xnu-2422.90.20.tar.gz

[apple/xnu.git] / osfmk / kern / timer_call.c

/*
 * Copyright (c) 1993-2008 Apple Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 * 
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 * 
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
 * 
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 * 
 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
 */
/*
 * Timer interrupt callout module.
 */

#include <mach/mach_types.h>

#include <kern/clock.h>
#include <kern/processor.h>
#include <kern/timer_call.h>
#include <kern/timer_queue.h>
#include <kern/call_entry.h>
#include <kern/thread.h>

#include <sys/kdebug.h>

#if CONFIG_DTRACE
#include <mach/sdt.h>
#endif


#if DEBUG
#define TIMER_ASSERT    1
#endif

//#define TIMER_ASSERT  1
//#define TIMER_DBG     1

#if TIMER_DBG
#define DBG(x...) kprintf("DBG: " x);
#else
#define DBG(x...)
#endif

#if TIMER_TRACE
#define TIMER_KDEBUG_TRACE      KERNEL_DEBUG_CONSTANT_IST
#else
#define TIMER_KDEBUG_TRACE(x...)
#endif


lck_grp_t               timer_call_lck_grp;
lck_attr_t              timer_call_lck_attr;
lck_grp_attr_t          timer_call_lck_grp_attr;

lck_grp_t               timer_longterm_lck_grp;
lck_attr_t              timer_longterm_lck_attr;
lck_grp_attr_t          timer_longterm_lck_grp_attr;


#define timer_queue_lock_spin(queue)                                    \
        lck_mtx_lock_spin_always(&queue->lock_data)

#define timer_queue_unlock(queue)               \
        lck_mtx_unlock_always(&queue->lock_data)


#define QUEUE(x)        ((queue_t)(x))
#define MPQUEUE(x)      ((mpqueue_head_t *)(x))
#define TIMER_CALL(x)   ((timer_call_t)(x))

/*
 * The longterm timer object is a global structure holding all timers
 * beyond the short-term, local timer queue threshold. The boot processor
 * is responsible for moving each timer to its local timer queue
 * if and when that timer becomes due within the threshold.
 */
#define TIMER_LONGTERM_NONE             EndOfAllTime
#if defined(__x86_64__)
#define TIMER_LONGTERM_THRESHOLD        (1ULL * NSEC_PER_SEC)
#else
#define TIMER_LONGTERM_THRESHOLD        TIMER_LONGTERM_NONE
#endif

typedef struct {
        uint64_t        interval;       /* longterm timer interval */
        uint64_t        margin;         /* fudge factor (10% of interval */
        uint64_t        deadline;       /* first/soonest longterm deadline */
        uint64_t        preempted;      /* sooner timer has pre-empted */
        timer_call_t    call;           /* first/soonest longterm timer call */
        uint64_t        deadline_set;   /* next timer set */
        timer_call_data_t timer;        /* timer used by threshold management */
                                        /* Stats: */
        uint64_t        scans;          /*   num threshold timer scans */
        uint64_t        preempts;       /*   num threshold reductions */
        uint64_t        latency;        /*   average threshold latency */       
        uint64_t        latency_min;    /*   minimum threshold latency */ 
        uint64_t        latency_max;    /*   maximum threshold latency */
} threshold_t;

typedef struct {
        mpqueue_head_t  queue;          /* longterm timer list */
        uint64_t        enqueues;       /* num timers queued */
        uint64_t        dequeues;       /* num timers dequeued */
        uint64_t        escalates;      /* num timers becoming shortterm */
        uint64_t        scan_time;      /* last time the list was scanned */
        threshold_t     threshold;      /* longterm timer threshold */
} timer_longterm_t;

timer_longterm_t                timer_longterm;

static mpqueue_head_t           *timer_longterm_queue = NULL;

static void                     timer_longterm_init(void);
static void                     timer_longterm_callout(
                                        timer_call_param_t      p0,
                                        timer_call_param_t      p1);
extern void                     timer_longterm_scan(    
                                        timer_longterm_t        *tlp,
                                        uint64_t                now);
static void                     timer_longterm_update(
                                        timer_longterm_t *tlp);
static void                     timer_longterm_update_locked(
                                        timer_longterm_t *tlp);
static mpqueue_head_t *         timer_longterm_enqueue_unlocked(
                                        timer_call_t            call,
                                        uint64_t                now,
                                        uint64_t                deadline,
                                        mpqueue_head_t **       old_queue);
static void                     timer_longterm_dequeued_locked(
                                        timer_call_t            call);

uint64_t past_deadline_timers;
uint64_t past_deadline_deltas;
uint64_t past_deadline_longest;
uint64_t past_deadline_shortest = ~0ULL;
enum {PAST_DEADLINE_TIMER_ADJUSTMENT_NS = 10 * 1000};

uint64_t past_deadline_timer_adjustment;

static boolean_t timer_call_enter_internal(timer_call_t call, timer_call_param_t param1, uint64_t deadline, uint64_t leeway, uint32_t flags, boolean_t ratelimited);
boolean_t       mach_timer_coalescing_enabled = TRUE;

mpqueue_head_t  *timer_call_enqueue_deadline_unlocked(
                        timer_call_t            call,
                        mpqueue_head_t          *queue,
                        uint64_t                deadline);

mpqueue_head_t  *timer_call_dequeue_unlocked(
                        timer_call_t            call);


void
timer_call_init(void)
{
        lck_attr_setdefault(&timer_call_lck_attr);
        lck_grp_attr_setdefault(&timer_call_lck_grp_attr);
        lck_grp_init(&timer_call_lck_grp, "timer_call", &timer_call_lck_grp_attr);
        nanotime_to_absolutetime(0, PAST_DEADLINE_TIMER_ADJUSTMENT_NS, &past_deadline_timer_adjustment);

        timer_longterm_init();
}


void
timer_call_queue_init(mpqueue_head_t *queue)
{
        DBG("timer_call_queue_init(%p)\n", queue);
        mpqueue_init(queue, &timer_call_lck_grp, &timer_call_lck_attr);
}


void
timer_call_setup(
        timer_call_t                    call,
        timer_call_func_t               func,
        timer_call_param_t              param0)
{
        DBG("timer_call_setup(%p,%p,%p)\n", call, func, param0);
        call_entry_setup(CE(call), func, param0);
        simple_lock_init(&(call)->lock, 0);
        call->async_dequeue = FALSE;
}

