1 /*-
2 * SPDX-License-Identifier: BSD-3-Clause
3 *
4 * Copyright (c) 1982, 1986, 1990, 1991, 1993
5 * The Regents of the University of California. All rights reserved.
6 * (c) UNIX System Laboratories, Inc.
7 * All or some portions of this file are derived from material licensed
8 * to the University of California by American Telephone and Telegraph
9 * Co. or Unix System Laboratories, Inc. and are reproduced herein with
10 * the permission of UNIX System Laboratories, Inc.
11 *
12 * Redistribution and use in source and binary forms, with or without
13 * modification, are permitted provided that the following conditions
14 * are met:
15 * 1. Redistributions of source code must retain the above copyright
16 * notice, this list of conditions and the following disclaimer.
17 * 2. Redistributions in binary form must reproduce the above copyright
18 * notice, this list of conditions and the following disclaimer in the
19 * documentation and/or other materials provided with the distribution.
20 * 3. Neither the name of the University nor the names of its contributors
21 * may be used to endorse or promote products derived from this software
22 * without specific prior written permission.
23 *
24 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
25 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
26 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
27 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
28 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
29 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
30 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
31 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
32 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
33 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
34 * SUCH DAMAGE.
35 *
36 * @(#)kern_synch.c 8.9 (Berkeley) 5/19/95
37 */
38
39 #include <sys/cdefs.h>
40 __FBSDID("$FreeBSD$");
41
42 #include "opt_ktrace.h"
43 #include "opt_sched.h"
44
45 #include <sys/param.h>
46 #include <sys/systm.h>
47 #include <sys/blockcount.h>
48 #include <sys/condvar.h>
49 #include <sys/kdb.h>
50 #include <sys/kernel.h>
51 #include <sys/ktr.h>
52 #include <sys/lock.h>
53 #include <sys/mutex.h>
54 #include <sys/proc.h>
55 #include <sys/resourcevar.h>
56 #include <sys/sched.h>
57 #include <sys/sdt.h>
58 #include <sys/signalvar.h>
59 #include <sys/sleepqueue.h>
60 #include <sys/smp.h>
61 #include <sys/sx.h>
62 #include <sys/sysctl.h>
63 #include <sys/sysproto.h>
64 #include <sys/vmmeter.h>
65 #ifdef KTRACE
66 #include <sys/uio.h>
67 #include <sys/ktrace.h>
68 #endif
69 #ifdef EPOCH_TRACE
70 #include <sys/epoch.h>
71 #endif
72
73 #include <machine/cpu.h>
74
75 static void synch_setup(void *dummy);
76 SYSINIT(synch_setup, SI_SUB_KICK_SCHEDULER, SI_ORDER_FIRST, synch_setup,
77 NULL);
78
79 int hogticks;
80 static const char pause_wchan[MAXCPU];
81
82 static struct callout loadav_callout;
83
84 struct loadavg averunnable =
85 { {0, 0, 0}, FSCALE }; /* load average, of runnable procs */
86 /*
87 * Constants for averages over 1, 5, and 15 minutes
88 * when sampling at 5 second intervals.
89 */
90 static fixpt_t cexp[3] = {
91 0.9200444146293232 * FSCALE, /* exp(-1/12) */
92 0.9834714538216174 * FSCALE, /* exp(-1/60) */
93 0.9944598480048967 * FSCALE, /* exp(-1/180) */
94 };
95
96 /* kernel uses `FSCALE', userland (SHOULD) use kern.fscale */
97 SYSCTL_INT(_kern, OID_AUTO, fscale, CTLFLAG_RD, SYSCTL_NULL_INT_PTR, FSCALE,
98 "Fixed-point scale factor used for calculating load average values");
99
100 static void loadav(void *arg);
101
102 SDT_PROVIDER_DECLARE(sched);
103 SDT_PROBE_DEFINE(sched, , , preempt);
104
105 static void
sleepinit(void * unused)106 sleepinit(void *unused)
107 {
108
109 hogticks = (hz / 10) * 2; /* Default only. */
110 init_sleepqueues();
111 }
112
113 /*
114 * vmem tries to lock the sleepq mutexes when free'ing kva, so make sure
115 * it is available.
