xnu-6153.141.1.tar.gz

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

/*
 * Copyright (c) 2000-2015 Apple Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 *
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 *
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
 *
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
 */

#include <mach/mach_types.h>
#include <mach/thread_act_server.h>

#include <kern/kern_types.h>
#include <kern/processor.h>
#include <kern/thread.h>
#include <kern/affinity.h>
#include <mach/task_policy.h>
#include <kern/sfi.h>
#include <kern/policy_internal.h>
#include <sys/errno.h>
#include <sys/ulock.h>

#include <mach/machine/sdt.h>

#ifdef MACH_BSD
extern int      proc_selfpid(void);
extern char *   proc_name_address(void *p);
extern void     rethrottle_thread(void * uthread);
#endif /* MACH_BSD */

#define QOS_EXTRACT(q)        ((q) & 0xff)

uint32_t qos_override_mode;
#define QOS_OVERRIDE_MODE_OVERHANG_PEAK 0
#define QOS_OVERRIDE_MODE_IGNORE_OVERRIDE 1
#define QOS_OVERRIDE_MODE_FINE_GRAINED_OVERRIDE 2
#define QOS_OVERRIDE_MODE_FINE_GRAINED_OVERRIDE_BUT_SINGLE_MUTEX_OVERRIDE 3

extern zone_t thread_qos_override_zone;

static void
proc_thread_qos_remove_override_internal(thread_t thread, user_addr_t resource, int resource_type, boolean_t reset);

/*
 * THREAD_QOS_UNSPECIFIED is assigned the highest tier available, so it does not provide a limit
 * to threads that don't have a QoS class set.
 */
const qos_policy_params_t thread_qos_policy_params = {
        /*
         * This table defines the starting base priority of the thread,
         * which will be modified by the thread importance and the task max priority
         * before being applied.
         */
        .qos_pri[THREAD_QOS_UNSPECIFIED]                = 0, /* not consulted */
        .qos_pri[THREAD_QOS_USER_INTERACTIVE]           = BASEPRI_BACKGROUND, /* i.e. 46 */
        .qos_pri[THREAD_QOS_USER_INITIATED]             = BASEPRI_USER_INITIATED,
        .qos_pri[THREAD_QOS_LEGACY]                     = BASEPRI_DEFAULT,
        .qos_pri[THREAD_QOS_UTILITY]                    = BASEPRI_UTILITY,
        .qos_pri[THREAD_QOS_BACKGROUND]                 = MAXPRI_THROTTLE,
        .qos_pri[THREAD_QOS_MAINTENANCE]                = MAXPRI_THROTTLE,

        /*
         * This table defines the highest IO priority that a thread marked with this
         * QoS class can have.
         */
        .qos_iotier[THREAD_QOS_UNSPECIFIED]             = THROTTLE_LEVEL_TIER0,
        .qos_iotier[THREAD_QOS_USER_INTERACTIVE]        = THROTTLE_LEVEL_TIER0,
        .qos_iotier[THREAD_QOS_USER_INITIATED]          = THROTTLE_LEVEL_TIER0,
        .qos_iotier[THREAD_QOS_LEGACY]                  = THROTTLE_LEVEL_TIER0,
        .qos_iotier[THREAD_QOS_UTILITY]                 = THROTTLE_LEVEL_TIER1,
        .qos_iotier[THREAD_QOS_BACKGROUND]              = THROTTLE_LEVEL_TIER2, /* possibly overridden by bg_iotier */
        .qos_iotier[THREAD_QOS_MAINTENANCE]             = THROTTLE_LEVEL_TIER3,

        /*
         * This table defines the highest QoS level that
         * a thread marked with this QoS class can have.
         */

        .qos_through_qos[THREAD_QOS_UNSPECIFIED]        = QOS_EXTRACT(THROUGHPUT_QOS_TIER_UNSPECIFIED),
        .qos_through_qos[THREAD_QOS_USER_INTERACTIVE]   = QOS_EXTRACT(THROUGHPUT_QOS_TIER_0),
        .qos_through_qos[THREAD_QOS_USER_INITIATED]     = QOS_EXTRACT(THROUGHPUT_QOS_TIER_1),
        .qos_through_qos[THREAD_QOS_LEGACY]             = QOS_EXTRACT(THROUGHPUT_QOS_TIER_1),
        .qos_through_qos[THREAD_QOS_UTILITY]            = QOS_EXTRACT(THROUGHPUT_QOS_TIER_2),
        .qos_through_qos[THREAD_QOS_BACKGROUND]         = QOS_EXTRACT(THROUGHPUT_QOS_TIER_5),
        .qos_through_qos[THREAD_QOS_MAINTENANCE]        = QOS_EXTRACT(THROUGHPUT_QOS_TIER_5),

        .qos_latency_qos[THREAD_QOS_UNSPECIFIED]        = QOS_EXTRACT(LATENCY_QOS_TIER_UNSPECIFIED),
        .qos_latency_qos[THREAD_QOS_USER_INTERACTIVE]   = QOS_EXTRACT(LATENCY_QOS_TIER_0),
        .qos_latency_qos[THREAD_QOS_USER_INITIATED]     = QOS_EXTRACT(LATENCY_QOS_TIER_1),
        .qos_latency_qos[THREAD_QOS_LEGACY]             = QOS_EXTRACT(LATENCY_QOS_TIER_1),
        .qos_latency_qos[THREAD_QOS_UTILITY]            = QOS_EXTRACT(LATENCY_QOS_TIER_3),
        .qos_latency_qos[THREAD_QOS_BACKGROUND]         = QOS_EXTRACT(LATENCY_QOS_TIER_3),
        .qos_latency_qos[THREAD_QOS_MAINTENANCE]        = QOS_EXTRACT(LATENCY_QOS_TIER_3),
};

static void
thread_set_user_sched_mode_and_recompute_pri(thread_t thread, sched_mode_t mode);

static int
thread_qos_scaled_relative_priority(int qos, int qos_relprio);

static void
proc_get_thread_policy_bitfield(thread_t thread, thread_policy_state_t info);

static void
proc_set_thread_policy_locked(thread_t thread, int category, int flavor, int value, int value2, task_pend_token_t pend_token);

static void
proc_set_thread_policy_spinlocked(thread_t thread, int category, int flavor, int value, int value2, task_pend_token_t pend_token);

static void
thread_set_requested_policy_spinlocked(thread_t thread, int category, int flavor, int value, int value2, task_pend_token_t pend_token);

static int
thread_get_requested_policy_spinlocked(thread_t thread, int category, int flavor, int* value2);

static int
proc_get_thread_policy_locked(thread_t thread, int category, int flavor, int* value2);

static void
thread_policy_update_spinlocked(thread_t thread, boolean_t recompute_priority, task_pend_token_t pend_token);

static void
thread_policy_update_internal_spinlocked(thread_t thread, boolean_t recompute_priority, task_pend_token_t pend_token);

void
thread_policy_init(void)
{
        if (PE_parse_boot_argn("qos_override_mode", &qos_override_mode, sizeof(qos_override_mode))) {
                printf("QOS override mode: 0x%08x\n", qos_override_mode);
        } else {
                qos_override_mode = QOS_OVERRIDE_MODE_FINE_GRAINED_OVERRIDE_BUT_SINGLE_MUTEX_OVERRIDE;
        }
}

boolean_t
thread_has_qos_policy(thread_t thread)
{
        return (proc_get_thread_policy(thread, TASK_POLICY_ATTRIBUTE, TASK_POLICY_QOS) != THREAD_QOS_UNSPECIFIED) ? TRUE : FALSE;
}


static void
thread_remove_qos_policy_locked(thread_t thread,
    task_pend_token_t pend_token)
{
        __unused int prev_qos = thread->requested_policy.thrp_qos;

        DTRACE_PROC2(qos__remove, thread_t, thread, int, prev_qos);

        proc_set_thread_policy_locked(thread, TASK_POLICY_ATTRIBUTE, TASK_POLICY_QOS_AND_RELPRIO,
            THREAD_QOS_UNSPECIFIED, 0, pend_token);
}

kern_return_t
thread_remove_qos_policy(thread_t thread)
{
        struct task_pend_token pend_token = {};

        thread_mtx_lock(thread);
        if (!thread->active) {
                thread_mtx_unlock(thread);
                return KERN_TERMINATED;
        }

        thread_remove_qos_policy_locked(thread, &pend_token);

        thread_mtx_unlock(thread);

        thread_policy_update_complete_unlocked(thread, &pend_token);

        return KERN_SUCCESS;
}


boolean_t
thread_is_static_param(thread_t thread)
{
        if (thread->static_param) {
                DTRACE_PROC1(qos__legacy__denied, thread_t, thread);
                return TRUE;
        }
        return FALSE;
}

/*
 * Relative priorities can range between 0REL and -15REL. These
 * map to QoS-specific ranges, to create non-overlapping priority
 * ranges.
 */
static int
thread_qos_scaled_relative_priority(int qos, int qos_relprio)
{
        int next_lower_qos;

        /* Fast path, since no validation or scaling is needed */
        if (qos_relprio == 0) {
                return 0;
        }

        switch (qos) {
        case THREAD_QOS_USER_INTERACTIVE:
                next_lower_qos = THREAD_QOS_USER_INITIATED;
                break;
        case THREAD_QOS_USER_INITIATED:
                next_lower_qos = THREAD_QOS_LEGACY;
                break;
        case THREAD_QOS_LEGACY:
                next_lower_qos = THREAD_QOS_UTILITY;
                break;
        case THREAD_QOS_UTILITY:
                next_lower_qos = THREAD_QOS_BACKGROUND;
                break;
        case THREAD_QOS_MAINTENANCE:
        case THREAD_QOS_BACKGROUND:
                next_lower_qos = 0;
                break;
        default:
                panic("Unrecognized QoS %d", qos);
                return 0;
        }

        int prio_range_max = thread_qos_policy_params.qos_pri[qos];
        int prio_range_min = next_lower_qos ? thread_qos_policy_params.qos_pri[next_lower_qos] : 0;

        /*
         * We now have the valid range that the scaled relative priority can map to. Note
         * that the lower bound is exclusive, but the upper bound is inclusive. If the
         * range is (21,31], 0REL should map to 31 and -15REL should map to 22. We use the
         * fact that the max relative priority is -15 and use ">>4" to divide by 16 and discard
         * remainder.
         */
        int scaled_relprio = -(((prio_range_max - prio_range_min) * (-qos_relprio)) >> 4);

        return scaled_relprio;
}

/*
 * flag set by -qos-policy-allow boot-arg to allow
 * testing thread qos policy from userspace
 */
boolean_t allow_qos_policy_set = FALSE;

kern_return_t
thread_policy_set(
        thread_t                                thread,
        thread_policy_flavor_t  flavor,
        thread_policy_t                 policy_info,
        mach_msg_type_number_t  count)
{
        thread_qos_policy_data_t req_qos;
        kern_return_t kr;

        req_qos.qos_tier = THREAD_QOS_UNSPECIFIED;

        if (thread == THREAD_NULL) {
                return KERN_INVALID_ARGUMENT;
        }

        if (allow_qos_policy_set == FALSE) {
                if (thread_is_static_param(thread)) {
                        return KERN_POLICY_STATIC;
                }

                if (flavor == THREAD_QOS_POLICY) {
                        return KERN_INVALID_ARGUMENT;
                }
        }

        /* Threads without static_param set reset their QoS when other policies are applied. */
        if (thread->requested_policy.thrp_qos != THREAD_QOS_UNSPECIFIED) {
                /* Store the existing tier, if we fail this call it is used to reset back. */
                req_qos.qos_tier = thread->requested_policy.thrp_qos;
                req_qos.tier_importance = thread->requested_policy.thrp_qos_relprio;

                kr = thread_remove_qos_policy(thread);
                if (kr != KERN_SUCCESS) {
                        return kr;
                }
        }

        kr = thread_policy_set_internal(thread, flavor, policy_info, count);

        /* Return KERN_QOS_REMOVED instead of KERN_SUCCESS if we succeeded. */
        if (req_qos.qos_tier != THREAD_QOS_UNSPECIFIED) {
                if (kr != KERN_SUCCESS) {
                        /* Reset back to our original tier as the set failed. */
                        (void)thread_policy_set_internal(thread, THREAD_QOS_POLICY, (thread_policy_t)&req_qos, THREAD_QOS_POLICY_COUNT);
                }
        }

        return kr;
}

kern_return_t
thread_policy_set_internal(
        thread_t                     thread,
        thread_policy_flavor_t       flavor,
        thread_policy_t              policy_info,
        mach_msg_type_number_t       count)
{
        kern_return_t result = KERN_SUCCESS;
        struct task_pend_token pend_token = {};

        thread_mtx_lock(thread);
        if (!thread->active) {
                thread_mtx_unlock(thread);

                return KERN_TERMINATED;
        }

        switch (flavor) {
        case THREAD_EXTENDED_POLICY:
        {
                boolean_t timeshare = TRUE;

                if (count >= THREAD_EXTENDED_POLICY_COUNT) {
                        thread_extended_policy_t info;

