xnu-344.23.tar.gz

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

/*
 * Copyright (c) 2000 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 <cpus.h>
#include <mach_kdb.h>
#include <simple_clock.h>
#include <power_save.h>
#include <task_swapper.h>

#include <ddb/db_output.h>
#include <mach/machine.h>
#include <machine/machine_routines.h>
#include <machine/sched_param.h>
#include <kern/ast.h>
#include <kern/clock.h>
#include <kern/counters.h>
#include <kern/cpu_number.h>
#include <kern/cpu_data.h>
#include <kern/etap_macros.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/thread_swap.h>
#include <vm/pmap.h>
#include <vm/vm_kern.h>
#include <vm/vm_map.h>
#include <mach/policy.h>
#include <mach/sync_policy.h>
#include <kern/mk_sp.h> /*** ??? fix so this can be removed ***/
#include <sys/kdebug.h>

#if     TASK_SWAPPER
#include <kern/task_swap.h>
extern int      task_swap_on;
#endif  /* TASK_SWAPPER */

extern int      hz;

#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;

uint32_t        std_quantum_us;

unsigned        sched_tick;

#if     SIMPLE_CLOCK
int                     sched_usec;
#endif  /* SIMPLE_CLOCK */

/* Forwards */
void            wait_queues_init(void);

thread_t        choose_pset_thread(
                                processor_t                     myprocessor,
                                processor_set_t         pset);

thread_t        choose_thread(
                                processor_t             myprocessor);

boolean_t       run_queue_enqueue(
                                run_queue_t             runq,
                                thread_t                thread,
                                boolean_t               tail);

void            do_thread_scan(void);

#if     DEBUG
void            dump_run_queues(
                                run_queue_t                     rq);
void            dump_run_queue_struct(
                                run_queue_t                     rq);
void            dump_processor(
                                processor_t             p);
void            dump_processor_set(
                                processor_set_t         ps);

void            checkrq(
                                run_queue_t             rq,
                                char                    *msg);

void            thread_check(
                                thread_t                thread,
                                run_queue_t             runq);

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)

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);

        wait_queues_init();
        pset_sys_bootstrap();           /* initialize processor mgmt. */
        processor_action();
        sched_tick = 0;
#if     SIMPLE_CLOCK
        sched_usec = 0;
#endif  /* SIMPLE_CLOCK */
        ast_init();
}

void
wait_queues_init(void)
{
        register int    i;

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

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

        s = splsched();
        wake_lock(thread);
        if (--thread->wait_timer_active == 1) {
                if (thread->wait_timer_is_set) {
                        thread->wait_timer_is_set = FALSE;
                        thread_lock(thread);
                        if (thread->active)
                                clear_wait_internal(thread, THREAD_TIMED_OUT);
                        thread_unlock(thread);
                }
        }
        else
        if (thread->wait_timer_active == 0)
                thread_wakeup_one(&thread->wait_timer_active);
        wake_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();
        wake_lock(thread);
        thread_lock(thread);
        if ((thread->state & TH_WAIT) != 0) {
                clock_interval_to_deadline(interval, scale_factor, &deadline);
                timer_call_enter(&thread->wait_timer, deadline);
                assert(!thread->wait_timer_is_set);
                thread->wait_timer_active++;
                thread->wait_timer_is_set = TRUE;
        }
        thread_unlock(thread);
        wake_unlock(thread);
        splx(s);
}

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

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

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

        s = splsched();
        wake_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;
        }
        wake_unlock(thread);
        splx(s);
}

/*
 * Set up thread timeout element when thread is created.
 */
void
thread_timer_setup(
         thread_t               thread)
{
        extern void     thread_depress_expire(
                                        timer_call_param_t      p0,
                                        timer_call_param_t      p1);

        timer_call_setup(&thread->wait_timer, thread_timer_expire, thread);
        thread->wait_timer_is_set = FALSE;
        thread->wait_timer_active = 1;

        timer_call_setup(&thread->depress_timer, thread_depress_expire, thread);
        thread->depress_timer_active = 1;

        thread->ref_count++;
}

void
thread_timer_terminate(void)
{
        thread_t                thread = current_thread();
        wait_result_t   res;
        spl_t                   s;

        s = splsched();
        wake_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->wait_timer_active--;

        while (thread->wait_timer_active > 0) {
                res = assert_wait((event_t)&thread->wait_timer_active, THREAD_UNINT);
                assert(res == THREAD_WAITING);
                wake_unlock(thread);
                splx(s);

                res = thread_block(THREAD_CONTINUE_NULL);
                assert(res == THREAD_AWAKENED);

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

        thread->depress_timer_active--;

        while (thread->depress_timer_active > 0) {
                res = assert_wait((event_t)&thread->depress_timer_active, THREAD_UNINT);
                assert(res == THREAD_WAITING);
                wake_unlock(thread);
                splx(s);

                res = thread_block(THREAD_CONTINUE_NULL);
                assert(res == THREAD_AWAKENED);

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

        wake_unlock(thread);
        splx(s);

        thread_deallocate(thread);
}

/*
 *      Routine:        thread_go_locked
 *      Purpose:
 *              Start a thread running.
 *      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_locked(
        thread_t                thread,
        wait_result_t   result)
{
        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) {
                thread->state &= ~(TH_WAIT|TH_UNINT);
                if (!(thread->state & TH_RUN)) {
                        thread->state |= TH_RUN;

                        if (thread->active_callout)
                                call_thread_unblock();

                        if (!(thread->state & TH_IDLE)) {
                                _mk_sp_thread_unblock(thread);
                                hw_atomic_add(&thread->processor_set->run_count, 1);
                        }
                }

                thread->wait_result = result;
                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)
{
        wait_result_t   wait_result;
        boolean_t                       at_safe_point;

        assert(thread == current_thread());

        /*
         *      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->interrupt_level)
                interruptible = thread->interrupt_level;

        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;
                thread->sleep_stamp = sched_tick;
                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->interrupt_level;

        thread->interrupt_level = new_level;
        return result;
}

/*
 *      Routine:        assert_wait_timeout
 *      Purpose:
 *              Assert that the thread intends to block,
 *              waiting for a timeout (no user known event).
 */
unsigned int assert_wait_timeout_event;

wait_result_t
assert_wait_timeout(
        mach_msg_timeout_t              msecs,
        wait_interrupt_t                interruptible)
{
        wait_result_t res;

        res = assert_wait((event_t)&assert_wait_timeout_event, interruptible);
        if (res == THREAD_WAITING)
                thread_set_timer(msecs, 1000*NSEC_PER_USEC);
        return res;
}

/*
 * 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;
        extern unsigned int debug_mode;

#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);
        assert(assert_wait_possible());

