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38 * @(#)kern_synch.c 8.9 (Berkeley) 5/19/95
39 * $FreeBSD: src/sys/kern/kern_synch.c,v 1.87.2.6 2002/10/13 07:29:53 kbyanc Exp $
40 * $DragonFly: src/sys/kern/kern_synch.c,v 1.54 2005/11/19 17:19:47 dillon Exp $
43 #include "opt_ktrace.h"
45 #include <sys/param.h>
46 #include <sys/systm.h>
48 #include <sys/kernel.h>
49 #include <sys/signalvar.h>
50 #include <sys/resourcevar.h>
51 #include <sys/vmmeter.h>
52 #include <sys/sysctl.h>
53 #include <sys/thread2.h>
57 #include <sys/ktrace.h>
59 #include <sys/xwait.h>
61 #include <machine/cpu.h>
62 #include <machine/ipl.h>
63 #include <machine/smp.h>
65 TAILQ_HEAD(tslpque, thread);
67 static void sched_setup (void *dummy);
68 SYSINIT(sched_setup, SI_SUB_KICK_SCHEDULER, SI_ORDER_FIRST, sched_setup, NULL)
73 int sched_quantum; /* Roundrobin scheduling quantum in ticks. */
75 int ncpus2, ncpus2_shift, ncpus2_mask;
78 static struct callout loadav_callout;
79 static struct callout schedcpu_callout;
80 MALLOC_DEFINE(M_TSLEEP, "tslpque", "tsleep queues");
82 struct loadavg averunnable =
83 { {0, 0, 0}, FSCALE }; /* load average, of runnable procs */
85 * Constants for averages over 1, 5, and 15 minutes
86 * when sampling at 5 second intervals.
88 static fixpt_t cexp[3] = {
89 0.9200444146293232 * FSCALE, /* exp(-1/12) */
90 0.9834714538216174 * FSCALE, /* exp(-1/60) */
91 0.9944598480048967 * FSCALE, /* exp(-1/180) */
94 static void endtsleep (void *);
95 static void unsleep_and_wakeup_thread(struct thread *td);
96 static void loadav (void *arg);
97 static void schedcpu (void *arg);
100 * Adjust the scheduler quantum. The quantum is specified in microseconds.
101 * Note that 'tick' is in microseconds per tick.
104 sysctl_kern_quantum(SYSCTL_HANDLER_ARGS)
108 new_val = sched_quantum * tick;
109 error = sysctl_handle_int(oidp, &new_val, 0, req);
110 if (error != 0 || req->newptr == NULL)
114 sched_quantum = new_val / tick;
115 hogticks = 2 * sched_quantum;
119 SYSCTL_PROC(_kern, OID_AUTO, quantum, CTLTYPE_INT|CTLFLAG_RW,
120 0, sizeof sched_quantum, sysctl_kern_quantum, "I", "");
123 * If `ccpu' is not equal to `exp(-1/20)' and you still want to use the
124 * faster/more-accurate formula, you'll have to estimate CCPU_SHIFT below
125 * and possibly adjust FSHIFT in "param.h" so that (FSHIFT >= CCPU_SHIFT).
127 * To estimate CCPU_SHIFT for exp(-1/20), the following formula was used:
128 * 1 - exp(-1/20) ~= 0.0487 ~= 0.0488 == 1 (fixed pt, *11* bits).
130 * If you don't want to bother with the faster/more-accurate formula, you
131 * can set CCPU_SHIFT to (FSHIFT + 1) which will use a slower/less-accurate
132 * (more general) method of calculating the %age of CPU used by a process.
134 * decay 95% of `p_pctcpu' in 60 seconds; see CCPU_SHIFT before changing
136 #define CCPU_SHIFT 11
138 static fixpt_t ccpu = 0.95122942450071400909 * FSCALE; /* exp(-1/20) */
139 SYSCTL_INT(_kern, OID_AUTO, ccpu, CTLFLAG_RD, &ccpu, 0, "");
142 * kernel uses `FSCALE', userland (SHOULD) use kern.fscale
144 static int fscale __unused = FSCALE;
145 SYSCTL_INT(_kern, OID_AUTO, fscale, CTLFLAG_RD, 0, FSCALE, "");
148 * Recompute process priorities, once a second.
150 * Since the userland schedulers are typically event oriented, if the
151 * estcpu calculation at wakeup() time is not sufficient to make a
152 * process runnable relative to other processes in the system we have
153 * a 1-second recalc to help out.
155 * This code also allows us to store sysclock_t data in the process structure
156 * without fear of an overrun, since sysclock_t are guarenteed to hold
157 * several seconds worth of count.