/*
 * Timer call entry locking model
 * ==============================
 *
 * Timer call entries are linked on per-cpu timer queues which are protected
 * by the queue lock and the call entry lock. The locking protocol is:
 *
 *  0) The canonical locking order is timer call entry followed by queue.
 *
 *  1) With only the entry lock held, entry.queue is valid:
 *    1a) NULL: the entry is not queued, or
 *    1b) non-NULL: this queue must be locked before the entry is modified.
 *        After locking the queue, the call.async_dequeue flag must be checked:
 *    1c) TRUE: the entry was removed from the queue by another thread
 *              and we must NULL the entry.queue and reset this flag, or
 *    1d) FALSE: (ie. queued), the entry can be manipulated.
 *
 *  2) If a queue lock is obtained first, the queue is stable:
 *    2a) If a try-lock of a queued entry succeeds, the call can be operated on
 *        and dequeued.
 *    2b) If a try-lock fails, it indicates that another thread is attempting
 *        to change the entry and move it to a different position in this queue
 *        or to different queue. The entry can be dequeued but it should not be
 *        operated upon since it is being changed. Furthermore, we don't null
 *        the entry.queue pointer (protected by the entry lock we don't own).
 *        Instead, we set the async_dequeue flag -- see (1c).
 *    2c) Same as 2b but occurring when a longterm timer is matured.
 */

/*
 * Inlines timer_call_entry_dequeue() and timer_call_entry_enqueue_deadline()
 * cast between pointer types (mpqueue_head_t *) and (queue_t) so that
 * we can use the call_entry_dequeue() and call_entry_enqueue_deadline()
 * methods to operate on timer_call structs as if they are call_entry structs.
 * These structures are identical except for their queue head pointer fields.
 *
 * In the debug case, we assert that the timer call locking protocol 
 * is being obeyed.
 */
#if TIMER_ASSERT
static __inline__ mpqueue_head_t *
timer_call_entry_dequeue(
        timer_call_t            entry)
{
        mpqueue_head_t  *old_queue = MPQUEUE(CE(entry)->queue);

        if (!hw_lock_held((hw_lock_t)&entry->lock))
                panic("_call_entry_dequeue() "
                        "entry %p is not locked\n", entry);
        /*
         * XXX The queue lock is actually a mutex in spin mode
         *     but there's no way to test for it being held
         *     so we pretend it's a spinlock!
         */
        if (!hw_lock_held((hw_lock_t)&old_queue->lock_data))
                panic("_call_entry_dequeue() "
                        "queue %p is not locked\n", old_queue);

        call_entry_dequeue(CE(entry));
        old_queue->count--;

        return (old_queue);
}

static __inline__ mpqueue_head_t *
timer_call_entry_enqueue_deadline(
        timer_call_t            entry,
        mpqueue_head_t          *queue,
        uint64_t                deadline)
{
        mpqueue_head_t  *old_queue = MPQUEUE(CE(entry)->queue);

        if (!hw_lock_held((hw_lock_t)&entry->lock))
                panic("_call_entry_enqueue_deadline() "
                        "entry %p is not locked\n", entry);
        /* XXX More lock pretense:  */
        if (!hw_lock_held((hw_lock_t)&queue->lock_data))
                panic("_call_entry_enqueue_deadline() "
                        "queue %p is not locked\n", queue);
        if (old_queue != NULL && old_queue != queue)
                panic("_call_entry_enqueue_deadline() "
                        "old_queue %p != queue", old_queue);

        call_entry_enqueue_deadline(CE(entry), QUEUE(queue), deadline);

/* For efficiency, track the earliest soft deadline on the queue, so that
 * fuzzy decisions can be made without lock acquisitions.
 */
        queue->earliest_soft_deadline = ((timer_call_t)queue_first(&queue->head))->soft_deadline;

        if (old_queue)
                old_queue->count--;
        queue->count++;

        return (old_queue);
}

#else

static __inline__ mpqueue_head_t *
timer_call_entry_dequeue(
        timer_call_t            entry)
{
        mpqueue_head_t  *old_queue = MPQUEUE(CE(entry)->queue);

        call_entry_dequeue(CE(entry));
        old_queue->count--;

        return old_queue;
}

static __inline__ mpqueue_head_t *
timer_call_entry_enqueue_deadline(
        timer_call_t                    entry,
        mpqueue_head_t                  *queue,
        uint64_t                        deadline)
{
        mpqueue_head_t  *old_queue = MPQUEUE(CE(entry)->queue);

        call_entry_enqueue_deadline(CE(entry), QUEUE(queue), deadline);

        /* For efficiency, track the earliest soft deadline on the queue,
         * so that fuzzy decisions can be made without lock acquisitions.
         */
        queue->earliest_soft_deadline = ((timer_call_t)queue_first(&queue->head))->soft_deadline;

        if (old_queue)
                old_queue->count--;
        queue->count++;

        return old_queue;
}

#endif

static __inline__ void
timer_call_entry_enqueue_tail(
        timer_call_t                    entry,
        mpqueue_head_t                  *queue)
{
        call_entry_enqueue_tail(CE(entry), QUEUE(queue));
        queue->count++;
        return;
}

/*
 * Remove timer entry from its queue but don't change the queue pointer
 * and set the async_dequeue flag. This is locking case 2b.
 */
static __inline__ void
timer_call_entry_dequeue_async(
        timer_call_t            entry)
{
        mpqueue_head_t  *old_queue = MPQUEUE(CE(entry)->queue);
        if (old_queue) {
                old_queue->count--;
                (void) remque(qe(entry));
                entry->async_dequeue = TRUE;
        }
        return;
}

#if TIMER_ASSERT
unsigned timer_call_enqueue_deadline_unlocked_async1;
unsigned timer_call_enqueue_deadline_unlocked_async2;
#endif
/*
 * Assumes call_entry and queues unlocked, interrupts disabled.
 */
__inline__ mpqueue_head_t *
timer_call_enqueue_deadline_unlocked(
        timer_call_t                    call,
        mpqueue_head_t                  *queue,
        uint64_t                        deadline)
{
        call_entry_t    entry = CE(call);
        mpqueue_head_t  *old_queue;

