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

/*
 * Copyright (c) 2000-2010 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,
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 * Please see the License for the specific language governing rights and
 * limitations under the License.
 * 
 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
 */
/*
 * @OSF_COPYRIGHT@
 */
/* 
 * Mach Operating System
 * Copyright (c) 1991,1990,1989,1988,1987 Carnegie Mellon University
 * All Rights Reserved.
 * 
 * Permission to use, copy, modify and distribute this software and its
 * documentation is hereby granted, provided that both the copyright
 * notice and this permission notice appear in all copies of the
 * software, derivative works or modified versions, and any portions
 * thereof, and that both notices appear in supporting documentation.
 * 
 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
 * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR
 * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
 * 
 * Carnegie Mellon requests users of this software to return to
 * 
 *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
 *  School of Computer Science
 *  Carnegie Mellon University
 *  Pittsburgh PA 15213-3890
 * 
 * any improvements or extensions that they make and grant Carnegie Mellon
 * the rights to redistribute these changes.
 */
/*
 */
/*
 *      File:   priority.c
 *      Author: Avadis Tevanian, Jr.
 *      Date:   1986
 *
 *      Priority related scheduler bits.
 */

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

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

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

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

        assert(processor == current_processor());

        SCHED_STATS_QUANTUM_TIMER_EXPIRATION(processor);

        /*
         * We bill CPU time to both the individual thread and its task.
         *
         * Because this balance adjustment could potentially attempt to wake this very
         * thread, we must credit the ledger before taking the thread lock. The ledger
         * pointers are only manipulated by the thread itself at the ast boundary.
         */
        ledger_credit(thread->t_ledger, task_ledgers.cpu_time, thread->quantum_remaining);
        ledger_credit(thread->t_threadledger, thread_ledgers.cpu_time, thread->quantum_remaining);
#ifdef CONFIG_BANK
        if (thread->t_bankledger) {
                ledger_credit(thread->t_bankledger, bank_ledgers.cpu_time,
                                (thread->quantum_remaining - thread->t_deduct_bank_ledger_time));
        }
        thread->t_deduct_bank_ledger_time = 0;
#endif

        ctime = mach_absolute_time();

        thread_lock(thread);

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

#ifdef CONFIG_MACH_APPROXIMATE_TIME
        commpage_update_mach_approximate_time(ctime);
#endif
        /*
         *      Check for fail-safe trip.
         */
        if ((thread->sched_mode == TH_MODE_REALTIME || thread->sched_mode == TH_MODE_FIXED) && 
            !(thread->sched_flags & TH_SFLAG_PROMOTED_MASK) &&
            !(thread->options & TH_OPT_SYSTEM_CRITICAL)) {
                uint64_t new_computation;
  
                new_computation = ctime - thread->computation_epoch;
                new_computation += thread->computation_metered;
                if (new_computation > max_unsafe_computation) {
                        KERNEL_DEBUG_CONSTANT(MACHDBG_CODE(DBG_MACH_SCHED, MACH_FAILSAFE)|DBG_FUNC_NONE,
                                        (uintptr_t)thread->sched_pri, (uintptr_t)thread->sched_mode, 0, 0, 0);

                        thread->safe_release = ctime + sched_safe_duration;

                        sched_thread_mode_demote(thread, TH_SFLAG_FAILSAFE);
                }
        }

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

        SCHED(quantum_expire)(thread);
        
        processor->current_pri = thread->sched_pri;
        processor->current_thmode = thread->sched_mode;

        /*
         *      This quantum is up, give this thread another.
         */
        if (first_timeslice(processor))
                processor->timeslice--;

        thread_quantum_init(thread);

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

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

        processor->quantum_end = ctime + thread->quantum_remaining;
        timer_call_enter1(&processor->quantum_timer, thread,
            processor->quantum_end, TIMER_CALL_SYS_CRITICAL | TIMER_CALL_LOCAL);

        /*
         *      Context switch check.
         */
        if ((preempt = csw_check(processor, AST_QUANTUM)) != AST_NONE)
                ast_on(preempt);

        thread_unlock(thread);

#if defined(CONFIG_SCHED_TIMESHARE_CORE)
        sched_traditional_consider_maintenance(ctime);
#endif /* CONFIG_SCHED_TIMESHARE_CORE */        
}

/*
 *      sched_set_thread_base_priority:
 *
 *      Set the base priority of the thread
 *      and reset its scheduled priority.
 *
 *      Called with the thread locked.
 */
void
sched_set_thread_base_priority(thread_t thread, int priority)
{
        thread->priority = priority;
        SCHED(compute_priority)(thread, FALSE);
}


