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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 1.28 2004/03/05 19:29:17 hsu 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. */
71 int ncpus2, ncpus2_shift, ncpus2_mask;
73 static struct callout loadav_callout;
75 struct loadavg averunnable =
76 { {0, 0, 0}, FSCALE }; /* load average, of runnable procs */
78 * Constants for averages over 1, 5, and 15 minutes
79 * when sampling at 5 second intervals.
81 static fixpt_t cexp[3] = {
82 0.9200444146293232 * FSCALE, /* exp(-1/12) */
83 0.9834714538216174 * FSCALE, /* exp(-1/60) */
84 0.9944598480048967 * FSCALE, /* exp(-1/180) */
87 static void endtsleep (void *);
88 static void loadav (void *arg);
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 roundrobin_interval(void)
116 return (sched_quantum);
120 * Force switch among equal priority processes every 100ms.
122 * WARNING! The MP lock is not held on ipi message remotes.
127 roundrobin_remote(void *arg)
129 struct proc *p = lwkt_preempted_proc();
130 if (p == NULL || RTP_PRIO_NEED_RR(p->p_rtprio.type))
137 roundrobin(void *arg)
139 struct proc *p = lwkt_preempted_proc();
140 if (p == NULL || RTP_PRIO_NEED_RR(p->p_rtprio.type))
143 lwkt_send_ipiq_mask(mycpu->gd_other_cpus, roundrobin_remote, NULL);
145 timeout(roundrobin, NULL, sched_quantum);
151 resched_cpus(u_int32_t mask)
153 lwkt_send_ipiq_mask(mask, roundrobin_remote, NULL);
159 * Constants for digital decay and forget:
160 * 90% of (p_estcpu) usage in 5 * loadav time
161 * 95% of (p_pctcpu) usage in 60 seconds (load insensitive)
162 * Note that, as ps(1) mentions, this can let percentages
163 * total over 100% (I've seen 137.9% for 3 processes).
165 * Note that schedulerclock() updates p_estcpu and p_cpticks asynchronously.
167 * We wish to decay away 90% of p_estcpu in (5 * loadavg) seconds.
168 * That is, the system wants to compute a value of decay such
169 * that the following for loop:
170 * for (i = 0; i < (5 * loadavg); i++)
174 * for all values of loadavg:
176 * Mathematically this loop can be expressed by saying:
177 * decay ** (5 * loadavg) ~= .1
179 * The system computes decay as:
180 * decay = (2 * loadavg) / (2 * loadavg + 1)
182 * We wish to prove that the system's computation of decay
183 * will always fulfill the equation:
184 * decay ** (5 * loadavg) ~= .1
186 * If we compute b as:
189 * decay = b / (b + 1)
191 * We now need to prove two things:
192 * 1) Given factor ** (5 * loadavg) ~= .1, prove factor == b/(b+1)
193 * 2) Given b/(b+1) ** power ~= .1, prove power == (5 * loadavg)
196 * For x close to zero, exp(x) =~ 1 + x, since
197 * exp(x) = 0! + x**1/1! + x**2/2! + ... .
198 * therefore exp(-1/b) =~ 1 - (1/b) = (b-1)/b.
199 * For x close to zero, ln(1+x) =~ x, since
200 * ln(1+x) = x - x**2/2 + x**3/3 - ... -1 < x < 1
201 * therefore ln(b/(b+1)) = ln(1 - 1/(b+1)) =~ -1/(b+1).