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


/*
 *      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.
 *
 *      JMM - Add hint to make sure mutex is available before rousting
 */
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(event, interruptible);
        if (res == THREAD_WAITING) {
                mutex_unlock(mutex);
                thread_set_timer_deadline(deadline);
                res = thread_block(THREAD_CONTINUE_NULL);
                if (res != THREAD_TIMED_OUT)
                        thread_cancel_timer();
                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.
 *
 *      JMM - Add hint to make sure mutex is available before rousting
 */
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_sleep_funnel:
 *
 *      Cause the current thread to wait until the specified event
 *      occurs.  If the thread is funnelled, the funnel will be released
 *      before giving up the cpu. The funnel will be re-acquired before returning.
 *
 *      JMM - Right now the funnel is dropped and re-acquired inside
 *                thread_block().  At some point, this may give thread_block() a hint.
 */
wait_result_t
thread_sleep_funnel(
        event_t                 event,
        wait_interrupt_t interruptible)
{
        wait_result_t   res;

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

/*
 * thread_[un]stop(thread)
 *      Once a thread has blocked interruptibly (via assert_wait) prevent 
 *      it from running until thread_unstop.
 *
 *      If someone else has already stopped the thread, wait for the
 *      stop to be cleared, and then stop it again.
 *
 *      Return FALSE if interrupted.
 *
 * NOTE: thread_hold/thread_suspend should be called on the activation
 *      before calling thread_stop.  TH_SUSP is only recognized when
 *      a thread blocks and only prevents clear_wait/thread_wakeup
 *      from restarting an interruptible wait.  The wake_active flag is
 *      used to indicate that someone is waiting on the thread.
 */
boolean_t
thread_stop(
        thread_t        thread)
{
        spl_t           s = splsched();

        wake_lock(thread);

        while (thread->state & TH_SUSP) {
                wait_result_t   result;

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

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

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

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

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

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

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

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

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

                if (result != 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);
}

/*
 *      Clear TH_SUSP and if the thread has been stopped and is now runnable,
 *      put it back on the run queue.
 */
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->state |= TH_RUN;

                assert(!(thread->state & TH_IDLE));
                _mk_sp_thread_unblock(thread);
                hw_atomic_add(&thread->processor_set->run_count, 1);
        }
        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);
}

/*
 * Wait for the thread's RUN bit to clear
 */
boolean_t
thread_wait(
        thread_t        thread)
{
        spl_t           s = splsched();

        wake_lock(thread);
        thread_lock(thread);

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

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

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

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

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

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

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

        return (TRUE);
}

/*
 *      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   result)
{
        wait_queue_t    wq = thread->wait_queue;
        kern_return_t   ret;
        int                             loop_count;

        loop_count = 0;
        do {
                if ((result == 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; /* we know it moved */
                                }
                                continue;
                        }
                }
                ret = thread_go_locked(thread, result);
                return ret; 
        } while (++loop_count < LockTimeOut);
        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.
 *      If the thread is currently executing, it may wait until its
 *      time slice is up before switching onto the specified processor.
 *
 *      A processor of PROCESSOR_NULL causes the thread to be unbound.
 *      xxx - DO NOT export this to users.
 */
void
thread_bind(
        register thread_t       thread,
        processor_t                     processor)
{
        spl_t           s;

        s = splsched();
        thread_lock(thread);
        thread_bind_locked(thread, processor);
        thread_unlock(thread);
        splx(s);
}

/*
 *      Select a thread for this processor (the current processor) to run.
 *      May select the current thread, which must already be locked.
 */
thread_t
thread_select(
        register processor_t    myprocessor)
{
        register thread_t               thread;
        processor_set_t                 pset;
        register run_queue_t    runq = &myprocessor->runq;
        boolean_t                               other_runnable;

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

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

        myprocessor->current_pri = thread->sched_pri;

        simple_lock(&runq->lock);
        simple_lock(&pset->runq.lock);

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

        if (    thread->state == TH_RUN                                                 &&
                        (!other_runnable                                                        ||
                         (runq->highq < thread->sched_pri               &&
                          pset->runq.highq < thread->sched_pri))                &&
                        thread->processor_set == pset                                   &&
                        (thread->bound_processor == PROCESSOR_NULL      ||
                         thread->bound_processor == myprocessor)                                ) {

                /* I am the highest priority runnable (non-idle) thread */
                simple_unlock(&pset->runq.lock);
                simple_unlock(&runq->lock);

                myprocessor->slice_quanta =
                                (thread->sched_mode & TH_MODE_TIMESHARE)? pset->set_quanta: 1;
        }
        else
        if (other_runnable)
                thread = choose_thread(myprocessor);
        else {
                simple_unlock(&pset->runq.lock);
                simple_unlock(&runq->lock);

                /*
                 *      Nothing is runnable, so set this processor idle if it
                 *      was running.  If it was in an assignment or shutdown,
                 *      leave it alone.  Return its idle thread.
                 */
                simple_lock(&pset->sched_lock);
                if (myprocessor->state == PROCESSOR_RUNNING) {
                        remqueue(&pset->active_queue, (queue_entry_t)myprocessor);
                        myprocessor->state = PROCESSOR_IDLE;

                        if (myprocessor == master_processor)
                                enqueue_tail(&pset->idle_queue, (queue_entry_t)myprocessor);
                        else
                                enqueue_head(&pset->idle_queue, (queue_entry_t)myprocessor);

                        pset->idle_count++;
                }
                simple_unlock(&pset->sched_lock);

                thread = myprocessor->idle_thread;
        }

        return (thread);
}


/*
 *      Stop running the current thread and start running the new thread.
 *      If continuation is non-zero, and the current thread is blocked,
 *      then it will resume by executing continuation on a new stack.
 *      Returns TRUE if the hand-off succeeds.
 *
 *      Assumes splsched.
 */

static thread_t
__current_thread(void)
{
  return (current_thread());
}

boolean_t
thread_invoke(
        register thread_t       old_thread,
        register thread_t       new_thread,
        int                                     reason,
        thread_continue_t       old_cont)
{
        thread_continue_t       new_cont;
        processor_t                     processor;

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

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

        assert(thread_runnable(new_thread));

        assert(old_thread->continuation == NULL);       

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

        if (old_cont != NULL) {
                if (new_thread->state & TH_STACK_HANDOFF) {
                        /*
                         * 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->stack_privilege &&
                                                        !new_thread->stack_privilege)
                                goto need_stack;

                        new_thread->state &= ~TH_STACK_HANDOFF;
                        new_cont = new_thread->continuation;
                        new_thread->continuation = NULL;

                        /*
                         * Set up ast context of new thread and switch
                         * to its timer.
                         */
                        processor = current_processor();
                        new_thread->last_processor = processor;
                        processor->current_pri = new_thread->sched_pri;
                        ast_context(new_thread->top_act, processor->slot_num);
                        timer_switch(&new_thread->system_timer);
                        thread_unlock(new_thread);
                
                        current_task()->csw++;

                        old_thread->reason = reason;
                        old_thread->continuation = old_cont;
           
                        _mk_sp_thread_done(old_thread, new_thread, processor);

                        stack_handoff(old_thread, new_thread);

                        _mk_sp_thread_begin(new_thread, processor);

                        wake_lock(old_thread);
                        thread_lock(old_thread);

                        /* 
                         * Inline thread_dispatch but
                         * don't free stack.
                         */

