xnu-792.24.17.tar.gz

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

/*
 * Copyright (c) 2000-2005 Apple Computer, Inc. All rights reserved.
 *
 * @APPLE_LICENSE_HEADER_START@
 * 
 * The contents of this file constitute Original Code as defined in and
 * are subject to the Apple Public Source License Version 1.1 (the
 * "License").  You may not use this file except in compliance with the
 * License.  Please obtain a copy of the License at
 * http://www.apple.com/publicsource and read it before using this file.
 * 
 * This 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 OR NON-INFRINGEMENT.  Please see the
 * License for the specific language governing rights and limitations
 * under the License.
 * 
 * @APPLE_LICENSE_HEADER_END@
 */
/*
 * @OSF_FREE_COPYRIGHT@
 */
/* 
 * Mach Operating System
 * Copyright (c) 1991,1990,1989,1988,1987 Carnegie Mellon University
 * All Rights Reserved.
 * 
 * Permission to use, copy, modify and distribute this software and its
 * documentation is hereby granted, provided that both the copyright
 * notice and this permission notice appear in all copies of the
 * software, derivative works or modified versions, and any portions
 * thereof, and that both notices appear in supporting documentation.
 * 
 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
 * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR
 * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
 * 
 * Carnegie Mellon requests users of this software to return to
 * 
 *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
 *  School of Computer Science
 *  Carnegie Mellon University
 *  Pittsburgh PA 15213-3890
 * 
 * any improvements or extensions that they make and grant Carnegie Mellon
 * the rights to redistribute these changes.
 */
/*
 */
/*
 *      File:   sched_prim.c
 *      Author: Avadis Tevanian, Jr.
 *      Date:   1986
 *
 *      Scheduling primitives
 *
 */

#include <debug.h>
#include <mach_kdb.h>

#include <ddb/db_output.h>

#include <mach/mach_types.h>
#include <mach/machine.h>
#include <mach/policy.h>
#include <mach/sync_policy.h>

#include <machine/machine_routines.h>
#include <machine/sched_param.h>

#include <kern/kern_types.h>
#include <kern/clock.h>
#include <kern/counters.h>
#include <kern/cpu_number.h>
#include <kern/cpu_data.h>
#include <kern/debug.h>
#include <kern/lock.h>
#include <kern/macro_help.h>
#include <kern/machine.h>
#include <kern/misc_protos.h>
#include <kern/processor.h>
#include <kern/queue.h>
#include <kern/sched.h>
#include <kern/sched_prim.h>
#include <kern/syscall_subr.h>
#include <kern/task.h>
#include <kern/thread.h>
#include <kern/wait_queue.h>

#include <vm/pmap.h>
#include <vm/vm_kern.h>
#include <vm/vm_map.h>

#include <sys/kdebug.h>

#ifdef __ppc__
#include <ppc/pms.h>
#endif

#define         DEFAULT_PREEMPTION_RATE         100             /* (1/s) */
int                     default_preemption_rate = DEFAULT_PREEMPTION_RATE;

#define         MAX_UNSAFE_QUANTA                       800
int                     max_unsafe_quanta = MAX_UNSAFE_QUANTA;

#define         MAX_POLL_QUANTA                         2
int                     max_poll_quanta = MAX_POLL_QUANTA;

#define         SCHED_POLL_YIELD_SHIFT          4               /* 1/16 */
int                     sched_poll_yield_shift = SCHED_POLL_YIELD_SHIFT;

uint64_t        max_unsafe_computation;
uint32_t        sched_safe_duration;
uint64_t        max_poll_computation;

uint32_t        std_quantum;
uint32_t        min_std_quantum;

uint32_t        std_quantum_us;

uint32_t        max_rt_quantum;
uint32_t        min_rt_quantum;

uint32_t        sched_cswtime;

static uint32_t         delay_idle_limit, delay_idle_spin;
static processor_t      delay_idle(
                                                processor_t             processor,
                                                thread_t                self);

unsigned        sched_tick;
uint32_t        sched_tick_interval;

uint32_t        sched_pri_shift;

/* Forwards */
void            wait_queues_init(void);

static void             load_shift_init(void);

static thread_t choose_thread(
                                        processor_set_t         pset,
                                        processor_t                     processor);

static void             thread_update_scan(void);

#if     DEBUG
static
boolean_t       thread_runnable(
                                thread_t                thread);

#endif  /*DEBUG*/


/*
 *      State machine
 *
 * states are combinations of:
 *  R   running
 *  W   waiting (or on wait queue)
 *  N   non-interruptible
 *  O   swapped out
 *  I   being swapped in
 *
 * init action 
 *      assert_wait thread_block    clear_wait          swapout swapin
 *
 * R    RW, RWN     R;   setrun     -                   -
 * RN   RWN         RN;  setrun     -                   -
 *
 * RW               W               R                   -
 * RWN              WN              RN                  -
 *
 * W                                R;   setrun         WO
 * WN                               RN;  setrun         -
 *
 * RO                               -                   -       R
 *
 */

/*
 *      Waiting protocols and implementation:
 *
 *      Each thread may be waiting for exactly one event; this event
 *      is set using assert_wait().  That thread may be awakened either
 *      by performing a thread_wakeup_prim() on its event,
 *      or by directly waking that thread up with clear_wait().
 *
 *      The implementation of wait events uses a hash table.  Each
 *      bucket is queue of threads having the same hash function
 *      value; the chain for the queue (linked list) is the run queue
 *      field.  [It is not possible to be waiting and runnable at the
 *      same time.]
 *
 *      Locks on both the thread and on the hash buckets govern the
 *      wait event field and the queue chain field.  Because wakeup
 *      operations only have the event as an argument, the event hash
 *      bucket must be locked before any thread.
 *
 *      Scheduling operations may also occur at interrupt level; therefore,
 *      interrupts below splsched() must be prevented when holding
 *      thread or hash bucket locks.
 *
 *      The wait event hash table declarations are as follows:
 */

#define NUMQUEUES       59

struct wait_queue wait_queues[NUMQUEUES];

#define wait_hash(event) \
        ((((int)(event) < 0)? ~(int)(event): (int)(event)) % NUMQUEUES)

int8_t          sched_load_shifts[NRQS];

void
sched_init(void)
{
        /*
         * Calculate the timeslicing quantum
         * in us.
         */
        if (default_preemption_rate < 1)
                default_preemption_rate = DEFAULT_PREEMPTION_RATE;
        std_quantum_us = (1000 * 1000) / default_preemption_rate;

        printf("standard timeslicing quantum is %d us\n", std_quantum_us);

        sched_safe_duration = (2 * max_unsafe_quanta / default_preemption_rate) *
                                                                                        (1 << SCHED_TICK_SHIFT);

        wait_queues_init();
        load_shift_init();
        pset_init(&default_pset);
        sched_tick = 0;
        ast_init();
}

void
sched_timebase_init(void)
{
        uint64_t        abstime;
        uint32_t        shift;

        /* standard timeslicing quantum */
        clock_interval_to_absolutetime_interval(
                                                        std_quantum_us, NSEC_PER_USEC, &abstime);
        assert((abstime >> 32) == 0 && (uint32_t)abstime != 0);
        std_quantum = abstime;

        /* smallest remaining quantum (250 us) */
        clock_interval_to_absolutetime_interval(250, NSEC_PER_USEC, &abstime);
        assert((abstime >> 32) == 0 && (uint32_t)abstime != 0);
        min_std_quantum = abstime;

        /* smallest rt computaton (50 us) */
        clock_interval_to_absolutetime_interval(50, NSEC_PER_USEC, &abstime);
        assert((abstime >> 32) == 0 && (uint32_t)abstime != 0);
        min_rt_quantum = abstime;

        /* maximum rt computation (50 ms) */
        clock_interval_to_absolutetime_interval(
                                                        50, 1000*NSEC_PER_USEC, &abstime);
        assert((abstime >> 32) == 0 && (uint32_t)abstime != 0);
        max_rt_quantum = abstime;

        /* scheduler tick interval */
        clock_interval_to_absolutetime_interval(USEC_PER_SEC >> SCHED_TICK_SHIFT,
                                                                                                        NSEC_PER_USEC, &abstime);
        assert((abstime >> 32) == 0 && (uint32_t)abstime != 0);
        sched_tick_interval = abstime;

        /*
         * Compute conversion factor from usage to
         * timesharing priorities with 5/8 ** n aging.
         */
        abstime = (abstime * 5) / 3;
        for (shift = 0; abstime > BASEPRI_DEFAULT; ++shift)
                abstime >>= 1;
        sched_pri_shift = shift;

        max_unsafe_computation = max_unsafe_quanta * std_quantum;
        max_poll_computation = max_poll_quanta * std_quantum;

        /* delay idle constant(s) (60, 1 us) */
        clock_interval_to_absolutetime_interval(60, NSEC_PER_USEC, &abstime);
        assert((abstime >> 32) == 0 && (uint32_t)abstime != 0);
        delay_idle_limit = abstime;

        clock_interval_to_absolutetime_interval(1, NSEC_PER_USEC, &abstime);
        assert((abstime >> 32) == 0 && (uint32_t)abstime != 0);
        delay_idle_spin = abstime;
}

void
wait_queues_init(void)
{
        register int    i;

        for (i = 0; i < NUMQUEUES; i++) {
                wait_queue_init(&wait_queues[i], SYNC_POLICY_FIFO);
        }
}

/*
 * Set up values for timeshare
 * loading factors.
 */
static void
load_shift_init(void)
{
        int8_t          k, *p = sched_load_shifts;
        uint32_t        i, j;

        *p++ = INT8_MIN; *p++ = 0;

        for (i = j = 2, k = 1; i < NRQS; ++k) {
                for (j <<= 1; i < j; ++i)
                        *p++ = k;
        }
}

/*
 *      Thread wait timer expiration.
 */
void
thread_timer_expire(
        void                    *p0,
        __unused void   *p1)
{
        thread_t                thread = p0;
        spl_t                   s;

        s = splsched();
        thread_lock(thread);
        if (--thread->wait_timer_active == 0) {
                if (thread->wait_timer_is_set) {
                        thread->wait_timer_is_set = FALSE;
                        clear_wait_internal(thread, THREAD_TIMED_OUT);
                }
        }
        thread_unlock(thread);
        splx(s);
}

