freebsd-skq/sys/kern/kern_clock.c

/*-
 * Copyright (c) 1982, 1986, 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. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by the University of
 *	California, Berkeley and its contributors.
 * 4. 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_clock.c	8.5 (Berkeley) 1/21/94
 * $Id: kern_clock.c,v 1.45 1997/11/24 15:15:27 bde Exp $
 */

/* Portions of this software are covered by the following: */
/******************************************************************************
 *                                                                            *
 * Copyright (c) David L. Mills 1993, 1994                                    *
 *                                                                            *
 * Permission to use, copy, modify, and distribute this software and its      *
 * documentation for any purpose and without fee is hereby granted, provided  *
 * that the above copyright notice appears in all copies and that both the    *
 * copyright notice and this permission notice appear in supporting           *
 * documentation, and that the name University of Delaware not be used in     *
 * advertising or publicity pertaining to distribution of the software        *
 * without specific, written prior permission.  The University of Delaware    *
 * makes no representations about the suitability this software for any       *
 * purpose.  It is provided "as is" without express or implied warranty.      *
 *                                                                            *
 *****************************************************************************/

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/dkstat.h>
#include <sys/callout.h>
#include <sys/kernel.h>
#include <sys/proc.h>
#include <sys/resourcevar.h>
#include <sys/signalvar.h>
#include <sys/timex.h>
#include <vm/vm.h>
#include <sys/lock.h>
#include <vm/pmap.h>
#include <vm/vm_map.h>
#include <sys/sysctl.h>

#include <machine/cpu.h>
#define CLOCK_HAIR		/* XXX */
#include <machine/clock.h>
#include <machine/limits.h>

#ifdef GPROF
#include <sys/gmon.h>
#endif

#if defined(SMP) && defined(BETTER_CLOCK)
#include <machine/smp.h>
#endif

static void initclocks __P((void *dummy));
SYSINIT(clocks, SI_SUB_CLOCKS, SI_ORDER_FIRST, initclocks, NULL)

/* Exported to machdep.c. */
struct callout *callout;
struct callout_list callfree;
int callwheelsize, callwheelbits, callwheelmask;
struct callout_tailq *callwheel;


/* Some of these don't belong here, but it's easiest to concentrate them. */
#if defined(SMP) && defined(BETTER_CLOCK)
long cp_time[CPUSTATES];
#else
static long cp_time[CPUSTATES];
#endif
long dk_seek[DK_NDRIVE];
static long dk_time[DK_NDRIVE];	/* time busy (in statclock ticks) */
long dk_wds[DK_NDRIVE];
long dk_wpms[DK_NDRIVE];
long dk_xfer[DK_NDRIVE];

int dk_busy;
int dk_ndrive = 0;
char dk_names[DK_NDRIVE][DK_NAMELEN];

long tk_cancc;
long tk_nin;
long tk_nout;
long tk_rawcc;

/*
 * Clock handling routines.
 *
 * This code is written to operate with two timers that run independently of
 * each other.  The main clock, running hz times per second, is used to keep
 * track of real time.  The second timer handles kernel and user profiling,
 * and does resource use estimation.  If the second timer is programmable,
 * it is randomized to avoid aliasing between the two clocks.  For example,
 * the randomization prevents an adversary from always giving up the cpu
 * just before its quantum expires.  Otherwise, it would never accumulate
 * cpu ticks.  The mean frequency of the second timer is stathz.
 *
 * If no second timer exists, stathz will be zero; in this case we drive
 * profiling and statistics off the main clock.  This WILL NOT be accurate;
 * do not do it unless absolutely necessary.
 *
 * The statistics clock may (or may not) be run at a higher rate while
 * profiling.  This profile clock runs at profhz.  We require that profhz
 * be an integral multiple of stathz.
 *
 * If the statistics clock is running fast, it must be divided by the ratio
 * profhz/stathz for statistics.  (For profiling, every tick counts.)
 */

/*
 * TODO:
 *	allocate more timeout table slots when table overflows.
 */

/*
 * Bump a timeval by a small number of usec's.
 */
#define BUMPTIME(t, usec) { \
	register volatile struct timeval *tp = (t); \
	register long us; \
 \
	tp->tv_usec = us = tp->tv_usec + (usec); \
	if (us >= 1000000) { \
		tp->tv_usec = us - 1000000; \
		tp->tv_sec++; \
	} \
}

int	stathz;
int	profhz;
static int profprocs;
int	ticks;
static int softticks;			/* Like ticks, but for softclock(). */
static struct callout *nextsoftcheck;	/* Next callout to be checked. */
static int psdiv, pscnt;		/* prof => stat divider */
int psratio;				/* ratio: prof / stat */

volatile struct	timeval time;
volatile struct	timeval mono_time;

/*
 * Phase/frequency-lock loop (PLL/FLL) definitions
 *
 * The following variables are read and set by the ntp_adjtime() system
 * call.
 *
 * time_state shows the state of the system clock, with values defined
 * in the timex.h header file.
 *
 * time_status shows the status of the system clock, with bits defined
 * in the timex.h header file.
 *
 * time_offset is used by the PLL/FLL to adjust the system time in small
 * increments.
 *
 * time_constant determines the bandwidth or "stiffness" of the PLL.
 *
 * time_tolerance determines maximum frequency error or tolerance of the
 * CPU clock oscillator and is a property of the architecture; however,
 * in principle it could change as result of the presence of external
 * discipline signals, for instance.
 *
 * time_precision is usually equal to the kernel tick variable; however,
 * in cases where a precision clock counter or external clock is
 * available, the resolution can be much less than this and depend on
 * whether the external clock is working or not.
 *
 * time_maxerror is initialized by a ntp_adjtime() call and increased by
 * the kernel once each second to reflect the maximum error
 * bound growth.
 *
 * time_esterror is set and read by the ntp_adjtime() call, but
 * otherwise not used by the kernel.
 */
int time_status = STA_UNSYNC;	/* clock status bits */
int time_state = TIME_OK;	/* clock state */
long time_offset = 0;		/* time offset (us) */
long time_constant = 0;		/* pll time constant */
long time_tolerance = MAXFREQ;	/* frequency tolerance (scaled ppm) */
long time_precision = 1;	/* clock precision (us) */
long time_maxerror = MAXPHASE;	/* maximum error (us) */
long time_esterror = MAXPHASE;	/* estimated error (us) */