168 * General process statistics once a second
170 FOREACH_PROC_IN_SYSTEM(p) {
173 if (p->p_stat == SSLEEP)
177 * Only recalculate processes that are active or have slept
178 * less then 2 seconds. The schedulers understand this.
180 if (p->p_slptime <= 1) {
181 p->p_usched->recalculate(&p->p_lwp);
183 p->p_pctcpu = (p->p_pctcpu * ccpu) >> FSHIFT;
189 * Resource checks. XXX break out since psignal/killproc can block,
190 * limiting us to one process killed per second. There is probably
193 FOREACH_PROC_IN_SYSTEM(p) {
195 if (p->p_stat == SZOMB ||
196 p->p_limit == NULL ||
202 ttime = p->p_thread->td_sticks + p->p_thread->td_uticks;
203 if (p->p_limit->p_cpulimit != RLIM_INFINITY &&
204 ttime > p->p_limit->p_cpulimit
206 rlim = &p->p_rlimit[RLIMIT_CPU];
207 if (ttime / (rlim_t)1000000 >= rlim->rlim_max) {
208 killproc(p, "exceeded maximum CPU limit");
211 if (rlim->rlim_cur < rlim->rlim_max) {
212 /* XXX: we should make a private copy */
222 wakeup((caddr_t)&lbolt);
223 wakeup((caddr_t)&lbolt_syncer);
224 callout_reset(&schedcpu_callout, hz, schedcpu, NULL);
228 * This is only used by ps. Generate a cpu percentage use over
229 * a period of one second.
232 updatepcpu(struct lwp *lp, int cpticks, int ttlticks)
237 acc = (cpticks << FSHIFT) / ttlticks;
238 if (ttlticks >= ESTCPUFREQ) {
239 lp->lwp_pctcpu = acc;
241 remticks = ESTCPUFREQ - ttlticks;
242 lp->lwp_pctcpu = (acc * ttlticks + lp->lwp_pctcpu * remticks) /
248 * We're only looking at 7 bits of the address; everything is
249 * aligned to 4, lots of things are aligned to greater powers
250 * of 2. Shift right by 8, i.e. drop the bottom 256 worth.
252 #define TABLESIZE 128
253 #define LOOKUP(x) (((intptr_t)(x) >> 8) & (TABLESIZE - 1))
255 static cpumask_t slpque_cpumasks[TABLESIZE];
258 * General scheduler initialization. We force a reschedule 25 times
259 * a second by default. Note that cpu0 is initialized in early boot and
260 * cannot make any high level calls.
262 * Each cpu has its own sleep queue.
265 sleep_gdinit(globaldata_t gd)
267 static struct tslpque slpque_cpu0[TABLESIZE];
270 if (gd->gd_cpuid == 0) {
271 sched_quantum = (hz + 24) / 25;
272 hogticks = 2 * sched_quantum;
274 gd->gd_tsleep_hash = slpque_cpu0;
276 gd->gd_tsleep_hash = malloc(sizeof(slpque_cpu0),
277 M_TSLEEP, M_WAITOK | M_ZERO);
279 for (i = 0; i < TABLESIZE; ++i)
280 TAILQ_INIT(&gd->gd_tsleep_hash[i]);
284 * General sleep call. Suspends the current process until a wakeup is
285 * performed on the specified identifier. The process will then be made
286 * runnable with the specified priority. Sleeps at most timo/hz seconds
287 * (0 means no timeout). If flags includes PCATCH flag, signals are checked
288 * before and after sleeping, else signals are not checked. Returns 0 if
289 * awakened, EWOULDBLOCK if the timeout expires. If PCATCH is set and a
290 * signal needs to be delivered, ERESTART is returned if the current system
291 * call should be restarted if possible, and EINTR is returned if the system
292 * call should be interrupted by the signal (return EINTR).
294 * Note that if we are a process, we release_curproc() before messing with
295 * the LWKT scheduler.
297 * During autoconfiguration or after a panic, a sleep will simply
298 * lower the priority briefly to allow interrupts, then return.
301 tsleep(void *ident, int flags, const char *wmesg, int timo)
303 struct thread *td = curthread;
304 struct proc *p = td->td_proc; /* may be NULL */
311 struct callout thandle;
314 * NOTE: removed KTRPOINT, it could cause races due to blocking
315 * even in stable. Just scrap it for now.
317 if (cold || panicstr) {
319 * After a panic, or during autoconfiguration,
320 * just give interrupts a chance, then just return;
321 * don't run any other procs or panic below,
322 * in case this is the idle process and already asleep.