#if defined(CONFIG_SCHED_TIMESHARE_CORE)

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

void
lightweight_update_priority(thread_t thread)
{
        if (thread->sched_mode == TH_MODE_TIMESHARE) {
                register uint32_t       delta;
                
                thread_timer_delta(thread, delta);
                
                /*
                 *      Accumulate timesharing usage only
                 *      during contention for processor
                 *      resources.
                 */
                if (thread->pri_shift < INT8_MAX)
                        thread->sched_usage += delta;
                
                thread->cpu_delta += delta;
                
                /*
                 * Adjust the scheduled priority if
                 * the thread has not been promoted
                 * and is not depressed.
                 */
                if (    !(thread->sched_flags & TH_SFLAG_PROMOTED_MASK) &&
                        !(thread->sched_flags & TH_SFLAG_DEPRESSED_MASK)                )
                        compute_my_priority(thread);
        }       
}

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

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

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


static int do_priority_computation(thread_t th) {                                                                                                                       
        register int priority = th->priority            /* start with base priority */          
            - (th->sched_usage >> th->pri_shift);                               
        if (priority < MINPRI_USER)                                                                                     
                priority = MINPRI_USER;                                                                                 
        else                                                                                                                            
        if (priority > MAXPRI_KERNEL)                                                                                   
                priority = MAXPRI_KERNEL;       

        return priority;                                                                                
}


/*
 *      compute_priority:
 *
 *      Reset the scheduled priority of the thread
 *      according to its base priority if the
 *      thread has not been promoted or depressed.
 *
 *      Called with the thread locked.
 */
void
compute_priority(
        register thread_t       thread,
        boolean_t                       override_depress)
{
        register int            priority;

        if (thread->sched_mode == TH_MODE_TIMESHARE)
                priority = do_priority_computation(thread);
        else
                priority = thread->priority;

        if ((!(thread->sched_flags & TH_SFLAG_PROMOTED_MASK) || (priority > thread->sched_pri)) &&
                (!(thread->sched_flags & TH_SFLAG_DEPRESSED_MASK) || override_depress)) {
                set_sched_pri(thread, priority);
        }
}

/*
 *      compute_my_priority:
 *
 *      Reset the scheduled priority for
 *      a timesharing thread.
 *
 *      Only for use on the current thread
 *      if timesharing and not depressed.
 *
 *      Called with the thread locked.
 */
void
compute_my_priority(
        register thread_t       thread)
{
        register int            priority;

        priority = do_priority_computation(thread);
        assert(thread->runq == PROCESSOR_NULL);

        if (priority != thread->sched_pri) {
                KERNEL_DEBUG_CONSTANT(MACHDBG_CODE(DBG_MACH_SCHED, MACH_SCHED_DECAY_PRIORITY)|DBG_FUNC_NONE,
                             (uintptr_t)thread_tid(thread),
                             thread->priority,
                             thread->sched_pri,
                             priority,
                             0);
        }
        thread->sched_pri = priority;
}

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

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

        ticks = sched_tick - thread->sched_stamp;
        assert(ticks != 0);
        thread->sched_stamp += ticks;
        if (sched_use_combined_fgbg_decay)
                thread->pri_shift = sched_combined_fgbg_pri_shift;
        else if (thread->sched_flags & TH_SFLAG_THROTTLED)
                thread->pri_shift = sched_background_pri_shift;
        else
                thread->pri_shift = sched_pri_shift;

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

        /*
         *      Gather cpu usage data.
         */
        thread_timer_delta(thread, delta);
        if (ticks < SCHED_DECAY_TICKS) {
                register struct shift_data      *shiftp;

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

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

                shiftp = &sched_decay_shifts[ticks];
                if (shiftp->shift2 > 0) {
                    thread->cpu_usage =
                                                (thread->cpu_usage >> shiftp->shift1) +
                                                (thread->cpu_usage >> shiftp->shift2);
                    thread->sched_usage =
                                                (thread->sched_usage >> shiftp->shift1) +
                                                (thread->sched_usage >> shiftp->shift2);
                }
                else {
                    thread->cpu_usage =
                                                (thread->cpu_usage >> shiftp->shift1) -
                                                (thread->cpu_usage >> -(shiftp->shift2));
                    thread->sched_usage =
                                                (thread->sched_usage >> shiftp->shift1) -
                                                (thread->sched_usage >> -(shiftp->shift2));
                }
        }
        else {
                thread->cpu_usage = thread->cpu_delta = 0;
                thread->sched_usage = 0;
        }