205 * Solve (factor)**(power) =~ .1 given power (5*loadav):
206 * solving for factor,
207 * ln(factor) =~ (-2.30/5*loadav), or
208 * factor =~ exp(-1/((5/2.30)*loadav)) =~ exp(-1/(2*loadav)) =
209 * exp(-1/b) =~ (b-1)/b =~ b/(b+1). QED
212 * Solve (factor)**(power) =~ .1 given factor == (b/(b+1)):
214 * power*ln(b/(b+1)) =~ -2.30, or
215 * power =~ 2.3 * (b + 1) = 4.6*loadav + 2.3 =~ 5*loadav. QED
217 * Actual power values for the implemented algorithm are as follows:
219 * power: 5.68 10.32 14.94 19.55
222 /* calculations for digital decay to forget 90% of usage in 5*loadav sec */
223 #define loadfactor(loadav) (2 * (loadav))
224 #define decay_cpu(loadfac, cpu) (((loadfac) * (cpu)) / ((loadfac) + FSCALE))
226 /* decay 95% of `p_pctcpu' in 60 seconds; see CCPU_SHIFT before changing */
227 static fixpt_t ccpu = 0.95122942450071400909 * FSCALE; /* exp(-1/20) */
228 SYSCTL_INT(_kern, OID_AUTO, ccpu, CTLFLAG_RD, &ccpu, 0, "");
230 /* kernel uses `FSCALE', userland (SHOULD) use kern.fscale */
231 static int fscale __unused = FSCALE;
232 SYSCTL_INT(_kern, OID_AUTO, fscale, CTLFLAG_RD, 0, FSCALE, "");
235 * If `ccpu' is not equal to `exp(-1/20)' and you still want to use the
236 * faster/more-accurate formula, you'll have to estimate CCPU_SHIFT below
237 * and possibly adjust FSHIFT in "param.h" so that (FSHIFT >= CCPU_SHIFT).
239 * To estimate CCPU_SHIFT for exp(-1/20), the following formula was used:
240 * 1 - exp(-1/20) ~= 0.0487 ~= 0.0488 == 1 (fixed pt, *11* bits).
242 * If you don't want to bother with the faster/more-accurate formula, you
243 * can set CCPU_SHIFT to (FSHIFT + 1) which will use a slower/less-accurate
244 * (more general) method of calculating the %age of CPU used by a process.
246 #define CCPU_SHIFT 11
249 * Recompute process priorities, every hz ticks.
255 fixpt_t loadfac = loadfactor(averunnable.ldavg[0]);
259 realstathz = stathz ? stathz : hz;
260 FOREACH_PROC_IN_SYSTEM(p) {
262 * Increment time in/out of memory and sleep time
263 * (if sleeping). We ignore overflow; with 16-bit int's
264 * (remember them?) overflow takes 45 days.
267 if (p->p_stat == SSLEEP || p->p_stat == SSTOP)
269 p->p_pctcpu = (p->p_pctcpu * ccpu) >> FSHIFT;
271 * If the process has slept the entire second,
272 * stop recalculating its priority until it wakes up.
274 if (p->p_slptime > 1)
276 s = splhigh(); /* prevent state changes and protect run queue */
278 * p_pctcpu is only for ps.
280 #if (FSHIFT >= CCPU_SHIFT)
281 p->p_pctcpu += (realstathz == 100)?
282 ((fixpt_t) p->p_cpticks) << (FSHIFT - CCPU_SHIFT):
283 100 * (((fixpt_t) p->p_cpticks)
284 << (FSHIFT - CCPU_SHIFT)) / realstathz;
286 p->p_pctcpu += ((FSCALE - ccpu) *
287 (p->p_cpticks * FSCALE / realstathz)) >> FSHIFT;
290 p->p_estcpu = decay_cpu(loadfac, p->p_estcpu);
294 wakeup((caddr_t)&lbolt);
295 timeout(schedcpu, (void *)0, hz);
299 * Recalculate the priority of a process after it has slept for a while.
300 * For all load averages >= 1 and max p_estcpu of 255, sleeping for at
301 * least six times the loadfactor will decay p_estcpu to zero.
304 updatepri(struct proc *p)
306 unsigned int newcpu = p->p_estcpu;
307 fixpt_t loadfac = loadfactor(averunnable.ldavg[0]);
309 if (p->p_slptime > 5 * loadfac) {
312 p->p_slptime--; /* the first time was done in schedcpu */
313 while (newcpu && --p->p_slptime)
314 newcpu = decay_cpu(loadfac, newcpu);
315 p->p_estcpu = newcpu;
321 * We're only looking at 7 bits of the address; everything is
322 * aligned to 4, lots of things are aligned to greater powers
323 * of 2. Shift right by 8, i.e. drop the bottom 256 worth.
325 #define TABLESIZE 128
326 static TAILQ_HEAD(slpquehead, thread) slpque[TABLESIZE];
327 #define LOOKUP(x) (((intptr_t)(x) >> 8) & (TABLESIZE - 1))
330 * During autoconfiguration or after a panic, a sleep will simply
331 * lower the priority briefly to allow interrupts, then return.
