FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_synch.c
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 int pause_wchan;
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 void
124 sleepinit(void)
125 {
126
127 hogticks = (hz / 10) * 2; /* Default only. */
128 init_sleepqueues();
129 }
130
131 /*
132 * General sleep call. Suspends the current thread until a wakeup is
133 * performed on the specified identifier. The thread will then be made
134 * runnable with the specified priority. Sleeps at most timo/hz seconds
135 * (0 means no timeout). If pri includes PCATCH flag, signals are checked
136 * before and after sleeping, else signals are not checked. Returns 0 if
137 * awakened, EWOULDBLOCK if the timeout expires. If PCATCH is set and a
138 * signal needs to be delivered, ERESTART is returned if the current system
139 * call should be restarted if possible, and EINTR is returned if the system
140 * call should be interrupted by the signal (return EINTR).
141 *
142 * The lock argument is unlocked before the caller is suspended, and
143 * re-locked before _sleep() returns. If priority includes the PDROP
144 * flag the lock is not re-locked before returning.
145 */
146 int
147 _sleep(void *ident, struct lock_object *lock, int priority,
148 const char *wmesg, int timo)
149 {
150 struct thread *td;
151 struct proc *p;
152 struct lock_class *class;
153 int catch, flags, lock_state, pri, rval;
154 WITNESS_SAVE_DECL(lock_witness);
155
156 td = curthread;
157 p = td->td_proc;
158 #ifdef KTRACE
159 if (KTRPOINT(td, KTR_CSW))
160 ktrcsw(1, 0, wmesg);
161 #endif
162 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock,
163 "Sleeping on \"%s\"", wmesg);
164 KASSERT(timo != 0 || mtx_owned(&Giant) || lock != NULL,
165 ("sleeping without a lock"));
166 KASSERT(p != NULL, ("msleep1"));
167 KASSERT(ident != NULL && TD_IS_RUNNING(td), ("msleep"));
168 if (priority & PDROP)
169 KASSERT(lock != NULL && lock != &Giant.lock_object,
170 ("PDROP requires a non-Giant lock"));
171 if (lock != NULL)
172 class = LOCK_CLASS(lock);
173 else
174 class = NULL;
175
176 if (cold || SCHEDULER_STOPPED()) {
177 /*
178 * During autoconfiguration, just return;
179 * don't run any other threads or panic below,
180 * in case this is the idle thread and already asleep.
181 * XXX: this used to do "s = splhigh(); splx(safepri);
182 * splx(s);" to give interrupts a chance, but there is
183 * no way to give interrupts a chance now.
184 */
185 if (lock != NULL && priority & PDROP)
186 class->lc_unlock(lock);
187 return (0);
188 }
189 catch = priority & PCATCH;
190 pri = priority & PRIMASK;
191
192 /*
193 * If we are already on a sleep queue, then remove us from that
194 * sleep queue first. We have to do this to handle recursive
195 * sleeps.
196 */
197 if (TD_ON_SLEEPQ(td))
198 sleepq_remove(td, td->td_wchan);
199
200 if (ident == &pause_wchan)
201 flags = SLEEPQ_PAUSE;
202 else
203 flags = SLEEPQ_SLEEP;
204 if (catch)
205 flags |= SLEEPQ_INTERRUPTIBLE;
206 if (priority & PBDRY)
207 flags |= SLEEPQ_STOP_ON_BDRY;
208
209 sleepq_lock(ident);
210 CTR5(KTR_PROC, "sleep: thread %ld (pid %ld, %s) on %s (%p)",
211 td->td_tid, p->p_pid, td->td_name, wmesg, ident);
212
213 if (lock == &Giant.lock_object)
214 mtx_assert(&Giant, MA_OWNED);
215 DROP_GIANT();
216 if (lock != NULL && lock != &Giant.lock_object &&
217 !(class->lc_flags & LC_SLEEPABLE)) {
218 WITNESS_SAVE(lock, lock_witness);
219 lock_state = class->lc_unlock(lock);
220 } else
221 /* GCC needs to follow the Yellow Brick Road */
222 lock_state = -1;
223
224 /*
225 * We put ourselves on the sleep queue and start our timeout
226 * before calling thread_suspend_check, as we could stop there,
227 * and a wakeup or a SIGCONT (or both) could occur while we were
228 * stopped without resuming us. Thus, we must be ready for sleep
229 * when cursig() is called. If the wakeup happens while we're
230 * stopped, then td will no longer be on a sleep queue upon
231 * return from cursig().