                        info = (thread_extended_policy_t)policy_info;
                        timeshare = info->timeshare;
                }

                sched_mode_t mode = (timeshare == TRUE) ? TH_MODE_TIMESHARE : TH_MODE_FIXED;

                spl_t s = splsched();
                thread_lock(thread);

                thread_set_user_sched_mode_and_recompute_pri(thread, mode);

                thread_unlock(thread);
                splx(s);

                pend_token.tpt_update_thread_sfi = 1;

                break;
        }

        case THREAD_TIME_CONSTRAINT_POLICY:
        {
                thread_time_constraint_policy_t info;

                if (count < THREAD_TIME_CONSTRAINT_POLICY_COUNT) {
                        result = KERN_INVALID_ARGUMENT;
                        break;
                }

                info = (thread_time_constraint_policy_t)policy_info;
                if (info->constraint < info->computation ||
                    info->computation > max_rt_quantum ||
                    info->computation < min_rt_quantum) {
                        result = KERN_INVALID_ARGUMENT;
                        break;
                }

                spl_t s = splsched();
                thread_lock(thread);

                thread->realtime.period         = info->period;
                thread->realtime.computation    = info->computation;
                thread->realtime.constraint     = info->constraint;
                thread->realtime.preemptible    = info->preemptible;

                thread_set_user_sched_mode_and_recompute_pri(thread, TH_MODE_REALTIME);

                thread_unlock(thread);
                splx(s);

                pend_token.tpt_update_thread_sfi = 1;

                break;
        }

        case THREAD_PRECEDENCE_POLICY:
        {
                thread_precedence_policy_t info;

                if (count < THREAD_PRECEDENCE_POLICY_COUNT) {
                        result = KERN_INVALID_ARGUMENT;
                        break;
                }
                info = (thread_precedence_policy_t)policy_info;

                spl_t s = splsched();
                thread_lock(thread);

                thread->importance = info->importance;

                thread_recompute_priority(thread);

                thread_unlock(thread);
                splx(s);

                break;
        }

        case THREAD_AFFINITY_POLICY:
        {
                thread_affinity_policy_t info;

                if (!thread_affinity_is_supported()) {
                        result = KERN_NOT_SUPPORTED;
                        break;
                }
                if (count < THREAD_AFFINITY_POLICY_COUNT) {
                        result = KERN_INVALID_ARGUMENT;
                        break;
                }

                info = (thread_affinity_policy_t) policy_info;
                /*
                 * Unlock the thread mutex here and
                 * return directly after calling thread_affinity_set().
                 * This is necessary for correct lock ordering because
                 * thread_affinity_set() takes the task lock.
                 */
                thread_mtx_unlock(thread);
                return thread_affinity_set(thread, info->affinity_tag);
        }

#if CONFIG_EMBEDDED
        case THREAD_BACKGROUND_POLICY:
        {
                thread_background_policy_t info;

                if (count < THREAD_BACKGROUND_POLICY_COUNT) {
                        result = KERN_INVALID_ARGUMENT;
                        break;
                }

                if (thread->task != current_task()) {
                        result = KERN_PROTECTION_FAILURE;
                        break;
                }

                info = (thread_background_policy_t) policy_info;

                int enable;

                if (info->priority == THREAD_BACKGROUND_POLICY_DARWIN_BG) {
                        enable = TASK_POLICY_ENABLE;
                } else {
                        enable = TASK_POLICY_DISABLE;
                }

                int category = (current_thread() == thread) ? TASK_POLICY_INTERNAL : TASK_POLICY_EXTERNAL;

                proc_set_thread_policy_locked(thread, category, TASK_POLICY_DARWIN_BG, enable, 0, &pend_token);

                break;
        }
#endif /* CONFIG_EMBEDDED */

        case THREAD_THROUGHPUT_QOS_POLICY:
        {
                thread_throughput_qos_policy_t info = (thread_throughput_qos_policy_t) policy_info;
                thread_throughput_qos_t tqos;

                if (count < THREAD_THROUGHPUT_QOS_POLICY_COUNT) {
                        result = KERN_INVALID_ARGUMENT;
                        break;
                }

                if ((result = qos_throughput_policy_validate(info->thread_throughput_qos_tier)) != KERN_SUCCESS) {
                        break;
                }

                tqos = qos_extract(info->thread_throughput_qos_tier);

                proc_set_thread_policy_locked(thread, TASK_POLICY_ATTRIBUTE,
                    TASK_POLICY_THROUGH_QOS, tqos, 0, &pend_token);

                break;
        }

        case THREAD_LATENCY_QOS_POLICY:
        {
                thread_latency_qos_policy_t info = (thread_latency_qos_policy_t) policy_info;
                thread_latency_qos_t lqos;

                if (count < THREAD_LATENCY_QOS_POLICY_COUNT) {
                        result = KERN_INVALID_ARGUMENT;
                        break;
                }

                if ((result = qos_latency_policy_validate(info->thread_latency_qos_tier)) != KERN_SUCCESS) {
                        break;
                }

                lqos = qos_extract(info->thread_latency_qos_tier);

                proc_set_thread_policy_locked(thread, TASK_POLICY_ATTRIBUTE,
                    TASK_POLICY_LATENCY_QOS, lqos, 0, &pend_token);

                break;
        }

        case THREAD_QOS_POLICY:
        {
                thread_qos_policy_t info = (thread_qos_policy_t)policy_info;

                if (count < THREAD_QOS_POLICY_COUNT) {
                        result = KERN_INVALID_ARGUMENT;
                        break;
                }

                if (info->qos_tier < 0 || info->qos_tier >= THREAD_QOS_LAST) {
                        result = KERN_INVALID_ARGUMENT;
                        break;
                }

                if (info->tier_importance > 0 || info->tier_importance < THREAD_QOS_MIN_TIER_IMPORTANCE) {
                        result = KERN_INVALID_ARGUMENT;
                        break;
                }

                if (info->qos_tier == THREAD_QOS_UNSPECIFIED && info->tier_importance != 0) {
                        result = KERN_INVALID_ARGUMENT;
                        break;
                }

                proc_set_thread_policy_locked(thread, TASK_POLICY_ATTRIBUTE, TASK_POLICY_QOS_AND_RELPRIO,
                    info->qos_tier, -info->tier_importance, &pend_token);

                break;
        }

        default:
                result = KERN_INVALID_ARGUMENT;
                break;
        }

        thread_mtx_unlock(thread);

        thread_policy_update_complete_unlocked(thread, &pend_token);

        return result;
}

/*
 * Note that there is no implemented difference between POLICY_RR and POLICY_FIFO.
 * Both result in FIXED mode scheduling.
 */
static sched_mode_t
convert_policy_to_sched_mode(integer_t policy)
{
        switch (policy) {
        case POLICY_TIMESHARE:
                return TH_MODE_TIMESHARE;
        case POLICY_RR:
        case POLICY_FIFO:
                return TH_MODE_FIXED;
        default:
                panic("unexpected sched policy: %d", policy);
                return TH_MODE_NONE;
        }
}

/*
 * Called either with the thread mutex locked
 * or from the pthread kext in a 'safe place'.
 */
static kern_return_t
thread_set_mode_and_absolute_pri_internal(thread_t              thread,
    sched_mode_t          mode,
    integer_t             priority,
    task_pend_token_t     pend_token)
{
        kern_return_t kr = KERN_SUCCESS;

        spl_t s = splsched();
        thread_lock(thread);

        /* This path isn't allowed to change a thread out of realtime. */
        if ((thread->sched_mode == TH_MODE_REALTIME) ||
            (thread->saved_mode == TH_MODE_REALTIME)) {
                kr = KERN_FAILURE;
                goto unlock;
        }

        if (thread->policy_reset) {
                kr = KERN_SUCCESS;
                goto unlock;
        }

        sched_mode_t old_mode = thread->sched_mode;

        /*
         * Reverse engineer and apply the correct importance value
         * from the requested absolute priority value.
         *
         * TODO: Store the absolute priority value instead
         */

        if (priority >= thread->max_priority) {
                priority = thread->max_priority - thread->task_priority;
        } else if (priority >= MINPRI_KERNEL) {
                priority -=  MINPRI_KERNEL;
        } else if (priority >= MINPRI_RESERVED) {
                priority -=  MINPRI_RESERVED;
        } else {
                priority -= BASEPRI_DEFAULT;
        }

        priority += thread->task_priority;

        if (priority > thread->max_priority) {
                priority = thread->max_priority;
        } else if (priority < MINPRI) {
                priority = MINPRI;
        }

        thread->importance = priority - thread->task_priority;

        thread_set_user_sched_mode_and_recompute_pri(thread, mode);

        if (mode != old_mode) {
                pend_token->tpt_update_thread_sfi = 1;
        }

unlock:
        thread_unlock(thread);
        splx(s);

        return kr;
}

void
thread_freeze_base_pri(thread_t thread)
{
        assert(thread == current_thread());

        spl_t s = splsched();
        thread_lock(thread);

        assert((thread->sched_flags & TH_SFLAG_BASE_PRI_FROZEN) == 0);
        thread->sched_flags |= TH_SFLAG_BASE_PRI_FROZEN;

        thread_unlock(thread);
        splx(s);
}

bool
thread_unfreeze_base_pri(thread_t thread)
{
        assert(thread == current_thread());
        integer_t base_pri;
        ast_t ast = 0;

        spl_t s = splsched();
        thread_lock(thread);

        assert(thread->sched_flags & TH_SFLAG_BASE_PRI_FROZEN);
        thread->sched_flags &= ~TH_SFLAG_BASE_PRI_FROZEN;

        base_pri = thread->req_base_pri;
        if (base_pri != thread->base_pri) {
                /*
                 * This function returns "true" if the base pri change
                 * is the most likely cause for the preemption.
                 */
                sched_set_thread_base_priority(thread, base_pri);
                ast = ast_peek(AST_PREEMPT);
        }

        thread_unlock(thread);
        splx(s);

        return ast != 0;
}

uint8_t
thread_workq_pri_for_qos(thread_qos_t qos)
{
        assert(qos < THREAD_QOS_LAST);
        return (uint8_t)thread_qos_policy_params.qos_pri[qos];
}

thread_qos_t
thread_workq_qos_for_pri(int priority)
{
        int qos;
        if (priority > thread_qos_policy_params.qos_pri[THREAD_QOS_USER_INTERACTIVE]) {
                // indicate that workq should map >UI threads to workq's
                // internal notation for above-UI work.
                return THREAD_QOS_UNSPECIFIED;
        }
        for (qos = THREAD_QOS_USER_INTERACTIVE; qos > THREAD_QOS_MAINTENANCE; qos--) {
                // map a given priority up to the next nearest qos band.
                if (thread_qos_policy_params.qos_pri[qos - 1] < priority) {
                        return qos;
                }
        }
        return THREAD_QOS_MAINTENANCE;
}

/*
 * private interface for pthread workqueues
 *
 * Set scheduling policy & absolute priority for thread
 * May be called with spinlocks held
 * Thread mutex lock is not held
 */
void
thread_reset_workq_qos(thread_t thread, uint32_t qos)
{
        struct task_pend_token pend_token = {};

        assert(qos < THREAD_QOS_LAST);

        spl_t s = splsched();
        thread_lock(thread);

        proc_set_thread_policy_spinlocked(thread, TASK_POLICY_ATTRIBUTE,
            TASK_POLICY_QOS_AND_RELPRIO, qos, 0, &pend_token);
        proc_set_thread_policy_spinlocked(thread, TASK_POLICY_ATTRIBUTE,
            TASK_POLICY_QOS_WORKQ_OVERRIDE, THREAD_QOS_UNSPECIFIED, 0,
            &pend_token);

        assert(pend_token.tpt_update_sockets == 0);

        thread_unlock(thread);
        splx(s);

        thread_policy_update_complete_unlocked(thread, &pend_token);
}

/*
 * private interface for pthread workqueues
 *
 * Set scheduling policy & absolute priority for thread
 * May be called with spinlocks held
 * Thread mutex lock is held
 */
void
thread_set_workq_override(thread_t thread, uint32_t qos)
{
        struct task_pend_token pend_token = {};

        assert(qos < THREAD_QOS_LAST);

        spl_t s = splsched();
        thread_lock(thread);

        proc_set_thread_policy_spinlocked(thread, TASK_POLICY_ATTRIBUTE,
            TASK_POLICY_QOS_WORKQ_OVERRIDE, qos, 0, &pend_token);

        assert(pend_token.tpt_update_sockets == 0);

        thread_unlock(thread);
        splx(s);

        thread_policy_update_complete_unlocked(thread, &pend_token);
}

/*
 * private interface for pthread workqueues
 *
 * Set scheduling policy & absolute priority for thread
 * May be called with spinlocks held
 * Thread mutex lock is not held
 */
void
thread_set_workq_pri(thread_t  thread,
    thread_qos_t qos,
    integer_t priority,
    integer_t policy)
{
        struct task_pend_token pend_token = {};
        sched_mode_t mode = convert_policy_to_sched_mode(policy);

        assert(qos < THREAD_QOS_LAST);
        assert(thread->static_param);

        if (!thread->static_param || !thread->active) {
                return;
        }

        spl_t s = splsched();
        thread_lock(thread);

        proc_set_thread_policy_spinlocked(thread, TASK_POLICY_ATTRIBUTE,
            TASK_POLICY_QOS_AND_RELPRIO, qos, 0, &pend_token);
        proc_set_thread_policy_spinlocked(thread, TASK_POLICY_ATTRIBUTE,
            TASK_POLICY_QOS_WORKQ_OVERRIDE, THREAD_QOS_UNSPECIFIED,
            0, &pend_token);

        thread_unlock(thread);
        splx(s);

