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kern_synch.c revision 1.43
      1 /*	$NetBSD: kern_synch.c,v 1.43 1996/11/06 20:20:00 cgd Exp $	*/
      2 
      3 /*-
      4  * Copyright (c) 1982, 1986, 1990, 1991, 1993
      5  *	The Regents of the University of California.  All rights reserved.
      6  * (c) UNIX System Laboratories, Inc.
      7  * All or some portions of this file are derived from material licensed
      8  * to the University of California by American Telephone and Telegraph
      9  * Co. or Unix System Laboratories, Inc. and are reproduced herein with
     10  * the permission of UNIX System Laboratories, Inc.
     11  *
     12  * Redistribution and use in source and binary forms, with or without
     13  * modification, are permitted provided that the following conditions
     14  * are met:
     15  * 1. Redistributions of source code must retain the above copyright
     16  *    notice, this list of conditions and the following disclaimer.
     17  * 2. Redistributions in binary form must reproduce the above copyright
     18  *    notice, this list of conditions and the following disclaimer in the
     19  *    documentation and/or other materials provided with the distribution.
     20  * 3. All advertising materials mentioning features or use of this software
     21  *    must display the following acknowledgement:
     22  *	This product includes software developed by the University of
     23  *	California, Berkeley and its contributors.
     24  * 4. Neither the name of the University nor the names of its contributors
     25  *    may be used to endorse or promote products derived from this software
     26  *    without specific prior written permission.
     27  *
     28  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     29  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     30  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     31  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     32  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     33  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     34  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     35  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     36  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     37  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     38  * SUCH DAMAGE.
     39  *
     40  *	@(#)kern_synch.c	8.6 (Berkeley) 1/21/94
     41  */
     42 
     43 #include <sys/param.h>
     44 #include <sys/systm.h>
     45 #include <sys/proc.h>
     46 #include <sys/kernel.h>
     47 #include <sys/buf.h>
     48 #include <sys/signalvar.h>
     49 #include <sys/resourcevar.h>
     50 #include <vm/vm.h>
     51 #ifdef KTRACE
     52 #include <sys/ktrace.h>
     53 #endif
     54 
     55 #include <machine/cpu.h>
     56 
     57 u_char	curpriority;		/* usrpri of curproc */
     58 int	lbolt;			/* once a second sleep address */
     59 
     60 void roundrobin __P((void *));
     61 void schedcpu __P((void *));
     62 void updatepri __P((struct proc *));
     63 void endtsleep __P((void *));
     64 
     65 /*
     66  * Force switch among equal priority processes every 100ms.
     67  */
     68 /* ARGSUSED */
     69 void
     70 roundrobin(arg)
     71 	void *arg;
     72 {
     73 
     74 	need_resched();
     75 	timeout(roundrobin, NULL, hz / 10);
     76 }
     77 
     78 /*
     79  * Constants for digital decay and forget:
     80  *	90% of (p_estcpu) usage in 5 * loadav time
     81  *	95% of (p_pctcpu) usage in 60 seconds (load insensitive)
     82  *          Note that, as ps(1) mentions, this can let percentages
     83  *          total over 100% (I've seen 137.9% for 3 processes).
     84  *
     85  * Note that hardclock updates p_estcpu and p_cpticks independently.
     86  *
     87  * We wish to decay away 90% of p_estcpu in (5 * loadavg) seconds.
     88  * That is, the system wants to compute a value of decay such
     89  * that the following for loop:
     90  * 	for (i = 0; i < (5 * loadavg); i++)
     91  * 		p_estcpu *= decay;
     92  * will compute
     93  * 	p_estcpu *= 0.1;
     94  * for all values of loadavg:
     95  *
     96  * Mathematically this loop can be expressed by saying:
     97  * 	decay ** (5 * loadavg) ~= .1
     98  *
     99  * The system computes decay as:
    100  * 	decay = (2 * loadavg) / (2 * loadavg + 1)
    101  *
    102  * We wish to prove that the system's computation of decay
    103  * will always fulfill the equation:
    104  * 	decay ** (5 * loadavg) ~= .1
    105  *
    106  * If we compute b as:
    107  * 	b = 2 * loadavg
    108  * then
    109  * 	decay = b / (b + 1)
    110  *
    111  * We now need to prove two things:
    112  *	1) Given factor ** (5 * loadavg) ~= .1, prove factor == b/(b+1)
    113  *	2) Given b/(b+1) ** power ~= .1, prove power == (5 * loadavg)
    114  *
    115  * Facts:
    116  *         For x close to zero, exp(x) =~ 1 + x, since
    117  *              exp(x) = 0! + x**1/1! + x**2/2! + ... .