325 oldpri = td->td_pri & TDPRI_MASK;
326 lwkt_setpri_self(safepri);
328 lwkt_setpri_self(oldpri);
332 KKASSERT(td != &gd->gd_idlethread); /* you must be kidding! */
335 * NOTE: all of this occurs on the current cpu, including any
336 * callout-based wakeups, so a critical section is a sufficient
339 * The entire sequence through to where we actually sleep must
340 * run without breaking the critical section.
343 catch = flags & PCATCH;
347 crit_enter_quick(td);
349 KASSERT(ident != NULL, ("tsleep: no ident"));
350 KASSERT(p == NULL || p->p_stat == SRUN, ("tsleep %p %s %d",
351 ident, wmesg, p->p_stat));
354 * Setup for the current process (if this is a process).
359 * Early termination if PCATCH was set and a
360 * signal is pending, interlocked with the
363 * Early termination only occurs when tsleep() is
364 * entered while in a normal SRUN state.
366 if ((sig = CURSIG(p)) != 0)
370 * Causes psignal to wake us up when.
372 p->p_flag |= P_SINTR;
376 * Make sure the current process has been untangled from
377 * the userland scheduler and initialize slptime to start
380 if (flags & PNORESCHED)
381 td->td_flags |= TDF_NORESCHED;
382 p->p_usched->release_curproc(&p->p_lwp);
387 * Move our thread to the correct queue and setup our wchan, etc.
389 lwkt_deschedule_self(td);
390 td->td_flags |= TDF_TSLEEPQ;
391 TAILQ_INSERT_TAIL(&gd->gd_tsleep_hash[id], td, td_threadq);
392 atomic_set_int(&slpque_cpumasks[id], gd->gd_cpumask);
394 td->td_wchan = ident;
395 td->td_wmesg = wmesg;
396 td->td_wdomain = flags & PDOMAIN_MASK;
399 * Setup the timeout, if any
402 callout_init(&thandle);
403 callout_reset(&thandle, timo, endtsleep, td);
411 * Ok, we are sleeping. Remove us from the userland runq
412 * and place us in the SSLEEP state.
414 if (p->p_flag & P_ONRUNQ)
415 p->p_usched->remrunqueue(&p->p_lwp);
417 p->p_stats->p_ru.ru_nvcsw++;
425 * Make sure we haven't switched cpus while we were asleep. It's
426 * not supposed to happen. Cleanup our temporary flags.
428 KKASSERT(gd == td->td_gd);
429 td->td_flags &= ~TDF_NORESCHED;
432 * Cleanup the timeout.
435 if (td->td_flags & TDF_TIMEOUT) {
436 td->td_flags &= ~TDF_TIMEOUT;
440 callout_stop(&thandle);
445 * Since td_threadq is used both for our run queue AND for the
446 * tsleep hash queue, we can't still be on it at this point because
447 * we've gotten cpu back.
449 KKASSERT((td->td_flags & TDF_TSLEEPQ) == 0);
455 * Figure out the correct error return
459 p->p_flag &= ~(P_BREAKTSLEEP | P_SINTR);
460 if (catch && error == 0 && (sig != 0 || (sig = CURSIG(p)))) {
461 if (SIGISMEMBER(p->p_sigacts->ps_sigintr, sig))
472 * This is a dandy function that allows us to interlock tsleep/wakeup
473 * operations with unspecified upper level locks, such as lockmgr locks,
474 * simply by holding a critical section. The sequence is:
476 * (enter critical section)
477 * (acquire upper level lock)
478 * tsleep_interlock(blah)
479 * (release upper level lock)
481 * (exit critical section)
483 * Basically this function sets our cpumask for the ident which informs
484 * other cpus that our cpu 'might' be waiting (or about to wait on) the
485 * hash index related to the ident. The critical section prevents another
486 * cpu's wakeup() from being processed on our cpu until we are actually
487 * able to enter the tsleep(). Thus, no race occurs between our attempt
488 * to release a resource and sleep, and another cpu's attempt to acquire
489 * a resource and call wakeup.
491 * There isn't much of a point to this function unless you call it while
492 * holding a critical section.
495 tsleep_interlock(void *ident)
497 int id = LOOKUP(ident);
499 atomic_set_int(&slpque_cpumasks[id], mycpu->gd_cpumask);
503 * Implement the timeout for tsleep.
505 * We set P_BREAKTSLEEP to indicate that an event has occured, but
506 * we only call setrunnable if the process is not stopped.
