xref: /freebsd-10.0-release/sys/kern/kern_timeout.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.
 * 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.
 *
 *	From: @(#)kern_clock.c	8.5 (Berkeley) 1/21/94
 */

#include <sys/cdefs.h>
__FBSDID("$FreeBSD: head/sys/kern/kern_timeout.c 248032 2013-03-08 10:37:17Z andre $");

#include "opt_callout_profiling.h"
#include "opt_kdtrace.h"
#if defined(__arm__)
#include "opt_timer.h"
#endif

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/bus.h>
#include <sys/callout.h>
#include <sys/file.h>
#include <sys/interrupt.h>
#include <sys/kernel.h>
#include <sys/ktr.h>
#include <sys/lock.h>
#include <sys/malloc.h>
#include <sys/mutex.h>
#include <sys/proc.h>
#include <sys/sdt.h>
#include <sys/sleepqueue.h>
#include <sys/sysctl.h>
#include <sys/smp.h>

#ifdef SMP
#include <machine/cpu.h>
#endif

#ifndef NO_EVENTTIMERS
DPCPU_DECLARE(sbintime_t, hardclocktime);
#endif

SDT_PROVIDER_DEFINE(callout_execute);
SDT_PROBE_DEFINE(callout_execute, kernel, , callout_start, callout-start);
SDT_PROBE_ARGTYPE(callout_execute, kernel, , callout_start, 0,
    "struct callout *");
SDT_PROBE_DEFINE(callout_execute, kernel, , callout_end, callout-end);
SDT_PROBE_ARGTYPE(callout_execute, kernel, , callout_end, 0,
    "struct callout *");

#ifdef CALLOUT_PROFILING
static int avg_depth;
SYSCTL_INT(_debug, OID_AUTO, to_avg_depth, CTLFLAG_RD, &avg_depth, 0,
    "Average number of items examined per softclock call. Units = 1/1000");
static int avg_gcalls;
SYSCTL_INT(_debug, OID_AUTO, to_avg_gcalls, CTLFLAG_RD, &avg_gcalls, 0,
    "Average number of Giant callouts made per softclock call. Units = 1/1000");
static int avg_lockcalls;
SYSCTL_INT(_debug, OID_AUTO, to_avg_lockcalls, CTLFLAG_RD, &avg_lockcalls, 0,
    "Average number of lock callouts made per softclock call. Units = 1/1000");
static int avg_mpcalls;
SYSCTL_INT(_debug, OID_AUTO, to_avg_mpcalls, CTLFLAG_RD, &avg_mpcalls, 0,
    "Average number of MP callouts made per softclock call. Units = 1/1000");
static int avg_depth_dir;
SYSCTL_INT(_debug, OID_AUTO, to_avg_depth_dir, CTLFLAG_RD, &avg_depth_dir, 0,
    "Average number of direct callouts examined per callout_process call. "
    "Units = 1/1000");
static int avg_lockcalls_dir;
SYSCTL_INT(_debug, OID_AUTO, to_avg_lockcalls_dir, CTLFLAG_RD,
    &avg_lockcalls_dir, 0, "Average number of lock direct callouts made per "
    "callout_process call. Units = 1/1000");
static int avg_mpcalls_dir;
SYSCTL_INT(_debug, OID_AUTO, to_avg_mpcalls_dir, CTLFLAG_RD, &avg_mpcalls_dir,
    0, "Average number of MP direct callouts made per callout_process call. "
    "Units = 1/1000");
#endif

static int ncallout;
SYSCTL_INT(_kern, OID_AUTO, ncallout, CTLFLAG_RDTUN, &ncallout, 0,
    "Number of entries in callwheel and size of timeout() preallocation");

/*
 * TODO:
 *	allocate more timeout table slots when table overflows.
 */
u_int callwheelsize, callwheelmask;

/*
 * The callout cpu exec entities represent informations necessary for
 * describing the state of callouts currently running on the CPU and the ones
 * necessary for migrating callouts to the new callout cpu. In particular,
 * the first entry of the array cc_exec_entity holds informations for callout
 * running in SWI thread context, while the second one holds informations
 * for callout running directly from hardware interrupt context.
 * The cached informations are very important for deferring migration when
 * the migrating callout is already running.
 */
struct cc_exec {
	struct callout		*cc_next;
	struct callout		*cc_curr;
#ifdef SMP
	void			(*ce_migration_func)(void *);
	void			*ce_migration_arg;
	int			ce_migration_cpu;
	sbintime_t		ce_migration_time;
#endif
	bool			cc_cancel;
	bool			cc_waiting;
};

/*
 * There is one struct callout_cpu per cpu, holding all relevant
 * state for the callout processing thread on the individual CPU.
 */
struct callout_cpu {
	struct mtx_padalign	cc_lock;
	struct cc_exec 		cc_exec_entity[2];
	struct callout		*cc_callout;
	struct callout_list	*cc_callwheel;
	struct callout_tailq	cc_expireq;
	struct callout_slist	cc_callfree;
	sbintime_t		cc_firstevent;
	sbintime_t		cc_lastscan;
	void			*cc_cookie;
	u_int			cc_bucket;
};

#define	cc_exec_curr		cc_exec_entity[0].cc_curr
#define	cc_exec_next		cc_exec_entity[0].cc_next
#define	cc_exec_cancel		cc_exec_entity[0].cc_cancel
#define	cc_exec_waiting		cc_exec_entity[0].cc_waiting
#define	cc_exec_curr_dir	cc_exec_entity[1].cc_curr
#define	cc_exec_next_dir	cc_exec_entity[1].cc_next
#define	cc_exec_cancel_dir	cc_exec_entity[1].cc_cancel
#define	cc_exec_waiting_dir	cc_exec_entity[1].cc_waiting