    118  *              therefore exp(-1/b) =~ 1 - (1/b) = (b-1)/b.
    119  *         For x close to zero, ln(1+x) =~ x, since
    120  *              ln(1+x) = x - x**2/2 + x**3/3 - ...     -1 < x < 1
    121  *              therefore ln(b/(b+1)) = ln(1 - 1/(b+1)) =~ -1/(b+1).
    122  *         ln(.1) =~ -2.30
    123  *
    124  * Proof of (1):
    125  *    Solve (factor)**(power) =~ .1 given power (5*loadav):
    126  *	solving for factor,
    127  *      ln(factor) =~ (-2.30/5*loadav), or
    128  *      factor =~ exp(-1/((5/2.30)*loadav)) =~ exp(-1/(2*loadav)) =
    129  *          exp(-1/b) =~ (b-1)/b =~ b/(b+1).                    QED
    130  *
    131  * Proof of (2):
    132  *    Solve (factor)**(power) =~ .1 given factor == (b/(b+1)):
    133  *	solving for power,
    134  *      power*ln(b/(b+1)) =~ -2.30, or
    135  *      power =~ 2.3 * (b + 1) = 4.6*loadav + 2.3 =~ 5*loadav.  QED
    136  *
    137  * Actual power values for the implemented algorithm are as follows:
    138  *      loadav: 1       2       3       4
    139  *      power:  5.68    10.32   14.94   19.55
    140  */
    141 
    142 /* calculations for digital decay to forget 90% of usage in 5*loadav sec */
    143 #define	loadfactor(loadav)	(2 * (loadav))
    144 #define	decay_cpu(loadfac, cpu)	(((loadfac) * (cpu)) / ((loadfac) + FSCALE))
    145 
    146 /* decay 95% of `p_pctcpu' in 60 seconds; see CCPU_SHIFT before changing */
    147 fixpt_t	ccpu = 0.95122942450071400909 * FSCALE;		/* exp(-1/20) */
    148 
    149 /*
    150  * If `ccpu' is not equal to `exp(-1/20)' and you still want to use the
    151  * faster/more-accurate formula, you'll have to estimate CCPU_SHIFT below
    152  * and possibly adjust FSHIFT in "param.h" so that (FSHIFT >= CCPU_SHIFT).
    153  *
    154  * To estimate CCPU_SHIFT for exp(-1/20), the following formula was used:
    155  *	1 - exp(-1/20) ~= 0.0487 ~= 0.0488 == 1 (fixed pt, *11* bits).
    156  *
    157  * If you dont want to bother with the faster/more-accurate formula, you
    158  * can set CCPU_SHIFT to (FSHIFT + 1) which will use a slower/less-accurate
    159  * (more general) method of calculating the %age of CPU used by a process.
    160  */
    161 #define	CCPU_SHIFT	11
    162 
    163 /*
    164  * Recompute process priorities, every hz ticks.
    165  */
    166 /* ARGSUSED */
    167 void
    168 schedcpu(arg)
    169 	void *arg;
    170 {
    171 	register fixpt_t loadfac = loadfactor(averunnable.ldavg[0]);
    172 	register struct proc *p;
    173 	register int s;
    174 	register unsigned int newcpu;
    175 
    176 	wakeup((caddr_t)&lbolt);
    177 	for (p = allproc.lh_first; p != 0; p = p->p_list.le_next) {
    178 		/*
    179 		 * Increment time in/out of memory and sleep time
    180 		 * (if sleeping).  We ignore overflow; with 16-bit int's
    181 		 * (remember them?) overflow takes 45 days.
    182 		 */
    183 		p->p_swtime++;
    184 		if (p->p_stat == SSLEEP || p->p_stat == SSTOP)
    185 			p->p_slptime++;
    186 		p->p_pctcpu = (p->p_pctcpu * ccpu) >> FSHIFT;
    187 		/*
    188 		 * If the process has slept the entire second,
    189 		 * stop recalculating its priority until it wakes up.
