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 static int fscale __unused = FSCALE;
106 SYSCTL_INT(_kern, OID_AUTO, fscale, CTLFLAG_RD, 0, FSCALE, "");
107
108 static void loadav(void *arg);
109
110 SDT_PROVIDER_DECLARE(sched);
111 SDT_PROBE_DEFINE(sched, , , preempt, preempt);
112
113 /*
114 * These probes reference Solaris features that are not implemented in FreeBSD.
115 * Create the probes anyway for compatibility with existing D scripts; they'll
116 * just never fire.
117 */
118 SDT_PROBE_DEFINE(sched, , , cpucaps_sleep, cpucaps-sleep);
119 SDT_PROBE_DEFINE(sched, , , cpucaps_wakeup, cpucaps-wakeup);
120 SDT_PROBE_DEFINE(sched, , , schedctl_nopreempt, schedctl-nopreempt);
121 SDT_PROBE_DEFINE(sched, , , schedctl_preempt, schedctl-preempt);
122 SDT_PROBE_DEFINE(sched, , , schedctl_yield, schedctl-yield);
123
124 void
125 sleepinit(void)
126 {
127
128 hogticks = (hz / 10) * 2; /* Default only. */
129 init_sleepqueues();
130 }
131
132 /*
133 * General sleep call. Suspends the current thread until a wakeup is
134 * performed on the specified identifier. The thread will then be made
135 * runnable with the specified priority. Sleeps at most timo/hz seconds
136 * (0 means no timeout). If pri includes PCATCH flag, signals are checked
137 * before and after sleeping, else signals are not checked. Returns 0 if
138 * awakened, EWOULDBLOCK if the timeout expires. If PCATCH is set and a
139 * signal needs to be delivered, ERESTART is returned if the current system
140 * call should be restarted if possible, and EINTR is returned if the system
141 * call should be interrupted by the signal (return EINTR).
142 *
143 * The lock argument is unlocked before the caller is suspended, and
144 * re-locked before _sleep() returns. If priority includes the PDROP
145 * flag the lock is not re-locked before returning.
146 */
147 int
148 _sleep(void *ident, struct lock_object *lock, int priority,
149 const char *wmesg, int timo)
150 {
151 struct thread *td;
152 struct proc *p;
153 struct lock_class *class;
154 int catch, flags, lock_state, pri, rval;
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(timo != 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 flags = SLEEPQ_PAUSE;
203 else
204 flags = SLEEPQ_SLEEP;
205 if (catch)
206 flags |= SLEEPQ_INTERRUPTIBLE;
207 if (priority & PBDRY)
208 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, flags, 0);
235 if (timo)
236 sleepq_set_timeout(ident, timo);
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 (timo && catch)
244 rval = sleepq_timedwait_sig(ident, pri);
245 else if (timo)
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
265 int
266 msleep_spin(void *ident, struct mtx *mtx, const char *wmesg, int timo)
267 {
268 struct thread *td;
269 struct proc *p;
270 int rval;
271 WITNESS_SAVE_DECL(mtx);
272
273 td = curthread;
274 p = td->td_proc;
275 KASSERT(mtx != NULL, ("sleeping without a mutex"));
276 KASSERT(p != NULL, ("msleep1"));
277 KASSERT(ident != NULL && TD_IS_RUNNING(td), ("msleep"));
278
279 if (cold || SCHEDULER_STOPPED()) {
280 /*
281 * During autoconfiguration, just return;
282 * don't run any other threads or panic below,
283 * in case this is the idle thread and already asleep.
284 * XXX: this used to do "s = splhigh(); splx(safepri);
285 * splx(s);" to give interrupts a chance, but there is
286 * no way to give interrupts a chance now.
287 */
288 return (0);
289 }
290
291 sleepq_lock(ident);
292 CTR5(KTR_PROC, "msleep_spin: thread %ld (pid %ld, %s) on %s (%p)",
293 td->td_tid, p->p_pid, td->td_name, wmesg, ident);
294
295 DROP_GIANT();
296 mtx_assert(mtx, MA_OWNED | MA_NOTRECURSED);
297 WITNESS_SAVE(&mtx->lock_object, mtx);
298 mtx_unlock_spin(mtx);
299
300 /*
301 * We put ourselves on the sleep queue and start our timeout.
302 */
303 sleepq_add(ident, &mtx->lock_object, wmesg, SLEEPQ_SLEEP, 0);
304 if (timo)
305 sleepq_set_timeout(ident, timo);
306
307 /*
308 * Can't call ktrace with any spin locks held so it can lock the
309 * ktrace_mtx lock, and WITNESS_WARN considers it an error to hold
310 * any spin lock. Thus, we have to drop the sleepq spin lock while
311 * we handle those requests. This is safe since we have placed our
312 * thread on the sleep queue already.
