freebsd-src/sys/kern/kern_timeout.c

/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * 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. 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.
 */

#include <sys/cdefs.h>
#include "opt_callout_profiling.h"
#include "opt_ddb.h"
#include "opt_rss.h"

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

#ifdef DDB
#include <ddb/ddb.h>
#include <ddb/db_sym.h>
#include <machine/_inttypes.h>
#endif

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

DPCPU_DECLARE(sbintime_t, hardclocktime);

SDT_PROVIDER_DEFINE(callout_execute);
SDT_PROBE_DEFINE1(callout_execute, , , callout__start, "struct callout *");
SDT_PROBE_DEFINE1(callout_execute, , , callout__end, "struct callout *");

static void	softclock_thread(void *arg);

#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 | CTLFLAG_NOFETCH, &ncallout, 0,
    "Number of entries in callwheel and size of timeout() preallocation");

#ifdef	RSS
static int pin_default_swi = 1;
static int pin_pcpu_swi = 1;
#else
static int pin_default_swi = 0;
static int pin_pcpu_swi = 0;
#endif

SYSCTL_INT(_kern, OID_AUTO, pin_default_swi, CTLFLAG_RDTUN | CTLFLAG_NOFETCH, &pin_default_swi,
    0, "Pin the default (non-per-cpu) swi (shared with PCPU 0 swi)");
SYSCTL_INT(_kern, OID_AUTO, pin_pcpu_swi, CTLFLAG_RDTUN | CTLFLAG_NOFETCH, &pin_pcpu_swi,
    0, "Pin the per-CPU swis (except PCPU 0, which is also default)");

/*
 * TODO:
 *	allocate more timeout table slots when table overflows.
 */
static u_int __read_mostly callwheelsize;
static u_int __read_mostly 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_curr;
	void			*cc_last_func;
	void			*cc_last_arg;
#ifdef SMP
	callout_func_t		*ce_migration_func;
	void			*ce_migration_arg;
	sbintime_t		ce_migration_time;
	sbintime_t		ce_migration_prec;
	int			ce_migration_cpu;
#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_next;
	struct callout_list	*cc_callwheel;
	struct callout_tailq	cc_expireq;
	sbintime_t		cc_firstevent;
	sbintime_t		cc_lastscan;
	struct thread		*cc_thread;
	u_int			cc_bucket;
#ifdef KTR
	char			cc_ktr_event_name[20];
#endif
};

#define	callout_migrating(c)	((c)->c_iflags & CALLOUT_DFRMIGRATION)

#define	cc_exec_curr(cc, dir)		cc->cc_exec_entity[dir].cc_curr
#define	cc_exec_last_func(cc, dir)	cc->cc_exec_entity[dir].cc_last_func
#define	cc_exec_last_arg(cc, dir)	cc->cc_exec_entity[dir].cc_last_arg
#define	cc_exec_next(cc)		cc->cc_next
#define	cc_exec_cancel(cc, dir)		cc->cc_exec_entity[dir].cc_cancel
#define	cc_exec_waiting(cc, dir)	cc->cc_exec_entity[dir].cc_waiting
#ifdef SMP
#define	cc_migration_func(cc, dir)	cc->cc_exec_entity[dir].ce_migration_func
#define	cc_migration_arg(cc, dir)	cc->cc_exec_entity[dir].ce_migration_arg
#define	cc_migration_cpu(cc, dir)	cc->cc_exec_entity[dir].ce_migration_cpu
#define	cc_migration_time(cc, dir)	cc->cc_exec_entity[dir].ce_migration_time
#define	cc_migration_prec(cc, dir)	cc->cc_exec_entity[dir].ce_migration_prec

DPCPU_DEFINE_STATIC(struct callout_cpu, cc_cpu);
#define	CPUBLOCK	MAXCPU
#define	CC_CPU(cpu)	DPCPU_ID_PTR(cpu, cc_cpu)
#define	CC_SELF()	CC_CPU(PCPU_GET(cpuid))
#else
static 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 __read_mostly cc_default_cpu;

static void	callout_cpu_init(struct callout_cpu *cc, int cpu);
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_call_cc() 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_exec_curr(cc, direct) = NULL;
	cc_exec_cancel(cc, direct) = false;
	cc_exec_waiting(cc, direct) = false;
#ifdef SMP
	cc_migration_cpu(cc, direct) = CPUBLOCK;
	cc_migration_time(cc, direct) = 0;
	cc_migration_prec(cc, direct) = 0;
	cc_migration_func(cc, direct) = NULL;
	cc_migration_arg(cc, direct) = 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_migration_cpu(cc, direct) != CPUBLOCK);
#else
	return (0);
#endif
}

