kern_timeout.c

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/*-
 * 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("$BSDSUniX$");

#include "opt_kdtrace.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/bus.h>
#include <sys/callout.h>
#include <sys/condvar.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

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

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");
/*
 * TODO:
 *      allocate more timeout table slots when table overflows.
 */
int callwheelsize, callwheelbits, callwheelmask;

/*
 * The callout cpu migration entity represents informations necessary for
 * describing the migrating callout to the new callout cpu.
 * The cached informations are very important for deferring migration when
 * the migrating callout is already running.
 */
struct cc_mig_ent {
#ifdef SMP
        void    (*ce_migration_func)(void *);
        void    *ce_migration_arg;
        int     ce_migration_cpu;
        int     ce_migration_ticks;
#endif
};
        
/*
 * There is one struct callout_cpu per cpu, holding all relevant
 * state for the callout processing thread on the individual CPU.
 * In particular:
 *      cc_ticks is incremented once per tick in callout_cpu().
 *      It tracks the global 'ticks' but in a way that the individual
 *      threads should not worry about races in the order in which
 *      hardclock() and hardclock_cpu() run on the various CPUs.
 *      cc_softclock is advanced in callout_cpu() to point to the
 *      first entry in cc_callwheel that may need handling. In turn,
 *      a softclock() is scheduled so it can serve the various entries i
 *      such that cc_softclock <= i <= cc_ticks .
 *      XXX maybe cc_softclock and cc_ticks should be volatile ?
 *
 *      cc_ticks is also used in callout_reset_cpu() to determine
 *      when the callout should be served.
 */
struct callout_cpu {
        struct cc_mig_ent       cc_migrating_entity;
        struct mtx              cc_lock;
        struct callout          *cc_callout;
        struct callout_tailq    *cc_callwheel;
        struct callout_list     cc_callfree;
        struct callout          *cc_next;
        struct callout          *cc_curr;
        void                    *cc_cookie;
        int                     cc_ticks;
        int                     cc_softticks;
        int                     cc_cancel;
        int                     cc_waiting;
        int                     cc_firsttick;
};

#ifdef SMP
#define cc_migration_func       cc_migrating_entity.ce_migration_func
#define cc_migration_arg        cc_migrating_entity.ce_migration_arg
#define cc_migration_cpu        cc_migrating_entity.ce_migration_cpu
#define cc_migration_ticks      cc_migrating_entity.ce_migration_ticks

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;
void (*callout_new_inserted)(int cpu, int ticks) = NULL;

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

/*
 * Resets the migration entity tied to a specific callout cpu.
 */
static void
cc_cme_cleanup(struct callout_cpu *cc)
{

#ifdef SMP
        cc->cc_migration_cpu = CPUBLOCK;
        cc->cc_migration_ticks = 0;
        cc->cc_migration_func = NULL;
        cc->cc_migration_arg = NULL;
#endif
}

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

#ifdef SMP
        return (cc->cc_migration_cpu != CPUBLOCK);
#else
        return (0);
#endif
}

/*
 * kern_timeout_callwheel_alloc() - kernel low level callwheel initialization 
 *
 *      This code is called very early in the kernel initialization sequence,
 *      and may be called more then once.
 */
caddr_t
kern_timeout_callwheel_alloc(caddr_t v)
{
        struct callout_cpu *cc;

        timeout_cpu = PCPU_GET(cpuid);
        cc = CC_CPU(timeout_cpu);
        /*
         * Calculate callout wheel size
         */
        for (callwheelsize = 1, callwheelbits = 0;
             callwheelsize < ncallout;
             callwheelsize <<= 1, ++callwheelbits)
                ;
        callwheelmask = callwheelsize - 1;

        cc->cc_callout = (struct callout *)v;
        v = (caddr_t)(cc->cc_callout + ncallout);
        cc->cc_callwheel = (struct callout_tailq *)v;
        v = (caddr_t)(cc->cc_callwheel + callwheelsize);
        return(v);
}

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);
        for (i = 0; i < callwheelsize; i++) {
                TAILQ_INIT(&cc->cc_callwheel[i]);
        }
        cc_cme_cleanup(cc);
        if (cc->cc_callout == NULL)
                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

/*
 * kern_timeout_callwheel_init() - initialize previously reserved callwheel
 *                                 space.
 *
 *      This code is called just once, after the space reserved for the
 *      callout wheel has been finalized.
 */
void
kern_timeout_callwheel_init(void)
{
        callout_cpu_init(CC_CPU(timeout_cpu));
}

/*
 * 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);
                if (swi_add(NULL, "clock", softclock, cc, SWI_CLOCK,
                    INTR_MPSAFE, &cc->cc_cookie))
                        panic("died while creating standard software ithreads");
                cc->cc_callout = NULL;  /* Only cpu0 handles timeout(). */
                cc->cc_callwheel = malloc(
                    sizeof(struct callout_tailq) * callwheelsize, M_CALLOUT,
                    M_WAITOK);
                callout_cpu_init(cc);
        }
#endif
}