        DBG("timer_call_enqueue_deadline_unlocked(%p,%p,)\n", call, queue);

        simple_lock(&call->lock);
        old_queue = MPQUEUE(entry->queue);
        if (old_queue != NULL) {
                timer_queue_lock_spin(old_queue);
                if (call->async_dequeue) {
                        /* collision (1c): timer already dequeued, clear flag */
#if TIMER_ASSERT
                        TIMER_KDEBUG_TRACE(KDEBUG_TRACE, 
                                DECR_TIMER_ASYNC_DEQ | DBG_FUNC_NONE,
                                call,
                                call->async_dequeue,
                                CE(call)->queue,
                                0x1c, 0);
                        timer_call_enqueue_deadline_unlocked_async1++;
#endif
                        call->async_dequeue = FALSE;
                        entry->queue = NULL;
                } else if (old_queue != queue) {
                        timer_call_entry_dequeue(call);
#if TIMER_ASSERT
                        timer_call_enqueue_deadline_unlocked_async2++;
#endif
                }
                if (old_queue == timer_longterm_queue)
                        timer_longterm_dequeued_locked(call);
                if (old_queue != queue) {
                        timer_queue_unlock(old_queue);
                        timer_queue_lock_spin(queue);
                }
        } else {
                timer_queue_lock_spin(queue);
        }

        timer_call_entry_enqueue_deadline(call, queue, deadline);
        timer_queue_unlock(queue);
        simple_unlock(&call->lock);

        return (old_queue);
}

#if TIMER_ASSERT
unsigned timer_call_dequeue_unlocked_async1;
unsigned timer_call_dequeue_unlocked_async2;
#endif
mpqueue_head_t *
timer_call_dequeue_unlocked(
        timer_call_t            call)
{
        call_entry_t    entry = CE(call);
        mpqueue_head_t  *old_queue;

        DBG("timer_call_dequeue_unlocked(%p)\n", call);

        simple_lock(&call->lock);
        old_queue = MPQUEUE(entry->queue);
#if TIMER_ASSERT
        TIMER_KDEBUG_TRACE(KDEBUG_TRACE, 
                DECR_TIMER_ASYNC_DEQ | DBG_FUNC_NONE,
                call,
                call->async_dequeue,
                CE(call)->queue,
                0, 0);
#endif
        if (old_queue != NULL) {
                timer_queue_lock_spin(old_queue);
                if (call->async_dequeue) {
                        /* collision (1c): timer already dequeued, clear flag */
#if TIMER_ASSERT
                        TIMER_KDEBUG_TRACE(KDEBUG_TRACE, 
                                DECR_TIMER_ASYNC_DEQ | DBG_FUNC_NONE,
                                call,
                                call->async_dequeue,
                                CE(call)->queue,
                                0x1c, 0);
                        timer_call_dequeue_unlocked_async1++;
#endif
                        call->async_dequeue = FALSE;
                        entry->queue = NULL;
                } else {
                        timer_call_entry_dequeue(call);
                }
                if (old_queue == timer_longterm_queue)
                        timer_longterm_dequeued_locked(call);
                timer_queue_unlock(old_queue);
        }
        simple_unlock(&call->lock);
        return (old_queue);
}

static boolean_t 
timer_call_enter_internal(
        timer_call_t            call,
        timer_call_param_t      param1,
        uint64_t                deadline,
        uint64_t                leeway,
        uint32_t                flags,
        boolean_t               ratelimited)
{
        mpqueue_head_t          *queue = NULL;
        mpqueue_head_t          *old_queue;
        spl_t                   s;
        uint64_t                slop;
        uint32_t                urgency;

        s = splclock();

        call->soft_deadline = deadline;
        call->flags = flags;

        uint64_t ctime = mach_absolute_time();

        TIMER_KDEBUG_TRACE(KDEBUG_TRACE,
                DECR_TIMER_ENTER | DBG_FUNC_START,
                call,
                param1, deadline, flags, 0); 

        urgency = (flags & TIMER_CALL_URGENCY_MASK);

        boolean_t slop_ratelimited = FALSE;
        slop = timer_call_slop(deadline, ctime, urgency, current_thread(), &slop_ratelimited);

        if ((flags & TIMER_CALL_LEEWAY) != 0 && leeway > slop)
                slop = leeway;

        if (UINT64_MAX - deadline <= slop) {
                deadline = UINT64_MAX;
        } else {
                deadline += slop;
        }

        if (__improbable(deadline < ctime)) {
                uint64_t delta = (ctime - deadline);

                past_deadline_timers++;
                past_deadline_deltas += delta;
                if (delta > past_deadline_longest)
                        past_deadline_longest = deadline;
                if (delta < past_deadline_shortest)
                        past_deadline_shortest = delta;

                deadline = ctime + past_deadline_timer_adjustment;
                call->soft_deadline = deadline;
        }

        /* Bit 0 of the "soft" deadline indicates that
         * this particular timer call requires rate-limiting
         * behaviour. Maintain the invariant deadline >= soft_deadline by
         * setting bit 0 of "deadline".
         */

        deadline |= 1;
        if (ratelimited || slop_ratelimited) {
                call->soft_deadline |= 1ULL;
        } else {
                call->soft_deadline &= ~0x1ULL;
        }

        call->ttd =  call->soft_deadline - ctime;

#if CONFIG_DTRACE
        DTRACE_TMR7(callout__create, timer_call_func_t, CE(call)->func,
        timer_call_param_t, CE(call)->param0, uint32_t, call->flags,
            (deadline - call->soft_deadline),
            (call->ttd >> 32), (unsigned) (call->ttd & 0xFFFFFFFF), call);
#endif

        if (!ratelimited && !slop_ratelimited) {
                queue = timer_longterm_enqueue_unlocked(call, ctime, deadline, &old_queue);
        }

        if (queue == NULL) {
                queue = timer_queue_assign(deadline);
                old_queue = timer_call_enqueue_deadline_unlocked(call, queue, deadline);
        }

        CE(call)->param1 = param1;
#if TIMER_TRACE
        CE(call)->entry_time = ctime;
#endif