    190 		 */
    191 		if (p->p_slptime > 1)
    192 			continue;
    193 		s = splstatclock();	/* prevent state changes */
    194 		/*
    195 		 * p_pctcpu is only for ps.
    196 		 */
    197 #if	(FSHIFT >= CCPU_SHIFT)
    198 		p->p_pctcpu += (hz == 100)?
    199 			((fixpt_t) p->p_cpticks) << (FSHIFT - CCPU_SHIFT):
    200                 	100 * (((fixpt_t) p->p_cpticks)
    201 				<< (FSHIFT - CCPU_SHIFT)) / hz;
    202 #else
    203 		p->p_pctcpu += ((FSCALE - ccpu) *
    204 			(p->p_cpticks * FSCALE / hz)) >> FSHIFT;
    205 #endif
    206 		p->p_cpticks = 0;
    207 		newcpu = (u_int)decay_cpu(loadfac, p->p_estcpu)
    208 		    + p->p_nice - NZERO;
    209 		p->p_estcpu = min(newcpu, UCHAR_MAX);
    210 		resetpriority(p);
    211 		if (p->p_priority >= PUSER) {
    212 #define	PPQ	(128 / NQS)		/* priorities per queue */
    213 			if ((p != curproc) &&
    214 			    p->p_stat == SRUN &&
    215 			    (p->p_flag & P_INMEM) &&
    216 			    (p->p_priority / PPQ) != (p->p_usrpri / PPQ)) {
    217 				remrunqueue(p);
    218 				p->p_priority = p->p_usrpri;
    219 				setrunqueue(p);
    220 			} else
    221 				p->p_priority = p->p_usrpri;
    222 		}
    223 		splx(s);
    224 	}
    225 	vmmeter();
    226 	if (bclnlist != NULL)
    227 		wakeup((caddr_t)pageproc);
    228 	timeout(schedcpu, (void *)0, hz);
    229 }
    230 
    231 /*
    232  * Recalculate the priority of a process after it has slept for a while.
    233  * For all load averages >= 1 and max p_estcpu of 255, sleeping for at
    234  * least six times the loadfactor will decay p_estcpu to zero.
    235  */
    236 void
    237 updatepri(p)
    238 	register struct proc *p;
    239 {
    240 	register unsigned int newcpu = p->p_estcpu;
    241 	register fixpt_t loadfac = loadfactor(averunnable.ldavg[0]);
    242 
    243 	if (p->p_slptime > 5 * loadfac)
    244 		p->p_estcpu = 0;
    245 	else {
    246 		p->p_slptime--;	/* the first time was done in schedcpu */
    247 		while (newcpu && --p->p_slptime)
    248 			newcpu = (int) decay_cpu(loadfac, newcpu);
    249 		p->p_estcpu = min(newcpu, UCHAR_MAX);
    250 	}
    251 	resetpriority(p);
    252 }
    253 
    254 /*
    255  * We're only looking at 7 bits of the address; everything is
    256  * aligned to 4, lots of things are aligned to greater powers
    257  * of 2.  Shift right by 8, i.e. drop the bottom 256 worth.
    258  */
    259 #define TABLESIZE	128
    260 #define LOOKUP(x)	(((long)(x) >> 8) & (TABLESIZE - 1))
    261 struct slpque {
    262 	struct proc *sq_head;
    263 	struct proc **sq_tailp;
    264 } slpque[TABLESIZE];
    265 
    266 /*
    267  * During autoconfiguration or after a panic, a sleep will simply
    268  * lower the priority briefly to allow interrupts, then return.
    269  * The priority to be used (safepri) is machine-dependent, thus this
    270  * value is initialized and maintained in the machine-dependent layers.
    271  * This priority will typically be 0, or the lowest priority
    272  * that is safe for use on the interrupt stack; it can be made
    273  * higher to block network software interrupts after panics.