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


        /*
         *      Recompute scheduled priority if appropriate.
         */
        if (    (thread->sched_mode == TH_MODE_TIMESHARE)       &&
                        !(thread->sched_flags & TH_SFLAG_PROMOTED_MASK) &&
                        !(thread->sched_flags & TH_SFLAG_DEPRESSED_MASK)                ) {
                register int            new_pri;

                new_pri = do_priority_computation(thread);
                if (new_pri != thread->sched_pri) {
                        boolean_t               removed = thread_run_queue_remove(thread);

#if 0
                        if (sched_use_combined_fgbg_decay && ((thread)->task->max_priority > MAXPRI_THROTTLE) && (new_pri == MAXPRI_THROTTLE)) {
                                /* with the alternate (new) algorithm, would we have decayed this far? */
                                int alt_pri = thread->priority - (thread->sched_usage >> sched_pri_shift);
                                if ((alt_pri > new_pri) && (sched_background_count > 0)) {
                                        printf("thread %p would have decayed to only %d instead of %d\n", thread, alt_pri, new_pri);
                                }
                        }
#endif

                        KERNEL_DEBUG_CONSTANT(MACHDBG_CODE(DBG_MACH_SCHED, MACH_SCHED_DECAY_PRIORITY)|DBG_FUNC_NONE,
                                                          (uintptr_t)thread_tid(thread),
                                                          thread->priority,
                                                          thread->sched_pri,
                                                          new_pri,
                                                          0);
                        thread->sched_pri = new_pri;

                        if (removed)
                                thread_setrun(thread, SCHED_TAILQ);
                }
        }
        
        return;
}

#endif /* CONFIG_SCHED_TIMESHARE_CORE */

#if MACH_ASSERT
/* sched_mode == TH_MODE_TIMESHARE controls whether a thread has a timeshare count when it has a run count */

void sched_share_incr(thread_t thread) {
        assert((thread->state & (TH_RUN|TH_IDLE)) == TH_RUN);
        assert(thread->sched_mode == TH_MODE_TIMESHARE);
        assert(thread->SHARE_COUNT == 0);
        thread->SHARE_COUNT++;
        (void)hw_atomic_add(&sched_share_count, 1);
}

void sched_share_decr(thread_t thread) {
        assert((thread->state & (TH_RUN|TH_IDLE)) != TH_RUN || thread->sched_mode != TH_MODE_TIMESHARE);
        assert(thread->SHARE_COUNT == 1);
        (void)hw_atomic_sub(&sched_share_count, 1);
        thread->SHARE_COUNT--;
}

/* TH_SFLAG_THROTTLED controls whether a thread has a background count when it has a run count and a share count */

void sched_background_incr(thread_t thread) {
        assert((thread->state & (TH_RUN|TH_IDLE)) == TH_RUN);
        assert(thread->sched_mode == TH_MODE_TIMESHARE);
        assert((thread->sched_flags & TH_SFLAG_THROTTLED) == TH_SFLAG_THROTTLED);

        assert(thread->BG_COUNT == 0);
        thread->BG_COUNT++;
        int val = hw_atomic_add(&sched_background_count, 1);
        assert(val >= 0);

        /* Always do the background change while holding a share count */
        assert(thread->SHARE_COUNT == 1);
}

void sched_background_decr(thread_t thread) {
        if ((thread->state & (TH_RUN|TH_IDLE)) == TH_RUN && thread->sched_mode == TH_MODE_TIMESHARE)
                assert((thread->sched_flags & TH_SFLAG_THROTTLED) != TH_SFLAG_THROTTLED);
        assert(thread->BG_COUNT == 1);
        int val = hw_atomic_sub(&sched_background_count, 1);
        thread->BG_COUNT--;
        assert(val >= 0);
        assert(thread->BG_COUNT == 0);

        /* Always do the background change while holding a share count */
        assert(thread->SHARE_COUNT == 1);
}


void
assert_thread_sched_count(thread_t thread) {
        /* Only 0 or 1 are acceptable values */
        assert(thread->BG_COUNT    == 0 || thread->BG_COUNT    == 1);
        assert(thread->SHARE_COUNT == 0 || thread->SHARE_COUNT == 1);