313 */
314 #ifdef KTRACE
315 if (KTRPOINT(td, KTR_CSW)) {
316 sleepq_release(ident);
317 ktrcsw(1, 0, wmesg);
318 sleepq_lock(ident);
319 }
320 #endif
321 #ifdef WITNESS
322 sleepq_release(ident);
323 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, "Sleeping on \"%s\"",
324 wmesg);
325 sleepq_lock(ident);
326 #endif
327 if (timo)
328 rval = sleepq_timedwait(ident, 0);
329 else {
330 sleepq_wait(ident, 0);
331 rval = 0;
332 }
333 #ifdef KTRACE
334 if (KTRPOINT(td, KTR_CSW))
335 ktrcsw(0, 0, wmesg);
336 #endif
337 PICKUP_GIANT();
338 mtx_lock_spin(mtx);
339 WITNESS_RESTORE(&mtx->lock_object, mtx);
340 return (rval);
341 }
342
343 /*
344 * pause() is like tsleep() except that the intention is to not be
345 * explicitly woken up by another thread. Instead, the current thread
346 * simply wishes to sleep until the timeout expires. It is
347 * implemented using a dummy wait channel.
348 */
349 int
350 pause(const char *wmesg, int timo)
351 {
352
353 KASSERT(timo != 0, ("pause: timeout required"));
354 return (tsleep(&pause_wchan, 0, wmesg, timo));
355 }
356
357 /*
358 * Make all threads sleeping on the specified identifier runnable.
359 */
360 void
361 wakeup(void *ident)
362 {
363 int wakeup_swapper;
364
365 sleepq_lock(ident);
366 wakeup_swapper = sleepq_broadcast(ident, SLEEPQ_SLEEP, 0, 0);
367 sleepq_release(ident);
368 if (wakeup_swapper) {
369 KASSERT(ident != &proc0,
370 ("wakeup and wakeup_swapper and proc0"));
371 kick_proc0();
372 }
373 }
374
375 /*
376 * Make a thread sleeping on the specified identifier runnable.
377 * May wake more than one thread if a target thread is currently
378 * swapped out.
379 */
380 void
381 wakeup_one(void *ident)
382 {
383 int wakeup_swapper;
384
385 sleepq_lock(ident);
386 wakeup_swapper = sleepq_signal(ident, SLEEPQ_SLEEP, 0, 0);
387 sleepq_release(ident);
388 if (wakeup_swapper)
389 kick_proc0();
390 }
391
392 static void
393 kdb_switch(void)
394 {
395 thread_unlock(curthread);
396 kdb_backtrace();
397 kdb_reenter();
398 panic("%s: did not reenter debugger", __func__);
399 }
400
401 /*
402 * The machine independent parts of context switching.
403 */
404 void
405 mi_switch(int flags, struct thread *newtd)
406 {
407 uint64_t runtime, new_switchtime;
408 struct thread *td;
409 struct proc *p;
410
411 td = curthread; /* XXX */
412 THREAD_LOCK_ASSERT(td, MA_OWNED | MA_NOTRECURSED);
413 p = td->td_proc; /* XXX */
414 KASSERT(!TD_ON_RUNQ(td), ("mi_switch: called by old code"));
415 #ifdef INVARIANTS
416 if (!TD_ON_LOCK(td) && !TD_IS_RUNNING(td))
417 mtx_assert(&Giant, MA_NOTOWNED);
418 #endif
419 KASSERT(td->td_critnest == 1 || panicstr,
420 ("mi_switch: switch in a critical section"));
421 KASSERT((flags & (SW_INVOL | SW_VOL)) != 0,
422 ("mi_switch: switch must be voluntary or involuntary"));
423 KASSERT(newtd != curthread, ("mi_switch: preempting back to ourself"));
424
425 /*
426 * Don't perform context switches from the debugger.
427 */
428 if (kdb_active)
429 kdb_switch();
430 if (SCHEDULER_STOPPED())
431 return;
432 if (flags & SW_VOL)
433 td->td_ru.ru_nvcsw++;
434 else
435 td->td_ru.ru_nivcsw++;
436 #ifdef SCHED_STATS
437 SCHED_STAT_INC(sched_switch_stats[flags & SW_TYPE_MASK]);
438 #endif
439 /*
440 * Compute the amount of time during which the current
441 * thread was running, and add that to its total so far.
