put the scheduler in its own file. reduces clutter, and logically separates

"put this process to sleep" and "find a process to run" operations.
no functional change.  ok art@

1 files changed, 688 insertions, 0 deletions

diff --git a/sys/kern/sched_bsd.c b/sys/kern/sched_bsd.c
new file mode 100644
index 00000000000..523e240a4b1
--- /dev/null
+++ b/sys/kern/sched_bsd.c
@@ -0,0 +1,688 @@
+/*	$OpenBSD: sched_bsd.c,v 1.1 2004/07/29 06:25:45 tedu Exp $	*/
+/*	$NetBSD: kern_synch.c,v 1.37 1996/04/22 01:38:37 christos Exp $	*/
+
+/*-
+ * Copyright (c) 1982, 1986, 1990, 1991, 1993
+ *	The Regents of the University of California.  All rights reserved.
+ * (c) UNIX System Laboratories, Inc.
+ * All or some portions of this file are derived from material licensed
+ * to the University of California by American Telephone and Telegraph
+ * Co. or Unix System Laboratories, Inc. and are reproduced herein with
+ * the permission of UNIX System Laboratories, Inc.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the University nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ *	@(#)kern_synch.c	8.6 (Berkeley) 1/21/94
+ */
+
+#include <sys/param.h>
+#include <sys/systm.h>
+#include <sys/proc.h>
+#include <sys/kernel.h>
+#include <sys/buf.h>
+#include <sys/signalvar.h>
+#include <sys/resourcevar.h>
+#include <uvm/uvm_extern.h>
+#include <sys/sched.h>
+#include <sys/timeout.h>
+
+#ifdef KTRACE
+#include <sys/ktrace.h>
+#endif
+
+#include <machine/cpu.h>
+
+#ifndef __HAVE_CPUINFO
+u_char	curpriority;		/* usrpri of curproc */
+#endif
+int	lbolt;			/* once a second sleep address */
+#ifdef __HAVE_CPUINFO
+int	rrticks_init;		/* # of hardclock ticks per roundrobin() */
+#endif
+
+int whichqs;			/* Bit mask summary of non-empty Q's. */
+struct prochd qs[NQS];
+
+struct SIMPLELOCK sched_lock;
+
+void scheduler_start(void);
+
+#ifdef __HAVE_CPUINFO
+void roundrobin(struct cpu_info *);
+#else
+void roundrobin(void *);
+#endif
+void schedcpu(void *);
+void updatepri(struct proc *);
+void endtsleep(void *);
+
+void
+scheduler_start()
+{
+#ifndef __HAVE_CPUINFO
+	static struct timeout roundrobin_to;
+#endif
+	static struct timeout schedcpu_to;
+
+	/*
+	 * We avoid polluting the global namespace by keeping the scheduler
+	 * timeouts static in this function.
+	 * We setup the timeouts here and kick schedcpu and roundrobin once to
+	 * make them do their job.
+	 */
+
+#ifndef __HAVE_CPUINFO
+	timeout_set(&roundrobin_to, roundrobin, &roundrobin_to);
+#endif
+	timeout_set(&schedcpu_to, schedcpu, &schedcpu_to);
+
+#ifdef __HAVE_CPUINFO
+	rrticks_init = hz / 10;
+#else
+	roundrobin(&roundrobin_to);
+#endif
+	schedcpu(&schedcpu_to);
+}
+
+/*
+ * Force switch among equal priority processes every 100ms.
+ */
+/* ARGSUSED */
+#ifdef __HAVE_CPUINFO
+void
+roundrobin(struct cpu_info *ci)
+{
+	struct schedstate_percpu *spc = &ci->ci_schedstate;
+	int s;
+
+	spc->spc_rrticks = rrticks_init;
+
+	if (curproc != NULL) {
+		s = splstatclock();
+		if (spc->spc_schedflags & SPCF_SEENRR) {
+			/*
+			 * The process has already been through a roundrobin
+			 * without switching and may be hogging the CPU.
+			 * Indicate that the process should yield.
