- Copy stable/10@285827 to releng/10.2 in preparation for 10.2-RC1

[FreeBSD/releng/10.2.git] / sys / kern / sched_4bsd.c

/*-
 * Copyright (c) 1982, 1986, 1990, 1991, 1993
 *      The Regents of the University of California.  All rights reserved.
 * (c) UNIX System Laboratories, Inc.
 * All or some portions of this file are derived from material licensed
 * to the University of California by American Telephone and Telegraph
 * Co. or Unix System Laboratories, Inc. and are reproduced herein with
 * the permission of UNIX System Laboratories, Inc.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");

#include "opt_hwpmc_hooks.h"
#include "opt_sched.h"
#include "opt_kdtrace.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/cpuset.h>
#include <sys/kernel.h>
#include <sys/ktr.h>
#include <sys/lock.h>
#include <sys/kthread.h>
#include <sys/mutex.h>
#include <sys/proc.h>
#include <sys/resourcevar.h>
#include <sys/sched.h>
#include <sys/sdt.h>
#include <sys/smp.h>
#include <sys/sysctl.h>
#include <sys/sx.h>
#include <sys/turnstile.h>
#include <sys/umtx.h>
#include <machine/pcb.h>
#include <machine/smp.h>

#ifdef HWPMC_HOOKS
#include <sys/pmckern.h>
#endif

#ifdef KDTRACE_HOOKS
#include <sys/dtrace_bsd.h>
int                             dtrace_vtime_active;
dtrace_vtime_switch_func_t      dtrace_vtime_switch_func;
#endif

/*
 * INVERSE_ESTCPU_WEIGHT is only suitable for statclock() frequencies in
 * the range 100-256 Hz (approximately).
 */
#define ESTCPULIM(e) \
    min((e), INVERSE_ESTCPU_WEIGHT * (NICE_WEIGHT * (PRIO_MAX - PRIO_MIN) - \
    RQ_PPQ) + INVERSE_ESTCPU_WEIGHT - 1)
#ifdef SMP
#define INVERSE_ESTCPU_WEIGHT   (8 * smp_cpus)
#else
#define INVERSE_ESTCPU_WEIGHT   8       /* 1 / (priorities per estcpu level). */
#endif
#define NICE_WEIGHT             1       /* Priorities per nice level. */

#define TS_NAME_LEN (MAXCOMLEN + sizeof(" td ") + sizeof(__XSTRING(UINT_MAX)))

/*
 * The schedulable entity that runs a context.
 * This is  an extension to the thread structure and is tailored to
 * the requirements of this scheduler
 */
struct td_sched {
        fixpt_t         ts_pctcpu;      /* (j) %cpu during p_swtime. */
        int             ts_cpticks;     /* (j) Ticks of cpu time. */
        int             ts_slptime;     /* (j) Seconds !RUNNING. */
        int             ts_slice;       /* Remaining part of time slice. */
        int             ts_flags;
        struct runq     *ts_runq;       /* runq the thread is currently on */
#ifdef KTR
        char            ts_name[TS_NAME_LEN];
#endif
};

/* flags kept in td_flags */
#define TDF_DIDRUN      TDF_SCHED0      /* thread actually ran. */
#define TDF_BOUND       TDF_SCHED1      /* Bound to one CPU. */
#define TDF_SLICEEND    TDF_SCHED2      /* Thread time slice is over. */

/* flags kept in ts_flags */
#define TSF_AFFINITY    0x0001          /* Has a non-"full" CPU set. */

#define SKE_RUNQ_PCPU(ts)                                               \
    ((ts)->ts_runq != 0 && (ts)->ts_runq != &runq)

