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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 1.25 2003/10/17 07:30:42 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>
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 roundrobin (void *arg);
89 static void schedcpu (void *arg);
90 static void updatepri (struct proc *p);
91 static void crit_panicints(void);
94 sysctl_kern_quantum(SYSCTL_HANDLER_ARGS)
98 new_val = sched_quantum * tick;
99 error = sysctl_handle_int(oidp, &new_val, 0, req);
100 if (error != 0 || req->newptr == NULL)
104 sched_quantum = new_val / tick;
105 hogticks = 2 * sched_quantum;
109 SYSCTL_PROC(_kern, OID_AUTO, quantum, CTLTYPE_INT|CTLFLAG_RW,
110 0, sizeof sched_quantum, sysctl_kern_quantum, "I", "");
113 roundrobin_interval(void)
115 return (sched_quantum);
119 * Force switch among equal priority processes every 100ms.
121 * WARNING! The MP lock is not held on ipi message remotes.
126 roundrobin_remote(void *arg)
128 struct proc *p = lwkt_preempted_proc();
129 if (p == NULL || RTP_PRIO_NEED_RR(p->p_rtprio.type))
136 roundrobin(void *arg)
138 struct proc *p = lwkt_preempted_proc();
139 if (p == NULL || RTP_PRIO_NEED_RR(p->p_rtprio.type))
142 lwkt_send_ipiq_mask(mycpu->gd_other_cpus, roundrobin_remote, NULL);
144 timeout(roundrobin, NULL, sched_quantum);
150 resched_cpus(u_int32_t mask)
152 lwkt_send_ipiq_mask(mask, roundrobin_remote, NULL);
158 * Constants for digital decay and forget:
159 * 90% of (p_estcpu) usage in 5 * loadav time
160 * 95% of (p_pctcpu) usage in 60 seconds (load insensitive)
161 * Note that, as ps(1) mentions, this can let percentages
162 * total over 100% (I've seen 137.9% for 3 processes).
164 * Note that schedclock() updates p_estcpu and p_cpticks asynchronously.
166 * We wish to decay away 90% of p_estcpu in (5 * loadavg) seconds.
167 * That is, the system wants to compute a value of decay such
168 * that the following for loop:
169 * for (i = 0; i < (5 * loadavg); i++)
173 * for all values of loadavg:
175 * Mathematically this loop can be expressed by saying:
176 * decay ** (5 * loadavg) ~= .1
178 * The system computes decay as:
179 * decay = (2 * loadavg) / (2 * loadavg + 1)
181 * We wish to prove that the system's computation of decay
182 * will always fulfill the equation:
183 * decay ** (5 * loadavg) ~= .1
185 * If we compute b as:
188 * decay = b / (b + 1)
190 * We now need to prove two things:
191 * 1) Given factor ** (5 * loadavg) ~= .1, prove factor == b/(b+1)
192 * 2) Given b/(b+1) ** power ~= .1, prove power == (5 * loadavg)
195 * For x close to zero, exp(x) =~ 1 + x, since
196 * exp(x) = 0! + x**1/1! + x**2/2! + ... .
197 * therefore exp(-1/b) =~ 1 - (1/b) = (b-1)/b.
198 * For x close to zero, ln(1+x) =~ x, since
199 * ln(1+x) = x - x**2/2 + x**3/3 - ... -1 < x < 1
200 * therefore ln(b/(b+1)) = ln(1 - 1/(b+1)) =~ -1/(b+1).
