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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);
146 if (KTRPOINT(td, KTR_CSW))
149 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock,
150 "Sleeping on \"%s\"", wmesg);
151 KASSERT(sbt != 0 || mtx_owned(&Giant) || lock != NULL,
152 ("sleeping without a lock"));
153 KASSERT(ident != NULL, ("_sleep: NULL ident"));
154 KASSERT(TD_IS_RUNNING(td), ("_sleep: curthread not running"));
155 if (priority & PDROP)
156 KASSERT(lock != NULL && lock != &Giant.lock_object,
157 ("PDROP requires a non-Giant lock"));
159 class = LOCK_CLASS(lock);
163 if (SCHEDULER_STOPPED_TD(td)) {
164 if (lock != NULL && priority & PDROP)
165 class->lc_unlock(lock);
168 catch = priority & PCATCH;
169 pri = priority & PRIMASK;
171 KASSERT(!TD_ON_SLEEPQ(td), ("recursive sleep"));
173 if ((uintptr_t)ident >= (uintptr_t)&pause_wchan[0] &&
174 (uintptr_t)ident <= (uintptr_t)&pause_wchan[MAXCPU - 1])
175 sleepq_flags = SLEEPQ_PAUSE;
177 sleepq_flags = SLEEPQ_SLEEP;
179 sleepq_flags |= SLEEPQ_INTERRUPTIBLE;
182 CTR5(KTR_PROC, "sleep: thread %ld (pid %ld, %s) on %s (%p)",
183 td->td_tid, td->td_proc->p_pid, td->td_name, wmesg, ident);
185 if (lock == &Giant.lock_object)
186 mtx_assert(&Giant, MA_OWNED);
188 if (lock != NULL && lock != &Giant.lock_object &&
189 !(class->lc_flags & LC_SLEEPABLE)) {
190 WITNESS_SAVE(lock, lock_witness);
191 lock_state = class->lc_unlock(lock);
193 /* GCC needs to follow the Yellow Brick Road */
197 * We put ourselves on the sleep queue and start our timeout
198 * before calling thread_suspend_check, as we could stop there,
199 * and a wakeup or a SIGCONT (or both) could occur while we were
200 * stopped without resuming us. Thus, we must be ready for sleep
201 * when cursig() is called. If the wakeup happens while we're
202 * stopped, then td will no longer be on a sleep queue upon
203 * return from cursig().
205 sleepq_add(ident, lock, wmesg, sleepq_flags, 0);
207 sleepq_set_timeout_sbt(ident, sbt, pr, flags);
208 if (lock != NULL && class->lc_flags & LC_SLEEPABLE) {
209 sleepq_release(ident);
210 WITNESS_SAVE(lock, lock_witness);
211 lock_state = class->lc_unlock(lock);
214 if (sbt != 0 && catch)
215 rval = sleepq_timedwait_sig(ident, pri);
217 rval = sleepq_timedwait(ident, pri);
219 rval = sleepq_wait_sig(ident, pri);
221 sleepq_wait(ident, pri);
225 if (KTRPOINT(td, KTR_CSW))
229 if (lock != NULL && lock != &Giant.lock_object && !(priority & PDROP)) {
230 class->lc_lock(lock, lock_state);
231 WITNESS_RESTORE(lock, lock_witness);
237 msleep_spin_sbt(const void *ident, struct mtx *mtx, const char *wmesg,
238 sbintime_t sbt, sbintime_t pr, int flags)
242 WITNESS_SAVE_DECL(mtx);
245 KASSERT(mtx != NULL, ("sleeping without a mutex"));
246 KASSERT(ident != NULL, ("msleep_spin_sbt: NULL ident"));
247 KASSERT(TD_IS_RUNNING(td), ("msleep_spin_sbt: curthread not running"));
249 if (SCHEDULER_STOPPED_TD(td))
253 CTR5(KTR_PROC, "msleep_spin: thread %ld (pid %ld, %s) on %s (%p)",
254 td->td_tid, td->td_proc->p_pid, td->td_name, wmesg, ident);
257 mtx_assert(mtx, MA_OWNED | MA_NOTRECURSED);
258 WITNESS_SAVE(&mtx->lock_object, mtx);
259 mtx_unlock_spin(mtx);
262 * We put ourselves on the sleep queue and start our timeout.
264 sleepq_add(ident, &mtx->lock_object, wmesg, SLEEPQ_SLEEP, 0);
266 sleepq_set_timeout_sbt(ident, sbt, pr, flags);
269 * Can't call ktrace with any spin locks held so it can lock the
270 * ktrace_mtx lock, and WITNESS_WARN considers it an error to hold
271 * any spin lock. Thus, we have to drop the sleepq spin lock while
272 * we handle those requests. This is safe since we have placed our
273 * thread on the sleep queue already.