                        switch (old_thread->state & (TH_RUN|TH_WAIT|TH_UNINT|TH_IDLE)) {
 
                        case TH_RUN                             | TH_UNINT:
                        case TH_RUN:
                                /*
                                 * Still running, put back
                                 * onto a run queue.
                                 */
                                old_thread->state |= TH_STACK_HANDOFF;
                                _mk_sp_thread_dispatch(old_thread);

                                thread_unlock(old_thread);
                                wake_unlock(old_thread);
                                break;

                        case TH_RUN | TH_WAIT   | TH_UNINT:
                        case TH_RUN | TH_WAIT:
                        {
                                boolean_t       reap, wake, callblock;

                                /*
                                 * Waiting.
                                 */
                                old_thread->sleep_stamp = sched_tick;
                                old_thread->state |= TH_STACK_HANDOFF;
                                old_thread->state &= ~TH_RUN;
                                hw_atomic_sub(&old_thread->processor_set->run_count, 1);
                                callblock = old_thread->active_callout;
                                wake = old_thread->wake_active;
                                old_thread->wake_active = FALSE;
                                reap = (old_thread->state & TH_TERMINATE)? TRUE: FALSE;

                                thread_unlock(old_thread);
                                wake_unlock(old_thread);

                                if (callblock)
                                        call_thread_block();

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

                                if (reap)
                                        thread_reaper_enqueue(old_thread);
                                break;
                        }

                        case TH_RUN                             | TH_IDLE:
                                /*
                                 * The idle threads don't go
                                 * onto a run queue.
                                 */
                                old_thread->state |= TH_STACK_HANDOFF;
                                thread_unlock(old_thread);
                                wake_unlock(old_thread);
                                break;

                        default:
                                panic("thread_invoke: state 0x%x\n", old_thread->state);
                        }

                        counter_always(c_thread_invoke_hits++);

                        if (new_thread->funnel_state & TH_FN_REFUNNEL) {
                                kern_return_t           wait_result = new_thread->wait_result;

                                new_thread->funnel_state = 0;
                                KERNEL_DEBUG(0x6032428 | DBG_FUNC_NONE,
                                                                        new_thread->funnel_lock, 2, 0, 0, 0);
                                funnel_lock(new_thread->funnel_lock);
                                KERNEL_DEBUG(0x6032430 | DBG_FUNC_NONE,
                                                                        new_thread->funnel_lock, 2, 0, 0, 0);
                                new_thread->funnel_state = TH_FN_OWNED;
                                new_thread->wait_result = wait_result;
                        }
                        (void) spllo();

                        assert(new_cont);
                        call_continuation(new_cont);
                        /*NOTREACHED*/
                        return (TRUE);
                }
                else
                if (new_thread->state & TH_STACK_ALLOC) {
                        /*
                         * Waiting for a stack
                         */
                        counter_always(c_thread_invoke_misses++);
                        thread_unlock(new_thread);
                        return (FALSE);
                }
                else
                if (new_thread == old_thread) {
                        /* same thread but with continuation */
                        counter(++c_thread_invoke_same);
                        thread_unlock(new_thread);

                        if (new_thread->funnel_state & TH_FN_REFUNNEL) {
                                kern_return_t   wait_result = new_thread->wait_result;

                                new_thread->funnel_state = 0;
                                KERNEL_DEBUG(0x6032428 | DBG_FUNC_NONE,
                                                                        new_thread->funnel_lock, 3, 0, 0, 0);
                                funnel_lock(new_thread->funnel_lock);
                                KERNEL_DEBUG(0x6032430 | DBG_FUNC_NONE,
                                                                        new_thread->funnel_lock, 3, 0, 0, 0);
                                new_thread->funnel_state = TH_FN_OWNED;
                                new_thread->wait_result = wait_result;
                        }
                        (void) spllo();
                        call_continuation(old_cont);
                        /*NOTREACHED*/
                }
        }
        else {
                /*
                 * Check that the new thread has a stack
                 */
                if (new_thread->state & TH_STACK_HANDOFF) {
need_stack:
                        if (!stack_alloc_try(new_thread, thread_continue)) {
                                counter_always(c_thread_invoke_misses++);
                                thread_swapin(new_thread);
                                return (FALSE);
                        }
         
                        new_thread->state &= ~TH_STACK_HANDOFF;
                }
                else
                if (new_thread->state & TH_STACK_ALLOC) {
                        /*
                         * Waiting for a stack
                         */
                        counter_always(c_thread_invoke_misses++);
                        thread_unlock(new_thread);
                        return (FALSE);
                }
                else
                if (old_thread == new_thread) {
                        counter(++c_thread_invoke_same);
                        thread_unlock(new_thread);
                        return (TRUE);
                }
        }

        /*
         * Set up ast context of new thread and switch to its timer.
         */
        processor = current_processor();
        new_thread->last_processor = processor;
        processor->current_pri = new_thread->sched_pri;
        ast_context(new_thread->top_act, processor->slot_num);
        timer_switch(&new_thread->system_timer);
        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;
        old_thread->continuation = old_cont;

        _mk_sp_thread_done(old_thread, new_thread, processor);

        /*
         *      switch_context is machine-dependent.  It does the
         *      machine-dependent components of a context-switch, like
         *      changing address spaces.  It updates active_threads.
         */
        old_thread = switch_context(old_thread, old_cont, new_thread);
        
        /* Now on new thread's stack.  Set a local variable to refer to it. */
        new_thread = __current_thread();
        assert(old_thread != new_thread);

        assert(thread_runnable(new_thread));
        _mk_sp_thread_begin(new_thread, new_thread->last_processor);

        /*
         *      We're back.  Now old_thread is the thread that resumed
         *      us, and we have to dispatch it.
         */
        thread_dispatch(old_thread);

        if (old_cont) {
                if (new_thread->funnel_state & TH_FN_REFUNNEL) {
                        kern_return_t           wait_result = new_thread->wait_result;

                        new_thread->funnel_state = 0;
                        KERNEL_DEBUG(0x6032428 | DBG_FUNC_NONE,
                                                                new_thread->funnel_lock, 3, 0, 0, 0);
                        funnel_lock(new_thread->funnel_lock);
                        KERNEL_DEBUG(0x6032430 | DBG_FUNC_NONE,
                                                                new_thread->funnel_lock, 3, 0, 0, 0);
                        new_thread->funnel_state = TH_FN_OWNED;
                        new_thread->wait_result = wait_result;
                }
                (void) spllo();
                call_continuation(old_cont);
                /*NOTREACHED*/
        }

        return (TRUE);
}

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

        _mk_sp_thread_begin(self, self->last_processor);
        
