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: head/sys/kern/kern_synch.c 234494 2012-04-20 15:32:36Z jhb $");
39
40 #include "opt_ktrace.h"
41 #include "opt_sched.h"
42
43 #include <sys/param.h>
44 #include <sys/systm.h>
45 #include <sys/condvar.h>
46 #include <sys/kdb.h>
47 #include <sys/kernel.h>
48 #include <sys/ktr.h>
49 #include <sys/lock.h>
50 #include <sys/mutex.h>
51 #include <sys/proc.h>
52 #include <sys/resourcevar.h>
53 #include <sys/sched.h>
54 #include <sys/signalvar.h>
55 #include <sys/sleepqueue.h>
56 #include <sys/smp.h>
57 #include <sys/sx.h>
58 #include <sys/sysctl.h>
59 #include <sys/sysproto.h>
60 #include <sys/vmmeter.h>
61 #ifdef KTRACE
62 #include <sys/uio.h>
63 #include <sys/ktrace.h>
64 #endif
65
66 #include <machine/cpu.h>
67
68 #ifdef XEN
69 #include <vm/vm.h>
70 #include <vm/vm_param.h>
71 #include <vm/pmap.h>
72 #endif
73
74 #define KTDSTATE(td) \
75 (((td)->td_inhibitors & TDI_SLEEPING) != 0 ? "sleep" : \
76 ((td)->td_inhibitors & TDI_SUSPENDED) != 0 ? "suspended" : \
77 ((td)->td_inhibitors & TDI_SWAPPED) != 0 ? "swapped" : \
78 ((td)->td_inhibitors & TDI_LOCK) != 0 ? "blocked" : \
79 ((td)->td_inhibitors & TDI_IWAIT) != 0 ? "iwait" : "yielding")
80
81 static void synch_setup(void *dummy);
82 SYSINIT(synch_setup, SI_SUB_KICK_SCHEDULER, SI_ORDER_FIRST, synch_setup,
83 NULL);
84
85 int hogticks;
86 static int pause_wchan;
87
88 static struct callout loadav_callout;
89
90 struct loadavg averunnable =
91 { {0, 0, 0}, FSCALE }; /* load average, of runnable procs */
92 /*
93 * Constants for averages over 1, 5, and 15 minutes
94 * when sampling at 5 second intervals.
95 */
96 static fixpt_t cexp[3] = {
97 0.9200444146293232 * FSCALE, /* exp(-1/12) */
98 0.9834714538216174 * FSCALE, /* exp(-1/60) */
99 0.9944598480048967 * FSCALE, /* exp(-1/180) */
100 };
101
102 /* kernel uses `FSCALE', userland (SHOULD) use kern.fscale */
103 static int fscale __unused = FSCALE;
104 SYSCTL_INT(_kern, OID_AUTO, fscale, CTLFLAG_RD, 0, FSCALE, "");
105
106 static void loadav(void *arg);
107
108 void
109 sleepinit(void)
110 {
111
112 hogticks = (hz / 10) * 2; /* Default only. */
113 init_sleepqueues();
114 }
115
116 /*
117 * General sleep call. Suspends the current thread until a wakeup is
118 * performed on the specified identifier. The thread will then be made
119 * runnable with the specified priority. Sleeps at most timo/hz seconds
120 * (0 means no timeout). If pri includes PCATCH flag, signals are checked
121 * before and after sleeping, else signals are not checked. Returns 0 if
122 * awakened, EWOULDBLOCK if the timeout expires. If PCATCH is set and a
123 * signal needs to be delivered, ERESTART is returned if the current system
124 * call should be restarted if possible, and EINTR is returned if the system
125 * call should be interrupted by the signal (return EINTR).
126 *
127 * The lock argument is unlocked before the caller is suspended, and
128 * re-locked before _sleep() returns. If priority includes the PDROP
129 * flag the lock is not re-locked before returning.