/*
 *      thread_set_timer:
 *
 *      Set a timer for the current thread, if the thread
 *      is ready to wait.  Must be called between assert_wait()
 *      and thread_block().
 */
void
thread_set_timer(
        uint32_t                interval,
        uint32_t                scale_factor)
{
        thread_t                thread = current_thread();
        uint64_t                deadline;
        spl_t                   s;

        s = splsched();
        thread_lock(thread);
        if ((thread->state & TH_WAIT) != 0) {
                clock_interval_to_deadline(interval, scale_factor, &deadline);
                if (!timer_call_enter(&thread->wait_timer, deadline))
                        thread->wait_timer_active++;
                thread->wait_timer_is_set = TRUE;
        }
        thread_unlock(thread);
        splx(s);
}

void
thread_set_timer_deadline(
        uint64_t                deadline)
{
        thread_t                thread = current_thread();
        spl_t                   s;

        s = splsched();
        thread_lock(thread);
        if ((thread->state & TH_WAIT) != 0) {
                if (!timer_call_enter(&thread->wait_timer, deadline))
                        thread->wait_timer_active++;
                thread->wait_timer_is_set = TRUE;
        }
        thread_unlock(thread);
        splx(s);
}

void
thread_cancel_timer(void)
{
        thread_t                thread = current_thread();
        spl_t                   s;

        s = splsched();
        thread_lock(thread);
        if (thread->wait_timer_is_set) {
                if (timer_call_cancel(&thread->wait_timer))
                        thread->wait_timer_active--;
                thread->wait_timer_is_set = FALSE;
        }
        thread_unlock(thread);
        splx(s);
}

/*
 *      thread_unblock:
 *
 *      Unblock thread on wake up.
 *
 *      Returns TRUE if the thread is still running.
 *
 *      Thread must be locked.
 */
boolean_t
thread_unblock(
        thread_t                thread,
        wait_result_t   wresult)
{
        boolean_t               result = FALSE;

        /*
         * Set wait_result.
         */
        thread->wait_result = wresult;

        /*
         * Cancel pending wait timer.
         */
        if (thread->wait_timer_is_set) {
                if (timer_call_cancel(&thread->wait_timer))
                        thread->wait_timer_active--;
                thread->wait_timer_is_set = FALSE;
        }

        /*
         * Update scheduling state.
         */
        thread->state &= ~(TH_WAIT|TH_UNINT);

        if (!(thread->state & TH_RUN)) {
                thread->state |= TH_RUN;

                /*
                 * Mark unblocked if call out.
                 */
                if (thread->options & TH_OPT_CALLOUT)
                        call_thread_unblock();

                /*
                 * Update pset run counts.
                 */
                pset_run_incr(thread->processor_set);
                if (thread->sched_mode & TH_MODE_TIMESHARE)
                        pset_share_incr(thread->processor_set);
        }
        else
                result = TRUE;

        /*
         * Calculate deadline for real-time threads.
         */
        if (thread->sched_mode & TH_MODE_REALTIME) {
                thread->realtime.deadline = mach_absolute_time();
                thread->realtime.deadline += thread->realtime.constraint;
        }

        /*
         * Clear old quantum, fail-safe computation, etc.
         */
        thread->current_quantum = 0;
        thread->computation_metered = 0;
        thread->reason = AST_NONE;

        KERNEL_DEBUG_CONSTANT(
                MACHDBG_CODE(DBG_MACH_SCHED,MACH_MAKE_RUNNABLE) | DBG_FUNC_NONE,
                                        (int)thread, (int)thread->sched_pri, 0, 0, 0);

        return (result);
}

/*
 *      Routine:        thread_go
 *      Purpose:
 *              Unblock and dispatch thread.
 *      Conditions:
 *              thread lock held, IPC locks may be held.
 *              thread must have been pulled from wait queue under same lock hold.
 *  Returns:
 *              KERN_SUCCESS - Thread was set running
 *              KERN_NOT_WAITING - Thread was not waiting
 */
kern_return_t
thread_go(
        thread_t                thread,
        wait_result_t   wresult)
{
        assert(thread->at_safe_point == FALSE);
        assert(thread->wait_event == NO_EVENT64);
        assert(thread->wait_queue == WAIT_QUEUE_NULL);

        if ((thread->state & (TH_WAIT|TH_TERMINATE)) == TH_WAIT) {
                if (!thread_unblock(thread, wresult))
                        thread_setrun(thread, SCHED_PREEMPT | SCHED_TAILQ);

                return (KERN_SUCCESS);
        }

        return (KERN_NOT_WAITING);
}

/*
 *      Routine:        thread_mark_wait_locked
 *      Purpose:
 *              Mark a thread as waiting.  If, given the circumstances,
 *              it doesn't want to wait (i.e. already aborted), then
 *              indicate that in the return value.
 *      Conditions:
 *              at splsched() and thread is locked.
 */
__private_extern__
wait_result_t
thread_mark_wait_locked(
        thread_t                        thread,
        wait_interrupt_t        interruptible)
{
        boolean_t               at_safe_point;

        /*
         *      The thread may have certain types of interrupts/aborts masked
         *      off.  Even if the wait location says these types of interrupts
         *      are OK, we have to honor mask settings (outer-scoped code may
         *      not be able to handle aborts at the moment).
         */
        if (interruptible > (thread->options & TH_OPT_INTMASK))
                interruptible = thread->options & TH_OPT_INTMASK;

        at_safe_point = (interruptible == THREAD_ABORTSAFE);

        if (    interruptible == THREAD_UNINT                   ||
                        !(thread->state & TH_ABORT)                             ||
                        (!at_safe_point &&
                         (thread->state & TH_ABORT_SAFELY))             ) {
                thread->state |= (interruptible) ? TH_WAIT : (TH_WAIT | TH_UNINT);
                thread->at_safe_point = at_safe_point;
                return (thread->wait_result = THREAD_WAITING);
        }
        else
        if (thread->state & TH_ABORT_SAFELY)
                thread->state &= ~(TH_ABORT|TH_ABORT_SAFELY);

        return (thread->wait_result = THREAD_INTERRUPTED);
}

/*
 *      Routine:        thread_interrupt_level
 *      Purpose:
 *              Set the maximum interruptible state for the
 *              current thread.  The effective value of any
 *              interruptible flag passed into assert_wait
 *              will never exceed this.
 *
 *              Useful for code that must not be interrupted,
 *              but which calls code that doesn't know that.
 *      Returns:
 *              The old interrupt level for the thread.
 */
__private_extern__ 
wait_interrupt_t
thread_interrupt_level(
        wait_interrupt_t new_level)
{
        thread_t thread = current_thread();
        wait_interrupt_t result = thread->options & TH_OPT_INTMASK;

        thread->options = (thread->options & ~TH_OPT_INTMASK) | (new_level & TH_OPT_INTMASK);

        return result;
}

/*
 * Check to see if an assert wait is possible, without actually doing one.
 * This is used by debug code in locks and elsewhere to verify that it is
 * always OK to block when trying to take a blocking lock (since waiting
 * for the actual assert_wait to catch the case may make it hard to detect
 * this case.
 */
boolean_t
assert_wait_possible(void)
{

        thread_t thread;

#if     DEBUG
        if(debug_mode) return TRUE;             /* Always succeed in debug mode */
#endif
        
        thread = current_thread();

        return (thread == NULL || wait_queue_assert_possible(thread));
}

/*
 *      assert_wait:
 *
 *      Assert that the current thread is about to go to
 *      sleep until the specified event occurs.
 */
wait_result_t
assert_wait(
        event_t                         event,
        wait_interrupt_t        interruptible)
{
        register wait_queue_t   wq;
        register int            index;

        assert(event != NO_EVENT);

        index = wait_hash(event);
        wq = &wait_queues[index];
        return wait_queue_assert_wait(wq, event, interruptible, 0);
}

wait_result_t
assert_wait_timeout(
        event_t                         event,
        wait_interrupt_t        interruptible,
        uint32_t                        interval,
        uint32_t                        scale_factor)
{
        thread_t                        thread = current_thread();
        wait_result_t           wresult;
        wait_queue_t            wqueue;
        uint64_t                        deadline;
        spl_t                           s;

        assert(event != NO_EVENT);
        wqueue = &wait_queues[wait_hash(event)];

        s = splsched();
        wait_queue_lock(wqueue);
        thread_lock(thread);

        clock_interval_to_deadline(interval, scale_factor, &deadline);
        wresult = wait_queue_assert_wait64_locked(wqueue, (uint32_t)event,
                                                                                                        interruptible, deadline, thread);

        thread_unlock(thread);
        wait_queue_unlock(wqueue);
        splx(s);

        return (wresult);
}

wait_result_t
assert_wait_deadline(
        event_t                         event,
        wait_interrupt_t        interruptible,
        uint64_t                        deadline)
{
        thread_t                        thread = current_thread();
        wait_result_t           wresult;
        wait_queue_t            wqueue;
        spl_t                           s;

        assert(event != NO_EVENT);
        wqueue = &wait_queues[wait_hash(event)];

        s = splsched();
        wait_queue_lock(wqueue);
        thread_lock(thread);

        wresult = wait_queue_assert_wait64_locked(wqueue, (uint32_t)event,
                                                                                                        interruptible, deadline, thread);

        thread_unlock(thread);
        wait_queue_unlock(wqueue);
        splx(s);

        return (wresult);
}

/*
 *      thread_sleep_fast_usimple_lock:
 *
 *      Cause the current thread to wait until the specified event
 *      occurs.  The specified simple_lock is unlocked before releasing
 *      the cpu and re-acquired as part of waking up.
 *
 *      This is the simple lock sleep interface for components that use a
 *      faster version of simple_lock() than is provided by usimple_lock().
 */
__private_extern__ wait_result_t
thread_sleep_fast_usimple_lock(
        event_t                 event,
        simple_lock_t           lock,
        wait_interrupt_t        interruptible)
{
        wait_result_t res;

        res = assert_wait(event, interruptible);
        if (res == THREAD_WAITING) {
                simple_unlock(lock);
                res = thread_block(THREAD_CONTINUE_NULL);
                simple_lock(lock);
        }
        return res;
}


/*
 *      thread_sleep_usimple_lock:
 *
 *      Cause the current thread to wait until the specified event
 *      occurs.  The specified usimple_lock is unlocked before releasing
 *      the cpu and re-acquired as part of waking up.
 *
 *      This is the simple lock sleep interface for components where
 *      simple_lock() is defined in terms of usimple_lock().
 */
wait_result_t
thread_sleep_usimple_lock(
        event_t                 event,
        usimple_lock_t          lock,
        wait_interrupt_t        interruptible)
{
        wait_result_t res;

        res = assert_wait(event, interruptible);
        if (res == THREAD_WAITING) {
                usimple_unlock(lock);
                res = thread_block(THREAD_CONTINUE_NULL);
                usimple_lock(lock);
        }
        return res;
}