204 * Solve (factor)**(power) =~ .1 given power (5*loadav):
205 * solving for factor,
206 * ln(factor) =~ (-2.30/5*loadav), or
207 * factor =~ exp(-1/((5/2.30)*loadav)) =~ exp(-1/(2*loadav)) =
208 * exp(-1/b) =~ (b-1)/b =~ b/(b+1). QED
211 * Solve (factor)**(power) =~ .1 given factor == (b/(b+1)):
213 * power*ln(b/(b+1)) =~ -2.30, or
214 * power =~ 2.3 * (b + 1) = 4.6*loadav + 2.3 =~ 5*loadav. QED
216 * Actual power values for the implemented algorithm are as follows:
218 * power: 5.68 10.32 14.94 19.55
221 /* calculations for digital decay to forget 90% of usage in 5*loadav sec */
222 #define loadfactor(loadav) (2 * (loadav))
223 #define decay_cpu(loadfac, cpu) (((loadfac) * (cpu)) / ((loadfac) + FSCALE))
225 /* decay 95% of `p_pctcpu' in 60 seconds; see CCPU_SHIFT before changing */
226 static fixpt_t ccpu = 0.95122942450071400909 * FSCALE; /* exp(-1/20) */
227 SYSCTL_INT(_kern, OID_AUTO, ccpu, CTLFLAG_RD, &ccpu, 0, "");
229 /* kernel uses `FSCALE', userland (SHOULD) use kern.fscale */
230 static int fscale __unused = FSCALE;
231 SYSCTL_INT(_kern, OID_AUTO, fscale, CTLFLAG_RD, 0, FSCALE, "");
234 * If `ccpu' is not equal to `exp(-1/20)' and you still want to use the
235 * faster/more-accurate formula, you'll have to estimate CCPU_SHIFT below
236 * and possibly adjust FSHIFT in "param.h" so that (FSHIFT >= CCPU_SHIFT).
238 * To estimate CCPU_SHIFT for exp(-1/20), the following formula was used:
239 * 1 - exp(-1/20) ~= 0.0487 ~= 0.0488 == 1 (fixed pt, *11* bits).
241 * If you don't want to bother with the faster/more-accurate formula, you
242 * can set CCPU_SHIFT to (FSHIFT + 1) which will use a slower/less-accurate
243 * (more general) method of calculating the %age of CPU used by a process.
245 #define CCPU_SHIFT 11
248 * Recompute process priorities, every hz ticks.
254 fixpt_t loadfac = loadfactor(averunnable.ldavg[0]);
258 realstathz = stathz ? stathz : hz;
259 FOREACH_PROC_IN_SYSTEM(p) {
261 * Increment time in/out of memory and sleep time
262 * (if sleeping). We ignore overflow; with 16-bit int's
263 * (remember them?) overflow takes 45 days.
266 if (p->p_stat == SSLEEP || p->p_stat == SSTOP)
268 p->p_pctcpu = (p->p_pctcpu * ccpu) >> FSHIFT;
270 * If the process has slept the entire second,
271 * stop recalculating its priority until it wakes up.
273 if (p->p_slptime > 1)
275 s = splhigh(); /* prevent state changes and protect run queue */
277 * p_pctcpu is only for ps.
279 #if (FSHIFT >= CCPU_SHIFT)
280 p->p_pctcpu += (realstathz == 100)?
281 ((fixpt_t) p->p_cpticks) << (FSHIFT - CCPU_SHIFT):
282 100 * (((fixpt_t) p->p_cpticks)
283 << (FSHIFT - CCPU_SHIFT)) / realstathz;
285 p->p_pctcpu += ((FSCALE - ccpu) *
286 (p->p_cpticks * FSCALE / realstathz)) >> FSHIFT;
289 p->p_estcpu = decay_cpu(loadfac, p->p_estcpu);
293 wakeup((caddr_t)&lbolt);
294 timeout(schedcpu, (void *)0, hz);
298 * Recalculate the priority of a process after it has slept for a while.
299 * For all load averages >= 1 and max p_estcpu of 255, sleeping for at
300 * least six times the loadfactor will decay p_estcpu to zero.
303 updatepri(struct proc *p)
305 unsigned int newcpu = p->p_estcpu;
306 fixpt_t loadfac = loadfactor(averunnable.ldavg[0]);
308 if (p->p_slptime > 5 * loadfac) {
311 p->p_slptime--; /* the first time was done in schedcpu */
312 while (newcpu && --p->p_slptime)
313 newcpu = decay_cpu(loadfac, newcpu);
314 p->p_estcpu = newcpu;
320 * We're only looking at 7 bits of the address; everything is
321 * aligned to 4, lots of things are aligned to greater powers
322 * of 2. Shift right by 8, i.e. drop the bottom 256 worth.
324 #define TABLESIZE 128
325 static TAILQ_HEAD(slpquehead, thread) slpque[TABLESIZE];
326 #define LOOKUP(x) (((intptr_t)(x) >> 8) & (TABLESIZE - 1))
329 * During autoconfiguration or after a panic, a sleep will simply
330 * lower the priority briefly to allow interrupts, then return.
331 * The priority to be used (safepri) is machine-dependent, thus this
332 * value is initialized and maintained in the machine-dependent layers.
