kern_synch.c revision 114750
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 * 3. All advertising materials mentioning features or use of this software 19 * must display the following acknowledgement: 20 * This product includes software developed by the University of 21 * California, Berkeley and its contributors. 22 * 4. Neither the name of the University nor the names of its contributors 23 * may be used to endorse or promote products derived from this software 24 * without specific prior written permission. 25 * 26 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 27 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 28 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 29 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 30 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 31 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 32 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 33 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 34 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 35 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 36 * SUCH DAMAGE. 37 * 38 * @(#)kern_synch.c 8.9 (Berkeley) 5/19/95 39 * $FreeBSD: head/sys/kern/kern_synch.c 114750 2003-05-05 21:12:36Z jhb $ 40 */ 41 42#include "opt_ddb.h" 43#include "opt_ktrace.h" 44#ifdef __i386__ 45#include "opt_swtch.h" 46#endif 47 48#include <sys/param.h> 49#include <sys/systm.h> 50#include <sys/condvar.h> 51#include <sys/kernel.h> 52#include <sys/ktr.h> 53#include <sys/lock.h> 54#include <sys/mutex.h> 55#include <sys/proc.h> 56#include <sys/resourcevar.h> 57#include <sys/sched.h> 58#include <sys/signalvar.h> 59#include <sys/smp.h> 60#include <sys/sx.h> 61#include <sys/sysctl.h> 62#include <sys/sysproto.h> 63#include <sys/vmmeter.h> 64#ifdef DDB 65#include <ddb/ddb.h> 66#endif 67#ifdef KTRACE 68#include <sys/uio.h> 69#include <sys/ktrace.h> 70#endif 71 72#include <machine/cpu.h> 73#ifdef SWTCH_OPTIM_STATS 74#include <machine/md_var.h> 75#endif 76 77static void sched_setup(void *dummy); 78SYSINIT(sched_setup, SI_SUB_KICK_SCHEDULER, SI_ORDER_FIRST, sched_setup, NULL) 79 80int hogticks; 81int lbolt; 82 83static struct callout loadav_callout; 84static struct callout lbolt_callout; 85 86struct loadavg averunnable = 87 { {0, 0, 0}, FSCALE }; /* load average, of runnable procs */ 88/* 89 * Constants for averages over 1, 5, and 15 minutes 90 * when sampling at 5 second intervals. 91 */ 92static fixpt_t cexp[3] = { 93 0.9200444146293232 * FSCALE, /* exp(-1/12) */ 94 0.9834714538216174 * FSCALE, /* exp(-1/60) */ 95 0.9944598480048967 * FSCALE, /* exp(-1/180) */ 96}; 97 98/* kernel uses `FSCALE', userland (SHOULD) use kern.fscale */ 99static int fscale __unused = FSCALE; 100SYSCTL_INT(_kern, OID_AUTO, fscale, CTLFLAG_RD, 0, FSCALE, ""); 101 102static void endtsleep(void *); 103static void loadav(void *arg); 104static void lboltcb(void *arg); 105 106/* 107 * We're only looking at 7 bits of the address; everything is 108 * aligned to 4, lots of things are aligned to greater powers 109 * of 2. Shift right by 8, i.e. drop the bottom 256 worth. 