#define THREAD_CAN_SCHED(td, cpu)       \
    CPU_ISSET((cpu), &(td)->td_cpuset->cs_mask)

static struct td_sched td_sched0;
struct mtx sched_lock;

static int      realstathz = 127; /* stathz is sometimes 0 and run off of hz. */
static int      sched_tdcnt;    /* Total runnable threads in the system. */
static int      sched_slice = 12; /* Thread run time before rescheduling. */

static void     setup_runqs(void);
static void     schedcpu(void);
static void     schedcpu_thread(void);
static void     sched_priority(struct thread *td, u_char prio);
static void     sched_setup(void *dummy);
static void     maybe_resched(struct thread *td);
static void     updatepri(struct thread *td);
static void     resetpriority(struct thread *td);
static void     resetpriority_thread(struct thread *td);
#ifdef SMP
static int      sched_pickcpu(struct thread *td);
static int      forward_wakeup(int cpunum);
static void     kick_other_cpu(int pri, int cpuid);
#endif

static struct kproc_desc sched_kp = {
        "schedcpu",
        schedcpu_thread,
        NULL
};
SYSINIT(schedcpu, SI_SUB_LAST, SI_ORDER_FIRST, kproc_start,
    &sched_kp);
SYSINIT(sched_setup, SI_SUB_RUN_QUEUE, SI_ORDER_FIRST, sched_setup, NULL);

static void sched_initticks(void *dummy);
SYSINIT(sched_initticks, SI_SUB_CLOCKS, SI_ORDER_THIRD, sched_initticks,
    NULL);

/*
 * Global run queue.
 */
static struct runq runq;

#ifdef SMP
/*
 * Per-CPU run queues
 */
static struct runq runq_pcpu[MAXCPU];
long runq_length[MAXCPU];

static cpuset_t idle_cpus_mask;
#endif

struct pcpuidlestat {
        u_int idlecalls;
        u_int oldidlecalls;
};
static DPCPU_DEFINE(struct pcpuidlestat, idlestat);

static void
setup_runqs(void)
{
#ifdef SMP
        int i;

        for (i = 0; i < MAXCPU; ++i)
                runq_init(&runq_pcpu[i]);
#endif

        runq_init(&runq);
}

static int
sysctl_kern_quantum(SYSCTL_HANDLER_ARGS)
{
        int error, new_val, period;

        period = 1000000 / realstathz;
        new_val = period * sched_slice;
        error = sysctl_handle_int(oidp, &new_val, 0, req);
        if (error != 0 || req->newptr == NULL)
                return (error);
        if (new_val <= 0)
                return (EINVAL);
        sched_slice = imax(1, (new_val + period / 2) / period);
        hogticks = imax(1, (2 * hz * sched_slice + realstathz / 2) /
            realstathz);
        return (0);
}

SYSCTL_NODE(_kern, OID_AUTO, sched, CTLFLAG_RD, 0, "Scheduler");

SYSCTL_STRING(_kern_sched, OID_AUTO, name, CTLFLAG_RD, "4BSD", 0,
    "Scheduler name");
SYSCTL_PROC(_kern_sched, OID_AUTO, quantum, CTLTYPE_INT | CTLFLAG_RW,
    NULL, 0, sysctl_kern_quantum, "I",
    "Quantum for timeshare threads in microseconds");
SYSCTL_INT(_kern_sched, OID_AUTO, slice, CTLFLAG_RW, &sched_slice, 0,
    "Quantum for timeshare threads in stathz ticks");
#ifdef SMP
/* Enable forwarding of wakeups to all other cpus */
static SYSCTL_NODE(_kern_sched, OID_AUTO, ipiwakeup, CTLFLAG_RD, NULL,
    "Kernel SMP");

static int runq_fuzz = 1;
SYSCTL_INT(_kern_sched, OID_AUTO, runq_fuzz, CTLFLAG_RW, &runq_fuzz, 0, "");

static int forward_wakeup_enabled = 1;
SYSCTL_INT(_kern_sched_ipiwakeup, OID_AUTO, enabled, CTLFLAG_RW,
           &forward_wakeup_enabled, 0,
           "Forwarding of wakeup to idle CPUs");