130 */
131 int
132 _sleep(void *ident, struct lock_object *lock, int priority,
133 const char *wmesg, int timo)
134 {
135 struct thread *td;
136 struct proc *p;
137 struct lock_class *class;
138 int catch, flags, lock_state, pri, rval;
139 WITNESS_SAVE_DECL(lock_witness);
140
141 td = curthread;
142 p = td->td_proc;
143 #ifdef KTRACE
144 if (KTRPOINT(td, KTR_CSW))
145 ktrcsw(1, 0, wmesg);
146 #endif
147 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock,
148 "Sleeping on \"%s\"", wmesg);
149 KASSERT(timo != 0 || mtx_owned(&Giant) || lock != NULL,
150 ("sleeping without a lock"));
151 KASSERT(p != NULL, ("msleep1"));
152 KASSERT(ident != NULL && TD_IS_RUNNING(td), ("msleep"));
153 if (priority & PDROP)
154 KASSERT(lock != NULL && lock != &Giant.lock_object,
155 ("PDROP requires a non-Giant lock"));
156 if (lock != NULL)
157 class = LOCK_CLASS(lock);
158 else
159 class = NULL;
160
161 if (cold || SCHEDULER_STOPPED()) {
162 /*
163 * During autoconfiguration, just return;
164 * don't run any other threads or panic below,
165 * in case this is the idle thread and already asleep.
166 * XXX: this used to do "s = splhigh(); splx(safepri);
167 * splx(s);" to give interrupts a chance, but there is
168 * no way to give interrupts a chance now.
169 */
170 if (lock != NULL && priority & PDROP)
171 class->lc_unlock(lock);
172 return (0);
173 }
174 catch = priority & PCATCH;
175 pri = priority & PRIMASK;
176
177 /*
178 * If we are already on a sleep queue, then remove us from that
179 * sleep queue first. We have to do this to handle recursive
180 * sleeps.
181 */
182 if (TD_ON_SLEEPQ(td))
183 sleepq_remove(td, td->td_wchan);
184
185 if (ident == &pause_wchan)
186 flags = SLEEPQ_PAUSE;
187 else
188 flags = SLEEPQ_SLEEP;
189 if (catch)
190 flags |= SLEEPQ_INTERRUPTIBLE;
191 if (priority & PBDRY)
192 flags |= SLEEPQ_STOP_ON_BDRY;
193
194 sleepq_lock(ident);
195 CTR5(KTR_PROC, "sleep: thread %ld (pid %ld, %s) on %s (%p)",
196 td->td_tid, p->p_pid, td->td_name, wmesg, ident);
197
198 if (lock == &Giant.lock_object)
199 mtx_assert(&Giant, MA_OWNED);
200 DROP_GIANT();
201 if (lock != NULL && lock != &Giant.lock_object &&
202 !(class->lc_flags & LC_SLEEPABLE)) {
203 WITNESS_SAVE(lock, lock_witness);
204 lock_state = class->lc_unlock(lock);
205 } else
206 /* GCC needs to follow the Yellow Brick Road */
207 lock_state = -1;
208
209 /*
210 * We put ourselves on the sleep queue and start our timeout
211 * before calling thread_suspend_check, as we could stop there,
212 * and a wakeup or a SIGCONT (or both) could occur while we were
213 * stopped without resuming us. Thus, we must be ready for sleep
214 * when cursig() is called. If the wakeup happens while we're
215 * stopped, then td will no longer be on a sleep queue upon
216 * return from cursig().
217 */
218 sleepq_add(ident, lock, wmesg, flags, 0);
219 if (timo)
220 sleepq_set_timeout(ident, timo);
221 if (lock != NULL && class->lc_flags & LC_SLEEPABLE) {
222 sleepq_release(ident);
223 WITNESS_SAVE(lock, lock_witness);
224 lock_state = class->lc_unlock(lock);
225 sleepq_lock(ident);
226 }
227 if (timo && catch)
228 rval = sleepq_timedwait_sig(ident, pri);
229 else if (timo)
230 rval = sleepq_timedwait(ident, pri);
231 else if (catch)
232 rval = sleepq_wait_sig(ident, pri);
233 else {
234 sleepq_wait(ident, pri);
235 rval = 0;
236 }
237 #ifdef KTRACE
238 if (KTRPOINT(td, KTR_CSW))
239 ktrcsw(0, 0, wmesg);
240 #endif
241 PICKUP_GIANT();
242 if (lock != NULL && lock != &Giant.lock_object && !(priority & PDROP)) {
243 class->lc_lock(lock, lock_state);
244 WITNESS_RESTORE(lock, lock_witness);
245 }
246 return (rval);
247 }
248
249 int
250 msleep_spin(void *ident, struct mtx *mtx, const char *wmesg, int timo)
251 {
252 struct thread *td;
253 struct proc *p;
254 int rval;
255 WITNESS_SAVE_DECL(mtx);
256
257 td = curthread;
258 p = td->td_proc;
259 KASSERT(mtx != NULL, ("sleeping without a mutex"));
260 KASSERT(p != NULL, ("msleep1"));
261 KASSERT(ident != NULL && TD_IS_RUNNING(td), ("msleep"));
262
263 if (cold || SCHEDULER_STOPPED()) {
264 /*
265 * During autoconfiguration, just return;
266 * don't run any other threads or panic below,
267 * in case this is the idle thread and already asleep.