        TIMER_KDEBUG_TRACE(KDEBUG_TRACE,
                DECR_TIMER_ENTER | DBG_FUNC_END,
                call,
                (old_queue != NULL), call->soft_deadline, queue->count, 0); 

        splx(s);

        return (old_queue != NULL);
}

/*
 * timer_call_*()
 *      return boolean indicating whether the call was previously queued.
 */
boolean_t
timer_call_enter(
        timer_call_t            call,
        uint64_t                deadline,
        uint32_t                flags)
{
        return timer_call_enter_internal(call, NULL, deadline, 0, flags, FALSE);
}

boolean_t
timer_call_enter1(
        timer_call_t            call,
        timer_call_param_t      param1,
        uint64_t                deadline,
        uint32_t                flags)
{
        return timer_call_enter_internal(call, param1, deadline, 0, flags, FALSE);
}

boolean_t
timer_call_enter_with_leeway(
        timer_call_t            call,
        timer_call_param_t      param1,
        uint64_t                deadline,
        uint64_t                leeway,
        uint32_t                flags,
        boolean_t               ratelimited)
{
        return timer_call_enter_internal(call, param1, deadline, leeway, flags, ratelimited);
}

boolean_t
timer_call_cancel(
        timer_call_t            call)
{
        mpqueue_head_t          *old_queue;
        spl_t                   s;

        s = splclock();

        TIMER_KDEBUG_TRACE(KDEBUG_TRACE,
                DECR_TIMER_CANCEL | DBG_FUNC_START,
                call,
                CE(call)->deadline, call->soft_deadline, call->flags, 0);

        old_queue = timer_call_dequeue_unlocked(call);

        if (old_queue != NULL) {
                timer_queue_lock_spin(old_queue);
                if (!queue_empty(&old_queue->head)) {
                        timer_queue_cancel(old_queue, CE(call)->deadline, CE(queue_first(&old_queue->head))->deadline);
                        old_queue->earliest_soft_deadline = ((timer_call_t)queue_first(&old_queue->head))->soft_deadline;
                }
                else {
                        timer_queue_cancel(old_queue, CE(call)->deadline, UINT64_MAX);
                        old_queue->earliest_soft_deadline = UINT64_MAX;
                }
                timer_queue_unlock(old_queue);
        }
        TIMER_KDEBUG_TRACE(KDEBUG_TRACE,
                DECR_TIMER_CANCEL | DBG_FUNC_END,
                call,
                old_queue,
                CE(call)->deadline - mach_absolute_time(),
                CE(call)->deadline - CE(call)->entry_time, 0);
        splx(s);

#if CONFIG_DTRACE
        DTRACE_TMR6(callout__cancel, timer_call_func_t, CE(call)->func,
            timer_call_param_t, CE(call)->param0, uint32_t, call->flags, 0,
            (call->ttd >> 32), (unsigned) (call->ttd & 0xFFFFFFFF));
#endif

        return (old_queue != NULL);
}

uint32_t        timer_queue_shutdown_lock_skips;
void
timer_queue_shutdown(
        mpqueue_head_t          *queue)
{
        timer_call_t            call;
        mpqueue_head_t          *new_queue;
        spl_t                   s;

        DBG("timer_queue_shutdown(%p)\n", queue);

        s = splclock();

        /* Note comma operator in while expression re-locking each iteration */
        while (timer_queue_lock_spin(queue), !queue_empty(&queue->head)) {
                call = TIMER_CALL(queue_first(&queue->head));
                if (!simple_lock_try(&call->lock)) {
                        /*
                         * case (2b) lock order inversion, dequeue and skip
                         * Don't change the call_entry queue back-pointer
                         * but set the async_dequeue field.
                         */
                        timer_queue_shutdown_lock_skips++;
                        timer_call_entry_dequeue_async(call);
#if TIMER_ASSERT
                        TIMER_KDEBUG_TRACE(KDEBUG_TRACE, 
                                DECR_TIMER_ASYNC_DEQ | DBG_FUNC_NONE,
                                call,
                                call->async_dequeue,
                                CE(call)->queue,
                                0x2b, 0);
#endif
                        timer_queue_unlock(queue);
                        continue;
                }

                /* remove entry from old queue */
                timer_call_entry_dequeue(call);
                timer_queue_unlock(queue);

                /* and queue it on new */
                new_queue = timer_queue_assign(CE(call)->deadline);
                timer_queue_lock_spin(new_queue);
                timer_call_entry_enqueue_deadline(
                        call, new_queue, CE(call)->deadline);
                timer_queue_unlock(new_queue);

                simple_unlock(&call->lock);
        }

        timer_queue_unlock(queue);
        splx(s);
}

uint32_t        timer_queue_expire_lock_skips;
uint64_t
timer_queue_expire_with_options(
        mpqueue_head_t          *queue,
        uint64_t                deadline,
        boolean_t               rescan)
{
        timer_call_t    call = NULL;
        uint32_t tc_iterations = 0;
        DBG("timer_queue_expire(%p,)\n", queue);

        uint64_t cur_deadline = deadline;
        timer_queue_lock_spin(queue);

        while (!queue_empty(&queue->head)) {
                /* Upon processing one or more timer calls, refresh the
                 * deadline to account for time elapsed in the callout
                 */
                if (++tc_iterations > 1)
                        cur_deadline = mach_absolute_time();

                if (call == NULL)
                        call = TIMER_CALL(queue_first(&queue->head));

                if (call->soft_deadline <= cur_deadline) {
                        timer_call_func_t               func;
                        timer_call_param_t              param0, param1;

                        TCOAL_DEBUG(0xDDDD0000, queue->earliest_soft_deadline, call->soft_deadline, 0, 0, 0);
                        TIMER_KDEBUG_TRACE(KDEBUG_TRACE, 
                                DECR_TIMER_EXPIRE | DBG_FUNC_NONE,
                                call,
                                call->soft_deadline,
                                CE(call)->deadline,
                                CE(call)->entry_time, 0);

                        /* Bit 0 of the "soft" deadline indicates that
                         * this particular timer call is rate-limited
                         * and hence shouldn't be processed before its
                         * hard deadline.
                         */
                        if ((call->soft_deadline & 0x1) &&
                            (CE(call)->deadline > cur_deadline)) {
                                if (rescan == FALSE)
                                        break;
                        }