508 * This type of callout timeout is scheduled on the same cpu the process
509 * is sleeping on. Also, at the moment, the MP lock is held.
517 ASSERT_MP_LOCK_HELD(curthread);
521 * cpu interlock. Thread flags are only manipulated on
522 * the cpu owning the thread. proc flags are only manipulated
523 * by the older of the MP lock. We have both.
525 if (td->td_flags & TDF_TSLEEPQ) {
526 td->td_flags |= TDF_TIMEOUT;
528 if ((p = td->td_proc) != NULL) {
529 p->p_flag |= P_BREAKTSLEEP;
530 if ((p->p_flag & P_STOPPED) == 0)
533 unsleep_and_wakeup_thread(td);
540 * Unsleep and wakeup a thread. This function runs without the MP lock
541 * which means that it can only manipulate thread state on the owning cpu,
542 * and cannot touch the process state at all.
546 unsleep_and_wakeup_thread(struct thread *td)
548 globaldata_t gd = mycpu;
552 if (td->td_gd != gd) {
553 lwkt_send_ipiq(td->td_gd, (ipifunc1_t)unsleep_and_wakeup_thread, td);
558 if (td->td_flags & TDF_TSLEEPQ) {
559 td->td_flags &= ~TDF_TSLEEPQ;
560 id = LOOKUP(td->td_wchan);
561 TAILQ_REMOVE(&gd->gd_tsleep_hash[id], td, td_threadq);
562 if (TAILQ_FIRST(&gd->gd_tsleep_hash[id]) == NULL)
563 atomic_clear_int(&slpque_cpumasks[id], gd->gd_cpumask);
570 * Make all processes sleeping on the specified identifier runnable.
571 * count may be zero or one only.
573 * The domain encodes the sleep/wakeup domain AND the first cpu to check
574 * (which is always the current cpu). As we iterate across cpus
576 * This call may run without the MP lock held. We can only manipulate thread
577 * state on the cpu owning the thread. We CANNOT manipulate process state
581 _wakeup(void *ident, int domain)
598 qp = &gd->gd_tsleep_hash[id];
600 for (td = TAILQ_FIRST(qp); td != NULL; td = ntd) {
601 ntd = TAILQ_NEXT(td, td_threadq);
602 if (td->td_wchan == ident &&
603 td->td_wdomain == (domain & PDOMAIN_MASK)
605 KKASSERT(td->td_flags & TDF_TSLEEPQ);
606 td->td_flags &= ~TDF_TSLEEPQ;
607 TAILQ_REMOVE(qp, td, td_threadq);
608 if (TAILQ_FIRST(qp) == NULL) {
609 atomic_clear_int(&slpque_cpumasks[id],
613 if (domain & PWAKEUP_ONE)
621 * We finished checking the current cpu but there still may be
622 * more work to do. Either wakeup_one was requested and no matching
623 * thread was found, or a normal wakeup was requested and we have
624 * to continue checking cpus.
626 * The cpu that started the wakeup sequence is encoded in the domain.
627 * We use this information to determine which cpus still need to be
628 * checked, locate a candidate cpu, and chain the wakeup
629 * asynchronously with an IPI message.
631 * It should be noted that this scheme is actually less expensive then
632 * the old scheme when waking up multiple threads, since we send
633 * only one IPI message per target candidate which may then schedule
634 * multiple threads. Before we could have wound up sending an IPI
635 * message for each thread on the target cpu (!= current cpu) that
636 * needed to be woken up.
638 * NOTE: Wakeups occuring on remote cpus are asynchronous. This
639 * should be ok since we are passing idents in the IPI rather then
642 if ((mask = slpque_cpumasks[id]) != 0) {
644 * Look for a cpu that might have work to do. Mask out cpus
645 * which have already been processed.
647 * 31xxxxxxxxxxxxxxxxxxxxxxxxxxxxx0
649 * start currentcpu start
652 * 11111111111111110000000000000111 case1
653 * 00000000111111110000000000000000 case2
655 * case1: We started at start_case1 and processed through
656 * to the current cpu. We have to check any bits
657 * after the current cpu, then check bits before
660 * case2: We have already checked all the bits from
661 * start_case2 to the end, and from 0 to the current
662 * cpu. We just have the bits from the current cpu
663 * to start_case2 left to check.