276 if (KTRPOINT(td, KTR_CSW)) {
277 sleepq_release(ident);
283 sleepq_release(ident);
284 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, "Sleeping on \"%s\"",
289 rval = sleepq_timedwait(ident, 0);
291 sleepq_wait(ident, 0);
295 if (KTRPOINT(td, KTR_CSW))
300 WITNESS_RESTORE(&mtx->lock_object, mtx);
305 * pause_sbt() delays the calling thread by the given signed binary
306 * time. During cold bootup, pause_sbt() uses the DELAY() function
307 * instead of the _sleep() function to do the waiting. The "sbt"
308 * argument must be greater than or equal to zero. A "sbt" value of
309 * zero is equivalent to a "sbt" value of one tick.
312 pause_sbt(const char *wmesg, sbintime_t sbt, sbintime_t pr, int flags)
314 KASSERT(sbt >= 0, ("pause_sbt: timeout must be >= 0"));
316 /* silently convert invalid timeouts */
320 if ((cold && curthread == &thread0) || kdb_active ||
321 SCHEDULER_STOPPED()) {
323 * We delay one second at a time to avoid overflowing the
324 * system specific DELAY() function(s):
326 while (sbt >= SBT_1S) {
330 /* Do the delay remainder, if any */
331 sbt = howmany(sbt, SBT_1US);
334 return (EWOULDBLOCK);
336 return (_sleep(&pause_wchan[curcpu], NULL,
337 (flags & C_CATCH) ? PCATCH : 0, wmesg, sbt, pr, flags));
341 * Make all threads sleeping on the specified identifier runnable.
344 wakeup(const void *ident)
349 wakeup_swapper = sleepq_broadcast(ident, SLEEPQ_SLEEP, 0, 0);
350 sleepq_release(ident);
351 if (wakeup_swapper) {
352 KASSERT(ident != &proc0,
353 ("wakeup and wakeup_swapper and proc0"));
359 * Make a thread sleeping on the specified identifier runnable.
360 * May wake more than one thread if a target thread is currently
364 wakeup_one(const void *ident)
369 wakeup_swapper = sleepq_signal(ident, SLEEPQ_SLEEP, 0, 0);
370 sleepq_release(ident);
376 wakeup_any(const void *ident)
381 wakeup_swapper = sleepq_signal(ident, SLEEPQ_SLEEP | SLEEPQ_UNFAIR,
383 sleepq_release(ident);
389 * Signal sleeping waiters after the counter has reached zero.
392 _blockcount_wakeup(blockcount_t *bc, u_int old)
395 KASSERT(_BLOCKCOUNT_WAITERS(old),
396 ("%s: no waiters on %p", __func__, bc));
398 if (atomic_cmpset_int(&bc->__count, _BLOCKCOUNT_WAITERS_FLAG, 0))
403 * Wait for a wakeup or a signal. This does not guarantee that the count is
404 * still zero on return. Callers wanting a precise answer should use
405 * blockcount_wait() with an interlock.
407 * If there is no work to wait for, return 0. If the sleep was interrupted by a
408 * signal, return EINTR or ERESTART, and return EAGAIN otherwise.
411 _blockcount_sleep(blockcount_t *bc, struct lock_object *lock, const char *wmesg,
415 uintptr_t lock_state;
420 KASSERT(lock != &Giant.lock_object,
421 ("%s: cannot use Giant as the interlock", __func__));
423 catch = (prio & PCATCH) != 0;
424 drop = (prio & PDROP) != 0;
428 * Synchronize with the fence in blockcount_release(). If we end up
429 * waiting, the sleepqueue lock acquisition will provide the required
432 * If there is no work to wait for, but waiters are present, try to put
433 * ourselves to sleep to avoid jumping ahead.
435 if (atomic_load_acq_int(&bc->__count) == 0) {
436 if (lock != NULL && drop)
437 LOCK_CLASS(lock)->lc_unlock(lock);
445 lock_state = LOCK_CLASS(lock)->lc_unlock(lock);
446 old = blockcount_read(bc);
449 if (_BLOCKCOUNT_COUNT(old) == 0) {
450 sleepq_release(wchan);
453 if (_BLOCKCOUNT_WAITERS(old))
455 } while (!atomic_fcmpset_int(&bc->__count, &old,
456 old | _BLOCKCOUNT_WAITERS_FLAG));
457 sleepq_add(wchan, NULL, wmesg, catch ? SLEEPQ_INTERRUPTIBLE : 0, 0);
459 ret = sleepq_wait_sig(wchan, prio);
461 sleepq_wait(wchan, prio);
467 if (lock != NULL && !drop)
468 LOCK_CLASS(lock)->lc_lock(lock, lock_state);
476 thread_unlock(curthread);
479 panic("%s: did not reenter debugger", __func__);
483 * The machine independent parts of context switching.
485 * The thread lock is required on entry and is no longer held on return.