        /*
         *      We must dispatch the old thread and then
         *      call the current thread's continuation.
         *      There might not be an old thread, if we are
         *      the first thread to run on this processor.
         */
        if (old_thread != THREAD_NULL)
                thread_dispatch(old_thread);

        if (self->funnel_state & TH_FN_REFUNNEL) {
                kern_return_t           wait_result = self->wait_result;

                self->funnel_state = 0;
                KERNEL_DEBUG(0x6032428 | DBG_FUNC_NONE, self->funnel_lock, 4, 0, 0, 0);
                funnel_lock(self->funnel_lock);
                KERNEL_DEBUG(0x6032430 | DBG_FUNC_NONE, self->funnel_lock, 4, 0, 0, 0);
                self->funnel_state = TH_FN_OWNED;
                self->wait_result = wait_result;
        }
        (void)spllo();
        assert(continuation);
        call_continuation(continuation);
        /*NOTREACHED*/
}

#if     MACH_LDEBUG || MACH_KDB

#define THREAD_LOG_SIZE         300

struct t64 {
        unsigned long h;
        unsigned long l;
};

struct {
        struct t64      stamp;
        thread_t        thread;
        long            info1;
        long            info2;
        long            info3;
        char            * action;
} thread_log[THREAD_LOG_SIZE];

int             thread_log_index;

void            check_thread_time(long n);


int     check_thread_time_crash;

#if 0
void
check_thread_time(long us)
{
        struct t64      temp;

        if (!check_thread_time_crash)
                return;

        temp = thread_log[0].stamp;
        cyctm05_diff (&thread_log[1].stamp, &thread_log[0].stamp, &temp);

        if (temp.l >= us && thread_log[1].info != 0x49) /* HACK!!! */
                panic ("check_thread_time");
}
#endif

void
log_thread_action(char * action, long info1, long info2, long info3)
{
        int     i;
        spl_t   x;
        static  unsigned int tstamp;

        x = splhigh();

        for (i = THREAD_LOG_SIZE-1; i > 0; i--) {
                thread_log[i] = thread_log[i-1];
        }

        thread_log[0].stamp.h = 0;
        thread_log[0].stamp.l = tstamp++;
        thread_log[0].thread = current_thread();
        thread_log[0].info1 = info1;
        thread_log[0].info2 = info2;
        thread_log[0].info3 = info3;
        thread_log[0].action = action;
/*      strcpy (&thread_log[0].action[0], action);*/

        splx(x);
}
#endif /* MACH_LDEBUG || MACH_KDB */

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

void
db_show_thread_log(void)
{
        int     i;

        db_printf ("%s %s %s %s %s %s\n", " Thread ", "  Info1 ", "  Info2 ",
                        "  Info3 ", "    Timestamp    ", "Action");

        for (i = 0; i < THREAD_LOG_SIZE; i++) {
                db_printf ("%08x %08x %08x %08x %08x/%08x %s\n",
                        thread_log[i].thread,
                        thread_log[i].info1,
                        thread_log[i].info2,
                        thread_log[i].info3,
                        thread_log[i].stamp.h,
                        thread_log[i].stamp.l,
                        thread_log[i].action);
        }
}
#endif  /* MACH_KDB */

/*
 *      thread_block_reason:
 *
 *      Block the current thread if a wait has been asserted,
 *      otherwise unconditionally yield the remainder of the
 *      current quantum unless reason contains AST_BLOCK.
 *      
 *      If a continuation is specified, then thread_block 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;)
 
int
thread_block_reason(
        thread_continue_t       continuation,
        ast_t                           reason)
{
        register thread_t               thread = current_thread();
        register processor_t    myprocessor;
        register thread_t               new_thread;
        spl_t                                   s;

        counter(++c_thread_block_calls);

        check_simple_locks();

        machine_clock_assist();

        s = splsched();

        if ((thread->funnel_state & TH_FN_OWNED) && !(reason & AST_PREEMPT)) {
                thread->funnel_state = TH_FN_REFUNNEL;
                KERNEL_DEBUG(
                        0x603242c | DBG_FUNC_NONE, thread->funnel_lock, 2, 0, 0, 0);
                funnel_unlock(thread->funnel_lock);
        }

        myprocessor = current_processor();

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

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

        thread_lock(thread);
        new_thread = thread_select(myprocessor);
        assert(new_thread && thread_runnable(new_thread));
        thread_unlock(thread);
        while (!thread_invoke(thread, new_thread, reason, continuation)) {
                thread_lock(thread);
                new_thread = thread_select(myprocessor);
                assert(new_thread && thread_runnable(new_thread));
                thread_unlock(thread);
        }

        if (thread->funnel_state & TH_FN_REFUNNEL) {
                kern_return_t   wait_result = thread->wait_result;

                thread->funnel_state = 0;
                KERNEL_DEBUG(
                        0x6032428 | DBG_FUNC_NONE, thread->funnel_lock, 5, 0, 0, 0);
                funnel_lock(thread->funnel_lock);
                KERNEL_DEBUG(
                        0x6032430 | DBG_FUNC_NONE, thread->funnel_lock, 5, 0, 0, 0);
                thread->funnel_state = TH_FN_OWNED;
                thread->wait_result = wait_result;
        }

        splx(s);

        return (thread->wait_result);
}

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

/*
 *      thread_run:
 *
 *      Switch directly from the current (old) thread to the
 *      specified thread, handing off our quantum if possible.
 *
 *      New thread must be runnable, and not on a run queue.
 *
 *  Assumption:
 *      at splsched.
 */
int
thread_run(
        thread_t                        old_thread,
        thread_continue_t       continuation,
        thread_t                        new_thread)
{
        ast_t           handoff = AST_HANDOFF;

        assert(old_thread == current_thread());

        machine_clock_assist();

        if (old_thread->funnel_state & TH_FN_OWNED) {
                old_thread->funnel_state = TH_FN_REFUNNEL;
                KERNEL_DEBUG(
                        0x603242c | DBG_FUNC_NONE, old_thread->funnel_lock, 3, 0, 0, 0);
                funnel_unlock(old_thread->funnel_lock);
        }

        while (!thread_invoke(old_thread, new_thread, handoff, continuation)) {
                register processor_t            myprocessor = current_processor();

                thread_lock(old_thread);
                new_thread = thread_select(myprocessor);
                thread_unlock(old_thread);
                handoff = AST_NONE;
        }

        /* if we fell thru */
        if (old_thread->funnel_state & TH_FN_REFUNNEL) {
                kern_return_t   wait_result = old_thread->wait_result;

                old_thread->funnel_state = 0;
                KERNEL_DEBUG(
                        0x6032428 | DBG_FUNC_NONE, old_thread->funnel_lock, 6, 0, 0, 0);
                funnel_lock(old_thread->funnel_lock);
                KERNEL_DEBUG(
                        0x6032430 | DBG_FUNC_NONE, old_thread->funnel_lock, 6, 0, 0, 0);
                old_thread->funnel_state = TH_FN_OWNED;
                old_thread->wait_result = wait_result;
        }

        return (old_thread->wait_result);
}

/*
 *      Dispatches a running thread that is not on a runq.
 *      Called at splsched.
 */
void
thread_dispatch(
        register thread_t       thread)
{
        wake_lock(thread);
        thread_lock(thread);