/*
 *      thread_sleep_mutex:
 *
 *      Cause the current thread to wait until the specified event
 *      occurs.  The specified mutex is unlocked before releasing
 *      the cpu. The mutex will be re-acquired before returning.
 *
 *      JMM - Add hint to make sure mutex is available before rousting
 */
wait_result_t
thread_sleep_mutex(
        event_t                 event,
        mutex_t                 *mutex,
        wait_interrupt_t interruptible)
{
        wait_result_t   res;

        res = assert_wait(event, interruptible);
        if (res == THREAD_WAITING) {
                mutex_unlock(mutex);
                res = thread_block(THREAD_CONTINUE_NULL);
                mutex_lock(mutex);
        }
        return res;
}
  
/*
 *      thread_sleep_mutex_deadline:
 *
 *      Cause the current thread to wait until the specified event
 *      (or deadline) occurs.  The specified mutex is unlocked before
 *      releasing the cpu. The mutex will be re-acquired before returning.
 */
wait_result_t
thread_sleep_mutex_deadline(
        event_t                 event,
        mutex_t                 *mutex,
        uint64_t                deadline,
        wait_interrupt_t interruptible)
{
        wait_result_t   res;

        res = assert_wait_deadline(event, interruptible, deadline);
        if (res == THREAD_WAITING) {
                mutex_unlock(mutex);
                res = thread_block(THREAD_CONTINUE_NULL);
                mutex_lock(mutex);
        }
        return res;
}

/*
 *      thread_sleep_lock_write:
 *
 *      Cause the current thread to wait until the specified event
 *      occurs.  The specified (write) lock is unlocked before releasing
 *      the cpu. The (write) lock will be re-acquired before returning.
 */
wait_result_t
thread_sleep_lock_write(
        event_t                 event,
        lock_t                  *lock,
        wait_interrupt_t interruptible)
{
        wait_result_t   res;

        res = assert_wait(event, interruptible);
        if (res == THREAD_WAITING) {
                lock_write_done(lock);
                res = thread_block(THREAD_CONTINUE_NULL);
                lock_write(lock);
        }
        return res;
}

/*
 * thread_stop:
 *
 * Force a preemption point for a thread and wait
 * for it to stop running.  Arbitrates access among
 * multiple stop requests. (released by unstop)
 *
 * The thread must enter a wait state and stop via a
 * separate means.
 *
 * Returns FALSE if interrupted.
 */
boolean_t
thread_stop(
        thread_t                thread)
{
        wait_result_t   wresult;
        spl_t                   s;

        s = splsched();
        wake_lock(thread);

        while (thread->state & TH_SUSP) {
                thread->wake_active = TRUE;
                wresult = assert_wait(&thread->wake_active, THREAD_ABORTSAFE);
                wake_unlock(thread);
                splx(s);

                if (wresult == THREAD_WAITING)
                        wresult = thread_block(THREAD_CONTINUE_NULL);

                if (wresult != THREAD_AWAKENED)
                        return (FALSE);

                s = splsched();
                wake_lock(thread);
        }

        thread_lock(thread);
        thread->state |= TH_SUSP;

        while (thread->state & TH_RUN) {
                processor_t             processor = thread->last_processor;

                if (    processor != PROCESSOR_NULL                                     &&
                                processor->state == PROCESSOR_RUNNING           &&
                                processor->active_thread == thread                      )
                        cause_ast_check(processor);
                thread_unlock(thread);

                thread->wake_active = TRUE;
                wresult = assert_wait(&thread->wake_active, THREAD_ABORTSAFE);
                wake_unlock(thread);
                splx(s);

                if (wresult == THREAD_WAITING)
                        wresult = thread_block(THREAD_CONTINUE_NULL);

                if (wresult != THREAD_AWAKENED) {
                        thread_unstop(thread);
                        return (FALSE);
                }

                s = splsched();
                wake_lock(thread);
                thread_lock(thread);
        }

        thread_unlock(thread);
        wake_unlock(thread);
        splx(s);

        return (TRUE);
}

/*
 * thread_unstop:
 *
 * Release a previous stop request and set
 * the thread running if appropriate.
 *
 * Use only after a successful stop operation.
 */
void
thread_unstop(
        thread_t        thread)
{
        spl_t           s = splsched();

        wake_lock(thread);
        thread_lock(thread);

        if ((thread->state & (TH_RUN|TH_WAIT|TH_SUSP)) == TH_SUSP) {
                thread->state &= ~TH_SUSP;
                thread_unblock(thread, THREAD_AWAKENED);

                thread_setrun(thread, SCHED_PREEMPT | SCHED_TAILQ);
        }
        else
        if (thread->state & TH_SUSP) {
                thread->state &= ~TH_SUSP;

                if (thread->wake_active) {
                        thread->wake_active = FALSE;
                        thread_unlock(thread);
                        wake_unlock(thread);
                        splx(s);

                        thread_wakeup(&thread->wake_active);
                        return;
                }
        }

        thread_unlock(thread);
        wake_unlock(thread);
        splx(s);
}

/*
 * thread_wait:
 *
 * Wait for a thread to stop running. (non-interruptible)
 *
 */
void
thread_wait(
        thread_t                thread)
{
        wait_result_t   wresult;
        spl_t                   s = splsched();

        wake_lock(thread);
        thread_lock(thread);

        while (thread->state & TH_RUN) {
                processor_t             processor = thread->last_processor;

                if (    processor != PROCESSOR_NULL                                     &&
                                processor->state == PROCESSOR_RUNNING           &&
                                processor->active_thread == thread                      )
                        cause_ast_check(processor);
                thread_unlock(thread);

                thread->wake_active = TRUE;
                wresult = assert_wait(&thread->wake_active, THREAD_UNINT);
                wake_unlock(thread);
                splx(s);

                if (wresult == THREAD_WAITING)
                        thread_block(THREAD_CONTINUE_NULL);

                s = splsched();
                wake_lock(thread);
                thread_lock(thread);
        }

        thread_unlock(thread);
        wake_unlock(thread);
        splx(s);
}

/*
 *      Routine: clear_wait_internal
 *
 *              Clear the wait condition for the specified thread.
 *              Start the thread executing if that is appropriate.
 *      Arguments:
 *              thread          thread to awaken
 *              result          Wakeup result the thread should see
 *      Conditions:
 *              At splsched
 *              the thread is locked.
 *      Returns:
 *              KERN_SUCCESS            thread was rousted out a wait
 *              KERN_FAILURE            thread was waiting but could not be rousted
 *              KERN_NOT_WAITING        thread was not waiting
 */
__private_extern__ kern_return_t
clear_wait_internal(
        thread_t                thread,
        wait_result_t   wresult)
{
        wait_queue_t    wq = thread->wait_queue;
        int                             i = LockTimeOut;

        do {
                if (wresult == THREAD_INTERRUPTED && (thread->state & TH_UNINT))
                        return (KERN_FAILURE);

                if (wq != WAIT_QUEUE_NULL) {
                        if (wait_queue_lock_try(wq)) {
                                wait_queue_pull_thread_locked(wq, thread, TRUE);
                                /* wait queue unlocked, thread still locked */
                        }
                        else {
                                thread_unlock(thread);
                                delay(1);

                                thread_lock(thread);
                                if (wq != thread->wait_queue)
                                        return (KERN_NOT_WAITING);

                                continue;
                        }
                }

                return (thread_go(thread, wresult));
        } while (--i > 0);

        panic("clear_wait_internal: deadlock: thread=0x%x, wq=0x%x, cpu=%d\n",
                  thread, wq, cpu_number());

        return (KERN_FAILURE);
}


/*
 *      clear_wait:
 *
 *      Clear the wait condition for the specified thread.  Start the thread
 *      executing if that is appropriate.
 *
 *      parameters:
 *        thread                thread to awaken
 *        result                Wakeup result the thread should see
 */
kern_return_t
clear_wait(
        thread_t                thread,
        wait_result_t   result)
{
        kern_return_t ret;
        spl_t           s;

        s = splsched();
        thread_lock(thread);
        ret = clear_wait_internal(thread, result);
        thread_unlock(thread);
        splx(s);
        return ret;
}


/*
 *      thread_wakeup_prim:
 *
 *      Common routine for thread_wakeup, thread_wakeup_with_result,
 *      and thread_wakeup_one.
 *
 */
kern_return_t
thread_wakeup_prim(
        event_t                 event,
        boolean_t               one_thread,
        wait_result_t   result)
{
        register wait_queue_t   wq;
        register int                    index;

        index = wait_hash(event);
        wq = &wait_queues[index];
        if (one_thread)
            return (wait_queue_wakeup_one(wq, event, result));
        else
            return (wait_queue_wakeup_all(wq, event, result));
}

/*
 *      thread_bind:
 *
 *      Force a thread to execute on the specified processor.
 *
 *      Returns the previous binding.  PROCESSOR_NULL means
 *      not bound.
 *
 *      XXX - DO NOT export this to users - XXX
 */
processor_t
thread_bind(
        register thread_t       thread,
        processor_t                     processor)
{
        processor_t             prev;
        run_queue_t             runq = RUN_QUEUE_NULL;
        spl_t                   s;

        s = splsched();
        thread_lock(thread);
        prev = thread->bound_processor;
        if (prev != PROCESSOR_NULL)
                runq = run_queue_remove(thread);

        thread->bound_processor = processor;

        if (runq != RUN_QUEUE_NULL)
                thread_setrun(thread, SCHED_PREEMPT | SCHED_TAILQ);
        thread_unlock(thread);
        splx(s);

        return (prev);
}

struct {
        uint32_t        idle_pset_last,
                                idle_pset_any,
                                idle_bound;

        uint32_t        pset_self,
                                pset_last,
                                pset_other,
                                bound_self,
                                bound_other;

        uint32_t        realtime_self,
                                realtime_last,
                                realtime_other;

        uint32_t        missed_realtime,
                                missed_other;
} dispatch_counts;

/*
 *      Select a thread for the current processor to run.
 *
 *      May select the current thread, which must be locked.
 */
thread_t
thread_select(
        register processor_t    processor)
{
        register thread_t               thread;
        processor_set_t                 pset;
        boolean_t                               other_runnable;

        /*
         *      Check for other non-idle runnable threads.
         */
        pset = processor->processor_set;
        thread = processor->active_thread;

