)->td_inhibitors & TDI_LOCK) != 0 ? "blocked" : \ 81343835Sdes ((td)->td_inhibitors & TDI_IWAIT) != 0 ? "iwait" : "yielding") 82343835Sdes 83343835Sdesstatic void synch_setup(void *dummy); 84343835SdesSYSINIT(synch_setup, SI_SUB_KICK_SCHEDULER, SI_ORDER_FIRST, synch_setup, 85343835Sdes NULL); 86343835Sdes 87343835Sdesint hogticks; 88343835Sdesstatic int pause_wchan; 89343835Sdes 90343835Sdesstatic struct callout loadav_callout; 91343835Sdes 92343835Sdesstruct loadavg averunnable = 93343835Sdes { {0, 0, 0}, FSCALE }; /* load average, of runnable procs */ 94343835Sdes/* 95343835Sdes * Constants for averages over 1, 5, and 15 minutes 96343835Sdes * when sampling at 5 second intervals. 97343835Sdes */ 98343835Sdesstatic fixpt_t cexp[3] = { 99343835Sdes 0.9200444146293232 * FSCALE, /* exp(-1/12) */ 100343835Sdes 0.9834714538216174 * FSCALE, /* exp(-1/60) */ 101343835Sdes 0.9944598480048967 * FSCALE, /* exp(-1/180) */ 102343835Sdes}; 103343835Sdes 104343835Sdes/* kernel uses `FSCALE', userland (SHOULD) use kern.fscale */ 105343835Sdesstatic int fscale __unused = FSCALE; 106343835SdesSYSCTL_INT(_kern, OID_AUTO, fscale, CTLFLAG_RD, 0, FSCALE, ""); 107343835Sdes 108343835Sdesstatic void loadav(void *arg); 109343835Sdes 110343835SdesSDT_PROVIDER_DECLARE(sched); 111343835SdesSDT_PROBE_DEFINE(sched, , , preempt, preempt); 112343835Sdes 113343835Sdes/* 114343835Sdes * These probes reference Solaris features that are not implemented in FreeBSD. 115343835Sdes * Create the probes anyway for compatibility with existing D scripts; they'll 116343835Sdes * just never fire. 117343835Sdes */ 118343835SdesSDT_PROBE_DEFINE(sched, , , cpucaps_sleep, cpucaps-sleep); 119343835SdesSDT_PROBE_DEFINE(sched, , , cpucaps_wakeup, cpucaps-wakeup); 120343835SdesSDT_PROBE_DEFINE(sched, , , schedctl_nopreempt, schedctl-nopreempt); 121343835SdesSDT_PROBE_DEFINE(sched, , , schedctl_preempt, schedctl-preempt); 122343835SdesSDT_PROBE_DEFINE(sched, , , schedctl_yield, schedctl-yield); 123343835Sdes 124343835Sdesvoid 125343835Sdessleepinit(void) 126343835Sdes{ 127343835Sdes 128343835Sdes hogticks = (hz / 10) * 2; /* Default only. */ 129343835Sdes init_sleepqueues(); 130343835Sdes} 131343835Sdes 132343835Sdes/* 133343835Sdes * General sleep call. Suspends the current thread until a wakeup is 134343835Sdes * performed on the specified identifier. The thread will then be made 135343835Sdes * runnable with the specified priority. Sleeps at most timo/hz seconds 136343835Sdes * (0 means no timeout). If pri includes the PCATCH flag, let signals 137343835Sdes * interrupt the sleep, otherwise ignore them while sleeping. Returns 0 if 138343835Sdes * awakened, EWOULDBLOCK if the timeout expires. If PCATCH is set and a 139343835Sdes * signal becomes pending, ERESTART is returned if the current system 140343835Sdes * call should be restarted if possible, and EINTR is returned if the system 141343835Sdes * call should be interrupted by the signal (return EINTR). 142343835Sdes * 143343835Sdes * The lock argument is unlocked before the caller is suspended, and 144343835Sdes * re-locked before _sleep() returns. If priority includes the PDROP 145343835Sdes * flag the lock is not re-locked before returning. 