/*
 * The following variables establish the state of the PLL/FLL and the
 * residual time and frequency offset of the local clock. The scale
 * factors are defined in the timex.h header file.
 *
 * time_phase and time_freq are the phase increment and the frequency
 * increment, respectively, of the kernel time variable at each tick of
 * the clock.
 *
 * time_freq is set via ntp_adjtime() from a value stored in a file when
 * the synchronization daemon is first started. Its value is retrieved
 * via ntp_adjtime() and written to the file about once per hour by the
 * daemon.
 *
 * time_adj is the adjustment added to the value of tick at each timer
 * interrupt and is recomputed from time_phase and time_freq at each
 * seconds rollover.
 *
 * time_reftime is the second's portion of the system time on the last
 * call to ntp_adjtime(). It is used to adjust the time_freq variable
 * and to increase the time_maxerror as the time since last update
 * increases.
 */
static long time_phase = 0;		/* phase offset (scaled us) */
long time_freq = 0;			/* frequency offset (scaled ppm) */
static long time_adj = 0;		/* tick adjust (scaled 1 / hz) */
static long time_reftime = 0;		/* time at last adjustment (s) */

#ifdef PPS_SYNC
/*
 * The following variables are used only if the kernel PPS discipline
 * code is configured (PPS_SYNC). The scale factors are defined in the
 * timex.h header file.
 *
 * pps_time contains the time at each calibration interval, as read by
 * microtime(). pps_count counts the seconds of the calibration
 * interval, the duration of which is nominally pps_shift in powers of
 * two.
 *
 * pps_offset is the time offset produced by the time median filter
 * pps_tf[], while pps_jitter is the dispersion (jitter) measured by
 * this filter.
 *
 * pps_freq is the frequency offset produced by the frequency median
 * filter pps_ff[], while pps_stabil is the dispersion (wander) measured
 * by this filter.
 *
 * pps_usec is latched from a high resolution counter or external clock
 * at pps_time. Here we want the hardware counter contents only, not the
 * contents plus the time_tv.usec as usual.
 *
 * pps_valid counts the number of seconds since the last PPS update. It
 * is used as a watchdog timer to disable the PPS discipline should the
 * PPS signal be lost.
 *
 * pps_glitch counts the number of seconds since the beginning of an
 * offset burst more than tick/2 from current nominal offset. It is used
 * mainly to suppress error bursts due to priority conflicts between the
 * PPS interrupt and timer interrupt.
 *
 * pps_intcnt counts the calibration intervals for use in the interval-
 * adaptation algorithm. It's just too complicated for words.
 */
struct timeval pps_time;	/* kernel time at last interval */
long pps_offset = 0;		/* pps time offset (us) */
long pps_jitter = MAXTIME;	/* pps time dispersion (jitter) (us) */
long pps_tf[] = {0, 0, 0};	/* pps time offset median filter (us) */
long pps_freq = 0;		/* frequency offset (scaled ppm) */
long pps_stabil = MAXFREQ;	/* frequency dispersion (scaled ppm) */
long pps_ff[] = {0, 0, 0};	/* frequency offset median filter */
long pps_usec = 0;		/* microsec counter at last interval */
long pps_valid = PPS_VALID;	/* pps signal watchdog counter */
int pps_glitch = 0;		/* pps signal glitch counter */
int pps_count = 0;		/* calibration interval counter (s) */
int pps_shift = PPS_SHIFT;	/* interval duration (s) (shift) */
int pps_intcnt = 0;		/* intervals at current duration */

/*
 * PPS signal quality monitors
 *
 * pps_jitcnt counts the seconds that have been discarded because the
 * jitter measured by the time median filter exceeds the limit MAXTIME
 * (100 us).
 *
 * pps_calcnt counts the frequency calibration intervals, which are
 * variable from 4 s to 256 s.
 *
 * pps_errcnt counts the calibration intervals which have been discarded
 * because the wander exceeds the limit MAXFREQ (100 ppm) or where the
 * calibration interval jitter exceeds two ticks.
 *
 * pps_stbcnt counts the calibration intervals that have been discarded
 * because the frequency wander exceeds the limit MAXFREQ / 4 (25 us).
 */
long pps_jitcnt = 0;		/* jitter limit exceeded */
long pps_calcnt = 0;		/* calibration intervals */
long pps_errcnt = 0;		/* calibration errors */
long pps_stbcnt = 0;		/* stability limit exceeded */
#endif /* PPS_SYNC */

/* XXX none of this stuff works under FreeBSD */
#ifdef EXT_CLOCK
/*
 * External clock definitions
 *
 * The following definitions and declarations are used only if an
 * external clock (HIGHBALL or TPRO) is configured on the system.
 */
#define CLOCK_INTERVAL 30	/* CPU clock update interval (s) */

/*
 * The clock_count variable is set to CLOCK_INTERVAL at each PPS
 * interrupt and decremented once each second.
 */
int clock_count = 0;		/* CPU clock counter */