        /* Update the thread's priority */
        if (thread->sched_stamp != sched_tick)
                update_priority(thread);

        processor->current_pri = thread->sched_pri;

        simple_lock(&pset->sched_lock);

        other_runnable = processor->runq.count > 0 || pset->runq.count > 0;

        if (    thread->state == TH_RUN                                                 &&
                        thread->processor_set == pset                                   &&
                        (thread->bound_processor == PROCESSOR_NULL      ||
                         thread->bound_processor == processor)                          ) {
                if (    thread->sched_pri >= BASEPRI_RTQUEUES   &&
                                                first_timeslice(processor)                      ) {
                        if (pset->runq.highq >= BASEPRI_RTQUEUES) {
                                register run_queue_t    runq = &pset->runq;
                                register queue_t                q;

                                q = runq->queues + runq->highq;
                                if (((thread_t)q->next)->realtime.deadline <
                                                                                                processor->deadline) {
                                        thread = (thread_t)q->next;
                                        ((queue_entry_t)thread)->next->prev = q;
                                        q->next = ((queue_entry_t)thread)->next;
                                        thread->runq = RUN_QUEUE_NULL;
                                        assert(thread->sched_mode & TH_MODE_PREEMPT);
                                        runq->count--; runq->urgency--;
                                        if (queue_empty(q)) {
                                                if (runq->highq != IDLEPRI)
                                                        clrbit(MAXPRI - runq->highq, runq->bitmap);
                                                runq->highq = MAXPRI - ffsbit(runq->bitmap);
                                        }
                                }
                        }

                        processor->deadline = thread->realtime.deadline;

                        simple_unlock(&pset->sched_lock);

                        return (thread);
                }

                if (    (!other_runnable                                                        ||
                                 (processor->runq.highq < thread->sched_pri             &&
                                  pset->runq.highq < thread->sched_pri))                        ) {

                        /* I am the highest priority runnable (non-idle) thread */

                        processor->deadline = UINT64_MAX;

                        simple_unlock(&pset->sched_lock);

                        return (thread);
                }
        }

        if (other_runnable)
                thread = choose_thread(pset, processor);
        else {
                /*
                 *      Nothing is runnable, so set this processor idle if it
                 *      was running.  Return its idle thread.
                 */
                if (processor->state == PROCESSOR_RUNNING) {
                        remqueue(&pset->active_queue, (queue_entry_t)processor);
                        processor->state = PROCESSOR_IDLE;

                        enqueue_tail(&pset->idle_queue, (queue_entry_t)processor);
                        pset->idle_count++;
                }

                processor->deadline = UINT64_MAX;

                thread = processor->idle_thread;
        }

        simple_unlock(&pset->sched_lock);

        return (thread);
}

/*
 *      Perform a context switch and start executing the new thread.
 *
 *      Returns FALSE on failure, and the thread is re-dispatched.
 *
 *      Called at splsched.
 */

#define funnel_release_check(thread, debug)                             \
MACRO_BEGIN                                                                                             \
        if ((thread)->funnel_state & TH_FN_OWNED) {                     \
                (thread)->funnel_state = TH_FN_REFUNNEL;                \
                KERNEL_DEBUG(0x603242c | DBG_FUNC_NONE,                 \
                        (thread)->funnel_lock, (debug), 0, 0, 0);       \
                funnel_unlock((thread)->funnel_lock);                   \
        }                                                                                                       \
MACRO_END

#define funnel_refunnel_check(thread, debug)                            \
MACRO_BEGIN                                                                                                     \
        if ((thread)->funnel_state & TH_FN_REFUNNEL) {                  \
                kern_return_t   result = (thread)->wait_result;         \
                                                                                                                        \
                (thread)->funnel_state = 0;                                                     \
                KERNEL_DEBUG(0x6032428 | DBG_FUNC_NONE,                         \
                        (thread)->funnel_lock, (debug), 0, 0, 0);               \
                funnel_lock((thread)->funnel_lock);                                     \
                KERNEL_DEBUG(0x6032430 | DBG_FUNC_NONE,                         \
                        (thread)->funnel_lock, (debug), 0, 0, 0);               \
                (thread)->funnel_state = TH_FN_OWNED;                           \
                (thread)->wait_result = result;                                         \
        }                                                                                                               \
MACRO_END

boolean_t
thread_invoke(
        register thread_t       old_thread,
        register thread_t       new_thread,
        ast_t                           reason)
{
        thread_continue_t       new_cont, continuation = old_thread->continuation;
        void                            *new_param, *parameter = old_thread->parameter;
        processor_t                     processor;
        thread_t                        prev_thread;

        if (get_preemption_level() != 0)
                panic("thread_invoke: preemption_level %d\n",
                                                                get_preemption_level());

        assert(old_thread == current_thread());

        /*
         * Mark thread interruptible.
         */
        thread_lock(new_thread);
        new_thread->state &= ~TH_UNINT;

        assert(thread_runnable(new_thread));

        /*
         * Allow time constraint threads to hang onto
         * a stack.
         */
        if (    (old_thread->sched_mode & TH_MODE_REALTIME)             &&
                                        !old_thread->reserved_stack                             ) {
                old_thread->reserved_stack = old_thread->kernel_stack;
        }

        if (continuation != NULL) {
                if (!new_thread->kernel_stack) {
                        /*
                         * If the old thread is using a privileged stack,
                         * check to see whether we can exchange it with
                         * that of the new thread.
                         */
                        if (    old_thread->kernel_stack == old_thread->reserved_stack  &&
                                                        !new_thread->reserved_stack)
                                goto need_stack;

                        /*
                         * Context switch by performing a stack handoff.
                         */
                        new_cont = new_thread->continuation;
                        new_thread->continuation = NULL;
                        new_param = new_thread->parameter;
                        new_thread->parameter = NULL;

                        processor = current_processor();
                        processor->active_thread = new_thread;
                        processor->current_pri = new_thread->sched_pri;
                        new_thread->last_processor = processor;
                        ast_context(new_thread);
                        thread_unlock(new_thread);
                
                        current_task()->csw++;

                        old_thread->reason = reason;

                        processor->last_dispatch = mach_absolute_time();
                        timer_event((uint32_t)processor->last_dispatch,
                                                                                &new_thread->system_timer);
           
                        thread_done(old_thread, new_thread, processor);

                        machine_stack_handoff(old_thread, new_thread);

                        thread_begin(new_thread, processor);

                        /*
                         * Now dispatch the old thread.
                         */
                        thread_dispatch(old_thread);

                        counter_always(c_thread_invoke_hits++);

                        funnel_refunnel_check(new_thread, 2);
                        (void) spllo();

                        assert(new_cont);
                        call_continuation(new_cont, new_param, new_thread->wait_result);
                        /*NOTREACHED*/
                }
                else
                if (new_thread == old_thread) {
                        /* same thread but with continuation */
                        counter(++c_thread_invoke_same);
                        thread_unlock(new_thread);

                        funnel_refunnel_check(new_thread, 3);
                        (void) spllo();

                        call_continuation(continuation, parameter, new_thread->wait_result);
                        /*NOTREACHED*/
                }
        }
        else {
                /*
                 * Check that the new thread has a stack
                 */
                if (!new_thread->kernel_stack) {
need_stack:
                        if (!stack_alloc_try(new_thread)) {
                                counter_always(c_thread_invoke_misses++);
                                thread_unlock(new_thread);
                                thread_stack_enqueue(new_thread);
                                return (FALSE);
                        }
                }
                else
                if (new_thread == old_thread) {
                        counter(++c_thread_invoke_same);
                        thread_unlock(new_thread);
                        return (TRUE);
                }
        }

        /*
         * Context switch by full context save.
         */
        processor = current_processor();
        processor->active_thread = new_thread;
        processor->current_pri = new_thread->sched_pri;
        new_thread->last_processor = processor;
        ast_context(new_thread);
        assert(thread_runnable(new_thread));
        thread_unlock(new_thread);

        counter_always(c_thread_invoke_csw++);
        current_task()->csw++;

        assert(old_thread->runq == RUN_QUEUE_NULL);
        old_thread->reason = reason;

        processor->last_dispatch = mach_absolute_time();
        timer_event((uint32_t)processor->last_dispatch, &new_thread->system_timer);

        thread_done(old_thread, new_thread, processor);

        /*
         * This is where we actually switch register context,
         * and address space if required.  Control will not
         * return here immediately.
         */
        prev_thread = machine_switch_context(old_thread, continuation, new_thread);

        /*
         * We are still old_thread, possibly on a different processor,
         * and new_thread is now stale.
         */
        thread_begin(old_thread, old_thread->last_processor);

        /*
         * Now dispatch the thread which resumed us.
         */
        thread_dispatch(prev_thread);

        if (continuation) {
                funnel_refunnel_check(old_thread, 3);
                (void) spllo();

                call_continuation(continuation, parameter, old_thread->wait_result);
                /*NOTREACHED*/
        }

        return (TRUE);
}

/*
 *      thread_done:
 *
 *      Perform calculations for thread
 *      finishing execution on the current processor.
 *
 *      Called at splsched.
 */
void
thread_done(
        thread_t                        old_thread,
        thread_t                        new_thread,
        processor_t                     processor)
{
        if (!(old_thread->state & TH_IDLE)) {
                /*
                 * Compute remainder of current quantum.
                 */
                if (    first_timeslice(processor)                                                      &&
                                processor->quantum_end > processor->last_dispatch               )
                        old_thread->current_quantum =
                                        (processor->quantum_end - processor->last_dispatch);
                else
                        old_thread->current_quantum = 0;

                if (old_thread->sched_mode & TH_MODE_REALTIME) {
                        /*
                         * Cancel the deadline if the thread has
                         * consumed the entire quantum.
                         */
                        if (old_thread->current_quantum == 0) {
                                old_thread->realtime.deadline = UINT64_MAX;
                                old_thread->reason |= AST_QUANTUM;
                        }
                }
                else {
                        /*
                         * For non-realtime threads treat a tiny
                         * remaining quantum as an expired quantum
                         * but include what's left next time.
                         */
                        if (old_thread->current_quantum < min_std_quantum) {
                                old_thread->reason |= AST_QUANTUM;
                                old_thread->current_quantum += std_quantum;
                        }
                }

                /*
                 * If we are doing a direct handoff then
                 * give the remainder of our quantum to
                 * the next thread.
                 */
                if ((old_thread->reason & (AST_HANDOFF|AST_QUANTUM)) == AST_HANDOFF) {
                        new_thread->current_quantum = old_thread->current_quantum;
                        old_thread->reason |= AST_QUANTUM;
                        old_thread->current_quantum = 0;
                }

                old_thread->last_switch = processor->last_dispatch;

                old_thread->computation_metered +=
                                (old_thread->last_switch - old_thread->computation_epoch);
        }
}