#ifdef SMP
#define	cc_migration_func	cc_exec_entity[0].ce_migration_func
#define	cc_migration_arg	cc_exec_entity[0].ce_migration_arg
#define	cc_migration_cpu	cc_exec_entity[0].ce_migration_cpu
#define	cc_migration_time	cc_exec_entity[0].ce_migration_time
#define	cc_migration_func_dir	cc_exec_entity[1].ce_migration_func
#define	cc_migration_arg_dir	cc_exec_entity[1].ce_migration_arg
#define	cc_migration_cpu_dir	cc_exec_entity[1].ce_migration_cpu
#define	cc_migration_time_dir	cc_exec_entity[1].ce_migration_time

struct callout_cpu cc_cpu[MAXCPU];
#define	CPUBLOCK	MAXCPU
#define	CC_CPU(cpu)	(&cc_cpu[(cpu)])
#define	CC_SELF()	CC_CPU(PCPU_GET(cpuid))
#else
struct callout_cpu cc_cpu;
#define	CC_CPU(cpu)	&cc_cpu
#define	CC_SELF()	&cc_cpu
#endif
#define	CC_LOCK(cc)	mtx_lock_spin(&(cc)->cc_lock)
#define	CC_UNLOCK(cc)	mtx_unlock_spin(&(cc)->cc_lock)
#define	CC_LOCK_ASSERT(cc)	mtx_assert(&(cc)->cc_lock, MA_OWNED)

static int timeout_cpu;

static void	callout_cpu_init(struct callout_cpu *cc);
static void	softclock_call_cc(struct callout *c, struct callout_cpu *cc,
#ifdef CALLOUT_PROFILING
		    int *mpcalls, int *lockcalls, int *gcalls,
#endif
		    int direct);

static MALLOC_DEFINE(M_CALLOUT, "callout", "Callout datastructures");

/**
 * Locked by cc_lock:
 *   cc_curr         - If a callout is in progress, it is cc_curr.
 *                     If cc_curr is non-NULL, threads waiting in
 *                     callout_drain() will be woken up as soon as the
 *                     relevant callout completes.
 *   cc_cancel       - Changing to 1 with both callout_lock and cc_lock held
 *                     guarantees that the current callout will not run.
 *                     The softclock() function sets this to 0 before it
 *                     drops callout_lock to acquire c_lock, and it calls
 *                     the handler only if curr_cancelled is still 0 after
 *                     cc_lock is successfully acquired.
 *   cc_waiting      - If a thread is waiting in callout_drain(), then
 *                     callout_wait is nonzero.  Set only when
 *                     cc_curr is non-NULL.
 */

/*
 * Resets the execution entity tied to a specific callout cpu.
 */
static void
cc_cce_cleanup(struct callout_cpu *cc, int direct)
{

	cc->cc_exec_entity[direct].cc_curr = NULL;
	cc->cc_exec_entity[direct].cc_next = NULL;
	cc->cc_exec_entity[direct].cc_cancel = false;
	cc->cc_exec_entity[direct].cc_waiting = false;
#ifdef SMP
	cc->cc_exec_entity[direct].ce_migration_cpu = CPUBLOCK;
	cc->cc_exec_entity[direct].ce_migration_time = 0;
	cc->cc_exec_entity[direct].ce_migration_func = NULL;
	cc->cc_exec_entity[direct].ce_migration_arg = NULL;
#endif
}

/*
 * Checks if migration is requested by a specific callout cpu.
 */
static int
cc_cce_migrating(struct callout_cpu *cc, int direct)
{

#ifdef SMP
	return (cc->cc_exec_entity[direct].ce_migration_cpu != CPUBLOCK);
#else
	return (0);
#endif
}

/*
 * Kernel low level callwheel initialization
 * called on cpu0 during kernel startup.
 */
static void
callout_callwheel_init(void *dummy)
{
	struct callout_cpu *cc;

	/*
	 * Calculate the size of the callout wheel and the preallocated
	 * timeout() structures.
	 */
	ncallout = imin(16 + maxproc + maxfiles, 18508);
	TUNABLE_INT_FETCH("kern.ncallout", &ncallout);

	/*
	 * Calculate callout wheel size, should be next power of two higher
	 * than 'ncallout'.
	 */
	callwheelsize = 1 << fls(ncallout);
	callwheelmask = callwheelsize - 1;

	/*
	 * Only cpu0 handles timeout(9) and receives a preallocation.
	 *
	 * XXX: Once all timeout(9) consumers are converted this can
	 * be removed.
	 */
	timeout_cpu = PCPU_GET(cpuid);
	cc = CC_CPU(timeout_cpu);
	cc->cc_callout = malloc(ncallout * sizeof(struct callout),
	    M_CALLOUT, M_WAITOK);
	callout_cpu_init(cc);
}
SYSINIT(callwheel_init, SI_SUB_CPU, SI_ORDER_ANY, callout_callwheel_init, NULL);

/*
 * Initialize the per-cpu callout structures.
 */
static void
callout_cpu_init(struct callout_cpu *cc)
{
	struct callout *c;
	int i;

	mtx_init(&cc->cc_lock, "callout", NULL, MTX_SPIN | MTX_RECURSE);
	SLIST_INIT(&cc->cc_callfree);
	cc->cc_callwheel = malloc(sizeof(struct callout_tailq) * callwheelsize,
	    M_CALLOUT, M_WAITOK);
	for (i = 0; i < callwheelsize; i++)
		LIST_INIT(&cc->cc_callwheel[i]);
	TAILQ_INIT(&cc->cc_expireq);
	cc->cc_firstevent = INT64_MAX;
	for (i = 0; i < 2; i++)
		cc_cce_cleanup(cc, i);
	if (cc->cc_callout == NULL)	/* Only cpu0 handles timeout(9) */
		return;
	for (i = 0; i < ncallout; i++) {
		c = &cc->cc_callout[i];
		callout_init(c, 0);
		c->c_flags = CALLOUT_LOCAL_ALLOC;
		SLIST_INSERT_HEAD(&cc->cc_callfree, c, c_links.sle);
	}
}

#ifdef SMP
/*
 * Switches the cpu tied to a specific callout.
 * The function expects a locked incoming callout cpu and returns with
 * locked outcoming callout cpu.
 */
static struct callout_cpu *
callout_cpu_switch(struct callout *c, struct callout_cpu *cc, int new_cpu)
{
	struct callout_cpu *new_cc;

	MPASS(c != NULL && cc != NULL);
	CC_LOCK_ASSERT(cc);

	/*
	 * Avoid interrupts and preemption firing after the callout cpu
	 * is blocked in order to avoid deadlocks as the new thread
	 * may be willing to acquire the callout cpu lock.
	 */
	c->c_cpu = CPUBLOCK;
	spinlock_enter();
	CC_UNLOCK(cc);
	new_cc = CC_CPU(new_cpu);
	CC_LOCK(new_cc);
	spinlock_exit();
	c->c_cpu = new_cpu;
	return (new_cc);
}
#endif