                        if (!simple_lock_try(&call->lock)) {
                                /* case (2b) lock inversion, dequeue and skip */
                                timer_queue_expire_lock_skips++;
                                timer_call_entry_dequeue_async(call);
                                call = NULL;
                                continue;
                        }

                        timer_call_entry_dequeue(call);

                        func = CE(call)->func;
                        param0 = CE(call)->param0;
                        param1 = CE(call)->param1;

                        simple_unlock(&call->lock);
                        timer_queue_unlock(queue);

                        TIMER_KDEBUG_TRACE(KDEBUG_TRACE, 
                                DECR_TIMER_CALLOUT | DBG_FUNC_START,
                                call, VM_KERNEL_UNSLIDE(func), param0, param1, 0);

#if CONFIG_DTRACE
                        DTRACE_TMR7(callout__start, timer_call_func_t, func,
                            timer_call_param_t, param0, unsigned, call->flags,
                            0, (call->ttd >> 32),
                            (unsigned) (call->ttd & 0xFFFFFFFF), call);
#endif
                        /* Maintain time-to-deadline in per-processor data
                         * structure for thread wakeup deadline statistics.
                         */
                        uint64_t *ttdp = &(PROCESSOR_DATA(current_processor(), timer_call_ttd));
                        *ttdp = call->ttd;
                        (*func)(param0, param1);
                        *ttdp = 0;
#if CONFIG_DTRACE
                        DTRACE_TMR4(callout__end, timer_call_func_t, func,
                            param0, param1, call);
#endif

                        TIMER_KDEBUG_TRACE(KDEBUG_TRACE, 
                                DECR_TIMER_CALLOUT | DBG_FUNC_END,
                                call, VM_KERNEL_UNSLIDE(func), param0, param1, 0);
                        call = NULL;
                        timer_queue_lock_spin(queue);
                } else {
                        if (__probable(rescan == FALSE)) {
                                break;
                        } else {
                                int64_t skew = CE(call)->deadline - call->soft_deadline;
                                assert(CE(call)->deadline >= call->soft_deadline);

                                /* DRK: On a latency quality-of-service level change,
                                 * re-sort potentially rate-limited timers. The platform
                                 * layer determines which timers require
                                 * this. In the absence of the per-callout
                                 * synchronization requirement, a global resort could
                                 * be more efficient. The re-sort effectively
                                 * annuls all timer adjustments, i.e. the "soft
                                 * deadline" is the sort key.
                                 */
        
                                if (timer_resort_threshold(skew)) {
                                        if (__probable(simple_lock_try(&call->lock))) {
                                                timer_call_entry_dequeue(call);
                                                timer_call_entry_enqueue_deadline(call, queue, call->soft_deadline);
                                                simple_unlock(&call->lock);
                                                call = NULL;
                                        }
                                }
                                if (call) {
                                        call = TIMER_CALL(queue_next(qe(call)));
                                        if (queue_end(&queue->head, qe(call)))
                                                break;
                                }
                        }
                }
        }

        if (!queue_empty(&queue->head)) {
                call = TIMER_CALL(queue_first(&queue->head));
                cur_deadline = CE(call)->deadline;
                queue->earliest_soft_deadline = call->soft_deadline;
        } else {
                queue->earliest_soft_deadline = cur_deadline = UINT64_MAX;
        }

        timer_queue_unlock(queue);

        return (cur_deadline);
}

uint64_t
timer_queue_expire(
        mpqueue_head_t          *queue,
        uint64_t                deadline)
{
        return timer_queue_expire_with_options(queue, deadline, FALSE);
}

extern int serverperfmode;
uint32_t        timer_queue_migrate_lock_skips;
/*
 * timer_queue_migrate() is called by timer_queue_migrate_cpu()
 * to move timer requests from the local processor (queue_from)
 * to a target processor's (queue_to).
 */
int
timer_queue_migrate(mpqueue_head_t *queue_from, mpqueue_head_t *queue_to)
{
        timer_call_t    call;
        timer_call_t    head_to;
        int             timers_migrated = 0;

        DBG("timer_queue_migrate(%p,%p)\n", queue_from, queue_to);

        assert(!ml_get_interrupts_enabled());
        assert(queue_from != queue_to);

        if (serverperfmode) {
                /*
                 * if we're running a high end server
                 * avoid migrations... they add latency
                 * and don't save us power under typical
                 * server workloads
                 */
                return -4;
        }

        /*
         * Take both local (from) and target (to) timer queue locks while
         * moving the timers from the local queue to the target processor.
         * We assume that the target is always the boot processor.
         * But only move if all of the following is true:
         *  - the target queue is non-empty
         *  - the local queue is non-empty
         *  - the local queue's first deadline is later than the target's
         *  - the local queue contains no non-migrateable "local" call
         * so that we need not have the target resync.
         */

        timer_queue_lock_spin(queue_to);

        head_to = TIMER_CALL(queue_first(&queue_to->head));
        if (queue_empty(&queue_to->head)) {
                timers_migrated = -1;
                goto abort1;
        }

        timer_queue_lock_spin(queue_from);

        if (queue_empty(&queue_from->head)) {
                timers_migrated = -2;
                goto abort2;
        }

        call = TIMER_CALL(queue_first(&queue_from->head));
        if (CE(call)->deadline < CE(head_to)->deadline) {
                timers_migrated = 0;
                goto abort2;
        }

        /* perform scan for non-migratable timers */
        do {
                if (call->flags & TIMER_CALL_LOCAL) {
                        timers_migrated = -3;
                        goto abort2;
                }
                call = TIMER_CALL(queue_next(qe(call)));
        } while (!queue_end(&queue_from->head, qe(call)));

