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

/*
 * Copyright (c) 2013 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 <kern/assert.h>
#include <kern/clock.h>
#include <kern/debug.h>
#include <kern/host.h>
#include <kern/kalloc.h>
#include <kern/kern_types.h>
#include <kern/machine.h>
#include <kern/simple_lock.h>
#include <kern/misc_protos.h>
#include <kern/sched.h>
#include <kern/sched_prim.h>
#include <kern/sfi.h>
#include <kern/timer_call.h>
#include <kern/wait_queue.h>
#include <kern/ledger.h>
#include <pexpert/pexpert.h>

#include <libkern/kernel_mach_header.h>

#include <sys/kdebug.h>

#define SFI_DEBUG 0

#if SFI_DEBUG
#define dprintf(...) kprintf(__VA_ARGS__)
#else
#define dprintf(...) do { } while(0)
#endif

#ifdef MACH_BSD
extern sched_call_t workqueue_get_sched_callback(void);
#endif /* MACH_BSD */

/*
 * SFI (Selective Forced Idle) operates by enabling a global
 * timer on the SFI window interval. When it fires, all processors
 * running a thread that should be SFI-ed are sent an AST.
 * As threads become runnable while in their "off phase", they
 * are placed on a deferred ready queue. When a per-class
 * "on timer" fires, the ready threads for that class are
 * re-enqueued for running. As an optimization to avoid spurious
 * wakeups, the timer may be lazily programmed.
 */

/*
 * The "sfi_lock" simple lock guards access to static configuration
 * parameters (as specified by userspace), dynamic state changes
 * (as updated by the timer event routine), and timer data structures.
 * Since it can be taken with interrupts disabled in some cases, all
 * uses should be taken with interrupts disabled at splsched(). The
 * "sfi_lock" also guards the "sfi_wait_class" field of thread_t, and
 * must only be accessed with it held.
 *
 * When an "on timer" fires, we must deterministically be able to drain
 * the wait queue, since if any threads are added to the queue afterwards,
 * they may never get woken out of SFI wait. So sfi_lock must be
 * taken before the wait queue's own spinlock.
 *
 * The wait queue will take the thread's scheduling lock. We may also take
 * the thread_lock directly to update the "sfi_class" field and determine
 * if the thread should block in the wait queue, but the lock will be
 * released before doing so.
 *
 * The pset lock may also be taken, but not while any other locks are held.
 *
 * splsched ---> sfi_lock ---> wait_queue ---> thread_lock
 *        \  \              \__ thread_lock (*)
 *         \  \__ pset_lock
 *          \
 *           \__ thread_lock
 */

decl_simple_lock_data(static,sfi_lock);
static timer_call_data_t        sfi_timer_call_entry;
volatile boolean_t      sfi_is_enabled;

boolean_t sfi_window_is_set;
uint64_t sfi_window_usecs;
uint64_t sfi_window_interval;
uint64_t sfi_next_off_deadline;

typedef struct {
        sfi_class_id_t  class_id;
        thread_continue_t       class_continuation;
        const char *    class_name;
        const char *    class_ledger_name;
} sfi_class_registration_t;

/*
 * To add a new SFI class:
 *
 * 1) Raise MAX_SFI_CLASS_ID in mach/sfi_class.h
 * 2) Add a #define for it to mach/sfi_class.h. It need not be inserted in order of restrictiveness.
 * 3) Add a call to SFI_CLASS_REGISTER below
 * 4) Augment sfi_thread_classify to categorize threads as early as possible for as restrictive as possible.
 * 5) Modify thermald to use the SFI class
 */

static inline void _sfi_wait_cleanup(sched_call_t callback);

#define SFI_CLASS_REGISTER(class_id, ledger_name)                                       \
extern char compile_time_assert_ ## class_id[SFI_CLASS_ ## class_id < MAX_SFI_CLASS_ID ? 1 : -1];  \
void __attribute__((noinline,noreturn)) SFI_ ## class_id ## _THREAD_IS_WAITING(void *callback, wait_result_t wret __unused); \
void SFI_ ## class_id ## _THREAD_IS_WAITING(void *callback, wait_result_t wret __unused) \
{                                                                                                                                               \
        _sfi_wait_cleanup(callback);                                                                            \
        thread_exception_return();                                                                                      \
}                                                                                                                                               \
                                                                                                                                                \
sfi_class_registration_t SFI_ ## class_id ## _registration __attribute__((section("__DATA,__sfi_class_reg"),used)) = { SFI_CLASS_ ## class_id, SFI_ ## class_id ## _THREAD_IS_WAITING, "SFI_CLASS_" # class_id, "SFI_CLASS_" # ledger_name };