116 */
117 SYSINIT(sleepinit, SI_SUB_KMEM, SI_ORDER_ANY, sleepinit, NULL);
118
119 /*
120 * General sleep call. Suspends the current thread until a wakeup is
121 * performed on the specified identifier. The thread will then be made
122 * runnable with the specified priority. Sleeps at most sbt units of time
123 * (0 means no timeout). If pri includes the PCATCH flag, let signals
124 * interrupt the sleep, otherwise ignore them while sleeping. Returns 0 if
125 * awakened, EWOULDBLOCK if the timeout expires. If PCATCH is set and a
126 * signal becomes pending, ERESTART is returned if the current system
127 * call should be restarted if possible, and EINTR is returned if the system
128 * call should be interrupted by the signal (return EINTR).
129 *
130 * The lock argument is unlocked before the caller is suspended, and
131 * re-locked before _sleep() returns. If priority includes the PDROP
132 * flag the lock is not re-locked before returning.
133 */
134 int
_sleep(const void * ident,struct lock_object * lock,int priority,const char * wmesg,sbintime_t sbt,sbintime_t pr,int flags)135 _sleep(const void *ident, struct lock_object *lock, int priority,
136 const char *wmesg, sbintime_t sbt, sbintime_t pr, int flags)
137 {
138 struct thread *td;
139 struct lock_class *class;
140 uintptr_t lock_state;
141 int catch, pri, rval, sleepq_flags;
142 WITNESS_SAVE_DECL(lock_witness);
143
144 TSENTER();
145 td = curthread;
146 #ifdef KTRACE
147 if (KTRPOINT(td, KTR_CSW))
148 ktrcsw(1, 0, wmesg);
149 #endif
150 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock,
151 "Sleeping on \"%s\"", wmesg);
152 KASSERT(sbt != 0 || mtx_owned(&Giant) || lock != NULL,
153 ("sleeping without a lock"));
154 KASSERT(ident != NULL, ("_sleep: NULL ident"));
155 KASSERT(TD_IS_RUNNING(td), ("_sleep: curthread not running"));
156 if (priority & PDROP)
157 KASSERT(lock != NULL && lock != &Giant.lock_object,
158 ("PDROP requires a non-Giant lock"));
159 if (lock != NULL)
160 class = LOCK_CLASS(lock);
161 else
162 class = NULL;
163
164 if (SCHEDULER_STOPPED_TD(td)) {
165 if (lock != NULL && priority & PDROP)
166 class->lc_unlock(lock);
167 return (0);
168 }
169 catch = priority & PCATCH;
170 pri = priority & PRIMASK;
171
172 KASSERT(!TD_ON_SLEEPQ(td), ("recursive sleep"));
173
174 if ((uintptr_t)ident >= (uintptr_t)&pause_wchan[0] &&
175 (uintptr_t)ident <= (uintptr_t)&pause_wchan[MAXCPU - 1])
176 sleepq_flags = SLEEPQ_PAUSE;
177 else
178 sleepq_flags = SLEEPQ_SLEEP;
179 if (catch)
180 sleepq_flags |= SLEEPQ_INTERRUPTIBLE;
181
182 sleepq_lock(ident);
183 CTR5(KTR_PROC, "sleep: thread %ld (pid %ld, %s) on %s (%p)",
184 td->td_tid, td->td_proc->p_pid, td->td_name, wmesg, ident);
185
186 if (lock == &Giant.lock_object)
187 mtx_assert(&Giant, MA_OWNED);
188 DROP_GIANT();
189 if (lock != NULL && lock != &Giant.lock_object &&
190 !(class->lc_flags & LC_SLEEPABLE)) {
191 KASSERT(!(class->lc_flags & LC_SPINLOCK),
192 ("spin locks can only use msleep_spin"));
193 WITNESS_SAVE(lock, lock_witness);
194 lock_state = class->lc_unlock(lock);
195 } else
196 /* GCC needs to follow the Yellow Brick Road */
197 lock_state = -1;
198
199 /*
200 * We put ourselves on the sleep queue and start our timeout
201 * before calling thread_suspend_check, as we could stop there,
202 * and a wakeup or a SIGCONT (or both) could occur while we were
203 * stopped without resuming us. Thus, we must be ready for sleep
204 * when cursig() is called. If the wakeup happens while we're
205 * stopped, then td will no longer be on a sleep queue upon
206 * return from cursig().