/*
 * Start standard softclock thread.
 */
static void
start_softclock(void *dummy)
{
	struct callout_cpu *cc;
#ifdef SMP
	int cpu;
#endif

	cc = CC_CPU(timeout_cpu);
	if (swi_add(&clk_intr_event, "clock", softclock, cc, SWI_CLOCK,
	    INTR_MPSAFE, &cc->cc_cookie))
		panic("died while creating standard software ithreads");
#ifdef SMP
	CPU_FOREACH(cpu) {
		if (cpu == timeout_cpu)
			continue;
		cc = CC_CPU(cpu);
		cc->cc_callout = NULL;	/* Only cpu0 handles timeout(9). */
		callout_cpu_init(cc);
		if (swi_add(NULL, "clock", softclock, cc, SWI_CLOCK,
		    INTR_MPSAFE, &cc->cc_cookie))
			panic("died while creating standard software ithreads");
	}
#endif
}
SYSINIT(start_softclock, SI_SUB_SOFTINTR, SI_ORDER_FIRST, start_softclock, NULL);

#define	CC_HASH_SHIFT	8

static inline u_int
callout_hash(sbintime_t sbt)
{

	return (sbt >> (32 - CC_HASH_SHIFT));
}

static inline u_int
callout_get_bucket(sbintime_t sbt)
{

	return (callout_hash(sbt) & callwheelmask);
}

void
callout_process(sbintime_t now)
{
	struct callout *tmp, *tmpn;
	struct callout_cpu *cc;
	struct callout_list *sc;
	sbintime_t first, last, max, tmp_max;
	uint32_t lookahead;
	u_int firstb, lastb, nowb;
#ifdef CALLOUT_PROFILING
	int depth_dir = 0, mpcalls_dir = 0, lockcalls_dir = 0;
#endif

	cc = CC_SELF();
	mtx_lock_spin_flags(&cc->cc_lock, MTX_QUIET);

	/* Compute the buckets of the last scan and present times. */
	firstb = callout_hash(cc->cc_lastscan);
	cc->cc_lastscan = now;
	nowb = callout_hash(now);

	/* Compute the last bucket and minimum time of the bucket after it. */
	if (nowb == firstb)
		lookahead = (SBT_1S / 16);
	else if (nowb - firstb == 1)
		lookahead = (SBT_1S / 8);
	else
		lookahead = (SBT_1S / 2);
	first = last = now;
	first += (lookahead / 2);
	last += lookahead;
	last &= (0xffffffffffffffffLLU << (32 - CC_HASH_SHIFT));
	lastb = callout_hash(last) - 1;
	max = last;

	/*
	 * Check if we wrapped around the entire wheel from the last scan.
	 * In case, we need to scan entirely the wheel for pending callouts.
	 */
	if (lastb - firstb >= callwheelsize) {
		lastb = firstb + callwheelsize - 1;
		if (nowb - firstb >= callwheelsize)
			nowb = lastb;
	}

	/* Iterate callwheel from firstb to nowb and then up to lastb. */
	do {
		sc = &cc->cc_callwheel[firstb & callwheelmask];
		tmp = LIST_FIRST(sc);
		while (tmp != NULL) {
			/* Run the callout if present time within allowed. */
			if (tmp->c_time <= now) {
				/*
				 * Consumer told us the callout may be run
				 * directly from hardware interrupt context.
				 */
				if (tmp->c_flags & CALLOUT_DIRECT) {
#ifdef CALLOUT_PROFILING
					++depth_dir;
#endif
					cc->cc_exec_next_dir =
					    LIST_NEXT(tmp, c_links.le);
					cc->cc_bucket = firstb & callwheelmask;
					LIST_REMOVE(tmp, c_links.le);
					softclock_call_cc(tmp, cc,
#ifdef CALLOUT_PROFILING
					    &mpcalls_dir, &lockcalls_dir, NULL,
#endif
					    1);
					tmp = cc->cc_exec_next_dir;
				} else {
					tmpn = LIST_NEXT(tmp, c_links.le);
					LIST_REMOVE(tmp, c_links.le);
					TAILQ_INSERT_TAIL(&cc->cc_expireq,
					    tmp, c_links.tqe);
					tmp->c_flags |= CALLOUT_PROCESSED;
					tmp = tmpn;
				}
				continue;
			}
			/* Skip events from distant future. */
			if (tmp->c_time >= max)
				goto next;
			/*
			 * Event minimal time is bigger than present maximal
			 * time, so it cannot be aggregated.
			 */
			if (tmp->c_time > last) {
				lastb = nowb;
				goto next;
			}
			/* Update first and last time, respecting this event. */
			if (tmp->c_time < first)
				first = tmp->c_time;
			tmp_max = tmp->c_time + tmp->c_precision;
			if (tmp_max < last)
				last = tmp_max;
next:
			tmp = LIST_NEXT(tmp, c_links.le);
		}
		/* Proceed with the next bucket. */
		firstb++;
		/*
		 * Stop if we looked after present time and found
		 * some event we can't execute at now.
		 * Stop if we looked far enough into the future.
		 */
	} while (((int)(firstb - lastb)) <= 0);
	cc->cc_firstevent = last;
#ifndef NO_EVENTTIMERS
	cpu_new_callout(curcpu, last, first);
#endif
#ifdef CALLOUT_PROFILING
	avg_depth_dir += (depth_dir * 1000 - avg_depth_dir) >> 8;
	avg_mpcalls_dir += (mpcalls_dir * 1000 - avg_mpcalls_dir) >> 8;
	avg_lockcalls_dir += (lockcalls_dir * 1000 - avg_lockcalls_dir) >> 8;
#endif
	mtx_unlock_spin_flags(&cc->cc_lock, MTX_QUIET);
	/*
	 * swi_sched acquires the thread lock, so we don't want to call it
	 * with cc_lock held; incorrect locking order.
	 */
	if (!TAILQ_EMPTY(&cc->cc_expireq))
		swi_sched(cc->cc_cookie, 0);
}

static struct callout_cpu *
callout_lock(struct callout *c)
{
	struct callout_cpu *cc;
	int cpu;

	for (;;) {
		cpu = c->c_cpu;
#ifdef SMP
		if (cpu == CPUBLOCK) {
			while (c->c_cpu == CPUBLOCK)
				cpu_spinwait();
			continue;
		}
#endif
		cc = CC_CPU(cpu);
		CC_LOCK(cc);
		if (cpu == c->c_cpu)
			break;
		CC_UNLOCK(cc);
	}
	return (cc);
}

static void
callout_cc_add(struct callout *c, struct callout_cpu *cc,
    sbintime_t sbt, sbintime_t precision, void (*func)(void *),
    void *arg, int cpu, int flags)
{
	int bucket;