        /*
         *      If we are discarding the thread's stack, we must do it
         *      before the thread has a chance to run.
         */
#ifndef i386
    if (thread->continuation != NULL) {
                assert((thread->state & TH_STACK_STATE) == 0);
                thread->state |= TH_STACK_HANDOFF;
                stack_free(thread);
        }
#endif

        switch (thread->state & (TH_RUN|TH_WAIT|TH_UNINT|TH_IDLE)) {

        case TH_RUN                              | TH_UNINT:
        case TH_RUN:
                /*
                 *      No reason to stop.  Put back on a run queue.
                 */
                _mk_sp_thread_dispatch(thread);
                break;

        case TH_RUN | TH_WAIT   | TH_UNINT:
        case TH_RUN | TH_WAIT:
        {
                boolean_t       reap, wake, callblock;
        
                /*
                 *      Waiting
                 */
                thread->sleep_stamp = sched_tick;
                thread->state &= ~TH_RUN;
                hw_atomic_sub(&thread->processor_set->run_count, 1);
                callblock = thread->active_callout;
                wake = thread->wake_active;
                thread->wake_active = FALSE;
                reap = (thread->state & TH_TERMINATE)? TRUE: FALSE;

                thread_unlock(thread);
                wake_unlock(thread);

                if (callblock)
                        call_thread_block();

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

                if (reap)
                        thread_reaper_enqueue(thread);

                return;
        }

        case TH_RUN                                             | TH_IDLE:
                /*
                 * The idle threads don't go
                 * onto a run queue.
                 */
                break;

        default:
                panic("thread_dispatch: bad thread state 0x%x\n", thread->state);
        }

        thread_unlock(thread);
        wake_unlock(thread);
}

/*
 * Enqueue thread on run queue.  Thread must be locked,
 * and not already be on a run queue.  Returns TRUE iff
 * the particular queue level was empty beforehand.
 */
boolean_t
run_queue_enqueue(
        register run_queue_t    rq,
        register thread_t               thread,
        boolean_t                               tail)
{
        register int                    whichq = thread->sched_pri;
        register queue_t                queue = &rq->queues[whichq];
        boolean_t                               result = FALSE;
        
        assert(whichq >= MINPRI && whichq <= MAXPRI);

        simple_lock(&rq->lock);
        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 (tail)
                enqueue_tail(queue, (queue_entry_t)thread);
        else
                enqueue_head(queue, (queue_entry_t)thread);

        thread->runq = rq;
        if (thread->sched_mode & TH_MODE_PREEMPT)
                rq->urgency++;
        rq->count++;
#if     DEBUG
        thread_check(thread, rq);
#endif  /* DEBUG */
        simple_unlock(&rq->lock);

        return (result);
}

struct {
        uint32_t        pset_idle_last,
                                pset_idle_any,
                                pset_self,
                                pset_last,
                                pset_other,
                                bound_idle,
                                bound_self,
                                bound_other;
} dispatch_counts;

/*
 *      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.
 *
 *      The tail parameter indicates the proper placement of
 *      the thread on a run queue.
 */
void
thread_setrun(
        register thread_t                       new_thread,
        boolean_t                                       tail)
{
        register processor_t            processor;
        register processor_set_t        pset;
        register thread_t                       thread;
        boolean_t                                       try_preempt = FALSE;
        ast_t                                           preempt = AST_BLOCK;

        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_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              ) {
                        simple_lock(&processor->lock);
                        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;
                                processor->state = PROCESSOR_DISPATCHING;
                                simple_unlock(&pset->sched_lock);
                                simple_unlock(&processor->lock);
                                if (processor != current_processor())
                                        machine_signal_idle(processor);
                                dispatch_counts.pset_idle_last++;
                                return;
                        }
                        simple_unlock(&processor->lock);
                }
                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;
                        processor->state = PROCESSOR_DISPATCHING;
                        simple_unlock(&pset->sched_lock);
                        if (processor != current_processor())   
                                machine_signal_idle(processor);
                        dispatch_counts.pset_idle_any++;
                        return;
                }

                /*
                 * Place thread on run queue.
                 */
                if (run_queue_enqueue(&pset->runq, new_thread, tail))
                        try_preempt = TRUE;

                /*
                 *      Update the timesharing quanta.
                 */
                pset_quanta_update(pset);
        
            /*
             *  Preempt check.
             */
            processor = current_processor();
                thread = processor->cpu_data->active_thread;
            if (try_preempt) {
                        /*
                         * First try the current processor
                         * if it is a member of the correct
                         * processor set.
                         */
                        if (    pset == processor->processor_set        &&
                                        csw_needed(thread, processor)           ) {
                                simple_unlock(&pset->sched_lock);

                                ast_on(preempt);
                                dispatch_counts.pset_self++;
                                return;
                        }

                        /*
                         * If that failed and we have other
                         * processors available keep trying.
                         */
                        if (    pset->processor_count > 1                       ||
                                        pset != processor->processor_set        ) {
                                queue_t                 active = &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  ) {
                                        cause_ast_check(processor);
                                        simple_unlock(&pset->sched_lock);
                                        dispatch_counts.pset_last++;
                                        return;
                                }

                                /*
                                 * Lastly, pick any other
                                 * available processor.
                                 */
                                lastprocessor = processor;
                                processor = (processor_t)queue_first(active);
                                while (!queue_end(active, (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(active, next)) {
                                                        remqueue(active, (queue_entry_t)processor);
                                                        enqueue_tail(active, (queue_entry_t)processor);
                                                }
                                                cause_ast_check(processor);
                                                simple_unlock(&pset->sched_lock);
                                                dispatch_counts.pset_other++;
                                                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.
             */
                if (processor->state == PROCESSOR_IDLE) {
                        simple_lock(&processor->lock);
                        pset = processor->processor_set;
                        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->state = PROCESSOR_DISPATCHING;
                                simple_unlock(&pset->sched_lock);
                                simple_unlock(&processor->lock);
                                if (processor != current_processor())   
                                        machine_signal_idle(processor);
                                dispatch_counts.bound_idle++;
                                return;
                        }
                        simple_unlock(&pset->sched_lock);
                        simple_unlock(&processor->lock);
                }
          
                if (run_queue_enqueue(&processor->runq, new_thread, tail))
                        try_preempt = TRUE;

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

                        if (processor->state == PROCESSOR_IDLE) {
                                machine_signal_idle(processor);
                                dispatch_counts.bound_idle++;
                        }
                }
        }
}

/*
 * Called at splsched by a thread on itself.
 */
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_quantum(processor)) {
                runq = &processor->processor_set->runq;
                if (runq->highq > current_pri) {
                        if (runq->urgency > 0)
                                return (AST_BLOCK | AST_URGENT);

                        result |= AST_BLOCK;
                }

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

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

                        result |= AST_BLOCK;
                }

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

                        result |= AST_BLOCK;
                }
        }

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

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

        return (result);
}

/*
 *      set_sched_pri:
 *
 *      Set the current scheduled priority of the specified thread.
 *      This may cause the thread to change queues.
 *
 *      The thread *must* be locked by the caller.
 */
void
set_sched_pri(
        thread_t                        thread,
        int                                     priority)
{
        register struct run_queue       *rq = rem_runq(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_FORCEDPREEMPT)           )       )
                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, TAIL_Q);
        else
        if ((thread->state & (TH_RUN|TH_WAIT)) == 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->cpu_data->active_thread == thread    )
                        cause_ast_check(processor);
        }
}