/* SFI_CLASS_UNSPECIFIED not included here */
SFI_CLASS_REGISTER(MAINTENANCE,               MAINTENANCE)
SFI_CLASS_REGISTER(DARWIN_BG,                 DARWIN_BG)
SFI_CLASS_REGISTER(APP_NAP,                   APP_NAP)
SFI_CLASS_REGISTER(MANAGED_FOCAL,             MANAGED)
SFI_CLASS_REGISTER(MANAGED_NONFOCAL,          MANAGED)
SFI_CLASS_REGISTER(UTILITY,                   UTILITY)
SFI_CLASS_REGISTER(DEFAULT_FOCAL,             DEFAULT)
SFI_CLASS_REGISTER(DEFAULT_NONFOCAL,          DEFAULT)
SFI_CLASS_REGISTER(LEGACY_FOCAL,              LEGACY)
SFI_CLASS_REGISTER(LEGACY_NONFOCAL,           LEGACY)
SFI_CLASS_REGISTER(USER_INITIATED_FOCAL,      USER_INITIATED)
SFI_CLASS_REGISTER(USER_INITIATED_NONFOCAL,   USER_INITIATED)
SFI_CLASS_REGISTER(USER_INTERACTIVE_FOCAL,    USER_INTERACTIVE)
SFI_CLASS_REGISTER(USER_INTERACTIVE_NONFOCAL, USER_INTERACTIVE)
SFI_CLASS_REGISTER(KERNEL,                    OPTED_OUT)
SFI_CLASS_REGISTER(OPTED_OUT,                 OPTED_OUT)

struct sfi_class_state {
        uint64_t        off_time_usecs;
        uint64_t        off_time_interval;

        timer_call_data_t       on_timer;
        boolean_t                       on_timer_programmed;

        boolean_t       class_sfi_is_enabled;
        volatile boolean_t      class_in_on_phase;

        struct wait_queue       wait_queue;     /* threads in ready state */
        thread_continue_t       continuation;

        const char *    class_name;
        const char *    class_ledger_name;
};

/* Static configuration performed in sfi_early_init() */
struct sfi_class_state sfi_classes[MAX_SFI_CLASS_ID];

int sfi_enabled_class_count;

static void sfi_timer_global_off(
        timer_call_param_t      param0,
        timer_call_param_t      param1);

static void sfi_timer_per_class_on(
        timer_call_param_t      param0,
        timer_call_param_t      param1);

static sfi_class_registration_t *
sfi_get_registration_data(unsigned long *count)
{
        unsigned long sectlen = 0;
        void *sectdata;

        sectdata = getsectdatafromheader(&_mh_execute_header, "__DATA", "__sfi_class_reg", &sectlen);
        if (sectdata) {

                if (sectlen % sizeof(sfi_class_registration_t) != 0) {
                        /* corrupt data? */
                        panic("__sfi_class_reg section has invalid size %lu", sectlen);
                        __builtin_unreachable();
                }

                *count = sectlen / sizeof(sfi_class_registration_t);
                return (sfi_class_registration_t *)sectdata;
        } else {
                panic("__sfi_class_reg section not found");
                __builtin_unreachable();
        }
}

/* Called early in boot, when kernel is single-threaded */
void sfi_early_init(void)
{
        unsigned long i, count;
        sfi_class_registration_t *registrations;

        registrations = sfi_get_registration_data(&count);
        for (i=0; i < count; i++) {
                sfi_class_id_t class_id = registrations[i].class_id;

                assert(class_id < MAX_SFI_CLASS_ID); /* should be caught at compile-time */
                if (class_id < MAX_SFI_CLASS_ID) {
                        if (sfi_classes[class_id].continuation != NULL) {
                                panic("Duplicate SFI registration for class 0x%x", class_id);
                        }
                        sfi_classes[class_id].class_sfi_is_enabled = FALSE;
                        sfi_classes[class_id].class_in_on_phase = TRUE;
                        sfi_classes[class_id].continuation = registrations[i].class_continuation;
                        sfi_classes[class_id].class_name = registrations[i].class_name;
                        sfi_classes[class_id].class_ledger_name = registrations[i].class_ledger_name;
                }
        }
}

void sfi_init(void)
{
        sfi_class_id_t i;
        kern_return_t kret;

        simple_lock_init(&sfi_lock, 0);
        timer_call_setup(&sfi_timer_call_entry, sfi_timer_global_off, NULL);
        sfi_window_is_set = FALSE;
        sfi_enabled_class_count = 0;
        sfi_is_enabled = FALSE;

        for (i = 0; i < MAX_SFI_CLASS_ID; i++) {
                /* If the class was set up in sfi_early_init(), initialize remaining fields */
                if (sfi_classes[i].continuation) {
                        timer_call_setup(&sfi_classes[i].on_timer, sfi_timer_per_class_on, (void *)(uintptr_t)i);
                        sfi_classes[i].on_timer_programmed = FALSE;
                        
