xnu-4903.221.2.tar.gz

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

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 * 
 * Please obtain a copy of the License at
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/*
 * @OSF_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:   priority.c
 *      Author: Avadis Tevanian, Jr.
 *      Date:   1986
 *
 *      Priority related scheduler bits.
 */

#include <mach/boolean.h>
#include <mach/kern_return.h>
#include <mach/machine.h>
#include <kern/host.h>
#include <kern/mach_param.h>
#include <kern/sched.h>
#include <sys/kdebug.h>
#include <kern/spl.h>
#include <kern/thread.h>
#include <kern/processor.h>
#include <kern/ledger.h>
#include <machine/machparam.h>
#include <kern/machine.h>

#ifdef CONFIG_MACH_APPROXIMATE_TIME
#include <machine/commpage.h>  /* for commpage_update_mach_approximate_time */
#endif

#if MONOTONIC
#include <kern/monotonic.h>
#endif /* MONOTONIC */

static void sched_update_thread_bucket(thread_t thread);

/*
 *      thread_quantum_expire:
 *
 *      Recalculate the quantum and priority for a thread.
 *
 *      Called at splsched.
 */

void
thread_quantum_expire(
        timer_call_param_t      p0,
        timer_call_param_t      p1)
{
        processor_t                     processor = p0;
        thread_t                        thread = p1;
        ast_t                           preempt;
        uint64_t                        ctime;
        int                                     urgency;
        uint64_t                        ignore1, ignore2;

        assert(processor == current_processor());
        assert(thread == current_thread());

        KERNEL_DEBUG_CONSTANT(MACHDBG_CODE(DBG_MACH_SCHED, MACH_SCHED_QUANTUM_EXPIRED) | DBG_FUNC_START, 0, 0, 0, 0, 0);

        SCHED_STATS_QUANTUM_TIMER_EXPIRATION(processor);

        /*
         * We bill CPU time to both the individual thread and its task.
         *
         * Because this balance adjustment could potentially attempt to wake this
         * very thread, we must credit the ledger before taking the thread lock.
         * The ledger pointers are only manipulated by the thread itself at the ast
         * boundary.
         *
         * TODO: This fails to account for the time between when the timer was
         * armed and when it fired.  It should be based on the system_timer and
         * running a timer_update operation here.
         */
        ledger_credit(thread->t_ledger, task_ledgers.cpu_time, thread->quantum_remaining);
        ledger_credit(thread->t_threadledger, thread_ledgers.cpu_time, thread->quantum_remaining);
        if (thread->t_bankledger) {
                ledger_credit(thread->t_bankledger, bank_ledgers.cpu_time,
                                (thread->quantum_remaining - thread->t_deduct_bank_ledger_time));
        }
        thread->t_deduct_bank_ledger_time = 0;

        ctime = mach_absolute_time();

#ifdef CONFIG_MACH_APPROXIMATE_TIME
        commpage_update_mach_approximate_time(ctime);
#endif

#if MONOTONIC
        mt_sched_update(thread);
#endif /* MONOTONIC */

        thread_lock(thread);

        /*
         * We've run up until our quantum expiration, and will (potentially)
         * continue without re-entering the scheduler, so update this now.
         */
        processor->last_dispatch = ctime;
        thread->last_run_time = ctime;

        /*
         *      Check for fail-safe trip.
         */
        if ((thread->sched_mode == TH_MODE_REALTIME || thread->sched_mode == TH_MODE_FIXED) &&
            !(thread->sched_flags & TH_SFLAG_PROMOTED) &&
            !(thread->sched_flags & TH_SFLAG_PROMOTE_REASON_MASK) &&
            !(thread->options & TH_OPT_SYSTEM_CRITICAL)) {
                uint64_t new_computation;

                new_computation = ctime - thread->computation_epoch;
                new_computation += thread->computation_metered;
                if (new_computation > max_unsafe_computation) {
                        KERNEL_DEBUG_CONSTANT(MACHDBG_CODE(DBG_MACH_SCHED, MACH_FAILSAFE)|DBG_FUNC_NONE,
                                        (uintptr_t)thread->sched_pri, (uintptr_t)thread->sched_mode, 0, 0, 0);

                        thread->safe_release = ctime + sched_safe_duration;