    274  */
    275 int safepri;
    276 
    277 /*
    278  * General sleep call.  Suspends the current process until a wakeup is
    279  * performed on the specified identifier.  The process will then be made
    280  * runnable with the specified priority.  Sleeps at most timo/hz seconds
    281  * (0 means no timeout).  If pri includes PCATCH flag, signals are checked
    282  * before and after sleeping, else signals are not checked.  Returns 0 if
    283  * awakened, EWOULDBLOCK if the timeout expires.  If PCATCH is set and a
    284  * signal needs to be delivered, ERESTART is returned if the current system
    285  * call should be restarted if possible, and EINTR is returned if the system
    286  * call should be interrupted by the signal (return EINTR).
    287  */
    288 int
    289 tsleep(ident, priority, wmesg, timo)
    290 	void *ident;
    291 	int priority, timo;
    292 	char *wmesg;
    293 {
    294 	register struct proc *p = curproc;
    295 	register struct slpque *qp;
    296 	register s;
    297 	int sig, catch = priority & PCATCH;
    298 	extern int cold;
    299 	void endtsleep __P((void *));
    300 
    301 	if (cold || panicstr) {
    302 		/*
    303 		 * After a panic, or during autoconfiguration,
    304 		 * just give interrupts a chance, then just return;
    305 		 * don't run any other procs or panic below,
    306 		 * in case this is the idle process and already asleep.
    307 		 */
    308 		s = splhigh();
    309 		splx(safepri);
    310 		splx(s);
    311 		return (0);
    312 	}
    313 
    314 #ifdef KTRACE
    315 	if (KTRPOINT(p, KTR_CSW))
    316 		ktrcsw(p->p_tracep, 1, 0);
    317 #endif
    318 	s = splhigh();
    319 
    320 #ifdef DIAGNOSTIC
    321 	if (ident == NULL || p->p_stat != SRUN || p->p_back)
    322 		panic("tsleep");
    323 #endif
    324 	p->p_wchan = ident;
    325 	p->p_wmesg = wmesg;
    326 	p->p_slptime = 0;
    327 	p->p_priority = priority & PRIMASK;
    328 	qp = &slpque[LOOKUP(ident)];
    329 	if (qp->sq_head == 0)
    330 		qp->sq_head = p;
    331 	else
    332 		*qp->sq_tailp = p;
    333 	*(qp->sq_tailp = &p->p_forw) = 0;
    334 	if (timo)
    335 		timeout(endtsleep, (void *)p, timo);
    336 	/*
    337 	 * We put ourselves on the sleep queue and start our timeout
    338 	 * before calling CURSIG, as we could stop there, and a wakeup
    339 	 * or a SIGCONT (or both) could occur while we were stopped.
    340 	 * A SIGCONT would cause us to be marked as SSLEEP
    341 	 * without resuming us, thus we must be ready for sleep
    342 	 * when CURSIG is called.  If the wakeup happens while we're
    343 	 * stopped, p->p_wchan will be 0 upon return from CURSIG.
    344 	 */
    345 	if (catch) {
    346 		p->p_flag |= P_SINTR;
    347 		if ((sig = CURSIG(p)) != 0) {
    348 			if (p->p_wchan)
    349 				unsleep(p);
    350 			p->p_stat = SRUN;
    351 			goto resume;
    352 		}
    353 		if (p->p_wchan == 0) {
    354 			catch = 0;
    355 			goto resume;
    356 		}
    357 	} else
    358 		sig = 0;
    359 	p->p_stat = SSLEEP;
    360 	p->p_stats->p_ru.ru_nvcsw++;
    361 	mi_switch();
    362 #ifdef	DDB
    363 	/* handy breakpoint location after process "wakes" */
    364 	asm(".globl bpendtsleep ; bpendtsleep:");
    365 #endif
    366 resume:
    367 	curpriority = p->p_usrpri;
    368 	splx(s);
    369 	p->p_flag &= ~P_SINTR;
    370 	if (p->p_flag & P_TIMEOUT) {
    371 		p->p_flag &= ~P_TIMEOUT;
    372 		if (sig == 0) {
    373 #ifdef KTRACE
    374 			if (KTRPOINT(p, KTR_CSW))
    375 				ktrcsw(p->p_tracep, 0, 0);
    376 #endif
    377 			return (EWOULDBLOCK);
    378 		}
    379 	} else if (timo)
    380 		untimeout(endtsleep, (void *)p);
    381 	if (catch && (sig != 0 || (sig = CURSIG(p)) != 0)) {
    382 #ifdef KTRACE
    383 		if (KTRPOINT(p, KTR_CSW))
    384 			ktrcsw(p->p_tracep, 0, 0);
    385 #endif
    386 		if (p->p_sigacts->ps_sigintr & sigmask(sig))
    387 			return (EINTR);
    388 		return (ERESTART);
    389 	}
    390 #ifdef KTRACE
    391 	if (KTRPOINT(p, KTR_CSW))
    392 		ktrcsw(p->p_tracep, 0, 0);
    393 #endif
    394 	return (0);
    395 }
    396 
    397 /*
    398  * Implement timeout for tsleep.