/*
 *      thread_begin:
 *
 *      Set up for thread beginning execution on
 *      the current processor.
 *
 *      Called at splsched.
 */
void
thread_begin(
        thread_t                        thread,
        processor_t                     processor)
{
        if (!(thread->state & TH_IDLE)) {
                /*
                 * Give the thread a new quantum
                 * if none remaining.
                 */
                if (thread->current_quantum == 0)
                        thread_quantum_init(thread);

                /*
                 * Set up quantum timer and timeslice.
                 */
                processor->quantum_end =
                                (processor->last_dispatch + thread->current_quantum);
                timer_call_enter1(&processor->quantum_timer,
                                                                thread, processor->quantum_end);

                processor_timeslice_setup(processor, thread);

                thread->last_switch = processor->last_dispatch;

                thread->computation_epoch = thread->last_switch;
        }
        else {
                timer_call_cancel(&processor->quantum_timer);
                processor->timeslice = 1;
        }
}

/*
 *      thread_dispatch:
 *
 *      Handle previous thread at context switch.  Re-dispatch
 *      if still running, otherwise update run state and perform
 *      special actions.
 *
 *      Called at splsched.
 */
void
thread_dispatch(
        register thread_t       thread)
{
        /*
         *      If blocked at a continuation, discard
         *      the stack.
         */
#ifndef i386
    if (thread->continuation != NULL && thread->kernel_stack)
                stack_free(thread);
#endif

        if (!(thread->state & TH_IDLE)) {
                wake_lock(thread);
                thread_lock(thread);

                if (!(thread->state & TH_WAIT)) {
                        /*
                         *      Still running.
                         */
                        if (thread->reason & AST_QUANTUM)
                                thread_setrun(thread, SCHED_TAILQ);
                        else
                        if (thread->reason & AST_PREEMPT)
                                thread_setrun(thread, SCHED_HEADQ);
                        else
                                thread_setrun(thread, SCHED_PREEMPT | SCHED_TAILQ);

                        thread->reason = AST_NONE;

                        thread_unlock(thread);
                        wake_unlock(thread);
                }
                else {
                        boolean_t               wake;

                        /*
                         *      Waiting.
                         */
                        thread->state &= ~TH_RUN;

                        wake = thread->wake_active;
                        thread->wake_active = FALSE;

                        if (thread->sched_mode & TH_MODE_TIMESHARE)
                                pset_share_decr(thread->processor_set);
                        pset_run_decr(thread->processor_set);

                        thread_unlock(thread);
                        wake_unlock(thread);

                        if (thread->options & TH_OPT_CALLOUT)
                                call_thread_block();

                        if (wake)
                                thread_wakeup((event_t)&thread->wake_active);

                        if (thread->state & TH_TERMINATE)
                                thread_terminate_enqueue(thread);
                }
        }
}

/*
 *      thread_block_reason:
 *
 *      Forces a reschedule, blocking the caller if a wait
 *      has been asserted.
 *
 *      If a continuation is specified, then thread_invoke will
 *      attempt to discard the thread's kernel stack.  When the
 *      thread resumes, it will execute the continuation function
 *      on a new kernel stack.
 */
counter(mach_counter_t  c_thread_block_calls = 0;)
 
wait_result_t
thread_block_reason(
        thread_continue_t       continuation,
        void                            *parameter,
        ast_t                           reason)
{
        register thread_t               self = current_thread();
        register processor_t    processor;
        register thread_t               new_thread;
        spl_t                                   s;

        counter(++c_thread_block_calls);

        s = splsched();

        if (!(reason & AST_PREEMPT))
                funnel_release_check(self, 2);

        processor = current_processor();

        /*
         * Delay switching to the idle thread under certain conditions.
         */
        if (s != FALSE && (self->state & (TH_IDLE|TH_TERMINATE|TH_WAIT)) == TH_WAIT) {
                if (    processor->processor_set->processor_count > 1   &&
                                processor->processor_set->runq.count == 0               &&
                                processor->runq.count == 0                                              )
                        processor = delay_idle(processor, self);
        }

        /* If we're explicitly yielding, force a subsequent quantum */
        if (reason & AST_YIELD)
                processor->timeslice = 0;

        /* We're handling all scheduling AST's */
        ast_off(AST_SCHEDULING);

        self->continuation = continuation;
        self->parameter = parameter;

        thread_lock(self);
        new_thread = thread_select(processor);
        assert(new_thread && thread_runnable(new_thread));
        thread_unlock(self);
        while (!thread_invoke(self, new_thread, reason)) {
                thread_lock(self);
                new_thread = thread_select(processor);
                assert(new_thread && thread_runnable(new_thread));
                thread_unlock(self);
        }

        funnel_refunnel_check(self, 5);
        splx(s);

        return (self->wait_result);
}

/*
 *      thread_block:
 *
 *      Block the current thread if a wait has been asserted.
 */
wait_result_t
thread_block(
        thread_continue_t       continuation)
{
        return thread_block_reason(continuation, NULL, AST_NONE);
}

wait_result_t
thread_block_parameter(
        thread_continue_t       continuation,
        void                            *parameter)
{
        return thread_block_reason(continuation, parameter, AST_NONE);
}

/*
 *      thread_run:
 *
 *      Switch directly from the current thread to the
 *      new thread, handing off our quantum if appropriate.
 *
 *      New thread must be runnable, and not on a run queue.
 *
 *      Called at splsched.
 */
int
thread_run(
        thread_t                        self,
        thread_continue_t       continuation,
        void                            *parameter,
        thread_t                        new_thread)
{
        ast_t           handoff = AST_HANDOFF;

        funnel_release_check(self, 3);

        self->continuation = continuation;
        self->parameter = parameter;

        while (!thread_invoke(self, new_thread, handoff)) {
                register processor_t            processor = current_processor();

                thread_lock(self);
                new_thread = thread_select(processor);
                thread_unlock(self);
                handoff = AST_NONE;
        }

        funnel_refunnel_check(self, 6);

        return (self->wait_result);
}

/*
 *      thread_continue:
 *
 *      Called at splsched when a thread first receives
 *      a new stack after a continuation.
 */
void
thread_continue(
        register thread_t       old_thread)
{
        register thread_t                       self = current_thread();
        register thread_continue_t      continuation;
        register void                           *parameter;
        
        continuation = self->continuation;
        self->continuation = NULL;
        parameter = self->parameter;
        self->parameter = NULL;

        thread_begin(self, self->last_processor);

        if (old_thread != THREAD_NULL)
                thread_dispatch(old_thread);

        funnel_refunnel_check(self, 4);

        if (old_thread != THREAD_NULL)
                (void)spllo();

        call_continuation(continuation, parameter, self->wait_result);
        /*NOTREACHED*/
}

/*
 *      Enqueue thread on run queue.  Thread must be locked,
 *      and not already be on a run queue.  Returns TRUE
 *      if a preemption is indicated based on the state
 *      of the run queue.
 *
 *      Run queue must be locked, see run_queue_remove()
 *      for more info.
 */
static boolean_t
run_queue_enqueue(
        register run_queue_t    rq,
        register thread_t               thread,
        integer_t                               options)
{
        register int                    whichq = thread->sched_pri;
        register queue_t                queue = &rq->queues[whichq];
        boolean_t                               result = FALSE;
        
        assert(whichq >= MINPRI && whichq <= MAXPRI);

        assert(thread->runq == RUN_QUEUE_NULL);
        if (queue_empty(queue)) {
                enqueue_tail(queue, (queue_entry_t)thread);

                setbit(MAXPRI - whichq, rq->bitmap);
                if (whichq > rq->highq) {
                        rq->highq = whichq;
                        result = TRUE;
                }
        }
        else
        if (options & SCHED_HEADQ)
                enqueue_head(queue, (queue_entry_t)thread);
        else
                enqueue_tail(queue, (queue_entry_t)thread);

        thread->runq = rq;
        if (thread->sched_mode & TH_MODE_PREEMPT)
                rq->urgency++;
        rq->count++;

        return (result);
}

/*
 *      Enqueue a thread for realtime execution, similar
 *      to above.  Handles preemption directly.
 */
static void
realtime_schedule_insert(
        register processor_set_t        pset,
        register thread_t                       thread)
{
        register run_queue_t    rq = &pset->runq;
        register int                    whichq = thread->sched_pri;
        register queue_t                queue = &rq->queues[whichq];
        uint64_t                                deadline = thread->realtime.deadline;
        boolean_t                               try_preempt = FALSE;

        assert(whichq >= BASEPRI_REALTIME && whichq <= MAXPRI);

        assert(thread->runq == RUN_QUEUE_NULL);
        if (queue_empty(queue)) {
                enqueue_tail(queue, (queue_entry_t)thread);

                setbit(MAXPRI - whichq, rq->bitmap);
                if (whichq > rq->highq)
                        rq->highq = whichq;
                try_preempt = TRUE;
        }
        else {
                register thread_t       entry = (thread_t)queue_first(queue);

                while (TRUE) {
                        if (    queue_end(queue, (queue_entry_t)entry)  ||
                                                deadline < entry->realtime.deadline             ) {
                                entry = (thread_t)queue_prev((queue_entry_t)entry);
                                break;
                        }

                        entry = (thread_t)queue_next((queue_entry_t)entry);
                }

                if ((queue_entry_t)entry == queue)
                        try_preempt = TRUE;

                insque((queue_entry_t)thread, (queue_entry_t)entry);
        }

        thread->runq = rq;
        assert(thread->sched_mode & TH_MODE_PREEMPT);
        rq->count++; rq->urgency++;

        if (try_preempt) {
                register processor_t    processor;

                processor = current_processor();
                if (    pset == processor->processor_set                                &&
                                (thread->sched_pri > processor->current_pri     ||
                                        deadline < processor->deadline                  )               ) {
                        dispatch_counts.realtime_self++;
                        simple_unlock(&pset->sched_lock);

                        ast_on(AST_PREEMPT | AST_URGENT);
                        return;
                }

                if (    pset->processor_count > 1                       ||
                                pset != processor->processor_set        ) {
                        processor_t             myprocessor, lastprocessor;
                        queue_entry_t   next;