442 */
443 new_switchtime = cpu_ticks();
444 runtime = new_switchtime - PCPU_GET(switchtime);
445 td->td_runtime += runtime;
446 td->td_incruntime += runtime;
447 PCPU_SET(switchtime, new_switchtime);
448 td->td_generation++; /* bump preempt-detect counter */
449 PCPU_INC(cnt.v_swtch);
450 PCPU_SET(switchticks, ticks);
451 CTR4(KTR_PROC, "mi_switch: old thread %ld (td_sched %p, pid %ld, %s)",
452 td->td_tid, td->td_sched, p->p_pid, td->td_name);
453 #if (KTR_COMPILE & KTR_SCHED) != 0
454 if (TD_IS_IDLETHREAD(td))
455 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(td), "idle",
456 "prio:%d", td->td_priority);
457 else
458 KTR_STATE3(KTR_SCHED, "thread", sched_tdname(td), KTDSTATE(td),
459 "prio:%d", td->td_priority, "wmesg:\"%s\"", td->td_wmesg,
460 "lockname:\"%s\"", td->td_lockname);
461 #endif
462 SDT_PROBE0(sched, , , preempt);
463 #ifdef XEN
464 PT_UPDATES_FLUSH();
465 #endif
466 sched_switch(td, newtd, flags);
467 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(td), "running",
468 "prio:%d", td->td_priority);
469
470 CTR4(KTR_PROC, "mi_switch: new thread %ld (td_sched %p, pid %ld, %s)",
471 td->td_tid, td->td_sched, p->p_pid, td->td_name);
472
473 /*
474 * If the last thread was exiting, finish cleaning it up.
475 */
476 if ((td = PCPU_GET(deadthread))) {
477 PCPU_SET(deadthread, NULL);
478 thread_stash(td);
479 }
480 }
481
482 /*
483 * Change thread state to be runnable, placing it on the run queue if
484 * it is in memory. If it is swapped out, return true so our caller
485 * will know to awaken the swapper.
486 */
487 int
488 setrunnable(struct thread *td)
489 {
490
491 THREAD_LOCK_ASSERT(td, MA_OWNED);
492 KASSERT(td->td_proc->p_state != PRS_ZOMBIE,
493 ("setrunnable: pid %d is a zombie", td->td_proc->p_pid));
494 switch (td->td_state) {
495 case TDS_RUNNING:
496 case TDS_RUNQ:
497 return (0);
498 case TDS_INHIBITED:
499 /*
500 * If we are only inhibited because we are swapped out
501 * then arange to swap in this process. Otherwise just return.
502 */
503 if (td->td_inhibitors != TDI_SWAPPED)
504 return (0);
505 /* FALLTHROUGH */
506 case TDS_CAN_RUN:
507 break;
508 default:
509 printf("state is 0x%x", td->td_state);
510 panic("setrunnable(2)");
511 }
512 if ((td->td_flags & TDF_INMEM) == 0) {
513 if ((td->td_flags & TDF_SWAPINREQ) == 0) {
514 td->td_flags |= TDF_SWAPINREQ;
515 return (1);
516 }
517 } else
518 sched_wakeup(td);
519 return (0);
520 }
521
522 /*
523 * Compute a tenex style load average of a quantity on
524 * 1, 5 and 15 minute intervals.
525 */
526 static void
527 loadav(void *arg)
528 {
529 int i, nrun;
530 struct loadavg *avg;
531
532 nrun = sched_load();
533 avg = &averunnable;
534
535 for (i = 0; i < 3; i++)
536 avg->ldavg[i] = (cexp[i] * avg->ldavg[i] +
537 nrun * FSCALE * (FSCALE - cexp[i])) >> FSHIFT;
538
539 /*
540 * Schedule the next update to occur after 5 seconds, but add a
541 * random variation to avoid synchronisation with processes that
542 * run at regular intervals.
543 */
544 callout_reset(&loadav_callout, hz * 4 + (int)(random() % (hz * 2 + 1)),
545 loadav, NULL);
546 }
547
548 /* ARGSUSED */
549 static void
550 synch_setup(void *dummy)
551 {
552 callout_init(&loadav_callout, CALLOUT_MPSAFE);
553
554 /* Kick off timeout driven events by calling first time. */
555 loadav(NULL);
556 }
557
558 int
559 should_yield(void)
560 {
561
562 return (ticks - PCPU_GET(switchticks) >= hogticks);
563 }
564
565 void
566 maybe_yield(void)
567 {
568
569 if (should_yield())
570 kern_yield(PRI_USER);
571 }
572
573 void
574 kern_yield(int prio)
575 {
576 struct thread *td;
577
578 td = curthread;
579 DROP_GIANT();
580 thread_lock(td);
581 if (prio == PRI_USER)
582 prio = td->td_user_pri;
583 if (prio >= 0)
584 sched_prio(td, prio);
585 mi_switch(SW_VOL | SWT_RELINQUISH, NULL);
586 thread_unlock(td);
587 PICKUP_GIANT();
588 }
589
590 /*
591 * General purpose yield system call.
592 */
593 int
594 yield(struct thread *td, struct yield_args *uap)
595 {
596
597 thread_lock(td);
598 if (PRI_BASE(td->td_pri_class) == PRI_TIMESHARE)
599 sched_prio(td, PRI_MAX_TIMESHARE);
600 mi_switch(SW_VOL | SWT_RELINQUISH, NULL);
601 thread_unlock(td);
602 td->td_retval[0] = 0;
603 return (0);
604 }
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