146343835Sdes */ 147343835Sdesint 148343835Sdes_sleep(void *ident, struct lock_object *lock, int priority, 149 const char *wmesg, sbintime_t sbt, sbintime_t pr, int flags) 150{ 151 struct thread *td; 152 struct proc *p; 153 struct lock_class *class; 154 int catch, lock_state, pri, rval, sleepq_flags; 155 WITNESS_SAVE_DECL(lock_witness); 156 157 td = curthread; 158 p = td->td_proc; 159#ifdef KTRACE 160 if (KTRPOINT(td, KTR_CSW)) 161 ktrcsw(1, 0, wmesg); 162#endif 163 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock, 164 "Sleeping on \"%s\"", wmesg); 165 KASSERT(sbt != 0 || mtx_owned(&Giant) || lock != NULL, 166 ("sleeping without a lock")); 167 KASSERT(p != NULL, ("msleep1")); 168 KASSERT(ident != NULL && TD_IS_RUNNING(td), ("msleep")); 169 if (priority & PDROP) 170 KASSERT(lock != NULL && lock != &Giant.lock_object, 171 ("PDROP requires a non-Giant lock")); 172 if (lock != NULL) 173 class = LOCK_CLASS(lock); 174 else 175 class = NULL; 176 177 if (cold || SCHEDULER_STOPPED()) { 178 /* 179 * During autoconfiguration, just return; 180 * don't run any other threads or panic below, 181 * in case this is the idle thread and already asleep. 182 * XXX: this used to do "s = splhigh(); splx(safepri); 183 * splx(s);" to give interrupts a chance, but there is 184 * no way to give interrupts a chance now. 185 */ 186 if (lock != NULL && priority & PDROP) 187 class->lc_unlock(lock); 188 return (0); 189 } 190 catch = priority & PCATCH; 191 pri = priority & PRIMASK; 192 193 /* 194 * If we are already on a sleep queue, then remove us from that 195 * sleep queue first. We have to do this to handle recursive 196 * sleeps. 197 */ 198 if (TD_ON_SLEEPQ(td)) 199 sleepq_remove(td, td->td_wchan); 200 201 if (ident == &pause_wchan) 202 sleepq_flags = SLEEPQ_PAUSE; 203 else 204 sleepq_flags = SLEEPQ_SLEEP; 205 if (catch) 206 sleepq_flags |= SLEEPQ_INTERRUPTIBLE; 207 if (priority & PBDRY) 208 sleepq_flags |= SLEEPQ_STOP_ON_BDRY; 209 210 sleepq_lock(ident); 211 CTR5(KTR_PROC, "sleep: thread %ld (pid %ld, %s) on %s (%p)", 212 td->td_tid, p->p_pid, td->td_name, wmesg, ident); 213 214 if (lock == &Giant.lock_object) 215 mtx_assert(&Giant, MA_OWNED); 216 DROP_GIANT(); 217 if (lock != NULL && lock != &Giant.lock_object && 218 !(class->lc_flags & LC_SLEEPABLE)) { 219 WITNESS_SAVE(lock, lock_witness); 220 lock_state = class->lc_unlock(lock); 221 } else 222 /* GCC needs to follow the Yellow Brick Road */ 223 lock_state = -1; 224 225 /* 226 * We put ourselves on the sleep queue and start our timeout 227 * before calling thread_suspend_check, as we could stop there, 228 * and a wakeup or a SIGCONT (or both) could occur while we were 229 * stopped without resuming us. Thus, we must be ready for sleep 230 * when cursig() is called. If the wakeup happens while we're 231 * stopped, then td will no longer be on a sleep queue upon 232 * return from cursig(). 233 */ 234 sleepq_add(ident, lock, wmesg, sleepq_flags, 0); 235 if (sbt != 0) 236 sleepq_set_timeout_sbt(ident, sbt, pr, flags); 237 if (lock != NULL && class->lc_flags & LC_SLEEPABLE) { 238 sleepq_release(ident); 239 WITNESS_SAVE(lock, lock_witness); 240 lock_state = class->lc_unlock(lock); 241 sleepq_lock(ident); 242 } 243 if (sbt != 0 && catch) 244 rval = sleepq_timedwait_sig(ident, pri); 245 else if (sbt != 0) 246 rval = sleepq_timedwait(ident, pri); 247 else if (catch) 248 rval = sleepq_wait_sig(ident, pri); 249 else { 250 sleepq_wait(ident, pri); 251 rval = 0; 252 } 253#ifdef KTRACE 254 if (KTRPOINT(td, KTR_CSW)) 255 ktrcsw(0, 0, wmesg); 256#endif 257 PICKUP_GIANT(); 258 if (lock != NULL && lock != &Giant.lock_object && !