        /* Concern: this doesn't hold the mutex... */

        __assert_only kern_return_t kr;
        kr = thread_set_mode_and_absolute_pri_internal(thread, mode, priority,
            &pend_token);
        assert(kr == KERN_SUCCESS);

        if (pend_token.tpt_update_thread_sfi) {
                sfi_reevaluate(thread);
        }
}

/*
 * thread_set_mode_and_absolute_pri:
 *
 * Set scheduling policy & absolute priority for thread, for deprecated
 * thread_set_policy and thread_policy interfaces.
 *
 * Called with nothing locked.
 */
kern_return_t
thread_set_mode_and_absolute_pri(thread_t   thread,
    integer_t  policy,
    integer_t  priority)
{
        kern_return_t kr = KERN_SUCCESS;
        struct task_pend_token pend_token = {};

        sched_mode_t mode = convert_policy_to_sched_mode(policy);

        thread_mtx_lock(thread);

        if (!thread->active) {
                kr = KERN_TERMINATED;
                goto unlock;
        }

        if (thread_is_static_param(thread)) {
                kr = KERN_POLICY_STATIC;
                goto unlock;
        }

        /* Setting legacy policies on threads kills the current QoS */
        if (thread->requested_policy.thrp_qos != THREAD_QOS_UNSPECIFIED) {
                thread_remove_qos_policy_locked(thread, &pend_token);
        }

        kr = thread_set_mode_and_absolute_pri_internal(thread, mode, priority, &pend_token);

unlock:
        thread_mtx_unlock(thread);

        thread_policy_update_complete_unlocked(thread, &pend_token);

        return kr;
}

/*
 * Set the thread's requested mode and recompute priority
 * Called with thread mutex and thread locked
 *
 * TODO: Mitigate potential problems caused by moving thread to end of runq
 * whenever its priority is recomputed
 *      Only remove when it actually changes? Attempt to re-insert at appropriate location?
 */
static void
thread_set_user_sched_mode_and_recompute_pri(thread_t thread, sched_mode_t mode)
{
        if (thread->policy_reset) {
                return;
        }

        boolean_t removed = thread_run_queue_remove(thread);

        /*
         * TODO: Instead of having saved mode, have 'user mode' and 'true mode'.
         * That way there's zero confusion over which the user wants
         * and which the kernel wants.
         */
        if (thread->sched_flags & TH_SFLAG_DEMOTED_MASK) {
                thread->saved_mode = mode;
        } else {
                sched_set_thread_mode(thread, mode);
        }

        thread_recompute_priority(thread);

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

/* called at splsched with thread lock locked */
static void
thread_update_qos_cpu_time_locked(thread_t thread)
{
        task_t task = thread->task;
        uint64_t timer_sum, timer_delta;

        /*
         * This is only as accurate as the distance between
         * last context switch (embedded) or last user/kernel boundary transition (desktop)
         * because user_timer and system_timer are only updated then.
         *
         * TODO: Consider running a timer_update operation here to update it first.
         *       Maybe doable with interrupts disabled from current thread.
         *       If the thread is on a different core, may not be easy to get right.
         *
         * TODO: There should be a function for this in timer.c
         */

        timer_sum = timer_grab(&thread->user_timer);
        timer_sum += timer_grab(&thread->system_timer);
        timer_delta = timer_sum - thread->vtimer_qos_save;

        thread->vtimer_qos_save = timer_sum;

        uint64_t* task_counter = NULL;

        /* Update the task-level effective and requested qos stats atomically, because we don't have the task lock. */
        switch (thread->effective_policy.thep_qos) {
        case THREAD_QOS_UNSPECIFIED:        task_counter = &task->cpu_time_eqos_stats.cpu_time_qos_default; break;
        case THREAD_QOS_MAINTENANCE:        task_counter = &task->cpu_time_eqos_stats.cpu_time_qos_maintenance; break;
        case THREAD_QOS_BACKGROUND:         task_counter = &task->cpu_time_eqos_stats.cpu_time_qos_background; break;
        case THREAD_QOS_UTILITY:            task_counter = &task->cpu_time_eqos_stats.cpu_time_qos_utility; break;
        case THREAD_QOS_LEGACY:             task_counter = &task->cpu_time_eqos_stats.cpu_time_qos_legacy; break;
        case THREAD_QOS_USER_INITIATED:     task_counter = &task->cpu_time_eqos_stats.cpu_time_qos_user_initiated; break;
        case THREAD_QOS_USER_INTERACTIVE:   task_counter = &task->cpu_time_eqos_stats.cpu_time_qos_user_interactive; break;
        default:
                panic("unknown effective QoS: %d", thread->effective_policy.thep_qos);
        }

        OSAddAtomic64(timer_delta, task_counter);

        /* Update the task-level qos stats atomically, because we don't have the task lock. */
        switch (thread->requested_policy.thrp_qos) {
        case THREAD_QOS_UNSPECIFIED:        task_counter = &task->cpu_time_rqos_stats.cpu_time_qos_default; break;
        case THREAD_QOS_MAINTENANCE:        task_counter = &task->cpu_time_rqos_stats.cpu_time_qos_maintenance; break;
        case THREAD_QOS_BACKGROUND:         task_counter = &task->cpu_time_rqos_stats.cpu_time_qos_background; break;
        case THREAD_QOS_UTILITY:            task_counter = &task->cpu_time_rqos_stats.cpu_time_qos_utility; break;
        case THREAD_QOS_LEGACY:             task_counter = &task->cpu_time_rqos_stats.cpu_time_qos_legacy; break;
        case THREAD_QOS_USER_INITIATED:     task_counter = &task->cpu_time_rqos_stats.cpu_time_qos_user_initiated; break;
        case THREAD_QOS_USER_INTERACTIVE:   task_counter = &task->cpu_time_rqos_stats.cpu_time_qos_user_interactive; break;
        default:
                panic("unknown requested QoS: %d", thread->requested_policy.thrp_qos);
        }

        OSAddAtomic64(timer_delta, task_counter);
}

/*
 * called with no thread locks held
 * may hold task lock
 */
void
thread_update_qos_cpu_time(thread_t thread)
{
        thread_mtx_lock(thread);

        spl_t s = splsched();
        thread_lock(thread);

        thread_update_qos_cpu_time_locked(thread);

        thread_unlock(thread);
        splx(s);

        thread_mtx_unlock(thread);
}

/*
 * Calculate base priority from thread attributes, and set it on the thread
 *
 * Called with thread_lock and thread mutex held.
 */
extern thread_t vm_pageout_scan_thread;
extern boolean_t vps_dynamic_priority_enabled;

void
thread_recompute_priority(
        thread_t                thread)
{
        integer_t               priority;

        if (thread->policy_reset) {
                return;
        }

        if (thread->sched_mode == TH_MODE_REALTIME) {
                sched_set_thread_base_priority(thread, BASEPRI_RTQUEUES);
                return;
        } else if (thread->effective_policy.thep_qos != THREAD_QOS_UNSPECIFIED) {
                int qos = thread->effective_policy.thep_qos;
                int qos_ui_is_urgent = thread->effective_policy.thep_qos_ui_is_urgent;
                int qos_relprio = -(thread->effective_policy.thep_qos_relprio); /* stored in task policy inverted */
                int qos_scaled_relprio;

                assert(qos >= 0 && qos < THREAD_QOS_LAST);
                assert(qos_relprio <= 0 && qos_relprio >= THREAD_QOS_MIN_TIER_IMPORTANCE);

                priority = thread_qos_policy_params.qos_pri[qos];
                qos_scaled_relprio = thread_qos_scaled_relative_priority(qos, qos_relprio);

                if (qos == THREAD_QOS_USER_INTERACTIVE && qos_ui_is_urgent == 1) {
                        /* Bump priority 46 to 47 when in a frontmost app */
                        qos_scaled_relprio += 1;
                }

                /* TODO: factor in renice priority here? */

                priority += qos_scaled_relprio;
        } else {
                if (thread->importance > MAXPRI) {
                        priority = MAXPRI;
                } else if (thread->importance < -MAXPRI) {
                        priority = -MAXPRI;
                } else {
                        priority = thread->importance;
                }

                priority += thread->task_priority;
        }

        priority = MAX(priority, thread->user_promotion_basepri);

        /*
         * Clamp priority back into the allowed range for this task.
         *  The initial priority value could be out of this range due to:
         *      Task clamped to BG or Utility (max-pri is 4, or 20)
         *      Task is user task (max-pri is 63)
         *      Task is kernel task (max-pri is 95)
         * Note that thread->importance is user-settable to any integer
         * via THREAD_PRECEDENCE_POLICY.
         */
        if (priority > thread->max_priority) {
                priority = thread->max_priority;
        } else if (priority < MINPRI) {
                priority = MINPRI;
        }

        if (thread->saved_mode == TH_MODE_REALTIME &&
            thread->sched_flags & TH_SFLAG_FAILSAFE) {
                priority = DEPRESSPRI;
        }

        if (thread->effective_policy.thep_terminated == TRUE) {
                /*
                 * We temporarily want to override the expected priority to
                 * ensure that the thread exits in a timely manner.
                 * Note that this is allowed to exceed thread->max_priority
                 * so that the thread is no longer clamped to background
                 * during the final exit phase.
                 */
                if (priority < thread->task_priority) {
                        priority = thread->task_priority;
                }
                if (priority < BASEPRI_DEFAULT) {
                        priority = BASEPRI_DEFAULT;
                }
        }

#if CONFIG_EMBEDDED
        /* No one can have a base priority less than MAXPRI_THROTTLE */
        if (priority < MAXPRI_THROTTLE) {
                priority = MAXPRI_THROTTLE;
        }
#endif /* CONFIG_EMBEDDED */

        sched_set_thread_base_priority(thread, priority);
}

/* Called with the task lock held, but not the thread mutex or spinlock */
void
thread_policy_update_tasklocked(
        thread_t           thread,
        integer_t          priority,
        integer_t          max_priority,
        task_pend_token_t  pend_token)
{
        thread_mtx_lock(thread);

        if (!thread->active || thread->policy_reset) {
                thread_mtx_unlock(thread);
                return;
        }

        spl_t s = splsched();
        thread_lock(thread);

        __unused
        integer_t old_max_priority = thread->max_priority;

        thread->task_priority = priority;
        thread->max_priority = max_priority;

#if CONFIG_EMBEDDED
        /*
         * When backgrounding a thread, iOS has the semantic that
         * realtime and fixed priority threads should be demoted
         * to timeshare background threads.
         *
         * On OSX, realtime and fixed priority threads don't lose their mode.
         *
         * TODO: Do this inside the thread policy update routine in order to avoid double
         * remove/reinsert for a runnable thread
         */
        if ((max_priority <= MAXPRI_THROTTLE) && (old_max_priority > MAXPRI_THROTTLE)) {
                sched_thread_mode_demote(thread, TH_SFLAG_THROTTLED);
        } else if ((max_priority > MAXPRI_THROTTLE) && (old_max_priority <= MAXPRI_THROTTLE)) {
                sched_thread_mode_undemote(thread, TH_SFLAG_THROTTLED);
        }
#endif /* CONFIG_EMBEDDED */

        thread_policy_update_spinlocked(thread, TRUE, pend_token);

        thread_unlock(thread);
        splx(s);

        thread_mtx_unlock(thread);
}

/*
 * Reset thread to default state in preparation for termination
 * Called with thread mutex locked
 *
 * Always called on current thread, so we don't need a run queue remove
 */
void
thread_policy_reset(
        thread_t                thread)
{
        spl_t           s;

        assert(thread == current_thread());

        s = splsched();
        thread_lock(thread);

        if (thread->sched_flags & TH_SFLAG_FAILSAFE) {
                sched_thread_mode_undemote(thread, TH_SFLAG_FAILSAFE);
        }

        if (thread->sched_flags & TH_SFLAG_THROTTLED) {
                sched_thread_mode_undemote(thread, TH_SFLAG_THROTTLED);
        }

        /* At this point, the various demotions should be inactive */
        assert(!(thread->sched_flags & TH_SFLAG_DEMOTED_MASK));
        assert(!(thread->sched_flags & TH_SFLAG_THROTTLED));
        assert(!(thread->sched_flags & TH_SFLAG_DEPRESSED_MASK));

        /* Reset thread back to task-default basepri and mode  */
        sched_mode_t newmode = SCHED(initial_thread_sched_mode)(thread->task);

        sched_set_thread_mode(thread, newmode);

        thread->importance = 0;