static int forward_wakeups_requested = 0;
SYSCTL_INT(_kern_sched_ipiwakeup, OID_AUTO, requested, CTLFLAG_RD,
           &forward_wakeups_requested, 0,
           "Requests for Forwarding of wakeup to idle CPUs");

static int forward_wakeups_delivered = 0;
SYSCTL_INT(_kern_sched_ipiwakeup, OID_AUTO, delivered, CTLFLAG_RD,
           &forward_wakeups_delivered, 0,
           "Completed Forwarding of wakeup to idle CPUs");

static int forward_wakeup_use_mask = 1;
SYSCTL_INT(_kern_sched_ipiwakeup, OID_AUTO, usemask, CTLFLAG_RW,
           &forward_wakeup_use_mask, 0,
           "Use the mask of idle cpus");

static int forward_wakeup_use_loop = 0;
SYSCTL_INT(_kern_sched_ipiwakeup, OID_AUTO, useloop, CTLFLAG_RW,
           &forward_wakeup_use_loop, 0,
           "Use a loop to find idle cpus");

#endif
#if 0
static int sched_followon = 0;
SYSCTL_INT(_kern_sched, OID_AUTO, followon, CTLFLAG_RW,
           &sched_followon, 0,
           "allow threads to share a quantum");
#endif

SDT_PROVIDER_DEFINE(sched);

SDT_PROBE_DEFINE3(sched, , , change__pri, "struct thread *", 
    "struct proc *", "uint8_t");
SDT_PROBE_DEFINE3(sched, , , dequeue, "struct thread *", 
    "struct proc *", "void *");
SDT_PROBE_DEFINE4(sched, , , enqueue, "struct thread *", 
    "struct proc *", "void *", "int");
SDT_PROBE_DEFINE4(sched, , , lend__pri, "struct thread *", 
    "struct proc *", "uint8_t", "struct thread *");
SDT_PROBE_DEFINE2(sched, , , load__change, "int", "int");
SDT_PROBE_DEFINE2(sched, , , off__cpu, "struct thread *",
    "struct proc *");
SDT_PROBE_DEFINE(sched, , , on__cpu);
SDT_PROBE_DEFINE(sched, , , remain__cpu);
SDT_PROBE_DEFINE2(sched, , , surrender, "struct thread *",
    "struct proc *");

static __inline void
sched_load_add(void)
{

        sched_tdcnt++;
        KTR_COUNTER0(KTR_SCHED, "load", "global load", sched_tdcnt);
        SDT_PROBE2(sched, , , load__change, NOCPU, sched_tdcnt);
}

static __inline void
sched_load_rem(void)
{

        sched_tdcnt--;
        KTR_COUNTER0(KTR_SCHED, "load", "global load", sched_tdcnt);
        SDT_PROBE2(sched, , , load__change, NOCPU, sched_tdcnt);
}
/*
 * Arrange to reschedule if necessary, taking the priorities and
 * schedulers into account.
 */
static void
maybe_resched(struct thread *td)
{

        THREAD_LOCK_ASSERT(td, MA_OWNED);
        if (td->td_priority < curthread->td_priority)
                curthread->td_flags |= TDF_NEEDRESCHED;
}

/*
 * This function is called when a thread is about to be put on run queue
 * because it has been made runnable or its priority has been adjusted.  It
 * determines if the new thread should be immediately preempted to.  If so,
 * it switches to it and eventually returns true.  If not, it returns false
 * so that the caller may place the thread on an appropriate run queue.
 */
int
maybe_preempt(struct thread *td)
{
#ifdef PREEMPTION
        struct thread *ctd;
        int cpri, pri;