+			 */
+			spc->spc_schedflags |= SPCF_SHOULDYIELD;
+		} else {
+			spc->spc_schedflags |= SPCF_SEENRR;
+		}
+		splx(s);
+	}
+
+	need_resched(curcpu());
+}
+#else
+void
+roundrobin(void *arg)
+{
+	struct timeout *to = (struct timeout *)arg;
+	struct proc *p = curproc;
+	int s;
+
+	if (p != NULL) {
+		s = splstatclock();
+		if (p->p_schedflags & PSCHED_SEENRR) {
+			/*
+			 * The process has already been through a roundrobin
+			 * without switching and may be hogging the CPU.
+			 * Indicate that the process should yield.
+			 */
+			p->p_schedflags |= PSCHED_SHOULDYIELD;
+		} else {
+			p->p_schedflags |= PSCHED_SEENRR;
+		}
+		splx(s);
+	}
+
+	need_resched(0);
+	timeout_add(to, hz / 10);
+}
+#endif
+
+/*
+ * Constants for digital decay and forget:
+ *	90% of (p_estcpu) usage in 5 * loadav time
+ *	95% of (p_pctcpu) usage in 60 seconds (load insensitive)
+ *          Note that, as ps(1) mentions, this can let percentages
+ *          total over 100% (I've seen 137.9% for 3 processes).
+ *
+ * Note that hardclock updates p_estcpu and p_cpticks independently.
+ *
+ * We wish to decay away 90% of p_estcpu in (5 * loadavg) seconds.
+ * That is, the system wants to compute a value of decay such
+ * that the following for loop:
+ * 	for (i = 0; i < (5 * loadavg); i++)
+ * 		p_estcpu *= decay;
+ * will compute
+ * 	p_estcpu *= 0.1;
+ * for all values of loadavg:
+ *
+ * Mathematically this loop can be expressed by saying:
+ * 	decay ** (5 * loadavg) ~= .1
+ *
+ * The system computes decay as:
+ * 	decay = (2 * loadavg) / (2 * loadavg + 1)
+ *
+ * We wish to prove that the system's computation of decay
+ * will always fulfill the equation:
+ * 	decay ** (5 * loadavg) ~= .1
+ *
+ * If we compute b as:
+ * 	b = 2 * loadavg
+ * then
+ * 	decay = b / (b + 1)
+ *
+ * We now need to prove two things:
+ *	1) Given factor ** (5 * loadavg) ~= .1, prove factor == b/(b+1)
+ *	2) Given b/(b+1) ** power ~= .1, prove power == (5 * loadavg)
+ *	
+ * Facts:
+ *         For x close to zero, exp(x) =~ 1 + x, since
+ *              exp(x) = 0! + x**1/1! + x**2/2! + ... .
+ *              therefore exp(-1/b) =~ 1 - (1/b) = (b-1)/b.
+ *         For x close to zero, ln(1+x) =~ x, since
+ *              ln(1+x) = x - x**2/2 + x**3/3 - ...     -1 < x < 1
+ *              therefore ln(b/(b+1)) = ln(1 - 1/(b+1)) =~ -1/(b+1).
+ *         ln(.1) =~ -2.30
+ *
+ * Proof of (1):
+ *    Solve (factor)**(power) =~ .1 given power (5*loadav):
+ *	solving for factor,
+ *      ln(factor) =~ (-2.30/5*loadav), or
+ *      factor =~ exp(-1/((5/2.30)*loadav)) =~ exp(-1/(2*loadav)) =
+ *          exp(-1/b) =~ (b-1)/b =~ b/(b+1).                    QED
+ *
+ * Proof of (2):
+ *    Solve (factor)**(power) =~ .1 given factor == (b/(b+1)):
+ *	solving for power,
+ *      power*ln(b/(b+1)) =~ -2.30, or
+ *      power =~ 2.3 * (b + 1) = 4.6*loadav + 2.3 =~ 5*loadav.  QED
+ *
+ * Actual power values for the implemented algorithm are as follows:
+ *      loadav: 1       2       3       4
+ *      power:  5.68    10.32   14.94   19.55
+ */
+
+/* calculations for digital decay to forget 90% of usage in 5*loadav sec */
+#define	loadfactor(loadav)	(2 * (loadav))
+#define	decay_cpu(loadfac, cpu)	(((loadfac) * (cpu)) / ((loadfac) + FSCALE))
+
+/* decay 95% of `p_pctcpu' in 60 seconds; see CCPU_SHIFT before changing */
+fixpt_t	ccpu = 0.95122942450071400909 * FSCALE;		/* exp(-1/20) */
+
+/*
+ * If `ccpu' is not equal to `exp(-1/20)' and you still want to use the
+ * faster/more-accurate formula, you'll have to estimate CCPU_SHIFT below
+ * and possibly adjust FSHIFT in "param.h" so that (FSHIFT >= CCPU_SHIFT).