	CC_LOCK_ASSERT(cc);
	if (sbt < cc->cc_lastscan)
		sbt = cc->cc_lastscan;
	c->c_arg = arg;
	c->c_flags |= (CALLOUT_ACTIVE | CALLOUT_PENDING);
	if (flags & C_DIRECT_EXEC)
		c->c_flags |= CALLOUT_DIRECT;
	c->c_flags &= ~CALLOUT_PROCESSED;
	c->c_func = func;
	c->c_time = sbt;
	c->c_precision = precision;
	bucket = callout_get_bucket(c->c_time);
	CTR3(KTR_CALLOUT, "precision set for %p: %d.%08x",
	    c, (int)(c->c_precision >> 32),
	    (u_int)(c->c_precision & 0xffffffff));
	LIST_INSERT_HEAD(&cc->cc_callwheel[bucket], c, c_links.le);
	if (cc->cc_bucket == bucket)
		cc->cc_exec_next_dir = c;
#ifndef NO_EVENTTIMERS
	/*
	 * Inform the eventtimers(4) subsystem there's a new callout
	 * that has been inserted, but only if really required.
	 */
	sbt = c->c_time + c->c_precision;
	if (sbt < cc->cc_firstevent) {
		cc->cc_firstevent = sbt;
		cpu_new_callout(cpu, sbt, c->c_time);
	}
#endif
}

static void
callout_cc_del(struct callout *c, struct callout_cpu *cc)
{

	if ((c->c_flags & CALLOUT_LOCAL_ALLOC) == 0)
		return;
	c->c_func = NULL;
	SLIST_INSERT_HEAD(&cc->cc_callfree, c, c_links.sle);
}

static void
softclock_call_cc(struct callout *c, struct callout_cpu *cc,
#ifdef CALLOUT_PROFILING
    int *mpcalls, int *lockcalls, int *gcalls,
#endif
    int direct)
{
	void (*c_func)(void *);
	void *c_arg;
	struct lock_class *class;
	struct lock_object *c_lock;
	int c_flags, sharedlock;
#ifdef SMP
	struct callout_cpu *new_cc;
	void (*new_func)(void *);
	void *new_arg;
	int flags, new_cpu;
	sbintime_t new_time;
#endif
#if defined(DIAGNOSTIC) || defined(CALLOUT_PROFILING)
	sbintime_t sbt1, sbt2;
	struct timespec ts2;
	static sbintime_t maxdt = 2 * SBT_1MS;	/* 2 msec */
	static timeout_t *lastfunc;
#endif

	KASSERT((c->c_flags & (CALLOUT_PENDING | CALLOUT_ACTIVE)) ==
	    (CALLOUT_PENDING | CALLOUT_ACTIVE),
	    ("softclock_call_cc: pend|act %p %x", c, c->c_flags));
	class = (c->c_lock != NULL) ? LOCK_CLASS(c->c_lock) : NULL;
	sharedlock = (c->c_flags & CALLOUT_SHAREDLOCK) ? 0 : 1;
	c_lock = c->c_lock;
	c_func = c->c_func;
	c_arg = c->c_arg;
	c_flags = c->c_flags;
	if (c->c_flags & CALLOUT_LOCAL_ALLOC)
		c->c_flags = CALLOUT_LOCAL_ALLOC;
	else
		c->c_flags &= ~CALLOUT_PENDING;
	cc->cc_exec_entity[direct].cc_curr = c;
	cc->cc_exec_entity[direct].cc_cancel = false;
	CC_UNLOCK(cc);
	if (c_lock != NULL) {
		class->lc_lock(c_lock, sharedlock);
		/*
		 * The callout may have been cancelled
		 * while we switched locks.
		 */
		if (cc->cc_exec_entity[direct].cc_cancel) {
			class->lc_unlock(c_lock);
			goto skip;
		}
		/* The callout cannot be stopped now. */
		cc->cc_exec_entity[direct].cc_cancel = true;
		if (c_lock == &Giant.lock_object) {
#ifdef CALLOUT_PROFILING
			(*gcalls)++;
#endif
			CTR3(KTR_CALLOUT, "callout giant %p func %p arg %p",
			    c, c_func, c_arg);
		} else {
#ifdef CALLOUT_PROFILING
			(*lockcalls)++;
#endif
			CTR3(KTR_CALLOUT, "callout lock %p func %p arg %p",
			    c, c_func, c_arg);
		}
	} else {
#ifdef CALLOUT_PROFILING
		(*mpcalls)++;
#endif
		CTR3(KTR_CALLOUT, "callout %p func %p arg %p",
		    c, c_func, c_arg);
	}
#if defined(DIAGNOSTIC) || defined(CALLOUT_PROFILING)
	sbt1 = sbinuptime();
#endif
	THREAD_NO_SLEEPING();
	SDT_PROBE(callout_execute, kernel, , callout_start, c, 0, 0, 0, 0);
	c_func(c_arg);
	SDT_PROBE(callout_execute, kernel, , callout_end, c, 0, 0, 0, 0);
	THREAD_SLEEPING_OK();
#if defined(DIAGNOSTIC) || defined(CALLOUT_PROFILING)
	sbt2 = sbinuptime();
	sbt2 -= sbt1;
	if (sbt2 > maxdt) {
		if (lastfunc != c_func || sbt2 > maxdt * 2) {
			ts2 = sbttots(sbt2);
			printf(
		"Expensive timeout(9) function: %p(%p) %jd.%09ld s\n",
			    c_func, c_arg, (intmax_t)ts2.tv_sec, ts2.tv_nsec);
		}
		maxdt = sbt2;
		lastfunc = c_func;
	}
#endif
	CTR1(KTR_CALLOUT, "callout %p finished", c);
	if ((c_flags & CALLOUT_RETURNUNLOCKED) == 0)
		class->lc_unlock(c_lock);
skip:
	CC_LOCK(cc);
	KASSERT(cc->cc_exec_entity[direct].cc_curr == c, ("mishandled cc_curr"));
	cc->cc_exec_entity[direct].cc_curr = NULL;
	if (cc->cc_exec_entity[direct].cc_waiting) {
		/*
		 * There is someone waiting for the
		 * callout to complete.
		 * If the callout was scheduled for
		 * migration just cancel it.
		 */
		if (cc_cce_migrating(cc, direct)) {
			cc_cce_cleanup(cc, direct);