110 */ 111#define TABLESIZE 128 112static TAILQ_HEAD(slpquehead, thread) slpque[TABLESIZE]; 113#define LOOKUP(x) (((intptr_t)(x) >> 8) & (TABLESIZE - 1)) 114 115void 116sleepinit(void) 117{ 118 int i; 119 120 hogticks = (hz / 10) * 2; /* Default only. */ 121 for (i = 0; i < TABLESIZE; i++) 122 TAILQ_INIT(&slpque[i]); 123} 124 125/* 126 * General sleep call. Suspends the current process until a wakeup is 127 * performed on the specified identifier. The process will then be made 128 * runnable with the specified priority. Sleeps at most timo/hz seconds 129 * (0 means no timeout). If pri includes PCATCH flag, signals are checked 130 * before and after sleeping, else signals are not checked. Returns 0 if 131 * awakened, EWOULDBLOCK if the timeout expires. If PCATCH is set and a 132 * signal needs to be delivered, ERESTART is returned if the current system 133 * call should be restarted if possible, and EINTR is returned if the system 134 * call should be interrupted by the signal (return EINTR). 135 * 136 * The mutex argument is exited before the caller is suspended, and 137 * entered before msleep returns. If priority includes the PDROP 138 * flag the mutex is not entered before returning. 139 */ 140 141int 142msleep(ident, mtx, priority, wmesg, timo) 143 void *ident; 144 struct mtx *mtx; 145 int priority, timo; 146 const char *wmesg; 147{ 148 struct thread *td = curthread; 149 struct proc *p = td->td_proc; 150 int sig, catch = priority & PCATCH; 151 int rval = 0; 152 WITNESS_SAVE_DECL(mtx); 153 154#ifdef KTRACE 155 if (KTRPOINT(td, KTR_CSW)) 156 ktrcsw(1, 0); 157#endif 158 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, &mtx->mtx_object, 159 "Sleeping on \"%s\"", wmesg); 160 KASSERT(timo != 0 || mtx_owned(&Giant) || mtx != NULL, 161 ("sleeping without a mutex")); 162 /* 163 * If we are capable of async syscalls and there isn't already 164 * another one ready to return, start a new thread 165 * and queue it as ready to run. Note that there is danger here 166 * because we need to make sure that we don't sleep allocating 167 * the thread (recursion here might be bad). 168 */ 169 mtx_lock_spin(&sched_lock); 170 if (p->p_flag & P_THREADED || p->p_numthreads > 1) { 171 /* 172 * Just don't bother if we are exiting 173 * and not the exiting thread or thread was marked as 174 * interrupted. 175 */ 176 if (catch && 177 (((p->p_flag & P_WEXIT) && (p->p_singlethread != td)) || 178 (td->td_flags & TDF_INTERRUPT))) { 179 td->td_flags &= ~TDF_INTERRUPT; 180 mtx_unlock_spin(&sched_lock); 181 return (EINTR); 182 } 183 } 184 if (cold ) { 185 /* 186 * During autoconfiguration, just give interrupts 187 * a chance, then just return. 188 * Don't run any other procs or panic below, 189 * in case this is the idle process and already asleep. 