333 * This priority will typically be 0, or the lowest priority
334 * that is safe for use on the interrupt stack; it can be made
335 * higher to block network software interrupts after panics.
344 sched_quantum = hz/10;
345 hogticks = 2 * sched_quantum;
346 for (i = 0; i < TABLESIZE; i++)
347 TAILQ_INIT(&slpque[i]);
351 * General sleep call. Suspends the current process until a wakeup is
352 * performed on the specified identifier. The process will then be made
353 * runnable with the specified priority. Sleeps at most timo/hz seconds
354 * (0 means no timeout). If flags includes PCATCH flag, signals are checked
355 * before and after sleeping, else signals are not checked. Returns 0 if
356 * awakened, EWOULDBLOCK if the timeout expires. If PCATCH is set and a
357 * signal needs to be delivered, ERESTART is returned if the current system
358 * call should be restarted if possible, and EINTR is returned if the system
359 * call should be interrupted by the signal (return EINTR).
361 * If the process has P_CURPROC set mi_switch() will not re-queue it to
362 * the userland scheduler queues because we are in a SSLEEP state. If
363 * we are not the current process then we have to remove ourselves from
364 * the scheduler queues.
366 * YYY priority now unused
369 tsleep(ident, flags, wmesg, timo)
374 struct thread *td = curthread;
375 struct proc *p = td->td_proc; /* may be NULL */
376 int s, sig = 0, catch = flags & PCATCH;
377 int id = LOOKUP(ident);
378 struct callout_handle thandle;
381 * NOTE: removed KTRPOINT, it could cause races due to blocking
382 * even in stable. Just scrap it for now.
384 if (cold || panicstr) {
386 * After a panic, or during autoconfiguration,
387 * just give interrupts a chance, then just return;
388 * don't run any other procs or panic below,
389 * in case this is the idle process and already asleep.
394 KKASSERT(td != &mycpu->gd_idlethread); /* you must be kidding! */
396 KASSERT(ident != NULL, ("tsleep: no ident"));
397 KASSERT(p == NULL || p->p_stat == SRUN, ("tsleep %p %s %d",
398 ident, wmesg, p->p_stat));
401 td->td_wchan = ident;
402 td->td_wmesg = wmesg;
405 lwkt_deschedule_self();
406 TAILQ_INSERT_TAIL(&slpque[id], td, td_threadq);
408 thandle = timeout(endtsleep, (void *)td, timo);
410 * We put ourselves on the sleep queue and start our timeout
411 * before calling CURSIG, as we could stop there, and a wakeup
412 * or a SIGCONT (or both) could occur while we were stopped.
413 * A SIGCONT would cause us to be marked as SSLEEP
414 * without resuming us, thus we must be ready for sleep
415 * when CURSIG is called. If the wakeup happens while we're
416 * stopped, td->td_wchan will be 0 upon return from CURSIG.
420 p->p_flag |= P_SINTR;
421 if ((sig = CURSIG(p))) {
424 lwkt_schedule_self();
429 if (td->td_wchan == NULL) {
438 * If we are not the current process we have to remove ourself
439 * from the run queue.
441 KASSERT(p->p_stat == SRUN, ("PSTAT NOT SRUN %d %d", p->p_pid, p->p_stat));
443 * If this is the current 'user' process schedule another one.
445 clrrunnable(p, SSLEEP);
446 p->p_stats->p_ru.ru_nvcsw++;
447 KKASSERT(td->td_release || (p->p_flag & P_CURPROC) == 0);
449 KASSERT(p->p_stat == SRUN, ("tsleep: stat not srun"));
456 p->p_flag &= ~P_SINTR;
458 if (td->td_flags & TDF_TIMEOUT) {
459 td->td_flags &= ~TDF_TIMEOUT;
461 return (EWOULDBLOCK);
463 untimeout(endtsleep, (void *)td, thandle);
464 } else if (td->td_wmesg) {
466 * This can happen if a thread is woken up directly. Clear
467 * wmesg to avoid debugging confusion.
472 if (catch && (sig != 0 || (sig = CURSIG(p)))) {
473 if (SIGISMEMBER(p->p_sigacts->ps_sigintr, sig))
482 * Implement the timeout for tsleep. We interlock against
483 * wchan when setting TDF_TIMEOUT. For processes we remove
484 * the sleep if the process is stopped rather then sleeping,
485 * so it remains stopped.
