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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 1.21 2003/08/26 21:09:02 rob 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>
56 #include <sys/ktrace.h>
58 #include <sys/xwait.h>
60 #include <machine/cpu.h>
61 #include <machine/ipl.h>
62 #include <machine/smp.h>
64 static void sched_setup (void *dummy);
65 SYSINIT(sched_setup, SI_SUB_KICK_SCHEDULER, SI_ORDER_FIRST, sched_setup, NULL)
69 int sched_quantum; /* Roundrobin scheduling quantum in ticks. */
72 static struct callout loadav_callout;
74 struct loadavg averunnable =
75 { {0, 0, 0}, FSCALE }; /* load average, of runnable procs */
77 * Constants for averages over 1, 5, and 15 minutes
78 * when sampling at 5 second intervals.
80 static fixpt_t cexp[3] = {
81 0.9200444146293232 * FSCALE, /* exp(-1/12) */
82 0.9834714538216174 * FSCALE, /* exp(-1/60) */
83 0.9944598480048967 * FSCALE, /* exp(-1/180) */
86 static void endtsleep (void *);
87 static void loadav (void *arg);
88 static void maybe_resched (struct proc *chk);
89 static void roundrobin (void *arg);
90 static void schedcpu (void *arg);
91 static void updatepri (struct proc *p);
92 static void crit_panicints(void);
95 sysctl_kern_quantum(SYSCTL_HANDLER_ARGS)
99 new_val = sched_quantum * tick;
100 error = sysctl_handle_int(oidp, &new_val, 0, req);
101 if (error != 0 || req->newptr == NULL)
105 sched_quantum = new_val / tick;
106 hogticks = 2 * sched_quantum;
110 SYSCTL_PROC(_kern, OID_AUTO, quantum, CTLTYPE_INT|CTLFLAG_RW,
111 0, sizeof sched_quantum, sysctl_kern_quantum, "I", "");
114 * Arrange to reschedule if necessary by checking to see if the current
115 * process is on the highest priority user scheduling queue. This may
116 * be run from an interrupt so we have to follow any preemption chains
117 * back to the original process.
120 maybe_resched(struct proc *chk)
122 struct proc *cur = lwkt_preempted_proc();
128 * Check the user queue (realtime, normal, idle). Lower numbers
129 * indicate higher priority queues. Lower numbers are also better
132 if (chk->p_rtprio.type < cur->p_rtprio.type) {
134 } else if (chk->p_rtprio.type == cur->p_rtprio.type) {
135 if (chk->p_rtprio.type == RTP_PRIO_NORMAL) {
136 if (chk->p_priority / PPQ < cur->p_priority / PPQ)
139 if (chk->p_rtprio.prio < cur->p_rtprio.prio)
146 roundrobin_interval(void)
148 return (sched_quantum);
152 * Force switch among equal priority processes every 100ms.
157 roundrobin_remote(void *arg)
159 struct proc *p = lwkt_preempted_proc();
160 if (p == NULL || RTP_PRIO_NEED_RR(p->p_rtprio.type))
167 roundrobin(void *arg)
169 struct proc *p = lwkt_preempted_proc();
170 if (p == NULL || RTP_PRIO_NEED_RR(p->p_rtprio.type))
173 lwkt_send_ipiq_mask(mycpu->gd_other_cpus, roundrobin_remote, NULL);
175 timeout(roundrobin, NULL, sched_quantum);
181 resched_cpus(u_int32_t mask)
183 lwkt_send_ipiq_mask(mask, roundrobin_remote, NULL);
189 * Constants for digital decay and forget:
190 * 90% of (p_estcpu) usage in 5 * loadav time
191 * 95% of (p_pctcpu) usage in 60 seconds (load insensitive)
192 * Note that, as ps(1) mentions, this can let percentages
193 * total over 100% (I've seen 137.9% for 3 processes).
195 * Note that schedclock() updates p_estcpu and p_cpticks asynchronously.
197 * We wish to decay away 90% of p_estcpu in (5 * loadavg) seconds.
198 * That is, the system wants to compute a value of decay such
199 * that the following for loop:
200 * for (i = 0; i < (5 * loadavg); i++)
204 * for all values of loadavg:
206 * Mathematically this loop can be expressed by saying:
207 * decay ** (5 * loadavg) ~= .1
209 * The system computes decay as:
210 * decay = (2 * loadavg) / (2 * loadavg + 1)
212 * We wish to prove that the system's computation of decay
213 * will always fulfill the equation:
214 * decay ** (5 * loadavg) ~= .1
216 * If we compute b as:
219 * decay = b / (b + 1)
221 * We now need to prove two things:
222 * 1) Given factor ** (5 * loadavg) ~= .1, prove factor == b/(b+1)
223 * 2) Given b/(b+1) ** power ~= .1, prove power == (5 * loadavg)
226 * For x close to zero, exp(x) =~ 1 + x, since
227 * exp(x) = 0! + x**1/1! + x**2/2! + ... .
