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36 * @(#)kern_synch.c 8.9 (Berkeley) 5/19/95
39 #include <sys/cdefs.h>
40 __FBSDID("$FreeBSD$");
42 #include "opt_ktrace.h"
43 #include "opt_sched.h"
45 #include <sys/param.h>
46 #include <sys/systm.h>
47 #include <sys/blockcount.h>
48 #include <sys/condvar.h>
50 #include <sys/kernel.h>
53 #include <sys/mutex.h>
55 #include <sys/resourcevar.h>
56 #include <sys/sched.h>
58 #include <sys/signalvar.h>
59 #include <sys/sleepqueue.h>
62 #include <sys/sysctl.h>
63 #include <sys/sysproto.h>
64 #include <sys/vmmeter.h>
67 #include <sys/ktrace.h>
70 #include <sys/epoch.h>
73 #include <machine/cpu.h>
75 static void synch_setup(void *dummy);
76 SYSINIT(synch_setup, SI_SUB_KICK_SCHEDULER, SI_ORDER_FIRST, synch_setup,
80 static const char pause_wchan[MAXCPU];
82 static struct callout loadav_callout;
84 struct loadavg averunnable =
85 { {0, 0, 0}, FSCALE }; /* load average, of runnable procs */
87 * Constants for averages over 1, 5, and 15 minutes
88 * when sampling at 5 second intervals.
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) */
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");
100 static void loadav(void *arg);
102 SDT_PROVIDER_DECLARE(sched);
103 SDT_PROBE_DEFINE(sched, , , preempt);
106 sleepinit(void *unused)
109 hogticks = (hz / 10) * 2; /* Default only. */
114 * vmem tries to lock the sleepq mutexes when free'ing kva, so make sure
117 SYSINIT(sleepinit, SI_SUB_KMEM, SI_ORDER_ANY, sleepinit, NULL);
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).
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.
135 _sleep(const void *ident, struct lock_object *lock, int priority,
136 const char *wmesg, sbintime_t sbt, sbintime_t pr, int flags)
139 struct lock_class *class;
140 uintptr_t lock_state;
141 int catch, pri, rval, sleepq_flags;
142 WITNESS_SAVE_DECL(lock_witness);
147 if (KTRPOINT(td, KTR_CSW))
150 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock,
151 "Sleeping on \"%s\"", wmesg);
152 KASSERT(sbt != 0 || mtx_owned(&Giant) || lock != NULL ||
153 (priority & PNOLOCK) != 0,
154 ("sleeping without a lock"));
155 KASSERT(ident != NULL, ("_sleep: NULL ident"));
156 KASSERT(TD_IS_RUNNING(td), ("_sleep: curthread not running"));
157 if (priority & PDROP)
158 KASSERT(lock != NULL && lock != &Giant.lock_object,
159 ("PDROP requires a non-Giant lock"));
161 class = LOCK_CLASS(lock);
165 if (SCHEDULER_STOPPED_TD(td)) {
166 if (lock != NULL && priority & PDROP)
167 class->lc_unlock(lock);
170 catch = priority & PCATCH;
171 pri = priority & PRIMASK;
173 KASSERT(!TD_ON_SLEEPQ(td), ("recursive sleep"));
175 if ((uintptr_t)ident >= (uintptr_t)&pause_wchan[0] &&
176 (uintptr_t)ident <= (uintptr_t)&pause_wchan[MAXCPU - 1])
177 sleepq_flags = SLEEPQ_PAUSE;
179 sleepq_flags = SLEEPQ_SLEEP;
181 sleepq_flags |= SLEEPQ_INTERRUPTIBLE;
184 CTR5(KTR_PROC, "sleep: thread %ld (pid %ld, %s) on %s (%p)",
185 td->td_tid, td->td_proc->p_pid, td->td_name, wmesg, ident);
187 if (lock == &Giant.lock_object)
188 mtx_assert(&Giant, MA_OWNED);
190 if (lock != NULL && lock != &Giant.lock_object &&
191 !(class->lc_flags & LC_SLEEPABLE)) {
192 KASSERT(!(class->lc_flags & LC_SPINLOCK),
193 ("spin locks can only use msleep_spin"));
194 WITNESS_SAVE(lock, lock_witness);
195 lock_state = class->lc_unlock(lock);
197 /* GCC needs to follow the Yellow Brick Road */
201 * We put ourselves on the sleep queue and start our timeout
202 * before calling thread_suspend_check, as we could stop there,
203 * and a wakeup or a SIGCONT (or both) could occur while we were
204 * stopped without resuming us. Thus, we must be ready for sleep
205 * when cursig() is called. If the wakeup happens while we're
206 * stopped, then td will no longer be on a sleep queue upon
207 * return from cursig().