        /* migration loop itself -- both queues are locked */
        while (!queue_empty(&queue_from->head)) {
                call = TIMER_CALL(queue_first(&queue_from->head));
                if (!simple_lock_try(&call->lock)) {
                        /* case (2b) lock order inversion, dequeue only */
#ifdef TIMER_ASSERT
                        TIMER_KDEBUG_TRACE(KDEBUG_TRACE, 
                                DECR_TIMER_ASYNC_DEQ | DBG_FUNC_NONE,
                                call,
                                CE(call)->queue,
                                call->lock.interlock.lock_data,
                                0x2b, 0);
#endif
                        timer_queue_migrate_lock_skips++;
                        timer_call_entry_dequeue_async(call);
                        continue;
                }
                timer_call_entry_dequeue(call);
                timer_call_entry_enqueue_deadline(
                        call, queue_to, CE(call)->deadline);
                timers_migrated++;
                simple_unlock(&call->lock);
        }
        queue_from->earliest_soft_deadline = UINT64_MAX;
abort2:
        timer_queue_unlock(queue_from);
abort1:
        timer_queue_unlock(queue_to);

        return timers_migrated;
}

void
timer_queue_trace_cpu(int ncpu)
{
        timer_call_nosync_cpu(
                ncpu,
                (void(*)())timer_queue_trace,
                (void*) timer_queue_cpu(ncpu));
}

void
timer_queue_trace(
        mpqueue_head_t                  *queue)
{
        timer_call_t    call;
        spl_t           s;

        if (!kdebug_enable)
                return;

        s = splclock();
        timer_queue_lock_spin(queue);

        TIMER_KDEBUG_TRACE(KDEBUG_TRACE,
                DECR_TIMER_QUEUE | DBG_FUNC_START,
                queue->count, mach_absolute_time(), 0, 0, 0); 

        if (!queue_empty(&queue->head)) {
                call = TIMER_CALL(queue_first(&queue->head));
                do {
                        TIMER_KDEBUG_TRACE(KDEBUG_TRACE,
                                DECR_TIMER_QUEUE | DBG_FUNC_NONE,
                                call->soft_deadline,
                                CE(call)->deadline,
                                CE(call)->entry_time,
                                CE(call)->func,
                                0);
                        call = TIMER_CALL(queue_next(qe(call)));
                } while (!queue_end(&queue->head, qe(call)));
        }

        TIMER_KDEBUG_TRACE(KDEBUG_TRACE,
                DECR_TIMER_QUEUE | DBG_FUNC_END,
                queue->count, mach_absolute_time(), 0, 0, 0); 

        timer_queue_unlock(queue);
        splx(s);
}

void
timer_longterm_dequeued_locked(timer_call_t call)
{
        timer_longterm_t        *tlp = &timer_longterm;

        tlp->dequeues++;
        if (call == tlp->threshold.call)
                tlp->threshold.call = NULL;
}

/*
 * Place a timer call in the longterm list
 * and adjust the next timer callout deadline if the new timer is first.
 */
mpqueue_head_t *
timer_longterm_enqueue_unlocked(timer_call_t    call,
                                uint64_t        now,
                                uint64_t        deadline,
                                mpqueue_head_t  **old_queue)
{
        timer_longterm_t        *tlp = &timer_longterm;
        boolean_t               update_required = FALSE;
        uint64_t                longterm_threshold;

        longterm_threshold = now + tlp->threshold.interval;

        /*
         * Return NULL without doing anything if:
         *  - this timer is local, or
         *  - the longterm mechanism is disabled, or
         *  - this deadline is too short.
         */
        if (__probable((call->flags & TIMER_CALL_LOCAL) != 0 ||
            (tlp->threshold.interval == TIMER_LONGTERM_NONE) ||
                (deadline <= longterm_threshold)))
                return NULL;

        /*
         * Remove timer from its current queue, if any.
         */
        *old_queue = timer_call_dequeue_unlocked(call);

        /*
         * Lock the longterm queue, queue timer and determine
         * whether an update is necessary.
         */
        assert(!ml_get_interrupts_enabled());
        simple_lock(&call->lock);
        timer_queue_lock_spin(timer_longterm_queue);
        timer_call_entry_enqueue_tail(call, timer_longterm_queue);
        CE(call)->deadline = deadline;
        
        tlp->enqueues++;

        /*
         * We'll need to update the currently set threshold timer
         * if the new deadline is sooner and no sooner update is in flight.
         */ 
        if (deadline < tlp->threshold.deadline &&
            deadline < tlp->threshold.preempted) {
                tlp->threshold.preempted = deadline;
                tlp->threshold.call = call;
                update_required = TRUE;
        }
        timer_queue_unlock(timer_longterm_queue);
        simple_unlock(&call->lock);
        
        if (update_required) {
                timer_call_nosync_cpu(
                        master_cpu,
                        (void (*)(void *)) timer_longterm_update,
                        (void *)tlp);
        }

        return timer_longterm_queue;
}

/*
 * Scan for timers below the longterm threshold.
 * Move these to the local timer queue (of the boot processor on which the
 * calling thread is running).
 * Both the local (boot) queue and the longterm queue are locked.
 * The scan is similar to the timer migrate sequence but is performed by
 * successively examining each timer on the longterm queue:
 *  - if within the short-term threshold
 *    - enter on the local queue (unless being deleted), 
 *  - otherwise:
 *    - if sooner, deadline becomes the next threshold deadline.
 */
void
timer_longterm_scan(timer_longterm_t    *tlp,
                    uint64_t            now)
{
        queue_entry_t   qe;
        timer_call_t    call;
        uint64_t        threshold;
        uint64_t        deadline;
        mpqueue_head_t  *timer_master_queue;

        assert(!ml_get_interrupts_enabled());
        assert(cpu_number() == master_cpu);

        if (tlp->threshold.interval != TIMER_LONGTERM_NONE)
                threshold = now + tlp->threshold.interval;
        else
                threshold = TIMER_LONGTERM_NONE;

        tlp->threshold.deadline = TIMER_LONGTERM_NONE;
        tlp->threshold.call = NULL;

        if (queue_empty(&timer_longterm_queue->head))
                return;

        timer_master_queue = timer_queue_cpu(master_cpu);
        timer_queue_lock_spin(timer_master_queue);