                        sched_thread_mode_demote(thread, TH_SFLAG_FAILSAFE);
                }
        }

        /*
         *      Recompute scheduled priority if appropriate.
         */
        if (SCHED(can_update_priority)(thread))
                SCHED(update_priority)(thread);
        else
                SCHED(lightweight_update_priority)(thread);

        if (thread->sched_mode != TH_MODE_REALTIME)
                SCHED(quantum_expire)(thread);

        processor_state_update_from_thread(processor, thread);

        /*
         *      This quantum is up, give this thread another.
         */
        processor->first_timeslice = FALSE;

        thread_quantum_init(thread);

        /* Reload precise timing global policy to thread-local policy */
        thread->precise_user_kernel_time = use_precise_user_kernel_time(thread);

        /*
         * Since non-precise user/kernel time doesn't update the state/thread timer
         * during privilege transitions, synthesize an event now.
         */
        if (!thread->precise_user_kernel_time) {
                timer_update(PROCESSOR_DATA(processor, current_state), ctime);
                timer_update(PROCESSOR_DATA(processor, thread_timer), ctime);
                timer_update(&thread->runnable_timer, ctime);
        }


        processor->quantum_end = ctime + thread->quantum_remaining;

        /*
         * Context switch check
         *
         * non-urgent flags don't affect kernel threads, so upgrade to urgent
         * to ensure that rebalancing and non-recommendation kick in quickly.
         */

        ast_t check_reason = AST_QUANTUM;
        if (thread->task == kernel_task)
                check_reason |= AST_URGENT;

        if ((preempt = csw_check(processor, check_reason)) != AST_NONE)
                ast_on(preempt);

        /*
         * AST_KEVENT does not send an IPI when setting the AST,
         * to avoid waiting for the next context switch to propagate the AST,
         * the AST is propagated here at quantum expiration.
         */
        ast_propagate(thread);

        thread_unlock(thread);

        timer_call_quantum_timer_enter(&processor->quantum_timer, thread,
                processor->quantum_end, ctime);

        /* Tell platform layer that we are still running this thread */
        urgency = thread_get_urgency(thread, &ignore1, &ignore2);
        machine_thread_going_on_core(thread, urgency, 0, 0, ctime);
        machine_switch_perfcontrol_state_update(QUANTUM_EXPIRY, ctime,
                0, thread);

#if defined(CONFIG_SCHED_TIMESHARE_CORE)
        sched_timeshare_consider_maintenance(ctime);
#endif /* CONFIG_SCHED_TIMESHARE_CORE */

#if __arm__ || __arm64__
        if (thread->sched_mode == TH_MODE_REALTIME)
                sched_consider_recommended_cores(ctime, thread);
#endif /* __arm__ || __arm64__ */

        KERNEL_DEBUG_CONSTANT(MACHDBG_CODE(DBG_MACH_SCHED, MACH_SCHED_QUANTUM_EXPIRED) | DBG_FUNC_END, preempt, 0, 0, 0, 0);
}

/*
 *      sched_set_thread_base_priority:
 *
 *      Set the base priority of the thread
 *      and reset its scheduled priority.
 *
 *      This is the only path to change base_pri.
 *
 *      Called with the thread locked.
 */
void
sched_set_thread_base_priority(thread_t thread, int priority)
{
        assert(priority >= MINPRI);
        uint64_t ctime = 0;

        if (thread->sched_mode == TH_MODE_REALTIME)
                assert(priority <= BASEPRI_RTQUEUES);
        else
                assert(priority < BASEPRI_RTQUEUES);

        int old_base_pri = thread->base_pri;
        thread->base_pri = priority;

        if ((thread->state & TH_RUN) == TH_RUN) {
                assert(thread->last_made_runnable_time != THREAD_NOT_RUNNABLE);
                ctime = mach_approximate_time();
                thread->last_basepri_change_time = ctime;
        } else {
                assert(thread->last_basepri_change_time == THREAD_NOT_RUNNABLE);
                assert(thread->last_made_runnable_time == THREAD_NOT_RUNNABLE);
        }