665 startcpu = PWAKEUP_DECODE(domain);
666 if (gd->gd_cpuid >= startcpu) {
670 tmask = mask & ~((gd->gd_cpumask << 1) - 1);
672 nextcpu = bsfl(mask & tmask);
673 lwkt_send_ipiq2(globaldata_find(nextcpu),
674 _wakeup, ident, domain);
676 tmask = (1 << startcpu) - 1;
678 nextcpu = bsfl(mask & tmask);
680 globaldata_find(nextcpu),
681 _wakeup, ident, domain);
688 tmask = ~((gd->gd_cpumask << 1) - 1) &
689 ((1 << startcpu) - 1);
691 nextcpu = bsfl(mask & tmask);
692 lwkt_send_ipiq2(globaldata_find(nextcpu),
693 _wakeup, ident, domain);
705 _wakeup(ident, PWAKEUP_ENCODE(0, mycpu->gd_cpuid));
709 wakeup_one(void *ident)
711 /* XXX potentially round-robin the first responding cpu */
712 _wakeup(ident, PWAKEUP_ENCODE(0, mycpu->gd_cpuid) | PWAKEUP_ONE);
716 wakeup_domain(void *ident, int domain)
718 _wakeup(ident, PWAKEUP_ENCODE(domain, mycpu->gd_cpuid));
722 wakeup_domain_one(void *ident, int domain)
724 /* XXX potentially round-robin the first responding cpu */
725 _wakeup(ident, PWAKEUP_ENCODE(domain, mycpu->gd_cpuid) | PWAKEUP_ONE);
731 * Make a process runnable. The MP lock must be held on call. This only
732 * has an effect if we are in SSLEEP. We only break out of the
733 * tsleep if P_BREAKTSLEEP is set, otherwise we just fix-up the state.
735 * NOTE: With the MP lock held we can only safely manipulate the process
736 * structure. We cannot safely manipulate the thread structure.
739 setrunnable(struct proc *p)
742 ASSERT_MP_LOCK_HELD(curthread);
743 p->p_flag &= ~P_STOPPED;
744 if (p->p_stat == SSLEEP && (p->p_flag & P_BREAKTSLEEP)) {
745 unsleep_and_wakeup_thread(p->p_thread);
751 * The process is stopped due to some condition, usually because P_STOPPED
752 * is set but also possibly due to being traced.
754 * NOTE! If the caller sets P_STOPPED, the caller must also clear P_WAITED
755 * because the parent may check the child's status before the child actually
756 * gets to this routine.
758 * This routine is called with the current process only, typically just
759 * before returning to userland.
761 * Setting P_BREAKTSLEEP before entering the tsleep will cause a passive
762 * SIGCONT to break out of the tsleep.
765 tstop(struct proc *p)
767 wakeup((caddr_t)p->p_pptr);
768 p->p_flag |= P_BREAKTSLEEP;
769 tsleep(p, 0, "stop", 0);
773 * Yield / synchronous reschedule. This is a bit tricky because the trap
774 * code might have set a lazy release on the switch function. Setting
775 * P_PASSIVE_ACQ will ensure that the lazy release executes when we call
776 * switch, and that we are given a greater chance of affinity with our
779 * We call lwkt_setpri_self() to rotate our thread to the end of the lwkt
780 * run queue. lwkt_switch() will also execute any assigned passive release
781 * (which usually calls release_curproc()), allowing a same/higher priority
782 * process to be designated as the current process.
784 * While it is possible for a lower priority process to be designated,
785 * it's call to lwkt_maybe_switch() in acquire_curproc() will likely
786 * round-robin back to us and we will be able to re-acquire the current
787 * process designation.
792 struct thread *td = curthread;
793 struct proc *p = td->td_proc;
795 lwkt_setpri_self(td->td_pri & TDPRI_MASK);
797 p->p_flag |= P_PASSIVE_ACQ;
799 p->p_flag &= ~P_PASSIVE_ACQ;
806 * Compute a tenex style load average of a quantity on
807 * 1, 5 and 15 minute intervals.
819 FOREACH_PROC_IN_SYSTEM(p) {
822 if ((td = p->p_thread) == NULL)
824 if (td->td_flags & TDF_BLOCKED)
834 for (i = 0; i < 3; i++)
835 avg->ldavg[i] = (cexp[i] * avg->ldavg[i] +
836 nrun * FSCALE * (FSCALE - cexp[i])) >> FSHIFT;
839 * Schedule the next update to occur after 5 seconds, but add a
840 * random variation to avoid synchronisation with processes that
841 * run at regular intervals.
843 callout_reset(&loadav_callout, hz * 4 + (int)(random() % (hz * 2 + 1)),
849 sched_setup(void *dummy)
851 callout_init(&loadav_callout);
852 callout_init(&schedcpu_callout);
854 /* Kick off timeout driven events by calling first time. */