207 */
208 sleepq_add(ident, lock, wmesg, sleepq_flags, 0);
209 if (sbt != 0)
210 sleepq_set_timeout_sbt(ident, sbt, pr, flags);
211 if (lock != NULL && class->lc_flags & LC_SLEEPABLE) {
212 sleepq_release(ident);
213 WITNESS_SAVE(lock, lock_witness);
214 lock_state = class->lc_unlock(lock);
215 sleepq_lock(ident);
216 }
217 if (sbt != 0 && catch)
218 rval = sleepq_timedwait_sig(ident, pri);
219 else if (sbt != 0)
220 rval = sleepq_timedwait(ident, pri);
221 else if (catch)
222 rval = sleepq_wait_sig(ident, pri);
223 else {
224 sleepq_wait(ident, pri);
225 rval = 0;
226 }
227 #ifdef KTRACE
228 if (KTRPOINT(td, KTR_CSW))
229 ktrcsw(0, 0, wmesg);
230 #endif
231 PICKUP_GIANT();
232 if (lock != NULL && lock != &Giant.lock_object && !(priority & PDROP)) {
233 class->lc_lock(lock, lock_state);
234 WITNESS_RESTORE(lock, lock_witness);
235 }
236 TSEXIT();
237 return (rval);
238 }
239
240 int
msleep_spin_sbt(const void * ident,struct mtx * mtx,const char * wmesg,sbintime_t sbt,sbintime_t pr,int flags)241 msleep_spin_sbt(const void *ident, struct mtx *mtx, const char *wmesg,
242 sbintime_t sbt, sbintime_t pr, int flags)
243 {
244 struct thread *td;
245 int rval;
246 WITNESS_SAVE_DECL(mtx);
247
248 td = curthread;
249 KASSERT(mtx != NULL, ("sleeping without a mutex"));
250 KASSERT(ident != NULL, ("msleep_spin_sbt: NULL ident"));
251 KASSERT(TD_IS_RUNNING(td), ("msleep_spin_sbt: curthread not running"));
252
253 if (SCHEDULER_STOPPED_TD(td))
254 return (0);
255
256 sleepq_lock(ident);
257 CTR5(KTR_PROC, "msleep_spin: thread %ld (pid %ld, %s) on %s (%p)",
258 td->td_tid, td->td_proc->p_pid, td->td_name, wmesg, ident);
259
260 DROP_GIANT();
261 mtx_assert(mtx, MA_OWNED | MA_NOTRECURSED);
262 WITNESS_SAVE(&mtx->lock_object, mtx);
263 mtx_unlock_spin(mtx);
264
265 /*
266 * We put ourselves on the sleep queue and start our timeout.
267 */
268 sleepq_add(ident, &mtx->lock_object, wmesg, SLEEPQ_SLEEP, 0);
269 if (sbt != 0)
270 sleepq_set_timeout_sbt(ident, sbt, pr, flags);
271
272 /*
273 * Can't call ktrace with any spin locks held so it can lock the
274 * ktrace_mtx lock, and WITNESS_WARN considers it an error to hold
275 * any spin lock. Thus, we have to drop the sleepq spin lock while
276 * we handle those requests. This is safe since we have placed our
277 * thread on the sleep queue already.