228 * therefore exp(-1/b) =~ 1 - (1/b) = (b-1)/b.
229 * For x close to zero, ln(1+x) =~ x, since
230 * ln(1+x) = x - x**2/2 + x**3/3 - ... -1 < x < 1
231 * therefore ln(b/(b+1)) = ln(1 - 1/(b+1)) =~ -1/(b+1).
235 * Solve (factor)**(power) =~ .1 given power (5*loadav):
236 * solving for factor,
237 * ln(factor) =~ (-2.30/5*loadav), or
238 * factor =~ exp(-1/((5/2.30)*loadav)) =~ exp(-1/(2*loadav)) =
239 * exp(-1/b) =~ (b-1)/b =~ b/(b+1). QED
242 * Solve (factor)**(power) =~ .1 given factor == (b/(b+1)):
244 * power*ln(b/(b+1)) =~ -2.30, or
245 * power =~ 2.3 * (b + 1) = 4.6*loadav + 2.3 =~ 5*loadav. QED
247 * Actual power values for the implemented algorithm are as follows:
249 * power: 5.68 10.32 14.94 19.55
252 /* calculations for digital decay to forget 90% of usage in 5*loadav sec */
253 #define loadfactor(loadav) (2 * (loadav))
254 #define decay_cpu(loadfac, cpu) (((loadfac) * (cpu)) / ((loadfac) + FSCALE))
256 /* decay 95% of `p_pctcpu' in 60 seconds; see CCPU_SHIFT before changing */
257 static fixpt_t ccpu = 0.95122942450071400909 * FSCALE; /* exp(-1/20) */
258 SYSCTL_INT(_kern, OID_AUTO, ccpu, CTLFLAG_RD, &ccpu, 0, "");
260 /* kernel uses `FSCALE', userland (SHOULD) use kern.fscale */
261 static int fscale __unused = FSCALE;
262 SYSCTL_INT(_kern, OID_AUTO, fscale, CTLFLAG_RD, 0, FSCALE, "");
265 * If `ccpu' is not equal to `exp(-1/20)' and you still want to use the
266 * faster/more-accurate formula, you'll have to estimate CCPU_SHIFT below
267 * and possibly adjust FSHIFT in "param.h" so that (FSHIFT >= CCPU_SHIFT).
269 * To estimate CCPU_SHIFT for exp(-1/20), the following formula was used:
270 * 1 - exp(-1/20) ~= 0.0487 ~= 0.0488 == 1 (fixed pt, *11* bits).
272 * If you don't want to bother with the faster/more-accurate formula, you
273 * can set CCPU_SHIFT to (FSHIFT + 1) which will use a slower/less-accurate
274 * (more general) method of calculating the %age of CPU used by a process.
276 #define CCPU_SHIFT 11
279 * Recompute process priorities, every hz ticks.
285 fixpt_t loadfac = loadfactor(averunnable.ldavg[0]);
290 curp = lwkt_preempted_proc(); /* YYY temporary hack */
292 realstathz = stathz ? stathz : hz;
293 FOREACH_PROC_IN_SYSTEM(p) {
295 * Increment time in/out of memory and sleep time
296 * (if sleeping). We ignore overflow; with 16-bit int's
297 * (remember them?) overflow takes 45 days.
300 if (p->p_stat == SSLEEP || p->p_stat == SSTOP)
302 p->p_pctcpu = (p->p_pctcpu * ccpu) >> FSHIFT;
304 * If the process has slept the entire second,
305 * stop recalculating its priority until it wakes up.
307 if (p->p_slptime > 1)
309 s = splhigh(); /* prevent state changes and protect run queue */
311 * p_pctcpu is only for ps.
313 #if (FSHIFT >= CCPU_SHIFT)
314 p->p_pctcpu += (realstathz == 100)?
315 ((fixpt_t) p->p_cpticks) << (FSHIFT - CCPU_SHIFT):
316 100 * (((fixpt_t) p->p_cpticks)
317 << (FSHIFT - CCPU_SHIFT)) / realstathz;
319 p->p_pctcpu += ((FSCALE - ccpu) *
320 (p->p_cpticks * FSCALE / realstathz)) >> FSHIFT;
323 p->p_estcpu = decay_cpu(loadfac, p->p_estcpu);
327 wakeup((caddr_t)&lbolt);
328 timeout(schedcpu, (void *)0, hz);
332 * Recalculate the priority of a process after it has slept for a while.
