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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/condvar.h>
49 #include <sys/kernel.h>
52 #include <sys/mutex.h>
54 #include <sys/resourcevar.h>
55 #include <sys/refcount.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 uint8_t 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, "");
99 static void loadav(void *arg);
101 SDT_PROVIDER_DECLARE(sched);
102 SDT_PROBE_DEFINE(sched, , , preempt);
105 sleepinit(void *unused)
108 hogticks = (hz / 10) * 2; /* Default only. */
113 * vmem tries to lock the sleepq mutexes when free'ing kva, so make sure
116 SYSINIT(sleepinit, SI_SUB_KMEM, SI_ORDER_ANY, sleepinit, NULL);
119 * General sleep call. Suspends the current thread until a wakeup is
120 * performed on the specified identifier. The thread will then be made
121 * runnable with the specified priority. Sleeps at most sbt units of time
122 * (0 means no timeout). If pri includes the PCATCH flag, let signals
123 * interrupt the sleep, otherwise ignore them while sleeping. Returns 0 if
124 * awakened, EWOULDBLOCK if the timeout expires. If PCATCH is set and a
125 * signal becomes pending, ERESTART is returned if the current system
126 * call should be restarted if possible, and EINTR is returned if the system
127 * call should be interrupted by the signal (return EINTR).
129 * The lock argument is unlocked before the caller is suspended, and
130 * re-locked before _sleep() returns. If priority includes the PDROP
131 * flag the lock is not re-locked before returning.
134 _sleep(void *ident, struct lock_object *lock, int priority,
135 const char *wmesg, sbintime_t sbt, sbintime_t pr, int flags)
138 struct lock_class *class;
139 uintptr_t lock_state;
140 int catch, pri, rval, sleepq_flags;
141 WITNESS_SAVE_DECL(lock_witness);
145 if (KTRPOINT(td, KTR_CSW))
148 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock,
149 "Sleeping on \"%s\"", wmesg);
150 KASSERT(sbt != 0 || mtx_owned(&Giant) || lock != NULL,
151 ("sleeping without a lock"));
152 KASSERT(ident != NULL, ("_sleep: NULL ident"));
153 KASSERT(TD_IS_RUNNING(td), ("_sleep: curthread not running"));
154 if (priority & PDROP)
155 KASSERT(lock != NULL && lock != &Giant.lock_object,
156 ("PDROP requires a non-Giant lock"));
158 class = LOCK_CLASS(lock);
162 if (SCHEDULER_STOPPED_TD(td)) {
163 if (lock != NULL && priority & PDROP)
164 class->lc_unlock(lock);
167 catch = priority & PCATCH;
168 pri = priority & PRIMASK;
170 KASSERT(!TD_ON_SLEEPQ(td), ("recursive sleep"));
172 if ((uint8_t *)ident >= &pause_wchan[0] &&
173 (uint8_t *)ident <= &pause_wchan[MAXCPU - 1])
174 sleepq_flags = SLEEPQ_PAUSE;
176 sleepq_flags = SLEEPQ_SLEEP;
178 sleepq_flags |= SLEEPQ_INTERRUPTIBLE;
181 CTR5(KTR_PROC, "sleep: thread %ld (pid %ld, %s) on %s (%p)",
182 td->td_tid, td->td_proc->p_pid, td->td_name, wmesg, ident);
184 if (lock == &Giant.lock_object)
185 mtx_assert(&Giant, MA_OWNED);
187 if (lock != NULL && lock != &Giant.lock_object &&
188 !(class->lc_flags & LC_SLEEPABLE)) {
189 WITNESS_SAVE(lock, lock_witness);
190 lock_state = class->lc_unlock(lock);
192 /* GCC needs to follow the Yellow Brick Road */
196 * We put ourselves on the sleep queue and start our timeout
197 * before calling thread_suspend_check, as we could stop there,
198 * and a wakeup or a SIGCONT (or both) could occur while we were
199 * stopped without resuming us. Thus, we must be ready for sleep
200 * when cursig() is called. If the wakeup happens while we're
201 * stopped, then td will no longer be on a sleep queue upon
202 * return from cursig().