        /* 
         * Currently the perfcontrol_attr depends on the base pri of the 
         * thread. Therefore, we use this function as the hook for the 
         * perfcontrol callout. 
         */
        if (thread == current_thread() && old_base_pri != priority) {
                if (!ctime) {
                    ctime = mach_approximate_time();
                }
                machine_switch_perfcontrol_state_update(PERFCONTROL_ATTR_UPDATE,
                        ctime, PERFCONTROL_CALLOUT_WAKE_UNSAFE, thread);
        }
        sched_update_thread_bucket(thread);

        thread_recompute_sched_pri(thread, SETPRI_DEFAULT);
}

/*
 *      thread_recompute_sched_pri:
 *
 *      Reset the scheduled priority of the thread
 *      according to its base priority if the
 *      thread has not been promoted or depressed.
 *
 *      This is the only way to push base_pri changes into sched_pri,
 *      or to recalculate the appropriate sched_pri after changing
 *      a promotion or depression.
 *
 *      Called at splsched with the thread locked.
 *
 *      TODO: Add an 'update urgency' flag to avoid urgency callouts on every rwlock operation
 */
void
thread_recompute_sched_pri(thread_t thread, set_sched_pri_options_t options)
{
        uint32_t     sched_flags = thread->sched_flags;
        sched_mode_t sched_mode  = thread->sched_mode;

        int priority = thread->base_pri;

        if (sched_mode == TH_MODE_TIMESHARE)
                priority = SCHED(compute_timeshare_priority)(thread);

        if (sched_flags & TH_SFLAG_DEPRESS) {
                /* thread_yield_internal overrides kernel mutex promotion */
                priority = DEPRESSPRI;
        } else {
                /* poll-depress is overridden by mutex promotion and promote-reasons */
                if ((sched_flags & TH_SFLAG_POLLDEPRESS)) {
                        priority = DEPRESSPRI;
                }

                if (sched_flags & TH_SFLAG_PROMOTED) {
                        priority = MAX(priority, thread->promotion_priority);

                        if (sched_mode != TH_MODE_REALTIME)
                                priority = MIN(priority, MAXPRI_PROMOTE);
                }

                if (sched_flags & TH_SFLAG_PROMOTE_REASON_MASK) {
                        if (sched_flags & TH_SFLAG_RW_PROMOTED)
                                priority = MAX(priority, MINPRI_RWLOCK);

                        if (sched_flags & TH_SFLAG_WAITQ_PROMOTED)
                                priority = MAX(priority, MINPRI_WAITQ);

                        if (sched_flags & TH_SFLAG_EXEC_PROMOTED)
                                priority = MAX(priority, MINPRI_EXEC);
                }
        }

        set_sched_pri(thread, priority, options);
}

void
sched_default_quantum_expire(thread_t thread __unused)
{
      /*
       * No special behavior when a timeshare, fixed, or realtime thread
       * uses up its entire quantum
       */
}

#if defined(CONFIG_SCHED_TIMESHARE_CORE)

/*
 *      lightweight_update_priority:
 *
 *      Update the scheduled priority for
 *      a timesharing thread.
 *
 *      Only for use on the current thread.
 *
 *      Called with the thread locked.
 */
void
lightweight_update_priority(thread_t thread)
{
        assert(thread->runq == PROCESSOR_NULL);
        assert(thread == current_thread());

        if (thread->sched_mode == TH_MODE_TIMESHARE) {
                int priority;
                uint32_t delta;

                thread_timer_delta(thread, delta);

                /*
                 *      Accumulate timesharing usage only
                 *      during contention for processor
                 *      resources.
                 */
                if (thread->pri_shift < INT8_MAX)
                        thread->sched_usage += delta;

                thread->cpu_delta += delta;

                priority = sched_compute_timeshare_priority(thread);

                if (priority != thread->sched_pri)
                        thread_recompute_sched_pri(thread, SETPRI_LAZY);
        }
}

/*
 *      Define shifts for simulating (5/8) ** n
 *
 *      Shift structures for holding update shifts.  Actual computation
 *      is  usage = (usage >> shift1) +/- (usage >> abs(shift2))  where the
 *      +/- is determined by the sign of shift 2.
 */
struct shift_data {
        int     shift1;
        int     shift2;
};