SYSINIT(start_softclock, SI_SUB_SOFTINTR, SI_ORDER_FIRST, start_softclock, NULL);

void
callout_tick(void)
{
        struct callout_cpu *cc;
        int need_softclock;
        int bucket;

        /*
         * Process callouts at a very low cpu priority, so we don't keep the
         * relatively high clock interrupt priority any longer than necessary.
         */
        need_softclock = 0;
        cc = CC_SELF();
        mtx_lock_spin_flags(&cc->cc_lock, MTX_QUIET);
        cc->cc_firsttick = cc->cc_ticks = ticks;
        for (; (cc->cc_softticks - cc->cc_ticks) <= 0; cc->cc_softticks++) {
                bucket = cc->cc_softticks & callwheelmask;
                if (!TAILQ_EMPTY(&cc->cc_callwheel[bucket])) {
                        need_softclock = 1;
                        break;
                }
        }
        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 (need_softclock)
                swi_sched(cc->cc_cookie, 0);
}

int
callout_tickstofirst(int limit)
{
        struct callout_cpu *cc;
        struct callout *c;
        struct callout_tailq *sc;
        int curticks;
        int skip = 1;

        cc = CC_SELF();
        mtx_lock_spin_flags(&cc->cc_lock, MTX_QUIET);
        curticks = cc->cc_ticks;
        while( skip < ncallout && skip < limit ) {
                sc = &cc->cc_callwheel[ (curticks+skip) & callwheelmask ];
                /* search scanning ticks */
                TAILQ_FOREACH( c, sc, c_links.tqe ){
                        if (c->c_time - curticks <= ncallout)
                                goto out;
                }
                skip++;
        }
out:
        cc->cc_firsttick = curticks + skip;
        mtx_unlock_spin_flags(&cc->cc_lock, MTX_QUIET);
        return (skip);
}

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, int to_ticks,
    void (*func)(void *), void *arg, int cpu)
{

        CC_LOCK_ASSERT(cc);

        if (to_ticks <= 0)
                to_ticks = 1;
        c->c_arg = arg;
        c->c_flags |= (CALLOUT_ACTIVE | CALLOUT_PENDING);
        c->c_func = func;
        c->c_time = ticks + to_ticks;
        TAILQ_INSERT_TAIL(&cc->cc_callwheel[c->c_time & callwheelmask], 
            c, c_links.tqe);
        if ((c->c_time - cc->cc_firsttick) < 0 &&
            callout_new_inserted != NULL) {
                cc->cc_firsttick = c->c_time;
                (*callout_new_inserted)(cpu,
                    to_ticks + (ticks - cc->cc_ticks));
        }
}

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, int *mpcalls,
    int *lockcalls, int *gcalls)
{
        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 new_cpu, new_ticks;
#endif
#ifdef DIAGNOSTIC
        struct bintime bt1, bt2;
        struct timespec ts2;
        static uint64_t maxdt = 36893488147419102LL;    /* 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_curr = c;
        cc->cc_cancel = 0;
        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_cancel) {
                        class->lc_unlock(c_lock);
                        goto skip;
                }
                /* The callout cannot be stopped now. */
                cc->cc_cancel = 1;

                if (c_lock == &Giant.lock_object) {
                        (*gcalls)++;
                        CTR3(KTR_CALLOUT, "callout %p func %p arg %p",
                            c, c_func, c_arg);
                } else {
                        (*lockcalls)++;
                        CTR3(KTR_CALLOUT, "callout lock %p func %p arg %p",
                            c, c_func, c_arg);
                }
        } else {
                (*mpcalls)++;
                CTR3(KTR_CALLOUT, "callout mpsafe %p func %p arg %p",
                    c, c_func, c_arg);
        }
#ifdef DIAGNOSTIC
        binuptime(&bt1);
#endif
        THREAD_NO_SLEEPING();
        SDT_PROBE1(callout_execute, kernel, , callout__start, c);
        c_func(c_arg);
        SDT_PROBE1(callout_execute, kernel, , callout__end, c);
        THREAD_SLEEPING_OK();
#ifdef DIAGNOSTIC
        binuptime(&bt2);
        bintime_sub(&bt2, &bt1);
        if (bt2.frac > maxdt) {
                if (lastfunc != c_func || bt2.frac > maxdt * 2) {
                        bintime2timespec(&bt2, &ts2);
                        printf(
                "Expensive timeout(9) function: %p(%p) %jd.%09ld s\n",
                            c_func, c_arg, (intmax_t)ts2.tv_sec, ts2.tv_nsec);
                }
                maxdt = bt2.frac;
                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_curr == c, ("mishandled cc_curr"));
        cc->cc_curr = NULL;
        if (cc->cc_waiting) {
                /*
                 * There is someone waiting for the
                 * callout to complete.
                 * If the callout was scheduled for
                 * migration just cancel it.
                 */
                if (cc_cme_migrating(cc)) {
                        cc_cme_cleanup(cc);