209 sleepq_add(ident, lock, wmesg, sleepq_flags, 0);
211 sleepq_set_timeout_sbt(ident, sbt, pr, flags);
212 if (lock != NULL && class->lc_flags & LC_SLEEPABLE) {
213 sleepq_release(ident);
214 WITNESS_SAVE(lock, lock_witness);
215 lock_state = class->lc_unlock(lock);
218 if (sbt != 0 && catch)
219 rval = sleepq_timedwait_sig(ident, pri);
221 rval = sleepq_timedwait(ident, pri);
223 rval = sleepq_wait_sig(ident, pri);
225 sleepq_wait(ident, pri);
229 if (KTRPOINT(td, KTR_CSW))
233 if (lock != NULL && lock != &Giant.lock_object && !(priority & PDROP)) {
234 class->lc_lock(lock, lock_state);
235 WITNESS_RESTORE(lock, lock_witness);
242 msleep_spin_sbt(const void *ident, struct mtx *mtx, const char *wmesg,
243 sbintime_t sbt, sbintime_t pr, int flags)
247 WITNESS_SAVE_DECL(mtx);
250 KASSERT(mtx != NULL, ("sleeping without a mutex"));
251 KASSERT(ident != NULL, ("msleep_spin_sbt: NULL ident"));
252 KASSERT(TD_IS_RUNNING(td), ("msleep_spin_sbt: curthread not running"));
254 if (SCHEDULER_STOPPED_TD(td))
258 CTR5(KTR_PROC, "msleep_spin: thread %ld (pid %ld, %s) on %s (%p)",
259 td->td_tid, td->td_proc->p_pid, td->td_name, wmesg, ident);
262 mtx_assert(mtx, MA_OWNED | MA_NOTRECURSED);
263 WITNESS_SAVE(&mtx->lock_object, mtx);
264 mtx_unlock_spin(mtx);
267 * We put ourselves on the sleep queue and start our timeout.
269 sleepq_add(ident, &mtx->lock_object, wmesg, SLEEPQ_SLEEP, 0);
271 sleepq_set_timeout_sbt(ident, sbt, pr, flags);
274 * Can't call ktrace with any spin locks held so it can lock the
275 * ktrace_mtx lock, and WITNESS_WARN considers it an error to hold
276 * any spin lock. Thus, we have to drop the sleepq spin lock while
277 * we handle those requests. This is safe since we have placed our
278 * thread on the sleep queue already.
281 if (KTRPOINT(td, KTR_CSW)) {
282 sleepq_release(ident);
288 sleepq_release(ident);
289 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, "Sleeping on \"%s\"",
294 rval = sleepq_timedwait(ident, 0);
296 sleepq_wait(ident, 0);
300 if (KTRPOINT(td, KTR_CSW))
305 WITNESS_RESTORE(&mtx->lock_object, mtx);
310 * pause_sbt() delays the calling thread by the given signed binary
311 * time. During cold bootup, pause_sbt() uses the DELAY() function
312 * instead of the _sleep() function to do the waiting. The "sbt"
313 * argument must be greater than or equal to zero. A "sbt" value of
314 * zero is equivalent to a "sbt" value of one tick.
317 pause_sbt(const char *wmesg, sbintime_t sbt, sbintime_t pr, int flags)
319 KASSERT(sbt >= 0, ("pause_sbt: timeout must be >= 0"));
321 /* silently convert invalid timeouts */
325 if ((cold && curthread == &thread0) || kdb_active ||
326 SCHEDULER_STOPPED()) {
328 * We delay one second at a time to avoid overflowing the
329 * system specific DELAY() function(s):
331 while (sbt >= SBT_1S) {
335 /* Do the delay remainder, if any */
336 sbt = howmany(sbt, SBT_1US);
339 return (EWOULDBLOCK);
341 return (_sleep(&pause_wchan[curcpu], NULL,
342 (flags & C_CATCH) ? PCATCH : 0, wmesg, sbt, pr, flags));
346 * Make all threads sleeping on the specified identifier runnable.