			/*
			 * It should be assert here that the callout is not
			 * destroyed but that is not easy.
			 */
			c->c_flags &= ~CALLOUT_DFRMIGRATION;
		}
		cc->cc_exec_entity[direct].cc_waiting = false;
		CC_UNLOCK(cc);
		wakeup(&cc->cc_exec_entity[direct].cc_waiting);
		CC_LOCK(cc);
	} else if (cc_cce_migrating(cc, direct)) {
		KASSERT((c_flags & CALLOUT_LOCAL_ALLOC) == 0,
		    ("Migrating legacy callout %p", c));
#ifdef SMP
		/*
		 * If the callout was scheduled for
		 * migration just perform it now.
		 */
		new_cpu = cc->cc_exec_entity[direct].ce_migration_cpu;
		new_time = cc->cc_exec_entity[direct].ce_migration_time;
		new_func = cc->cc_exec_entity[direct].ce_migration_func;
		new_arg = cc->cc_exec_entity[direct].ce_migration_arg;
		cc_cce_cleanup(cc, direct);

		/*
		 * It should be assert here that the callout is not destroyed
		 * but that is not easy.
		 *
		 * As first thing, handle deferred callout stops.
		 */
		if ((c->c_flags & CALLOUT_DFRMIGRATION) == 0) {
			CTR3(KTR_CALLOUT,
			     "deferred cancelled %p func %p arg %p",
			     c, new_func, new_arg);
			callout_cc_del(c, cc);
			return;
		}
		c->c_flags &= ~CALLOUT_DFRMIGRATION;

		new_cc = callout_cpu_switch(c, cc, new_cpu);
		flags = (direct) ? C_DIRECT_EXEC : 0;
		callout_cc_add(c, new_cc, new_time, c->c_precision, new_func,
		    new_arg, new_cpu, flags);
		CC_UNLOCK(new_cc);
		CC_LOCK(cc);
#else
		panic("migration should not happen");
#endif
	}
	/*
	 * If the current callout is locally allocated (from
	 * timeout(9)) then put it on the freelist.
	 *
	 * Note: we need to check the cached copy of c_flags because
	 * if it was not local, then it's not safe to deref the
	 * callout pointer.
	 */
	KASSERT((c_flags & CALLOUT_LOCAL_ALLOC) == 0 ||
	    c->c_flags == CALLOUT_LOCAL_ALLOC,
	    ("corrupted callout"));
	if (c_flags & CALLOUT_LOCAL_ALLOC)
		callout_cc_del(c, cc);
}

/*
 * 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 T. 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.
 */
void
softclock(void *arg)
{
	struct callout_cpu *cc;
	struct callout *c;
#ifdef CALLOUT_PROFILING
	int depth = 0, gcalls = 0, lockcalls = 0, mpcalls = 0;
#endif

	cc = (struct callout_cpu *)arg;
	CC_LOCK(cc);
	while ((c = TAILQ_FIRST(&cc->cc_expireq)) != NULL) {
		TAILQ_REMOVE(&cc->cc_expireq, c, c_links.tqe);
		softclock_call_cc(c, cc,
#ifdef CALLOUT_PROFILING
		    &mpcalls, &lockcalls, &gcalls,
#endif
		    0);
#ifdef CALLOUT_PROFILING
		++depth;
#endif
	}
#ifdef CALLOUT_PROFILING
	avg_depth += (depth * 1000 - avg_depth) >> 8;
	avg_mpcalls += (mpcalls * 1000 - avg_mpcalls) >> 8;
	avg_lockcalls += (lockcalls * 1000 - avg_lockcalls) >> 8;
	avg_gcalls += (gcalls * 1000 - avg_gcalls) >> 8;
#endif
	CC_UNLOCK(cc);
}

/*
 * 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;
	int to_ticks;
{
	struct callout_cpu *cc;
	struct callout *new;
	struct callout_handle handle;

	cc = CC_CPU(timeout_cpu);
	CC_LOCK(cc);
	/* Fill in the next free callout structure. */
	new = SLIST_FIRST(&cc->cc_callfree);
	if (new == NULL)
		/* XXX Attempt to malloc first */
		panic("timeout table full");
	SLIST_REMOVE_HEAD(&cc->cc_callfree, c_links.sle);
	callout_reset(new, to_ticks, ftn, arg);
	handle.callout = new;
	CC_UNLOCK(cc);

	return (handle);
}

void
untimeout(ftn, arg, handle)
	timeout_t *ftn;
	void *arg;
	struct callout_handle handle;
{
	struct callout_cpu *cc;

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

	cc = callout_lock(handle.callout);
	if (handle.callout->c_func == ftn && handle.callout->c_arg == arg)
		callout_stop(handle.callout);
	CC_UNLOCK(cc);
}

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

/*
 * New interface; clients allocate their own callout structures.
 *
 * callout_reset() - establish or change a timeout
 * callout_stop() - disestablish a timeout
 * callout_init() - initialize a callout structure so that it can
 *	safely be passed to callout_reset() and callout_stop()
 *
 * <sys/callout.h> defines three convenience macros:
 *
 * callout_active() - returns truth if callout has not been stopped,
 *	drained, or deactivated since the last time the callout was
 *	reset.
 * callout_pending() - returns truth if callout is still waiting for timeout
 * callout_deactivate() - marks the callout as having been serviced
 */
int
callout_reset_sbt_on(struct callout *c, sbintime_t sbt, sbintime_t precision,
    void (*ftn)(void *), void *arg, int cpu, int flags)
{
	sbintime_t to_sbt, pr;
	struct callout_cpu *cc;
	int cancelled, direct;

	cancelled = 0;
	if (flags & C_ABSOLUTE) {
		to_sbt = sbt;
	} else {
		if ((flags & C_HARDCLOCK) && (sbt < tick_sbt))
			sbt = tick_sbt;
		if ((flags & C_HARDCLOCK) ||
#ifdef NO_EVENTTIMERS
		    sbt >= sbt_timethreshold) {
			to_sbt = getsbinuptime();