232 */
233 sleepq_add(ident, lock, wmesg, flags, 0);
234 if (timo)
235 sleepq_set_timeout(ident, timo);
236 if (lock != NULL && class->lc_flags & LC_SLEEPABLE) {
237 sleepq_release(ident);
238 WITNESS_SAVE(lock, lock_witness);
239 lock_state = class->lc_unlock(lock);
240 sleepq_lock(ident);
241 }
242 if (timo && catch)
243 rval = sleepq_timedwait_sig(ident, pri);
244 else if (timo)
245 rval = sleepq_timedwait(ident, pri);
246 else if (catch)
247 rval = sleepq_wait_sig(ident, pri);
248 else {
249 sleepq_wait(ident, pri);
250 rval = 0;
251 }
252 #ifdef KTRACE
253 if (KTRPOINT(td, KTR_CSW))
254 ktrcsw(0, 0, wmesg);
255 #endif
256 PICKUP_GIANT();
257 if (lock != NULL && lock != &Giant.lock_object && !(priority & PDROP)) {
258 class->lc_lock(lock, lock_state);
259 WITNESS_RESTORE(lock, lock_witness);
260 }
261 return (rval);
262 }
263
264 int
265 msleep_spin(void *ident, struct mtx *mtx, const char *wmesg, int timo)
266 {
267 struct thread *td;
268 struct proc *p;
269 int rval;
270 WITNESS_SAVE_DECL(mtx);
271
272 td = curthread;
273 p = td->td_proc;
274 KASSERT(mtx != NULL, ("sleeping without a mutex"));
275 KASSERT(p != NULL, ("msleep1"));
276 KASSERT(ident != NULL && TD_IS_RUNNING(td), ("msleep"));
277
278 if (cold || SCHEDULER_STOPPED()) {
279 /*
280 * During autoconfiguration, just return;
281 * don't run any other threads or panic below,
282 * in case this is the idle thread and already asleep.
283 * XXX: this used to do "s = splhigh(); splx(safepri);
284 * splx(s);" to give interrupts a chance, but there is
285 * no way to give interrupts a chance now.
286 */
287 return (0);
288 }
289
290 sleepq_lock(ident);
291 CTR5(KTR_PROC, "msleep_spin: thread %ld (pid %ld, %s) on %s (%p)",
292 td->td_tid, p->p_pid, td->td_name, wmesg, ident);
293
294 DROP_GIANT();
295 mtx_assert(mtx, MA_OWNED | MA_NOTRECURSED);
296 WITNESS_SAVE(&mtx->lock_object, mtx);
297 mtx_unlock_spin(mtx);
298
299 /*
300 * We put ourselves on the sleep queue and start our timeout.
301 */
302 sleepq_add(ident, &mtx->lock_object, wmesg, SLEEPQ_SLEEP, 0);
303 if (timo)
304 sleepq_set_timeout(ident, timo);
305
306 /*
307 * Can't call ktrace with any spin locks held so it can lock the
308 * ktrace_mtx lock, and WITNESS_WARN considers it an error to hold
309 * any spin lock. Thus, we have to drop the sleepq spin lock while
310 * we handle those requests. This is safe since we have placed our
311 * thread on the sleep queue already.
312 */
313 #ifdef KTRACE
314 if (KTRPOINT(td, KTR_CSW)) {
315 sleepq_release(ident);
316 ktrcsw(1, 0, wmesg);
317 sleepq_lock(ident);
318 }
319 #endif
320 #ifdef WITNESS
321 sleepq_release(ident);
322 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, "Sleeping on \"%s\"",
323 wmesg);
324 sleepq_lock(ident);
325 #endif
326 if (timo)
327 rval = sleepq_timedwait(ident, 0);
328 else {
329 sleepq_wait(ident, 0);
330 rval = 0;
331 }
332 #ifdef KTRACE
333 if (KTRPOINT(td, KTR_CSW))
334 ktrcsw(0, 0, wmesg);
335 #endif
336 PICKUP_GIANT();
337 mtx_lock_spin(mtx);
338 WITNESS_RESTORE(&mtx->lock_object, mtx);
339 return (rval);
340 }
341
342 /*
343 * pause() delays the calling thread by the given number of system ticks.
344 * During cold bootup, pause() uses the DELAY() function instead of
345 * the tsleep() function to do the waiting. The "timo" argument must be
346 * greater than or equal to zero. A "timo" value of zero is equivalent
347 * to a "timo" value of one.