                        kret = wait_queue_init(&sfi_classes[i].wait_queue, SYNC_POLICY_FIFO);
                        assert(kret == KERN_SUCCESS);
                } else {
                        /* The only allowed gap is for SFI_CLASS_UNSPECIFIED */
                        if(i != SFI_CLASS_UNSPECIFIED) {
                                panic("Gap in registered SFI classes");
                        }
                }
        }
}

/* Can be called before sfi_init() by task initialization, but after sfi_early_init() */
sfi_class_id_t
sfi_get_ledger_alias_for_class(sfi_class_id_t class_id)
{
        sfi_class_id_t i;
        const char *ledger_name = NULL;

        ledger_name = sfi_classes[class_id].class_ledger_name;

        /* Find the first class in the registration table with this ledger name */
        if (ledger_name) {
                for (i = SFI_CLASS_UNSPECIFIED + 1; i < class_id; i++) {
                        if (0 == strcmp(sfi_classes[i].class_ledger_name, ledger_name)) {
                                dprintf("sfi_get_ledger_alias_for_class(0x%x) -> 0x%x\n", class_id, i);
                                return i;
                        }
                }

                /* This class is the primary one for the ledger, so there is no alias */
                dprintf("sfi_get_ledger_alias_for_class(0x%x) -> 0x%x\n", class_id, SFI_CLASS_UNSPECIFIED);
                return SFI_CLASS_UNSPECIFIED;
        }

        /* We are permissive on SFI class lookup failures. In sfi_init(), we assert more */
        return SFI_CLASS_UNSPECIFIED;
}

int
sfi_ledger_entry_add(ledger_template_t template, sfi_class_id_t class_id)
{
        const char *ledger_name = NULL;

        ledger_name = sfi_classes[class_id].class_ledger_name;

        dprintf("sfi_ledger_entry_add(%p, 0x%x) -> %s\n", template, class_id, ledger_name);
        return ledger_entry_add(template, ledger_name, "sfi", "MATUs");
}

static void sfi_timer_global_off(
        timer_call_param_t      param0 __unused,
        timer_call_param_t      param1 __unused)
{
        uint64_t        now = mach_absolute_time();
        sfi_class_id_t  i;
        processor_set_t pset, nset;
        processor_t             processor;
        uint32_t                needs_cause_ast_mask = 0x0;
        spl_t           s;

        s = splsched();

        simple_lock(&sfi_lock);
        if (!sfi_is_enabled) {
                /* If SFI has been disabled, let all "on" timers drain naturally */
                KERNEL_DEBUG_CONSTANT(MACHDBG_CODE(DBG_MACH_SFI, SFI_OFF_TIMER) | DBG_FUNC_NONE, 1, 0, 0, 0, 0);

                simple_unlock(&sfi_lock);
                splx(s);
                return;
        }

        KERNEL_DEBUG_CONSTANT(MACHDBG_CODE(DBG_MACH_SFI, SFI_OFF_TIMER) | DBG_FUNC_START, 0, 0, 0, 0, 0);

        /* First set all configured classes into the off state, and program their "on" timer */
        for (i = 0; i < MAX_SFI_CLASS_ID; i++) {
                if (sfi_classes[i].class_sfi_is_enabled) {
                        uint64_t on_timer_deadline;
                        
                        sfi_classes[i].class_in_on_phase = FALSE;
                        sfi_classes[i].on_timer_programmed = TRUE;

                        /* Push out on-timer */
                        on_timer_deadline = now + sfi_classes[i].off_time_interval;
                        timer_call_enter1(&sfi_classes[i].on_timer, NULL, on_timer_deadline, TIMER_CALL_SYS_CRITICAL);
                } else {
                        /* If this class no longer needs SFI, make sure the timer is cancelled */
                        sfi_classes[i].class_in_on_phase = TRUE;
                        if (sfi_classes[i].on_timer_programmed) {
                                sfi_classes[i].on_timer_programmed = FALSE;
                                timer_call_cancel(&sfi_classes[i].on_timer);
                        }
                }
        }
        simple_unlock(&sfi_lock);

        /* Iterate over processors, call cause_ast_check() on ones running a thread that should be in an off phase */
        processor = processor_list;
        pset = processor->processor_set;
        
        pset_lock(pset);
        
        do {
                nset = processor->processor_set;
                if (nset != pset) {
                        pset_unlock(pset);
                        pset = nset;
                        pset_lock(pset);
                }