+ *
+ * To estimate CCPU_SHIFT for exp(-1/20), the following formula was used:
+ *	1 - exp(-1/20) ~= 0.0487 ~= 0.0488 == 1 (fixed pt, *11* bits).
+ *
+ * If you dont want to bother with the faster/more-accurate formula, you
+ * can set CCPU_SHIFT to (FSHIFT + 1) which will use a slower/less-accurate
+ * (more general) method of calculating the %age of CPU used by a process.
+ */
+#define	CCPU_SHIFT	11
+
+/*
+ * Recompute process priorities, every hz ticks.
+ */
+/* ARGSUSED */
+void
+schedcpu(arg)
+	void *arg;
+{
+	struct timeout *to = (struct timeout *)arg;
+	fixpt_t loadfac = loadfactor(averunnable.ldavg[0]);
+	struct proc *p;
+	int s;
+	unsigned int newcpu;
+	int phz;
+
+	/*
+	 * If we have a statistics clock, use that to calculate CPU
+	 * time, otherwise revert to using the profiling clock (which,
+	 * in turn, defaults to hz if there is no separate profiling
+	 * clock available)
+	 */
+	phz = stathz ? stathz : profhz;
+	KASSERT(phz);
+
+	for (p = LIST_FIRST(&allproc); p != 0; p = LIST_NEXT(p, p_list)) {
+		/*
+		 * Increment time in/out of memory and sleep time
+		 * (if sleeping).  We ignore overflow; with 16-bit int's
+		 * (remember them?) overflow takes 45 days.
+		 */
+		p->p_swtime++;
+		if (p->p_stat == SSLEEP || p->p_stat == SSTOP)
+			p->p_slptime++;
+		p->p_pctcpu = (p->p_pctcpu * ccpu) >> FSHIFT;
+		/*
+		 * If the process has slept the entire second,
+		 * stop recalculating its priority until it wakes up.
+		 */
+		if (p->p_slptime > 1)
+			continue;
+		s = splstatclock();	/* prevent state changes */
+		/*
+		 * p_pctcpu is only for ps.
+		 */
+#if	(FSHIFT >= CCPU_SHIFT)
+		p->p_pctcpu += (phz == 100)?
+			((fixpt_t) p->p_cpticks) << (FSHIFT - CCPU_SHIFT):
+                	100 * (((fixpt_t) p->p_cpticks)
+				<< (FSHIFT - CCPU_SHIFT)) / phz;
+#else
+		p->p_pctcpu += ((FSCALE - ccpu) *
+			(p->p_cpticks * FSCALE / phz)) >> FSHIFT;
+#endif
+		p->p_cpticks = 0;
+		newcpu = (u_int) decay_cpu(loadfac, p->p_estcpu);
+		p->p_estcpu = newcpu;
+		splx(s);
+		SCHED_LOCK(s);
+		resetpriority(p);
+		if (p->p_priority >= PUSER) {
+			if ((p != curproc) &&
+			    p->p_stat == SRUN &&
+			    (p->p_flag & P_INMEM) &&
+			    (p->p_priority / PPQ) != (p->p_usrpri / PPQ)) {
+				remrunqueue(p);
+				p->p_priority = p->p_usrpri;
+				setrunqueue(p);
+			} else
+				p->p_priority = p->p_usrpri;
+		}
+		SCHED_UNLOCK(s);
+	}
+	uvm_meter();
+	wakeup((caddr_t)&lbolt);
+	timeout_add(to, hz);
+}
+
+/*
+ * Recalculate the priority of a process after it has slept for a while.