(priority & PDROP)) { 259 class->lc_lock(lock, lock_state); 260 WITNESS_RESTORE(lock, lock_witness); 261 } 262 return (rval); 263} 264 265int 266msleep_spin_sbt(void *ident, struct mtx *mtx, const char *wmesg, 267 sbintime_t sbt, sbintime_t pr, int flags) 268{ 269 struct thread *td; 270 struct proc *p; 271 int rval; 272 WITNESS_SAVE_DECL(mtx); 273 274 td = curthread; 275 p = td->td_proc; 276 KASSERT(mtx != NULL, ("sleeping without a mutex")); 277 KASSERT(p != NULL, ("msleep1")); 278 KASSERT(ident != NULL && TD_IS_RUNNING(td), ("msleep")); 279 280 if (cold || SCHEDULER_STOPPED()) { 281 /* 282 * During autoconfiguration, just return; 283 * don't run any other threads or panic below, 284 * in case this is the idle thread and already asleep. 285 * XXX: this used to do "s = splhigh(); splx(safepri); 286 * splx(s);" to give interrupts a chance, but there is 287 * no way to give interrupts a chance now. 288 */ 289 return (0); 290 } 291 292 sleepq_lock(ident); 293 CTR5(KTR_PROC, "msleep_spin: thread %ld (pid %ld, %s) on %s (%p)", 294 td->td_tid, p->p_pid, td->td_name, wmesg, ident); 295 296 DROP_GIANT(); 297 mtx_assert(mtx, MA_OWNED | MA_NOTRECURSED); 298 WITNESS_SAVE(&mtx->lock_object, mtx); 299 mtx_unlock_spin(mtx); 300 301 /* 302 * We put ourselves on the sleep queue and start our timeout. 303 */ 304 sleepq_add(ident, &mtx->lock_object, wmesg, SLEEPQ_SLEEP, 0); 305 if (sbt != 0) 306 sleepq_set_timeout_sbt(ident, sbt, pr, flags); 307 308 /* 309 * Can't call ktrace with any spin locks held so it can lock the 310 * ktrace_mtx lock, and WITNESS_WARN considers it an error to hold 311 * any spin lock. Thus, we have to drop the sleepq spin lock while 312 * we handle those requests. This is safe since we have placed our 313 * thread on the sleep queue already. 314 */ 315#ifdef KTRACE 316 if (KTRPOINT(td, KTR_CSW)) { 317 sleepq_release(ident); 318 ktrcsw(1, 0, wmesg); 319 sleepq_lock(ident); 320 } 321#endif 322#ifdef WITNESS 323 sleepq_release(ident); 324 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, "Sleeping on \"%s\"", 325 wmesg); 326 sleepq_lock(ident); 327#endif 328 if (sbt != 0) 329 rval = sleepq_timedwait(ident, 0); 330 else { 331 sleepq_wait(ident, 0); 332 rval = 0; 333 } 334#ifdef KTRACE 335 if (KTRPOINT(td, KTR_CSW)) 336 ktrcsw(0, 0, wmesg); 337#endif 338 PICKUP_GIANT(); 339 mtx_lock_spin(mtx); 340 WITNESS_RESTORE(&mtx->lock_object, mtx); 341 return (rval); 342} 343 344/* 345 * pause() delays the calling thread by the given number of system ticks. 346 * During cold bootup, pause() uses the DELAY() function instead of 347 * the tsleep() function to do the waiting. The "timo" argument must be 348 * greater than or equal to zero. A "timo" value of zero is equivalent 349 * to a "timo" value of one. 350 */ 351int 352pause_sbt(const char *wmesg, sbintime_t sbt, sbintime_t pr, int flags) 353{ 354 int sbt_sec; 355 356 sbt_sec = sbintime_getsec(sbt); 357 KASSERT(sbt_sec >= 0, ("pause: timo must be >= 0")); 358 359 /* silently convert invalid timeouts */ 360 if (sbt == 0) 361 sbt = tick_sbt; 362 363 if (cold) { 364 /* 365 * We delay one second at a time to avoid overflowing the 366 * system specific DELAY() function(s): 367 */ 368 while (sbt_sec > 0) { 369 DELAY(1000000); 370 sbt_sec--; 371 } 372 DELAY((sbt & 0xffffffff) / SBT_1US); 373 return (0); 374 } 375 return (_sleep(&pause_wchan, NULL, 0, wmesg, sbt, pr, flags)); 376} 377 378/* 379 * Make all threads sleeping on the specified identifier runnable. 