349 wakeup(const void *ident)
354 wakeup_swapper = sleepq_broadcast(ident, SLEEPQ_SLEEP, 0, 0);
355 sleepq_release(ident);
356 if (wakeup_swapper) {
357 KASSERT(ident != &proc0,
358 ("wakeup and wakeup_swapper and proc0"));
364 * Make a thread sleeping on the specified identifier runnable.
365 * May wake more than one thread if a target thread is currently
369 wakeup_one(const void *ident)
374 wakeup_swapper = sleepq_signal(ident, SLEEPQ_SLEEP | SLEEPQ_DROP, 0, 0);
380 wakeup_any(const void *ident)
385 wakeup_swapper = sleepq_signal(ident, SLEEPQ_SLEEP | SLEEPQ_UNFAIR |
392 * Signal sleeping waiters after the counter has reached zero.
395 _blockcount_wakeup(blockcount_t *bc, u_int old)
398 KASSERT(_BLOCKCOUNT_WAITERS(old),
399 ("%s: no waiters on %p", __func__, bc));
401 if (atomic_cmpset_int(&bc->__count, _BLOCKCOUNT_WAITERS_FLAG, 0))
406 * Wait for a wakeup or a signal. This does not guarantee that the count is
407 * still zero on return. Callers wanting a precise answer should use
408 * blockcount_wait() with an interlock.
410 * If there is no work to wait for, return 0. If the sleep was interrupted by a
411 * signal, return EINTR or ERESTART, and return EAGAIN otherwise.
414 _blockcount_sleep(blockcount_t *bc, struct lock_object *lock, const char *wmesg,
418 uintptr_t lock_state;
423 KASSERT(lock != &Giant.lock_object,
424 ("%s: cannot use Giant as the interlock", __func__));
426 catch = (prio & PCATCH) != 0;
427 drop = (prio & PDROP) != 0;
431 * Synchronize with the fence in blockcount_release(). If we end up
432 * waiting, the sleepqueue lock acquisition will provide the required
435 * If there is no work to wait for, but waiters are present, try to put
436 * ourselves to sleep to avoid jumping ahead.
438 if (atomic_load_acq_int(&bc->__count) == 0) {
439 if (lock != NULL && drop)
440 LOCK_CLASS(lock)->lc_unlock(lock);
448 lock_state = LOCK_CLASS(lock)->lc_unlock(lock);
449 old = blockcount_read(bc);
452 if (_BLOCKCOUNT_COUNT(old) == 0) {
453 sleepq_release(wchan);
456 if (_BLOCKCOUNT_WAITERS(old))
458 } while (!atomic_fcmpset_int(&bc->__count, &old,
459 old | _BLOCKCOUNT_WAITERS_FLAG));
460 sleepq_add(wchan, NULL, wmesg, catch ? SLEEPQ_INTERRUPTIBLE : 0, 0);
462 ret = sleepq_wait_sig(wchan, prio);
464 sleepq_wait(wchan, prio);
470 if (lock != NULL && !drop)
471 LOCK_CLASS(lock)->lc_lock(lock, lock_state);
479 thread_unlock(curthread);
482 panic("%s: did not reenter debugger", __func__);
486 * The machine independent parts of context switching.
488 * The thread lock is required on entry and is no longer held on return.
493 uint64_t runtime, new_switchtime;
496 td = curthread; /* XXX */
497 THREAD_LOCK_ASSERT(td, MA_OWNED | MA_NOTRECURSED);
498 KASSERT(!TD_ON_RUNQ(td), ("mi_switch: called by old code"));
500 if (!TD_ON_LOCK(td) && !TD_IS_RUNNING(td))
501 mtx_assert(&Giant, MA_NOTOWNED);
503 KASSERT(td->td_critnest == 1 || KERNEL_PANICKED(),
504 ("mi_switch: switch in a critical section"));
505 KASSERT((flags & (SW_INVOL | SW_VOL)) != 0,
506 ("mi_switch: switch must be voluntary or involuntary"));
509 * Don't perform context switches from the debugger.
513 if (SCHEDULER_STOPPED_TD(td))
515 if (flags & SW_VOL) {
516 td->td_ru.ru_nvcsw++;
517 td->td_swvoltick = ticks;
519 td->td_ru.ru_nivcsw++;
520 td->td_swinvoltick = ticks;
523 SCHED_STAT_INC(sched_switch_stats[flags & SW_TYPE_MASK]);
526 * Compute the amount of time during which the current
527 * thread was running, and add that to its total so far.