+ * For all load averages >= 1 and max p_estcpu of 255, sleeping for at
+ * least six times the loadfactor will decay p_estcpu to zero.
+ */
+void
+updatepri(p)
+	register struct proc *p;
+{
+	register unsigned int newcpu = p->p_estcpu;
+	register fixpt_t loadfac = loadfactor(averunnable.ldavg[0]);
+
+	SCHED_ASSERT_LOCKED();
+
+	if (p->p_slptime > 5 * loadfac)
+		p->p_estcpu = 0;
+	else {
+		p->p_slptime--;	/* the first time was done in schedcpu */
+		while (newcpu && --p->p_slptime)
+			newcpu = (int) decay_cpu(loadfac, newcpu);
+		p->p_estcpu = newcpu;
+	}
+	resetpriority(p);
+}
+
+#if defined(MULTIPROCESSOR) || defined(LOCKDEBUG)
+void
+sched_unlock_idle(void)
+{
+	SIMPLE_UNLOCK(&sched_lock);
+}
+
+void
+sched_lock_idle(void)
+{
+	SIMPLE_LOCK(&sched_lock);
+}
+#endif /* MULTIPROCESSOR || LOCKDEBUG */
+
+/*
+ * General yield call.  Puts the current process back on its run queue and
+ * performs a voluntary context switch.
+ */
+void
+yield()
+{
+	struct proc *p = curproc;
+	int s;
+
+	SCHED_LOCK(s);
+	p->p_priority = p->p_usrpri;
+	setrunqueue(p);
+	p->p_stats->p_ru.ru_nvcsw++;
+	mi_switch();
+	SCHED_ASSERT_UNLOCKED();
+	splx(s);
+}
+
+/*
+ * General preemption call.  Puts the current process back on its run queue
+ * and performs an involuntary context switch.  If a process is supplied,
+ * we switch to that process.  Otherwise, we use the normal process selection
+ * criteria.
+ */
+void
+preempt(newp)
+	struct proc *newp;
+{
+	struct proc *p = curproc;
+	int s;
+
+	/*
+	 * XXX Switching to a specific process is not supported yet.
+	 */
+	if (newp != NULL)
+		panic("preempt: cpu_preempt not yet implemented");
+
+	SCHED_LOCK(s);
+	p->p_priority = p->p_usrpri;
+	p->p_stat = SRUN;
+	setrunqueue(p);
+	p->p_stats->p_ru.ru_nivcsw++;
+	mi_switch();
+	SCHED_ASSERT_UNLOCKED();
+	splx(s);
+}
+
+
+/*
+ * Must be called at splstatclock() or higher.
+ */
+void
+mi_switch()
+{
+	struct proc *p = curproc;	/* XXX */
+	struct rlimit *rlim;
+	struct timeval tv;
+#if defined(MULTIPROCESSOR)
+	int hold_count;
+#endif
+#ifdef __HAVE_CPUINFO
+	struct schedstate_percpu *spc = &p->p_cpu->ci_schedstate;
+#endif
+
+	SCHED_ASSERT_LOCKED();
+
+#if defined(MULTIPROCESSOR)
+	/*
+	 * Release the kernel_lock, as we are about to yield the CPU.
+	 * The scheduler lock is still held until cpu_switch()
+	 * selects a new process and removes it from the run queue.
+	 */
+	if (p->p_flag & P_BIGLOCK)
+#ifdef notyet
+		hold_count = spinlock_release_all(&kernel_lock);
+#else
+		hold_count = __mp_release_all(&kernel_lock);
+#endif
+#endif
+
+	/*
+	 * Compute the amount of time during which the current
+	 * process was running, and add that to its total so far.
+	 * XXX - use microuptime here to avoid strangeness.