                        myprocessor = processor;
                        processor = thread->last_processor;
                        if (    processor != myprocessor                                                &&
                                        processor != PROCESSOR_NULL                                             &&
                                        processor->processor_set == pset                                &&
                                        processor->state == PROCESSOR_RUNNING                   &&
                                        (thread->sched_pri > processor->current_pri     ||
                                                deadline < processor->deadline                  )               ) {
                                dispatch_counts.realtime_last++;
                                cause_ast_check(processor);
                                simple_unlock(&pset->sched_lock);
                                return;
                        }

                        lastprocessor = processor;
                        queue = &pset->active_queue;
                        processor = (processor_t)queue_first(queue);
                        while (!queue_end(queue, (queue_entry_t)processor)) {
                                next = queue_next((queue_entry_t)processor);

                                if (    processor != myprocessor                                                &&
                                                processor != lastprocessor                                              &&
                                                (thread->sched_pri > processor->current_pri     ||
                                                        deadline < processor->deadline                  )               ) {
                                        if (!queue_end(queue, next)) {
                                                remqueue(queue, (queue_entry_t)processor);
                                                enqueue_tail(queue, (queue_entry_t)processor);
                                        }
                                        dispatch_counts.realtime_other++;
                                        cause_ast_check(processor);
                                        simple_unlock(&pset->sched_lock);
                                        return;
                                }

                                processor = (processor_t)next;
                        }
                }
        }

        simple_unlock(&pset->sched_lock);
}

/*
 *      thread_setrun:
 *
 *      Dispatch thread for execution, directly onto an idle
 *      processor if possible.  Else put on appropriate run
 *      queue. (local if bound, else processor set)
 *
 *      Thread must be locked.
 */
void
thread_setrun(
        register thread_t                       new_thread,
        integer_t                                       options)
{
        register processor_t            processor;
        register processor_set_t        pset;
        register thread_t                       thread;
        ast_t                                           preempt = (options & SCHED_PREEMPT)?
                                                                                                        AST_PREEMPT: AST_NONE;

        assert(thread_runnable(new_thread));
        
        /*
         *      Update priority if needed.
         */
        if (new_thread->sched_stamp != sched_tick)
                update_priority(new_thread);

        /*
         *      Check for urgent preemption.
         */
        if (new_thread->sched_mode & TH_MODE_PREEMPT)
                preempt = (AST_PREEMPT | AST_URGENT);

        assert(new_thread->runq == RUN_QUEUE_NULL);

        if ((processor = new_thread->bound_processor) == PROCESSOR_NULL) {
            /*
             *  First try to dispatch on
                 *      the last processor.
             */
            pset = new_thread->processor_set;
                processor = new_thread->last_processor;
                if (    pset->processor_count > 1                               &&
                                processor != PROCESSOR_NULL                             &&
                                processor->state == PROCESSOR_IDLE              ) {
                        processor_lock(processor);
                        simple_lock(&pset->sched_lock);
                        if (    processor->processor_set == pset                &&
                                        processor->state == PROCESSOR_IDLE              ) {
                                remqueue(&pset->idle_queue, (queue_entry_t)processor);
                                pset->idle_count--;
                                processor->next_thread = new_thread;
                                if (new_thread->sched_pri >= BASEPRI_RTQUEUES)
                                        processor->deadline = new_thread->realtime.deadline;
                                else
                                        processor->deadline = UINT64_MAX;
                                processor->state = PROCESSOR_DISPATCHING;
                                dispatch_counts.idle_pset_last++;
                                simple_unlock(&pset->sched_lock);
                                processor_unlock(processor);
                                if (processor != current_processor())
                                        machine_signal_idle(processor);
                                return;
                        }
                        processor_unlock(processor);
                }
                else
                simple_lock(&pset->sched_lock);

                /*
                 *      Next pick any idle processor
                 *      in the processor set.
                 */
                if (pset->idle_count > 0) {
                        processor = (processor_t)dequeue_head(&pset->idle_queue);
                        pset->idle_count--;
                        processor->next_thread = new_thread;
                        if (new_thread->sched_pri >= BASEPRI_RTQUEUES)
                                processor->deadline = new_thread->realtime.deadline;
                        else
                                processor->deadline = UINT64_MAX;
                        processor->state = PROCESSOR_DISPATCHING;
                        dispatch_counts.idle_pset_any++;
                        simple_unlock(&pset->sched_lock);
                        if (processor != current_processor())   
                                machine_signal_idle(processor);
                        return;
                }

                if (new_thread->sched_pri >= BASEPRI_RTQUEUES)
                        realtime_schedule_insert(pset, new_thread);
                else {
                        if (!run_queue_enqueue(&pset->runq, new_thread, options))
                                preempt = AST_NONE;

                        /*
                         *      Update the timesharing quanta.
                         */
                        timeshare_quanta_update(pset);
        
                        /*
                         *      Preempt check.
                         */
                        if (preempt != AST_NONE) {
                                /*
                                 * First try the current processor
                                 * if it is a member of the correct
                                 * processor set.
                                 */
                                processor = current_processor();
                                thread = processor->active_thread;
                                if (    pset == processor->processor_set        &&
                                                csw_needed(thread, processor)           ) {
                                        dispatch_counts.pset_self++;
                                        simple_unlock(&pset->sched_lock);

                                        ast_on(preempt);
                                        return;
                                }

                                /*
                                 * If that failed and we have other
                                 * processors available keep trying.
                                 */
                                if (    pset->processor_count > 1                       ||
                                                pset != processor->processor_set        ) {
                                        queue_t                 queue = &pset->active_queue;
                                        processor_t             myprocessor, lastprocessor;
                                        queue_entry_t   next;

                                        /*
                                         * Next try the last processor
                                         * dispatched on.
                                         */
                                        myprocessor = processor;
                                        processor = new_thread->last_processor;
                                        if (    processor != myprocessor                                                &&
                                                        processor != PROCESSOR_NULL                                             &&
                                                        processor->processor_set == pset                                &&
                                                        processor->state == PROCESSOR_RUNNING                   &&
                                                        new_thread->sched_pri > processor->current_pri  ) {
                                                dispatch_counts.pset_last++;
                                                cause_ast_check(processor);
                                                simple_unlock(&pset->sched_lock);
                                                return;
                                        }

                                        /*
                                         * Lastly, pick any other
                                         * available processor.
                                         */
                                        lastprocessor = processor;
                                        processor = (processor_t)queue_first(queue);
                                        while (!queue_end(queue, (queue_entry_t)processor)) {
                                                next = queue_next((queue_entry_t)processor);

                                                if (    processor != myprocessor                        &&
                                                                processor != lastprocessor                      &&
                                                                new_thread->sched_pri >
                                                                                        processor->current_pri          ) {
                                                        if (!queue_end(queue, next)) {
                                                                remqueue(queue, (queue_entry_t)processor);
                                                                enqueue_tail(queue, (queue_entry_t)processor);
                                                        }
                                                        dispatch_counts.pset_other++;
                                                        cause_ast_check(processor);
                                                        simple_unlock(&pset->sched_lock);
                                                        return;
                                                }

                                                processor = (processor_t)next;
                                        }
                                }
                        }

                        simple_unlock(&pset->sched_lock);
                }
        }
        else {
            /*
             *  Bound, can only run on bound processor.  Have to lock
             *  processor here because it may not be the current one.
             */
                processor_lock(processor);
                pset = processor->processor_set;
                if (pset != PROCESSOR_SET_NULL) {
                        simple_lock(&pset->sched_lock);
                        if (processor->state == PROCESSOR_IDLE) {
                                remqueue(&pset->idle_queue, (queue_entry_t)processor);
                                pset->idle_count--;
                                processor->next_thread = new_thread;
                                processor->deadline = UINT64_MAX;
                                processor->state = PROCESSOR_DISPATCHING;
                                dispatch_counts.idle_bound++;
                                simple_unlock(&pset->sched_lock);
                                processor_unlock(processor);
                                if (processor != current_processor())   
                                        machine_signal_idle(processor);
                                return;
                        }
                }
          
                if (!run_queue_enqueue(&processor->runq, new_thread, options))
                        preempt = AST_NONE;

                if (preempt != AST_NONE) {
                        if (processor == current_processor()) {
                                thread = processor->active_thread;
                                if (csw_needed(thread, processor)) {
                                        dispatch_counts.bound_self++;
                                        ast_on(preempt);
                                }
                        }
                        else
                        if (    processor->state == PROCESSOR_RUNNING                   &&
                                        new_thread->sched_pri > processor->current_pri  ) {
                                dispatch_counts.bound_other++;
                                cause_ast_check(processor);
                        }
                }

                if (pset != PROCESSOR_SET_NULL)
                        simple_unlock(&pset->sched_lock);

                processor_unlock(processor);
        }
}

/*
 *      Check for a possible preemption point in
 *      the (current) thread.
 *
 *      Called at splsched.
 */
ast_t
csw_check(
        thread_t                thread,
        processor_t             processor)
{
        int                             current_pri = thread->sched_pri;
        ast_t                   result = AST_NONE;
        run_queue_t             runq;

        if (first_timeslice(processor)) {
                runq = &processor->processor_set->runq;
                if (runq->highq >= BASEPRI_RTQUEUES)
                        return (AST_PREEMPT | AST_URGENT);

                if (runq->highq > current_pri) {
                        if (runq->urgency > 0)
                                return (AST_PREEMPT | AST_URGENT);

                        result |= AST_PREEMPT;
                }

                runq = &processor->runq;
                if (runq->highq > current_pri) {
                        if (runq->urgency > 0)
                                return (AST_PREEMPT | AST_URGENT);

                        result |= AST_PREEMPT;
                }
        }
        else {
                runq = &processor->processor_set->runq;
                if (runq->highq >= current_pri) {
                        if (runq->urgency > 0)
                                return (AST_PREEMPT | AST_URGENT);

                        result |= AST_PREEMPT;
                }

                runq = &processor->runq;
                if (runq->highq >= current_pri) {
                        if (runq->urgency > 0)
                                return (AST_PREEMPT | AST_URGENT);