#define SCHED_DECAY_TICKS       32
static struct shift_data        sched_decay_shifts[SCHED_DECAY_TICKS] = {
        {1,1},{1,3},{1,-3},{2,-7},{3,5},{3,-5},{4,-8},{5,7},
        {5,-7},{6,-10},{7,10},{7,-9},{8,-11},{9,12},{9,-11},{10,-13},
        {11,14},{11,-13},{12,-15},{13,17},{13,-15},{14,-17},{15,19},{16,18},
        {16,-19},{17,22},{18,20},{18,-20},{19,26},{20,22},{20,-22},{21,-27}
};

/*
 *      sched_compute_timeshare_priority:
 *
 *      Calculate the timesharing priority based upon usage and load.
 */
extern int sched_pri_decay_band_limit;

#ifdef CONFIG_EMBEDDED

int
sched_compute_timeshare_priority(thread_t thread)
{
        int decay_amount = (thread->sched_usage >> thread->pri_shift);
        int decay_limit = sched_pri_decay_band_limit;

        if (thread->base_pri > BASEPRI_FOREGROUND) {
                decay_limit += (thread->base_pri - BASEPRI_FOREGROUND);
        }

        if (decay_amount > decay_limit) {
                decay_amount = decay_limit;
        }

        /* start with base priority */
        int priority = thread->base_pri - decay_amount;

        if (priority < MAXPRI_THROTTLE) {
                if (thread->task->max_priority > MAXPRI_THROTTLE) {
                        priority = MAXPRI_THROTTLE;
                } else if (priority < MINPRI_USER) {
                        priority = MINPRI_USER;
                }
        } else if (priority > MAXPRI_KERNEL) {
                priority = MAXPRI_KERNEL;
        }

        return priority;
}

#else /* CONFIG_EMBEDDED */

int
sched_compute_timeshare_priority(thread_t thread)
{
        /* start with base priority */
        int priority = thread->base_pri - (thread->sched_usage >> thread->pri_shift);

        if (priority < MINPRI_USER)
                priority = MINPRI_USER;
        else if (priority > MAXPRI_KERNEL)
                priority = MAXPRI_KERNEL;

        return priority;
}

#endif /* CONFIG_EMBEDDED */

/*
 *      can_update_priority
 *
 *      Make sure we don't do re-dispatches more frequently than a scheduler tick.
 *
 *      Called with the thread locked.
 */
boolean_t
can_update_priority(
                                        thread_t        thread)
{
        if (sched_tick == thread->sched_stamp)
                return (FALSE);
        else
                return (TRUE);
}

/*
 *      update_priority
 *
 *      Perform housekeeping operations driven by scheduler tick.
 *
 *      Called with the thread locked.
 */
void
update_priority(
        thread_t        thread)
{
        uint32_t ticks, delta;

        ticks = sched_tick - thread->sched_stamp;
        assert(ticks != 0);

        thread->sched_stamp += ticks;

        /* If requested, accelerate aging of sched_usage */
        if (sched_decay_usage_age_factor > 1)
                ticks *= sched_decay_usage_age_factor;

        /*
         *      Gather cpu usage data.
         */
        thread_timer_delta(thread, delta);
        if (ticks < SCHED_DECAY_TICKS) {
                /*
                 *      Accumulate timesharing usage only during contention for processor
                 *      resources. Use the pri_shift from the previous tick window to 
                 *      determine if the system was in a contended state.
                 */
                if (thread->pri_shift < INT8_MAX)
                        thread->sched_usage += delta;

                thread->cpu_usage += delta + thread->cpu_delta;
                thread->cpu_delta = 0;

                struct shift_data *shiftp = &sched_decay_shifts[ticks];

                if (shiftp->shift2 > 0) {
                        thread->cpu_usage =   (thread->cpu_usage >> shiftp->shift1) +
                                              (thread->cpu_usage >> shiftp->shift2);
                        thread->sched_usage = (thread->sched_usage >> shiftp->shift1) +
                                              (thread->sched_usage >> shiftp->shift2);
                } else {
                        thread->cpu_usage =   (thread->cpu_usage >>   shiftp->shift1) -
                                              (thread->cpu_usage >> -(shiftp->shift2));
                        thread->sched_usage = (thread->sched_usage >>   shiftp->shift1) -
                                              (thread->sched_usage >> -(shiftp->shift2));
                }
        } else {
                thread->cpu_usage = thread->cpu_delta = 0;
                thread->sched_usage = 0;
        }