/*
 *      rem_runq:
 *
 *      Remove a thread from its run queue.
 *      The run queue that the process was on is returned
 *      (or RUN_QUEUE_NULL if not on a run queue).  Thread *must* be locked
 *      before calling this routine.  Unusual locking protocol on runq
 *      field in thread structure makes this code interesting; see thread.h.
 */
run_queue_t
rem_runq(
        thread_t                        thread)
{
        register struct run_queue       *rq;

        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 runq, but could leave.
         */
        if (rq != RUN_QUEUE_NULL) {
                simple_lock(&rq->lock);
                if (rq == thread->runq) {
                        /*
                         *      Thread is in a runq and we have a lock on
                         *      that runq.
                         */
#if     DEBUG
                        thread_check(thread, rq);
#endif  /* DEBUG */
                        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;
                        simple_unlock(&rq->lock);
                }
                else {
                        /*
                         *      The thread left the runq before we could
                         *      lock the runq.  It is not on a runq now, and
                         *      can't move again because this routine's
                         *      caller locked the thread.
                         */
                        assert(thread->runq == RUN_QUEUE_NULL);
                        simple_unlock(&rq->lock);
                        rq = RUN_QUEUE_NULL;
                }
        }

        return (rq);
}

/*
 *      choose_thread:
 *
 *      Choose a thread to execute.  The thread chosen is removed
 *      from its run queue.  Note that this requires only that the runq
 *      lock be held.
 *
 *      Strategy:
 *              Check processor runq first; if anything found, run it.
 *              Else check pset runq; if nothing found, return idle thread.
 *
 *      Second line of strategy is implemented by choose_pset_thread.
 *
 *      Called with both the local & pset run queues locked, returned
 *      unlocked.
 */
thread_t
choose_thread(
        processor_t             myprocessor)
{
        thread_t                                thread;
        register queue_t                q;
        register run_queue_t    runq;
        processor_set_t                 pset;

        runq = &myprocessor->runq;
        pset = myprocessor->processor_set;

        if (runq->count > 0 && runq->highq >= pset->runq.highq) {
                simple_unlock(&pset->runq.lock);
                q = runq->queues + runq->highq;
#if     MACH_ASSERT
                if (!queue_empty(q)) {
#endif  /*MACH_ASSERT*/
                        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);
                        }
                        simple_unlock(&runq->lock);
                        return (thread);
#if     MACH_ASSERT
                }
                panic("choose_thread");
#endif  /*MACH_ASSERT*/
                /*NOTREACHED*/
        }
        simple_unlock(&myprocessor->runq.lock);

        return (choose_pset_thread(myprocessor, pset));
}

/*
 *      choose_pset_thread:  choose a thread from processor_set runq or
 *              set processor idle and choose its idle thread.
 *
 *      This routine chooses and removes a thread from the runq if there
 *      is one (and returns it), else it sets the processor idle and
 *      returns its idle thread.
 *
 *      Called with both local & pset run queues locked, returned
 *      unlocked.
 */
thread_t
choose_pset_thread(
        register processor_t    myprocessor,
        processor_set_t                 pset)
{
        register run_queue_t    runq;
        register thread_t               thread;
        register queue_t                q;

        runq = &pset->runq;
        if (runq->count > 0) {
                q = runq->queues + runq->highq;
#if     MACH_ASSERT
                if (!queue_empty(q)) {
#endif  /*MACH_ASSERT*/
                        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);
                        }
                        pset_quanta_update(pset);
                        simple_unlock(&runq->lock);
                        return (thread);
#if     MACH_ASSERT
                }
                panic("choose_pset_thread");
#endif  /*MACH_ASSERT*/
                /*NOTREACHED*/
        }
        simple_unlock(&runq->lock);

        /*
         *      Nothing is runnable, so set this processor idle if it
         *      was running.  If it was in an assignment or shutdown,
         *      leave it alone.  Return its idle thread.
         */
        simple_lock(&pset->sched_lock);
        if (myprocessor->state == PROCESSOR_RUNNING) {
                remqueue(&pset->active_queue, (queue_entry_t)myprocessor);
            myprocessor->state = PROCESSOR_IDLE;

            if (myprocessor == master_processor)
                        enqueue_tail(&pset->idle_queue, (queue_entry_t)myprocessor);
            else
                        enqueue_head(&pset->idle_queue, (queue_entry_t)myprocessor);

            pset->idle_count++;
        }
        simple_unlock(&pset->sched_lock);

        return (myprocessor->idle_thread);
}

/*
 *      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 thread, which just looks for other threads
 *      to execute.
 */
void
idle_thread_continue(void)
{
        register processor_t            myprocessor;
        register volatile thread_t      *threadp;
        register volatile int           *gcount;
        register volatile int           *lcount;
        register thread_t                       new_thread;
        register int                            state;
        register processor_set_t        pset;
        int                                                     mycpu;

        mycpu = cpu_number();
        myprocessor = cpu_to_processor(mycpu);
        threadp = (volatile thread_t *) &myprocessor->next_thread;
        lcount = (volatile int *) &myprocessor->runq.count;

        for (;;) {
                gcount = (volatile int *)&myprocessor->processor_set->runq.count;

                (void)splsched();
                while ( (*threadp == (volatile thread_t)THREAD_NULL)    &&
                                        (*gcount == 0) && (*lcount == 0)                                ) {

                        /* check for ASTs while we wait */
                        if (need_ast[mycpu] &~ (        AST_SCHEDULING | AST_BSD        )) {
                                /* don't allow scheduling ASTs */
                                need_ast[mycpu] &= ~(   AST_SCHEDULING | AST_BSD        );
                                ast_taken(AST_ALL, TRUE);       /* back at spllo */
                        }
                        else
#ifdef  __ppc__
                                machine_idle();
#else
                                (void)spllo();
#endif
                machine_clock_assist();

                        (void)splsched();
                }

                /*
                 *      This is not a switch statement to avoid the
                 *      bounds checking code in the common case.
                 */
                pset = myprocessor->processor_set;
                simple_lock(&pset->sched_lock);
retry:
                state = myprocessor->state;
                if (state == PROCESSOR_DISPATCHING) {
                        /*
                         *      Commmon case -- cpu dispatched.
                         */
                        new_thread = *threadp;
                        *threadp = (volatile thread_t) THREAD_NULL;
                        myprocessor->state = PROCESSOR_RUNNING;
                        enqueue_tail(&pset->active_queue, (queue_entry_t)myprocessor);
                        simple_unlock(&pset->sched_lock);

                        if (    myprocessor->runq.highq > new_thread->sched_pri         ||
                                        pset->runq.highq > new_thread->sched_pri                                ) {
                                thread_lock(new_thread);
                                thread_setrun(new_thread, HEAD_Q);
                                thread_unlock(new_thread);