+	 */
+	microuptime(&tv);
+#ifdef __HAVE_CPUINFO
+	if (timercmp(&tv, &spc->spc_runtime, <)) {
+#if 0
+		printf("uptime is not monotonic! "
+		    "tv=%lu.%06lu, runtime=%lu.%06lu\n",
+		    tv.tv_sec, tv.tv_usec, spc->spc_runtime.tv_sec,
+		    spc->spc_runtime.tv_usec);
+#endif
+	} else {
+		timersub(&tv, &spc->spc_runtime, &tv);
+		timeradd(&p->p_rtime, &tv, &p->p_rtime);
+	}
+#else
+	if (timercmp(&tv, &runtime, <)) {
+#if 0
+		printf("uptime is not monotonic! "
+		    "tv=%lu.%06lu, runtime=%lu.%06lu\n",
+		    tv.tv_sec, tv.tv_usec, runtime.tv_sec, runtime.tv_usec);
+#endif
+	} else {
+		timersub(&tv, &runtime, &tv);
+		timeradd(&p->p_rtime, &tv, &p->p_rtime);
+	}
+#endif
+
+	/*
+	 * Check if the process exceeds its cpu resource allocation.
+	 * If over max, kill it.
+	 */
+	rlim = &p->p_rlimit[RLIMIT_CPU];
+	if ((rlim_t)p->p_rtime.tv_sec >= rlim->rlim_cur) {
+		if ((rlim_t)p->p_rtime.tv_sec >= rlim->rlim_max) {
+			psignal(p, SIGKILL);
+		} else {
+			psignal(p, SIGXCPU);
+			if (rlim->rlim_cur < rlim->rlim_max)
+				rlim->rlim_cur += 5;
+		}
+	}
+
+	/*
+	 * Process is about to yield the CPU; clear the appropriate
+	 * scheduling flags.
+	 */
+#ifdef __HAVE_CPUINFO
+	spc->spc_schedflags &= ~SPCF_SWITCHCLEAR;
+#else
+	p->p_schedflags &= ~PSCHED_SWITCHCLEAR;
+#endif
+
+	/*
+	 * Pick a new current process and record its start time.
+	 */
+	uvmexp.swtch++;
+	cpu_switch(p);
+
+	/*
+	 * Make sure that MD code released the scheduler lock before
+	 * resuming us.
+	 */
+	SCHED_ASSERT_UNLOCKED();
+
+	/*
+	 * We're running again; record our new start time.  We might
+	 * be running on a new CPU now, so don't use the cache'd
+	 * schedstate_percpu pointer.
+	 */
+#ifdef __HAVE_CPUINFO
+	KDASSERT(p->p_cpu != NULL);
+	KDASSERT(p->p_cpu == curcpu());
+	microuptime(&p->p_cpu->ci_schedstate.spc_runtime);
+#else
+	microuptime(&runtime);
+#endif
+
+#if defined(MULTIPROCESSOR)
+	/*
+	 * Reacquire the kernel_lock now.  We do this after we've
+	 * released the scheduler lock to avoid deadlock, and before
+	 * we reacquire the interlock.
+	 */
+	if (p->p_flag & P_BIGLOCK)
+#ifdef notyet
+		spinlock_acquire_count(&kernel_lock, hold_count);
+#else
+		__mp_acquire_count(&kernel_lock, hold_count);
+#endif
+#endif
+}
+
+/*
+ * Initialize the (doubly-linked) run queues
+ * to be empty.
+ */
+void
+rqinit()
+{
+	register int i;
+
+	for (i = 0; i < NQS; i++)
+		qs[i].ph_link = qs[i].ph_rlink = (struct proc *)&qs[i];
+	SIMPLE_LOCK_INIT(&sched_lock);
+}
+
+static __inline void
+resched_proc(struct proc *p, u_char pri)
+{
+#ifdef __HAVE_CPUINFO
+	struct cpu_info *ci;
+#endif
+
+	/*
+	 * XXXSMP
+	 * Since p->p_cpu persists across a context switch,
+	 * this gives us *very weak* processor affinity, in
+	 * that we notify the CPU on which the process last
+	 * ran that it should try to switch.