        /* Prevent further changes to thread base priority or mode */
        thread->policy_reset = 1;

        sched_set_thread_base_priority(thread, thread->task_priority);

        thread_unlock(thread);
        splx(s);
}

kern_return_t
thread_policy_get(
        thread_t                                thread,
        thread_policy_flavor_t  flavor,
        thread_policy_t                 policy_info,
        mach_msg_type_number_t  *count,
        boolean_t                               *get_default)
{
        kern_return_t                   result = KERN_SUCCESS;

        if (thread == THREAD_NULL) {
                return KERN_INVALID_ARGUMENT;
        }

        thread_mtx_lock(thread);
        if (!thread->active) {
                thread_mtx_unlock(thread);

                return KERN_TERMINATED;
        }

        switch (flavor) {
        case THREAD_EXTENDED_POLICY:
        {
                boolean_t               timeshare = TRUE;

                if (!(*get_default)) {
                        spl_t s = splsched();
                        thread_lock(thread);

                        if ((thread->sched_mode != TH_MODE_REALTIME) &&
                            (thread->saved_mode != TH_MODE_REALTIME)) {
                                if (!(thread->sched_flags & TH_SFLAG_DEMOTED_MASK)) {
                                        timeshare = (thread->sched_mode == TH_MODE_TIMESHARE) != 0;
                                } else {
                                        timeshare = (thread->saved_mode == TH_MODE_TIMESHARE) != 0;
                                }
                        } else {
                                *get_default = TRUE;
                        }

                        thread_unlock(thread);
                        splx(s);
                }

                if (*count >= THREAD_EXTENDED_POLICY_COUNT) {
                        thread_extended_policy_t        info;

                        info = (thread_extended_policy_t)policy_info;
                        info->timeshare = timeshare;
                }

                break;
        }

        case THREAD_TIME_CONSTRAINT_POLICY:
        {
                thread_time_constraint_policy_t         info;

                if (*count < THREAD_TIME_CONSTRAINT_POLICY_COUNT) {
                        result = KERN_INVALID_ARGUMENT;
                        break;
                }

                info = (thread_time_constraint_policy_t)policy_info;

                if (!(*get_default)) {
                        spl_t s = splsched();
                        thread_lock(thread);

                        if ((thread->sched_mode == TH_MODE_REALTIME) ||
                            (thread->saved_mode == TH_MODE_REALTIME)) {
                                info->period = thread->realtime.period;
                                info->computation = thread->realtime.computation;
                                info->constraint = thread->realtime.constraint;
                                info->preemptible = thread->realtime.preemptible;
                        } else {
                                *get_default = TRUE;
                        }

                        thread_unlock(thread);
                        splx(s);
                }

                if (*get_default) {
                        info->period = 0;
                        info->computation = default_timeshare_computation;
                        info->constraint = default_timeshare_constraint;
                        info->preemptible = TRUE;
                }

                break;
        }

        case THREAD_PRECEDENCE_POLICY:
        {
                thread_precedence_policy_t              info;

                if (*count < THREAD_PRECEDENCE_POLICY_COUNT) {
                        result = KERN_INVALID_ARGUMENT;
                        break;
                }

                info = (thread_precedence_policy_t)policy_info;

                if (!(*get_default)) {
                        spl_t s = splsched();
                        thread_lock(thread);

                        info->importance = thread->importance;

                        thread_unlock(thread);
                        splx(s);
                } else {
                        info->importance = 0;
                }

                break;
        }

        case THREAD_AFFINITY_POLICY:
        {
                thread_affinity_policy_t                info;

                if (!thread_affinity_is_supported()) {
                        result = KERN_NOT_SUPPORTED;
                        break;
                }
                if (*count < THREAD_AFFINITY_POLICY_COUNT) {
                        result = KERN_INVALID_ARGUMENT;
                        break;
                }

                info = (thread_affinity_policy_t)policy_info;

                if (!(*get_default)) {
                        info->affinity_tag = thread_affinity_get(thread);
                } else {
                        info->affinity_tag = THREAD_AFFINITY_TAG_NULL;
                }

                break;
        }

        case THREAD_POLICY_STATE:
        {
                thread_policy_state_t           info;

                if (*count < THREAD_POLICY_STATE_COUNT) {
                        result = KERN_INVALID_ARGUMENT;
                        break;
                }

                /* Only root can get this info */
                if (current_task()->sec_token.val[0] != 0) {
                        result = KERN_PROTECTION_FAILURE;
                        break;
                }

                info = (thread_policy_state_t)(void*)policy_info;

                if (!(*get_default)) {
                        info->flags = 0;

                        spl_t s = splsched();
                        thread_lock(thread);

                        info->flags |= (thread->static_param ? THREAD_POLICY_STATE_FLAG_STATIC_PARAM : 0);

                        info->thps_requested_policy = *(uint64_t*)(void*)(&thread->requested_policy);
                        info->thps_effective_policy = *(uint64_t*)(void*)(&thread->effective_policy);

                        info->thps_user_promotions          = 0;
                        info->thps_user_promotion_basepri   = thread->user_promotion_basepri;
                        info->thps_ipc_overrides            = thread->kevent_overrides;

                        proc_get_thread_policy_bitfield(thread, info);

                        thread_unlock(thread);
                        splx(s);
                } else {
                        info->requested = 0;
                        info->effective = 0;
                        info->pending = 0;
                }

                break;
        }

        case THREAD_LATENCY_QOS_POLICY:
        {
                thread_latency_qos_policy_t info = (thread_latency_qos_policy_t) policy_info;
                thread_latency_qos_t plqos;

                if (*count < THREAD_LATENCY_QOS_POLICY_COUNT) {
                        result = KERN_INVALID_ARGUMENT;
                        break;
                }

                if (*get_default) {
                        plqos = 0;
                } else {
                        plqos = proc_get_thread_policy_locked(thread, TASK_POLICY_ATTRIBUTE, TASK_POLICY_LATENCY_QOS, NULL);
                }

                info->thread_latency_qos_tier = qos_latency_policy_package(plqos);
        }
        break;

        case THREAD_THROUGHPUT_QOS_POLICY:
        {
                thread_throughput_qos_policy_t info = (thread_throughput_qos_policy_t) policy_info;
                thread_throughput_qos_t ptqos;

                if (*count < THREAD_THROUGHPUT_QOS_POLICY_COUNT) {
                        result = KERN_INVALID_ARGUMENT;
                        break;
                }

                if (*get_default) {
                        ptqos = 0;
                } else {
                        ptqos = proc_get_thread_policy_locked(thread, TASK_POLICY_ATTRIBUTE, TASK_POLICY_THROUGH_QOS, NULL);
                }

                info->thread_throughput_qos_tier = qos_throughput_policy_package(ptqos);
        }
        break;

        case THREAD_QOS_POLICY:
        {
                thread_qos_policy_t info = (thread_qos_policy_t)policy_info;

                if (*count < THREAD_QOS_POLICY_COUNT) {
                        result = KERN_INVALID_ARGUMENT;
                        break;
                }

                if (!(*get_default)) {
                        int relprio_value = 0;
                        info->qos_tier = proc_get_thread_policy_locked(thread, TASK_POLICY_ATTRIBUTE,
                            TASK_POLICY_QOS_AND_RELPRIO, &relprio_value);

                        info->tier_importance = -relprio_value;
                } else {
                        info->qos_tier = THREAD_QOS_UNSPECIFIED;
                        info->tier_importance = 0;
                }

                break;
        }

        default:
                result = KERN_INVALID_ARGUMENT;
                break;
        }

        thread_mtx_unlock(thread);

        return result;
}

void
thread_policy_create(thread_t thread)
{
        KERNEL_DEBUG_CONSTANT_IST(KDEBUG_TRACE,
            (IMPORTANCE_CODE(IMP_UPDATE, (IMP_UPDATE_TASK_CREATE | TASK_POLICY_THREAD))) | DBG_FUNC_START,
            thread_tid(thread), theffective_0(thread),
            theffective_1(thread), thread->base_pri, 0);

        /* We pass a pend token but ignore it */
        struct task_pend_token pend_token = {};

        thread_policy_update_internal_spinlocked(thread, TRUE, &pend_token);

        KERNEL_DEBUG_CONSTANT_IST(KDEBUG_TRACE,
            (IMPORTANCE_CODE(IMP_UPDATE, (IMP_UPDATE_TASK_CREATE | TASK_POLICY_THREAD))) | DBG_FUNC_END,
            thread_tid(thread), theffective_0(thread),
            theffective_1(thread), thread->base_pri, 0);
}

static void
thread_policy_update_spinlocked(thread_t thread, boolean_t recompute_priority, task_pend_token_t pend_token)
{
        KERNEL_DEBUG_CONSTANT_IST(KDEBUG_TRACE,
            (IMPORTANCE_CODE(IMP_UPDATE, TASK_POLICY_THREAD) | DBG_FUNC_START),
            thread_tid(thread), theffective_0(thread),
            theffective_1(thread), thread->base_pri, 0);

        thread_policy_update_internal_spinlocked(thread, recompute_priority, pend_token);

        KERNEL_DEBUG_CONSTANT_IST(KDEBUG_TRACE,
            (IMPORTANCE_CODE(IMP_UPDATE, TASK_POLICY_THREAD)) | DBG_FUNC_END,
            thread_tid(thread), theffective_0(thread),
            theffective_1(thread), thread->base_pri, 0);
}



/*
 * One thread state update function TO RULE THEM ALL
 *
 * This function updates the thread effective policy fields
 * and pushes the results to the relevant subsystems.
 *
 * Returns TRUE if a pended action needs to be run.
 *
 * Called with thread spinlock locked, task may be locked, thread mutex may be locked
 */
static void
thread_policy_update_internal_spinlocked(thread_t thread, boolean_t recompute_priority,
    task_pend_token_t pend_token)
{
        /*
         * Step 1:
         *  Gather requested policy and effective task state
         */

        struct thread_requested_policy requested = thread->requested_policy;
        struct task_effective_policy task_effective = thread->task->effective_policy;

        /*
         * Step 2:
         *  Calculate new effective policies from requested policy, task and thread state
         *  Rules:
         *      Don't change requested, it won't take effect
         */

        struct thread_effective_policy next = {};

        next.thep_qos_ui_is_urgent = task_effective.tep_qos_ui_is_urgent;

        uint32_t next_qos = requested.thrp_qos;

        if (requested.thrp_qos != THREAD_QOS_UNSPECIFIED) {
                next_qos = MAX(requested.thrp_qos_override, next_qos);
                next_qos = MAX(requested.thrp_qos_promote, next_qos);
                next_qos = MAX(requested.thrp_qos_kevent_override, next_qos);
                next_qos = MAX(requested.thrp_qos_wlsvc_override, next_qos);
                next_qos = MAX(requested.thrp_qos_workq_override, next_qos);
        }

        next.thep_qos = next_qos;

        /* A task clamp will result in an effective QoS even when requested is UNSPECIFIED */
        if (task_effective.tep_qos_clamp != THREAD_QOS_UNSPECIFIED) {
                if (next.thep_qos != THREAD_QOS_UNSPECIFIED) {
                        next.thep_qos = MIN(task_effective.tep_qos_clamp, next.thep_qos);
                } else {
                        next.thep_qos = task_effective.tep_qos_clamp;
                }
        }

        /*
         * Extract outbound-promotion QoS before applying task ceiling or BG clamp
         * This allows QoS promotions to work properly even after the process is unclamped.
         */
        next.thep_qos_promote = next.thep_qos;

        /* The ceiling only applies to threads that are in the QoS world */
        if (task_effective.tep_qos_ceiling != THREAD_QOS_UNSPECIFIED &&
            next.thep_qos != THREAD_QOS_UNSPECIFIED) {
                next.thep_qos = MIN(task_effective.tep_qos_ceiling, next.thep_qos);
        }

        /* Apply the sync ipc qos override */
        assert(requested.thrp_qos_sync_ipc_override == THREAD_QOS_UNSPECIFIED);

        /*
         * The QoS relative priority is only applicable when the original programmer's
         * intended (requested) QoS is in effect. When the QoS is clamped (e.g.
         * USER_INITIATED-13REL clamped to UTILITY), the relative priority is not honored,
         * since otherwise it would be lower than unclamped threads. Similarly, in the
         * presence of boosting, the programmer doesn't know what other actors
         * are boosting the thread.
         */
        if ((requested.thrp_qos != THREAD_QOS_UNSPECIFIED) &&
            (requested.thrp_qos == next.thep_qos) &&
            (requested.thrp_qos_override == THREAD_QOS_UNSPECIFIED)) {
                next.thep_qos_relprio = requested.thrp_qos_relprio;
        } else {
                next.thep_qos_relprio = 0;
        }

        /* Calculate DARWIN_BG */
        boolean_t wants_darwinbg        = FALSE;
        boolean_t wants_all_sockets_bg  = FALSE; /* Do I want my existing sockets to be bg */

        /*
         * If DARWIN_BG has been requested at either level, it's engaged.
         * darwinbg threads always create bg sockets,
         * but only some types of darwinbg change the sockets
         * after they're created
         */
        if (requested.thrp_int_darwinbg || requested.thrp_ext_darwinbg) {
                wants_all_sockets_bg = wants_darwinbg = TRUE;
        }

        if (requested.thrp_pidbind_bg) {
                wants_all_sockets_bg = wants_darwinbg = TRUE;
        }

        if (task_effective.tep_darwinbg) {
                wants_darwinbg = TRUE;
        }

        if (next.thep_qos == THREAD_QOS_BACKGROUND ||
            next.thep_qos == THREAD_QOS_MAINTENANCE) {
                wants_darwinbg = TRUE;
        }