204 sleepq_add(ident, lock, wmesg, sleepq_flags, 0);
206 sleepq_set_timeout_sbt(ident, sbt, pr, flags);
207 if (lock != NULL && class->lc_flags & LC_SLEEPABLE) {
208 sleepq_release(ident);
209 WITNESS_SAVE(lock, lock_witness);
210 lock_state = class->lc_unlock(lock);
213 if (sbt != 0 && catch)
214 rval = sleepq_timedwait_sig(ident, pri);
216 rval = sleepq_timedwait(ident, pri);
218 rval = sleepq_wait_sig(ident, pri);
220 sleepq_wait(ident, pri);
224 if (KTRPOINT(td, KTR_CSW))
228 if (lock != NULL && lock != &Giant.lock_object && !(priority & PDROP)) {
229 class->lc_lock(lock, lock_state);
230 WITNESS_RESTORE(lock, lock_witness);
236 msleep_spin_sbt(void *ident, struct mtx *mtx, const char *wmesg,
237 sbintime_t sbt, sbintime_t pr, int flags)
241 WITNESS_SAVE_DECL(mtx);
244 KASSERT(mtx != NULL, ("sleeping without a mutex"));
245 KASSERT(ident != NULL, ("msleep_spin_sbt: NULL ident"));
246 KASSERT(TD_IS_RUNNING(td), ("msleep_spin_sbt: curthread not running"));
248 if (SCHEDULER_STOPPED_TD(td))
252 CTR5(KTR_PROC, "msleep_spin: thread %ld (pid %ld, %s) on %s (%p)",
253 td->td_tid, td->td_proc->p_pid, td->td_name, wmesg, ident);
256 mtx_assert(mtx, MA_OWNED | MA_NOTRECURSED);
257 WITNESS_SAVE(&mtx->lock_object, mtx);
258 mtx_unlock_spin(mtx);
261 * We put ourselves on the sleep queue and start our timeout.
263 sleepq_add(ident, &mtx->lock_object, wmesg, SLEEPQ_SLEEP, 0);
265 sleepq_set_timeout_sbt(ident, sbt, pr, flags);
268 * Can't call ktrace with any spin locks held so it can lock the
269 * ktrace_mtx lock, and WITNESS_WARN considers it an error to hold
270 * any spin lock. Thus, we have to drop the sleepq spin lock while
271 * we handle those requests. This is safe since we have placed our
272 * thread on the sleep queue already.
275 if (KTRPOINT(td, KTR_CSW)) {
276 sleepq_release(ident);
282 sleepq_release(ident);
283 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, "Sleeping on \"%s\"",
288 rval = sleepq_timedwait(ident, 0);
290 sleepq_wait(ident, 0);
294 if (KTRPOINT(td, KTR_CSW))
299 WITNESS_RESTORE(&mtx->lock_object, mtx);
304 * pause_sbt() delays the calling thread by the given signed binary
305 * time. During cold bootup, pause_sbt() uses the DELAY() function
306 * instead of the _sleep() function to do the waiting. The "sbt"
307 * argument must be greater than or equal to zero. A "sbt" value of
308 * zero is equivalent to a "sbt" value of one tick.
311 pause_sbt(const char *wmesg, sbintime_t sbt, sbintime_t pr, int flags)
313 KASSERT(sbt >= 0, ("pause_sbt: timeout must be >= 0"));
315 /* silently convert invalid timeouts */
319 if ((cold && curthread == &thread0) || kdb_active ||
320 SCHEDULER_STOPPED()) {
322 * We delay one second at a time to avoid overflowing the
323 * system specific DELAY() function(s):
325 while (sbt >= SBT_1S) {
329 /* Do the delay remainder, if any */
330 sbt = howmany(sbt, SBT_1US);
333 return (EWOULDBLOCK);
335 return (_sleep(&pause_wchan[curcpu], NULL,
336 (flags & C_CATCH) ? PCATCH : 0, wmesg, sbt, pr, flags));
340 * Potentially release the last reference for refcount. Check for
341 * unlikely conditions and signal the caller as to whether it was
345 refcount_release_last(volatile u_int *count, u_int n, u_int old)
349 waiter = old & REFCOUNT_WAITER;
350 old = REFCOUNT_COUNT(old);
351 if (__predict_false(n > old || REFCOUNT_SATURATED(old))) {
353 * Avoid multiple destructor invocations if underflow occurred.