268 * XXX: this used to do "s = splhigh(); splx(safepri);
269 * splx(s);" to give interrupts a chance, but there is
270 * no way to give interrupts a chance now.
271 */
272 return (0);
273 }
274
275 sleepq_lock(ident);
276 CTR5(KTR_PROC, "msleep_spin: thread %ld (pid %ld, %s) on %s (%p)",
277 td->td_tid, p->p_pid, td->td_name, wmesg, ident);
278
279 DROP_GIANT();
280 mtx_assert(mtx, MA_OWNED | MA_NOTRECURSED);
281 WITNESS_SAVE(&mtx->lock_object, mtx);
282 mtx_unlock_spin(mtx);
283
284 /*
285 * We put ourselves on the sleep queue and start our timeout.
286 */
287 sleepq_add(ident, &mtx->lock_object, wmesg, SLEEPQ_SLEEP, 0);
288 if (timo)
289 sleepq_set_timeout(ident, timo);
290
291 /*
292 * Can't call ktrace with any spin locks held so it can lock the
293 * ktrace_mtx lock, and WITNESS_WARN considers it an error to hold
294 * any spin lock. Thus, we have to drop the sleepq spin lock while
295 * we handle those requests. This is safe since we have placed our
296 * thread on the sleep queue already.
297 */
298 #ifdef KTRACE
299 if (KTRPOINT(td, KTR_CSW)) {
300 sleepq_release(ident);
301 ktrcsw(1, 0, wmesg);
302 sleepq_lock(ident);
303 }
304 #endif
305 #ifdef WITNESS
306 sleepq_release(ident);
307 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, "Sleeping on \"%s\"",
308 wmesg);
309 sleepq_lock(ident);
310 #endif
311 if (timo)
312 rval = sleepq_timedwait(ident, 0);
313 else {
314 sleepq_wait(ident, 0);
315 rval = 0;
316 }
317 #ifdef KTRACE
318 if (KTRPOINT(td, KTR_CSW))
319 ktrcsw(0, 0, wmesg);
320 #endif
321 PICKUP_GIANT();
322 mtx_lock_spin(mtx);
323 WITNESS_RESTORE(&mtx->lock_object, mtx);
324 return (rval);
325 }
326
327 /*
328 * pause() delays the calling thread by the given number of system ticks.
329 * During cold bootup, pause() uses the DELAY() function instead of
330 * the tsleep() function to do the waiting. The "timo" argument must be
331 * greater than or equal to zero. A "timo" value of zero is equivalent
332 * to a "timo" value of one.
333 */
334 int
335 pause(const char *wmesg, int timo)
336 {
337 KASSERT(timo >= 0, ("pause: timo must be >= 0"));
338
339 /* silently convert invalid timeouts */
340 if (timo < 1)
341 timo = 1;
342
343 if (cold) {
344 /*
345 * We delay one HZ at a time to avoid overflowing the
346 * system specific DELAY() function(s):
347 */
348 while (timo >= hz) {
349 DELAY(1000000);
350 timo -= hz;
351 }
352 if (timo > 0)
353 DELAY(timo * tick);
354 return (0);
355 }
356 return (tsleep(&pause_wchan, 0, wmesg, timo));
357 }
358
359 /*
360 * Make all threads sleeping on the specified identifier runnable.