        qe = queue_first(&timer_longterm_queue->head);
        while (!queue_end(&timer_longterm_queue->head, qe)) {
                call = TIMER_CALL(qe);
                deadline = call->soft_deadline;
                qe = queue_next(qe);
                if (!simple_lock_try(&call->lock)) {
                        /* case (2c) lock order inversion, dequeue only */
#ifdef TIMER_ASSERT
                        TIMER_KDEBUG_TRACE(KDEBUG_TRACE,
                                DECR_TIMER_ASYNC_DEQ | DBG_FUNC_NONE,
                                call,
                                CE(call)->queue,
                                call->lock.interlock.lock_data,
                                0x2c, 0);
#endif
                        timer_call_entry_dequeue_async(call);
                        continue;
                }
                if (deadline < threshold) {
                        /*
                         * This timer needs moving (escalating)
                         * to the local (boot) processor's queue.
                         */
#ifdef TIMER_ASSERT
                        if (deadline < now)
                                TIMER_KDEBUG_TRACE(KDEBUG_TRACE,
                                        DECR_TIMER_OVERDUE | DBG_FUNC_NONE,
                                        call,
                                        deadline,
                                        now,
                                        threshold,
                                        0);
#endif
                        TIMER_KDEBUG_TRACE(KDEBUG_TRACE,
                                DECR_TIMER_ESCALATE | DBG_FUNC_NONE,
                                call,
                                CE(call)->deadline,
                                CE(call)->entry_time,
                                CE(call)->func,
                                0);
                        tlp->escalates++;
                        timer_call_entry_dequeue(call);
                        timer_call_entry_enqueue_deadline(
                                call, timer_master_queue, CE(call)->deadline);
                        /*
                         * A side-effect of the following call is to update
                         * the actual hardware deadline if required.
                         */
                        (void) timer_queue_assign(deadline);
                } else {
                        if (deadline < tlp->threshold.deadline) {
                                tlp->threshold.deadline = deadline;
                                tlp->threshold.call = call;
                        }
                }
                simple_unlock(&call->lock);
        }

        timer_queue_unlock(timer_master_queue);
}

void
timer_longterm_callout(timer_call_param_t p0, __unused timer_call_param_t p1)
{
        timer_longterm_t        *tlp = (timer_longterm_t *) p0;

        timer_longterm_update(tlp);
}

void
timer_longterm_update_locked(timer_longterm_t *tlp)
{
        uint64_t        latency;

        TIMER_KDEBUG_TRACE(KDEBUG_TRACE, 
                DECR_TIMER_UPDATE | DBG_FUNC_START,
                &tlp->queue,
                tlp->threshold.deadline,
                tlp->threshold.preempted,
                tlp->queue.count, 0);

        tlp->scan_time = mach_absolute_time();
        if (tlp->threshold.preempted != TIMER_LONGTERM_NONE) {
                tlp->threshold.preempts++;
                tlp->threshold.deadline = tlp->threshold.preempted;
                tlp->threshold.preempted = TIMER_LONGTERM_NONE;
                /*
                 * Note: in the unlikely event that a pre-empted timer has
                 * itself been cancelled, we'll simply re-scan later at the
                 * time of the preempted/cancelled timer.
                 */
        } else {
                tlp->threshold.scans++;

                /*
                 * Maintain a moving average of our wakeup latency.
                 * Clamp latency to 0 and ignore above threshold interval.
                 */
                if (tlp->scan_time > tlp->threshold.deadline_set)
                        latency = tlp->scan_time - tlp->threshold.deadline_set;
                else
                        latency = 0;
                if (latency < tlp->threshold.interval) {
                        tlp->threshold.latency_min =
                                MIN(tlp->threshold.latency_min, latency);
                        tlp->threshold.latency_max =
                                MAX(tlp->threshold.latency_max, latency);
                        tlp->threshold.latency =
                                (tlp->threshold.latency*99 + latency) / 100;
                }

                timer_longterm_scan(tlp, tlp->scan_time); 
        }

        tlp->threshold.deadline_set = tlp->threshold.deadline;
        /* The next deadline timer to be set is adjusted */
        if (tlp->threshold.deadline != TIMER_LONGTERM_NONE) {
                tlp->threshold.deadline_set -= tlp->threshold.margin;
                tlp->threshold.deadline_set -= tlp->threshold.latency;
        }

        TIMER_KDEBUG_TRACE(KDEBUG_TRACE, 
                DECR_TIMER_UPDATE | DBG_FUNC_END,
                &tlp->queue,
                tlp->threshold.deadline,
                tlp->threshold.scans,
                tlp->queue.count, 0);
}

void
timer_longterm_update(timer_longterm_t *tlp)
{
        spl_t   s = splclock();

        timer_queue_lock_spin(timer_longterm_queue);

        if (cpu_number() != master_cpu)
                panic("timer_longterm_update_master() on non-boot cpu");

        timer_longterm_update_locked(tlp);

        if (tlp->threshold.deadline != TIMER_LONGTERM_NONE)
                timer_call_enter(
                        &tlp->threshold.timer,
                        tlp->threshold.deadline_set,
                        TIMER_CALL_LOCAL | TIMER_CALL_SYS_CRITICAL);
        
        timer_queue_unlock(timer_longterm_queue);
        splx(s);
}

void
timer_longterm_init(void)
{
        uint32_t                longterm;
        timer_longterm_t        *tlp = &timer_longterm;

        DBG("timer_longterm_init() tlp: %p, queue: %p\n", tlp, &tlp->queue);

        /*
         * Set the longterm timer threshold. Defaults to TIMER_LONGTERM_THRESHOLD
         * or TIMER_LONGTERM_NONE (disabled) for server;
         * overridden longterm boot-arg 
         */
        tlp->threshold.interval = serverperfmode ? TIMER_LONGTERM_NONE
                                                 : TIMER_LONGTERM_THRESHOLD;
        if (PE_parse_boot_argn("longterm", &longterm, sizeof (longterm))) {
                tlp->threshold.interval = (longterm == 0) ?
                                                TIMER_LONGTERM_NONE :
                                                longterm * NSEC_PER_MSEC;
        }
        if (tlp->threshold.interval != TIMER_LONGTERM_NONE) {
                printf("Longterm timer threshold: %llu ms\n",
                        tlp->threshold.interval / NSEC_PER_MSEC); 
                kprintf("Longterm timer threshold: %llu ms\n",
                        tlp->threshold.interval / NSEC_PER_MSEC); 
                nanoseconds_to_absolutetime(tlp->threshold.interval,
                                            &tlp->threshold.interval);
                tlp->threshold.margin = tlp->threshold.interval / 10;
                tlp->threshold.latency_min = EndOfAllTime;
                tlp->threshold.latency_max = 0;
        }

        tlp->threshold.preempted = TIMER_LONGTERM_NONE;
        tlp->threshold.deadline = TIMER_LONGTERM_NONE;