354 * This is not perfect since the memory backing the containing
355 * object may already have been reallocated.
357 _refcount_update_saturated(count);
362 * Attempt to atomically clear the waiter bit. Wakeup waiters
363 * if we are successful.
365 if (waiter != 0 && atomic_cmpset_int(count, REFCOUNT_WAITER, 0))
366 wakeup(__DEVOLATILE(u_int *, count));
369 * Last reference. Signal the user to call the destructor.
371 * Ensure that the destructor sees all updates. The fence_rel
372 * at the start of refcount_releasen synchronizes with this fence.
374 atomic_thread_fence_acq();
379 * Wait for a refcount wakeup. This does not guarantee that the ref is still
380 * zero on return and may be subject to transient wakeups. Callers wanting
381 * a precise answer should use refcount_wait().
384 refcount_sleep(volatile u_int *count, const char *wmesg, int pri)
389 if (REFCOUNT_COUNT(*count) == 0)
391 wchan = __DEVOLATILE(void *, count);
395 if (REFCOUNT_COUNT(old) == 0) {
396 sleepq_release(wchan);
399 if (old & REFCOUNT_WAITER)
401 if (atomic_fcmpset_int(count, &old, old | REFCOUNT_WAITER))
404 sleepq_add(wchan, NULL, wmesg, 0, 0);
405 sleepq_wait(wchan, pri);
409 * Make all threads sleeping on the specified identifier runnable.
417 wakeup_swapper = sleepq_broadcast(ident, SLEEPQ_SLEEP, 0, 0);
418 sleepq_release(ident);
419 if (wakeup_swapper) {
420 KASSERT(ident != &proc0,
421 ("wakeup and wakeup_swapper and proc0"));
427 * Make a thread sleeping on the specified identifier runnable.
428 * May wake more than one thread if a target thread is currently
432 wakeup_one(void *ident)
437 wakeup_swapper = sleepq_signal(ident, SLEEPQ_SLEEP, 0, 0);
438 sleepq_release(ident);
444 wakeup_any(void *ident)
449 wakeup_swapper = sleepq_signal(ident, SLEEPQ_SLEEP | SLEEPQ_UNFAIR,
451 sleepq_release(ident);
459 thread_unlock(curthread);
462 panic("%s: did not reenter debugger", __func__);
466 * The machine independent parts of context switching.
468 * The thread lock is required on entry and is no longer held on return.
473 uint64_t runtime, new_switchtime;
476 td = curthread; /* XXX */
477 THREAD_LOCK_ASSERT(td, MA_OWNED | MA_NOTRECURSED);
478 KASSERT(!TD_ON_RUNQ(td), ("mi_switch: called by old code"));
480 if (!TD_ON_LOCK(td) && !TD_IS_RUNNING(td))
481 mtx_assert(&Giant, MA_NOTOWNED);
483 KASSERT(td->td_critnest == 1 || panicstr,
484 ("mi_switch: switch in a critical section"));
485 KASSERT((flags & (SW_INVOL | SW_VOL)) != 0,
486 ("mi_switch: switch must be voluntary or involuntary"));
489 * Don't perform context switches from the debugger.
493 if (SCHEDULER_STOPPED_TD(td))
495 if (flags & SW_VOL) {
496 td->td_ru.ru_nvcsw++;
497 td->td_swvoltick = ticks;
499 td->td_ru.ru_nivcsw++;
500 td->td_swinvoltick = ticks;
503 SCHED_STAT_INC(sched_switch_stats[flags & SW_TYPE_MASK]);
506 * Compute the amount of time during which the current
507 * thread was running, and add that to its total so far.