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

	/*
	 * Calculate the size of the callout wheel and the preallocated
	 * timeout() structures.
	 * XXX: Clip callout to result of previous function of maxusers
	 * maximum 384.  This is still huge, but acceptable.
	 */
	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;

	/*
	 * Fetch whether we're pinning the swi's or not.
	 */
	TUNABLE_INT_FETCH("kern.pin_default_swi", &pin_default_swi);
	TUNABLE_INT_FETCH("kern.pin_pcpu_swi", &pin_pcpu_swi);

	/*
	 * Initialize callout wheels.  The software interrupt threads
	 * are created later.
	 */
	cc_default_cpu = PCPU_GET(cpuid);
	CPU_FOREACH(cpu) {
		cc = CC_CPU(cpu);
		callout_cpu_init(cc, cpu);
	}
}
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, int cpu)
{
	int i;

	mtx_init(&cc->cc_lock, "callout", NULL, MTX_SPIN);
	cc->cc_callwheel = malloc_domainset(sizeof(struct callout_list) *
	    callwheelsize, M_CALLOUT,
	    DOMAINSET_PREF(pcpu_find(cpu)->pc_domain), M_WAITOK);
	for (i = 0; i < callwheelsize; i++)
		LIST_INIT(&cc->cc_callwheel[i]);
	TAILQ_INIT(&cc->cc_expireq);
	cc->cc_firstevent = SBT_MAX;
	for (i = 0; i < 2; i++)
		cc_cce_cleanup(cc, i);
#ifdef KTR
	snprintf(cc->cc_ktr_event_name, sizeof(cc->cc_ktr_event_name),
	    "callwheel cpu %d", cpu);
#endif
}

#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 softclock threads.
 */
static void
start_softclock(void *dummy)
{
	struct proc *p;
	struct thread *td;
	struct callout_cpu *cc;
	int cpu, error;
	bool pin_swi;

	p = NULL;
	CPU_FOREACH(cpu) {
		cc = CC_CPU(cpu);
		error = kproc_kthread_add(softclock_thread, cc, &p, &td,
		    RFSTOPPED, 0, "clock", "clock (%d)", cpu);
		if (error != 0)
			panic("failed to create softclock thread for cpu %d: %d",
			    cpu, error);
		CC_LOCK(cc);
		cc->cc_thread = td;
		thread_lock(td);
		sched_class(td, PRI_ITHD);
		sched_ithread_prio(td, PI_SOFTCLOCK);
		TD_SET_IWAIT(td);
		thread_lock_set(td, (struct mtx *)&cc->cc_lock);
		thread_unlock(td);
		if (cpu == cc_default_cpu)
			pin_swi = pin_default_swi;
		else
			pin_swi = pin_pcpu_swi;
		if (pin_swi) {
			error = cpuset_setithread(td->td_tid, cpu);
			if (error != 0)
				printf("%s: %s clock couldn't be pinned to cpu %d: %d\n",
				    __func__, cpu == cc_default_cpu ?
				    "default" : "per-cpu", cpu, error);
		}
	}
}
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_entropy {
		struct callout_cpu *cc;
		struct thread *td;
		sbintime_t now;
	} entropy;
	struct callout *c, *next;
	struct callout_cpu *cc;
	struct callout_list *sc;
	struct thread *td;
	sbintime_t first, last, lookahead, max, tmp_max;
	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;
	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];
		LIST_FOREACH_SAFE(c, sc, c_links.le, next) {
			/* Run the callout if present time within allowed. */
			if (c->c_time <= now) {
				/*
				 * Consumer told us the callout may be run
				 * directly from hardware interrupt context.
				 */
				if (c->c_iflags & CALLOUT_DIRECT) {
#ifdef CALLOUT_PROFILING
					++depth_dir;
#endif
					cc_exec_next(cc) = next;
					cc->cc_bucket = firstb & callwheelmask;
					LIST_REMOVE(c, c_links.le);
					softclock_call_cc(c, cc,
#ifdef CALLOUT_PROFILING
					    &mpcalls_dir, &lockcalls_dir, NULL,
#endif
					    1);
					next = cc_exec_next(cc);
					cc_exec_next(cc) = NULL;
				} else {
					LIST_REMOVE(c, c_links.le);
					TAILQ_INSERT_TAIL(&cc->cc_expireq,
					    c, c_links.tqe);
					c->c_iflags |= CALLOUT_PROCESSED;
				}
			} else if (c->c_time >= max) {
				/*
				 * Skip events in the distant future.
				 */
				;
			} else if (c->c_time > last) {
				/*
				 * Event minimal time is bigger than present
				 * maximal time, so it cannot be aggregated.
				 */
				lastb = nowb;
			} else {
				/*
				 * Update first and last time, respecting this
				 * event.
				 */
				if (c->c_time < first)
					first = c->c_time;
				tmp_max = c->c_time + c->c_precision;
				if (tmp_max < last)
					last = tmp_max;
			}
		}
		/* 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;
	cpu_new_callout(curcpu, last, first);