333 * For all load averages >= 1 and max p_estcpu of 255, sleeping for at
334 * least six times the loadfactor will decay p_estcpu to zero.
337 updatepri(struct proc *p)
339 unsigned int newcpu = p->p_estcpu;
340 fixpt_t loadfac = loadfactor(averunnable.ldavg[0]);
342 if (p->p_slptime > 5 * loadfac) {
345 p->p_slptime--; /* the first time was done in schedcpu */
346 while (newcpu && --p->p_slptime)
347 newcpu = decay_cpu(loadfac, newcpu);
348 p->p_estcpu = newcpu;
354 * We're only looking at 7 bits of the address; everything is
355 * aligned to 4, lots of things are aligned to greater powers
356 * of 2. Shift right by 8, i.e. drop the bottom 256 worth.
358 #define TABLESIZE 128
359 static TAILQ_HEAD(slpquehead, thread) slpque[TABLESIZE];
360 #define LOOKUP(x) (((intptr_t)(x) >> 8) & (TABLESIZE - 1))
363 * During autoconfiguration or after a panic, a sleep will simply
364 * lower the priority briefly to allow interrupts, then return.
365 * The priority to be used (safepri) is machine-dependent, thus this
366 * value is initialized and maintained in the machine-dependent layers.
367 * This priority will typically be 0, or the lowest priority
368 * that is safe for use on the interrupt stack; it can be made
369 * higher to block network software interrupts after panics.
378 sched_quantum = hz/10;
379 hogticks = 2 * sched_quantum;
380 for (i = 0; i < TABLESIZE; i++)
381 TAILQ_INIT(&slpque[i]);
385 * General sleep call. Suspends the current process until a wakeup is
386 * performed on the specified identifier. The process will then be made
387 * runnable with the specified priority. Sleeps at most timo/hz seconds
388 * (0 means no timeout). If flags includes PCATCH flag, signals are checked
389 * before and after sleeping, else signals are not checked. Returns 0 if
390 * awakened, EWOULDBLOCK if the timeout expires. If PCATCH is set and a
391 * signal needs to be delivered, ERESTART is returned if the current system
392 * call should be restarted if possible, and EINTR is returned if the system
393 * call should be interrupted by the signal (return EINTR).
395 * If the process has P_CURPROC set mi_switch() will not re-queue it to
396 * the userland scheduler queues because we are in a SSLEEP state. If
397 * we are not the current process then we have to remove ourselves from
398 * the scheduler queues.
400 * YYY priority now unused
403 tsleep(ident, flags, wmesg, timo)
408 struct thread *td = curthread;
409 struct proc *p = td->td_proc; /* may be NULL */
410 int s, sig = 0, catch = flags & PCATCH;
411 int id = LOOKUP(ident);
412 struct callout_handle thandle;
415 * NOTE: removed KTRPOINT, it could cause races due to blocking
416 * even in stable. Just scrap it for now.
418 if (cold || panicstr) {
420 * After a panic, or during autoconfiguration,
421 * just give interrupts a chance, then just return;
422 * don't run any other procs or panic below,
423 * in case this is the idle process and already asleep.
428 KKASSERT(td != &mycpu->gd_idlethread); /* you must be kidding! */
430 KASSERT(ident != NULL, ("tsleep: no ident"));
431 KASSERT(p == NULL || p->p_stat == SRUN, ("tsleep %p %s %d",
432 ident, wmesg, p->p_stat));
435 td->td_wchan = ident;
436 td->td_wmesg = wmesg;
439 lwkt_deschedule_self();
440 TAILQ_INSERT_TAIL(&slpque[id], td, td_threadq);
442 thandle = timeout(endtsleep, (void *)td, timo);
444 * We put ourselves on the sleep queue and start our timeout
445 * before calling CURSIG, as we could stop there, and a wakeup
446 * or a SIGCONT (or both) could occur while we were stopped.
447 * A SIGCONT would cause us to be marked as SSLEEP
448 * without resuming us, thus we must be ready for sleep
449 * when CURSIG is called. If the wakeup happens while we're
450 * stopped, td->td_wchan will be 0 upon return from CURSIG.
454 p->p_flag |= P_SINTR;
455 if ((sig = CURSIG(p))) {
458 lwkt_schedule_self();
463 if (td->td_wchan == NULL) {
472 * If we are not the current process we have to remove ourself
473 * from the run queue.