    399  * If process hasn't been awakened (wchan non-zero),
    400  * set timeout flag and undo the sleep.  If proc
    401  * is stopped, just unsleep so it will remain stopped.
    402  */
    403 void
    404 endtsleep(arg)
    405 	void *arg;
    406 {
    407 	register struct proc *p;
    408 	int s;
    409 
    410 	p = (struct proc *)arg;
    411 	s = splhigh();
    412 	if (p->p_wchan) {
    413 		if (p->p_stat == SSLEEP)
    414 			setrunnable(p);
    415 		else
    416 			unsleep(p);
    417 		p->p_flag |= P_TIMEOUT;
    418 	}
    419 	splx(s);
    420 }
    421 
    422 /*
    423  * Short-term, non-interruptable sleep.
    424  */
    425 void
    426 sleep(ident, priority)
    427 	void *ident;
    428 	int priority;
    429 {
    430 	register struct proc *p = curproc;
    431 	register struct slpque *qp;
    432 	register s;
    433 	extern int cold;
    434 
    435 #ifdef DIAGNOSTIC
    436 	if (priority > PZERO) {
    437 		printf("sleep called with priority %d > PZERO, wchan: %p\n",
    438 		    priority, ident);
    439 		panic("old sleep");
    440 	}
    441 #endif
    442 	s = splhigh();
    443 	if (cold || panicstr) {
    444 		/*
    445 		 * After a panic, or during autoconfiguration,
    446 		 * just give interrupts a chance, then just return;
    447 		 * don't run any other procs or panic below,
    448 		 * in case this is the idle process and already asleep.
    449 		 */
    450 		splx(safepri);
    451 		splx(s);
    452 		return;
    453 	}
    454 #ifdef DIAGNOSTIC
    455 	if (ident == NULL || p->p_stat != SRUN || p->p_back)
    456 		panic("sleep");
    457 #endif
    458 	p->p_wchan = ident;
    459 	p->p_wmesg = NULL;
    460 	p->p_slptime = 0;
    461 	p->p_priority = priority;
    462 	qp = &slpque[LOOKUP(ident)];
    463 	if (qp->sq_head == 0)
    464 		qp->sq_head = p;
    465 	else
    466 		*qp->sq_tailp = p;
    467 	*(qp->sq_tailp = &p->p_forw) = 0;
    468 	p->p_stat = SSLEEP;
    469 	p->p_stats->p_ru.ru_nvcsw++;
    470 #ifdef KTRACE
    471 	if (KTRPOINT(p, KTR_CSW))
    472 		ktrcsw(p->p_tracep, 1, 0);
    473 #endif
    474 	mi_switch();
    475 #ifdef	DDB
    476 	/* handy breakpoint location after process "wakes" */
    477 	asm(".globl bpendsleep ; bpendsleep:");
    478 #endif
    479 #ifdef KTRACE
    480 	if (KTRPOINT(p, KTR_CSW))
    481 		ktrcsw(p->p_tracep, 0, 0);
    482 #endif
    483 	curpriority = p->p_usrpri;
    484 	splx(s);
    485 }
    486 
    487 /*
    488  * Remove a process from its wait queue
    489  */
    490 void
    491 unsleep(p)
    492 	register struct proc *p;
    493 {
    494 	register struct slpque *qp;
    495 	register struct proc **hp;
    496 	int s;
    497 
    498 	s = splhigh();
    499 	if (p->p_wchan) {
    500 		hp = &(qp = &slpque[LOOKUP(p->p_wchan)])->sq_head;
    501 		while (*hp != p)
    502 			hp = &(*hp)->p_forw;
    503 		*hp = p->p_forw;
    504 		if (qp->sq_tailp == &p->p_forw)
    505 			qp->sq_tailp = hp;
    506 		p->p_wchan = 0;
    507 	}
    508 	splx(s);
    509 }
    510 
    511 /*
    512  * Make all processes sleeping on the specified identifier runnable.