190 */ 191 if (mtx != NULL && priority & PDROP) 192 mtx_unlock(mtx); 193 mtx_unlock_spin(&sched_lock); 194 return (0); 195 } 196 197 DROP_GIANT(); 198 199 if (mtx != NULL) { 200 mtx_assert(mtx, MA_OWNED | MA_NOTRECURSED); 201 WITNESS_SAVE(&mtx->mtx_object, mtx); 202 mtx_unlock(mtx); 203 if (priority & PDROP) 204 mtx = NULL; 205 } 206 207 KASSERT(p != NULL, ("msleep1")); 208 KASSERT(ident != NULL && TD_IS_RUNNING(td), ("msleep")); 209 210 CTR5(KTR_PROC, "msleep: thread %p (pid %d, %s) on %s (%p)", 211 td, p->p_pid, p->p_comm, wmesg, ident); 212 213 td->td_wchan = ident; 214 td->td_wmesg = wmesg; 215 TAILQ_INSERT_TAIL(&slpque[LOOKUP(ident)], td, td_slpq); 216 TD_SET_ON_SLEEPQ(td); 217 if (timo) 218 callout_reset(&td->td_slpcallout, timo, endtsleep, td); 219 /* 220 * We put ourselves on the sleep queue and start our timeout 221 * before calling thread_suspend_check, as we could stop there, and 222 * a wakeup or a SIGCONT (or both) could occur while we were stopped. 223 * without resuming us, thus we must be ready for sleep 224 * when cursig is called. If the wakeup happens while we're 225 * stopped, td->td_wchan will be 0 upon return from cursig. 226 */ 227 if (catch) { 228 CTR3(KTR_PROC, "msleep caught: thread %p (pid %d, %s)", td, 229 p->p_pid, p->p_comm); 230 td->td_flags |= TDF_SINTR; 231 mtx_unlock_spin(&sched_lock); 232 PROC_LOCK(p); 233 sig = cursig(td); 234 if (sig == 0 && thread_suspend_check(1)) 235 sig = SIGSTOP; 236 mtx_lock_spin(&sched_lock); 237 PROC_UNLOCK(p); 238 if (sig != 0) { 239 if (TD_ON_SLEEPQ(td)) 240 unsleep(td); 241 } else if (!TD_ON_SLEEPQ(td)) 242 catch = 0; 243 } else 244 sig = 0; 245 246 /* 247 * Let the scheduler know we're about to voluntarily go to sleep. 248 */ 249 sched_sleep(td, priority & PRIMASK); 250 251 if (TD_ON_SLEEPQ(td)) { 252 p->p_stats->p_ru.ru_nvcsw++; 253 TD_SET_SLEEPING(td); 254 mi_switch(); 255 } 256 /* 257 * We're awake from voluntary sleep. 258 */ 259 CTR3(KTR_PROC, "msleep resume: thread %p (pid %d, %s)", td, p->p_pid, 260 p->p_comm); 261 KASSERT(TD_IS_RUNNING(td), ("running but not TDS_RUNNING")); 262 td->td_flags &= ~TDF_SINTR; 263 if (td->td_flags & TDF_TIMEOUT) { 264 td->td_flags &= ~TDF_TIMEOUT; 265 if (sig == 0) 266 rval = EWOULDBLOCK; 267 } else if (td->td_flags & TDF_TIMOFAIL) { 268 td->td_flags &= ~TDF_TIMOFAIL; 269 } else if (timo && callout_stop(&td->td_slpcallout) == 0) { 270 /* 271 * This isn't supposed to be pretty. If we are here, then 272 * the endtsleep() callout is currently executing on another 273 * CPU and is either spinning on the sched_lock or will be 274 * soon. If we don't synchronize here, there is a chance 275 * that this process may msleep() again before the callout 276 * has a chance to run and the callout may end up waking up 277 * the wrong msleep(). Yuck. 278 */ 279 TD_SET_SLEEPING(td); 280 p->p_stats->p_ru.ru_nivcsw++; 281 mi_switch(); 282 td->td_flags &= ~TDF_TIMOFAIL; 283 } 284 if ((td->td_flags & TDF_INTERRUPT) && (priority & PCATCH) && 285 (rval == 0)) { 286 td->td_flags &= ~TDF_INTERRUPT; 287 rval = EINTR; 288 } 289 mtx_unlock_spin(&sched_lock); 290 291 if (rval == 0 && catch) { 292 PROC_LOCK(p); 293 /* XXX: shouldn't we always be calling cursig() */ 294 if (sig != 0 || (sig = cursig(td))) { 295 if (SIGISMEMBER(p->p_sigacts->ps_sigintr, sig)) 296 rval = EINTR; 297 else 298 rval = ERESTART; 299 } 300 PROC_UNLOCK(p); 301 } 302#ifdef KTRACE 303 if (KTRPOINT(td, KTR_CSW)) 304 ktrcsw(0, 0); 305#endif 306 PICKUP_GIANT(); 307 if (mtx != NULL) { 308 mtx_lock(mtx); 309 WITNESS_RESTORE(&mtx->mtx_object, mtx); 310 } 311 return (rval); 312} 313 314/* 315 * Implement timeout for msleep() 316 * 317 * If process hasn't been awakened (wchan non-zero), 318 * set timeout flag and undo the sleep. If proc 319 * is stopped, just unsleep so it will remain stopped. 