                /* "processor" and its pset are locked */
                if (processor->state == PROCESSOR_RUNNING) {
                        if (AST_NONE != sfi_processor_needs_ast(processor)) {
                                needs_cause_ast_mask |= (1U << processor->cpu_id);
                        }
                }
        } while ((processor = processor->processor_list) != NULL);

        pset_unlock(pset);

        processor = processor_list;
        do {
                if (needs_cause_ast_mask & (1U << processor->cpu_id)) {
                        if (processor == current_processor())
                                ast_on(AST_SFI);
                        else
                                cause_ast_check(processor);
                }
        } while ((processor = processor->processor_list) != NULL);

        /* Re-arm timer if still enabled */
        simple_lock(&sfi_lock);
        if (sfi_is_enabled) {
                clock_deadline_for_periodic_event(sfi_window_interval,
                                                                                  now,
                                                                                  &sfi_next_off_deadline);
                timer_call_enter1(&sfi_timer_call_entry,
                                                  NULL,
                                                  sfi_next_off_deadline,
                                                  TIMER_CALL_SYS_CRITICAL);
        }

        KERNEL_DEBUG_CONSTANT(MACHDBG_CODE(DBG_MACH_SFI, SFI_OFF_TIMER) | DBG_FUNC_END, 0, 0, 0, 0, 0);

        simple_unlock(&sfi_lock);

        splx(s);
}

static void sfi_timer_per_class_on(
        timer_call_param_t      param0,
        timer_call_param_t      param1 __unused)
{
        sfi_class_id_t sfi_class_id = (sfi_class_id_t)(uintptr_t)param0;
        struct sfi_class_state  *sfi_class = &sfi_classes[sfi_class_id];
        kern_return_t   kret;
        spl_t           s;

        s = splsched();

        simple_lock(&sfi_lock);

        KERNEL_DEBUG_CONSTANT(MACHDBG_CODE(DBG_MACH_SFI, SFI_ON_TIMER) | DBG_FUNC_START, sfi_class_id, 0, 0, 0, 0);

        /*
         * Any threads that may have accumulated in the ready queue for this class should get re-enqueued.
         * Since we have the sfi_lock held and have changed "class_in_on_phase", we expect
         * no new threads to be put on this wait queue until the global "off timer" has fired.
         */
        sfi_class->class_in_on_phase = TRUE;
        kret = wait_queue_wakeup64_all(&sfi_class->wait_queue,
                                                                   CAST_EVENT64_T(sfi_class_id),
                                                                   THREAD_AWAKENED);
        assert(kret == KERN_SUCCESS || kret == KERN_NOT_WAITING);

        KERNEL_DEBUG_CONSTANT(MACHDBG_CODE(DBG_MACH_SFI, SFI_ON_TIMER) | DBG_FUNC_END, 0, 0, 0, 0, 0);

        simple_unlock(&sfi_lock);

        splx(s);
}


kern_return_t sfi_set_window(uint64_t window_usecs)
{
        uint64_t        interval, deadline;
        uint64_t        now = mach_absolute_time();
        sfi_class_id_t  i;
        spl_t           s;
        uint64_t        largest_class_off_interval = 0;

        if (window_usecs < MIN_SFI_WINDOW_USEC)
                window_usecs = MIN_SFI_WINDOW_USEC;

        if (window_usecs > UINT32_MAX)
                return (KERN_INVALID_ARGUMENT);

        KERNEL_DEBUG_CONSTANT(MACHDBG_CODE(DBG_MACH_SFI, SFI_SET_WINDOW), window_usecs, 0, 0, 0, 0);

        clock_interval_to_absolutetime_interval((uint32_t)window_usecs, NSEC_PER_USEC, &interval);
        deadline = now + interval;

        s = splsched();

        simple_lock(&sfi_lock);

        /* Check that we are not bringing in the SFI window smaller than any class */
        for (i = 0; i < MAX_SFI_CLASS_ID; i++) {
                if (sfi_classes[i].class_sfi_is_enabled) {
                        largest_class_off_interval = MAX(largest_class_off_interval, sfi_classes[i].off_time_interval);
                }
        }

        /*
         * Off window must be strictly greater than all enabled classes,
         * otherwise threads would build up on ready queue and never be able to run.
         */
        if (interval <= largest_class_off_interval) {
                simple_unlock(&sfi_lock);
                splx(s);
                return (KERN_INVALID_ARGUMENT);
        }