332 * The priority to be used (safepri) is machine-dependent, thus this
333 * value is initialized and maintained in the machine-dependent layers.
334 * This priority will typically be 0, or the lowest priority
335 * that is safe for use on the interrupt stack; it can be made
336 * higher to block network software interrupts after panics.
345 sched_quantum = hz/10;
346 hogticks = 2 * sched_quantum;
347 for (i = 0; i < TABLESIZE; i++)
348 TAILQ_INIT(&slpque[i]);
352 * General sleep call. Suspends the current process until a wakeup is
353 * performed on the specified identifier. The process will then be made
354 * runnable with the specified priority. Sleeps at most timo/hz seconds
355 * (0 means no timeout). If flags includes PCATCH flag, signals are checked
356 * before and after sleeping, else signals are not checked. Returns 0 if
357 * awakened, EWOULDBLOCK if the timeout expires. If PCATCH is set and a
358 * signal needs to be delivered, ERESTART is returned if the current system
359 * call should be restarted if possible, and EINTR is returned if the system
360 * call should be interrupted by the signal (return EINTR).
362 * If the process has P_CURPROC set mi_switch() will not re-queue it to
363 * the userland scheduler queues because we are in a SSLEEP state. If
364 * we are not the current process then we have to remove ourselves from
365 * the scheduler queues.
367 * YYY priority now unused
370 tsleep(ident, flags, wmesg, timo)
375 struct thread *td = curthread;
376 struct proc *p = td->td_proc; /* may be NULL */
377 int s, sig = 0, catch = flags & PCATCH;
378 int id = LOOKUP(ident);
379 struct callout_handle thandle;
382 * NOTE: removed KTRPOINT, it could cause races due to blocking
383 * even in stable. Just scrap it for now.
385 if (cold || panicstr) {
387 * After a panic, or during autoconfiguration,
388 * just give interrupts a chance, then just return;
389 * don't run any other procs or panic below,
390 * in case this is the idle process and already asleep.
395 KKASSERT(td != &mycpu->gd_idlethread); /* you must be kidding! */
397 KASSERT(ident != NULL, ("tsleep: no ident"));
398 KASSERT(p == NULL || p->p_stat == SRUN, ("tsleep %p %s %d",
399 ident, wmesg, p->p_stat));
402 td->td_wchan = ident;
403 td->td_wmesg = wmesg;
406 lwkt_deschedule_self();
407 TAILQ_INSERT_TAIL(&slpque[id], td, td_threadq);
409 thandle = timeout(endtsleep, (void *)td, timo);
411 * We put ourselves on the sleep queue and start our timeout
412 * before calling CURSIG, as we could stop there, and a wakeup
413 * or a SIGCONT (or both) could occur while we were stopped.
414 * A SIGCONT would cause us to be marked as SSLEEP
415 * without resuming us, thus we must be ready for sleep
416 * when CURSIG is called. If the wakeup happens while we're
417 * stopped, td->td_wchan will be 0 upon return from CURSIG.
421 p->p_flag |= P_SINTR;
422 if ((sig = CURSIG(p))) {
425 lwkt_schedule_self();
430 if (td->td_wchan == NULL) {
439 * If we are not the current process we have to remove ourself
440 * from the run queue.
442 KASSERT(p->p_stat == SRUN, ("PSTAT NOT SRUN %d %d", p->p_pid, p->p_stat));
444 * If this is the current 'user' process schedule another one.
446 clrrunnable(p, SSLEEP);
447 p->p_stats->p_ru.ru_nvcsw++;
448 KKASSERT(td->td_release || (p->p_flag & P_CURPROC) == 0);
450 KASSERT(p->p_stat == SRUN, ("tsleep: stat not srun"));
457 p->p_flag &= ~P_SINTR;
459 if (td->td_flags & TDF_TIMEOUT) {
460 td->td_flags &= ~TDF_TIMEOUT;
462 return (EWOULDBLOCK);
464 untimeout(endtsleep, (void *)td, thandle);
465 } else if (td->td_wmesg) {
467 * This can happen if a thread is woken up directly. Clear
468 * wmesg to avoid debugging confusion.