348 */
349 int
350 pause(const char *wmesg, int timo)
351 {
352 KASSERT(timo >= 0, ("pause: timo must be >= 0"));
353
354 /* silently convert invalid timeouts */
355 if (timo < 1)
356 timo = 1;
357
358 if (cold || kdb_active || SCHEDULER_STOPPED()) {
359 /*
360 * We delay one HZ at a time to avoid overflowing the
361 * system specific DELAY() function(s):
362 */
363 while (timo >= hz) {
364 DELAY(1000000);
365 timo -= hz;
366 }
367 if (timo > 0)
368 DELAY(timo * tick);
369 return (0);
370 }
371 return (tsleep(&pause_wchan, 0, wmesg, timo));
372 }
373
374 /*
375 * Make all threads sleeping on the specified identifier runnable.
376 */
377 void
378 wakeup(void *ident)
379 {
380 int wakeup_swapper;
381
382 sleepq_lock(ident);
383 wakeup_swapper = sleepq_broadcast(ident, SLEEPQ_SLEEP, 0, 0);
384 sleepq_release(ident);
385 if (wakeup_swapper) {
386 KASSERT(ident != &proc0,
387 ("wakeup and wakeup_swapper and proc0"));
388 kick_proc0();
389 }
390 }
391
392 /*
393 * Make a thread sleeping on the specified identifier runnable.
394 * May wake more than one thread if a target thread is currently
395 * swapped out.
396 */
397 void
398 wakeup_one(void *ident)
399 {
400 int wakeup_swapper;
401
402 sleepq_lock(ident);
403 wakeup_swapper = sleepq_signal(ident, SLEEPQ_SLEEP, 0, 0);
404 sleepq_release(ident);
405 if (wakeup_swapper)
406 kick_proc0();
407 }
408
409 static void
410 kdb_switch(void)
411 {
412 thread_unlock(curthread);
413 kdb_backtrace();
414 kdb_reenter();
415 panic("%s: did not reenter debugger", __func__);
416 }
417
418 /*
419 * The machine independent parts of context switching.
420 */
421 void
422 mi_switch(int flags, struct thread *newtd)
423 {
424 uint64_t runtime, new_switchtime;
425 struct thread *td;
426 struct proc *p;
427
428 td = curthread; /* XXX */
429 THREAD_LOCK_ASSERT(td, MA_OWNED | MA_NOTRECURSED);
430 p = td->td_proc; /* XXX */
431 KASSERT(!TD_ON_RUNQ(td), ("mi_switch: called by old code"));
432 #ifdef INVARIANTS
433 if (!TD_ON_LOCK(td) && !TD_IS_RUNNING(td))
434 mtx_assert(&Giant, MA_NOTOWNED);
435 #endif
436 KASSERT(td->td_critnest == 1 || panicstr,
437 ("mi_switch: switch in a critical section"));
438 KASSERT((flags & (SW_INVOL | SW_VOL)) != 0,
439 ("mi_switch: switch must be voluntary or involuntary"));
440 KASSERT(newtd != curthread, ("mi_switch: preempting back to ourself"));
441
442 /*
443 * Don't perform context switches from the debugger.
444 */
445 if (kdb_active)
446 kdb_switch();
447 if (SCHEDULER_STOPPED())
448 return;
449 if (flags & SW_VOL) {
450 td->td_ru.ru_nvcsw++;
451 td->td_swvoltick = ticks;
452 } else
453 td->td_ru.ru_nivcsw++;
454 #ifdef SCHED_STATS
455 SCHED_STAT_INC(sched_switch_stats[flags & SW_TYPE_MASK]);
456 #endif
457 /*
458 * Compute the amount of time during which the current
459 * thread was running, and add that to its total so far.
460 */
461 new_switchtime = cpu_ticks();
462 runtime = new_switchtime - PCPU_GET(switchtime);
463 td->td_runtime += runtime;
464 td->td_incruntime += runtime;
465 PCPU_SET(switchtime, new_switchtime);
466 td->td_generation++; /* bump preempt-detect counter */
467 PCPU_INC(cnt.v_swtch);
468 PCPU_SET(switchticks, ticks);
469 CTR4(KTR_PROC, "mi_switch: old thread %ld (td_sched %p, pid %ld, %s)",
470 td->td_tid, td->td_sched, p->p_pid, td->td_name);
471 #if (KTR_COMPILE & KTR_SCHED) != 0
472 if (TD_IS_IDLETHREAD(td))
473 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(td), "idle",
474 "prio:%d", td->td_priority);
475 else
476 KTR_STATE3(KTR_SCHED, "thread", sched_tdname(td), KTDSTATE(td),
477 "prio:%d", td->td_priority, "wmesg:\"%s\"", td->td_wmesg,
478 "lockname:\"%s\"", td->td_lockname);
479 #endif
480 SDT_PROBE0(sched, , , preempt);
481 #ifdef XEN
482 PT_UPDATES_FLUSH();
483 #endif
484 sched_switch(td, newtd, flags);
485 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(td), "running",
486 "prio:%d", td->td_priority);
487
488 CTR4(KTR_PROC, "mi_switch: new thread %ld (td_sched %p, pid %ld, %s)",
489 td->td_tid, td->td_sched, p->p_pid, td->td_name);
490
491 /*
492 * If the last thread was exiting, finish cleaning it up.