278 */
279 #ifdef KTRACE
280 if (KTRPOINT(td, KTR_CSW)) {
281 sleepq_release(ident);
282 ktrcsw(1, 0, wmesg);
283 sleepq_lock(ident);
284 }
285 #endif
286 #ifdef WITNESS
287 sleepq_release(ident);
288 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, "Sleeping on \"%s\"",
289 wmesg);
290 sleepq_lock(ident);
291 #endif
292 if (sbt != 0)
293 rval = sleepq_timedwait(ident, 0);
294 else {
295 sleepq_wait(ident, 0);
296 rval = 0;
297 }
298 #ifdef KTRACE
299 if (KTRPOINT(td, KTR_CSW))
300 ktrcsw(0, 0, wmesg);
301 #endif
302 PICKUP_GIANT();
303 mtx_lock_spin(mtx);
304 WITNESS_RESTORE(&mtx->lock_object, mtx);
305 return (rval);
306 }
307
308 /*
309 * pause_sbt() delays the calling thread by the given signed binary
310 * time. During cold bootup, pause_sbt() uses the DELAY() function
311 * instead of the _sleep() function to do the waiting. The "sbt"
312 * argument must be greater than or equal to zero. A "sbt" value of
313 * zero is equivalent to a "sbt" value of one tick.
314 */
315 int
pause_sbt(const char * wmesg,sbintime_t sbt,sbintime_t pr,int flags)316 pause_sbt(const char *wmesg, sbintime_t sbt, sbintime_t pr, int flags)
317 {
318 KASSERT(sbt >= 0, ("pause_sbt: timeout must be >= 0"));
319
320 /* silently convert invalid timeouts */
321 if (sbt == 0)
322 sbt = tick_sbt;
323
324 if ((cold && curthread == &thread0) || kdb_active ||
325 SCHEDULER_STOPPED()) {
326 /*
327 * We delay one second at a time to avoid overflowing the
328 * system specific DELAY() function(s):
329 */
330 while (sbt >= SBT_1S) {
331 DELAY(1000000);
332 sbt -= SBT_1S;
333 }
334 /* Do the delay remainder, if any */
335 sbt = howmany(sbt, SBT_1US);
336 if (sbt > 0)
337 DELAY(sbt);
338 return (EWOULDBLOCK);
339 }
340 return (_sleep(&pause_wchan[curcpu], NULL,
341 (flags & C_CATCH) ? PCATCH : 0, wmesg, sbt, pr, flags));
342 }
343
344 /*
345 * Make all threads sleeping on the specified identifier runnable.
346 */
347 void
wakeup(const void * ident)348 wakeup(const void *ident)
349 {
350 int wakeup_swapper;
351
352 sleepq_lock(ident);
353 wakeup_swapper = sleepq_broadcast(ident, SLEEPQ_SLEEP, 0, 0);
354 sleepq_release(ident);
355 if (wakeup_swapper) {
356 KASSERT(ident != &proc0,
357 ("wakeup and wakeup_swapper and proc0"));
358 kick_proc0();
359 }
360 }
361
362 /*
363 * Make a thread sleeping on the specified identifier runnable.
364 * May wake more than one thread if a target thread is currently
365 * swapped out.
366 */
367 void
wakeup_one(const void * ident)368 wakeup_one(const void *ident)
369 {
370 int wakeup_swapper;
371
372 sleepq_lock(ident);
373 wakeup_swapper = sleepq_signal(ident, SLEEPQ_SLEEP | SLEEPQ_DROP, 0, 0);
374 if (wakeup_swapper)
375 kick_proc0();
376 }
377
378 void
wakeup_any(const void * ident)379 wakeup_any(const void *ident)
380 {
381 int wakeup_swapper;
382
383 sleepq_lock(ident);
384 wakeup_swapper = sleepq_signal(ident, SLEEPQ_SLEEP | SLEEPQ_UNFAIR |
385 SLEEPQ_DROP, 0, 0);
386 if (wakeup_swapper)
387 kick_proc0();
388 }
389
390 /*
391 * Signal sleeping waiters after the counter has reached zero.