472 /* inline of iscaught() */
474 if (catch && (sig != 0 || (sig = CURSIG(p)))) {
475 if (SIGISMEMBER(p->p_sigacts->ps_sigintr, sig))
484 * Implement the timeout for tsleep. We interlock against
485 * wchan when setting TDF_TIMEOUT. For processes we remove
486 * the sleep if the process is stopped rather then sleeping,
487 * so it remains stopped.
498 td->td_flags |= TDF_TIMEOUT;
499 if ((p = td->td_proc) != NULL) {
500 if (p->p_stat == SSLEEP)
513 * Remove a process from its wait queue
516 unsleep(struct thread *td)
523 if (p->p_flag & P_XSLEEP) {
524 struct xwait *w = p->p_wchan;
525 TAILQ_REMOVE(&w->waitq, p, p_procq);
526 p->p_flag &= ~P_XSLEEP;
529 TAILQ_REMOVE(&slpque[LOOKUP(td->td_wchan)], td, td_threadq);
537 * Make all processes sleeping on the explicit lock structure runnable.
540 xwakeup(struct xwait *w)
547 while ((p = TAILQ_FIRST(&w->waitq)) != NULL) {
548 TAILQ_REMOVE(&w->waitq, p, p_procq);
549 KASSERT(p->p_wchan == w && (p->p_flag & P_XSLEEP),
550 ("xwakeup: wchan mismatch for %p (%p/%p) %08x", p, p->p_wchan, w, p->p_flag & P_XSLEEP));
552 p->p_flag &= ~P_XSLEEP;
553 if (p->p_stat == SSLEEP) {
554 /* OPTIMIZED EXPANSION OF setrunnable(p); */
555 if (p->p_slptime > 1)
559 if (p->p_flag & P_INMEM) {
562 p->p_flag |= P_SWAPINREQ;
563 wakeup((caddr_t)&proc0);
572 * Make all processes sleeping on the specified identifier runnable.
575 _wakeup(void *ident, int count)
577 struct slpquehead *qp;
582 int id = LOOKUP(ident);
587 for (td = TAILQ_FIRST(qp); td != NULL; td = ntd) {
588 ntd = TAILQ_NEXT(td, td_threadq);
589 if (td->td_wchan == ident) {
590 TAILQ_REMOVE(qp, td, td_threadq);
592 if ((p = td->td_proc) != NULL && p->p_stat == SSLEEP) {
593 /* OPTIMIZED EXPANSION OF setrunnable(p); */
594 if (p->p_slptime > 1)
598 if (p->p_flag & P_INMEM) {
601 p->p_flag |= P_SWAPINREQ;
602 wakeup((caddr_t)&proc0);
604 /* END INLINE EXPANSION */
605 } else if (p == NULL) {
623 wakeup_one(void *ident)
629 * The machine independent parts of mi_switch().
630 * Must be called at splstatclock() or higher.
635 struct thread *td = curthread;
636 struct proc *p = td->td_proc; /* XXX */
642 * XXX this spl is almost unnecessary. It is partly to allow for
643 * sloppy callers that don't do it (issignal() via CURSIG() is the
644 * main offender). It is partly to work around a bug in the i386
645 * cpu_switch() (the ipl is not preserved). We ran for years
646 * without it. I think there was only a interrupt latency problem.
647 * The main caller, tsleep(), does an splx() a couple of instructions
648 * after calling here. The buggy caller, issignal(), usually calls
649 * here at spl0() and sometimes returns at splhigh(). The process
650 * then runs for a little too long at splhigh(). The ipl gets fixed
651 * when the process returns to user mode (or earlier).
653 * It would probably be better to always call here at spl0(). Callers
654 * are prepared to give up control to another process, so they must
655 * be prepared to be interrupted. The clock stuff here may not
656 * actually need splstatclock().
662 * Check if the process exceeds its cpu resource allocation.
663 * If over max, kill it. Time spent in interrupts is not
664 * included. YYY 64 bit match is expensive. Ick.
666 ttime = td->td_sticks + td->td_uticks;
667 if (p->p_stat != SZOMB && p->p_limit->p_cpulimit != RLIM_INFINITY &&
668 ttime > p->p_limit->p_cpulimit) {
669 rlim = &p->p_rlimit[RLIMIT_CPU];
670 if (ttime / (rlim_t)1000000 >= rlim->rlim_max) {
671 killproc(p, "exceeded maximum CPU limit");
674 if (rlim->rlim_cur < rlim->rlim_max) {
675 /* XXX: we should make a private copy */
682 * Pick a new current process and record its start time. If we
683 * are in a SSTOPped state we deschedule ourselves. YYY this needs
684 * to be cleaned up, remember that LWKTs stay on their run queue
685 * which works differently then the user scheduler which removes
686 * the process from the runq when it runs it.