#ifdef HIGHBALL
/*
 * The clock_offset and clock_cpu variables are used by the HIGHBALL
 * interface. The clock_offset variable defines the offset between
 * system time and the HIGBALL counters. The clock_cpu variable contains
 * the offset between the system clock and the HIGHBALL clock for use in
 * disciplining the kernel time variable.
 */
extern struct timeval clock_offset; /* Highball clock offset */
long clock_cpu = 0;		/* CPU clock adjust */
#endif /* HIGHBALL */
#endif /* EXT_CLOCK */

/*
 * hardupdate() - local clock update
 *
 * This routine is called by ntp_adjtime() to update the local clock
 * phase and frequency. The implementation is of an adaptive-parameter,
 * hybrid phase/frequency-lock loop (PLL/FLL). The routine computes new
 * time and frequency offset estimates for each call. If the kernel PPS
 * discipline code is configured (PPS_SYNC), the PPS signal itself
 * determines the new time offset, instead of the calling argument.
 * Presumably, calls to ntp_adjtime() occur only when the caller
 * believes the local clock is valid within some bound (+-128 ms with
 * NTP). If the caller's time is far different than the PPS time, an
 * argument will ensue, and it's not clear who will lose.
 *
 * For uncompensated quartz crystal oscillatores and nominal update
 * intervals less than 1024 s, operation should be in phase-lock mode
 * (STA_FLL = 0), where the loop is disciplined to phase. For update
 * intervals greater than thiss, operation should be in frequency-lock
 * mode (STA_FLL = 1), where the loop is disciplined to frequency.
 *
 * Note: splclock() is in effect.
 */
void
hardupdate(offset)
	long offset;
{
	long ltemp, mtemp;

	if (!(time_status & STA_PLL) && !(time_status & STA_PPSTIME))
		return;
	ltemp = offset;
#ifdef PPS_SYNC
	if (time_status & STA_PPSTIME && time_status & STA_PPSSIGNAL)
		ltemp = pps_offset;
#endif /* PPS_SYNC */

	/*
	 * Scale the phase adjustment and clamp to the operating range.
	 */
	if (ltemp > MAXPHASE)
		time_offset = MAXPHASE << SHIFT_UPDATE;
	else if (ltemp < -MAXPHASE)
		time_offset = -(MAXPHASE << SHIFT_UPDATE);
	else
		time_offset = ltemp << SHIFT_UPDATE;

	/*
	 * Select whether the frequency is to be controlled and in which
	 * mode (PLL or FLL). Clamp to the operating range. Ugly
	 * multiply/divide should be replaced someday.
	 */
	if (time_status & STA_FREQHOLD || time_reftime == 0)
		time_reftime = time.tv_sec;
	mtemp = time.tv_sec - time_reftime;
	time_reftime = time.tv_sec;
	if (time_status & STA_FLL) {
		if (mtemp >= MINSEC) {
			ltemp = ((time_offset / mtemp) << (SHIFT_USEC -
			    SHIFT_UPDATE));
			if (ltemp < 0)
				time_freq -= -ltemp >> SHIFT_KH;
			else
				time_freq += ltemp >> SHIFT_KH;
		}
	} else {
		if (mtemp < MAXSEC) {
			ltemp *= mtemp;
			if (ltemp < 0)
				time_freq -= -ltemp >> (time_constant +
				    time_constant + SHIFT_KF -
				    SHIFT_USEC);
			else
				time_freq += ltemp >> (time_constant +
				    time_constant + SHIFT_KF -
				    SHIFT_USEC);
		}
	}
	if (time_freq > time_tolerance)
		time_freq = time_tolerance;
	else if (time_freq < -time_tolerance)
		time_freq = -time_tolerance;
}



/*
 * Initialize clock frequencies and start both clocks running.
 */
/* ARGSUSED*/
static void
initclocks(dummy)
	void *dummy;
{
	register int i;

	/*
	 * Set divisors to 1 (normal case) and let the machine-specific
	 * code do its bit.
	 */
	psdiv = pscnt = 1;
	cpu_initclocks();

	/*
	 * Compute profhz/stathz, and fix profhz if needed.
	 */
	i = stathz ? stathz : hz;
	if (profhz == 0)
		profhz = i;
	psratio = profhz / i;
}

/*
 * The real-time timer, interrupting hz times per second.
 */
void
hardclock(frame)
	register struct clockframe *frame;
{
	register struct proc *p;

	p = curproc;
	if (p) {
		register struct pstats *pstats;

		/*
		 * Run current process's virtual and profile time, as needed.
		 */
		pstats = p->p_stats;
		if (CLKF_USERMODE(frame) &&
		    timerisset(&pstats->p_timer[ITIMER_VIRTUAL].it_value) &&
		    itimerdecr(&pstats->p_timer[ITIMER_VIRTUAL], tick) == 0)
			psignal(p, SIGVTALRM);
		if (timerisset(&pstats->p_timer[ITIMER_PROF].it_value) &&
		    itimerdecr(&pstats->p_timer[ITIMER_PROF], tick) == 0)
			psignal(p, SIGPROF);
	}

#if defined(SMP) && defined(BETTER_CLOCK)
	forward_hardclock(pscnt);
#endif
	/*
	 * If no separate statistics clock is available, run it from here.
	 */
	if (stathz == 0)
		statclock(frame);

	/*
	 * Increment the time-of-day.
	 */
	ticks++;
	{
		int time_update;
		struct timeval newtime = time;
		long ltemp;

		if (timedelta == 0) {
			time_update = CPU_THISTICKLEN(tick);
		} else {
			time_update = CPU_THISTICKLEN(tick) + tickdelta;
			timedelta -= tickdelta;
		}
		BUMPTIME(&mono_time, time_update);