#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
	if (!TAILQ_EMPTY(&cc->cc_expireq)) {
		entropy.cc = cc;
		entropy.td = curthread;
		entropy.now = now;
		random_harvest_queue(&entropy, sizeof(entropy), RANDOM_CALLOUT);

		td = cc->cc_thread;
		if (TD_AWAITING_INTR(td)) {
			thread_lock_block_wait(td);
			THREAD_LOCK_ASSERT(td, MA_OWNED);
			TD_CLR_IWAIT(td);
			sched_wakeup(td, SRQ_INTR);
		} else
			mtx_unlock_spin_flags(&cc->cc_lock, MTX_QUIET);
	} else
		mtx_unlock_spin_flags(&cc->cc_lock, MTX_QUIET);
}

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 flags)
{
	int bucket;

	CC_LOCK_ASSERT(cc);
	if (sbt < cc->cc_lastscan)
		sbt = cc->cc_lastscan;
	c->c_arg = arg;
	c->c_iflags |= CALLOUT_PENDING;
	c->c_iflags &= ~CALLOUT_PROCESSED;
	c->c_flags |= CALLOUT_ACTIVE;
	if (flags & C_DIRECT_EXEC)
		c->c_iflags |= CALLOUT_DIRECT;
	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_exec_next(cc) = c;

	/*
	 * Inform the eventtimers(4) subsystem there's a new callout
	 * that has been inserted, but only if really required.
	 */
	if (SBT_MAX - c->c_time < c->c_precision)
		c->c_precision = SBT_MAX - c->c_time;
	sbt = c->c_time + c->c_precision;
	if (sbt < cc->cc_firstevent) {
		cc->cc_firstevent = sbt;
		cpu_new_callout(c->c_cpu, sbt, c->c_time);
	}
}

static void
softclock_call_cc(struct callout *c, struct callout_cpu *cc,
#ifdef CALLOUT_PROFILING
    int *mpcalls, int *lockcalls, int *gcalls,
#endif
    int direct)
{
	struct rm_priotracker tracker;
	callout_func_t *c_func;
	void *c_arg;
	struct lock_class *class;
	struct lock_object *c_lock;
	uintptr_t lock_status;
	int c_iflags;
#ifdef SMP
	struct callout_cpu *new_cc;
	callout_func_t *new_func;
	void *new_arg;
	int flags, new_cpu;
	sbintime_t new_prec, 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 callout_func_t *lastfunc;
#endif

	KASSERT((c->c_iflags & CALLOUT_PENDING) == CALLOUT_PENDING,
	    ("softclock_call_cc: pend %p %x", c, c->c_iflags));
	KASSERT((c->c_flags & CALLOUT_ACTIVE) == CALLOUT_ACTIVE,
	    ("softclock_call_cc: act %p %x", c, c->c_flags));
	class = (c->c_lock != NULL) ? LOCK_CLASS(c->c_lock) : NULL;
	lock_status = 0;
	if (c->c_iflags & CALLOUT_SHAREDLOCK) {
		if (class == &lock_class_rm)
			lock_status = (uintptr_t)&tracker;
		else
			lock_status = 1;
	}
	c_lock = c->c_lock;
	c_func = c->c_func;
	c_arg = c->c_arg;
	c_iflags = c->c_iflags;
	c->c_iflags &= ~CALLOUT_PENDING;