688 mycpu->gd_cnt.v_swtch++;
689 if (p->p_stat == SSTOP)
690 lwkt_deschedule_self();
697 * Change process state to be runnable,
698 * placing it on the run queue if it is in memory,
699 * and awakening the swapper if it isn't in memory.
702 setrunnable(struct proc *p)
712 panic("setrunnable");
715 unsleep(p->p_thread); /* e.g. when sending signals */
722 if (p->p_flag & P_INMEM)
725 if (p->p_slptime > 1)
728 if ((p->p_flag & P_INMEM) == 0) {
729 p->p_flag |= P_SWAPINREQ;
730 wakeup((caddr_t)&proc0);
735 * Change the process state to NOT be runnable, removing it from the run
736 * queue. If P_CURPROC is not set and we are in SRUN the process is on the
737 * run queue (If P_INMEM is not set then it isn't because it is swapped).
740 clrrunnable(struct proc *p, int stat)
747 if (p->p_flag & P_ONRUNQ)
758 * Compute the priority of a process when running in user mode.
759 * Arrange to reschedule if the resulting priority is better
760 * than that of the current process.
763 resetpriority(struct proc *p)
765 unsigned int newpriority;
770 * Set p_priority for general process comparisons
772 switch(p->p_rtprio.type) {
773 case RTP_PRIO_REALTIME:
774 p->p_priority = PRIBASE_REALTIME + p->p_rtprio.prio;
776 case RTP_PRIO_NORMAL:
779 p->p_priority = PRIBASE_IDLE + p->p_rtprio.prio;
781 case RTP_PRIO_THREAD:
782 p->p_priority = PRIBASE_THREAD + p->p_rtprio.prio;
787 * NORMAL priorities fall through. These are based on niceness
790 newpriority = NICE_ADJUST(p->p_nice - PRIO_MIN) +
791 p->p_estcpu / ESTCPURAMP;
792 newpriority = min(newpriority, MAXPRI);
793 npq = newpriority / PPQ;
795 opq = (p->p_priority & PRIMASK) / PPQ;
796 if (p->p_stat == SRUN && (p->p_flag & P_ONRUNQ) && opq != npq) {
798 * We have to move the process to another queue
801 p->p_priority = PRIBASE_NORMAL + newpriority;
805 * We can just adjust the priority and it will be picked
808 KKASSERT(opq == npq || (p->p_flag & P_ONRUNQ) == 0);
809 p->p_priority = PRIBASE_NORMAL + newpriority;
815 * Compute a tenex style load average of a quantity on
816 * 1, 5 and 15 minute intervals.
827 FOREACH_PROC_IN_SYSTEM(p) {
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)),
853 callout_init(&loadav_callout);
855 /* Kick off timeout driven events by calling first time. */
862 * We adjust the priority of the current process. The priority of
863 * a process gets worse as it accumulates CPU time. The cpu usage
864 * estimator (p_estcpu) is increased here. resetpriority() will
865 * compute a different priority each time p_estcpu increases by
866 * INVERSE_ESTCPU_WEIGHT * (until MAXPRI is reached).
868 * The cpu usage estimator ramps up quite quickly when the process is
869 * running (linearly), and decays away exponentially, at a rate which
870 * is proportionally slower when the system is busy. The basic principle
871 * is that the system will 90% forget that the process used a lot of CPU
872 * time in 5 * loadav seconds. This causes the system to favor processes
873 * which haven't run much recently, and to round-robin among other processes.
875 * WARNING! called from a fast-int or an IPI, the MP lock MIGHT NOT BE HELD
876 * and we cannot block.
879 schedulerclock(void *dummy)
885 if ((p = td->td_proc) != NULL) {
887 p->p_estcpu = ESTCPULIM(p->p_estcpu + 1);
888 if ((p->p_estcpu % PPQ) == 0 && try_mplock()) {
903 cpri = crit_panic_save();
905 crit_panic_restore(cpri);