		/*
		 * Compute the phase adjustment. If the low-order bits
		 * (time_phase) of the update overflow, bump the high-order bits
		 * (time_update).
		 */
		time_phase += time_adj;
		if (time_phase <= -FINEUSEC) {
		  ltemp = -time_phase >> SHIFT_SCALE;
		  time_phase += ltemp << SHIFT_SCALE;
		  time_update -= ltemp;
		}
		else if (time_phase >= FINEUSEC) {
		  ltemp = time_phase >> SHIFT_SCALE;
		  time_phase -= ltemp << SHIFT_SCALE;
		  time_update += ltemp;
		}

		newtime.tv_usec += time_update;
		/*
		 * On rollover of the second the phase adjustment to be used for
		 * the next second is calculated. Also, the maximum error is
		 * increased by the tolerance. If the PPS frequency discipline
		 * code is present, the phase is increased to compensate for the
		 * CPU clock oscillator frequency error.
		 *
		 * On a 32-bit machine and given parameters in the timex.h
		 * header file, the maximum phase adjustment is +-512 ms and
		 * maximum frequency offset is a tad less than) +-512 ppm. On a
		 * 64-bit machine, you shouldn't need to ask.
		 */
		if (newtime.tv_usec >= 1000000) {
		  newtime.tv_usec -= 1000000;
		  newtime.tv_sec++;
		  time_maxerror += time_tolerance >> SHIFT_USEC;

		  /*
		   * Compute the phase adjustment for the next second. In
		   * PLL mode, the offset is reduced by a fixed factor
		   * times the time constant. In FLL mode the offset is
		   * used directly. In either mode, the maximum phase
		   * adjustment for each second is clamped so as to spread
		   * the adjustment over not more than the number of
		   * seconds between updates.
		   */
		  if (time_offset < 0) {
		    ltemp = -time_offset;
		    if (!(time_status & STA_FLL))
			ltemp >>= SHIFT_KG + time_constant;
		    if (ltemp > (MAXPHASE / MINSEC) << SHIFT_UPDATE)
			ltemp = (MAXPHASE / MINSEC) <<
			    SHIFT_UPDATE;
		    time_offset += ltemp;
		    time_adj = -ltemp << (SHIFT_SCALE - SHIFT_HZ -
			SHIFT_UPDATE);
		    } else {
		        ltemp = time_offset;
			if (!(time_status & STA_FLL))
				ltemp >>= SHIFT_KG + time_constant;
			if (ltemp > (MAXPHASE / MINSEC) << SHIFT_UPDATE)
				ltemp = (MAXPHASE / MINSEC) <<
				    SHIFT_UPDATE;
			time_offset -= ltemp;
			time_adj = ltemp << (SHIFT_SCALE - SHIFT_HZ -
			    SHIFT_UPDATE);
		    }

		  /*
		   * Compute the frequency estimate and additional phase
		   * adjustment due to frequency error for the next
		   * second. When the PPS signal is engaged, gnaw on the
		   * watchdog counter and update the frequency computed by
		   * the pll and the PPS signal.
		   */
#ifdef PPS_SYNC
		  pps_valid++;
		  if (pps_valid == PPS_VALID) {
		    pps_jitter = MAXTIME;
		    pps_stabil = MAXFREQ;
		    time_status &= ~(STA_PPSSIGNAL | STA_PPSJITTER |
				     STA_PPSWANDER | STA_PPSERROR);
		  }
		  ltemp = time_freq + pps_freq;
#else
		  ltemp = time_freq;
#endif /* PPS_SYNC */
		  if (ltemp < 0)
		    time_adj -= -ltemp >>
		      (SHIFT_USEC + SHIFT_HZ - SHIFT_SCALE);
		  else
		    time_adj += ltemp >>
		      (SHIFT_USEC + SHIFT_HZ - SHIFT_SCALE);

#if SHIFT_HZ == 7
		  /*
		   * When the CPU clock oscillator frequency is not a
		   * power of two in Hz, the SHIFT_HZ is only an
		   * approximate scale factor. In the SunOS kernel, this
		   * results in a PLL gain factor of 1/1.28 = 0.78 what it
		   * should be. In the following code the overall gain is
		   * increased by a factor of 1.25, which results in a
		   * residual error less than 3 percent.
		   */
		  /* Same thing applies for FreeBSD --GAW */
		  if (hz == 100) {
		    if (time_adj < 0)
		      time_adj -= -time_adj >> 2;
		    else
		      time_adj += time_adj >> 2;
		  }
#endif /* SHIFT_HZ */

		  /* XXX - this is really bogus, but can't be fixed until
		     xntpd's idea of the system clock is fixed to know how
		     the user wants leap seconds handled; in the mean time,
		     we assume that users of NTP are running without proper
		     leap second support (this is now the default anyway) */
		  /*
		   * Leap second processing. If in leap-insert state at
		   * the end of the day, the system clock is set back one
		   * second; if in leap-delete state, the system clock is
		   * set ahead one second. The microtime() routine or
		   * external clock driver will insure that reported time
		   * is always monotonic. The ugly divides should be
		   * replaced.
		   */
		  switch (time_state) {

		  case TIME_OK:
		    if (time_status & STA_INS)
		      time_state = TIME_INS;
		    else if (time_status & STA_DEL)
		      time_state = TIME_DEL;
		    break;

		  case TIME_INS:
		    if (newtime.tv_sec % 86400 == 0) {
		      newtime.tv_sec--;
		      time_state = TIME_OOP;
		    }
		    break;

		  case TIME_DEL:
		    if ((newtime.tv_sec + 1) % 86400 == 0) {
		      newtime.tv_sec++;
		      time_state = TIME_WAIT;
		    }
		    break;

		  case TIME_OOP:
		    time_state = TIME_WAIT;
		    break;

		  case TIME_WAIT:
		    if (!(time_status & (STA_INS | STA_DEL)))
		      time_state = TIME_OK;
		  }
		}
		CPU_CLOCKUPDATE(&time, &newtime);
	}

