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