        /*
         *      Check for fail-safe release.
         */
        if ((thread->sched_flags & TH_SFLAG_FAILSAFE) &&
            mach_absolute_time() >= thread->safe_release) {
                sched_thread_mode_undemote(thread, TH_SFLAG_FAILSAFE);
        }

        /*
         * Now that the thread's CPU usage has been accumulated and aged
         * based on contention of the previous tick window, update the
         * pri_shift of the thread to match the current global load/shift
         * values. The updated pri_shift would be used to calculate the
         * new priority of the thread.
         */
        thread->pri_shift = sched_pri_shifts[thread->th_sched_bucket];

        /* Recompute scheduled priority if appropriate. */
        if (thread->sched_mode == TH_MODE_TIMESHARE)
                thread_recompute_sched_pri(thread, SETPRI_LAZY);
}

#endif /* CONFIG_SCHED_TIMESHARE_CORE */


/*
 * TH_BUCKET_RUN is a count of *all* runnable non-idle threads.
 * Each other bucket is a count of the runnable non-idle threads
 * with that property.
 */
volatile uint32_t       sched_run_buckets[TH_BUCKET_MAX];

static void
sched_incr_bucket(sched_bucket_t bucket)
{
        assert(bucket >= TH_BUCKET_FIXPRI &&
               bucket <= TH_BUCKET_SHARE_BG);

        hw_atomic_add(&sched_run_buckets[bucket], 1);
}

static void
sched_decr_bucket(sched_bucket_t bucket)
{
        assert(bucket >= TH_BUCKET_FIXPRI &&
               bucket <= TH_BUCKET_SHARE_BG);

        assert(sched_run_buckets[bucket] > 0);

        hw_atomic_sub(&sched_run_buckets[bucket], 1);
}

/* TH_RUN & !TH_IDLE controls whether a thread has a run count */

uint32_t
sched_run_incr(thread_t thread)
{
        assert((thread->state & (TH_RUN|TH_IDLE)) == TH_RUN);

        uint32_t new_count = hw_atomic_add(&sched_run_buckets[TH_BUCKET_RUN], 1);

        sched_incr_bucket(thread->th_sched_bucket);

        return new_count;
}

uint32_t
sched_run_decr(thread_t thread)
{
        assert((thread->state & (TH_RUN|TH_IDLE)) != TH_RUN);

        sched_decr_bucket(thread->th_sched_bucket);

        uint32_t new_count = hw_atomic_sub(&sched_run_buckets[TH_BUCKET_RUN], 1);

        return new_count;
}

static void
sched_update_thread_bucket(thread_t thread)
{
        sched_bucket_t old_bucket = thread->th_sched_bucket;
        sched_bucket_t new_bucket = TH_BUCKET_RUN;

        switch (thread->sched_mode) {
        case TH_MODE_FIXED:
        case TH_MODE_REALTIME:
                new_bucket = TH_BUCKET_FIXPRI;
                break;

        case TH_MODE_TIMESHARE:
                if (thread->base_pri > BASEPRI_DEFAULT)
                        new_bucket = TH_BUCKET_SHARE_FG;
                else if (thread->base_pri > BASEPRI_UTILITY)
                        new_bucket = TH_BUCKET_SHARE_DF;
                else if (thread->base_pri > MAXPRI_THROTTLE)
                        new_bucket = TH_BUCKET_SHARE_UT;
                else
                        new_bucket = TH_BUCKET_SHARE_BG;
                break;

        default:
                panic("unexpected mode: %d", thread->sched_mode);
                break;
        }

        if (old_bucket != new_bucket) {
                thread->th_sched_bucket = new_bucket;
                thread->pri_shift = sched_pri_shifts[new_bucket];

                if ((thread->state & (TH_RUN|TH_IDLE)) == TH_RUN) {
                        sched_decr_bucket(old_bucket);
                        sched_incr_bucket(new_bucket);
                }
        }
}