	cc_exec_curr(cc, direct) = c;
	cc_exec_last_func(cc, direct) = c_func;
	cc_exec_last_arg(cc, direct) = c_arg;
	cc_exec_cancel(cc, direct) = false;
	CC_UNLOCK(cc);
	if (c_lock != NULL) {
		class->lc_lock(c_lock, lock_status);
		/*
		 * The callout may have been cancelled
		 * while we switched locks.
		 */
		if (cc_exec_cancel(cc, direct)) {
			class->lc_unlock(c_lock);
			goto skip;
		}
		/* The callout cannot be stopped now. */
		cc_exec_cancel(cc, direct) = 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);
	}
	KTR_STATE3(KTR_SCHED, "callout", cc->cc_ktr_event_name, "running",
	    "func:%p", c_func, "arg:%p", c_arg, "direct:%d", direct);
#if defined(DIAGNOSTIC) || defined(CALLOUT_PROFILING)
	sbt1 = sbinuptime();
#endif
	THREAD_NO_SLEEPING();
	SDT_PROBE1(callout_execute, , , callout__start, c);
	c_func(c_arg);
	SDT_PROBE1(callout_execute, , , callout__end, c);
	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 callout(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
	KTR_STATE0(KTR_SCHED, "callout", cc->cc_ktr_event_name, "idle");
	CTR1(KTR_CALLOUT, "callout %p finished", c);
	if ((c_iflags & CALLOUT_RETURNUNLOCKED) == 0)
		class->lc_unlock(c_lock);
skip:
	CC_LOCK(cc);
	KASSERT(cc_exec_curr(cc, direct) == c, ("mishandled cc_curr"));
	cc_exec_curr(cc, direct) = NULL;
	if (cc_exec_waiting(cc, direct)) {
		/*
		 * 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_iflags &= ~CALLOUT_DFRMIGRATION;
		}
		cc_exec_waiting(cc, direct) = false;
		CC_UNLOCK(cc);
		wakeup(&cc_exec_waiting(cc, direct));
		CC_LOCK(cc);
	} else if (cc_cce_migrating(cc, direct)) {
#ifdef SMP
		/*
		 * If the callout was scheduled for
		 * migration just perform it now.
		 */
		new_cpu = cc_migration_cpu(cc, direct);
		new_time = cc_migration_time(cc, direct);
		new_prec = cc_migration_prec(cc, direct);
		new_func = cc_migration_func(cc, direct);
		new_arg = cc_migration_arg(cc, direct);
		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 (!callout_migrating(c)) {
			CTR3(KTR_CALLOUT,
			     "deferred cancelled %p func %p arg %p",
			     c, new_func, new_arg);
			return;
		}
		c->c_iflags &= ~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, new_prec, new_func,
		    new_arg, flags);
		CC_UNLOCK(new_cc);
		CC_LOCK(cc);
#else
		panic("migration should not happen");
#endif
	}
}

/*
 * 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 thread handler.
 * Run periodic events from timeout queue.
 */
static void
softclock_thread(void *arg)
{
	struct thread *td = curthread;
	struct callout_cpu *cc;
	struct callout *c;
#ifdef CALLOUT_PROFILING
	int depth, gcalls, lockcalls, mpcalls;
#endif

	cc = (struct callout_cpu *)arg;
	CC_LOCK(cc);
	for (;;) {
		while (TAILQ_EMPTY(&cc->cc_expireq)) {
			/*
			 * Use CC_LOCK(cc) as the thread_lock while
			 * idle.
			 */
			thread_lock(td);
			thread_lock_set(td, (struct mtx *)&cc->cc_lock);
			TD_SET_IWAIT(td);
			mi_switch(SW_VOL | SWT_IWAIT);