        /*
         * The new thread should not preempt the current thread if any of the
         * following conditions are true:
         *
         *  - The kernel is in the throes of crashing (panicstr).
         *  - The current thread has a higher (numerically lower) or
         *    equivalent priority.  Note that this prevents curthread from
         *    trying to preempt to itself.
         *  - It is too early in the boot for context switches (cold is set).
         *  - The current thread has an inhibitor set or is in the process of
         *    exiting.  In this case, the current thread is about to switch
         *    out anyways, so there's no point in preempting.  If we did,
         *    the current thread would not be properly resumed as well, so
         *    just avoid that whole landmine.
         *  - If the new thread's priority is not a realtime priority and
         *    the current thread's priority is not an idle priority and
         *    FULL_PREEMPTION is disabled.
         *
         * If all of these conditions are false, but the current thread is in
         * a nested critical section, then we have to defer the preemption
         * until we exit the critical section.  Otherwise, switch immediately
         * to the new thread.
         */
        ctd = curthread;
        THREAD_LOCK_ASSERT(td, MA_OWNED);
        KASSERT((td->td_inhibitors == 0),
                        ("maybe_preempt: trying to run inhibited thread"));
        pri = td->td_priority;
        cpri = ctd->td_priority;
        if (panicstr != NULL || pri >= cpri || cold /* || dumping */ ||
            TD_IS_INHIBITED(ctd))
                return (0);
#ifndef FULL_PREEMPTION
        if (pri > PRI_MAX_ITHD && cpri < PRI_MIN_IDLE)
                return (0);
#endif

        if (ctd->td_critnest > 1) {
                CTR1(KTR_PROC, "maybe_preempt: in critical section %d",
                    ctd->td_critnest);
                ctd->td_owepreempt = 1;
                return (0);
        }
        /*
         * Thread is runnable but not yet put on system run queue.
         */
        MPASS(ctd->td_lock == td->td_lock);
        MPASS(TD_ON_RUNQ(td));
        TD_SET_RUNNING(td);
        CTR3(KTR_PROC, "preempting to thread %p (pid %d, %s)\n", td,
            td->td_proc->p_pid, td->td_name);
        mi_switch(SW_INVOL | SW_PREEMPT | SWT_PREEMPT, td);
        /*
         * td's lock pointer may have changed.  We have to return with it
         * locked.
         */
        spinlock_enter();
        thread_unlock(ctd);
        thread_lock(td);
        spinlock_exit();
        return (1);
#else
        return (0);
#endif
}

/*
 * Constants for digital decay and forget:
 *      90% of (td_estcpu) usage in 5 * loadav time
 *      95% of (ts_pctcpu) usage in 60 seconds (load insensitive)
 *          Note that, as ps(1) mentions, this can let percentages
 *          total over 100% (I've seen 137.9% for 3 processes).
 *
 * Note that schedclock() updates td_estcpu and p_cpticks asynchronously.
 *
 * We wish to decay away 90% of td_estcpu in (5 * loadavg) seconds.
 * That is, the system wants to compute a value of decay such
 * that the following for loop:
 *      for (i = 0; i < (5 * loadavg); i++)
 *              td_estcpu *= decay;
 * will compute
 *      td_estcpu *= 0.1;
 * for all values of loadavg:
 *
 * Mathematically this loop can be expressed by saying:
 *      decay ** (5 * loadavg) ~= .1
 *
 * The system computes decay as:
 *      decay = (2 * loadavg) / (2 * loadavg + 1)
 *
 * We wish to prove that the system's computation of decay
 * will always fulfill the equation:
 *      decay ** (5 * loadavg) ~= .1
 *
 * If we compute b as:
 *      b = 2 * loadavg
 * then
 *      decay = b / (b + 1)
 *
 * We now need to prove two things:
 *      1) Given factor ** (5 * loadavg) ~= .1, prove factor == b/(b+1)
 *      2) Given b/(b+1) ** power ~= .1, prove power == (5 * loadavg)
 *
 * Facts:
 *         For x close to zero, exp(x) =~ 1 + x, since
 *              exp(x) = 0! + x**1/1! + x**2/2! + ... .
 *              therefore exp(-1/b) =~ 1 - (1/b) = (b-1)/b.
 *         For x close to zero, ln(1+x) =~ x, since
 *              ln(1+x) = x - x**2/2 + x**3/3 - ...     -1 < x < 1
 *              therefore ln(b/(b+1)) = ln(1 - 1/(b+1)) =~ -1/(b+1).
 *         ln(.1) =~ -2.30
 *
 * Proof of (1):
 *    Solve (factor)**(power) =~ .1 given power (5*loadav):
 *      solving for factor,
 *      ln(factor) =~ (-2.30/5*loadav), or
 *      factor =~ exp(-1/((5/2.30)*loadav)) =~ exp(-1/(2*loadav)) =
 *          exp(-1/b) =~ (b-1)/b =~ b/(b+1).                    QED
 *
 * Proof of (2):
 *    Solve (factor)**(power) =~ .1 given factor == (b/(b+1)):
 *      solving for power,
 *      power*ln(b/(b+1)) =~ -2.30, or
 *      power =~ 2.3 * (b + 1) = 4.6*loadav + 2.3 =~ 5*loadav.  QED
 *
 * Actual power values for the implemented algorithm are as follows:
 *      loadav: 1       2       3       4
 *      power:  5.68    10.32   14.94   19.55
 */