			/* Add safety belt for the case of hz > 1000. */
			to_sbt += tc_tick_sbt - tick_sbt;
#else
		    sbt >= sbt_tickthreshold) {
			/*
			 * Obtain the time of the last hardclock() call on
			 * this CPU directly from the kern_clocksource.c.
			 * This value is per-CPU, but it is equal for all
			 * active ones.
			 */
#ifdef __LP64__
			to_sbt = DPCPU_GET(hardclocktime);
#else
			spinlock_enter();
			to_sbt = DPCPU_GET(hardclocktime);
			spinlock_exit();
#endif
#endif
			if ((flags & C_HARDCLOCK) == 0)
				to_sbt += tick_sbt;
		} else
			to_sbt = sbinuptime();
		to_sbt += sbt;
		pr = ((C_PRELGET(flags) < 0) ? sbt >> tc_precexp :
		    sbt >> C_PRELGET(flags));
		if (pr > precision)
			precision = pr;
	}
	/*
	 * Don't allow migration of pre-allocated callouts lest they
	 * become unbalanced.
	 */
	if (c->c_flags & CALLOUT_LOCAL_ALLOC)
		cpu = c->c_cpu;
	direct = (c->c_flags & CALLOUT_DIRECT) != 0;
	KASSERT(!direct || c->c_lock == NULL,
	    ("%s: direct callout %p has lock", __func__, c));
	cc = callout_lock(c);
	if (cc->cc_exec_entity[direct].cc_curr == c) {
		/*
		 * We're being asked to reschedule a callout which is
		 * currently in progress.  If there is a lock then we
		 * can cancel the callout if it has not really started.
		 */
		if (c->c_lock != NULL && !cc->cc_exec_entity[direct].cc_cancel)
			cancelled = cc->cc_exec_entity[direct].cc_cancel = true;
		if (cc->cc_exec_entity[direct].cc_waiting) {
			/*
			 * Someone has called callout_drain to kill this
			 * callout.  Don't reschedule.
			 */
			CTR4(KTR_CALLOUT, "%s %p func %p arg %p",
			    cancelled ? "cancelled" : "failed to cancel",
			    c, c->c_func, c->c_arg);
			CC_UNLOCK(cc);
			return (cancelled);
		}
	}
	if (c->c_flags & CALLOUT_PENDING) {
		if ((c->c_flags & CALLOUT_PROCESSED) == 0) {
			if (cc->cc_exec_next_dir == c)
				cc->cc_exec_next_dir = LIST_NEXT(c, c_links.le);
			LIST_REMOVE(c, c_links.le);
		} else
			TAILQ_REMOVE(&cc->cc_expireq, c, c_links.tqe);
		cancelled = 1;
		c->c_flags &= ~(CALLOUT_ACTIVE | CALLOUT_PENDING);
	}

#ifdef SMP
	/*
	 * If the callout must migrate try to perform it immediately.
	 * If the callout is currently running, just defer the migration
	 * to a more appropriate moment.
	 */
	if (c->c_cpu != cpu) {
		if (cc->cc_exec_entity[direct].cc_curr == c) {
			cc->cc_exec_entity[direct].ce_migration_cpu = cpu;
			cc->cc_exec_entity[direct].ce_migration_time
			    = to_sbt;
			cc->cc_exec_entity[direct].ce_migration_func = ftn;
			cc->cc_exec_entity[direct].ce_migration_arg = arg;
			c->c_flags |= CALLOUT_DFRMIGRATION;
			CTR6(KTR_CALLOUT,
		    "migration of %p func %p arg %p in %d.%08x to %u deferred",
			    c, c->c_func, c->c_arg, (int)(to_sbt >> 32),
			    (u_int)(to_sbt & 0xffffffff), cpu);
			CC_UNLOCK(cc);
			return (cancelled);
		}
		cc = callout_cpu_switch(c, cc, cpu);
	}
#endif

	callout_cc_add(c, cc, to_sbt, precision, ftn, arg, cpu, flags);
	CTR6(KTR_CALLOUT, "%sscheduled %p func %p arg %p in %d.%08x",
	    cancelled ? "re" : "", c, c->c_func, c->c_arg, (int)(to_sbt >> 32),
	    (u_int)(to_sbt & 0xffffffff));
	CC_UNLOCK(cc);

	return (cancelled);
}

/*
 * Common idioms that can be optimized in the future.
 */
int
callout_schedule_on(struct callout *c, int to_ticks, int cpu)
{
	return callout_reset_on(c, to_ticks, c->c_func, c->c_arg, cpu);
}

int
callout_schedule(struct callout *c, int to_ticks)
{
	return callout_reset_on(c, to_ticks, c->c_func, c->c_arg, c->c_cpu);
}

int
_callout_stop_safe(c, safe)
	struct	callout *c;
	int	safe;
{
	struct callout_cpu *cc, *old_cc;
	struct lock_class *class;
	int direct, sq_locked, use_lock;

	/*
	 * Some old subsystems don't hold Giant while running a callout_stop(),
	 * so just discard this check for the moment.
	 */
	if (!safe && c->c_lock != NULL) {
		if (c->c_lock == &Giant.lock_object)
			use_lock = mtx_owned(&Giant);
		else {
			use_lock = 1;
			class = LOCK_CLASS(c->c_lock);
			class->lc_assert(c->c_lock, LA_XLOCKED);
		}
	} else
		use_lock = 0;
	direct = (c->c_flags & CALLOUT_DIRECT) != 0;
	sq_locked = 0;
	old_cc = NULL;
again:
	cc = callout_lock(c);

	/*
	 * If the callout was migrating while the callout cpu lock was
	 * dropped,  just drop the sleepqueue lock and check the states
	 * again.
	 */
	if (sq_locked != 0 && cc != old_cc) {
#ifdef SMP
		CC_UNLOCK(cc);
		sleepq_release(&old_cc->cc_exec_entity[direct].cc_waiting);
		sq_locked = 0;
		old_cc = NULL;
		goto again;
#else
		panic("migration should not happen");
#endif
	}

	/*
	 * If the callout isn't pending, it's not on the queue, so
	 * don't attempt to remove it from the queue.  We can try to
	 * stop it by other means however.
	 */
	if (!(c->c_flags & CALLOUT_PENDING)) {
		c->c_flags &= ~CALLOUT_ACTIVE;