        /*
         * If the new "off" deadline is further out than the current programmed timer,
         * just let the current one expire (and the new cadence will be established thereafter).
         * If the new "off" deadline is nearer than the current one, bring it in, so we
         * can start the new behavior sooner. Note that this may cause the "off" timer to
         * fire before some of the class "on" timers have fired.
         */
        sfi_window_usecs = window_usecs;
        sfi_window_interval = interval;
        sfi_window_is_set = TRUE;

        if (sfi_enabled_class_count == 0) {
                /* Can't program timer yet */
        } else if (!sfi_is_enabled) {
                sfi_is_enabled = TRUE;
                sfi_next_off_deadline = deadline;
                timer_call_enter1(&sfi_timer_call_entry,
                                                  NULL,
                                                  sfi_next_off_deadline,
                                                  TIMER_CALL_SYS_CRITICAL);             
        } else if (deadline >= sfi_next_off_deadline) {
                sfi_next_off_deadline = deadline;
        } else {
                sfi_next_off_deadline = deadline;
                timer_call_enter1(&sfi_timer_call_entry,
                                                  NULL,
                                                  sfi_next_off_deadline,
                                                  TIMER_CALL_SYS_CRITICAL);             
        }

        simple_unlock(&sfi_lock);
        splx(s);

        return (KERN_SUCCESS);
}

kern_return_t sfi_window_cancel(void)
{
        spl_t           s;

        s = splsched();

        KERNEL_DEBUG_CONSTANT(MACHDBG_CODE(DBG_MACH_SFI, SFI_CANCEL_WINDOW), 0, 0, 0, 0, 0);

        /* Disable globals so that global "off-timer" is not re-armed */
        simple_lock(&sfi_lock);
        sfi_window_is_set = FALSE;
        sfi_window_usecs = 0;
        sfi_window_interval = 0;
        sfi_next_off_deadline = 0;
        sfi_is_enabled = FALSE;
        simple_unlock(&sfi_lock);

        splx(s);

        return (KERN_SUCCESS);
}


kern_return_t sfi_get_window(uint64_t *window_usecs)
{
        spl_t           s;
        uint64_t        off_window_us;

        s = splsched();
        simple_lock(&sfi_lock);

        off_window_us = sfi_window_usecs;

        simple_unlock(&sfi_lock);
        splx(s);

        *window_usecs = off_window_us;

        return (KERN_SUCCESS);
}


kern_return_t sfi_set_class_offtime(sfi_class_id_t class_id, uint64_t offtime_usecs)
{
        uint64_t        interval;
        spl_t           s;
        uint64_t        off_window_interval;

        if (offtime_usecs < MIN_SFI_WINDOW_USEC)
                offtime_usecs = MIN_SFI_WINDOW_USEC;

        if (class_id == SFI_CLASS_UNSPECIFIED || class_id >= MAX_SFI_CLASS_ID)
                return (KERN_INVALID_ARGUMENT);

        if (offtime_usecs > UINT32_MAX)
                return (KERN_INVALID_ARGUMENT);

        KERNEL_DEBUG_CONSTANT(MACHDBG_CODE(DBG_MACH_SFI, SFI_SET_CLASS_OFFTIME), offtime_usecs, class_id, 0, 0, 0);

        clock_interval_to_absolutetime_interval((uint32_t)offtime_usecs, NSEC_PER_USEC, &interval);

        s = splsched();

        simple_lock(&sfi_lock);
        off_window_interval = sfi_window_interval;

        /* Check that we are not bringing in class off-time larger than the SFI window */
        if (off_window_interval && (interval >= off_window_interval)) {
                simple_unlock(&sfi_lock);
                splx(s);
                return (KERN_INVALID_ARGUMENT);
        }

        /* We never re-program the per-class on-timer, but rather just let it expire naturally */
        if (!sfi_classes[class_id].class_sfi_is_enabled) {
                sfi_enabled_class_count++;
        }
        sfi_classes[class_id].off_time_usecs = offtime_usecs;
        sfi_classes[class_id].off_time_interval = interval;
        sfi_classes[class_id].class_sfi_is_enabled = TRUE;

        if (sfi_window_is_set && !sfi_is_enabled) {
                /* start global off timer */
                sfi_is_enabled = TRUE;
                sfi_next_off_deadline = mach_absolute_time() + sfi_window_interval;
                timer_call_enter1(&sfi_timer_call_entry,
                                                  NULL,
                                                  sfi_next_off_deadline,
                                                  TIMER_CALL_SYS_CRITICAL);             
        }

        simple_unlock(&sfi_lock);

        splx(s);

        return (KERN_SUCCESS);
}

kern_return_t sfi_class_offtime_cancel(sfi_class_id_t class_id)
{
        spl_t           s;

        if (class_id == SFI_CLASS_UNSPECIFIED || class_id >= MAX_SFI_CLASS_ID)
                return (KERN_INVALID_ARGUMENT);

        s = splsched();

        KERNEL_DEBUG_CONSTANT(MACHDBG_CODE(DBG_MACH_SFI, SFI_CANCEL_CLASS_OFFTIME), class_id, 0, 0, 0, 0);

        simple_lock(&sfi_lock);