493 */
494 if ((td = PCPU_GET(deadthread))) {
495 PCPU_SET(deadthread, NULL);
496 thread_stash(td);
497 }
498 }
499
500 /*
501 * Change thread state to be runnable, placing it on the run queue if
502 * it is in memory. If it is swapped out, return true so our caller
503 * will know to awaken the swapper.
504 */
505 int
506 setrunnable(struct thread *td)
507 {
508
509 THREAD_LOCK_ASSERT(td, MA_OWNED);
510 KASSERT(td->td_proc->p_state != PRS_ZOMBIE,
511 ("setrunnable: pid %d is a zombie", td->td_proc->p_pid));
512 switch (td->td_state) {
513 case TDS_RUNNING:
514 case TDS_RUNQ:
515 return (0);
516 case TDS_INHIBITED:
517 /*
518 * If we are only inhibited because we are swapped out
519 * then arange to swap in this process. Otherwise just return.
520 */
521 if (td->td_inhibitors != TDI_SWAPPED)
522 return (0);
523 /* FALLTHROUGH */
524 case TDS_CAN_RUN:
525 break;
526 default:
527 printf("state is 0x%x", td->td_state);
528 panic("setrunnable(2)");
529 }
530 if ((td->td_flags & TDF_INMEM) == 0) {
531 if ((td->td_flags & TDF_SWAPINREQ) == 0) {
532 td->td_flags |= TDF_SWAPINREQ;
533 return (1);
534 }
535 } else
536 sched_wakeup(td);
537 return (0);
538 }
539
540 /*
541 * Compute a tenex style load average of a quantity on
542 * 1, 5 and 15 minute intervals.
543 */
544 static void
545 loadav(void *arg)
546 {
547 int i, nrun;
548 struct loadavg *avg;
549
550 nrun = sched_load();
551 avg = &averunnable;
552
553 for (i = 0; i < 3; i++)
554 avg->ldavg[i] = (cexp[i] * avg->ldavg[i] +
555 nrun * FSCALE * (FSCALE - cexp[i])) >> FSHIFT;
556
557 /*
558 * Schedule the next update to occur after 5 seconds, but add a
559 * random variation to avoid synchronisation with processes that
560 * run at regular intervals.
561 */
562 callout_reset(&loadav_callout, hz * 4 + (int)(random() % (hz * 2 + 1)),
563 loadav, NULL);
564 }
565
566 /* ARGSUSED */
567 static void
568 synch_setup(void *dummy)
569 {
570 callout_init(&loadav_callout, CALLOUT_MPSAFE);
571
572 /* Kick off timeout driven events by calling first time. */
573 loadav(NULL);
574 }
575
576 int
577 should_yield(void)
578 {
579
580 return ((u_int)ticks - (u_int)curthread->td_swvoltick >= hogticks);
581 }
582
583 void
584 maybe_yield(void)
585 {
586
587 if (should_yield())
588 kern_yield(PRI_USER);
589 }
590
591 void
592 kern_yield(int prio)
593 {
594 struct thread *td;
595
596 td = curthread;
597 DROP_GIANT();
598 thread_lock(td);
599 if (prio == PRI_USER)
600 prio = td->td_user_pri;
601 if (prio >= 0)
602 sched_prio(td, prio);
603 mi_switch(SW_VOL | SWT_RELINQUISH, NULL);
604 thread_unlock(td);
605 PICKUP_GIANT();
606 }
607
608 /*
609 * General purpose yield system call.
610 */
611 int
612 sys_yield(struct thread *td, struct yield_args *uap)
613 {
614
615 thread_lock(td);
616 if (PRI_BASE(td->td_pri_class) == PRI_TIMESHARE)
617 sched_prio(td, PRI_MAX_TIMESHARE);
618 mi_switch(SW_VOL | SWT_RELINQUISH, NULL);
619 thread_unlock(td);
620 td->td_retval[0] = 0;
621 return (0);
622 }
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