        /* Calculate side effects of DARWIN_BG */

        if (wants_darwinbg) {
                next.thep_darwinbg = 1;
        }

        if (next.thep_darwinbg || task_effective.tep_new_sockets_bg) {
                next.thep_new_sockets_bg = 1;
        }

        /* Don't use task_effective.tep_all_sockets_bg here */
        if (wants_all_sockets_bg) {
                next.thep_all_sockets_bg = 1;
        }

        /* darwinbg implies background QOS (or lower) */
        if (next.thep_darwinbg &&
            (next.thep_qos > THREAD_QOS_BACKGROUND || next.thep_qos == THREAD_QOS_UNSPECIFIED)) {
                next.thep_qos = THREAD_QOS_BACKGROUND;
                next.thep_qos_relprio = 0;
        }

        /* Calculate IO policy */

        int iopol = THROTTLE_LEVEL_TIER0;

        /* Factor in the task's IO policy */
        if (next.thep_darwinbg) {
                iopol = MAX(iopol, task_effective.tep_bg_iotier);
        }

        iopol = MAX(iopol, task_effective.tep_io_tier);

        /* Look up the associated IO tier value for the QoS class */
        iopol = MAX(iopol, thread_qos_policy_params.qos_iotier[next.thep_qos]);

        iopol = MAX(iopol, requested.thrp_int_iotier);
        iopol = MAX(iopol, requested.thrp_ext_iotier);

        next.thep_io_tier = iopol;

        /*
         * If a QoS override is causing IO to go into a lower tier, we also set
         * the passive bit so that a thread doesn't end up stuck in its own throttle
         * window when the override goes away.
         */
        boolean_t qos_io_override_active = FALSE;
        if (thread_qos_policy_params.qos_iotier[next.thep_qos] <
            thread_qos_policy_params.qos_iotier[requested.thrp_qos]) {
                qos_io_override_active = TRUE;
        }

        /* Calculate Passive IO policy */
        if (requested.thrp_ext_iopassive ||
            requested.thrp_int_iopassive ||
            qos_io_override_active ||
            task_effective.tep_io_passive) {
                next.thep_io_passive = 1;
        }

        /* Calculate timer QOS */
        uint32_t latency_qos = requested.thrp_latency_qos;

        latency_qos = MAX(latency_qos, task_effective.tep_latency_qos);
        latency_qos = MAX(latency_qos, thread_qos_policy_params.qos_latency_qos[next.thep_qos]);

        next.thep_latency_qos = latency_qos;

        /* Calculate throughput QOS */
        uint32_t through_qos = requested.thrp_through_qos;

        through_qos = MAX(through_qos, task_effective.tep_through_qos);
        through_qos = MAX(through_qos, thread_qos_policy_params.qos_through_qos[next.thep_qos]);

        next.thep_through_qos = through_qos;

        if (task_effective.tep_terminated || requested.thrp_terminated) {
                /* Shoot down the throttles that slow down exit or response to SIGTERM */
                next.thep_terminated    = 1;
                next.thep_darwinbg      = 0;
                next.thep_io_tier       = THROTTLE_LEVEL_TIER0;
                next.thep_qos           = THREAD_QOS_UNSPECIFIED;
                next.thep_latency_qos   = LATENCY_QOS_TIER_UNSPECIFIED;
                next.thep_through_qos   = THROUGHPUT_QOS_TIER_UNSPECIFIED;
        }

        /*
         * Step 3:
         *  Swap out old policy for new policy
         */

        struct thread_effective_policy prev = thread->effective_policy;

        thread_update_qos_cpu_time_locked(thread);

        /* This is the point where the new values become visible to other threads */
        thread->effective_policy = next;

        /*
         * Step 4:
         *  Pend updates that can't be done while holding the thread lock
         */

        if (prev.thep_all_sockets_bg != next.thep_all_sockets_bg) {
                pend_token->tpt_update_sockets = 1;
        }

        /* TODO: Doesn't this only need to be done if the throttle went up? */
        if (prev.thep_io_tier != next.thep_io_tier) {
                pend_token->tpt_update_throttle = 1;
        }

        /*
         * Check for the attributes that sfi_thread_classify() consults,
         *  and trigger SFI re-evaluation.
         */
        if (prev.thep_qos != next.thep_qos ||
            prev.thep_darwinbg != next.thep_darwinbg) {
                pend_token->tpt_update_thread_sfi = 1;
        }

        integer_t old_base_pri = thread->base_pri;

        /*
         * Step 5:
         *  Update other subsystems as necessary if something has changed
         */

        /* Check for the attributes that thread_recompute_priority() consults */
        if (prev.thep_qos != next.thep_qos ||
            prev.thep_qos_relprio != next.thep_qos_relprio ||
            prev.thep_qos_ui_is_urgent != next.thep_qos_ui_is_urgent ||
            prev.thep_terminated != next.thep_terminated ||
            pend_token->tpt_force_recompute_pri == 1 ||
            recompute_priority) {
                thread_recompute_priority(thread);
        }

        /*
         * Check if the thread is waiting on a turnstile and needs priority propagation.
         */
        if (pend_token->tpt_update_turnstile &&
            ((old_base_pri == thread->base_pri) ||
            !thread_get_waiting_turnstile(thread))) {
                /*
                 * Reset update turnstile pend token since either
                 * the thread priority did not change or thread is
                 * not blocked on a turnstile.
                 */
                pend_token->tpt_update_turnstile = 0;
        }
}


/*
 * Initiate a thread policy state transition on a thread with its TID
 * Useful if you cannot guarantee the thread won't get terminated
 * Precondition: No locks are held
 * Will take task lock - using the non-tid variant is faster
 * if you already have a thread ref.
 */
void
proc_set_thread_policy_with_tid(task_t     task,
    uint64_t   tid,
    int        category,
    int        flavor,
    int        value)
{
        /* takes task lock, returns ref'ed thread or NULL */
        thread_t thread = task_findtid(task, tid);

        if (thread == THREAD_NULL) {
                return;
        }

        proc_set_thread_policy(thread, category, flavor, value);

        thread_deallocate(thread);
}

/*
 * Initiate a thread policy transition on a thread
 * This path supports networking transitions (i.e. darwinbg transitions)
 * Precondition: No locks are held
 */
void
proc_set_thread_policy(thread_t   thread,
    int        category,
    int        flavor,
    int        value)
{
        struct task_pend_token pend_token = {};

        thread_mtx_lock(thread);

        proc_set_thread_policy_locked(thread, category, flavor, value, 0, &pend_token);

        thread_mtx_unlock(thread);

        thread_policy_update_complete_unlocked(thread, &pend_token);
}

/*
 * Do the things that can't be done while holding a thread mutex.
 * These are set up to call back into thread policy to get the latest value,
 * so they don't have to be synchronized with the update.
 * The only required semantic is 'call this sometime after updating effective policy'
 *
 * Precondition: Thread mutex is not held
 *
 * This may be called with the task lock held, but in that case it won't be
 * called with tpt_update_sockets set.
 */
void
thread_policy_update_complete_unlocked(thread_t thread, task_pend_token_t pend_token)
{
#ifdef MACH_BSD
        if (pend_token->tpt_update_sockets) {
                proc_apply_task_networkbg(thread->task->bsd_info, thread);
        }
#endif /* MACH_BSD */

        if (pend_token->tpt_update_throttle) {
                rethrottle_thread(thread->uthread);
        }

        if (pend_token->tpt_update_thread_sfi) {
                sfi_reevaluate(thread);
        }

        if (pend_token->tpt_update_turnstile) {
                turnstile_update_thread_priority_chain(thread);
        }
}

/*
 * Set and update thread policy
 * Thread mutex might be held
 */
static void
proc_set_thread_policy_locked(thread_t          thread,
    int               category,
    int               flavor,
    int               value,
    int               value2,
    task_pend_token_t pend_token)
{
        spl_t s = splsched();
        thread_lock(thread);

        proc_set_thread_policy_spinlocked(thread, category, flavor, value, value2, pend_token);

        thread_unlock(thread);
        splx(s);
}

/*
 * Set and update thread policy
 * Thread spinlock is held
 */
static void
proc_set_thread_policy_spinlocked(thread_t          thread,
    int               category,
    int               flavor,
    int               value,
    int               value2,
    task_pend_token_t pend_token)
{
        KERNEL_DEBUG_CONSTANT_IST(KDEBUG_TRACE,
            (IMPORTANCE_CODE(flavor, (category | TASK_POLICY_THREAD))) | DBG_FUNC_START,
            thread_tid(thread), threquested_0(thread),
            threquested_1(thread), value, 0);

        thread_set_requested_policy_spinlocked(thread, category, flavor, value, value2, pend_token);

        thread_policy_update_spinlocked(thread, FALSE, pend_token);

        KERNEL_DEBUG_CONSTANT_IST(KDEBUG_TRACE,
            (IMPORTANCE_CODE(flavor, (category | TASK_POLICY_THREAD))) | DBG_FUNC_END,
            thread_tid(thread), threquested_0(thread),
            threquested_1(thread), tpending(pend_token), 0);
}

/*
 * Set the requested state for a specific flavor to a specific value.
 */
static void
thread_set_requested_policy_spinlocked(thread_t     thread,
    int               category,
    int               flavor,
    int               value,
    int               value2,
    task_pend_token_t pend_token)
{
        int tier, passive;

        struct thread_requested_policy requested = thread->requested_policy;

        switch (flavor) {
        /* Category: EXTERNAL and INTERNAL, thread and task */

        case TASK_POLICY_DARWIN_BG:
                if (category == TASK_POLICY_EXTERNAL) {
                        requested.thrp_ext_darwinbg = value;
                } else {
                        requested.thrp_int_darwinbg = value;
                }
                break;

        case TASK_POLICY_IOPOL:
                proc_iopol_to_tier(value, &tier, &passive);
                if (category == TASK_POLICY_EXTERNAL) {
                        requested.thrp_ext_iotier  = tier;
                        requested.thrp_ext_iopassive = passive;
                } else {
                        requested.thrp_int_iotier  = tier;
                        requested.thrp_int_iopassive = passive;
                }
                break;

        case TASK_POLICY_IO:
                if (category == TASK_POLICY_EXTERNAL) {
                        requested.thrp_ext_iotier = value;
                } else {
                        requested.thrp_int_iotier = value;
                }
                break;

        case TASK_POLICY_PASSIVE_IO:
                if (category == TASK_POLICY_EXTERNAL) {
                        requested.thrp_ext_iopassive = value;
                } else {
                        requested.thrp_int_iopassive = value;
                }
                break;

        /* Category: ATTRIBUTE, thread only */

        case TASK_POLICY_PIDBIND_BG:
                assert(category == TASK_POLICY_ATTRIBUTE);
                requested.thrp_pidbind_bg = value;
                break;

        case TASK_POLICY_LATENCY_QOS:
                assert(category == TASK_POLICY_ATTRIBUTE);
                requested.thrp_latency_qos = value;
                break;

        case TASK_POLICY_THROUGH_QOS:
                assert(category == TASK_POLICY_ATTRIBUTE);
                requested.thrp_through_qos = value;
                break;

        case TASK_POLICY_QOS_OVERRIDE:
                assert(category == TASK_POLICY_ATTRIBUTE);
                requested.thrp_qos_override = value;
                pend_token->tpt_update_turnstile = 1;
                break;

        case TASK_POLICY_QOS_AND_RELPRIO:
                assert(category == TASK_POLICY_ATTRIBUTE);
                requested.thrp_qos = value;
                requested.thrp_qos_relprio = value2;
                pend_token->tpt_update_turnstile = 1;
                DTRACE_BOOST3(qos_set, uint64_t, thread->thread_id, int, requested.thrp_qos, int, requested.thrp_qos_relprio);
                break;

        case TASK_POLICY_QOS_WORKQ_OVERRIDE:
                assert(category == TASK_POLICY_ATTRIBUTE);
                requested.thrp_qos_workq_override = value;
                pend_token->tpt_update_turnstile = 1;
                break;

        case TASK_POLICY_QOS_PROMOTE:
                assert(category == TASK_POLICY_ATTRIBUTE);
                requested.thrp_qos_promote = value;
                break;

        case TASK_POLICY_QOS_KEVENT_OVERRIDE:
                assert(category == TASK_POLICY_ATTRIBUTE);
                requested.thrp_qos_kevent_override = value;
                pend_token->tpt_update_turnstile = 1;
                break;

        case TASK_POLICY_QOS_SERVICER_OVERRIDE:
                assert(category == TASK_POLICY_ATTRIBUTE);
                requested.thrp_qos_wlsvc_override = value;
                pend_token->tpt_update_turnstile = 1;
                break;

        case TASK_POLICY_TERMINATED:
                assert(category == TASK_POLICY_ATTRIBUTE);
                requested.thrp_terminated = value;
                break;

        default:
                panic("unknown task policy: %d %d %d", category, flavor, value);
                break;
        }