                        result |= AST_PREEMPT;
                }
        }

        if (result != AST_NONE)
                return (result);

        if (thread->state & TH_SUSP)
                result |= AST_PREEMPT;

        return (result);
}

/*
 *      set_sched_pri:
 *
 *      Set the scheduled priority of the specified thread.
 *
 *      This may cause the thread to change queues.
 *
 *      Thread must be locked.
 */
void
set_sched_pri(
        thread_t                        thread,
        int                                     priority)
{
        register struct run_queue       *rq = run_queue_remove(thread);

        if (    !(thread->sched_mode & TH_MODE_TIMESHARE)                               &&
                        (priority >= BASEPRI_PREEMPT                                            ||
                         (thread->task_priority < MINPRI_KERNEL                 &&
                          thread->task_priority >= BASEPRI_BACKGROUND   &&
                          priority > thread->task_priority)                                     )       )
                thread->sched_mode |= TH_MODE_PREEMPT;
        else
                thread->sched_mode &= ~TH_MODE_PREEMPT;

        thread->sched_pri = priority;
        if (rq != RUN_QUEUE_NULL)
                thread_setrun(thread, SCHED_PREEMPT | SCHED_TAILQ);
        else
        if (thread->state & TH_RUN) {
                processor_t             processor = thread->last_processor;

                if (thread == current_thread()) {
                        ast_t           preempt = csw_check(thread, processor);

                        if (preempt != AST_NONE)
                                ast_on(preempt);
                        processor->current_pri = priority;
                }
                else
                if (    processor != PROCESSOR_NULL                                             &&
                                processor->active_thread == thread      )
                        cause_ast_check(processor);
        }
}

#if             0

static void
run_queue_check(
        run_queue_t             rq,
        thread_t                thread)
{
        queue_t                 q;
        queue_entry_t   qe;

        if (rq != thread->runq)
                panic("run_queue_check: thread runq");

        if (thread->sched_pri > MAXPRI || thread->sched_pri < MINPRI)
                panic("run_queue_check: thread sched_pri");

        q = &rq->queues[thread->sched_pri];
        qe = queue_first(q);
        while (!queue_end(q, qe)) {
                if (qe == (queue_entry_t)thread)
                        return;

                qe = queue_next(qe);
        }

        panic("run_queue_check: end");
}

#endif  /* DEBUG */

/*
 *      run_queue_remove:
 *
 *      Remove a thread from its current run queue and
 *      return the run queue if successful.
 *
 *      Thread must be locked.
 */
run_queue_t
run_queue_remove(
        thread_t                        thread)
{
        register run_queue_t    rq = thread->runq;

        /*
         *      If rq is RUN_QUEUE_NULL, the thread will stay out of the
         *      run queues because the caller locked the thread.  Otherwise
         *      the thread is on a run queue, but could be chosen for dispatch
         *      and removed.
         */
        if (rq != RUN_QUEUE_NULL) {
                processor_set_t         pset = thread->processor_set;
                processor_t                     processor = thread->bound_processor;

                /*
                 *      The run queues are locked by the pset scheduling
                 *      lock, except when a processor is off-line the
                 *      local run queue is locked by the processor lock.
                 */
                if (processor != PROCESSOR_NULL) {
                        processor_lock(processor);
                        pset = processor->processor_set;
                }

                if (pset != PROCESSOR_SET_NULL)
                        simple_lock(&pset->sched_lock);

                if (rq == thread->runq) {
                        /*
                         *      Thread is on a run queue and we have a lock on
                         *      that run queue.
                         */
                        remqueue(&rq->queues[0], (queue_entry_t)thread);
                        rq->count--;
                        if (thread->sched_mode & TH_MODE_PREEMPT)
                                rq->urgency--;
                        assert(rq->urgency >= 0);

                        if (queue_empty(rq->queues + thread->sched_pri)) {
                                /* update run queue status */
                                if (thread->sched_pri != IDLEPRI)
                                        clrbit(MAXPRI - thread->sched_pri, rq->bitmap);
                                rq->highq = MAXPRI - ffsbit(rq->bitmap);
                        }

                        thread->runq = RUN_QUEUE_NULL;
                }
                else {
                        /*
                         *      The thread left the run queue before we could
                         *      lock the run queue.
                         */
                        assert(thread->runq == RUN_QUEUE_NULL);
                        rq = RUN_QUEUE_NULL;
                }

                if (pset != PROCESSOR_SET_NULL)
                        simple_unlock(&pset->sched_lock);

                if (processor != PROCESSOR_NULL)
                        processor_unlock(processor);
        }

        return (rq);
}

/*
 *      choose_thread:
 *
 *      Remove a thread to execute from the run queues
 *      and return it.
 *
 *      Called with pset scheduling lock held.
 */
static thread_t
choose_thread(
        processor_set_t         pset,
        processor_t                     processor)
{
        register run_queue_t    runq;
        register thread_t               thread;
        register queue_t                q;

        runq = &processor->runq;

        if (runq->count > 0 && runq->highq >= pset->runq.highq) {
                q = runq->queues + runq->highq;

                thread = (thread_t)q->next;
                ((queue_entry_t)thread)->next->prev = q;
                q->next = ((queue_entry_t)thread)->next;
                thread->runq = RUN_QUEUE_NULL;
                runq->count--;
                if (thread->sched_mode & TH_MODE_PREEMPT)
                        runq->urgency--;
                assert(runq->urgency >= 0);
                if (queue_empty(q)) {
                        if (runq->highq != IDLEPRI)
                                clrbit(MAXPRI - runq->highq, runq->bitmap);
                        runq->highq = MAXPRI - ffsbit(runq->bitmap);
                }

                processor->deadline = UINT64_MAX;

                return (thread);
        }

        runq = &pset->runq;

        assert(runq->count > 0);
        q = runq->queues + runq->highq;

        thread = (thread_t)q->next;
        ((queue_entry_t)thread)->next->prev = q;
        q->next = ((queue_entry_t)thread)->next;
        thread->runq = RUN_QUEUE_NULL;
        runq->count--;
        if (runq->highq >= BASEPRI_RTQUEUES)
                processor->deadline = thread->realtime.deadline;
        else
                processor->deadline = UINT64_MAX;
        if (thread->sched_mode & TH_MODE_PREEMPT)
                runq->urgency--;
        assert(runq->urgency >= 0);
        if (queue_empty(q)) {
                if (runq->highq != IDLEPRI)
                        clrbit(MAXPRI - runq->highq, runq->bitmap);
                runq->highq = MAXPRI - ffsbit(runq->bitmap);
        }

        timeshare_quanta_update(pset);

        return (thread);
}

static processor_t
delay_idle(
        processor_t             processor,
        thread_t                self)
{
        int                             *gcount, *lcount;
        uint64_t                abstime, spin, limit;

        lcount = &processor->runq.count;
        gcount = &processor->processor_set->runq.count;

        abstime = mach_absolute_time();
        limit = abstime + delay_idle_limit;
        spin = abstime + delay_idle_spin;

        timer_event((uint32_t)abstime, &processor->idle_thread->system_timer);

        self->options |= TH_OPT_DELAYIDLE;

        while (         *gcount == 0 && *lcount == 0    &&
                                (self->state & TH_WAIT) != 0    &&
                                        abstime < limit                         ) {
                if (abstime >= spin) {
                        (void)spllo();

                        (void)splsched();
                        processor = current_processor();
                        lcount = &processor->runq.count;
                        gcount = &processor->processor_set->runq.count;

                        abstime = mach_absolute_time();
                        spin = abstime + delay_idle_spin;

                        timer_event((uint32_t)abstime, &processor->idle_thread->system_timer);
                }
                else
                        abstime = mach_absolute_time();
        }

        timer_event((uint32_t)abstime, &self->system_timer);

        self->options &= ~TH_OPT_DELAYIDLE;

        return (processor);
}

/*
 *      no_dispatch_count counts number of times processors go non-idle
 *      without being dispatched.  This should be very rare.
 */
int     no_dispatch_count = 0;

/*
 *      This is the idle processor thread, which just looks for other threads
 *      to execute.
 */
void
idle_thread(void)
{
        register processor_t            processor;
        register thread_t                       *threadp;
        register int                            *gcount;
        register int                            *lcount;
        register thread_t                       new_thread;
        register int                            state;
        register processor_set_t        pset;
        ast_t                                           *myast = ast_pending();

        processor = current_processor();

        threadp = &processor->next_thread;
        lcount = &processor->runq.count;
        gcount = &processor->processor_set->runq.count;


        (void)splsched();                       /* Turn interruptions off */

#ifdef __ppc__
        pmsDown();                                      /* Step power down.  Note: interruptions must be disabled for this call */
#endif

        while ( (*threadp == THREAD_NULL)                               &&
                                (*gcount == 0) && (*lcount == 0)        ) {

                /* check for ASTs while we wait */
                if (*myast &~ (AST_SCHEDULING | AST_BSD)) {
                        /* no ASTs for us */
                        *myast &= AST_NONE;
                        (void)spllo();
                }
                else
                        machine_idle();

                (void)splsched();
        }

        /*
         *      This is not a switch statement to avoid the
         *      bounds checking code in the common case.
         */
        pset = processor->processor_set;
        simple_lock(&pset->sched_lock);

#ifdef __ppc__
        pmsStep(0);                                     /* Step up out of idle power, may start timer for next step */
#endif

        state = processor->state;
        if (state == PROCESSOR_DISPATCHING) {
                /*
                 *      Commmon case -- cpu dispatched.
                 */
                new_thread = *threadp;
                *threadp = (volatile thread_t) THREAD_NULL;
                processor->state = PROCESSOR_RUNNING;
                enqueue_tail(&pset->active_queue, (queue_entry_t)processor);

                if (    pset->runq.highq >= BASEPRI_RTQUEUES                    &&
                                new_thread->sched_pri >= BASEPRI_RTQUEUES               ) {
                        register run_queue_t    runq = &pset->runq;
                        register queue_t                q;

                        q = runq->queues + runq->highq;
                        if (((thread_t)q->next)->realtime.deadline <
                                                                                        processor->deadline) {
                                thread_t        thread = new_thread;

                                new_thread = (thread_t)q->next;
                                ((queue_entry_t)new_thread)->next->prev = q;
                                q->next = ((queue_entry_t)new_thread)->next;
                                new_thread->runq = RUN_QUEUE_NULL;
                                processor->deadline = new_thread->realtime.deadline;
                                assert(new_thread->sched_mode & TH_MODE_PREEMPT);
                                runq->count--; runq->urgency--;
                                if (queue_empty(q)) {
                                        if (runq->highq != IDLEPRI)
                                                clrbit(MAXPRI - runq->highq, runq->bitmap);
                                        runq->highq = MAXPRI - ffsbit(runq->bitmap);
                                }
                                dispatch_counts.missed_realtime++;
                                simple_unlock(&pset->sched_lock);

                                thread_lock(thread);
                                thread_setrun(thread, SCHED_HEADQ);
                                thread_unlock(thread);

                                counter(c_idle_thread_handoff++);
                                thread_run(processor->idle_thread, (thread_continue_t)idle_thread, NULL, new_thread);
                                /*NOTREACHED*/
                        }
                        simple_unlock(&pset->sched_lock);