	/*
	 * Process callouts at a very low cpu priority, so we don't keep the
	 * relatively high clock interrupt priority any longer than necessary.
	 */
	if (TAILQ_FIRST(&callwheel[ticks & callwheelmask]) != NULL) {
		if (CLKF_BASEPRI(frame)) {
			/*
			 * Save the overhead of a software interrupt;
			 * it will happen as soon as we return, so do it now.
			 */
			(void)splsoftclock();
			softclock();
		} else
			setsoftclock();
	} else if (softticks + 1 == ticks) {
		++softticks;
	}
}

/*
 * The callout mechanism is based on the work of Adam M. Costello and 
 * George Varghese, published in a technical report entitled "Redesigning
 * the BSD Callout and Timer Facilities" and modified slightly for inclusion
 * in FreeBSD by Justin T. Gibbs.  The original work on the data structures
 * used in this implementation was published by G.Varghese and A. Lauck in
 * the paper "Hashed and Hierarchical Timing Wheels: Data Structures for
 * the Efficient Implementation of a Timer Facility" in the Proceedings of
 * the 11th ACM Annual Symposium on Operating Systems Principles,
 * Austin, Texas Nov 1987.
 */
/*
 * Software (low priority) clock interrupt.
 * Run periodic events from timeout queue.
 */
/*ARGSUSED*/
void
softclock()
{
	register struct callout *c;
	register struct callout_tailq *bucket;
	register int s;
	register int curticks;
	register int steps;	/*
				 * Number of steps taken since
				 * we last allowed interrupts.
				 */

	#ifndef MAX_SOFTCLOCK_STEPS
	#define MAX_SOFTCLOCK_STEPS 100 /* Maximum allowed value of steps. */
	#endif /* MAX_SOFTCLOCK_STEPS */

	steps = 0;
	s = splhigh();
	while (softticks != ticks) {
		softticks++;
		/*
		 * softticks may be modified by hard clock, so cache
		 * it while we work on a given bucket.
		 */
		curticks = softticks;
		bucket = &callwheel[curticks & callwheelmask];
		c = TAILQ_FIRST(bucket);
		while (c) {
			if (c->c_time != curticks) {
				c = TAILQ_NEXT(c, c_links.tqe);
				++steps;
				if (steps >= MAX_SOFTCLOCK_STEPS) {
					nextsoftcheck = c;
					/* Give interrupts a chance. */
					splx(s);
					s = splhigh();
					c = nextsoftcheck;
					steps = 0;
				}
			} else {
				void (*c_func)(void *);
				void *c_arg;

				nextsoftcheck = TAILQ_NEXT(c, c_links.tqe);
				TAILQ_REMOVE(bucket, c, c_links.tqe);
				c_func = c->c_func;
				c_arg = c->c_arg;
				c->c_func = NULL;
				SLIST_INSERT_HEAD(&callfree, c, c_links.sle);
				splx(s);
				c_func(c_arg);
				s = splhigh();
				steps = 0;
				c = nextsoftcheck;
			}
		}
	}
	nextsoftcheck = NULL;
	splx(s);
}

/*
 * timeout --
 *	Execute a function after a specified length of time.
 *
 * untimeout --
 *	Cancel previous timeout function call.
 *
 * callout_handle_init --
 *	Initialize a handle so that using it with untimeout is benign.
 *
 *	See AT&T BCI Driver Reference Manual for specification.  This
 *	implementation differs from that one in that although an 
 *	identification value is returned from timeout, the original
 *	arguments to timeout as well as the identifier are used to
 *	identify entries for untimeout.
 */
struct callout_handle
timeout(ftn, arg, to_ticks)
	timeout_t ftn;
	void *arg;
	register int to_ticks;
{
	int s;
	struct callout *new;
	struct callout_handle handle;

	if (to_ticks <= 0)
		to_ticks = 1;

	/* Lock out the clock. */
	s = splhigh();

	/* Fill in the next free callout structure. */
	new = SLIST_FIRST(&callfree);
	if (new == NULL)
		/* XXX Attempt to malloc first */
		panic("timeout table full");

	SLIST_REMOVE_HEAD(&callfree, c_links.sle);
	new->c_arg = arg;
	new->c_func = ftn;
	new->c_time = ticks + to_ticks;
	TAILQ_INSERT_TAIL(&callwheel[new->c_time & callwheelmask],
			  new, c_links.tqe);

	splx(s);
	handle.callout = new;
	return (handle);
}

void
untimeout(ftn, arg, handle)
	timeout_t ftn;
	void *arg;
	struct callout_handle handle;
{
	register int s;

	/*
	 * Check for a handle that was initialized
	 * by callout_handle_init, but never used
	 * for a real timeout.
	 */
	if (handle.callout == NULL)
		return;

	s = splhigh();
	if ((handle.callout->c_func == ftn)
	 && (handle.callout->c_arg == arg)) {
		if (nextsoftcheck == handle.callout) {
			nextsoftcheck = TAILQ_NEXT(handle.callout, c_links.tqe);
		}
		TAILQ_REMOVE(&callwheel[handle.callout->c_time & callwheelmask],
			     handle.callout, c_links.tqe);
		handle.callout->c_func = NULL;
		SLIST_INSERT_HEAD(&callfree, handle.callout, c_links.sle);
	}
	splx(s);
}

void
callout_handle_init(struct callout_handle *handle)
{
	handle->callout = NULL;
}

void
gettime(struct timeval *tvp)
{
	int s;

	s = splclock();
	/* XXX should use microtime() iff tv_usec is used. */
	*tvp = time;
	splx(s);
}

/*
 * Compute number of hz until specified time.  Used to
 * compute third argument to timeout() from an absolute time.
 */
int
hzto(tv)
	struct timeval *tv;
{
	register unsigned long ticks;
	register long sec, usec;
	int s;