320 * MP-safe, called without the Giant mutex. 321 */ 322static void 323endtsleep(arg) 324 void *arg; 325{ 326 register struct thread *td = arg; 327 328 CTR3(KTR_PROC, "endtsleep: thread %p (pid %d, %s)", 329 td, td->td_proc->p_pid, td->td_proc->p_comm); 330 mtx_lock_spin(&sched_lock); 331 /* 332 * This is the other half of the synchronization with msleep() 333 * described above. If the TDS_TIMEOUT flag is set, we lost the 334 * race and just need to put the process back on the runqueue. 335 */ 336 if (TD_ON_SLEEPQ(td)) { 337 TAILQ_REMOVE(&slpque[LOOKUP(td->td_wchan)], td, td_slpq); 338 TD_CLR_ON_SLEEPQ(td); 339 td->td_flags |= TDF_TIMEOUT; 340 td->td_wmesg = NULL; 341 } else { 342 td->td_flags |= TDF_TIMOFAIL; 343 } 344 TD_CLR_SLEEPING(td); 345 setrunnable(td); 346 mtx_unlock_spin(&sched_lock); 347} 348 349/* 350 * Abort a thread, as if an interrupt had occured. Only abort 351 * interruptable waits (unfortunatly it isn't only safe to abort others). 352 * This is about identical to cv_abort(). 353 * Think about merging them? 354 * Also, whatever the signal code does... 355 */ 356void 357abortsleep(struct thread *td) 358{ 359 360 mtx_assert(&sched_lock, MA_OWNED); 361 /* 362 * If the TDF_TIMEOUT flag is set, just leave. A 363 * timeout is scheduled anyhow. 364 */ 365 if ((td->td_flags & (TDF_TIMEOUT | TDF_SINTR)) == TDF_SINTR) { 366 if (TD_ON_SLEEPQ(td)) { 367 unsleep(td); 368 TD_CLR_SLEEPING(td); 369 setrunnable(td); 370 } 371 } 372} 373 374/* 375 * Remove a process from its wait queue 376 */ 377void 378unsleep(struct thread *td) 379{ 380 381 mtx_lock_spin(&sched_lock); 382 if (TD_ON_SLEEPQ(td)) { 383 TAILQ_REMOVE(&slpque[LOOKUP(td->td_wchan)], td, td_slpq); 384 TD_CLR_ON_SLEEPQ(td); 385 td->td_wmesg = NULL; 386 } 387 mtx_unlock_spin(&sched_lock); 388} 389 390/* 391 * Make all processes sleeping on the specified identifier runnable. 392 */ 393void 394wakeup(ident) 395 register void *ident; 396{ 397 register struct slpquehead *qp; 398 register struct thread *td; 399 struct thread *ntd; 400 struct proc *p; 401 402 mtx_lock_spin(&sched_lock); 403 qp = &slpque[LOOKUP(ident)]; 404restart: 405 for (td = TAILQ_FIRST(qp); td != NULL; td = ntd) { 406 ntd = TAILQ_NEXT(td, td_slpq); 407 if (td->td_wchan == ident) { 408 unsleep(td); 409 TD_CLR_SLEEPING(td); 410 setrunnable(td); 411 p = td->td_proc; 412 CTR3(KTR_PROC,"wakeup: thread %p (pid %d, %s)", 413 td, p->p_pid, p->p_comm); 414 goto restart; 415 } 416 } 417 mtx_unlock_spin(&sched_lock); 418} 419 420/* 421 * Make a process sleeping on the specified identifier runnable. 422 * May wake more than one process if a target process is currently 423 * swapped out. 424 */ 425void 426wakeup_one(ident) 427 register void *ident; 428{ 429 register struct slpquehead *qp; 430 register struct thread *td; 431 register struct proc *p; 432 struct thread *ntd; 433 434 mtx_lock_spin(&sched_lock); 435 qp = &slpque[LOOKUP(ident)]; 436 for (td = TAILQ_FIRST(qp); td != NULL; td = ntd) { 437 ntd = TAILQ_NEXT(td, td_slpq); 438 if (td->td_wchan == ident) { 439 unsleep(td); 440 TD_CLR_SLEEPING(td); 441 setrunnable(td); 442 p = td->td_proc; 443 CTR3(KTR_PROC,"wakeup1: thread %p (pid %d, %s)", 444 td, p->p_pid, p->p_comm); 445 break; 446 } 447 } 448 mtx_unlock_spin(&sched_lock); 449} 450 451/* 452 * The machine independent parts of mi_switch(). 