        /* We never re-program the per-class on-timer, but rather just let it expire naturally */
        if (sfi_classes[class_id].class_sfi_is_enabled) {
                sfi_enabled_class_count--;
        }
        sfi_classes[class_id].off_time_usecs = 0;
        sfi_classes[class_id].off_time_interval = 0;
        sfi_classes[class_id].class_sfi_is_enabled = FALSE;

        if (sfi_enabled_class_count == 0) {
                sfi_is_enabled = FALSE;
        }

        simple_unlock(&sfi_lock);

        splx(s);

        return (KERN_SUCCESS);
}

kern_return_t sfi_get_class_offtime(sfi_class_id_t class_id, uint64_t *offtime_usecs)
{
        uint64_t        off_time_us;
        spl_t           s;

        if (class_id == SFI_CLASS_UNSPECIFIED || class_id >= MAX_SFI_CLASS_ID)
                return (0);

        s = splsched();

        simple_lock(&sfi_lock);
        off_time_us = sfi_classes[class_id].off_time_usecs;
        simple_unlock(&sfi_lock);

        splx(s);

        *offtime_usecs = off_time_us;

        return (KERN_SUCCESS);
}

/*
 * sfi_thread_classify and sfi_processor_active_thread_classify perform the critical
 * role of quickly categorizing a thread into its SFI class so that an AST_SFI can be
 * set. As the thread is unwinding to userspace, sfi_ast() performs full locking
 * and determines whether the thread should enter an SFI wait state. Because of
 * the inherent races between the time the AST is set and when it is evaluated,
 * thread classification can be inaccurate (but should always be safe). This is
 * especially the case for sfi_processor_active_thread_classify, which must
 * classify the active thread on a remote processor without taking the thread lock.
 * When in doubt, classification should err on the side of *not* classifying a
 * thread at all, and wait for the thread itself to either hit a quantum expiration
 * or block inside the kernel.
 */

/*
 * Thread must be locked. Ultimately, the real decision to enter
 * SFI wait happens at the AST boundary.
 */
sfi_class_id_t sfi_thread_classify(thread_t thread)
{
        task_t task = thread->task;
        boolean_t is_kernel_thread = (task == kernel_task);
        sched_mode_t thmode = thread->sched_mode;
        int latency_qos = proc_get_effective_task_policy(task, TASK_POLICY_LATENCY_QOS);
        int task_role = proc_get_effective_task_policy(task, TASK_POLICY_ROLE);
        int thread_bg = proc_get_effective_thread_policy(thread, TASK_POLICY_DARWIN_BG);
        int managed_task = proc_get_effective_task_policy(task, TASK_POLICY_SFI_MANAGED);
        int thread_qos = proc_get_effective_thread_policy(thread, TASK_POLICY_QOS);

        /* kernel threads never reach the user AST boundary, and are in a separate world for SFI */
        if (is_kernel_thread) {
                return SFI_CLASS_KERNEL;
        }

        if (thread_qos == THREAD_QOS_MAINTENANCE)
                return SFI_CLASS_MAINTENANCE;

        if (thread_bg || thread_qos == THREAD_QOS_BACKGROUND) {
                return SFI_CLASS_DARWIN_BG;
        }

        if (latency_qos != 0) {
                int latency_qos_wtf = latency_qos - 1;

                if ((latency_qos_wtf >= 4) && (latency_qos_wtf <= 5)) {
                        return SFI_CLASS_APP_NAP;
                }
        }

        /*
         * Realtime and fixed priority threads express their duty cycle constraints
         * via other mechanisms, and are opted out of (most) forms of SFI
         */
        if (thmode == TH_MODE_REALTIME || thmode == TH_MODE_FIXED || task_role == TASK_GRAPHICS_SERVER) {
                return SFI_CLASS_OPTED_OUT;
        }

        /*
         * Threads with unspecified or legacy QOS class can be individually managed
         */
        if (managed_task &&
            (thread_qos == THREAD_QOS_UNSPECIFIED || thread_qos == THREAD_QOS_LEGACY)) {
                if (task_role == TASK_FOREGROUND_APPLICATION || task_role == TASK_CONTROL_APPLICATION)
                        return SFI_CLASS_MANAGED_FOCAL;
                else
                        return SFI_CLASS_MANAGED_NONFOCAL;
        }

        if (thread_qos == THREAD_QOS_UTILITY)
                return SFI_CLASS_UTILITY;