+	 *
+	 * This does not guarantee that the process will run on
+	 * that processor next, because another processor might
+	 * grab it the next time it performs a context switch.
+	 *
+	 * This also does not handle the case where its last
+	 * CPU is running a higher-priority process, but every
+	 * other CPU is running a lower-priority process.  There
+	 * are ways to handle this situation, but they're not
+	 * currently very pretty, and we also need to weigh the
+	 * cost of moving a process from one CPU to another.
+	 *
+	 * XXXSMP
+	 * There is also the issue of locking the other CPU's
+	 * sched state, which we currently do not do.
+	 */
+#ifdef __HAVE_CPUINFO
+	ci = (p->p_cpu != NULL) ? p->p_cpu : curcpu();
+	if (pri < ci->ci_schedstate.spc_curpriority)
+		need_resched(ci);
+#else
+	if (pri < curpriority)
+		need_resched(0);
+#endif
+}
+
+/*
+ * Change process state to be runnable,
+ * placing it on the run queue if it is in memory,
+ * and awakening the swapper if it isn't in memory.
+ */
+void
+setrunnable(p)
+	register struct proc *p;
+{
+	SCHED_ASSERT_LOCKED();
+
+	switch (p->p_stat) {
+	case 0:
+	case SRUN:
+	case SONPROC:
+	case SZOMB:
+	case SDEAD:
+	default:
+		panic("setrunnable");
+	case SSTOP:
+		/*
+		 * If we're being traced (possibly because someone attached us
+		 * while we were stopped), check for a signal from the debugger.
+		 */
+		if ((p->p_flag & P_TRACED) != 0 && p->p_xstat != 0)
+			p->p_siglist |= sigmask(p->p_xstat);
+	case SSLEEP:
+		unsleep(p);		/* e.g. when sending signals */
+		break;
+	case SIDL:
+		break;
+	}
+	p->p_stat = SRUN;
+	if (p->p_flag & P_INMEM)
+		setrunqueue(p);
+	if (p->p_slptime > 1)
+		updatepri(p);
+	p->p_slptime = 0;
+	if ((p->p_flag & P_INMEM) == 0)
+		wakeup((caddr_t)&proc0);
+	else
+		resched_proc(p, p->p_priority);
+}
+
+/*
+ * Compute the priority of a process when running in user mode.
+ * Arrange to reschedule if the resulting priority is better
+ * than that of the current process.
+ */
+void
+resetpriority(p)
+	register struct proc *p;
+{
+	register unsigned int newpriority;
+
+	SCHED_ASSERT_LOCKED();
+
+	newpriority = PUSER + p->p_estcpu + NICE_WEIGHT * (p->p_nice - NZERO);
+	newpriority = min(newpriority, MAXPRI);
+	p->p_usrpri = newpriority;
+	resched_proc(p, p->p_usrpri);
+}
+
+/*
+ * We adjust the priority of the current process.  The priority of a process
+ * gets worse as it accumulates CPU time.  The cpu usage estimator (p_estcpu)
+ * is increased here.  The formula for computing priorities (in kern_synch.c)
+ * will compute a different value each time p_estcpu increases. This can
+ * cause a switch, but unless the priority crosses a PPQ boundary the actual
+ * queue will not change.  The cpu usage estimator ramps up quite quickly
+ * when the process is running (linearly), and decays away exponentially, at
+ * a rate which is proportionally slower when the system is busy.  The basic
+ * principle is that the system will 90% forget that the process used a lot
+ * of CPU time in 5 * loadav seconds.  This causes the system to favor
+ * processes which haven't run much recently, and to round-robin among other
+ * processes.
+ */
+
+void
+schedclock(p)
+	struct proc *p;
+{
+	int s;
+
+	p->p_estcpu = ESTCPULIM(p->p_estcpu + 1);
+	SCHED_LOCK(s);
+	resetpriority(p);
+	SCHED_UNLOCK(s);
+	if (p->p_priority >= PUSER)
+		p->p_priority = p->p_usrpri;
+}