529 new_switchtime = cpu_ticks();
530 runtime = new_switchtime - PCPU_GET(switchtime);
531 td->td_runtime += runtime;
532 td->td_incruntime += runtime;
533 PCPU_SET(switchtime, new_switchtime);
534 td->td_generation++; /* bump preempt-detect counter */
536 PCPU_SET(switchticks, ticks);
537 CTR4(KTR_PROC, "mi_switch: old thread %ld (td_sched %p, pid %ld, %s)",
538 td->td_tid, td_get_sched(td), td->td_proc->p_pid, td->td_name);
540 if (SDT_PROBES_ENABLED() &&
541 ((flags & SW_PREEMPT) != 0 || ((flags & SW_INVOL) != 0 &&
542 (flags & SW_TYPE_MASK) == SWT_NEEDRESCHED)))
543 SDT_PROBE0(sched, , , preempt);
545 sched_switch(td, flags);
546 CTR4(KTR_PROC, "mi_switch: new thread %ld (td_sched %p, pid %ld, %s)",
547 td->td_tid, td_get_sched(td), td->td_proc->p_pid, td->td_name);
550 * If the last thread was exiting, finish cleaning it up.
552 if ((td = PCPU_GET(deadthread))) {
553 PCPU_SET(deadthread, NULL);
560 * Change thread state to be runnable, placing it on the run queue if
561 * it is in memory. If it is swapped out, return true so our caller
562 * will know to awaken the swapper.
564 * Requires the thread lock on entry, drops on exit.
567 setrunnable(struct thread *td, int srqflags)
571 THREAD_LOCK_ASSERT(td, MA_OWNED);
572 KASSERT(td->td_proc->p_state != PRS_ZOMBIE,
573 ("setrunnable: pid %d is a zombie", td->td_proc->p_pid));
576 switch (TD_GET_STATE(td)) {
581 KASSERT((td->td_flags & TDF_INMEM) != 0,
582 ("setrunnable: td %p not in mem, flags 0x%X inhibit 0x%X",
583 td, td->td_flags, td->td_inhibitors));
584 /* unlocks thread lock according to flags */
585 sched_wakeup(td, srqflags);
589 * If we are only inhibited because we are swapped out
590 * arrange to swap in this process.
592 if (td->td_inhibitors == TDI_SWAPPED &&
593 (td->td_flags & TDF_SWAPINREQ) == 0) {
594 td->td_flags |= TDF_SWAPINREQ;
599 panic("setrunnable: state 0x%x", TD_GET_STATE(td));
601 if ((srqflags & (SRQ_HOLD | SRQ_HOLDTD)) == 0)
608 * Compute a tenex style load average of a quantity on
609 * 1, 5 and 15 minute intervals.
620 for (i = 0; i < 3; i++)
621 avg->ldavg[i] = (cexp[i] * avg->ldavg[i] +
622 nrun * FSCALE * (FSCALE - cexp[i])) >> FSHIFT;
625 * Schedule the next update to occur after 5 seconds, but add a
626 * random variation to avoid synchronisation with processes that
627 * run at regular intervals.
629 callout_reset_sbt(&loadav_callout,
630 SBT_1US * (4000000 + (int)(random() % 2000001)), SBT_1US,
631 loadav, NULL, C_DIRECT_EXEC | C_PREL(32));
636 synch_setup(void *dummy)
638 callout_init(&loadav_callout, 1);
640 /* Kick off timeout driven events by calling first time. */
648 return ((u_int)ticks - (u_int)curthread->td_swvoltick >= hogticks);
656 kern_yield(PRI_USER);
667 if (prio == PRI_USER)
668 prio = td->td_user_pri;
670 sched_prio(td, prio);
671 mi_switch(SW_VOL | SWT_RELINQUISH);
676 * General purpose yield system call.
679 sys_yield(struct thread *td, struct yield_args *uap)
683 if (PRI_BASE(td->td_pri_class) == PRI_TIMESHARE)
684 sched_prio(td, PRI_MAX_TIMESHARE);
685 mi_switch(SW_VOL | SWT_RELINQUISH);
686 td->td_retval[0] = 0;