361 */
362 void
363 wakeup(void *ident)
364 {
365 int wakeup_swapper;
366
367 sleepq_lock(ident);
368 wakeup_swapper = sleepq_broadcast(ident, SLEEPQ_SLEEP, 0, 0);
369 sleepq_release(ident);
370 if (wakeup_swapper) {
371 KASSERT(ident != &proc0,
372 ("wakeup and wakeup_swapper and proc0"));
373 kick_proc0();
374 }
375 }
376
377 /*
378 * Make a thread sleeping on the specified identifier runnable.
379 * May wake more than one thread if a target thread is currently
380 * swapped out.
381 */
382 void
383 wakeup_one(void *ident)
384 {
385 int wakeup_swapper;
386
387 sleepq_lock(ident);
388 wakeup_swapper = sleepq_signal(ident, SLEEPQ_SLEEP, 0, 0);
389 sleepq_release(ident);
390 if (wakeup_swapper)
391 kick_proc0();
392 }
393
394 static void
395 kdb_switch(void)
396 {
397 thread_unlock(curthread);
398 kdb_backtrace();
399 kdb_reenter();
400 panic("%s: did not reenter debugger", __func__);
401 }
402
403 /*
404 * The machine independent parts of context switching.
405 */
406 void
407 mi_switch(int flags, struct thread *newtd)
408 {
409 uint64_t runtime, new_switchtime;
410 struct thread *td;
411 struct proc *p;
412
413 td = curthread; /* XXX */
414 THREAD_LOCK_ASSERT(td, MA_OWNED | MA_NOTRECURSED);
415 p = td->td_proc; /* XXX */
416 KASSERT(!TD_ON_RUNQ(td), ("mi_switch: called by old code"));
417 #ifdef INVARIANTS
418 if (!TD_ON_LOCK(td) && !TD_IS_RUNNING(td))
419 mtx_assert(&Giant, MA_NOTOWNED);
420 #endif
421 KASSERT(td->td_critnest == 1 || panicstr,
422 ("mi_switch: switch in a critical section"));
423 KASSERT((flags & (SW_INVOL | SW_VOL)) != 0,
424 ("mi_switch: switch must be voluntary or involuntary"));
425 KASSERT(newtd != curthread, ("mi_switch: preempting back to ourself"));
426
427 /*
428 * Don't perform context switches from the debugger.
429 */
430 if (kdb_active)
431 kdb_switch();
432 if (SCHEDULER_STOPPED())
433 return;
434 if (flags & SW_VOL) {
435 td->td_ru.ru_nvcsw++;
436 td->td_swvoltick = ticks;
437 } else
438 td->td_ru.ru_nivcsw++;
439 #ifdef SCHED_STATS
440 SCHED_STAT_INC(sched_switch_stats[flags & SW_TYPE_MASK]);
441 #endif
442 /*
443 * Compute the amount of time during which the current
444 * thread was running, and add that to its total so far.
445 */
446 new_switchtime = cpu_ticks();
447 runtime = new_switchtime - PCPU_GET(switchtime);
448 td->td_runtime += runtime;
449 td->td_incruntime += runtime;
450 PCPU_SET(switchtime, new_switchtime);
451 td->td_generation++; /* bump preempt-detect counter */
452 PCPU_INC(cnt.v_swtch);
453 PCPU_SET(switchticks, ticks);
454 CTR4(KTR_PROC, "mi_switch: old thread %ld (td_sched %p, pid %ld, %s)",
455 td->td_tid, td->td_sched, p->p_pid, td->td_name);
456 #if (KTR_COMPILE & KTR_SCHED) != 0
457 if (TD_IS_IDLETHREAD(td))
458 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(td), "idle",
459 "prio:%d", td->td_priority);
460 else
461 KTR_STATE3(KTR_SCHED, "thread", sched_tdname(td), KTDSTATE(td),
462 "prio:%d", td->td_priority, "wmesg:\"%s\"", td->td_wmesg,
463 "lockname:\"%s\"", td->td_lockname);
464 #endif
465 #ifdef XEN
466 PT_UPDATES_FLUSH();
467 #endif
468 sched_switch(td, newtd, flags);
469 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(td), "running",
470 "prio:%d", td->td_priority);
471
472 CTR4(KTR_PROC, "mi_switch: new thread %ld (td_sched %p, pid %ld, %s)",
473 td->td_tid, td->td_sched, p->p_pid, td->td_name);
474
475 /*
476 * If the last thread was exiting, finish cleaning it up.