		/*
		 * If it wasn't on the queue and it isn't the current
		 * callout, then we can't stop it, so just bail.
		 */
		if (cc->cc_exec_entity[direct].cc_curr != c) {
			CTR3(KTR_CALLOUT, "failed to stop %p func %p arg %p",
			    c, c->c_func, c->c_arg);
			CC_UNLOCK(cc);
			if (sq_locked)
				sleepq_release(
				    &cc->cc_exec_entity[direct].cc_waiting);
			return (0);
		}

		if (safe) {
			/*
			 * The current callout is running (or just
			 * about to run) and blocking is allowed, so
			 * just wait for the current invocation to
			 * finish.
			 */
			while (cc->cc_exec_entity[direct].cc_curr == c) {
				/*
				 * Use direct calls to sleepqueue interface
				 * instead of cv/msleep in order to avoid
				 * a LOR between cc_lock and sleepqueue
				 * chain spinlocks.  This piece of code
				 * emulates a msleep_spin() call actually.
				 *
				 * If we already have the sleepqueue chain
				 * locked, then we can safely block.  If we
				 * don't already have it locked, however,
				 * we have to drop the cc_lock to lock
				 * it.  This opens several races, so we
				 * restart at the beginning once we have
				 * both locks.  If nothing has changed, then
				 * we will end up back here with sq_locked
				 * set.
				 */
				if (!sq_locked) {
					CC_UNLOCK(cc);
					sleepq_lock(
					&cc->cc_exec_entity[direct].cc_waiting);
					sq_locked = 1;
					old_cc = cc;
					goto again;
				}

				/*
				 * Migration could be cancelled here, but
				 * as long as it is still not sure when it
				 * will be packed up, just let softclock()
				 * take care of it.
				 */
				cc->cc_exec_entity[direct].cc_waiting = true;
				DROP_GIANT();
				CC_UNLOCK(cc);
				sleepq_add(
				    &cc->cc_exec_entity[direct].cc_waiting,
				    &cc->cc_lock.lock_object, "codrain",
				    SLEEPQ_SLEEP, 0);
				sleepq_wait(
				    &cc->cc_exec_entity[direct].cc_waiting,
					     0);
				sq_locked = 0;
				old_cc = NULL;

				/* Reacquire locks previously released. */
				PICKUP_GIANT();
				CC_LOCK(cc);
			}
		} else if (use_lock &&
			    !cc->cc_exec_entity[direct].cc_cancel) {
			/*
			 * The current callout is waiting for its
			 * lock which we hold.  Cancel the callout
			 * and return.  After our caller drops the
			 * lock, the callout will be skipped in
			 * softclock().
			 */
			cc->cc_exec_entity[direct].cc_cancel = true;
			CTR3(KTR_CALLOUT, "cancelled %p func %p arg %p",
			    c, c->c_func, c->c_arg);
			KASSERT(!cc_cce_migrating(cc, direct),
			    ("callout wrongly scheduled for migration"));
			CC_UNLOCK(cc);
			KASSERT(!sq_locked, ("sleepqueue chain locked"));
			return (1);
		} else if ((c->c_flags & CALLOUT_DFRMIGRATION) != 0) {
			c->c_flags &= ~CALLOUT_DFRMIGRATION;
			CTR3(KTR_CALLOUT, "postponing stop %p func %p arg %p",
			    c, c->c_func, c->c_arg);
			CC_UNLOCK(cc);
			return (1);
		}
		CTR3(KTR_CALLOUT, "failed to stop %p func %p arg %p",
		    c, c->c_func, c->c_arg);
		CC_UNLOCK(cc);
		KASSERT(!sq_locked, ("sleepqueue chain still locked"));
		return (0);
	}
	if (sq_locked)
		sleepq_release(&cc->cc_exec_entity[direct].cc_waiting);

	c->c_flags &= ~(CALLOUT_ACTIVE | CALLOUT_PENDING);

	CTR3(KTR_CALLOUT, "cancelled %p func %p arg %p",
	    c, c->c_func, c->c_arg);
	if ((c->c_flags & CALLOUT_PROCESSED) == 0) {
		if (cc->cc_exec_next_dir == c)
			cc->cc_exec_next_dir = LIST_NEXT(c, c_links.le);
		LIST_REMOVE(c, c_links.le);
	} else
		TAILQ_REMOVE(&cc->cc_expireq, c, c_links.tqe);
	callout_cc_del(c, cc);

	CC_UNLOCK(cc);
	return (1);
}

void
callout_init(c, mpsafe)
	struct	callout *c;
	int mpsafe;
{
	bzero(c, sizeof *c);
	if (mpsafe) {
		c->c_lock = NULL;
		c->c_flags = CALLOUT_RETURNUNLOCKED;
	} else {
		c->c_lock = &Giant.lock_object;
		c->c_flags = 0;
	}
	c->c_cpu = timeout_cpu;
}

void
_callout_init_lock(c, lock, flags)
	struct	callout *c;
	struct	lock_object *lock;
	int flags;
{
	bzero(c, sizeof *c);
	c->c_lock = lock;
	KASSERT((flags & ~(CALLOUT_RETURNUNLOCKED | CALLOUT_SHAREDLOCK)) == 0,
	    ("callout_init_lock: bad flags %d", flags));
	KASSERT(lock != NULL || (flags & CALLOUT_RETURNUNLOCKED) == 0,
	    ("callout_init_lock: CALLOUT_RETURNUNLOCKED with no lock"));
	KASSERT(lock == NULL || !(LOCK_CLASS(lock)->lc_flags &
	    (LC_SPINLOCK | LC_SLEEPABLE)), ("%s: invalid lock class",
	    __func__));
	c->c_flags = flags & (CALLOUT_RETURNUNLOCKED | CALLOUT_SHAREDLOCK);
	c->c_cpu = timeout_cpu;
}

#ifdef APM_FIXUP_CALLTODO
/*
 * Adjust the kernel calltodo timeout list.  This routine is used after
 * an APM resume to recalculate the calltodo timer list values with the
 * number of hz's we have been sleeping.  The next hardclock() will detect
 * that there are fired timers and run softclock() to execute them.
 *
 * Please note, I have not done an exhaustive analysis of what code this
 * might break.  I am motivated to have my select()'s and alarm()'s that
 * have expired during suspend firing upon resume so that the applications
 * which set the timer can do the maintanence the timer was for as close
 * as possible to the originally intended time.  Testing this code for a
 * week showed that resuming from a suspend resulted in 22 to 25 timers
 * firing, which seemed independant on whether the suspend was 2 hours or
 * 2 days.  Your milage may vary.   - Ken Key <key@cs.utk.edu>
 */
void
adjust_timeout_calltodo(time_change)
    struct timeval *time_change;
{
	register struct callout *p;
	unsigned long delta_ticks;