                                counter(c_idle_thread_block++);
                                thread_block(idle_thread_continue);
                                /* NOTREACHED */
                        }
                        else {
                                counter(c_idle_thread_handoff++);
                                thread_run(myprocessor->idle_thread,
                                                                        idle_thread_continue, new_thread);
                                /* NOTREACHED */
                        }
                }
                else
                if (state == PROCESSOR_IDLE) {
                        if (myprocessor->state != PROCESSOR_IDLE) {
                                /*
                                 *      Something happened, try again.
                                 */
                                goto retry;
                        }
                        /*
                         *      Processor was not dispatched (Rare).
                         *      Set it running again.
                         */
                        no_dispatch_count++;
                        pset->idle_count--;
                        remqueue(&pset->idle_queue, (queue_entry_t)myprocessor);
                        myprocessor->state = PROCESSOR_RUNNING;
                        enqueue_tail(&pset->active_queue, (queue_entry_t)myprocessor);
                        simple_unlock(&pset->sched_lock);

                        counter(c_idle_thread_block++);
                        thread_block(idle_thread_continue);
                        /* NOTREACHED */
                }
                else
                if (    state == PROCESSOR_ASSIGN               ||
                                state == PROCESSOR_SHUTDOWN                     ) {
                        /*
                         *      Changing processor sets, or going off-line.
                         *      Release next_thread if there is one.  Actual
                         *      thread to run is on a runq.
                         */
                        if ((new_thread = (thread_t)*threadp) != THREAD_NULL) {
                                *threadp = (volatile thread_t) THREAD_NULL;
                                simple_unlock(&pset->sched_lock);

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

                        counter(c_idle_thread_block++);
                        thread_block(idle_thread_continue);
                        /* NOTREACHED */
                }
                else {
                        simple_unlock(&pset->sched_lock);

                        panic("idle_thread: bad processor state %d\n", cpu_state(mycpu));
                }

                (void)spllo();
        }
}

void
idle_thread(void)
{
        thread_t                self = current_thread();
        spl_t                   s;

        stack_privilege(self);

        s = splsched();
        thread_lock(self);
        self->priority = IDLEPRI;
        set_sched_pri(self, self->priority);
        thread_unlock(self);
        splx(s);

        counter(c_idle_thread_block++);
        thread_block(idle_thread_continue);
        /*NOTREACHED*/
}

static uint64_t                         sched_tick_interval, sched_tick_deadline;

void    sched_tick_thread(void);

void
sched_tick_init(void)
{
        kernel_thread_with_priority(
                                                kernel_task, MAXPRI_STANDARD,
                                                                sched_tick_thread, TRUE, TRUE);
}

/*
 *      sched_tick_thread
 *
 *      Update the priorities of all threads periodically.
 */
void
sched_tick_thread_continue(void)
{
        uint64_t                        abstime;
#if     SIMPLE_CLOCK
        int                                     new_usec;
#endif  /* SIMPLE_CLOCK */

        clock_get_uptime(&abstime);

        sched_tick++;           /* age usage one more time */
#if     SIMPLE_CLOCK
        /*
         *      Compensate for clock drift.  sched_usec is an
         *      exponential average of the number of microseconds in
         *      a second.  It decays in the same fashion as cpu_usage.
         */
        new_usec = sched_usec_elapsed();
        sched_usec = (5*sched_usec + 3*new_usec)/8;
#endif  /* SIMPLE_CLOCK */

        /*
         *  Compute the scheduler load factors.
         */
        compute_mach_factor();

        /*
         *  Scan the run queues for runnable threads that need to
         *  have their priorities recalculated.
         */
        do_thread_scan();

        clock_deadline_for_periodic_event(sched_tick_interval, abstime,
                                                                                                                &sched_tick_deadline);

        assert_wait((event_t)sched_tick_thread_continue, THREAD_INTERRUPTIBLE);
        thread_set_timer_deadline(sched_tick_deadline);
        thread_block(sched_tick_thread_continue);
        /*NOTREACHED*/
}

void
sched_tick_thread(void)
{
        thread_t                self = current_thread();
        natural_t               rate;
        spl_t                   s;

        stack_privilege(self);

        rate = (1000 >> SCHED_TICK_SHIFT);
        clock_interval_to_absolutetime_interval(rate, USEC_PER_SEC,
                                                                                                &sched_tick_interval);
        clock_get_uptime(&sched_tick_deadline);

        thread_block(sched_tick_thread_continue);
        /*NOTREACHED*/
}

#define MAX_STUCK_THREADS       128

/*
 *      do_thread_scan: scan for stuck threads.  A thread is stuck if
 *      it is runnable but its priority is so low that it has not
 *      run for several seconds.  Its priority should be higher, but
 *      won't be until it runs and calls update_priority.  The scanner
 *      finds these threads and does the updates.
 *
 *      Scanner runs in two passes.  Pass one squirrels likely
 *      thread ids away in an array  (takes out references for them).
 *      Pass two does the priority updates.  This is necessary because
 *      the run queue lock is required for the candidate scan, but
 *      cannot be held during updates.
 *
 *      Array length should be enough so that restart isn't necessary,
 *      but restart logic is included.
 *
 */
thread_t                stuck_threads[MAX_STUCK_THREADS];
int                             stuck_count = 0;

/*
 *      do_runq_scan is the guts of pass 1.  It scans a runq for
 *      stuck threads.  A boolean is returned indicating whether
 *      a retry is needed.
 */
boolean_t
do_runq_scan(
        run_queue_t                             runq)
{
        register queue_t                q;
        register thread_t               thread;
        register int                    count;
        spl_t                                   s;
        boolean_t                               result = FALSE;

        s = splsched();
        simple_lock(&runq->lock);
        if ((count = runq->count) > 0) {
            q = runq->queues + runq->highq;
                while (count > 0) {
                        queue_iterate(q, thread, thread_t, links) {
                                if (    !(thread->state & (TH_WAIT|TH_SUSP))            &&
                                                (thread->sched_mode & TH_MODE_TIMESHARE)        ) {
                                        if (thread->sched_stamp != sched_tick) {
                                                /*
                                                 *      Stuck, save its id for later.
                                                 */
                                                if (stuck_count == MAX_STUCK_THREADS) {
                                                        /*
                                                         *      !@#$% No more room.
                                                         */
                                                        simple_unlock(&runq->lock);
                                                        splx(s);

                                                        return (TRUE);
                                                }

                                                /*
                                                 * Inline version of thread_reference
                                                 * XXX - lock ordering problem here:
                                                 * thread locks should be taken before runq
                                                 * locks: just try and get the thread's locks
                                                 * and ignore this thread if we fail, we might
                                                 * have better luck next time.
                                                 */
                                                if (thread_lock_try(thread)) {
                                                        thread->ref_count++;
                                                        thread_unlock(thread);
                                                        stuck_threads[stuck_count++] = thread;
                                                }
                                                else
                                                        result = TRUE;
                                        }
                                }