/*
 * Set the thread's true scheduling mode
 * Called with thread mutex and thread locked
 * The thread has already been removed from the runqueue.
 *
 * (saved_mode is handled before this point)
 */
void
sched_set_thread_mode(thread_t thread, sched_mode_t new_mode)
{
        assert(thread->runq == PROCESSOR_NULL);

        switch (new_mode) {
        case TH_MODE_FIXED:
        case TH_MODE_REALTIME:
        case TH_MODE_TIMESHARE:
                break;

        default:
                panic("unexpected mode: %d", new_mode);
                break;
        }

        thread->sched_mode = new_mode;

        sched_update_thread_bucket(thread);
}

/*
 * Demote the true scheduler mode to timeshare (called with the thread locked)
 */
void
sched_thread_mode_demote(thread_t thread, uint32_t reason)
{
        assert(reason & TH_SFLAG_DEMOTED_MASK);
        assert((thread->sched_flags & reason) != reason);

        if (thread->policy_reset)
                return;

        if (thread->sched_flags & TH_SFLAG_DEMOTED_MASK) {
                /* Another demotion reason is already active */
                thread->sched_flags |= reason;
                return;
        }

        assert(thread->saved_mode == TH_MODE_NONE);

        boolean_t removed = thread_run_queue_remove(thread);

        thread->sched_flags |= reason;

        thread->saved_mode = thread->sched_mode;

        sched_set_thread_mode(thread, TH_MODE_TIMESHARE);

        thread_recompute_priority(thread);

        if (removed)
                thread_run_queue_reinsert(thread, SCHED_TAILQ);
}

/*
 * Un-demote the true scheduler mode back to the saved mode (called with the thread locked)
 */
void
sched_thread_mode_undemote(thread_t thread, uint32_t reason)
{
        assert(reason & TH_SFLAG_DEMOTED_MASK);
        assert((thread->sched_flags & reason) == reason);
        assert(thread->saved_mode != TH_MODE_NONE);
        assert(thread->sched_mode == TH_MODE_TIMESHARE);
        assert(thread->policy_reset == 0);

        thread->sched_flags &= ~reason;

        if (thread->sched_flags & TH_SFLAG_DEMOTED_MASK) {
                /* Another demotion reason is still active */
                return;
        }

        boolean_t removed = thread_run_queue_remove(thread);

        sched_set_thread_mode(thread, thread->saved_mode);

        thread->saved_mode = TH_MODE_NONE;

        thread_recompute_priority(thread);

        if (removed)
                thread_run_queue_reinsert(thread, SCHED_TAILQ);
}

/*
 * Promote thread to a specific priority
 *
 * Promotion must not last past syscall boundary
 * Clients must always pair promote and unpromote 1:1
 *
 * Called at splsched with thread locked
 */
void
sched_thread_promote_to_pri(thread_t    thread,
                            int         priority,
              __kdebug_only uintptr_t   trace_obj /* already unslid */)
{
        assert((thread->sched_flags & TH_SFLAG_PROMOTED) != TH_SFLAG_PROMOTED);
        assert(thread->promotion_priority == 0);
        assert(priority <= MAXPRI_PROMOTE);
        assert(priority > 0);

        KDBG(MACHDBG_CODE(DBG_MACH_SCHED, MACH_PROMOTED),
             thread_tid(thread), trace_obj, priority);

        thread->sched_flags |= TH_SFLAG_PROMOTED;
        thread->promotion_priority = priority;

        thread_recompute_sched_pri(thread, SETPRI_DEFAULT);
}


/*
 * Update a pre-existing priority promotion to have a higher priority floor
 * Priority can only go up from the previous value
 * Update must occur while a promotion is active
 *
 * Called at splsched with thread locked
 */
void
sched_thread_update_promotion_to_pri(thread_t   thread,
                                     int        priority,
                       __kdebug_only uintptr_t  trace_obj /* already unslid */)
{
        assert(thread->promotions > 0);
        assert((thread->sched_flags & TH_SFLAG_PROMOTED) == TH_SFLAG_PROMOTED);
        assert(thread->promotion_priority > 0);
        assert(priority <= MAXPRI_PROMOTE);

        if (thread->promotion_priority < priority) {
                KDBG(MACHDBG_CODE(DBG_MACH_SCHED, MACH_PROMOTED_UPDATE),
                     thread_tid(thread), trace_obj, priority);

                thread->promotion_priority = priority;
                thread_recompute_sched_pri(thread, SETPRI_DEFAULT);
        }
}