475 KASSERT(p->p_stat == SRUN, ("PSTAT NOT SRUN %d %d", p->p_pid, p->p_stat));
477 * If this is the current 'user' process schedule another one.
479 clrrunnable(p, SSLEEP);
480 p->p_stats->p_ru.ru_nvcsw++;
481 KKASSERT(td->td_release || (p->p_flag & P_CURPROC) == 0);
483 KASSERT(p->p_stat == SRUN, ("tsleep: stat not srun"));
490 p->p_flag &= ~P_SINTR;
492 if (td->td_flags & TDF_TIMEOUT) {
493 td->td_flags &= ~TDF_TIMEOUT;
495 return (EWOULDBLOCK);
497 untimeout(endtsleep, (void *)td, thandle);
500 if (catch && (sig != 0 || (sig = CURSIG(p)))) {
501 if (SIGISMEMBER(p->p_sigacts->ps_sigintr, sig))
510 * Implement the timeout for tsleep. We interlock against
511 * wchan when setting TDF_TIMEOUT. For processes we remove
512 * the sleep if the process is stopped rather then sleeping,
513 * so it remains stopped.
524 td->td_flags |= TDF_TIMEOUT;
525 if ((p = td->td_proc) != NULL) {
526 if (p->p_stat == SSLEEP)
539 * Remove a process from its wait queue
542 unsleep(struct thread *td)
549 if (p->p_flag & P_XSLEEP) {
550 struct xwait *w = p->p_wchan;
551 TAILQ_REMOVE(&w->waitq, p, p_procq);
552 p->p_flag &= ~P_XSLEEP;
555 TAILQ_REMOVE(&slpque[LOOKUP(td->td_wchan)], td, td_threadq);
563 * Make all processes sleeping on the explicit lock structure runnable.
566 xwakeup(struct xwait *w)
573 while ((p = TAILQ_FIRST(&w->waitq)) != NULL) {
574 TAILQ_REMOVE(&w->waitq, p, p_procq);
575 KASSERT(p->p_wchan == w && (p->p_flag & P_XSLEEP),
576 ("xwakeup: wchan mismatch for %p (%p/%p) %08x", p, p->p_wchan, w, p->p_flag & P_XSLEEP));
578 p->p_flag &= ~P_XSLEEP;
579 if (p->p_stat == SSLEEP) {
580 /* OPTIMIZED EXPANSION OF setrunnable(p); */
581 if (p->p_slptime > 1)
585 if (p->p_flag & P_INMEM) {
589 p->p_flag |= P_SWAPINREQ;
590 wakeup((caddr_t)&proc0);
599 * Make all processes sleeping on the specified identifier runnable.
602 _wakeup(void *ident, int count)
604 struct slpquehead *qp;
609 int id = LOOKUP(ident);
614 for (td = TAILQ_FIRST(qp); td != NULL; td = ntd) {
615 ntd = TAILQ_NEXT(td, td_threadq);
616 if (td->td_wchan == ident) {
617 TAILQ_REMOVE(qp, td, td_threadq);
619 if ((p = td->td_proc) != NULL && p->p_stat == SSLEEP) {
620 /* OPTIMIZED EXPANSION OF setrunnable(p); */
621 if (p->p_slptime > 1)
625 if (p->p_flag & P_INMEM) {
627 if (p->p_flag & P_CURPROC)
630 p->p_flag |= P_SWAPINREQ;
631 wakeup((caddr_t)&proc0);
633 /* END INLINE EXPANSION */
634 } else if (p == NULL) {
652 wakeup_one(void *ident)
658 * The machine independent parts of mi_switch().
659 * Must be called at splstatclock() or higher.
664 struct thread *td = curthread;
665 struct proc *p = td->td_proc; /* XXX */
671 * XXX this spl is almost unnecessary. It is partly to allow for
672 * sloppy callers that don't do it (issignal() via CURSIG() is the
673 * main offender). It is partly to work around a bug in the i386
674 * cpu_switch() (the ipl is not preserved). We ran for years
675 * without it. I think there was only a interrupt latency problem.
676 * The main caller, tsleep(), does an splx() a couple of instructions
677 * after calling here. The buggy caller, issignal(), usually calls
678 * here at spl0() and sometimes returns at splhigh(). The process
679 * then runs for a little too long at splhigh(). The ipl gets fixed
680 * when the process returns to user mode (or earlier).
682 * It would probably be better to always call here at spl0(). Callers
683 * are prepared to give up control to another process, so they must
684 * be prepared to be interrupted. The clock stuff here may not
685 * actually need splstatclock().
691 * Check if the process exceeds its cpu resource allocation.