                        counter(c_idle_thread_handoff++);
                        thread_run(processor->idle_thread, (thread_continue_t)idle_thread, NULL, new_thread);
                        /*NOTREACHED*/
                }

                if (    processor->runq.highq > new_thread->sched_pri           ||
                                pset->runq.highq > new_thread->sched_pri                                ) {
                        thread_t        thread = new_thread;

                        new_thread = choose_thread(pset, processor);
                        dispatch_counts.missed_other++;
                        simple_unlock(&pset->sched_lock);

                        thread_lock(thread);
                        thread_setrun(thread, SCHED_HEADQ);
                        thread_unlock(thread);

                        counter(c_idle_thread_handoff++);
                        thread_run(processor->idle_thread, (thread_continue_t)idle_thread, NULL, new_thread);
                        /* NOTREACHED */
                }
                else {
                        simple_unlock(&pset->sched_lock);

                        counter(c_idle_thread_handoff++);
                        thread_run(processor->idle_thread, (thread_continue_t)idle_thread, NULL, new_thread);
                        /* NOTREACHED */
                }
        }
        else
        if (state == PROCESSOR_IDLE) {
                /*
                 *      Processor was not dispatched (Rare).
                 *      Set it running again and force a
                 *      reschedule.
                 */
                no_dispatch_count++;
                pset->idle_count--;
                remqueue(&pset->idle_queue, (queue_entry_t)processor);
                processor->state = PROCESSOR_RUNNING;
                enqueue_tail(&pset->active_queue, (queue_entry_t)processor);
                simple_unlock(&pset->sched_lock);

                counter(c_idle_thread_block++);
                thread_block((thread_continue_t)idle_thread);
                /* NOTREACHED */
        }
        else
        if (state == PROCESSOR_SHUTDOWN) {
                /*
                 *      Going off-line.  Force a
                 *      reschedule.
                 */
                if ((new_thread = (thread_t)*threadp) != THREAD_NULL) {
                        *threadp = (volatile thread_t) THREAD_NULL;
                        processor->deadline = UINT64_MAX;
                        simple_unlock(&pset->sched_lock);

                        thread_lock(new_thread);
                        thread_setrun(new_thread, SCHED_HEADQ);
                        thread_unlock(new_thread);
                }
                else
                        simple_unlock(&pset->sched_lock);

                counter(c_idle_thread_block++);
                thread_block((thread_continue_t)idle_thread);
                /* NOTREACHED */
        }

        simple_unlock(&pset->sched_lock);

        panic("idle_thread: state %d\n", processor->state);
        /*NOTREACHED*/
}

kern_return_t
idle_thread_create(
        processor_t             processor)
{
        kern_return_t   result;
        thread_t                thread;
        spl_t                   s;

        result = kernel_thread_create((thread_continue_t)idle_thread, NULL, MAXPRI_KERNEL, &thread);
        if (result != KERN_SUCCESS)
                return (result);

        s = splsched();
        thread_lock(thread);
        thread->bound_processor = processor;
        processor->idle_thread = thread;
        thread->sched_pri = thread->priority = IDLEPRI;
        thread->state = (TH_RUN | TH_IDLE);
        thread_unlock(thread);
        splx(s);

        thread_deallocate(thread);

        return (KERN_SUCCESS);
}

static uint64_t         sched_tick_deadline;

/*
 * sched_startup:
 *
 * Kicks off scheduler services.
 *
 * Called at splsched.
 */
void
sched_startup(void)
{
        kern_return_t   result;
        thread_t                thread;

        result = kernel_thread_start_priority((thread_continue_t)sched_tick_thread, NULL, MAXPRI_KERNEL, &thread);
        if (result != KERN_SUCCESS)
                panic("sched_startup");

        thread_deallocate(thread);

        /*
         * Yield to the sched_tick_thread while it times
         * a series of context switches back.  It stores
         * the baseline value in sched_cswtime.
         *
         * The current thread is the only other thread
         * active at this point.
         */
        while (sched_cswtime == 0)
                thread_block(THREAD_CONTINUE_NULL);

        thread_daemon_init();

        thread_call_initialize();
}

/*
 *      sched_tick_thread:
 *
 *      Perform periodic bookkeeping functions about ten
 *      times per second.
 */
static void
sched_tick_continue(void)
{
        uint64_t                        abstime = mach_absolute_time();

        sched_tick++;

        /*
         *  Compute various averages.
         */
        compute_averages();

        /*
         *  Scan the run queues for threads which
         *  may need to be updated.
         */
        thread_update_scan();

        clock_deadline_for_periodic_event(sched_tick_interval, abstime,
                                                                                                                &sched_tick_deadline);

        assert_wait_deadline((event_t)sched_tick_thread, THREAD_UNINT, sched_tick_deadline);
        thread_block((thread_continue_t)sched_tick_continue);
        /*NOTREACHED*/
}

/*
 * Time a series of context switches to determine
 * a baseline.  Toss the high and low and return
 * the one-way value.
 */
static uint32_t
time_cswitch(void)
{
        uint32_t        new, hi, low, accum;
        uint64_t        abstime;
        int                     i, tries = 7;

        accum = hi = low = 0;
        for (i = 0; i < tries; ++i) {
                abstime = mach_absolute_time();
                thread_block(THREAD_CONTINUE_NULL);

                new = mach_absolute_time() - abstime;

                if (i == 0)
                        accum = hi = low = new;
                else {
                        if (new < low)
                                low = new;
                        else
                        if (new > hi)
                                hi = new;
                        accum += new;
                }
        }

        return ((accum - hi - low) / (2 * (tries - 2)));
}

void
sched_tick_thread(void)
{
        sched_cswtime = time_cswitch();

        sched_tick_deadline = mach_absolute_time();

        sched_tick_continue();
        /*NOTREACHED*/
}

/*
 *      thread_update_scan / runq_scan:
 *
 *      Scan the run queues to account for timesharing threads 
 *      which need to be updated.
 *
 *      Scanner runs in two passes.  Pass one squirrels likely
 *      threads away in an array, pass two does the update.
 *
 *      This is necessary because the run queue is locked for
 *      the candidate scan, but the thread is locked for the update.
 *
 *      Array should be sized to make forward progress, without
 *      disabling preemption for long periods.
 */

#define THREAD_UPDATE_SIZE              128

static thread_t         thread_update_array[THREAD_UPDATE_SIZE];
static int                      thread_update_count = 0;

/*
 *      Scan a runq for candidate threads.
 *
 *      Returns TRUE if retry is needed.
 */
static boolean_t
runq_scan(
        run_queue_t                             runq)
{
        register int                    count;
        register queue_t                q;
        register thread_t               thread;

        if ((count = runq->count) > 0) {
            q = runq->queues + runq->highq;
                while (count > 0) {
                        queue_iterate(q, thread, thread_t, links) {
                                if (            thread->sched_stamp != sched_tick               &&
                                                (thread->sched_mode & TH_MODE_TIMESHARE)        ) {
                                        if (thread_update_count == THREAD_UPDATE_SIZE)
                                                return (TRUE);

                                        thread_update_array[thread_update_count++] = thread;
                                        thread_reference_internal(thread);
                                }

                                count--;
                        }

                        q--;
                }
        }

        return (FALSE);
}

static void
thread_update_scan(void)
{
        register boolean_t                      restart_needed;
        register processor_set_t        pset = &default_pset;
        register processor_t            processor;
        register thread_t                       thread;
        spl_t                                           s;

        do {
                s = splsched();
                simple_lock(&pset->sched_lock);
            restart_needed = runq_scan(&pset->runq);
                simple_unlock(&pset->sched_lock);

                if (!restart_needed) {
                        simple_lock(&pset->sched_lock);
                        processor = (processor_t)queue_first(&pset->processors);
                        while (!queue_end(&pset->processors, (queue_entry_t)processor)) {
                                if ((restart_needed = runq_scan(&processor->runq)) != 0)
                                        break;

                                thread = processor->idle_thread;
                                if (thread->sched_stamp != sched_tick) {
                                        if (thread_update_count == THREAD_UPDATE_SIZE) {
                                                restart_needed = TRUE;
                                                break;
                                        }

                                        thread_update_array[thread_update_count++] = thread;
                                        thread_reference_internal(thread);
                                }

                                processor = (processor_t)queue_next(&processor->processors);
                        }
                        simple_unlock(&pset->sched_lock);
                }
                splx(s);

            /*
             *  Ok, we now have a collection of candidates -- fix them.
             */
            while (thread_update_count > 0) {
                        thread = thread_update_array[--thread_update_count];
                        thread_update_array[thread_update_count] = THREAD_NULL;

                        s = splsched();
                        thread_lock(thread);
                        if (    !(thread->state & (TH_WAIT|TH_SUSP))    &&
                                                thread->sched_stamp != sched_tick       )
                                update_priority(thread);
                        thread_unlock(thread);
                        splx(s);

                        thread_deallocate(thread);
            }
        } while (restart_needed);
}
                
/*
 *      Just in case someone doesn't use the macro
 */
#undef  thread_wakeup
void
thread_wakeup(
        event_t         x);

void
thread_wakeup(
        event_t         x)
{
        thread_wakeup_with_result(x, THREAD_AWAKENED);
}

boolean_t
preemption_enabled(void)
{
        return (get_preemption_level() == 0 && ml_get_interrupts_enabled());
}

#if     DEBUG
static boolean_t
thread_runnable(
        thread_t        thread)
{
        return ((thread->state & (TH_RUN|TH_WAIT)) == TH_RUN);
}
#endif  /* DEBUG */

#if     MACH_KDB
#include <ddb/db_output.h>
#define printf          kdbprintf
void                    db_sched(void);

void
db_sched(void)
{
        iprintf("Scheduling Statistics:\n");
        db_indent += 2;
        iprintf("Thread invocations:  csw %d same %d\n",
                c_thread_invoke_csw, c_thread_invoke_same);
#if     MACH_COUNTERS
        iprintf("Thread block:  calls %d\n",
                c_thread_block_calls);
        iprintf("Idle thread:\n\thandoff %d block %d no_dispatch %d\n",
                c_idle_thread_handoff,
                c_idle_thread_block, no_dispatch_count);
        iprintf("Sched thread blocks:  %d\n", c_sched_thread_block);
#endif  /* MACH_COUNTERS */
        db_indent -= 2;
}

#include <ddb/db_output.h>
void            db_show_thread_log(void);

void
db_show_thread_log(void)
{
}
#endif  /* MACH_KDB */