/*
 * End a priority promotion
 * Demotes a thread back to its expected priority without the promotion in place
 *
 * Called at splsched with thread locked
 */
void
sched_thread_unpromote(thread_t     thread,
         __kdebug_only uintptr_t    trace_obj /* already unslid */)
{
        assert((thread->sched_flags & TH_SFLAG_PROMOTED) == TH_SFLAG_PROMOTED);
        assert(thread->promotion_priority > 0);

        KDBG(MACHDBG_CODE(DBG_MACH_SCHED, MACH_UNPROMOTED),
             thread_tid(thread), trace_obj, 0);

        thread->sched_flags &= ~TH_SFLAG_PROMOTED;
        thread->promotion_priority = 0;

        thread_recompute_sched_pri(thread, SETPRI_DEFAULT);
}

/* called with thread locked */
void
assert_promotions_invariant(thread_t thread)
{
        if (thread->promotions > 0)
                assert((thread->sched_flags & TH_SFLAG_PROMOTED) == TH_SFLAG_PROMOTED);

        if (thread->promotions == 0)
                assert((thread->sched_flags & TH_SFLAG_PROMOTED) != TH_SFLAG_PROMOTED);
}

/*
 * Promote thread to have a sched pri floor for a specific reason
 *
 * Promotion must not last past syscall boundary
 * Clients must always pair promote and demote 1:1,
 * Handling nesting of the same promote reason is the client's responsibility
 *
 * Called at splsched with thread locked
 */
void
sched_thread_promote_reason(thread_t    thread,
                            uint32_t    reason,
              __kdebug_only uintptr_t   trace_obj /* already unslid */)
{
        assert(reason & TH_SFLAG_PROMOTE_REASON_MASK);
        assert((thread->sched_flags & reason) != reason);

        switch (reason) {
        case TH_SFLAG_RW_PROMOTED:
                KDBG(MACHDBG_CODE(DBG_MACH_SCHED, MACH_RW_PROMOTE),
                     thread_tid(thread), thread->sched_pri,
                     thread->base_pri, trace_obj);
                break;
        case TH_SFLAG_WAITQ_PROMOTED:
                KDBG(MACHDBG_CODE(DBG_MACH_SCHED, MACH_WAITQ_PROMOTE),
                     thread_tid(thread), thread->sched_pri,
                     thread->base_pri, trace_obj);
                break;
        case TH_SFLAG_EXEC_PROMOTED:
                KDBG(MACHDBG_CODE(DBG_MACH_SCHED, MACH_EXEC_PROMOTE),
                     thread_tid(thread), thread->sched_pri,
                     thread->base_pri, trace_obj);
                break;
        }

        thread->sched_flags |= reason;

        thread_recompute_sched_pri(thread, SETPRI_DEFAULT);
}

/*
 * End a specific promotion reason
 * Demotes a thread back to its expected priority without the promotion in place
 *
 * Called at splsched with thread locked
 */
void
sched_thread_unpromote_reason(thread_t  thread,
                              uint32_t  reason,
                __kdebug_only uintptr_t trace_obj /* already unslid */)
{
        assert(reason & TH_SFLAG_PROMOTE_REASON_MASK);
        assert((thread->sched_flags & reason) == reason);

        switch (reason) {
        case TH_SFLAG_RW_PROMOTED:
                KDBG(MACHDBG_CODE(DBG_MACH_SCHED, MACH_RW_DEMOTE),
                     thread_tid(thread), thread->sched_pri,
                     thread->base_pri, trace_obj);
                break;
        case TH_SFLAG_WAITQ_PROMOTED:
                KDBG(MACHDBG_CODE(DBG_MACH_SCHED, MACH_WAITQ_DEMOTE),
                     thread_tid(thread), thread->sched_pri,
                     thread->base_pri, trace_obj);
                break;
        case TH_SFLAG_EXEC_PROMOTED:
                KDBG(MACHDBG_CODE(DBG_MACH_SCHED, MACH_EXEC_DEMOTE),
                     thread_tid(thread), thread->sched_pri,
                     thread->base_pri, trace_obj);
                break;
        }

        thread->sched_flags &= ~reason;

        thread_recompute_sched_pri(thread, SETPRI_DEFAULT);
}