490 uint64_t runtime, new_switchtime;
493 td = curthread; /* XXX */
494 THREAD_LOCK_ASSERT(td, MA_OWNED | MA_NOTRECURSED);
495 KASSERT(!TD_ON_RUNQ(td), ("mi_switch: called by old code"));
497 if (!TD_ON_LOCK(td) && !TD_IS_RUNNING(td))
498 mtx_assert(&Giant, MA_NOTOWNED);
500 KASSERT(td->td_critnest == 1 || KERNEL_PANICKED(),
501 ("mi_switch: switch in a critical section"));
502 KASSERT((flags & (SW_INVOL | SW_VOL)) != 0,
503 ("mi_switch: switch must be voluntary or involuntary"));
506 * Don't perform context switches from the debugger.
510 if (SCHEDULER_STOPPED_TD(td))
512 if (flags & SW_VOL) {
513 td->td_ru.ru_nvcsw++;
514 td->td_swvoltick = ticks;
516 td->td_ru.ru_nivcsw++;
517 td->td_swinvoltick = ticks;
520 SCHED_STAT_INC(sched_switch_stats[flags & SW_TYPE_MASK]);
523 * Compute the amount of time during which the current
524 * thread was running, and add that to its total so far.
526 new_switchtime = cpu_ticks();
527 runtime = new_switchtime - PCPU_GET(switchtime);
528 td->td_runtime += runtime;
529 td->td_incruntime += runtime;
530 PCPU_SET(switchtime, new_switchtime);
531 td->td_generation++; /* bump preempt-detect counter */
533 PCPU_SET(switchticks, ticks);
534 CTR4(KTR_PROC, "mi_switch: old thread %ld (td_sched %p, pid %ld, %s)",
535 td->td_tid, td_get_sched(td), td->td_proc->p_pid, td->td_name);
537 if (SDT_PROBES_ENABLED() &&
538 ((flags & SW_PREEMPT) != 0 || ((flags & SW_INVOL) != 0 &&
539 (flags & SW_TYPE_MASK) == SWT_NEEDRESCHED)))
540 SDT_PROBE0(sched, , , preempt);
542 sched_switch(td, flags);
543 CTR4(KTR_PROC, "mi_switch: new thread %ld (td_sched %p, pid %ld, %s)",
544 td->td_tid, td_get_sched(td), td->td_proc->p_pid, td->td_name);
547 * If the last thread was exiting, finish cleaning it up.
549 if ((td = PCPU_GET(deadthread))) {
550 PCPU_SET(deadthread, NULL);
557 * Change thread state to be runnable, placing it on the run queue if
558 * it is in memory. If it is swapped out, return true so our caller
559 * will know to awaken the swapper.
561 * Requires the thread lock on entry, drops on exit.
564 setrunnable(struct thread *td, int srqflags)
568 THREAD_LOCK_ASSERT(td, MA_OWNED);
569 KASSERT(td->td_proc->p_state != PRS_ZOMBIE,
570 ("setrunnable: pid %d is a zombie", td->td_proc->p_pid));
573 switch (td->td_state) {
578 KASSERT((td->td_flags & TDF_INMEM) != 0,
579 ("setrunnable: td %p not in mem, flags 0x%X inhibit 0x%X",
580 td, td->td_flags, td->td_inhibitors));
581 /* unlocks thread lock according to flags */
582 sched_wakeup(td, srqflags);
586 * If we are only inhibited because we are swapped out
587 * arrange to swap in this process.
589 if (td->td_inhibitors == TDI_SWAPPED &&
590 (td->td_flags & TDF_SWAPINREQ) == 0) {
591 td->td_flags |= TDF_SWAPINREQ;
596 panic("setrunnable: state 0x%x", td->td_state);
598 if ((srqflags & (SRQ_HOLD | SRQ_HOLDTD)) == 0)
605 * Compute a tenex style load average of a quantity on
606 * 1, 5 and 15 minute intervals.
617 for (i = 0; i < 3; i++)
618 avg->ldavg[i] = (cexp[i] * avg->ldavg[i] +
619 nrun * FSCALE * (FSCALE - cexp[i])) >> FSHIFT;
622 * Schedule the next update to occur after 5 seconds, but add a
623 * random variation to avoid synchronisation with processes that
624 * run at regular intervals.
626 callout_reset_sbt(&loadav_callout,
627 SBT_1US * (4000000 + (int)(random() % 2000001)), SBT_1US,
628 loadav, NULL, C_DIRECT_EXEC | C_PREL(32));
633 synch_setup(void *dummy)
635 callout_init(&loadav_callout, 1);
637 /* Kick off timeout driven events by calling first time. */
645 return ((u_int)ticks - (u_int)curthread->td_swvoltick >= hogticks);
653 kern_yield(PRI_USER);
664 if (prio == PRI_USER)
665 prio = td->td_user_pri;
667 sched_prio(td, prio);
668 mi_switch(SW_VOL | SWT_RELINQUISH);
673 * General purpose yield system call.
676 sys_yield(struct thread *td, struct yield_args *uap)
680 if (PRI_BASE(td->td_pri_class) == PRI_TIMESHARE)
681 sched_prio(td, PRI_MAX_TIMESHARE);
682 mi_switch(SW_VOL | SWT_RELINQUISH);
683 td->td_retval[0] = 0;