/* calculations for digital decay to forget 90% of usage in 5*loadav sec */
#define loadfactor(loadav)      (2 * (loadav))
#define decay_cpu(loadfac, cpu) (((loadfac) * (cpu)) / ((loadfac) + FSCALE))

/* decay 95% of `ts_pctcpu' in 60 seconds; see CCPU_SHIFT before changing */
static fixpt_t  ccpu = 0.95122942450071400909 * FSCALE; /* exp(-1/20) */
SYSCTL_UINT(_kern, OID_AUTO, ccpu, CTLFLAG_RD, &ccpu, 0, "");

/*
 * If `ccpu' is not equal to `exp(-1/20)' and you still want to use the
 * faster/more-accurate formula, you'll have to estimate CCPU_SHIFT below
 * and possibly adjust FSHIFT in "param.h" so that (FSHIFT >= CCPU_SHIFT).
 *
 * To estimate CCPU_SHIFT for exp(-1/20), the following formula was used:
 *      1 - exp(-1/20) ~= 0.0487 ~= 0.0488 == 1 (fixed pt, *11* bits).
 *
 * If you don't want to bother with the faster/more-accurate formula, you
 * can set CCPU_SHIFT to (FSHIFT + 1) which will use a slower/less-accurate
 * (more general) method of calculating the %age of CPU used by a process.
 */
#define CCPU_SHIFT      11

/*
 * Recompute process priorities, every hz ticks.
 * MP-safe, called without the Giant mutex.
 */
/* ARGSUSED */
static void
schedcpu(void)
{
        register fixpt_t loadfac = loadfactor(averunnable.ldavg[0]);
        struct thread *td;
        struct proc *p;
        struct td_sched *ts;
        int awake;

        sx_slock(&allproc_lock);
        FOREACH_PROC_IN_SYSTEM(p) {
                PROC_LOCK(p);
                if (p->p_state == PRS_NEW) {
                        PROC_UNLOCK(p);
                        continue;
                }
                FOREACH_THREAD_IN_PROC(p, td) {
                        awake = 0;
                        thread_lock(td);
                        ts = td->td_sched;
                        /*
                         * Increment sleep time (if sleeping).  We
                         * ignore overflow, as above.
                         */
                        /*
                         * The td_sched slptimes are not touched in wakeup
                         * because the thread may not HAVE everything in
                         * memory? XXX I think this is out of date.
                         */
                        if (TD_ON_RUNQ(td)) {
                                awake = 1;
                                td->td_flags &= ~TDF_DIDRUN;
                        } else if (TD_IS_RUNNING(td)) {
                                awake = 1;
                                /* Do not clear TDF_DIDRUN */
                        } else if (td->td_flags & TDF_DIDRUN) {
                                awake = 1;
                                td->td_flags &= ~TDF_DIDRUN;
                        }