	/*
	 * If the number of usecs in the whole seconds part of the time
	 * difference fits in a long, then the total number of usecs will
	 * fit in an unsigned long.  Compute the total and convert it to
	 * ticks, rounding up and adding 1 to allow for the current tick
	 * to expire.  Rounding also depends on unsigned long arithmetic
	 * to avoid overflow.
	 *
	 * Otherwise, if the number of ticks in the whole seconds part of
	 * the time difference fits in a long, then convert the parts to
	 * ticks separately and add, using similar rounding methods and
	 * overflow avoidance.  This method would work in the previous
	 * case but it is slightly slower and assumes that hz is integral.
	 *
	 * Otherwise, round the time difference down to the maximum
	 * representable value.
	 *
	 * If ints have 32 bits, then the maximum value for any timeout in
	 * 10ms ticks is 248 days.
	 */
	s = splclock();
	sec = tv->tv_sec - time.tv_sec;
	usec = tv->tv_usec - time.tv_usec;
	splx(s);
	if (usec < 0) {
		sec--;
		usec += 1000000;
	}
	if (sec < 0) {
#ifdef DIAGNOSTIC
		printf("hzto: negative time difference %ld sec %ld usec\n",
		       sec, usec);
#endif
		ticks = 1;
	} else if (sec <= LONG_MAX / 1000000)
		ticks = (sec * 1000000 + (unsigned long)usec + (tick - 1))
			/ tick + 1;
	else if (sec <= LONG_MAX / hz)
		ticks = sec * hz
			+ ((unsigned long)usec + (tick - 1)) / tick + 1;
	else
		ticks = LONG_MAX;
	if (ticks > INT_MAX)
		ticks = INT_MAX;
	return (ticks);
}

/*
 * Start profiling on a process.
 *
 * Kernel profiling passes proc0 which never exits and hence
 * keeps the profile clock running constantly.
 */
void
startprofclock(p)
	register struct proc *p;
{
	int s;

	if ((p->p_flag & P_PROFIL) == 0) {
		p->p_flag |= P_PROFIL;
		if (++profprocs == 1 && stathz != 0) {
			s = splstatclock();
			psdiv = pscnt = psratio;
			setstatclockrate(profhz);
			splx(s);
		}
	}
}

/*
 * Stop profiling on a process.
 */
void
stopprofclock(p)
	register struct proc *p;
{
	int s;

	if (p->p_flag & P_PROFIL) {
		p->p_flag &= ~P_PROFIL;
		if (--profprocs == 0 && stathz != 0) {
			s = splstatclock();
			psdiv = pscnt = 1;
			setstatclockrate(stathz);
			splx(s);
		}
	}
}

/*
 * Statistics clock.  Grab profile sample, and if divider reaches 0,
 * do process and kernel statistics.
 */
void
statclock(frame)
	register struct clockframe *frame;
{
#ifdef GPROF
	register struct gmonparam *g;
#endif
	register struct proc *p;
	register int i;
	struct pstats *pstats;
	long rss;
	struct rusage *ru;
	struct vmspace *vm;

	if (CLKF_USERMODE(frame)) {
		p = curproc;
		if (p->p_flag & P_PROFIL)
			addupc_intr(p, CLKF_PC(frame), 1);
#if defined(SMP) && defined(BETTER_CLOCK)
		if (stathz != 0)
			forward_statclock(pscnt);
#endif
		if (--pscnt > 0)
			return;
		/*
		 * Came from user mode; CPU was in user state.
		 * If this process is being profiled record the tick.
		 */
		p->p_uticks++;
		if (p->p_nice > NZERO)
			cp_time[CP_NICE]++;
		else
			cp_time[CP_USER]++;
	} else {
#ifdef GPROF
		/*
		 * Kernel statistics are just like addupc_intr, only easier.
		 */
		g = &_gmonparam;
		if (g->state == GMON_PROF_ON) {
			i = CLKF_PC(frame) - g->lowpc;
			if (i < g->textsize) {
				i /= HISTFRACTION * sizeof(*g->kcount);
				g->kcount[i]++;
			}
		}
#endif
#if defined(SMP) && defined(BETTER_CLOCK)
		if (stathz != 0)
			forward_statclock(pscnt);
#endif
		if (--pscnt > 0)
			return;
		/*
		 * Came from kernel mode, so we were:
		 * - handling an interrupt,
		 * - doing syscall or trap work on behalf of the current
		 *   user process, or
		 * - spinning in the idle loop.
		 * Whichever it is, charge the time as appropriate.
		 * Note that we charge interrupts to the current process,
		 * regardless of whether they are ``for'' that process,
		 * so that we know how much of its real time was spent
		 * in ``non-process'' (i.e., interrupt) work.
		 */
		p = curproc;
		if (CLKF_INTR(frame)) {
			if (p != NULL)
				p->p_iticks++;
			cp_time[CP_INTR]++;
		} else if (p != NULL) {
			p->p_sticks++;
			cp_time[CP_SYS]++;
		} else
			cp_time[CP_IDLE]++;
	}
	pscnt = psdiv;

	/*
	 * We maintain statistics shown by user-level statistics
	 * programs:  the amount of time in each cpu state, and
	 * the amount of time each of DK_NDRIVE ``drives'' is busy.
	 *
	 * XXX	should either run linked list of drives, or (better)
	 *	grab timestamps in the start & done code.
	 */
	for (i = 0; i < DK_NDRIVE; i++)
		if (dk_busy & (1 << i))
			dk_time[i]++;