                        /*
                         * It should be assert here that the callout is not
                         * destroyed but that is not easy.
                         */
                        c->c_flags &= ~CALLOUT_DFRMIGRATION;
                }
                cc->cc_waiting = 0;
                CC_UNLOCK(cc);
                wakeup(&cc->cc_waiting);
                CC_LOCK(cc);
        } else if (cc_cme_migrating(cc)) {
                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_migration_cpu;
                new_ticks = cc->cc_migration_ticks;
                new_func = cc->cc_migration_func;
                new_arg = cc->cc_migration_arg;
                cc_cme_cleanup(cc);

                /*
                 * 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);
                callout_cc_add(c, new_cc, new_ticks, new_func, new_arg,
                    new_cpu);
                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;
        struct callout_tailq *bucket;
        int curticks;
        int steps;      /* #steps since we last allowed interrupts */
        int depth;
        int mpcalls;
        int lockcalls;
        int gcalls;

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

        mpcalls = 0;
        lockcalls = 0;
        gcalls = 0;
        depth = 0;
        steps = 0;
        cc = (struct callout_cpu *)arg;
        CC_LOCK(cc);
        while (cc->cc_softticks - 1 != cc->cc_ticks) {
                /*
                 * cc_softticks may be modified by hard clock, so cache
                 * it while we work on a given bucket.
                 */
                curticks = cc->cc_softticks;
                cc->cc_softticks++;
                bucket = &cc->cc_callwheel[curticks & callwheelmask];
                c = TAILQ_FIRST(bucket);
                while (c != NULL) {
                        depth++;
                        if (c->c_time != curticks) {
                                c = TAILQ_NEXT(c, c_links.tqe);
                                ++steps;
                                if (steps >= MAX_SOFTCLOCK_STEPS) {
                                        cc->cc_next = c;
                                        /* Give interrupts a chance. */
                                        CC_UNLOCK(cc);
                                        ;       /* nothing */
                                        CC_LOCK(cc);
                                        c = cc->cc_next;
                                        steps = 0;
                                }
                        } else {
                                cc->cc_next = TAILQ_NEXT(c, c_links.tqe);
                                TAILQ_REMOVE(bucket, c, c_links.tqe);
                                softclock_call_cc(c, cc, &mpcalls,
                                    &lockcalls, &gcalls);
                                steps = 0;
                                c = cc->cc_next;
                        }
                }
        }
        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;
        cc->cc_next = NULL;
        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_on(struct callout *c, int to_ticks, void (*ftn)(void *),
    void *arg, int cpu)
{
        struct callout_cpu *cc;
        int cancelled = 0;

        /*
         * Don't allow migration of pre-allocated callouts lest they
         * become unbalanced.
         */
        if (c->c_flags & CALLOUT_LOCAL_ALLOC)
                cpu = c->c_cpu;
        cc = callout_lock(c);
        if (cc->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_cancel)
                        cancelled = cc->cc_cancel = 1;
                if (cc->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 (cc->cc_next == c) {
                        cc->cc_next = TAILQ_NEXT(c, c_links.tqe);
                }
                TAILQ_REMOVE(&cc->cc_callwheel[c->c_time & callwheelmask], 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_curr == c) {
                        cc->cc_migration_cpu = cpu;
                        cc->cc_migration_ticks = to_ticks;
                        cc->cc_migration_func = ftn;
                        cc->cc_migration_arg = arg;
                        c->c_flags |= CALLOUT_DFRMIGRATION;
                        CTR5(KTR_CALLOUT,
                    "migration of %p func %p arg %p in %d to %u deferred",
                            c, c->c_func, c->c_arg, to_ticks, cpu);
                        CC_UNLOCK(cc);
                        return (cancelled);
                }
                cc = callout_cpu_switch(c, cc, cpu);
        }
#endif

        callout_cc_add(c, cc, to_ticks, ftn, arg, cpu);
        CTR5(KTR_CALLOUT, "%sscheduled %p func %p arg %p in %d",
            cancelled ? "re" : "", c, c->c_func, c->c_arg, to_ticks);
        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 use_lock, sq_locked;

        /*
         * 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;

        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_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_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_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_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_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_waiting = 1;
                                DROP_GIANT();
                                CC_UNLOCK(cc);
                                sleepq_add(&cc->cc_waiting,
                                    &cc->cc_lock.lock_object, "codrain",
                                    SLEEPQ_SLEEP, 0);
                                sleepq_wait(&cc->cc_waiting, 0);
                                sq_locked = 0;
                                old_cc = NULL;

                                /* Reacquire locks previously released. */
                                PICKUP_GIANT();
                                CC_LOCK(cc);
                        }
                } else if (use_lock && !cc->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_cancel = 1;
                        CTR3(KTR_CALLOUT, "cancelled %p func %p arg %p",
                            c, c->c_func, c->c_arg);
                        KASSERT(!cc_cme_migrating(cc),
                            ("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_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 (cc->cc_next == c)
                cc->cc_next = TAILQ_NEXT(c, c_links.tqe);
        TAILQ_REMOVE(&cc->cc_callwheel[c->c_time & callwheelmask], 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 */