        if (task_role == TASK_FOREGROUND_APPLICATION || task_role == TASK_CONTROL_APPLICATION) {
                switch (thread_qos) {
                case THREAD_QOS_USER_INTERACTIVE:
                        return SFI_CLASS_USER_INTERACTIVE_FOCAL;
                case THREAD_QOS_USER_INITIATED:
                        return SFI_CLASS_USER_INITIATED_FOCAL;
                case THREAD_QOS_LEGACY:
                        return SFI_CLASS_LEGACY_FOCAL;
                default:
                        return SFI_CLASS_DEFAULT_FOCAL;
                }
        } else {
                switch (thread_qos) {
                case THREAD_QOS_USER_INTERACTIVE:
                        return SFI_CLASS_USER_INTERACTIVE_NONFOCAL;
                case THREAD_QOS_USER_INITIATED:
                        return SFI_CLASS_USER_INITIATED_NONFOCAL;
                case THREAD_QOS_LEGACY:
                        return SFI_CLASS_LEGACY_NONFOCAL;
                default:
                        return SFI_CLASS_DEFAULT_NONFOCAL;
                }
        }
}

/*
 * pset must be locked.
 */
sfi_class_id_t sfi_processor_active_thread_classify(processor_t processor)
{
        return processor->current_sfi_class;
}

/*
 * thread must be locked. This is inherently racy, with the intent that
 * at the AST boundary, it will be fully evaluated whether we need to
 * perform an AST wait
 */
ast_t sfi_thread_needs_ast(thread_t thread, sfi_class_id_t *out_class)
{
        sfi_class_id_t class_id;

        class_id = sfi_thread_classify(thread);

        if (out_class)
                *out_class = class_id;

        /* No lock taken, so a stale value may be used. */
        if (!sfi_classes[class_id].class_in_on_phase)
                return AST_SFI;
        else
                return AST_NONE;
}

/*
 * pset must be locked. We take the SFI class for
 * the currently running thread which is cached on
 * the processor_t, and assume it is accurate. In the
 * worst case, the processor will get an IPI and be asked
 * to evaluate if the current running thread at that
 * later point in time should be in an SFI wait.
 */
ast_t sfi_processor_needs_ast(processor_t processor)
{
        sfi_class_id_t class_id;

        class_id = sfi_processor_active_thread_classify(processor);

        /* No lock taken, so a stale value may be used. */
        if (!sfi_classes[class_id].class_in_on_phase)
                return AST_SFI;
        else
                return AST_NONE;

}

static inline void _sfi_wait_cleanup(sched_call_t callback) {
        thread_t self = current_thread();
        sfi_class_id_t current_sfi_wait_class = SFI_CLASS_UNSPECIFIED;
        int64_t sfi_wait_time, sfi_wait_begin = 0;

        spl_t s = splsched();
        thread_lock(self);
        if (callback) {
                thread_sched_call(self, callback);
        }
        sfi_wait_begin = self->wait_sfi_begin_time;
        thread_unlock(self);

        simple_lock(&sfi_lock);
        sfi_wait_time = mach_absolute_time() - sfi_wait_begin;
        current_sfi_wait_class = self->sfi_wait_class;
        self->sfi_wait_class = SFI_CLASS_UNSPECIFIED;
        simple_unlock(&sfi_lock);
        splx(s);
        assert(SFI_CLASS_UNSPECIFIED < current_sfi_wait_class < MAX_SFI_CLASS_ID);
        ledger_credit(self->task->ledger, task_ledgers.sfi_wait_times[current_sfi_wait_class], sfi_wait_time);
}

/*
 * Called at AST context to fully evaluate if the current thread
 * (which is obviously running) should instead block in an SFI wait.
 * We must take the sfi_lock to check whether we are in the "off" period
 * for the class, and if so, block.
 */
void sfi_ast(thread_t thread)
{
        sfi_class_id_t class_id;
        spl_t           s;
        struct sfi_class_state  *sfi_class;
        wait_result_t   waitret;
        boolean_t       did_wait = FALSE;
        uint64_t        tid;
        thread_continue_t       continuation;
        sched_call_t    workq_callback = workqueue_get_sched_callback();
        boolean_t       did_clear_wq = FALSE;

        s = splsched();

        simple_lock(&sfi_lock);

        if (!sfi_is_enabled) {
                /*
                 * SFI is not enabled, or has recently been disabled.
                 * There is no point putting this thread on a deferred ready
                 * queue, even if it were classified as needing it, since
                 * SFI will truly be off at the next global off timer
                 */
                simple_unlock(&sfi_lock);
                splx(s);

                return;
        }

        thread_lock(thread);
        thread->sfi_class = class_id = sfi_thread_classify(thread);
        tid = thread_tid(thread);