453 */ 454void 455mi_switch(void) 456{ 457 struct bintime new_switchtime; 458 struct thread *td; 459#if defined(__i386__) || defined(__sparc64__) || defined(__amd64__) 460 struct thread *newtd; 461#endif 462 struct proc *p; 463 u_int sched_nest; 464 465 mtx_assert(&sched_lock, MA_OWNED | MA_NOTRECURSED); 466 td = curthread; /* XXX */ 467 p = td->td_proc; /* XXX */ 468 KASSERT(!TD_ON_RUNQ(td), ("mi_switch: called by old code")); 469#ifdef INVARIANTS 470 if (!TD_ON_LOCK(td) && !TD_IS_RUNNING(td)) 471 mtx_assert(&Giant, MA_NOTOWNED); 472#endif 473 KASSERT(td->td_critnest == 1, 474 ("mi_switch: switch in a critical section")); 475 476 /* 477 * Compute the amount of time during which the current 478 * process was running, and add that to its total so far. 479 */ 480 binuptime(&new_switchtime); 481 bintime_add(&p->p_runtime, &new_switchtime); 482 bintime_sub(&p->p_runtime, PCPU_PTR(switchtime)); 483 484#ifdef DDB 485 /* 486 * Don't perform context switches from the debugger. 487 */ 488 if (db_active) { 489 mtx_unlock_spin(&sched_lock); 490 db_print_backtrace(); 491 db_error("Context switches not allowed in the debugger."); 492 } 493#endif 494 495 /* 496 * Check if the process exceeds its cpu resource allocation. If 497 * over max, arrange to kill the process in ast(). 498 */ 499 if (p->p_cpulimit != RLIM_INFINITY && 500 p->p_runtime.sec > p->p_cpulimit) { 501 p->p_sflag |= PS_XCPU; 502 td->td_flags |= TDF_ASTPENDING; 503 } 504 505 /* 506 * Finish up stats for outgoing thread. 507 */ 508 cnt.v_swtch++; 509 PCPU_SET(switchtime, new_switchtime); 510 CTR3(KTR_PROC, "mi_switch: old thread %p (pid %d, %s)", td, p->p_pid, 511 p->p_comm); 512 sched_nest = sched_lock.mtx_recurse; 513 if (td->td_proc->p_flag & P_THREADED) 514 thread_switchout(td); 515 sched_switchout(td); 516 517#if defined(__i386__) || defined(__sparc64__) || defined(__amd64__) 518 newtd = choosethread(); 519 if (td != newtd) 520 cpu_switch(td, newtd); /* SHAZAM!! */ 521#ifdef SWTCH_OPTIM_STATS 522 else 523 stupid_switch++; 524#endif 525#else 526 cpu_switch(); /* SHAZAM!!*/ 527#endif 528 529 sched_lock.mtx_recurse = sched_nest; 530 sched_lock.mtx_lock = (uintptr_t)td; 531 sched_switchin(td); 532 533 /* 534 * Start setting up stats etc. for the incoming thread. 535 * Similar code in fork_exit() is returned to by cpu_switch() 536 * in the case of a new thread/process. 537 */ 538 CTR3(KTR_PROC, "mi_switch: new thread %p (pid %d, %s)", td, p->p_pid, 539 p->p_comm); 540 if (PCPU_GET(switchtime.sec) == 0) 541 binuptime(PCPU_PTR(switchtime)); 542 PCPU_SET(switchticks, ticks); 543 544 /* 545 * Call the switchin function while still holding the scheduler lock 546 * (used by the idlezero code and the general page-zeroing code) 547 */ 548 if (td->td_switchin) 549 td->td_switchin(); 550 551 /* 552 * If the last thread was exiting, finish cleaning it up. 553 */ 554 if ((td = PCPU_GET(deadthread))) { 555 PCPU_SET(deadthread, NULL); 556 thread_stash(td); 557 } 558} 559 560/* 561 * Change process state to be runnable, 562 * placing it on the run queue if it is in memory, 563 * and awakening the swapper if it isn't in memory. 