        lck_attr_setdefault(&timer_longterm_lck_attr);
        lck_grp_attr_setdefault(&timer_longterm_lck_grp_attr);
        lck_grp_init(&timer_longterm_lck_grp,
                     "timer_longterm", &timer_longterm_lck_grp_attr);
        mpqueue_init(&tlp->queue,
                     &timer_longterm_lck_grp, &timer_longterm_lck_attr);

        timer_call_setup(&tlp->threshold.timer,
                         timer_longterm_callout, (timer_call_param_t) tlp);

        timer_longterm_queue = &tlp->queue;
}

enum {
        THRESHOLD, QCOUNT,
        ENQUEUES, DEQUEUES, ESCALATES, SCANS, PREEMPTS,
        LATENCY, LATENCY_MIN, LATENCY_MAX
};
uint64_t
timer_sysctl_get(int oid)
{
        timer_longterm_t        *tlp = &timer_longterm;

        switch (oid) {
        case THRESHOLD:
                return (tlp->threshold.interval == TIMER_LONGTERM_NONE) ?
                        0 : tlp->threshold.interval / NSEC_PER_MSEC;
        case QCOUNT:
                return tlp->queue.count;
        case ENQUEUES:
                return tlp->enqueues;
        case DEQUEUES:
                return tlp->dequeues;
        case ESCALATES:
                return tlp->escalates;
        case SCANS:
                return tlp->threshold.scans;
        case PREEMPTS:
                return tlp->threshold.preempts;
        case LATENCY:
                return tlp->threshold.latency;
        case LATENCY_MIN:
                return tlp->threshold.latency_min;
        case LATENCY_MAX:
                return tlp->threshold.latency_max;
        default:
                return 0;
        }
}

/*
 * timer_master_scan() is the inverse of timer_longterm_scan()
 * since it un-escalates timers to the longterm queue.
 */
static void
timer_master_scan(timer_longterm_t      *tlp,
                  uint64_t              now)
{
        queue_entry_t   qe;
        timer_call_t    call;
        uint64_t        threshold;
        uint64_t        deadline;
        mpqueue_head_t  *timer_master_queue;

        if (tlp->threshold.interval != TIMER_LONGTERM_NONE)
                threshold = now + tlp->threshold.interval;
        else
                threshold = TIMER_LONGTERM_NONE;

        timer_master_queue = timer_queue_cpu(master_cpu);
        timer_queue_lock_spin(timer_master_queue);

        qe = queue_first(&timer_master_queue->head);
        while (!queue_end(&timer_master_queue->head, qe)) {
                call = TIMER_CALL(qe);
                deadline = CE(call)->deadline;
                qe = queue_next(qe);
                if ((call->flags & TIMER_CALL_LOCAL) != 0)
                        continue;
                if (!simple_lock_try(&call->lock)) {
                        /* case (2c) lock order inversion, dequeue only */
                        timer_call_entry_dequeue_async(call);
                        continue;
                }
                if (deadline > threshold) {
                        /* move from master to longterm */
                        timer_call_entry_dequeue(call);
                        timer_call_entry_enqueue_tail(call, timer_longterm_queue);
                        if (deadline < tlp->threshold.deadline) {
                                tlp->threshold.deadline = deadline;
                                tlp->threshold.call = call;
                        }
                }
                simple_unlock(&call->lock);
        }
        timer_queue_unlock(timer_master_queue);
}

static void
timer_sysctl_set_threshold(uint64_t value)
{
        timer_longterm_t        *tlp = &timer_longterm;
        spl_t                   s = splclock();
        boolean_t               threshold_increase;

        timer_queue_lock_spin(timer_longterm_queue);

        timer_call_cancel(&tlp->threshold.timer);

        /*
         * Set the new threshold and note whther it's increasing.
         */
        if (value == 0) {
                tlp->threshold.interval = TIMER_LONGTERM_NONE;
                threshold_increase = TRUE;
                timer_call_cancel(&tlp->threshold.timer);
        } else {
                uint64_t        old_interval = tlp->threshold.interval;
                tlp->threshold.interval = value * NSEC_PER_MSEC;
                nanoseconds_to_absolutetime(tlp->threshold.interval,
                                            &tlp->threshold.interval);
                tlp->threshold.margin = tlp->threshold.interval / 10;
                if  (old_interval == TIMER_LONGTERM_NONE)
                        threshold_increase = FALSE;
                else
                        threshold_increase = (tlp->threshold.interval > old_interval);
        }

        if (threshold_increase /* or removal */) {
                /* Escalate timers from the longterm queue */
                timer_longterm_scan(tlp, mach_absolute_time());
        } else /* decrease or addition  */ {
                /*
                 * We scan the local/master queue for timers now longterm.
                 * To be strictly correct, we should scan all processor queues
                 * but timer migration results in most timers gravitating to the
                 * master processor in any case.
                 */
                timer_master_scan(tlp, mach_absolute_time());
        }

        /* Set new timer accordingly */
        tlp->threshold.deadline_set = tlp->threshold.deadline;
        if (tlp->threshold.deadline != TIMER_LONGTERM_NONE) {
                tlp->threshold.deadline_set -= tlp->threshold.margin;
                tlp->threshold.deadline_set -= tlp->threshold.latency;
                timer_call_enter(
                        &tlp->threshold.timer,
                        tlp->threshold.deadline_set,
                        TIMER_CALL_LOCAL | TIMER_CALL_SYS_CRITICAL);
        }

        /* Reset stats */
        tlp->enqueues = 0;
        tlp->dequeues = 0;
        tlp->escalates = 0;
        tlp->threshold.scans = 0;
        tlp->threshold.preempts = 0;
        tlp->threshold.latency = 0;
        tlp->threshold.latency_min = EndOfAllTime;
        tlp->threshold.latency_max = 0;

        timer_queue_unlock(timer_longterm_queue);
        splx(s);
}

int
timer_sysctl_set(int oid, uint64_t value)
{
        switch (oid) {
        case THRESHOLD:
                timer_call_cpu(
                        master_cpu,
                        (void (*)(void *)) timer_sysctl_set_threshold,
                        (void *) value);
                return KERN_SUCCESS;
        default:
                return KERN_INVALID_ARGUMENT;
        }
}