496 td->td_flags |= TDF_TIMEOUT;
497 if ((p = td->td_proc) != NULL) {
498 if (p->p_stat == SSLEEP)
511 * Remove a process from its wait queue
514 unsleep(struct thread *td)
521 if (p->p_flag & P_XSLEEP) {
522 struct xwait *w = p->p_wchan;
523 TAILQ_REMOVE(&w->waitq, p, p_procq);
524 p->p_flag &= ~P_XSLEEP;
527 TAILQ_REMOVE(&slpque[LOOKUP(td->td_wchan)], td, td_threadq);
535 * Make all processes sleeping on the explicit lock structure runnable.
538 xwakeup(struct xwait *w)
545 while ((p = TAILQ_FIRST(&w->waitq)) != NULL) {
546 TAILQ_REMOVE(&w->waitq, p, p_procq);
547 KASSERT(p->p_wchan == w && (p->p_flag & P_XSLEEP),
548 ("xwakeup: wchan mismatch for %p (%p/%p) %08x", p, p->p_wchan, w, p->p_flag & P_XSLEEP));
550 p->p_flag &= ~P_XSLEEP;
551 if (p->p_stat == SSLEEP) {
552 /* OPTIMIZED EXPANSION OF setrunnable(p); */
553 if (p->p_slptime > 1)
557 if (p->p_flag & P_INMEM) {
560 p->p_flag |= P_SWAPINREQ;
561 wakeup((caddr_t)&proc0);
570 * Make all processes sleeping on the specified identifier runnable.
573 _wakeup(void *ident, int count)
575 struct slpquehead *qp;
580 int id = LOOKUP(ident);
585 for (td = TAILQ_FIRST(qp); td != NULL; td = ntd) {
586 ntd = TAILQ_NEXT(td, td_threadq);
587 if (td->td_wchan == ident) {
588 TAILQ_REMOVE(qp, td, td_threadq);
590 if ((p = td->td_proc) != NULL && p->p_stat == SSLEEP) {
591 /* OPTIMIZED EXPANSION OF setrunnable(p); */
592 if (p->p_slptime > 1)
596 if (p->p_flag & P_INMEM) {
599 p->p_flag |= P_SWAPINREQ;
600 wakeup((caddr_t)&proc0);
602 /* END INLINE EXPANSION */
603 } else if (p == NULL) {
621 wakeup_one(void *ident)
627 * The machine independent parts of mi_switch().
628 * Must be called at splstatclock() or higher.
633 struct thread *td = curthread;
634 struct proc *p = td->td_proc; /* XXX */
640 * XXX this spl is almost unnecessary. It is partly to allow for
641 * sloppy callers that don't do it (issignal() via CURSIG() is the
642 * main offender). It is partly to work around a bug in the i386
643 * cpu_switch() (the ipl is not preserved). We ran for years
644 * without it. I think there was only a interrupt latency problem.
645 * The main caller, tsleep(), does an splx() a couple of instructions
646 * after calling here. The buggy caller, issignal(), usually calls
647 * here at spl0() and sometimes returns at splhigh(). The process
648 * then runs for a little too long at splhigh(). The ipl gets fixed
649 * when the process returns to user mode (or earlier).
651 * It would probably be better to always call here at spl0(). Callers
652 * are prepared to give up control to another process, so they must
653 * be prepared to be interrupted. The clock stuff here may not
654 * actually need splstatclock().
660 * Check if the process exceeds its cpu resource allocation.
661 * If over max, kill it. Time spent in interrupts is not
662 * included. YYY 64 bit match is expensive. Ick.
664 ttime = td->td_sticks + td->td_uticks;
665 if (p->p_stat != SZOMB && p->p_limit->p_cpulimit != RLIM_INFINITY &&
666 ttime > p->p_limit->p_cpulimit) {
667 rlim = &p->p_rlimit[RLIMIT_CPU];
668 if (ttime / (rlim_t)1000000 >= rlim->rlim_max) {
669 killproc(p, "exceeded maximum CPU limit");
672 if (rlim->rlim_cur < rlim->rlim_max) {
673 /* XXX: we should make a private copy */
680 * Pick a new current process and record its start time. If we
681 * are in a SSTOPped state we deschedule ourselves. YYY this needs
682 * to be cleaned up, remember that LWKTs stay on their run queue
683 * which works differently then the user scheduler which removes
684 * the process from the runq when it runs it.