380 */ 381void 382wakeup(void *ident) 383{ 384 int wakeup_swapper; 385 386 sleepq_lock(ident); 387 wakeup_swapper = sleepq_broadcast(ident, SLEEPQ_SLEEP, 0, 0); 388 sleepq_release(ident); 389 if (wakeup_swapper) { 390 KASSERT(ident != &proc0, 391 ("wakeup and wakeup_swapper and proc0")); 392 kick_proc0(); 393 } 394} 395 396/* 397 * Make a thread sleeping on the specified identifier runnable. 398 * May wake more than one thread if a target thread is currently 399 * swapped out. 400 */ 401void 402wakeup_one(void *ident) 403{ 404 int wakeup_swapper; 405 406 sleepq_lock(ident); 407 wakeup_swapper = sleepq_signal(ident, SLEEPQ_SLEEP, 0, 0); 408 sleepq_release(ident); 409 if (wakeup_swapper) 410 kick_proc0(); 411} 412 413static void 414kdb_switch(void) 415{ 416 thread_unlock(curthread); 417 kdb_backtrace(); 418 kdb_reenter(); 419 panic("%s: did not reenter debugger", __func__); 420} 421 422/* 423 * The machine independent parts of context switching. 424 */ 425void 426mi_switch(int flags, struct thread *newtd) 427{ 428 uint64_t runtime, new_switchtime; 429 struct thread *td; 430 struct proc *p; 431 432 td = curthread; /* XXX */ 433 THREAD_LOCK_ASSERT(td, MA_OWNED | MA_NOTRECURSED); 434 p = td->td_proc; /* XXX */ 435 KASSERT(!TD_ON_RUNQ(td), ("mi_switch: called by old code")); 436#ifdef INVARIANTS 437 if (!TD_ON_LOCK(td) && !TD_IS_RUNNING(td)) 438 mtx_assert(&Giant, MA_NOTOWNED); 439#endif 440 KASSERT(td->td_critnest == 1 || panicstr, 441 ("mi_switch: switch in a critical section")); 442 KASSERT((flags & (SW_INVOL | SW_VOL)) != 0, 443 ("mi_switch: switch must be voluntary or involuntary")); 444 KASSERT(newtd != curthread, ("mi_switch: preempting back to ourself")); 445 446 /* 447 * Don't perform context switches from the debugger. 448 */ 449 if (kdb_active) 450 kdb_switch(); 451 if (SCHEDULER_STOPPED()) 452 return; 453 if (flags & SW_VOL) { 454 td->td_ru.ru_nvcsw++; 455 td->td_swvoltick = ticks; 456 } else 457 td->td_ru.ru_nivcsw++; 458#ifdef SCHED_STATS 459 SCHED_STAT_INC(sched_switch_stats[flags & SW_TYPE_MASK]); 460#endif 461 /* 462 * Compute the amount of time during which the current 463 * thread was running, and add that to its total so far. 464 */ 465 new_switchtime = cpu_ticks(); 466 runtime = new_switchtime - PCPU_GET(switchtime); 467 td->td_runtime += runtime; 468 td->td_incruntime += runtime; 469 PCPU_SET(switchtime, new_switchtime); 470 td->td_generation++; /* bump preempt-detect counter */ 471 PCPU_INC(cnt.v_swtch); 472 PCPU_SET(switchticks, ticks); 473 CTR4(KTR_PROC, "mi_switch: old thread %ld (td_sched %p, pid %ld, %s)", 474 td->td_tid, td->td_sched, p->p_pid, td->td_name); 475#if (KTR_COMPILE & KTR_SCHED) != 0 476 if (TD_IS_IDLETHREAD(td)) 477 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(td), "idle", 478 "prio:%d", td->td_priority); 479 else 480 KTR_STATE3(KTR_SCHED, "thread", sched_tdname(td), KTDSTATE(td), 481 "prio:%d", td->td_priority, "wmesg:\"%s\"", td->td_wmesg, 482 "lockname:\"%s\"", td->td_lockname); 483#endif 484 SDT_PROBE0(sched, , , preempt); 485#ifdef XEN 486 PT_UPDATES_FLUSH(); 