			/* mi_switch() drops thread_lock(). */
			CC_LOCK(cc);
		}

#ifdef CALLOUT_PROFILING
		depth = gcalls = lockcalls = mpcalls = 0;
#endif
		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
	}
}

void
callout_when(sbintime_t sbt, sbintime_t precision, int flags,
    sbintime_t *res, sbintime_t *prec_res)
{
	sbintime_t to_sbt, to_pr;

	if ((flags & (C_ABSOLUTE | C_PRECALC)) != 0) {
		*res = sbt;
		*prec_res = precision;
		return;
	}
	if ((flags & C_HARDCLOCK) != 0 && sbt < tick_sbt)
		sbt = tick_sbt;
	if ((flags & C_HARDCLOCK) != 0 || 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
		if (cold && to_sbt == 0)
			to_sbt = sbinuptime();
		if ((flags & C_HARDCLOCK) == 0)
			to_sbt += tick_sbt;
	} else
		to_sbt = sbinuptime();
	if (SBT_MAX - to_sbt < sbt)
		to_sbt = SBT_MAX;
	else
		to_sbt += sbt;
	*res = to_sbt;
	to_pr = ((C_PRELGET(flags) < 0) ? sbt >> tc_precexp :
	    sbt >> C_PRELGET(flags));
	*prec_res = to_pr > precision ? to_pr : precision;
}

/*
 * 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 prec,
    callout_func_t *ftn, void *arg, int cpu, int flags)
{
	sbintime_t to_sbt, precision;
	struct callout_cpu *cc;
	int cancelled, direct;

	cancelled = 0;
	callout_when(sbt, prec, flags, &to_sbt, &precision);

	/* 
	 * This flag used to be added by callout_cc_add, but the
	 * first time you call this we could end up with the
	 * wrong direct flag if we don't do it before we add.
	 */
	if (flags & C_DIRECT_EXEC) {
		direct = 1;
	} else {
		direct = 0;
	}
	KASSERT(!direct || c->c_lock == NULL ||
	    (LOCK_CLASS(c->c_lock)->lc_flags & LC_SPINLOCK),
	    ("%s: direct callout %p has non-spin lock", __func__, c));

	cc = callout_lock(c);
	if (cpu == -1)
		cpu = c->c_cpu;
	KASSERT(cpu >= 0 && cpu <= mp_maxid && !CPU_ABSENT(cpu),
	    ("%s: invalid cpu %d", __func__, cpu));

	if (cc_exec_curr(cc, direct) == 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_exec_cancel(cc, direct))
			cancelled = cc_exec_cancel(cc, direct) = true;
		if (cc_exec_waiting(cc, direct)) {
			/*
			 * 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);
		}
#ifdef SMP
		if (callout_migrating(c)) {
			/* 
			 * This only occurs when a second callout_reset_sbt_on
			 * is made after a previous one moved it into
			 * deferred migration (below). Note we do *not* change
			 * the prev_cpu even though the previous target may
			 * be different.
			 */
			cc_migration_cpu(cc, direct) = cpu;
			cc_migration_time(cc, direct) = to_sbt;
			cc_migration_prec(cc, direct) = precision;
			cc_migration_func(cc, direct) = ftn;
			cc_migration_arg(cc, direct) = arg;
			cancelled = 1;
			CC_UNLOCK(cc);
			return (cancelled);
		}
#endif
	}
	if (c->c_iflags & CALLOUT_PENDING) {
		if ((c->c_iflags & CALLOUT_PROCESSED) == 0) {
			if (cc_exec_next(cc) == c)
				cc_exec_next(cc) = 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_iflags &= ~ CALLOUT_PENDING;
		c->c_flags &= ~ CALLOUT_ACTIVE;
	}

#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_exec_curr(cc, direct) == c) {
			/* 
			 * Pending will have been removed since we are
			 * actually executing the callout on another
			 * CPU. That callout should be waiting on the
			 * lock the caller holds. If we set both
			 * active/and/pending after we return and the
			 * lock on the executing callout proceeds, it
			 * will then see pending is true and return.
			 * At the return from the actual callout execution
			 * the migration will occur in softclock_call_cc
			 * and this new callout will be placed on the 
			 * new CPU via a call to callout_cpu_switch() which
			 * will get the lock on the right CPU followed
			 * by a call callout_cc_add() which will add it there.
			 * (see above in softclock_call_cc()).
			 */
			cc_migration_cpu(cc, direct) = cpu;
			cc_migration_time(cc, direct) = to_sbt;
			cc_migration_prec(cc, direct) = precision;
			cc_migration_func(cc, direct) = ftn;
			cc_migration_arg(cc, direct) = arg;
			c->c_iflags |= (CALLOUT_DFRMIGRATION | CALLOUT_PENDING);
			c->c_flags |= CALLOUT_ACTIVE;
			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, 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(struct callout *c, int flags)
{
	struct callout_cpu *cc, *old_cc;
	struct lock_class *class;
	int direct, sq_locked, use_lock;
	int cancelled, not_on_a_list;

	if ((flags & CS_DRAIN) != 0)
		WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, c->c_lock,
		    "calling %s", __func__);