    513  */
    514 void
    515 wakeup(ident)
    516 	register void *ident;
    517 {
    518 	register struct slpque *qp;
    519 	register struct proc *p, **q;
    520 	int s;
    521 
    522 	s = splhigh();
    523 	qp = &slpque[LOOKUP(ident)];
    524 restart:
    525 	for (q = &qp->sq_head; (p = *q) != NULL; ) {
    526 #ifdef DIAGNOSTIC
    527 		if (p->p_back || (p->p_stat != SSLEEP && p->p_stat != SSTOP))
    528 			panic("wakeup");
    529 #endif
    530 		if (p->p_wchan == ident) {
    531 			p->p_wchan = 0;
    532 			*q = p->p_forw;
    533 			if (qp->sq_tailp == &p->p_forw)
    534 				qp->sq_tailp = q;
    535 			if (p->p_stat == SSLEEP) {
    536 				/* OPTIMIZED EXPANSION OF setrunnable(p); */
    537 				if (p->p_slptime > 1)
    538 					updatepri(p);
    539 				p->p_slptime = 0;
    540 				p->p_stat = SRUN;
    541 				if (p->p_flag & P_INMEM)
    542 					setrunqueue(p);
    543 				/*
    544 				 * Since curpriority is a user priority,
    545 				 * p->p_priority is always better than
    546 				 * curpriority.
    547 				 */
    548 				if ((p->p_flag & P_INMEM) == 0)
    549 					wakeup((caddr_t)&proc0);
    550 				else
    551 					need_resched();
    552 				/* END INLINE EXPANSION */
    553 				goto restart;
    554 			}
    555 		} else
    556 			q = &p->p_forw;
    557 	}
    558 	splx(s);
    559 }
    560 
    561 /*
    562  * The machine independent parts of mi_switch().
    563  * Must be called at splstatclock() or higher.
    564  */
    565 void
    566 mi_switch()
    567 {
    568 	register struct proc *p = curproc;	/* XXX */
    569 	register struct rlimit *rlim;
    570 	register long s, u;
    571 	struct timeval tv;
    572 
    573 	/*
    574 	 * Compute the amount of time during which the current
    575 	 * process was running, and add that to its total so far.
    576 	 */
    577 	microtime(&tv);
    578 	u = p->p_rtime.tv_usec + (tv.tv_usec - runtime.tv_usec);
    579 	s = p->p_rtime.tv_sec + (tv.tv_sec - runtime.tv_sec);
    580 	if (u < 0) {
    581 		u += 1000000;
    582 		s--;
    583 	} else if (u >= 1000000) {
    584 		u -= 1000000;
    585 		s++;
    586 	}
    587 	p->p_rtime.tv_usec = u;
    588 	p->p_rtime.tv_sec = s;
    589 
    590 	/*
    591 	 * Check if the process exceeds its cpu resource allocation.
    592 	 * If over max, kill it.  In any case, if it has run for more
    593 	 * than 10 minutes, reduce priority to give others a chance.
    594 	 */
    595 	rlim = &p->p_rlimit[RLIMIT_CPU];
    596 	if (s >= rlim->rlim_cur) {
    597 		if (s >= rlim->rlim_max)
    598 			psignal(p, SIGKILL);
    599 		else {
    600 			psignal(p, SIGXCPU);
    601 			if (rlim->rlim_cur < rlim->rlim_max)
    602 				rlim->rlim_cur += 5;
    603 		}
    604 	}
    605 	if (autonicetime && s > autonicetime && p->p_ucred->cr_uid && p->p_nice == NZERO) {
    606 		p->p_nice = autoniceval + NZERO;
    607 		resetpriority(p);
    608 	}
    609 
    610 	/*
    611 	 * Pick a new current process and record its start time.
    612 	 */
    613 	cnt.v_swtch++;
    614 	cpu_switch(p);
    615 	microtime(&runtime);
    616 }
    617 
    618 /*
    619  * Initialize the (doubly-linked) run queues
    620  * to be empty.