392 */
393 void
_blockcount_wakeup(blockcount_t * bc,u_int old)394 _blockcount_wakeup(blockcount_t *bc, u_int old)
395 {
396
397 KASSERT(_BLOCKCOUNT_WAITERS(old),
398 ("%s: no waiters on %p", __func__, bc));
399
400 if (atomic_cmpset_int(&bc->__count, _BLOCKCOUNT_WAITERS_FLAG, 0))
401 wakeup(bc);
402 }
403
404 /*
405 * Wait for a wakeup or a signal. This does not guarantee that the count is
406 * still zero on return. Callers wanting a precise answer should use
407 * blockcount_wait() with an interlock.
408 *
409 * If there is no work to wait for, return 0. If the sleep was interrupted by a
410 * signal, return EINTR or ERESTART, and return EAGAIN otherwise.
411 */
412 int
_blockcount_sleep(blockcount_t * bc,struct lock_object * lock,const char * wmesg,int prio)413 _blockcount_sleep(blockcount_t *bc, struct lock_object *lock, const char *wmesg,
414 int prio)
415 {
416 void *wchan;
417 uintptr_t lock_state;
418 u_int old;
419 int ret;
420 bool catch, drop;
421
422 KASSERT(lock != &Giant.lock_object,
423 ("%s: cannot use Giant as the interlock", __func__));
424
425 catch = (prio & PCATCH) != 0;
426 drop = (prio & PDROP) != 0;
427 prio &= PRIMASK;
428
429 /*
430 * Synchronize with the fence in blockcount_release(). If we end up
431 * waiting, the sleepqueue lock acquisition will provide the required
432 * side effects.
433 *
434 * If there is no work to wait for, but waiters are present, try to put
435 * ourselves to sleep to avoid jumping ahead.
436 */
437 if (atomic_load_acq_int(&bc->__count) == 0) {
438 if (lock != NULL && drop)
439 LOCK_CLASS(lock)->lc_unlock(lock);
440 return (0);
441 }
442 lock_state = 0;
443 wchan = bc;
444 sleepq_lock(wchan);
445 DROP_GIANT();
446 if (lock != NULL)
447 lock_state = LOCK_CLASS(lock)->lc_unlock(lock);
448 old = blockcount_read(bc);
449 ret = 0;
450 do {
451 if (_BLOCKCOUNT_COUNT(old) == 0) {
452 sleepq_release(wchan);
453 goto out;
454 }
455 if (_BLOCKCOUNT_WAITERS(old))
456 break;
457 } while (!atomic_fcmpset_int(&bc->__count, &old,
458 old | _BLOCKCOUNT_WAITERS_FLAG));
459 sleepq_add(wchan, NULL, wmesg, catch ? SLEEPQ_INTERRUPTIBLE : 0, 0);
460 if (catch)
461 ret = sleepq_wait_sig(wchan, prio);
462 else
463 sleepq_wait(wchan, prio);
464 if (ret == 0)
465 ret = EAGAIN;
466
467 out:
468 PICKUP_GIANT();
469 if (lock != NULL && !drop)
470 LOCK_CLASS(lock)->lc_lock(lock, lock_state);
471
472 return (ret);
473 }
474
475 static void
kdb_switch(void)476 kdb_switch(void)
477 {
478 thread_unlock(curthread);
479 kdb_backtrace();
480 kdb_reenter();
481 panic("%s: did not reenter debugger", __func__);
482 }
483
484 /*
485 * The machine independent parts of context switching.
486 *
487 * The thread lock is required on entry and is no longer held on return.