	/*
	 * Some old subsystems don't hold Giant while running a callout_stop(),
	 * so just discard this check for the moment.
	 */
	if ((flags & CS_DRAIN) == 0 && 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;
	if (c->c_iflags & CALLOUT_DIRECT) {
		direct = 1;
	} else {
		direct = 0;
	}
	sq_locked = 0;
	old_cc = NULL;
again:
	cc = callout_lock(c);

	if ((c->c_iflags & (CALLOUT_DFRMIGRATION | CALLOUT_PENDING)) ==
	    (CALLOUT_DFRMIGRATION | CALLOUT_PENDING) &&
	    ((c->c_flags & CALLOUT_ACTIVE) == CALLOUT_ACTIVE)) {
		/*
		 * Special case where this slipped in while we
		 * were migrating *as* the callout is about to
		 * execute. The caller probably holds the lock
		 * the callout wants.
		 *
		 * Get rid of the migration first. Then set
		 * the flag that tells this code *not* to
		 * try to remove it from any lists (its not
		 * on one yet). When the callout wheel runs,
		 * it will ignore this callout.
		 */
		c->c_iflags &= ~CALLOUT_PENDING;
		c->c_flags &= ~CALLOUT_ACTIVE;
		not_on_a_list = 1;
	} else {
		not_on_a_list = 0;
	}

	/*
	 * 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(&cc_exec_waiting(old_cc, direct));
		sq_locked = 0;
		old_cc = NULL;
		goto again;
#else
		panic("migration should not happen");
#endif
	}

	/*
	 * If the callout is running, try to stop it or drain it.
	 */
	if (cc_exec_curr(cc, direct) == c) {
		/*
		 * Succeed we to stop it or not, we must clear the
		 * active flag - this is what API users expect.  If we're
		 * draining and the callout is currently executing, first wait
		 * until it finishes.
		 */
		if ((flags & CS_DRAIN) == 0)
			c->c_flags &= ~CALLOUT_ACTIVE;

		if ((flags & CS_DRAIN) != 0) {
			/*
			 * The current callout is running (or just
			 * about to run) and blocking is allowed, so
			 * just wait for the current invocation to
			 * finish.
			 */
			if (cc_exec_curr(cc, direct) == 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_exec_waiting(cc, direct));
					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_exec_waiting(cc, direct) = true;
				DROP_GIANT();
				CC_UNLOCK(cc);
				sleepq_add(
				    &cc_exec_waiting(cc, direct),
				    &cc->cc_lock.lock_object, "codrain",
				    SLEEPQ_SLEEP, 0);
				sleepq_wait(
				    &cc_exec_waiting(cc, direct),
					     0);
				sq_locked = 0;
				old_cc = NULL;

				/* Reacquire locks previously released. */
				PICKUP_GIANT();
				goto again;
			}
			c->c_flags &= ~CALLOUT_ACTIVE;
		} else if (use_lock && !cc_exec_cancel(cc, direct)) {
			
			/*
			 * 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(). This *only* works with a
			 * callout_stop() *not* with callout_drain().
			 */
			cc_exec_cancel(cc, direct) = 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"));
			if (callout_migrating(c)) {
				c->c_iflags &= ~CALLOUT_DFRMIGRATION;
#ifdef SMP
				cc_migration_cpu(cc, direct) = CPUBLOCK;
				cc_migration_time(cc, direct) = 0;
				cc_migration_prec(cc, direct) = 0;
				cc_migration_func(cc, direct) = NULL;
				cc_migration_arg(cc, direct) = NULL;
#endif
			}
			CC_UNLOCK(cc);
			KASSERT(!sq_locked, ("sleepqueue chain locked"));
			return (1);
		} else if (callout_migrating(c)) {
			/*
			 * The callout is currently being serviced
			 * and the "next" callout is scheduled at
			 * its completion with a migration. We remove
			 * the migration flag so it *won't* get rescheduled,
			 * but we can't stop the one thats running so
			 * we return 0.
			 */
			c->c_iflags &= ~CALLOUT_DFRMIGRATION;
#ifdef SMP
			/* 
			 * We can't call cc_cce_cleanup here since
			 * if we do it will remove .ce_curr and
			 * its still running. This will prevent a
			 * reschedule of the callout when the 
			 * execution completes.
			 */
			cc_migration_cpu(cc, direct) = CPUBLOCK;
			cc_migration_time(cc, direct) = 0;
			cc_migration_prec(cc, direct) = 0;
			cc_migration_func(cc, direct) = NULL;
			cc_migration_arg(cc, direct) = NULL;
#endif
			CTR3(KTR_CALLOUT, "postponing stop %p func %p arg %p",
			    c, c->c_func, c->c_arg);
			CC_UNLOCK(cc);
			return (0);
		} else {
			CTR3(KTR_CALLOUT, "failed to stop %p func %p arg %p",
			    c, c->c_func, c->c_arg);
		}
		KASSERT(!sq_locked, ("sleepqueue chain still locked"));
		cancelled = 0;
	} else
		cancelled = 1;