        thread->requested_policy = requested;
}

/*
 * Gets what you set. Effective values may be different.
 * Precondition: No locks are held
 */
int
proc_get_thread_policy(thread_t   thread,
    int        category,
    int        flavor)
{
        int value = 0;
        thread_mtx_lock(thread);
        value = proc_get_thread_policy_locked(thread, category, flavor, NULL);
        thread_mtx_unlock(thread);
        return value;
}

static int
proc_get_thread_policy_locked(thread_t   thread,
    int        category,
    int        flavor,
    int*       value2)
{
        int value = 0;

        spl_t s = splsched();
        thread_lock(thread);

        value = thread_get_requested_policy_spinlocked(thread, category, flavor, value2);

        thread_unlock(thread);
        splx(s);

        return value;
}

/*
 * Gets what you set. Effective values may be different.
 */
static int
thread_get_requested_policy_spinlocked(thread_t thread,
    int      category,
    int      flavor,
    int*     value2)
{
        int value = 0;

        struct thread_requested_policy requested = thread->requested_policy;

        switch (flavor) {
        case TASK_POLICY_DARWIN_BG:
                if (category == TASK_POLICY_EXTERNAL) {
                        value = requested.thrp_ext_darwinbg;
                } else {
                        value = requested.thrp_int_darwinbg;
                }
                break;
        case TASK_POLICY_IOPOL:
                if (category == TASK_POLICY_EXTERNAL) {
                        value = proc_tier_to_iopol(requested.thrp_ext_iotier,
                            requested.thrp_ext_iopassive);
                } else {
                        value = proc_tier_to_iopol(requested.thrp_int_iotier,
                            requested.thrp_int_iopassive);
                }
                break;
        case TASK_POLICY_IO:
                if (category == TASK_POLICY_EXTERNAL) {
                        value = requested.thrp_ext_iotier;
                } else {
                        value = requested.thrp_int_iotier;
                }
                break;
        case TASK_POLICY_PASSIVE_IO:
                if (category == TASK_POLICY_EXTERNAL) {
                        value = requested.thrp_ext_iopassive;
                } else {
                        value = requested.thrp_int_iopassive;
                }
                break;
        case TASK_POLICY_QOS:
                assert(category == TASK_POLICY_ATTRIBUTE);
                value = requested.thrp_qos;
                break;
        case TASK_POLICY_QOS_OVERRIDE:
                assert(category == TASK_POLICY_ATTRIBUTE);
                value = requested.thrp_qos_override;
                break;
        case TASK_POLICY_LATENCY_QOS:
                assert(category == TASK_POLICY_ATTRIBUTE);
                value = requested.thrp_latency_qos;
                break;
        case TASK_POLICY_THROUGH_QOS:
                assert(category == TASK_POLICY_ATTRIBUTE);
                value = requested.thrp_through_qos;
                break;
        case TASK_POLICY_QOS_WORKQ_OVERRIDE:
                assert(category == TASK_POLICY_ATTRIBUTE);
                value = requested.thrp_qos_workq_override;
                break;
        case TASK_POLICY_QOS_AND_RELPRIO:
                assert(category == TASK_POLICY_ATTRIBUTE);
                assert(value2 != NULL);
                value = requested.thrp_qos;
                *value2 = requested.thrp_qos_relprio;
                break;
        case TASK_POLICY_QOS_PROMOTE:
                assert(category == TASK_POLICY_ATTRIBUTE);
                value = requested.thrp_qos_promote;
                break;
        case TASK_POLICY_QOS_KEVENT_OVERRIDE:
                assert(category == TASK_POLICY_ATTRIBUTE);
                value = requested.thrp_qos_kevent_override;
                break;
        case TASK_POLICY_QOS_SERVICER_OVERRIDE:
                assert(category == TASK_POLICY_ATTRIBUTE);
                value = requested.thrp_qos_wlsvc_override;
                break;
        case TASK_POLICY_TERMINATED:
                assert(category == TASK_POLICY_ATTRIBUTE);
                value = requested.thrp_terminated;
                break;

        default:
                panic("unknown policy_flavor %d", flavor);
                break;
        }

        return value;
}

/*
 * Gets what is actually in effect, for subsystems which pull policy instead of receive updates.
 *
 * NOTE: This accessor does not take the task or thread lock.
 * Notifications of state updates need to be externally synchronized with state queries.
 * This routine *MUST* remain interrupt safe, as it is potentially invoked
 * within the context of a timer interrupt.
 *
 * TODO: I think we can get away with architecting this such that we don't need to look at the task ever.
 *      Is that a good idea? Maybe it's best to avoid evaluate-all-the-threads updates.
 *      I don't think that cost is worth not having the right answer.
 */
int
proc_get_effective_thread_policy(thread_t thread,
    int      flavor)
{
        int value = 0;

        switch (flavor) {
        case TASK_POLICY_DARWIN_BG:
                /*
                 * This call is used within the timer layer, as well as
                 * prioritizing requests to the graphics system.
                 * It also informs SFI and originator-bg-state.
                 * Returns 1 for background mode, 0 for normal mode
                 */

                value = thread->effective_policy.thep_darwinbg ? 1 : 0;
                break;
        case TASK_POLICY_IO:
                /*
                 * The I/O system calls here to find out what throttling tier to apply to an operation.
                 * Returns THROTTLE_LEVEL_* values
                 */
                value = thread->effective_policy.thep_io_tier;
                if (thread->iotier_override != THROTTLE_LEVEL_NONE) {
                        value = MIN(value, thread->iotier_override);
                }
                break;
        case TASK_POLICY_PASSIVE_IO:
                /*
                 * The I/O system calls here to find out whether an operation should be passive.
                 * (i.e. not cause operations with lower throttle tiers to be throttled)
                 * Returns 1 for passive mode, 0 for normal mode
                 *
                 * If an override is causing IO to go into a lower tier, we also set
                 * the passive bit so that a thread doesn't end up stuck in its own throttle
                 * window when the override goes away.
                 */
                value = thread->effective_policy.thep_io_passive ? 1 : 0;
                if (thread->iotier_override != THROTTLE_LEVEL_NONE &&
                    thread->iotier_override < thread->effective_policy.thep_io_tier) {
                        value = 1;
                }
                break;
        case TASK_POLICY_ALL_SOCKETS_BG:
                /*
                 * do_background_socket() calls this to determine whether
                 * it should change the thread's sockets
                 * Returns 1 for background mode, 0 for normal mode
                 * This consults both thread and task so un-DBGing a thread while the task is BG
                 * doesn't get you out of the network throttle.
                 */
                value = (thread->effective_policy.thep_all_sockets_bg ||
                    thread->task->effective_policy.tep_all_sockets_bg) ? 1 : 0;
                break;
        case TASK_POLICY_NEW_SOCKETS_BG:
                /*
                 * socreate() calls this to determine if it should mark a new socket as background
                 * Returns 1 for background mode, 0 for normal mode
                 */
                value = thread->effective_policy.thep_new_sockets_bg ? 1 : 0;
                break;
        case TASK_POLICY_LATENCY_QOS:
                /*
                 * timer arming calls into here to find out the timer coalescing level
                 * Returns a latency QoS tier (0-6)
                 */
                value = thread->effective_policy.thep_latency_qos;
                break;
        case TASK_POLICY_THROUGH_QOS:
                /*
                 * This value is passed into the urgency callout from the scheduler
                 * to the performance management subsystem.
                 *
                 * Returns a throughput QoS tier (0-6)
                 */
                value = thread->effective_policy.thep_through_qos;
                break;
        case TASK_POLICY_QOS:
                /*
                 * This is communicated to the performance management layer and SFI.
                 *
                 * Returns a QoS policy tier
                 */
                value = thread->effective_policy.thep_qos;
                break;
        default:
                panic("unknown thread policy flavor %d", flavor);
                break;
        }

        return value;
}


/*
 * (integer_t) casts limit the number of bits we can fit here
 * this interface is deprecated and replaced by the _EXT struct ?
 */
static void
proc_get_thread_policy_bitfield(thread_t thread, thread_policy_state_t info)
{
        uint64_t bits = 0;
        struct thread_requested_policy requested = thread->requested_policy;

        bits |= (requested.thrp_int_darwinbg    ? POLICY_REQ_INT_DARWIN_BG  : 0);
        bits |= (requested.thrp_ext_darwinbg    ? POLICY_REQ_EXT_DARWIN_BG  : 0);
        bits |= (requested.thrp_int_iotier      ? (((uint64_t)requested.thrp_int_iotier) << POLICY_REQ_INT_IO_TIER_SHIFT) : 0);
        bits |= (requested.thrp_ext_iotier      ? (((uint64_t)requested.thrp_ext_iotier) << POLICY_REQ_EXT_IO_TIER_SHIFT) : 0);
        bits |= (requested.thrp_int_iopassive   ? POLICY_REQ_INT_PASSIVE_IO : 0);
        bits |= (requested.thrp_ext_iopassive   ? POLICY_REQ_EXT_PASSIVE_IO : 0);

        bits |= (requested.thrp_qos             ? (((uint64_t)requested.thrp_qos) << POLICY_REQ_TH_QOS_SHIFT) : 0);
        bits |= (requested.thrp_qos_override    ? (((uint64_t)requested.thrp_qos_override) << POLICY_REQ_TH_QOS_OVER_SHIFT)   : 0);

        bits |= (requested.thrp_pidbind_bg      ? POLICY_REQ_PIDBIND_BG     : 0);

        bits |= (requested.thrp_latency_qos     ? (((uint64_t)requested.thrp_latency_qos) << POLICY_REQ_BASE_LATENCY_QOS_SHIFT) : 0);
        bits |= (requested.thrp_through_qos     ? (((uint64_t)requested.thrp_through_qos) << POLICY_REQ_BASE_THROUGH_QOS_SHIFT) : 0);

        info->requested = (integer_t) bits;
        bits = 0;

        struct thread_effective_policy effective = thread->effective_policy;

        bits |= (effective.thep_darwinbg        ? POLICY_EFF_DARWIN_BG      : 0);

        bits |= (effective.thep_io_tier         ? (((uint64_t)effective.thep_io_tier) << POLICY_EFF_IO_TIER_SHIFT) : 0);
        bits |= (effective.thep_io_passive      ? POLICY_EFF_IO_PASSIVE     : 0);
        bits |= (effective.thep_all_sockets_bg  ? POLICY_EFF_ALL_SOCKETS_BG : 0);
        bits |= (effective.thep_new_sockets_bg  ? POLICY_EFF_NEW_SOCKETS_BG : 0);

        bits |= (effective.thep_qos             ? (((uint64_t)effective.thep_qos) << POLICY_EFF_TH_QOS_SHIFT) : 0);

        bits |= (effective.thep_latency_qos     ? (((uint64_t)effective.thep_latency_qos) << POLICY_EFF_LATENCY_QOS_SHIFT) : 0);
        bits |= (effective.thep_through_qos     ? (((uint64_t)effective.thep_through_qos) << POLICY_EFF_THROUGH_QOS_SHIFT) : 0);

        info->effective = (integer_t)bits;
        bits = 0;

        info->pending = 0;
}

/*
 * Sneakily trace either the task and thread requested
 * or just the thread requested, depending on if we have enough room.
 * We do have room on LP64. On LP32, we have to split it between two uintptr_t's.
 *
 *                                LP32            LP64
 * threquested_0(thread)          thread[0]       task[0]
 * threquested_1(thread)          thread[1]       thread[0]
 *
 */

uintptr_t
threquested_0(thread_t thread)
{
        static_assert(sizeof(struct thread_requested_policy) == sizeof(uint64_t), "size invariant violated");

        uintptr_t* raw = (uintptr_t*)(void*)&thread->requested_policy;

        return raw[0];
}

uintptr_t
threquested_1(thread_t thread)
{
#if defined __LP64__
        return *(uintptr_t*)&thread->task->requested_policy;
#else
        uintptr_t* raw = (uintptr_t*)(void*)&thread->requested_policy;
        return raw[1];
#endif
}

uintptr_t
theffective_0(thread_t thread)
{
        static_assert(sizeof(struct thread_effective_policy) == sizeof(uint64_t), "size invariant violated");

        uintptr_t* raw = (uintptr_t*)(void*)&thread->effective_policy;
        return raw[0];
}

uintptr_t
theffective_1(thread_t thread)
{
#if defined __LP64__
        return *(uintptr_t*)&thread->task->effective_policy;
#else
        uintptr_t* raw = (uintptr_t*)(void*)&thread->effective_policy;
        return raw[1];
#endif
}


/*
 * Set an override on the thread which is consulted with a
 * higher priority than the task/thread policy. This should
 * only be set for temporary grants until the thread
 * returns to the userspace boundary
 *
 * We use atomic operations to swap in the override, with
 * the assumption that the thread itself can
 * read the override and clear it on return to userspace.
 *
 * No locking is performed, since it is acceptable to see
 * a stale override for one loop through throttle_lowpri_io().
 * However a thread reference must be held on the thread.
 */

void
set_thread_iotier_override(thread_t thread, int policy)
{
        int current_override;