487#endif 488 sched_switch(td, newtd, flags); 489 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(td), "running", 490 "prio:%d", td->td_priority); 491 492 CTR4(KTR_PROC, "mi_switch: new thread %ld (td_sched %p, pid %ld, %s)", 493 td->td_tid, td->td_sched, p->p_pid, td->td_name); 494 495 /* 496 * If the last thread was exiting, finish cleaning it up. 497 */ 498 if ((td = PCPU_GET(deadthread))) { 499 PCPU_SET(deadthread, NULL); 500 thread_stash(td); 501 } 502} 503 504/* 505 * Change thread state to be runnable, placing it on the run queue if 506 * it is in memory. If it is swapped out, return true so our caller 507 * will know to awaken the swapper. 508 */ 509int 510setrunnable(struct thread *td) 511{ 512 513 THREAD_LOCK_ASSERT(td, MA_OWNED); 514 KASSERT(td->td_proc->p_state != PRS_ZOMBIE, 515 ("setrunnable: pid %d is a zombie", td->td_proc->p_pid)); 516 switch (td->td_state) { 517 case TDS_RUNNING: 518 case TDS_RUNQ: 519 return (0); 520 case TDS_INHIBITED: 521 /* 522 * If we are only inhibited because we are swapped out 523 * then arange to swap in this process. Otherwise just return. 524 */ 525 if (td->td_inhibitors != TDI_SWAPPED) 526 return (0); 527 /* FALLTHROUGH */ 528 case TDS_CAN_RUN: 529 break; 530 default: 531 printf("state is 0x%x", td->td_state); 532 panic("setrunnable(2)"); 533 } 534 if ((td->td_flags & TDF_INMEM) == 0) { 535 if ((td->td_flags & TDF_SWAPINREQ) == 0) { 536 td->td_flags |= TDF_SWAPINREQ; 537 return (1); 538 } 539 } else 540 sched_wakeup(td); 541 return (0); 542} 543 544/* 545 * Compute a tenex style load average of a quantity on 546 * 1, 5 and 15 minute intervals. 547 */ 548static void 549loadav(void *arg) 550{ 551 int i, nrun; 552 struct loadavg *avg; 553 554 nrun = sched_load(); 555 avg = &averunnable; 556 557 for (i = 0; i < 3; i++) 558 avg->ldavg[i] = (cexp[i] * avg->ldavg[i] + 559 nrun * FSCALE * (FSCALE - cexp[i])) >> FSHIFT; 560 561 /* 562 * Schedule the next update to occur after 5 seconds, but add a 563 * random variation to avoid synchronisation with processes that 564 * run at regular intervals. 565 */ 566 callout_reset_sbt(&loadav_callout, 567 tick_sbt * (hz * 4 + (int)(random() % (hz * 2 + 1))), 0, 568 loadav, NULL, C_DIRECT_EXEC | C_HARDCLOCK); 569} 570 571/* ARGSUSED */ 572static void 573synch_setup(void *dummy) 574{ 575 callout_init(&loadav_callout, CALLOUT_MPSAFE); 576 577 /* Kick off timeout driven events by calling first time. */ 578 loadav(NULL); 579} 580 581int 582should_yield(void) 583{ 584 585 return (ticks - curthread->td_swvoltick >= hogticks); 586} 587 588void 589maybe_yield(void) 590{ 591 592 if (should_yield()) 593 kern_yield(PRI_USER); 594} 595 596void 597kern_yield(int prio) 598{ 599 struct thread *td; 600 601 td = curthread; 602 DROP_GIANT(); 603 thread_lock(td); 604 if (prio == PRI_USER) 605 prio = td->td_user_pri; 606 if (prio >= 0) 607 sched_prio(td, prio); 608 mi_switch(SW_VOL | SWT_RELINQUISH, NULL); 609 thread_unlock(td); 610 PICKUP_GIANT(); 611} 612 613/* 614 * General purpose yield system call. 615 */ 616int 617sys_yield(struct thread *td, struct yield_args *uap) 618{ 619 620 thread_lock(td); 621 if (PRI_BASE(td->td_pri_class) == PRI_TIMESHARE) 622 sched_prio(td, PRI_MAX_TIMESHARE); 623 mi_switch(SW_VOL | SWT_RELINQUISH, NULL); 624 thread_unlock(td); 625 td->td_retval[0] = 0; 626 return (0); 627} 628