	/*
	 * How many ticks were we asleep?
	 * (stolen from tvtohz()).
	 */

	/* Don't do anything */
	if (time_change->tv_sec < 0)
		return;
	else if (time_change->tv_sec <= LONG_MAX / 1000000)
		delta_ticks = (time_change->tv_sec * 1000000 +
			       time_change->tv_usec + (tick - 1)) / tick + 1;
	else if (time_change->tv_sec <= LONG_MAX / hz)
		delta_ticks = time_change->tv_sec * hz +
			      (time_change->tv_usec + (tick - 1)) / tick + 1;
	else
		delta_ticks = LONG_MAX;

	if (delta_ticks > INT_MAX)
		delta_ticks = INT_MAX;

	/*
	 * Now rip through the timer calltodo list looking for timers
	 * to expire.
	 */

	/* don't collide with softclock() */
	CC_LOCK(cc);
	for (p = calltodo.c_next; p != NULL; p = p->c_next) {
		p->c_time -= delta_ticks;

		/* Break if the timer had more time on it than delta_ticks */
		if (p->c_time > 0)
			break;

		/* take back the ticks the timer didn't use (p->c_time <= 0) */
		delta_ticks = -p->c_time;
	}
	CC_UNLOCK(cc);

	return;
}
#endif /* APM_FIXUP_CALLTODO */

static int
flssbt(sbintime_t sbt)
{

	sbt += (uint64_t)sbt >> 1;
	if (sizeof(long) >= sizeof(sbintime_t))
		return (flsl(sbt));
	if (sbt >= SBT_1S)
		return (flsl(((uint64_t)sbt) >> 32) + 32);
	return (flsl(sbt));
}

/*
 * Dump immediate statistic snapshot of the scheduled callouts.
 */
static int
sysctl_kern_callout_stat(SYSCTL_HANDLER_ARGS)
{
	struct callout *tmp;
	struct callout_cpu *cc;
	struct callout_list *sc;
	sbintime_t maxpr, maxt, medpr, medt, now, spr, st, t;
	int ct[64], cpr[64], ccpbk[32];
	int error, val, i, count, tcum, pcum, maxc, c, medc;
#ifdef SMP
	int cpu;
#endif

	val = 0;
	error = sysctl_handle_int(oidp, &val, 0, req);
	if (error != 0 || req->newptr == NULL)
		return (error);
	count = maxc = 0;
	st = spr = maxt = maxpr = 0;
	bzero(ccpbk, sizeof(ccpbk));
	bzero(ct, sizeof(ct));
	bzero(cpr, sizeof(cpr));
	now = sbinuptime();
#ifdef SMP
	CPU_FOREACH(cpu) {
		cc = CC_CPU(cpu);
#else
		cc = CC_CPU(timeout_cpu);
#endif
		CC_LOCK(cc);
		for (i = 0; i < callwheelsize; i++) {
			sc = &cc->cc_callwheel[i];
			c = 0;
			LIST_FOREACH(tmp, sc, c_links.le) {
				c++;
				t = tmp->c_time - now;
				if (t < 0)
					t = 0;
				st += t / SBT_1US;
				spr += tmp->c_precision / SBT_1US;
				if (t > maxt)
					maxt = t;
				if (tmp->c_precision > maxpr)
					maxpr = tmp->c_precision;
				ct[flssbt(t)]++;
				cpr[flssbt(tmp->c_precision)]++;
			}
			if (c > maxc)
				maxc = c;
			ccpbk[fls(c + c / 2)]++;
			count += c;
		}
		CC_UNLOCK(cc);
#ifdef SMP
	}
#endif

	for (i = 0, tcum = 0; i < 64 && tcum < count / 2; i++)
		tcum += ct[i];
	medt = (i >= 2) ? (((sbintime_t)1) << (i - 2)) : 0;
	for (i = 0, pcum = 0; i < 64 && pcum < count / 2; i++)
		pcum += cpr[i];
	medpr = (i >= 2) ? (((sbintime_t)1) << (i - 2)) : 0;
	for (i = 0, c = 0; i < 32 && c < count / 2; i++)
		c += ccpbk[i];
	medc = (i >= 2) ? (1 << (i - 2)) : 0;

	printf("Scheduled callouts statistic snapshot:\n");
	printf("  Callouts: %6d  Buckets: %6d*%-3d  Bucket size: 0.%06ds\n",
	    count, callwheelsize, mp_ncpus, 1000000 >> CC_HASH_SHIFT);
	printf("  C/Bk: med %5d         avg %6d.%06jd  max %6d\n",
	    medc,
	    count / callwheelsize / mp_ncpus,
	    (uint64_t)count * 1000000 / callwheelsize / mp_ncpus % 1000000,
	    maxc);
	printf("  Time: med %5jd.%06jds avg %6jd.%06jds max %6jd.%06jds\n",
	    medt / SBT_1S, (medt & 0xffffffff) * 1000000 >> 32,
	    (st / count) / 1000000, (st / count) % 1000000,
	    maxt / SBT_1S, (maxt & 0xffffffff) * 1000000 >> 32);
	printf("  Prec: med %5jd.%06jds avg %6jd.%06jds max %6jd.%06jds\n",
	    medpr / SBT_1S, (medpr & 0xffffffff) * 1000000 >> 32,
	    (spr / count) / 1000000, (spr / count) % 1000000,
	    maxpr / SBT_1S, (maxpr & 0xffffffff) * 1000000 >> 32);
	printf("  Distribution:       \tbuckets\t   time\t   tcum\t"
	    "   prec\t   pcum\n");
	for (i = 0, tcum = pcum = 0; i < 64; i++) {
		if (ct[i] == 0 && cpr[i] == 0)
			continue;
		t = (i != 0) ? (((sbintime_t)1) << (i - 1)) : 0;
		tcum += ct[i];
		pcum += cpr[i];
		printf("  %10jd.%06jds\t 2**%d\t%7d\t%7d\t%7d\t%7d\n",
		    t / SBT_1S, (t & 0xffffffff) * 1000000 >> 32,
		    i - 1 - (32 - CC_HASH_SHIFT),
		    ct[i], tcum, cpr[i], pcum);
	}
	return (error);
}
SYSCTL_PROC(_kern, OID_AUTO, callout_stat,
    CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_MPSAFE,
    0, 0, sysctl_kern_callout_stat, "I",
    "Dump immediate statistic snapshot of the scheduled callouts");