        /* Let most aggressive I/O policy win until user boundary */
        do {
                current_override = thread->iotier_override;

                if (current_override != THROTTLE_LEVEL_NONE) {
                        policy = MIN(current_override, policy);
                }

                if (current_override == policy) {
                        /* no effective change */
                        return;
                }
        } while (!OSCompareAndSwap(current_override, policy, &thread->iotier_override));

        /*
         * Since the thread may be currently throttled,
         * re-evaluate tiers and potentially break out
         * of an msleep
         */
        rethrottle_thread(thread->uthread);
}

/*
 * Userspace synchronization routines (like pthread mutexes, pthread reader-writer locks,
 * semaphores, dispatch_sync) may result in priority inversions where a higher priority
 * (i.e. scheduler priority, I/O tier, QoS tier) is waiting on a resource owned by a lower
 * priority thread. In these cases, we attempt to propagate the priority token, as long
 * as the subsystem informs us of the relationships between the threads. The userspace
 * synchronization subsystem should maintain the information of owner->resource and
 * resource->waiters itself.
 */

/*
 * This helper canonicalizes the resource/resource_type given the current qos_override_mode
 * in effect. Note that wildcards (THREAD_QOS_OVERRIDE_RESOURCE_WILDCARD) may need
 * to be handled specially in the future, but for now it's fine to slam
 * *resource to USER_ADDR_NULL even if it was previously a wildcard.
 */
static void
canonicalize_resource_and_type(user_addr_t *resource, int *resource_type)
{
        if (qos_override_mode == QOS_OVERRIDE_MODE_OVERHANG_PEAK || qos_override_mode == QOS_OVERRIDE_MODE_IGNORE_OVERRIDE) {
                /* Map all input resource/type to a single one */
                *resource = USER_ADDR_NULL;
                *resource_type = THREAD_QOS_OVERRIDE_TYPE_UNKNOWN;
        } else if (qos_override_mode == QOS_OVERRIDE_MODE_FINE_GRAINED_OVERRIDE) {
                /* no transform */
        } else if (qos_override_mode == QOS_OVERRIDE_MODE_FINE_GRAINED_OVERRIDE_BUT_SINGLE_MUTEX_OVERRIDE) {
                /* Map all mutex overrides to a single one, to avoid memory overhead */
                if (*resource_type == THREAD_QOS_OVERRIDE_TYPE_PTHREAD_MUTEX) {
                        *resource = USER_ADDR_NULL;
                }
        }
}

/* This helper routine finds an existing override if known. Locking should be done by caller */
static struct thread_qos_override *
find_qos_override(thread_t thread,
    user_addr_t resource,
    int resource_type)
{
        struct thread_qos_override *override;

        override = thread->overrides;
        while (override) {
                if (override->override_resource == resource &&
                    override->override_resource_type == resource_type) {
                        return override;
                }

                override = override->override_next;
        }

        return NULL;
}

static void
find_and_decrement_qos_override(thread_t       thread,
    user_addr_t    resource,
    int            resource_type,
    boolean_t      reset,
    struct thread_qos_override **free_override_list)
{
        struct thread_qos_override *override, *override_prev;

        override_prev = NULL;
        override = thread->overrides;
        while (override) {
                struct thread_qos_override *override_next = override->override_next;

                if ((THREAD_QOS_OVERRIDE_RESOURCE_WILDCARD == resource || override->override_resource == resource) &&
                    (THREAD_QOS_OVERRIDE_TYPE_WILDCARD == resource_type || override->override_resource_type == resource_type)) {
                        if (reset) {
                                override->override_contended_resource_count = 0;
                        } else {
                                override->override_contended_resource_count--;
                        }

                        if (override->override_contended_resource_count == 0) {
                                if (override_prev == NULL) {
                                        thread->overrides = override_next;
                                } else {
                                        override_prev->override_next = override_next;
                                }

                                /* Add to out-param for later zfree */
                                override->override_next = *free_override_list;
                                *free_override_list = override;
                        } else {
                                override_prev = override;
                        }

                        if (THREAD_QOS_OVERRIDE_RESOURCE_WILDCARD != resource) {
                                return;
                        }
                } else {
                        override_prev = override;
                }

                override = override_next;
        }
}

/* This helper recalculates the current requested override using the policy selected at boot */
static int
calculate_requested_qos_override(thread_t thread)
{
        if (qos_override_mode == QOS_OVERRIDE_MODE_IGNORE_OVERRIDE) {
                return THREAD_QOS_UNSPECIFIED;
        }

        /* iterate over all overrides and calculate MAX */
        struct thread_qos_override *override;
        int qos_override = THREAD_QOS_UNSPECIFIED;

        override = thread->overrides;
        while (override) {
                qos_override = MAX(qos_override, override->override_qos);
                override = override->override_next;
        }

        return qos_override;
}

/*
 * Returns:
 * - 0 on success
 * - EINVAL if some invalid input was passed
 */
static int
proc_thread_qos_add_override_internal(thread_t         thread,
    int              override_qos,
    boolean_t        first_override_for_resource,
    user_addr_t      resource,
    int              resource_type)
{
        struct task_pend_token pend_token = {};
        int rc = 0;

        thread_mtx_lock(thread);

        KERNEL_DEBUG_CONSTANT((IMPORTANCE_CODE(IMP_USYNCH_QOS_OVERRIDE, IMP_USYNCH_ADD_OVERRIDE)) | DBG_FUNC_START,
            thread_tid(thread), override_qos, first_override_for_resource ? 1 : 0, 0, 0);

        DTRACE_BOOST5(qos_add_override_pre, uint64_t, thread_tid(thread),
            uint64_t, thread->requested_policy.thrp_qos,
            uint64_t, thread->effective_policy.thep_qos,
            int, override_qos, boolean_t, first_override_for_resource);

        struct thread_qos_override *override;
        struct thread_qos_override *override_new = NULL;
        int new_qos_override, prev_qos_override;
        int new_effective_qos;

        canonicalize_resource_and_type(&resource, &resource_type);

        override = find_qos_override(thread, resource, resource_type);
        if (first_override_for_resource && !override) {
                /* We need to allocate a new object. Drop the thread lock and
                 * recheck afterwards in case someone else added the override
                 */
                thread_mtx_unlock(thread);
                override_new = zalloc(thread_qos_override_zone);
                thread_mtx_lock(thread);
                override = find_qos_override(thread, resource, resource_type);
        }
        if (first_override_for_resource && override) {
                /* Someone else already allocated while the thread lock was dropped */
                override->override_contended_resource_count++;
        } else if (!override && override_new) {
                override = override_new;
                override_new = NULL;
                override->override_next = thread->overrides;
                /* since first_override_for_resource was TRUE */
                override->override_contended_resource_count = 1;
                override->override_resource = resource;
                override->override_resource_type = resource_type;
                override->override_qos = THREAD_QOS_UNSPECIFIED;
                thread->overrides = override;
        }

        if (override) {
                if (override->override_qos == THREAD_QOS_UNSPECIFIED) {
                        override->override_qos = override_qos;
                } else {
                        override->override_qos = MAX(override->override_qos, override_qos);
                }
        }

        /* Determine how to combine the various overrides into a single current
         * requested override
         */
        new_qos_override = calculate_requested_qos_override(thread);

        prev_qos_override = proc_get_thread_policy_locked(thread,
            TASK_POLICY_ATTRIBUTE, TASK_POLICY_QOS_OVERRIDE, NULL);

        if (new_qos_override != prev_qos_override) {
                proc_set_thread_policy_locked(thread, TASK_POLICY_ATTRIBUTE,
                    TASK_POLICY_QOS_OVERRIDE,
                    new_qos_override, 0, &pend_token);
        }

        new_effective_qos = proc_get_effective_thread_policy(thread, TASK_POLICY_QOS);

        thread_mtx_unlock(thread);

        thread_policy_update_complete_unlocked(thread, &pend_token);

        if (override_new) {
                zfree(thread_qos_override_zone, override_new);
        }

        DTRACE_BOOST4(qos_add_override_post, int, prev_qos_override,
            int, new_qos_override, int, new_effective_qos, int, rc);

        KERNEL_DEBUG_CONSTANT((IMPORTANCE_CODE(IMP_USYNCH_QOS_OVERRIDE, IMP_USYNCH_ADD_OVERRIDE)) | DBG_FUNC_END,
            new_qos_override, resource, resource_type, 0, 0);

        return rc;
}

int
proc_thread_qos_add_override(task_t           task,
    thread_t         thread,
    uint64_t         tid,
    int              override_qos,
    boolean_t        first_override_for_resource,
    user_addr_t      resource,
    int              resource_type)
{
        boolean_t has_thread_reference = FALSE;
        int rc = 0;

        if (thread == THREAD_NULL) {
                thread = task_findtid(task, tid);
                /* returns referenced thread */

                if (thread == THREAD_NULL) {
                        KERNEL_DEBUG_CONSTANT((IMPORTANCE_CODE(IMP_USYNCH_QOS_OVERRIDE, IMP_USYNCH_ADD_OVERRIDE)) | DBG_FUNC_NONE,
                            tid, 0, 0xdead, 0, 0);
                        return ESRCH;
                }
                has_thread_reference = TRUE;
        } else {
                assert(thread->task == task);
        }
        rc = proc_thread_qos_add_override_internal(thread, override_qos,
            first_override_for_resource, resource, resource_type);
        if (has_thread_reference) {
                thread_deallocate(thread);
        }

        return rc;
}

static void
proc_thread_qos_remove_override_internal(thread_t       thread,
    user_addr_t    resource,
    int            resource_type,
    boolean_t      reset)
{
        struct task_pend_token pend_token = {};

        struct thread_qos_override *deferred_free_override_list = NULL;
        int new_qos_override, prev_qos_override, new_effective_qos;

        thread_mtx_lock(thread);

        canonicalize_resource_and_type(&resource, &resource_type);

        find_and_decrement_qos_override(thread, resource, resource_type, reset, &deferred_free_override_list);

        KERNEL_DEBUG_CONSTANT((IMPORTANCE_CODE(IMP_USYNCH_QOS_OVERRIDE, IMP_USYNCH_REMOVE_OVERRIDE)) | DBG_FUNC_START,
            thread_tid(thread), resource, reset, 0, 0);

        DTRACE_BOOST3(qos_remove_override_pre, uint64_t, thread_tid(thread),
            uint64_t, thread->requested_policy.thrp_qos,
            uint64_t, thread->effective_policy.thep_qos);

        /* Determine how to combine the various overrides into a single current requested override */
        new_qos_override = calculate_requested_qos_override(thread);

        spl_t s = splsched();
        thread_lock(thread);

        /*
         * The override chain and therefore the value of the current override is locked with thread mutex,
         * so we can do a get/set without races.  However, the rest of thread policy is locked under the spinlock.
         * This means you can't change the current override from a spinlock-only setter.
         */
        prev_qos_override = thread_get_requested_policy_spinlocked(thread, TASK_POLICY_ATTRIBUTE, TASK_POLICY_QOS_OVERRIDE, NULL);

        if (new_qos_override != prev_qos_override) {
                proc_set_thread_policy_spinlocked(thread, TASK_POLICY_ATTRIBUTE, TASK_POLICY_QOS_OVERRIDE, new_qos_override, 0, &pend_token);
        }

        new_effective_qos = proc_get_effective_thread_policy(thread, TASK_POLICY_QOS);

        thread_unlock(thread);
        splx(s);

        thread_mtx_unlock(thread);

        thread_policy_update_complete_unlocked(thread, &pend_token);

        while (deferred_free_override_list) {
                struct thread_qos_override *override_next = deferred_free_override_list->override_next;

                zfree(thread_qos_override_zone, deferred_free_override_list);
                deferred_free_override_list = override_next;
        }

        DTRACE_BOOST3(qos_remove_override_post, int, prev_qos_override,
            int, new_qos_override, int, new_effective_qos);

        KERNEL_DEBUG_CONSTANT((IMPORTANCE_CODE(IMP_USYNCH_QOS_OVERRIDE, IMP_USYNCH_REMOVE_OVERRIDE)) | DBG_FUNC_END,
            thread_tid(thread), 0, 0, 0, 0);
}

int
proc_thread_qos_remove_override(task_t      task,
    thread_t    thread,
    uint64_t    tid,
    user_addr_t resource,
    int         resource_type)
{
        boolean_t has_thread_reference = FALSE;

        if (thread == THREAD_NULL) {
                thread = task_findtid(task, tid);
                /* returns referenced thread */

                if (thread == THREAD_NULL) {
                        KERNEL_DEBUG_CONSTANT((IMPORTANCE_CODE(IMP_USYNCH_QOS_OVERRIDE, IMP_USYNCH_REMOVE_OVERRIDE)) | DBG_FUNC_NONE,
                            tid, 0, 0xdead, 0, 0);
                        return ESRCH;
                }
                has_thread_reference = TRUE;
        } else {
                assert(task == thread->task);
        }

        proc_thread_qos_remove_override_internal(thread, resource, resource_type, FALSE);

        if (has_thread_reference) {
                thread_deallocate(thread);
        }

        return 0;
}

/* Deallocate before thread termination */
void
proc_thread_qos_deallocate(thread_t thread)
{
        /* This thread must have no more IPC overrides. */
        assert(thread->kevent_overrides == 0);
        assert(thread->requested_policy.thrp_qos_kevent_override == THREAD_QOS_UNSPECIFIED);
        assert(thread->requested_policy.thrp_qos_wlsvc_override == THREAD_QOS_UNSPECIFIED);