488 */
489 void
mi_switch(int flags)490 mi_switch(int flags)
491 {
492 uint64_t runtime, new_switchtime;
493 struct thread *td;
494
495 td = curthread; /* XXX */
496 THREAD_LOCK_ASSERT(td, MA_OWNED | MA_NOTRECURSED);
497 KASSERT(!TD_ON_RUNQ(td), ("mi_switch: called by old code"));
498 #ifdef INVARIANTS
499 if (!TD_ON_LOCK(td) && !TD_IS_RUNNING(td))
500 mtx_assert(&Giant, MA_NOTOWNED);
501 #endif
502 KASSERT(td->td_critnest == 1 || KERNEL_PANICKED(),
503 ("mi_switch: switch in a critical section"));
504 KASSERT((flags & (SW_INVOL | SW_VOL)) != 0,
505 ("mi_switch: switch must be voluntary or involuntary"));
506
507 /*
508 * Don't perform context switches from the debugger.
509 */
510 if (kdb_active)
511 kdb_switch();
512 if (SCHEDULER_STOPPED_TD(td))
513 return;
514 if (flags & SW_VOL) {
515 td->td_ru.ru_nvcsw++;
516 td->td_swvoltick = ticks;
517 } else {
518 td->td_ru.ru_nivcsw++;
519 td->td_swinvoltick = ticks;
520 }
521 #ifdef SCHED_STATS
522 SCHED_STAT_INC(sched_switch_stats[flags & SW_TYPE_MASK]);
523 #endif
524 /*
525 * Compute the amount of time during which the current
526 * thread was running, and add that to its total so far.
527 */
528 new_switchtime = cpu_ticks();
529 runtime = new_switchtime - PCPU_GET(switchtime);
530 td->td_runtime += runtime;
531 td->td_incruntime += runtime;
532 PCPU_SET(switchtime, new_switchtime);
533 td->td_generation++; /* bump preempt-detect counter */
534 VM_CNT_INC(v_swtch);
535 PCPU_SET(switchticks, ticks);
536 CTR4(KTR_PROC, "mi_switch: old thread %ld (td_sched %p, pid %ld, %s)",
537 td->td_tid, td_get_sched(td), td->td_proc->p_pid, td->td_name);
538 #ifdef KDTRACE_HOOKS
539 if (SDT_PROBES_ENABLED() &&
540 ((flags & SW_PREEMPT) != 0 || ((flags & SW_INVOL) != 0 &&
541 (flags & SW_TYPE_MASK) == SWT_NEEDRESCHED)))
542 SDT_PROBE0(sched, , , preempt);
543 #endif
544 sched_switch(td, flags);
545 CTR4(KTR_PROC, "mi_switch: new thread %ld (td_sched %p, pid %ld, %s)",
546 td->td_tid, td_get_sched(td), td->td_proc->p_pid, td->td_name);
547
548 /*
549 * If the last thread was exiting, finish cleaning it up.
550 */
551 if ((td = PCPU_GET(deadthread))) {
552 PCPU_SET(deadthread, NULL);
553 thread_stash(td);
554 }
555 spinlock_exit();
556 }
557
558 /*
559 * Change thread state to be runnable, placing it on the run queue if
560 * it is in memory. If it is swapped out, return true so our caller
561 * will know to awaken the swapper.
562 *
563 * Requires the thread lock on entry, drops on exit.