        /* BG is only allowed when you already have a share count */
        if (thread->BG_COUNT == 1)
                assert(thread->SHARE_COUNT == 1);
        if (thread->SHARE_COUNT == 0)
                assert(thread->BG_COUNT == 0);

        if ((thread->state & (TH_RUN|TH_IDLE)) != TH_RUN ||
            (thread->sched_mode != TH_MODE_TIMESHARE))
                assert(thread->SHARE_COUNT == 0);

        if ((thread->state & (TH_RUN|TH_IDLE)) == TH_RUN &&
            (thread->sched_mode == TH_MODE_TIMESHARE))
                assert(thread->SHARE_COUNT == 1);

        if ((thread->state & (TH_RUN|TH_IDLE)) != TH_RUN ||
            (thread->sched_mode != TH_MODE_TIMESHARE)    ||
            !(thread->sched_flags & TH_SFLAG_THROTTLED))
                assert(thread->BG_COUNT == 0);

        if ((thread->state & (TH_RUN|TH_IDLE)) == TH_RUN &&
            (thread->sched_mode == TH_MODE_TIMESHARE)    &&
            (thread->sched_flags & TH_SFLAG_THROTTLED))
                assert(thread->BG_COUNT == 1);
}

#endif /* MACH_ASSERT */

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

        sched_mode_t old_mode = thread->sched_mode;

        thread->sched_mode = new_mode;

        switch (new_mode) {
                case TH_MODE_FIXED:
                case TH_MODE_REALTIME:
                        if (old_mode == TH_MODE_TIMESHARE) {
                                if ((thread->state & (TH_RUN|TH_IDLE)) == TH_RUN) {
                                        if (thread->sched_flags & TH_SFLAG_THROTTLED)
                                                sched_background_decr(thread);

                                        sched_share_decr(thread);
                                }
                        }
                        break;

                case TH_MODE_TIMESHARE:
                        if (old_mode != TH_MODE_TIMESHARE) {
                                if ((thread->state & (TH_RUN|TH_IDLE)) == TH_RUN) {
                                        sched_share_incr(thread);

                                        if (thread->sched_flags & TH_SFLAG_THROTTLED)
                                                sched_background_incr(thread);
                                }
                        }
                        break;

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

        assert_thread_sched_count(thread);
}

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

        if (thread->policy_reset)
                return;

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

        assert(thread->saved_mode == TH_MODE_NONE);

        boolean_t removed = thread_run_queue_remove(thread);

        if (thread->sched_mode == TH_MODE_REALTIME)
                thread->priority = DEPRESSPRI;

        thread->sched_flags |= reason;

        thread->saved_mode = thread->sched_mode;

        sched_set_thread_mode(thread, TH_MODE_TIMESHARE);

        if (removed)
                thread_setrun(thread, SCHED_TAILQ);

        assert_thread_sched_count(thread);
}

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

        assert_thread_sched_count(thread);

        thread->sched_flags &= ~reason;

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

        boolean_t removed = thread_run_queue_remove(thread);

        sched_set_thread_mode(thread, thread->saved_mode);

        thread->saved_mode = TH_MODE_NONE;

        if (thread->sched_mode == TH_MODE_REALTIME) {
                thread->priority = BASEPRI_RTQUEUES;
        }

        SCHED(compute_priority)(thread, FALSE);

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

/*
 * Set the thread to be categorized as 'background'
 * Called with thread mutex and thread lock held
 *
 * TODO: Eventually, 'background' should be a true sched_mode.
 */
void
sched_set_thread_throttled(thread_t thread, boolean_t wants_throttle)
{
        if (thread->policy_reset)
                return;

        assert(((thread->sched_flags & TH_SFLAG_THROTTLED) ? TRUE : FALSE) != wants_throttle);

        assert_thread_sched_count(thread);

        /*
         * 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.
         */

        if (wants_throttle) {
                thread->sched_flags |= TH_SFLAG_THROTTLED;
                if ((thread->state & (TH_RUN|TH_IDLE)) == TH_RUN && thread->sched_mode == TH_MODE_TIMESHARE) {
                        sched_background_incr(thread);
                }

                assert_thread_sched_count(thread);

        } else {
                thread->sched_flags &= ~TH_SFLAG_THROTTLED;
                if ((thread->state & (TH_RUN|TH_IDLE)) == TH_RUN && thread->sched_mode == TH_MODE_TIMESHARE) {
                        sched_background_decr(thread);
                }

                assert_thread_sched_count(thread);

        }

        assert_thread_sched_count(thread);
}