        /*
         * Once the sfi_lock is taken and the thread's ->sfi_class field is updated, we
         * are committed to transitioning to whatever state is indicated by "->class_in_on_phase".
         * If another thread tries to call sfi_reevaluate() after this point, it will take the
         * sfi_lock and see the thread in this wait state. If another thread calls
         * sfi_reevaluate() before this point, it would see a runnable thread and at most
         * attempt to send an AST to this processor, but we would have the most accurate
         * classification.
         */

        /* Optimistically clear workq callback while thread is already locked */
        if (workq_callback && (thread->sched_call == workq_callback)) {
                thread_sched_call(thread, NULL);
                did_clear_wq = TRUE;
        }
        thread_unlock(thread);

        sfi_class = &sfi_classes[class_id];
        if (!sfi_class->class_in_on_phase) {
                /* Need to block thread in wait queue */
                KERNEL_DEBUG_CONSTANT(MACHDBG_CODE(DBG_MACH_SFI, SFI_THREAD_DEFER), tid, class_id, 0, 0, 0);

                waitret = wait_queue_assert_wait64(&sfi_class->wait_queue,
                                                   CAST_EVENT64_T(class_id),
                                                   THREAD_INTERRUPTIBLE,
                                                   0);
                if (waitret == THREAD_WAITING) {
                        thread->sfi_wait_class = class_id;
                        did_wait = TRUE;
                        continuation = sfi_class->continuation;
                } else {
                        /* thread may be exiting already, all other errors are unexpected */
                        assert(waitret == THREAD_INTERRUPTED);
                }
        }
        simple_unlock(&sfi_lock);
        
        splx(s);

        if (did_wait) {
                thread_block_reason(continuation, did_clear_wq ? workq_callback : NULL, AST_SFI);
        } else {
                if (did_clear_wq) {
                        s = splsched();
                        thread_lock(thread);
                        thread_sched_call(thread, workq_callback);
                        thread_unlock(thread);
                        splx(s);
                }
        }
}

/* Thread must be unlocked */
void sfi_reevaluate(thread_t thread)
{
        kern_return_t kret;
        spl_t           s;
        sfi_class_id_t class_id, current_class_id;
        ast_t           sfi_ast;

        s = splsched();

        simple_lock(&sfi_lock);

        thread_lock(thread);
        sfi_ast = sfi_thread_needs_ast(thread, &class_id);
        thread->sfi_class = class_id;

        /*
         * This routine chiefly exists to boost threads out of an SFI wait
         * if their classification changes before the "on" timer fires.
         *
         * If we calculate that a thread is in a different ->sfi_wait_class
         * than we think it should be (including no-SFI-wait), we need to
         * correct that:
         *
         * If the thread is in SFI wait and should not be (or should be waiting
         * on a different class' "on" timer), we wake it up. If needed, the
         * thread may immediately block again in the different SFI wait state.
         *
         * If the thread is not in an SFI wait state and it should be, we need
         * to get that thread's attention, possibly by sending an AST to another
         * processor.
         */

        if ((current_class_id = thread->sfi_wait_class) != SFI_CLASS_UNSPECIFIED) {

                thread_unlock(thread); /* not needed anymore */

                assert(current_class_id < MAX_SFI_CLASS_ID);

                if ((sfi_ast == AST_NONE) || (class_id != current_class_id)) {
                        struct sfi_class_state  *sfi_class = &sfi_classes[current_class_id];

                        KERNEL_DEBUG_CONSTANT(MACHDBG_CODE(DBG_MACH_SFI, SFI_WAIT_CANCELED), thread_tid(thread), current_class_id, class_id, 0, 0);

                        kret = wait_queue_wakeup64_thread(&sfi_class->wait_queue,
                                                                                          CAST_EVENT64_T(current_class_id),
                                                                                          thread,
                                                                                          THREAD_AWAKENED);
                        assert(kret == KERN_SUCCESS || kret == KERN_NOT_WAITING);
                }
        } else {
                /*
                 * Thread's current SFI wait class is not set, and because we
                 * have the sfi_lock, it won't get set.
                 */

                if ((thread->state & (TH_RUN | TH_IDLE)) == TH_RUN) {
                        if (sfi_ast != AST_NONE) {
                                if (thread == current_thread())
                                        ast_on(sfi_ast);
                                else {
                                        processor_t             processor = thread->last_processor;
                                        
                                        if (processor != PROCESSOR_NULL &&
                                                processor->state == PROCESSOR_RUNNING &&
                                                processor->active_thread == thread) {
                                                cause_ast_check(processor);
                                        } else {
                                                /*
                                                 * Runnable thread that's not on a CPU currently. When a processor
                                                 * does context switch to it, the AST will get set based on whether
                                                 * the thread is in its "off time".
                                                 */
                                        }
                                }
                        }
                }

                thread_unlock(thread);
        }

        simple_unlock(&sfi_lock);
        splx(s);
}