692 * If over max, kill it. Time spent in interrupts is not
693 * included. YYY 64 bit match is expensive. Ick.
695 ttime = td->td_sticks + td->td_uticks;
696 if (p->p_stat != SZOMB && p->p_limit->p_cpulimit != RLIM_INFINITY &&
697 ttime > p->p_limit->p_cpulimit) {
698 rlim = &p->p_rlimit[RLIMIT_CPU];
699 if (ttime / (rlim_t)1000000 >= rlim->rlim_max) {
700 killproc(p, "exceeded maximum CPU limit");
703 if (rlim->rlim_cur < rlim->rlim_max) {
704 /* XXX: we should make a private copy */
711 * Pick a new current process and record its start time. If we
712 * are in a SSTOPped state we deschedule ourselves. YYY this needs
713 * to be cleaned up, remember that LWKTs stay on their run queue
714 * which works differently then the user scheduler which removes
715 * the process from the runq when it runs it.
717 mycpu->gd_cnt.v_swtch++;
718 if (p->p_stat == SSTOP)
719 lwkt_deschedule_self();
726 * Change process state to be runnable,
727 * placing it on the run queue if it is in memory,
728 * and awakening the swapper if it isn't in memory.
731 setrunnable(struct proc *p)
741 panic("setrunnable");
744 unsleep(p->p_thread); /* e.g. when sending signals */
751 if (p->p_flag & P_INMEM)
754 if (p->p_slptime > 1)
757 if ((p->p_flag & P_INMEM) == 0) {
758 p->p_flag |= P_SWAPINREQ;
759 wakeup((caddr_t)&proc0);
766 * Change the process state to NOT be runnable, removing it from the run
767 * queue. If P_CURPROC is not set and we are in SRUN the process is on the
768 * run queue (If P_INMEM is not set then it isn't because it is swapped).
771 clrrunnable(struct proc *p, int stat)
778 if (p->p_flag & P_ONRUNQ)
789 * Compute the priority of a process when running in user mode.
790 * Arrange to reschedule if the resulting priority is better
791 * than that of the current process.
793 * YYY real time / idle procs do not use p_priority XXX
796 resetpriority(struct proc *p)
798 unsigned int newpriority;
802 if (p->p_rtprio.type != RTP_PRIO_NORMAL)
804 newpriority = PUSER + p->p_estcpu / INVERSE_ESTCPU_WEIGHT +
805 NICE_WEIGHT * p->p_nice;
806 newpriority = min(newpriority, MAXPRI);
807 npq = newpriority / PPQ;
809 opq = p->p_priority / PPQ;
810 if (p->p_stat == SRUN && (p->p_flag & P_ONRUNQ) && opq != npq) {
812 * We have to move the process to another queue
815 p->p_priority = newpriority;
819 * We can just adjust the priority and it will be picked
822 KKASSERT(opq == npq || (p->p_flag & P_ONRUNQ) == 0);
823 p->p_priority = newpriority;
830 * Compute a tenex style load average of a quantity on
831 * 1, 5 and 15 minute intervals.
842 FOREACH_PROC_IN_SYSTEM(p) {
849 for (i = 0; i < 3; i++)
850 avg->ldavg[i] = (cexp[i] * avg->ldavg[i] +
851 nrun * FSCALE * (FSCALE - cexp[i])) >> FSHIFT;
854 * Schedule the next update to occur after 5 seconds, but add a
855 * random variation to avoid synchronisation with processes that
856 * run at regular intervals.
858 callout_reset(&loadav_callout, hz * 4 + (int)(random() % (hz * 2 + 1)),
868 callout_init(&loadav_callout);
870 /* Kick off timeout driven events by calling first time. */
877 * We adjust the priority of the current process. The priority of
878 * a process gets worse as it accumulates CPU time. The cpu usage
879 * estimator (p_estcpu) is increased here. resetpriority() will
880 * compute a different priority each time p_estcpu increases by
881 * INVERSE_ESTCPU_WEIGHT
882 * (until MAXPRI is reached). The cpu usage estimator ramps up
883 * quite quickly when the process is running (linearly), and decays
884 * away exponentially, at a rate which is proportionally slower when
885 * the system is busy. The basic principle is that the system will
886 * 90% forget that the process used a lot of CPU time in 5 * loadav
887 * seconds. This causes the system to favor processes which haven't
888 * run much recently, and to round-robin among other processes.
896 p->p_estcpu = ESTCPULIM(p->p_estcpu + 1);
897 if ((p->p_estcpu % INVERSE_ESTCPU_WEIGHT) == 0)
909 cpri = crit_panic_save();
911 crit_panic_restore(cpri);