    621  */
    622 void
    623 rqinit()
    624 {
    625 	register int i;
    626 
    627 	for (i = 0; i < NQS; i++)
    628 		qs[i].ph_link = qs[i].ph_rlink = (struct proc *)&qs[i];
    629 }
    630 
    631 /*
    632  * Change process state to be runnable,
    633  * placing it on the run queue if it is in memory,
    634  * and awakening the swapper if it isn't in memory.
    635  */
    636 void
    637 setrunnable(p)
    638 	register struct proc *p;
    639 {
    640 	register int s;
    641 
    642 	s = splhigh();
    643 	switch (p->p_stat) {
    644 	case 0:
    645 	case SRUN:
    646 	case SZOMB:
    647 	default:
    648 		panic("setrunnable");
    649 	case SSTOP:
    650 		/*
    651 		 * If we're being traced (possibly because someone attached us
    652 		 * while we were stopped), check for a signal from the debugger.
    653 		 */
    654 		if ((p->p_flag & P_TRACED) != 0 && p->p_xstat != 0)
    655 			p->p_siglist |= sigmask(p->p_xstat);
    656 	case SSLEEP:
    657 		unsleep(p);		/* e.g. when sending signals */
    658 		break;
    659 
    660 	case SIDL:
    661 		break;
    662 	}
    663 	p->p_stat = SRUN;
    664 	if (p->p_flag & P_INMEM)
    665 		setrunqueue(p);
    666 	splx(s);
    667 	if (p->p_slptime > 1)
    668 		updatepri(p);
    669 	p->p_slptime = 0;
    670 	if ((p->p_flag & P_INMEM) == 0)
    671 		wakeup((caddr_t)&proc0);
    672 	else if (p->p_priority < curpriority)
    673 		need_resched();
    674 }
    675 
    676 /*
    677  * Compute the priority of a process when running in user mode.
    678  * Arrange to reschedule if the resulting priority is better
    679  * than that of the current process.
    680  */
    681 void
    682 resetpriority(p)
    683 	register struct proc *p;
    684 {
    685 	register unsigned int newpriority;
    686 
    687 	newpriority = PUSER + p->p_estcpu / 4 + 2 * (p->p_nice - NZERO);
    688 	newpriority = min(newpriority, MAXPRI);
    689 	p->p_usrpri = newpriority;
    690 	if (newpriority < curpriority)
    691 		need_resched();
    692 }
    693 
    694 #ifdef DDB
    695 #include <machine/db_machdep.h>
    696 
    697 #include <ddb/db_interface.h>
    698 #include <ddb/db_output.h>
    699 
    700 void
    701 db_show_all_procs(addr, haddr, count, modif)
    702 	db_expr_t addr;
    703 	int haddr;
    704 	db_expr_t count;
    705 	char *modif;
    706 {
    707 	int map = modif[0] == 'm';
    708 	int doingzomb = 0;
    709 	struct proc *p, *pp;
    710 
    711 	p = allproc.lh_first;
    712 	db_printf("  pid proc     addr     %s comm         wchan\n",
    713 	    map ? "map     " : "uid  ppid  pgrp  flag stat em ");
    714 	while (p != 0) {
    715 		pp = p->p_pptr;
    716 		if (p->p_stat) {
    717 			db_printf("%5d %p %p ",
    718 			    p->p_pid, p, p->p_addr);
    719 			if (map)
    720 				db_printf("%p %s   ",
    721 				    p->p_vmspace, p->p_comm);
    722 			else
    723 				db_printf("%3d %5d %5d  %06x  %d  %s  %s   ",
    724 				    p->p_cred->p_ruid, pp ? pp->p_pid : -1,
    725 				    p->p_pgrp->pg_id, p->p_flag, p->p_stat,
    726 				    p->p_emul->e_name, p->p_comm);
    727 			if (p->p_wchan) {
    728 				if (p->p_wmesg)
    729 					db_printf("%s ", p->p_wmesg);
    730 				db_printf("%p", p->p_wchan);
    731 			}
    732 			db_printf("\n");
    733 		}
    734 		p = p->p_list.le_next;
    735 		if (p == 0 && doingzomb == 0) {
    736 			doingzomb = 1;
    737 			p = zombproc.lh_first;
    738 		}
    739 	}
    740 }
    741 #endif
    742