	/*
	 * 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 by 4.  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 principal 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.
	 */
	if (p != NULL) {
		p->p_cpticks++;
		if (++p->p_estcpu == 0)
			p->p_estcpu--;
		if ((p->p_estcpu & 3) == 0) {
			resetpriority(p);
			if (p->p_priority >= PUSER)
				p->p_priority = p->p_usrpri;
		}

		/* Update resource usage integrals and maximums. */
		if ((pstats = p->p_stats) != NULL &&
		    (ru = &pstats->p_ru) != NULL &&
		    (vm = p->p_vmspace) != NULL) {
			ru->ru_ixrss += vm->vm_tsize * PAGE_SIZE / 1024;
			ru->ru_idrss += vm->vm_dsize * PAGE_SIZE / 1024;
			ru->ru_isrss += vm->vm_ssize * PAGE_SIZE / 1024;
			rss = vm->vm_pmap.pm_stats.resident_count *
			      PAGE_SIZE / 1024;
			if (ru->ru_maxrss < rss)
				ru->ru_maxrss = rss;
        	}
	}
}

/*
 * Return information about system clocks.
 */
static int
sysctl_kern_clockrate SYSCTL_HANDLER_ARGS
{
	struct clockinfo clkinfo;
	/*
	 * Construct clockinfo structure.
	 */
	clkinfo.hz = hz;
	clkinfo.tick = tick;
	clkinfo.tickadj = tickadj;
	clkinfo.profhz = profhz;
	clkinfo.stathz = stathz ? stathz : hz;
	return (sysctl_handle_opaque(oidp, &clkinfo, sizeof clkinfo, req));
}

SYSCTL_PROC(_kern, KERN_CLOCKRATE, clockrate, CTLTYPE_STRUCT|CTLFLAG_RD,
	0, 0, sysctl_kern_clockrate, "S,clockinfo","");

#ifdef PPS_SYNC
/*
 * hardpps() - discipline CPU clock oscillator to external PPS signal
 *
 * This routine is called at each PPS interrupt in order to discipline
 * the CPU clock oscillator to the PPS signal. It measures the PPS phase
 * and leaves it in a handy spot for the hardclock() routine. It
 * integrates successive PPS phase differences and calculates the
 * frequency offset. This is used in hardclock() to discipline the CPU
 * clock oscillator so that intrinsic frequency error is cancelled out.
 * The code requires the caller to capture the time and hardware counter
 * value at the on-time PPS signal transition.
 *
 * Note that, on some Unix systems, this routine runs at an interrupt
 * priority level higher than the timer interrupt routine hardclock().
 * Therefore, the variables used are distinct from the hardclock()
 * variables, except for certain exceptions: The PPS frequency pps_freq
 * and phase pps_offset variables are determined by this routine and
 * updated atomically. The time_tolerance variable can be considered a
 * constant, since it is infrequently changed, and then only when the
 * PPS signal is disabled. The watchdog counter pps_valid is updated
 * once per second by hardclock() and is atomically cleared in this
 * routine.
 */
void
hardpps(tvp, usec)
	struct timeval *tvp;		/* time at PPS */
	long usec;			/* hardware counter at PPS */
{
	long u_usec, v_usec, bigtick;
	long cal_sec, cal_usec;

	/*
	 * An occasional glitch can be produced when the PPS interrupt
	 * occurs in the hardclock() routine before the time variable is
	 * updated. Here the offset is discarded when the difference
	 * between it and the last one is greater than tick/2, but not
	 * if the interval since the first discard exceeds 30 s.
	 */
	time_status |= STA_PPSSIGNAL;
	time_status &= ~(STA_PPSJITTER | STA_PPSWANDER | STA_PPSERROR);
	pps_valid = 0;
	u_usec = -tvp->tv_usec;
	if (u_usec < -500000)
		u_usec += 1000000;
	v_usec = pps_offset - u_usec;
	if (v_usec < 0)
		v_usec = -v_usec;
	if (v_usec > (tick >> 1)) {
		if (pps_glitch > MAXGLITCH) {
			pps_glitch = 0;
			pps_tf[2] = u_usec;
			pps_tf[1] = u_usec;
		} else {
			pps_glitch++;
			u_usec = pps_offset;
		}
	} else
		pps_glitch = 0;

	/*
	 * A three-stage median filter is used to help deglitch the pps
	 * time. The median sample becomes the time offset estimate; the
	 * difference between the other two samples becomes the time
	 * dispersion (jitter) estimate.
	 */
	pps_tf[2] = pps_tf[1];
	pps_tf[1] = pps_tf[0];
	pps_tf[0] = u_usec;
	if (pps_tf[0] > pps_tf[1]) {
		if (pps_tf[1] > pps_tf[2]) {
			pps_offset = pps_tf[1];		/* 0 1 2 */
			v_usec = pps_tf[0] - pps_tf[2];
		} else if (pps_tf[2] > pps_tf[0]) {
			pps_offset = pps_tf[0];		/* 2 0 1 */
			v_usec = pps_tf[2] - pps_tf[1];
		} else {
			pps_offset = pps_tf[2];		/* 0 2 1 */
			v_usec = pps_tf[0] - pps_tf[1];
		}
	} else {
		if (pps_tf[1] < pps_tf[2]) {
			pps_offset = pps_tf[1];		/* 2 1 0 */
			v_usec = pps_tf[2] - pps_tf[0];
		} else  if (pps_tf[2] < pps_tf[0]) {
			pps_offset = pps_tf[0];		/* 1 0 2 */
			v_usec = pps_tf[1] - pps_tf[2];
		} else {
			pps_offset = pps_tf[2];		/* 1 2 0 */
			v_usec = pps_tf[1] - pps_tf[0];
		}
	}
	if (v_usec > MAXTIME)
		pps_jitcnt++;
	v_usec = (v_usec << PPS_AVG) - pps_jitter;
	if (v_usec < 0)
		pps_jitter -= -v_usec >> PPS_AVG;
	else
		pps_jitter += v_usec >> PPS_AVG;
	if (pps_jitter > (MAXTIME >> 1))
		time_status |= STA_PPSJITTER;