509 new_switchtime = cpu_ticks();
510 runtime = new_switchtime - PCPU_GET(switchtime);
511 td->td_runtime += runtime;
512 td->td_incruntime += runtime;
513 PCPU_SET(switchtime, new_switchtime);
514 td->td_generation++; /* bump preempt-detect counter */
516 PCPU_SET(switchticks, ticks);
517 CTR4(KTR_PROC, "mi_switch: old thread %ld (td_sched %p, pid %ld, %s)",
518 td->td_tid, td_get_sched(td), td->td_proc->p_pid, td->td_name);
520 if (SDT_PROBES_ENABLED() &&
521 ((flags & SW_PREEMPT) != 0 || ((flags & SW_INVOL) != 0 &&
522 (flags & SW_TYPE_MASK) == SWT_NEEDRESCHED)))
523 SDT_PROBE0(sched, , , preempt);
525 sched_switch(td, flags);
526 CTR4(KTR_PROC, "mi_switch: new thread %ld (td_sched %p, pid %ld, %s)",
527 td->td_tid, td_get_sched(td), td->td_proc->p_pid, td->td_name);
530 * If the last thread was exiting, finish cleaning it up.
532 if ((td = PCPU_GET(deadthread))) {
533 PCPU_SET(deadthread, NULL);
540 * Change thread state to be runnable, placing it on the run queue if
541 * it is in memory. If it is swapped out, return true so our caller
542 * will know to awaken the swapper.
544 * Requires the thread lock on entry, drops on exit.
547 setrunnable(struct thread *td, int srqflags)
551 THREAD_LOCK_ASSERT(td, MA_OWNED);
552 KASSERT(td->td_proc->p_state != PRS_ZOMBIE,
553 ("setrunnable: pid %d is a zombie", td->td_proc->p_pid));
556 switch (td->td_state) {
561 KASSERT((td->td_flags & TDF_INMEM) != 0,
562 ("setrunnable: td %p not in mem, flags 0x%X inhibit 0x%X",
563 td, td->td_flags, td->td_inhibitors));
564 /* unlocks thread lock according to flags */
565 sched_wakeup(td, srqflags);
569 * If we are only inhibited because we are swapped out
570 * arrange to swap in this process.
572 if (td->td_inhibitors == TDI_SWAPPED &&
573 (td->td_flags & TDF_SWAPINREQ) == 0) {
574 td->td_flags |= TDF_SWAPINREQ;
579 panic("setrunnable: state 0x%x", td->td_state);
581 if ((srqflags & (SRQ_HOLD | SRQ_HOLDTD)) == 0)
588 * Compute a tenex style load average of a quantity on
589 * 1, 5 and 15 minute intervals.
600 for (i = 0; i < 3; i++)
601 avg->ldavg[i] = (cexp[i] * avg->ldavg[i] +
602 nrun * FSCALE * (FSCALE - cexp[i])) >> FSHIFT;
605 * Schedule the next update to occur after 5 seconds, but add a
606 * random variation to avoid synchronisation with processes that
607 * run at regular intervals.
609 callout_reset_sbt(&loadav_callout,
610 SBT_1US * (4000000 + (int)(random() % 2000001)), SBT_1US,
611 loadav, NULL, C_DIRECT_EXEC | C_PREL(32));
616 synch_setup(void *dummy)
618 callout_init(&loadav_callout, 1);
620 /* Kick off timeout driven events by calling first time. */
628 return ((u_int)ticks - (u_int)curthread->td_swvoltick >= hogticks);
636 kern_yield(PRI_USER);
647 if (prio == PRI_USER)
648 prio = td->td_user_pri;
650 sched_prio(td, prio);
651 mi_switch(SW_VOL | SWT_RELINQUISH);
656 * General purpose yield system call.
659 sys_yield(struct thread *td, struct yield_args *uap)
663 if (PRI_BASE(td->td_pri_class) == PRI_TIMESHARE)
664 sched_prio(td, PRI_MAX_TIMESHARE);
665 mi_switch(SW_VOL | SWT_RELINQUISH);
666 td->td_retval[0] = 0;