564 */
565 int
setrunnable(struct thread * td,int srqflags)566 setrunnable(struct thread *td, int srqflags)
567 {
568 int swapin;
569
570 THREAD_LOCK_ASSERT(td, MA_OWNED);
571 KASSERT(td->td_proc->p_state != PRS_ZOMBIE,
572 ("setrunnable: pid %d is a zombie", td->td_proc->p_pid));
573
574 swapin = 0;
575 switch (td->td_state) {
576 case TDS_RUNNING:
577 case TDS_RUNQ:
578 break;
579 case TDS_CAN_RUN:
580 KASSERT((td->td_flags & TDF_INMEM) != 0,
581 ("setrunnable: td %p not in mem, flags 0x%X inhibit 0x%X",
582 td, td->td_flags, td->td_inhibitors));
583 /* unlocks thread lock according to flags */
584 sched_wakeup(td, srqflags);
585 return (0);
586 case TDS_INHIBITED:
587 /*
588 * If we are only inhibited because we are swapped out
589 * arrange to swap in this process.
590 */
591 if (td->td_inhibitors == TDI_SWAPPED &&
592 (td->td_flags & TDF_SWAPINREQ) == 0) {
593 td->td_flags |= TDF_SWAPINREQ;
594 swapin = 1;
595 }
596 break;
597 default:
598 panic("setrunnable: state 0x%x", td->td_state);
599 }
600 if ((srqflags & (SRQ_HOLD | SRQ_HOLDTD)) == 0)
601 thread_unlock(td);
602
603 return (swapin);
604 }
605
606 /*
607 * Compute a tenex style load average of a quantity on
608 * 1, 5 and 15 minute intervals.
609 */
610 static void
loadav(void * arg)611 loadav(void *arg)
612 {
613 int i, nrun;
614 struct loadavg *avg;
615
616 nrun = sched_load();
617 avg = &averunnable;
618
619 for (i = 0; i < 3; i++)
620 avg->ldavg[i] = (cexp[i] * avg->ldavg[i] +
621 nrun * FSCALE * (FSCALE - cexp[i])) >> FSHIFT;
622
623 /*
624 * Schedule the next update to occur after 5 seconds, but add a
625 * random variation to avoid synchronisation with processes that
626 * run at regular intervals.
627 */
628 callout_reset_sbt(&loadav_callout,
629 SBT_1US * (4000000 + (int)(random() % 2000001)), SBT_1US,
630 loadav, NULL, C_DIRECT_EXEC | C_PREL(32));
631 }
632
633 /* ARGSUSED */
634 static void
synch_setup(void * dummy)635 synch_setup(void *dummy)
636 {
637 callout_init(&loadav_callout, 1);
638
639 /* Kick off timeout driven events by calling first time. */
640 loadav(NULL);
641 }
642
643 int
should_yield(void)644 should_yield(void)
645 {
646
647 return ((u_int)ticks - (u_int)curthread->td_swvoltick >= hogticks);
648 }
649
650 void
maybe_yield(void)651 maybe_yield(void)
652 {
653
654 if (should_yield())
655 kern_yield(PRI_USER);
656 }
657
658 void
kern_yield(int prio)659 kern_yield(int prio)
660 {
661 struct thread *td;
662
663 td = curthread;
664 DROP_GIANT();
665 thread_lock(td);
666 if (prio == PRI_USER)
667 prio = td->td_user_pri;
668 if (prio >= 0)
669 sched_prio(td, prio);
670 mi_switch(SW_VOL | SWT_RELINQUISH);
671 PICKUP_GIANT();
672 }
673
674 /*
675 * General purpose yield system call.
676 */
677 int
sys_yield(struct thread * td,struct yield_args * uap)678 sys_yield(struct thread *td, struct yield_args *uap)
679 {
680
681 thread_lock(td);
682 if (PRI_BASE(td->td_pri_class) == PRI_TIMESHARE)
683 sched_prio(td, PRI_MAX_TIMESHARE);
684 mi_switch(SW_VOL | SWT_RELINQUISH);
685 td->td_retval[0] = 0;
686 return (0);
687 }
688
689 int
sys_sched_getcpu(struct thread * td,struct sched_getcpu_args * uap)690 sys_sched_getcpu(struct thread *td, struct sched_getcpu_args *uap)
691 {
692 td->td_retval[0] = td->td_oncpu;
693 return (0);
694 }
695