	/*
	 * During the calibration interval adjust the starting time when
	 * the tick overflows. At the end of the interval compute the
	 * duration of the interval and the difference of the hardware
	 * counters at the beginning and end of the interval. This code
	 * is deliciously complicated by the fact valid differences may
	 * exceed the value of tick when using long calibration
	 * intervals and small ticks. Note that the counter can be
	 * greater than tick if caught at just the wrong instant, but
	 * the values returned and used here are correct.
	 */
	bigtick = (long)tick << SHIFT_USEC;
	pps_usec -= pps_freq;
	if (pps_usec >= bigtick)
		pps_usec -= bigtick;
	if (pps_usec < 0)
		pps_usec += bigtick;
	pps_time.tv_sec++;
	pps_count++;
	if (pps_count < (1 << pps_shift))
		return;
	pps_count = 0;
	pps_calcnt++;
	u_usec = usec << SHIFT_USEC;
	v_usec = pps_usec - u_usec;
	if (v_usec >= bigtick >> 1)
		v_usec -= bigtick;
	if (v_usec < -(bigtick >> 1))
		v_usec += bigtick;
	if (v_usec < 0)
		v_usec = -(-v_usec >> pps_shift);
	else
		v_usec = v_usec >> pps_shift;
	pps_usec = u_usec;
	cal_sec = tvp->tv_sec;
	cal_usec = tvp->tv_usec;
	cal_sec -= pps_time.tv_sec;
	cal_usec -= pps_time.tv_usec;
	if (cal_usec < 0) {
		cal_usec += 1000000;
		cal_sec--;
	}
	pps_time = *tvp;

	/*
	 * Check for lost interrupts, noise, excessive jitter and
	 * excessive frequency error. The number of timer ticks during
	 * the interval may vary +-1 tick. Add to this a margin of one
	 * tick for the PPS signal jitter and maximum frequency
	 * deviation. If the limits are exceeded, the calibration
	 * interval is reset to the minimum and we start over.
	 */
	u_usec = (long)tick << 1;
	if (!((cal_sec == -1 && cal_usec > (1000000 - u_usec))
	    || (cal_sec == 0 && cal_usec < u_usec))
	    || v_usec > time_tolerance || v_usec < -time_tolerance) {
		pps_errcnt++;
		pps_shift = PPS_SHIFT;
		pps_intcnt = 0;
		time_status |= STA_PPSERROR;
		return;
	}

	/*
	 * A three-stage median filter is used to help deglitch the pps
	 * frequency. The median sample becomes the frequency offset
	 * estimate; the difference between the other two samples
	 * becomes the frequency dispersion (stability) estimate.
	 */
	pps_ff[2] = pps_ff[1];
	pps_ff[1] = pps_ff[0];
	pps_ff[0] = v_usec;
	if (pps_ff[0] > pps_ff[1]) {
		if (pps_ff[1] > pps_ff[2]) {
			u_usec = pps_ff[1];		/* 0 1 2 */
			v_usec = pps_ff[0] - pps_ff[2];
		} else if (pps_ff[2] > pps_ff[0]) {
			u_usec = pps_ff[0];		/* 2 0 1 */
			v_usec = pps_ff[2] - pps_ff[1];
		} else {
			u_usec = pps_ff[2];		/* 0 2 1 */
			v_usec = pps_ff[0] - pps_ff[1];
		}
	} else {
		if (pps_ff[1] < pps_ff[2]) {
			u_usec = pps_ff[1];		/* 2 1 0 */
			v_usec = pps_ff[2] - pps_ff[0];
		} else  if (pps_ff[2] < pps_ff[0]) {
			u_usec = pps_ff[0];		/* 1 0 2 */
			v_usec = pps_ff[1] - pps_ff[2];
		} else {
			u_usec = pps_ff[2];		/* 1 2 0 */
			v_usec = pps_ff[1] - pps_ff[0];
		}
	}

	/*
	 * Here the frequency dispersion (stability) is updated. If it
	 * is less than one-fourth the maximum (MAXFREQ), the frequency
	 * offset is updated as well, but clamped to the tolerance. It
	 * will be processed later by the hardclock() routine.
	 */
	v_usec = (v_usec >> 1) - pps_stabil;
	if (v_usec < 0)
		pps_stabil -= -v_usec >> PPS_AVG;
	else
		pps_stabil += v_usec >> PPS_AVG;
	if (pps_stabil > MAXFREQ >> 2) {
		pps_stbcnt++;
		time_status |= STA_PPSWANDER;
		return;
	}
	if (time_status & STA_PPSFREQ) {
		if (u_usec < 0) {
			pps_freq -= -u_usec >> PPS_AVG;
			if (pps_freq < -time_tolerance)
				pps_freq = -time_tolerance;
			u_usec = -u_usec;
		} else {
			pps_freq += u_usec >> PPS_AVG;
			if (pps_freq > time_tolerance)
				pps_freq = time_tolerance;
		}
	}

	/*
	 * Here the calibration interval is adjusted. If the maximum
	 * time difference is greater than tick / 4, reduce the interval
	 * by half. If this is not the case for four consecutive
	 * intervals, double the interval.
	 */
	if (u_usec << pps_shift > bigtick >> 2) {
		pps_intcnt = 0;
		if (pps_shift > PPS_SHIFT)
			pps_shift--;
	} else if (pps_intcnt >= 4) {
		pps_intcnt = 0;
		if (pps_shift < PPS_SHIFTMAX)
			pps_shift++;
	} else
		pps_intcnt++;
}
#endif /* PPS_SYNC */