                                count--;
                        }

                        q--;
                }
        }
        simple_unlock(&runq->lock);
        splx(s);

        return (result);
}

boolean_t       thread_scan_enabled = TRUE;

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

        if (!thread_scan_enabled)
                return;

        do {
            restart_needed = do_runq_scan(&pset->runq);
                if (!restart_needed) {
                        simple_lock(&pset->processors_lock);
                        processor = (processor_t)queue_first(&pset->processors);
                        while (!queue_end(&pset->processors, (queue_entry_t)processor)) {
                                if (restart_needed = do_runq_scan(&processor->runq))
                                        break;

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

                                        stuck_threads[stuck_count++] = thread;
                                }

                                processor = (processor_t)queue_next(&processor->processors);
                        }
                        simple_unlock(&pset->processors_lock);
                }

            /*
             *  Ok, we now have a collection of candidates -- fix them.
             */
            while (stuck_count > 0) {
                        thread = stuck_threads[--stuck_count];
                        stuck_threads[stuck_count] = THREAD_NULL;
                        s = splsched();
                        thread_lock(thread);
                        if (    (thread->sched_mode & TH_MODE_TIMESHARE)        ||
                                                        (thread->state & TH_IDLE)                               ) {
                                if (    !(thread->state & (TH_WAIT|TH_SUSP))    &&
                                                thread->sched_stamp != sched_tick               )
                                        update_priority(thread);
                        }
                        thread_unlock(thread);
                        splx(s);
                        if (!(thread->state & TH_IDLE))
                                thread_deallocate(thread);
            }

                if (restart_needed)
                        delay(1);                       /* XXX */
                
        } 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);
}


#if     DEBUG

static boolean_t
thread_runnable(
        thread_t        thread)
{
        return ((thread->state & (TH_RUN|TH_WAIT)) == TH_RUN);
}

void
dump_processor_set(
        processor_set_t ps)
{
    printf("processor_set: %08x\n",ps);
    printf("idle_queue: %08x %08x, idle_count:      0x%x\n",
        ps->idle_queue.next,ps->idle_queue.prev,ps->idle_count);
    printf("processors: %08x %08x, processor_count: 0x%x\n",
        ps->processors.next,ps->processors.prev,ps->processor_count);
    printf("tasks:      %08x %08x, task_count:      0x%x\n",
        ps->tasks.next,ps->tasks.prev,ps->task_count);
    printf("threads:    %08x %08x, thread_count:    0x%x\n",
        ps->threads.next,ps->threads.prev,ps->thread_count);
    printf("ref_count: 0x%x, active: %x\n",
        ps->ref_count,ps->active);
    printf("pset_self: %08x, pset_name_self: %08x\n",ps->pset_self, ps->pset_name_self);
    printf("set_quanta: 0x%x\n", ps->set_quanta);
}

#define processor_state(s) (((s)>PROCESSOR_SHUTDOWN)?"*unknown*":states[s])

void
dump_processor(
        processor_t     p)
{
    char *states[]={"OFF_LINE","RUNNING","IDLE","DISPATCHING",
                   "ASSIGN","SHUTDOWN"};

    printf("processor: %08x\n",p);
    printf("processor_queue: %08x %08x\n",
        p->processor_queue.next,p->processor_queue.prev);
    printf("state: %8s, next_thread: %08x, idle_thread: %08x\n",
        processor_state(p->state), p->next_thread, p->idle_thread);
    printf("slice_quanta: %x\n", p->slice_quanta);
    printf("processor_set: %08x, processor_set_next: %08x\n",
        p->processor_set, p->processor_set_next);
    printf("processors: %08x %08x\n", p->processors.next,p->processors.prev);
    printf("processor_self: %08x, slot_num: 0x%x\n", p->processor_self, p->slot_num);
}

void
dump_run_queue_struct(
        run_queue_t     rq)
{
    char dump_buf[80];
    int i;

    for( i=0; i < NRQS; ) {
        int j;

        printf("%6s",(i==0)?"runq:":"");
        for( j=0; (j<8) && (i < NRQS); j++,i++ ) {
            if( rq->queues[i].next == &rq->queues[i] )
                printf( " --------");
            else
                printf(" %08x",rq->queues[i].next);
        }
        printf("\n");
    }
    for( i=0; i < NRQBM; ) {
        register unsigned int mask;
        char *d=dump_buf;

        mask = ~0;
        mask ^= (mask>>1);

        do {
            *d++ = ((rq->bitmap[i]&mask)?'r':'e');
            mask >>=1;
        } while( mask );
        *d = '\0';
        printf("%8s%s\n",((i==0)?"bitmap:":""),dump_buf);
        i++;
    }   
    printf("highq: 0x%x, count: %u\n", rq->highq, rq->count);
}
 
void
dump_run_queues(
        run_queue_t     runq)
{
        register queue_t        q1;
        register int            i;
        register queue_entry_t  e;

        q1 = runq->queues;
        for (i = 0; i < NRQS; i++) {
            if (q1->next != q1) {
                int t_cnt;

                printf("[%u]",i);
                for (t_cnt=0, e = q1->next; e != q1; e = e->next) {
                    printf("\t0x%08x",e);
                    if( (t_cnt = ++t_cnt%4) == 0 )
                        printf("\n");
                }
                if( t_cnt )
                        printf("\n");
            }
            /* else
                printf("[%u]\t<empty>\n",i);
             */
            q1++;
        }
}

void
checkrq(
        run_queue_t     rq,
        char            *msg)
{
        register queue_t        q1;
        register int            i, j;
        register queue_entry_t  e;
        register int            highq;

        highq = NRQS;
        j = 0;
        q1 = rq->queues;
        for (i = MAXPRI; i >= 0; i--) {
            if (q1->next == q1) {
                if (q1->prev != q1) {
                    panic("checkrq: empty at %s", msg);
                }
            }
            else {
                if (highq == -1)
                    highq = i;
                
                for (e = q1->next; e != q1; e = e->next) {
                    j++;
                    if (e->next->prev != e)
                        panic("checkrq-2 at %s", msg);
                    if (e->prev->next != e)
                        panic("checkrq-3 at %s", msg);
                }
            }
            q1++;
        }
        if (j != rq->count)
            panic("checkrq: count wrong at %s", msg);
        if (rq->count != 0 && highq > rq->highq)
            panic("checkrq: highq wrong at %s", msg);
}

void
thread_check(
        register thread_t               thread,
        register run_queue_t    rq)
{
        register int                    whichq = thread->sched_pri;
        register queue_entry_t  queue, entry;

        if (whichq < MINPRI || whichq > MAXPRI)
                panic("thread_check: bad pri");

        queue = &rq->queues[whichq];
        entry = queue_first(queue);
        while (!queue_end(queue, entry)) {
                if (entry == (queue_entry_t)thread)
                        return;

                entry = queue_next(entry);
        }

        panic("thread_check: not found");
}

#endif  /* DEBUG */

#if     MACH_KDB
#include <ddb/db_output.h>
#define printf          kdbprintf
extern int              db_indent;
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;
}
#endif  /* MACH_KDB */