477 */
478 if ((td = PCPU_GET(deadthread))) {
479 PCPU_SET(deadthread, NULL);
480 thread_stash(td);
481 }
482 }
483
484 /*
485 * Change thread state to be runnable, placing it on the run queue if
486 * it is in memory. If it is swapped out, return true so our caller
487 * will know to awaken the swapper.
488 */
489 int
490 setrunnable(struct thread *td)
491 {
492
493 THREAD_LOCK_ASSERT(td, MA_OWNED);
494 KASSERT(td->td_proc->p_state != PRS_ZOMBIE,
495 ("setrunnable: pid %d is a zombie", td->td_proc->p_pid));
496 switch (td->td_state) {
497 case TDS_RUNNING:
498 case TDS_RUNQ:
499 return (0);
500 case TDS_INHIBITED:
501 /*
502 * If we are only inhibited because we are swapped out
503 * then arange to swap in this process. Otherwise just return.
504 */
505 if (td->td_inhibitors != TDI_SWAPPED)
506 return (0);
507 /* FALLTHROUGH */
508 case TDS_CAN_RUN:
509 break;
510 default:
511 printf("state is 0x%x", td->td_state);
512 panic("setrunnable(2)");
513 }
514 if ((td->td_flags & TDF_INMEM) == 0) {
515 if ((td->td_flags & TDF_SWAPINREQ) == 0) {
516 td->td_flags |= TDF_SWAPINREQ;
517 return (1);
518 }
519 } else
520 sched_wakeup(td);
521 return (0);
522 }
523
524 /*
525 * Compute a tenex style load average of a quantity on
526 * 1, 5 and 15 minute intervals.
527 */
528 static void
529 loadav(void *arg)
530 {
531 int i, nrun;
532 struct loadavg *avg;
533
534 nrun = sched_load();
535 avg = &averunnable;
536
537 for (i = 0; i < 3; i++)
538 avg->ldavg[i] = (cexp[i] * avg->ldavg[i] +
539 nrun * FSCALE * (FSCALE - cexp[i])) >> FSHIFT;
540
541 /*
542 * Schedule the next update to occur after 5 seconds, but add a
543 * random variation to avoid synchronisation with processes that
544 * run at regular intervals.
545 */
546 callout_reset(&loadav_callout, hz * 4 + (int)(random() % (hz * 2 + 1)),
547 loadav, NULL);
548 }
549
550 /* ARGSUSED */
551 static void
552 synch_setup(void *dummy)
553 {
554 callout_init(&loadav_callout, CALLOUT_MPSAFE);
555
556 /* Kick off timeout driven events by calling first time. */
557 loadav(NULL);
558 }
559
560 int
561 should_yield(void)
562 {
563
564 return (ticks - curthread->td_swvoltick >= hogticks);
565 }
566
567 void
568 maybe_yield(void)
569 {
570
571 if (should_yield())
572 kern_yield(PRI_USER);
573 }
574
575 void
576 kern_yield(int prio)
577 {
578 struct thread *td;
579
580 td = curthread;
581 DROP_GIANT();
582 thread_lock(td);
583 if (prio == PRI_USER)
584 prio = td->td_user_pri;
585 if (prio >= 0)
586 sched_prio(td, prio);
587 mi_switch(SW_VOL | SWT_RELINQUISH, NULL);
588 thread_unlock(td);
589 PICKUP_GIANT();
590 }
591
592 /*
593 * General purpose yield system call.
594 */
595 int
596 sys_yield(struct thread *td, struct yield_args *uap)
597 {
598
599 thread_lock(td);
600 if (PRI_BASE(td->td_pri_class) == PRI_TIMESHARE)
601 sched_prio(td, PRI_MAX_TIMESHARE);
602 mi_switch(SW_VOL | SWT_RELINQUISH, NULL);
603 thread_unlock(td);
604 td->td_retval[0] = 0;
605 return (0);
606 }
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