	if (sq_locked)
		sleepq_release(&cc_exec_waiting(cc, direct));

	if ((c->c_iflags & CALLOUT_PENDING) == 0) {
		CTR3(KTR_CALLOUT, "failed to stop %p func %p arg %p",
		    c, c->c_func, c->c_arg);
		/*
		 * For not scheduled and not executing callout return
		 * negative value.
		 */
		if (cc_exec_curr(cc, direct) != c)
			cancelled = -1;
		CC_UNLOCK(cc);
		return (cancelled);
	}

	c->c_iflags &= ~CALLOUT_PENDING;
	c->c_flags &= ~CALLOUT_ACTIVE;

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

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

void
_callout_init_lock(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_SLEEPABLE),
	    ("%s: callout %p has sleepable lock", __func__, c));
	c->c_iflags = flags & (CALLOUT_RETURNUNLOCKED | CALLOUT_SHAREDLOCK);
	c->c_cpu = cc_default_cpu;
}

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;
	int cpu;

	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();
	CPU_FOREACH(cpu) {
		cc = CC_CPU(cpu);
		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);
	}

	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");

#ifdef DDB
static void
_show_callout(struct callout *c)
{

	db_printf("callout %p\n", c);
#define	C_DB_PRINTF(f, e)	db_printf("   %s = " f "\n", #e, c->e);
	db_printf("   &c_links = %p\n", &(c->c_links));
	C_DB_PRINTF("%" PRId64,	c_time);
	C_DB_PRINTF("%" PRId64,	c_precision);
	C_DB_PRINTF("%p",	c_arg);
	C_DB_PRINTF("%p",	c_func);
	C_DB_PRINTF("%p",	c_lock);
	C_DB_PRINTF("%#x",	c_flags);
	C_DB_PRINTF("%#x",	c_iflags);
	C_DB_PRINTF("%d",	c_cpu);
#undef	C_DB_PRINTF
}

DB_SHOW_COMMAND(callout, db_show_callout)
{

	if (!have_addr) {
		db_printf("usage: show callout <struct callout *>\n");
		return;
	}

	_show_callout((struct callout *)addr);
}

static void
_show_last_callout(int cpu, int direct, const char *dirstr)
{
	struct callout_cpu *cc;
	void *func, *arg;

	cc = CC_CPU(cpu);
	func = cc_exec_last_func(cc, direct);
	arg = cc_exec_last_arg(cc, direct);
	db_printf("cpu %d last%s callout function: %p ", cpu, dirstr, func);
	db_printsym((db_expr_t)func, DB_STGY_ANY);
	db_printf("\ncpu %d last%s callout argument: %p\n", cpu, dirstr, arg);
}

DB_SHOW_COMMAND_FLAGS(callout_last, db_show_callout_last, DB_CMD_MEMSAFE)
{
	int cpu, last;

	if (have_addr) {
		if (addr < 0 || addr > mp_maxid || CPU_ABSENT(addr)) {
			db_printf("no such cpu: %d\n", (int)addr);
			return;
		}
		cpu = last = addr;
	} else {
		cpu = 0;
		last = mp_maxid;
	}

	while (cpu <= last) {
		if (!CPU_ABSENT(cpu)) {
			_show_last_callout(cpu, 0, "");
			_show_last_callout(cpu, 1, " direct");
		}
		cpu++;
	}
}
#endif /* DDB */