        /*
         * Clear out any lingering override objects.
         */
        struct thread_qos_override *override;

        thread_mtx_lock(thread);
        override = thread->overrides;
        thread->overrides = NULL;
        thread->requested_policy.thrp_qos_override = THREAD_QOS_UNSPECIFIED;
        /* We don't need to re-evaluate thread policy here because the thread has already exited */
        thread_mtx_unlock(thread);

        while (override) {
                struct thread_qos_override *override_next = override->override_next;

                zfree(thread_qos_override_zone, override);
                override = override_next;
        }
}

/*
 * Set up the primordial thread's QoS
 */
void
task_set_main_thread_qos(task_t task, thread_t thread)
{
        struct task_pend_token pend_token = {};

        assert(thread->task == task);

        thread_mtx_lock(thread);

        KERNEL_DEBUG_CONSTANT_IST(KDEBUG_TRACE,
            (IMPORTANCE_CODE(IMP_MAIN_THREAD_QOS, 0)) | DBG_FUNC_START,
            thread_tid(thread), threquested_0(thread), threquested_1(thread),
            thread->requested_policy.thrp_qos, 0);

        int primordial_qos = task_compute_main_thread_qos(task);

        proc_set_thread_policy_locked(thread, TASK_POLICY_ATTRIBUTE, TASK_POLICY_QOS_AND_RELPRIO,
            primordial_qos, 0, &pend_token);

        thread_mtx_unlock(thread);

        thread_policy_update_complete_unlocked(thread, &pend_token);

        KERNEL_DEBUG_CONSTANT_IST(KDEBUG_TRACE,
            (IMPORTANCE_CODE(IMP_MAIN_THREAD_QOS, 0)) | DBG_FUNC_END,
            thread_tid(thread), threquested_0(thread), threquested_1(thread),
            primordial_qos, 0);
}

/*
 * KPI for pthread kext
 *
 * Return a good guess at what the initial manager QoS will be
 * Dispatch can override this in userspace if it so chooses
 */
int
task_get_default_manager_qos(task_t task)
{
        int primordial_qos = task_compute_main_thread_qos(task);

        if (primordial_qos == THREAD_QOS_LEGACY) {
                primordial_qos = THREAD_QOS_USER_INITIATED;
        }

        return primordial_qos;
}

/*
 * Check if the kernel promotion on thread has changed
 * and apply it.
 *
 * thread locked on entry and exit
 */
boolean_t
thread_recompute_kernel_promotion_locked(thread_t thread)
{
        boolean_t needs_update = FALSE;
        int kern_promotion_schedpri = thread_get_inheritor_turnstile_sched_priority(thread);

        /*
         * For now just assert that kern_promotion_schedpri <= MAXPRI_PROMOTE.
         * TURNSTILE_KERNEL_PROMOTE adds threads on the waitq already capped to MAXPRI_PROMOTE
         * and propagates the priority through the chain with the same cap, because as of now it does
         * not differenciate on the kernel primitive.
         *
         * If this assumption will change with the adoption of a kernel primitive that does not
         * cap the when adding/propagating,
         * then here is the place to put the generic cap for all kernel primitives
         * (converts the assert to kern_promotion_schedpri = MIN(priority, MAXPRI_PROMOTE))
         */
        assert(kern_promotion_schedpri <= MAXPRI_PROMOTE);

        if (kern_promotion_schedpri != thread->kern_promotion_schedpri) {
                KDBG(MACHDBG_CODE(
                            DBG_MACH_SCHED, MACH_TURNSTILE_KERNEL_CHANGE) | DBG_FUNC_NONE,
                    thread_tid(thread),
                    kern_promotion_schedpri,
                    thread->kern_promotion_schedpri);

                needs_update = TRUE;
                thread->kern_promotion_schedpri = kern_promotion_schedpri;
                thread_recompute_sched_pri(thread, SETPRI_DEFAULT);
        }

        return needs_update;
}

/*
 * Check if the user promotion on thread has changed
 * and apply it.
 *
 * thread locked on entry, might drop the thread lock
 * and reacquire it.
 */
boolean_t
thread_recompute_user_promotion_locked(thread_t thread)
{
        boolean_t needs_update = FALSE;
        struct task_pend_token pend_token = {};
        int user_promotion_basepri = MIN(thread_get_inheritor_turnstile_base_priority(thread), MAXPRI_USER);
        int old_base_pri = thread->base_pri;
        thread_qos_t qos_promotion;

        /* Check if user promotion has changed */
        if (thread->user_promotion_basepri == user_promotion_basepri) {
                return needs_update;
        } else {
                KERNEL_DEBUG_CONSTANT_IST(KDEBUG_TRACE,
                    (TURNSTILE_CODE(TURNSTILE_PRIORITY_OPERATIONS, (THREAD_USER_PROMOTION_CHANGE))) | DBG_FUNC_NONE,
                    thread_tid(thread),
                    user_promotion_basepri,
                    thread->user_promotion_basepri,
                    0, 0);
                KDBG(MACHDBG_CODE(
                            DBG_MACH_SCHED, MACH_TURNSTILE_USER_CHANGE) | DBG_FUNC_NONE,
                    thread_tid(thread),
                    user_promotion_basepri,
                    thread->user_promotion_basepri);
        }

        /* Update the user promotion base pri */
        thread->user_promotion_basepri = user_promotion_basepri;
        pend_token.tpt_force_recompute_pri = 1;

        if (user_promotion_basepri <= MAXPRI_THROTTLE) {
                qos_promotion = THREAD_QOS_UNSPECIFIED;
        } else {
                qos_promotion = thread_user_promotion_qos_for_pri(user_promotion_basepri);
        }

        proc_set_thread_policy_spinlocked(thread, TASK_POLICY_ATTRIBUTE,
            TASK_POLICY_QOS_PROMOTE, qos_promotion, 0, &pend_token);

        if (thread_get_waiting_turnstile(thread) &&
            thread->base_pri != old_base_pri) {
                needs_update = TRUE;
        }

        thread_unlock(thread);

        thread_policy_update_complete_unlocked(thread, &pend_token);

        thread_lock(thread);

        return needs_update;
}

/*
 * Convert the thread user promotion base pri to qos for threads in qos world.
 * For priority above UI qos, the qos would be set to UI.
 */
thread_qos_t
thread_user_promotion_qos_for_pri(int priority)
{
        int qos;
        for (qos = THREAD_QOS_USER_INTERACTIVE; qos > THREAD_QOS_MAINTENANCE; qos--) {
                if (thread_qos_policy_params.qos_pri[qos] <= priority) {
                        return qos;
                }
        }
        return THREAD_QOS_MAINTENANCE;
}

/*
 * Set the thread's QoS Kevent override
 * Owned by the Kevent subsystem
 *
 * May be called with spinlocks held, but not spinlocks
 * that may deadlock against the thread lock, the throttle lock, or the SFI lock.
 *
 * One 'add' must be balanced by one 'drop'.
 * Between 'add' and 'drop', the overide QoS value may be updated with an 'update'.
 * Before the thread is deallocated, there must be 0 remaining overrides.
 */
static void
thread_kevent_override(thread_t    thread,
    uint32_t    qos_override,
    boolean_t   is_new_override)
{
        struct task_pend_token pend_token = {};
        boolean_t needs_update;

        spl_t s = splsched();
        thread_lock(thread);

        uint32_t old_override = thread->requested_policy.thrp_qos_kevent_override;

        assert(qos_override > THREAD_QOS_UNSPECIFIED);
        assert(qos_override < THREAD_QOS_LAST);

        if (is_new_override) {
                if (thread->kevent_overrides++ == 0) {
                        /* This add is the first override for this thread */
                        assert(old_override == THREAD_QOS_UNSPECIFIED);
                } else {
                        /* There are already other overrides in effect for this thread */
                        assert(old_override > THREAD_QOS_UNSPECIFIED);
                }
        } else {
                /* There must be at least one override (the previous add call) in effect */
                assert(thread->kevent_overrides > 0);
                assert(old_override > THREAD_QOS_UNSPECIFIED);
        }

        /*
         * We can't allow lowering if there are several IPC overrides because
         * the caller can't possibly know the whole truth
         */
        if (thread->kevent_overrides == 1) {
                needs_update = qos_override != old_override;
        } else {
                needs_update = qos_override > old_override;
        }

        if (needs_update) {
                proc_set_thread_policy_spinlocked(thread, TASK_POLICY_ATTRIBUTE,
                    TASK_POLICY_QOS_KEVENT_OVERRIDE,
                    qos_override, 0, &pend_token);
                assert(pend_token.tpt_update_sockets == 0);
        }

        thread_unlock(thread);
        splx(s);

        thread_policy_update_complete_unlocked(thread, &pend_token);
}

void
thread_add_kevent_override(thread_t thread, uint32_t qos_override)
{
        thread_kevent_override(thread, qos_override, TRUE);
}

void
thread_update_kevent_override(thread_t thread, uint32_t qos_override)
{
        thread_kevent_override(thread, qos_override, FALSE);
}

void
thread_drop_kevent_override(thread_t thread)
{
        struct task_pend_token pend_token = {};

        spl_t s = splsched();
        thread_lock(thread);

        assert(thread->kevent_overrides > 0);

        if (--thread->kevent_overrides == 0) {
                /*
                 * There are no more overrides for this thread, so we should
                 * clear out the saturated override value
                 */

                proc_set_thread_policy_spinlocked(thread, TASK_POLICY_ATTRIBUTE,
                    TASK_POLICY_QOS_KEVENT_OVERRIDE, THREAD_QOS_UNSPECIFIED,
                    0, &pend_token);
        }

        thread_unlock(thread);
        splx(s);

        thread_policy_update_complete_unlocked(thread, &pend_token);
}

/*
 * Set the thread's QoS Workloop Servicer override
 * Owned by the Kevent subsystem
 *
 * May be called with spinlocks held, but not spinlocks
 * that may deadlock against the thread lock, the throttle lock, or the SFI lock.
 *
 * One 'add' must be balanced by one 'drop'.
 * Between 'add' and 'drop', the overide QoS value may be updated with an 'update'.
 * Before the thread is deallocated, there must be 0 remaining overrides.
 */
static void
thread_servicer_override(thread_t    thread,
    uint32_t    qos_override,
    boolean_t   is_new_override)
{
        struct task_pend_token pend_token = {};

        spl_t s = splsched();
        thread_lock(thread);

        if (is_new_override) {
                assert(!thread->requested_policy.thrp_qos_wlsvc_override);
        } else {
                assert(thread->requested_policy.thrp_qos_wlsvc_override);
        }

        proc_set_thread_policy_spinlocked(thread, TASK_POLICY_ATTRIBUTE,
            TASK_POLICY_QOS_SERVICER_OVERRIDE,
            qos_override, 0, &pend_token);

        thread_unlock(thread);
        splx(s);

        assert(pend_token.tpt_update_sockets == 0);
        thread_policy_update_complete_unlocked(thread, &pend_token);
}

void
thread_add_servicer_override(thread_t thread, uint32_t qos_override)
{
        assert(qos_override > THREAD_QOS_UNSPECIFIED);
        assert(qos_override < THREAD_QOS_LAST);

        thread_servicer_override(thread, qos_override, TRUE);
}

void
thread_update_servicer_override(thread_t thread, uint32_t qos_override)
{
        assert(qos_override > THREAD_QOS_UNSPECIFIED);
        assert(qos_override < THREAD_QOS_LAST);

        thread_servicer_override(thread, qos_override, FALSE);
}

void
thread_drop_servicer_override(thread_t thread)
{
        thread_servicer_override(thread, THREAD_QOS_UNSPECIFIED, FALSE);
}


/* Get current requested qos / relpri, may be called from spinlock context */
thread_qos_t
thread_get_requested_qos(thread_t thread, int *relpri)
{
        int relprio_value = 0;
        thread_qos_t qos;

        qos = proc_get_thread_policy_locked(thread, TASK_POLICY_ATTRIBUTE,
            TASK_POLICY_QOS_AND_RELPRIO, &relprio_value);
        if (relpri) {
                *relpri = -relprio_value;
        }
        return qos;
}

/*
 * This function will promote the thread priority
 * since exec could block other threads calling
 * proc_find on the proc. This boost must be removed
 * via call to thread_clear_exec_promotion.
 *
 * This should be replaced with a generic 'priority inheriting gate' mechanism (24194397)
 */
void
thread_set_exec_promotion(thread_t thread)
{
        spl_t s = splsched();
        thread_lock(thread);

        sched_thread_promote_reason(thread, TH_SFLAG_EXEC_PROMOTED, 0);

        thread_unlock(thread);
        splx(s);
}

/*
 * This function will clear the exec thread
 * promotion set on the thread by thread_set_exec_promotion.
 */
void
thread_clear_exec_promotion(thread_t thread)
{
        spl_t s = splsched();
        thread_lock(thread);

        sched_thread_unpromote_reason(thread, TH_SFLAG_EXEC_PROMOTED, 0);

        thread_unlock(thread);
        splx(s);
}