686 mycpu->gd_cnt.v_swtch++;
687 if (p->p_stat == SSTOP)
688 lwkt_deschedule_self();
695 * Change process state to be runnable,
696 * placing it on the run queue if it is in memory,
697 * and awakening the swapper if it isn't in memory.
700 setrunnable(struct proc *p)
710 panic("setrunnable");
713 unsleep(p->p_thread); /* e.g. when sending signals */
720 if (p->p_flag & P_INMEM)
723 if (p->p_slptime > 1)
726 if ((p->p_flag & P_INMEM) == 0) {
727 p->p_flag |= P_SWAPINREQ;
728 wakeup((caddr_t)&proc0);
733 * Change the process state to NOT be runnable, removing it from the run
734 * queue. If P_CURPROC is not set and we are in SRUN the process is on the
735 * run queue (If P_INMEM is not set then it isn't because it is swapped).
738 clrrunnable(struct proc *p, int stat)
745 if (p->p_flag & P_ONRUNQ)
756 * Compute the priority of a process when running in user mode.
757 * Arrange to reschedule if the resulting priority is better
758 * than that of the current process.
761 resetpriority(struct proc *p)
763 unsigned int newpriority;
768 * Set p_priority for general process comparisons
770 switch(p->p_rtprio.type) {
771 case RTP_PRIO_REALTIME:
772 p->p_priority = PRIBASE_REALTIME + p->p_rtprio.prio;
774 case RTP_PRIO_NORMAL:
777 p->p_priority = PRIBASE_IDLE + p->p_rtprio.prio;
779 case RTP_PRIO_THREAD:
780 p->p_priority = PRIBASE_THREAD + p->p_rtprio.prio;
785 * NORMAL priorities fall through. These are based on niceness
788 newpriority = NICE_ADJUST(p->p_nice - PRIO_MIN) +
789 p->p_estcpu / ESTCPURAMP;
790 newpriority = min(newpriority, MAXPRI);
791 npq = newpriority / PPQ;
793 opq = (p->p_priority & PRIMASK) / PPQ;
794 if (p->p_stat == SRUN && (p->p_flag & P_ONRUNQ) && opq != npq) {
796 * We have to move the process to another queue
799 p->p_priority = PRIBASE_NORMAL + newpriority;
803 * We can just adjust the priority and it will be picked
806 KKASSERT(opq == npq || (p->p_flag & P_ONRUNQ) == 0);
807 p->p_priority = PRIBASE_NORMAL + newpriority;
813 * Compute a tenex style load average of a quantity on
814 * 1, 5 and 15 minute intervals.
825 FOREACH_PROC_IN_SYSTEM(p) {
832 for (i = 0; i < 3; i++)
833 avg->ldavg[i] = (cexp[i] * avg->ldavg[i] +
834 nrun * FSCALE * (FSCALE - cexp[i])) >> FSHIFT;
837 * Schedule the next update to occur after 5 seconds, but add a
838 * random variation to avoid synchronisation with processes that
839 * run at regular intervals.
841 callout_reset(&loadav_callout, hz * 4 + (int)(random() % (hz * 2 + 1)),
851 callout_init(&loadav_callout);
853 /* Kick off timeout driven events by calling first time. */
860 * We adjust the priority of the current process. The priority of
861 * a process gets worse as it accumulates CPU time. The cpu usage
862 * estimator (p_estcpu) is increased here. resetpriority() will
863 * compute a different priority each time p_estcpu increases by
864 * INVERSE_ESTCPU_WEIGHT * (until MAXPRI is reached).
866 * The cpu usage estimator ramps up quite quickly when the process is
867 * running (linearly), and decays away exponentially, at a rate which
868 * is proportionally slower when the system is busy. The basic principle
869 * is that the system will 90% forget that the process used a lot of CPU
870 * time in 5 * loadav seconds. This causes the system to favor processes
871 * which haven't run much recently, and to round-robin among other processes.
876 schedclock(void *dummy)
882 if ((p = td->td_proc) != NULL) {
884 p->p_estcpu = ESTCPULIM(p->p_estcpu + 1);
885 if ((p->p_estcpu % PPQ) == 0 && try_mplock()) {
900 cpri = crit_panic_save();
902 crit_panic_restore(cpri);