564 */ 565void 566setrunnable(struct thread *td) 567{ 568 struct proc *p = td->td_proc; 569 570 mtx_assert(&sched_lock, MA_OWNED); 571 switch (p->p_state) { 572 case PRS_ZOMBIE: 573 panic("setrunnable(1)"); 574 default: 575 break; 576 } 577 switch (td->td_state) { 578 case TDS_RUNNING: 579 case TDS_RUNQ: 580 return; 581 case TDS_INHIBITED: 582 /* 583 * If we are only inhibited because we are swapped out 584 * then arange to swap in this process. Otherwise just return. 585 */ 586 if (td->td_inhibitors != TDI_SWAPPED) 587 return; 588 case TDS_CAN_RUN: 589 break; 590 default: 591 printf("state is 0x%x", td->td_state); 592 panic("setrunnable(2)"); 593 } 594 if ((p->p_sflag & PS_INMEM) == 0) { 595 if ((p->p_sflag & PS_SWAPPINGIN) == 0) { 596 p->p_sflag |= PS_SWAPINREQ; 597 wakeup(&proc0); 598 } 599 } else 600 sched_wakeup(td); 601} 602 603/* 604 * Compute a tenex style load average of a quantity on 605 * 1, 5 and 15 minute intervals. 606 * XXXKSE Needs complete rewrite when correct info is available. 607 * Completely Bogus.. only works with 1:1 (but compiles ok now :-) 608 */ 609static void 610loadav(void *arg) 611{ 612 int i, nrun; 613 struct loadavg *avg; 614 struct proc *p; 615 struct thread *td; 616 617 avg = &averunnable; 618 sx_slock(&allproc_lock); 619 nrun = 0; 620 FOREACH_PROC_IN_SYSTEM(p) { 621 FOREACH_THREAD_IN_PROC(p, td) { 622 switch (td->td_state) { 623 case TDS_RUNQ: 624 case TDS_RUNNING: 625 if ((p->p_flag & P_NOLOAD) != 0) 626 goto nextproc; 627 nrun++; /* XXXKSE */ 628 default: 629 break; 630 } 631nextproc: 632 continue; 633 } 634 } 635 sx_sunlock(&allproc_lock); 636 for (i = 0; i < 3; i++) 637 avg->ldavg[i] = (cexp[i] * avg->ldavg[i] + 638 nrun * FSCALE * (FSCALE - cexp[i])) >> FSHIFT; 639 640 /* 641 * Schedule the next update to occur after 5 seconds, but add a 642 * random variation to avoid synchronisation with processes that 643 * run at regular intervals. 644 */ 645 callout_reset(&loadav_callout, hz * 4 + (int)(random() % (hz * 2 + 1)), 646 loadav, NULL); 647} 648 649static void 650lboltcb(void *arg) 651{ 652 wakeup(&lbolt); 653 callout_reset(&lbolt_callout, hz, lboltcb, NULL); 654} 655 656/* ARGSUSED */ 657static void 658sched_setup(dummy) 659 void *dummy; 660{ 661 callout_init(&loadav_callout, 0); 662 callout_init(&lbolt_callout, 1); 663 664 /* Kick off timeout driven events by calling first time. */ 665 loadav(NULL); 666 lboltcb(NULL); 667} 668 669/* 670 * General purpose yield system call 671 */ 672int 673yield(struct thread *td, struct yield_args *uap) 674{ 675 struct ksegrp *kg = td->td_ksegrp; 676 677 mtx_assert(&Giant, MA_NOTOWNED); 678 mtx_lock_spin(&sched_lock); 679 kg->kg_proc->p_stats->p_ru.ru_nvcsw++; 680 sched_prio(td, PRI_MAX_TIMESHARE); 681 mi_switch(); 682 mtx_unlock_spin(&sched_lock); 683 td->td_retval[0] = 0; 684 685 return (0); 686} 687 688