                        /*
                         * ts_pctcpu is only for ps and ttyinfo().
                         */
                        ts->ts_pctcpu = (ts->ts_pctcpu * ccpu) >> FSHIFT;
                        /*
                         * If the td_sched has been idle the entire second,
                         * stop recalculating its priority until
                         * it wakes up.
                         */
                        if (ts->ts_cpticks != 0) {
#if     (FSHIFT >= CCPU_SHIFT)
                                ts->ts_pctcpu += (realstathz == 100)
                                    ? ((fixpt_t) ts->ts_cpticks) <<
                                    (FSHIFT - CCPU_SHIFT) :
                                    100 * (((fixpt_t) ts->ts_cpticks)
                                    << (FSHIFT - CCPU_SHIFT)) / realstathz;
#else
                                ts->ts_pctcpu += ((FSCALE - ccpu) *
                                    (ts->ts_cpticks *
                                    FSCALE / realstathz)) >> FSHIFT;
#endif
                                ts->ts_cpticks = 0;
                        }
                        /*
                         * If there are ANY running threads in this process,
                         * then don't count it as sleeping.
                         * XXX: this is broken.
                         */
                        if (awake) {
                                if (ts->ts_slptime > 1) {
                                        /*
                                         * In an ideal world, this should not
                                         * happen, because whoever woke us
                                         * up from the long sleep should have
                                         * unwound the slptime and reset our
                                         * priority before we run at the stale
                                         * priority.  Should KASSERT at some
                                         * point when all the cases are fixed.
                                         */
                                        updatepri(td);
                                }
                                ts->ts_slptime = 0;
                        } else
                                ts->ts_slptime++;
                        if (ts->ts_slptime > 1) {
                                thread_unlock(td);
                                continue;
                        }
                        td->td_estcpu = decay_cpu(loadfac, td->td_estcpu);
                        resetpriority(td);
                        resetpriority_thread(td);
                        thread_unlock(td);
                }
                PROC_UNLOCK(p);
        }
        sx_sunlock(&allproc_lock);
}

/*
 * Main loop for a kthread that executes schedcpu once a second.
 */
static void
schedcpu_thread(void)
{

        for (;;) {
                schedcpu();
                pause("-", hz);
        }
}

/*
 * Recalculate the priority of a process after it has slept for a while.
 * For all load averages >= 1 and max td_estcpu of 255, sleeping for at
 * least six times the loadfactor will decay td_estcpu to zero.
 */
static void
updatepri(struct thread *td)
{
        struct td_sched *ts;
        fixpt_t loadfac;
        unsigned int newcpu;

        ts = td->td_sched;
        loadfac = loadfactor(averunnable.ldavg[0]);
        if (ts->ts_slptime > 5 * loadfac)
                td->td_estcpu = 0;
        else {
                newcpu = td->td_estcpu;
                ts->ts_slptime--;       /* was incremented in schedcpu() */
                while (newcpu && --ts->ts_slptime)
                        newcpu = decay_cpu(loadfac, newcpu);
                td->td_estcpu = newcpu;
        }
}

/*
 * Compute the priority of a process when running in user mode.
 * Arrange to reschedule if the resulting priority is better
 * than that of the current process.
 */
static void
resetpriority(struct thread *td)
{
        register unsigned int newpriority;

        if (td->td_pri_class == PRI_TIMESHARE) {
                newpriority = PUSER + td->td_estcpu / INVERSE_ESTCPU_WEIGHT +
                    NICE_WEIGHT * (td->td_proc->p_nice - PRIO_MIN);
                newpriority = min(max(newpriority, PRI_MIN_TIMESHARE),
                    PRI_MAX_TIMESHARE);
                sched_user_prio(td, newpriority);
        }
}

/*
 * Update the thread's priority when the associated process's user
 * priority changes.
 */
static void
resetpriority_thread(struct thread *td)
{

        /* Only change threads with a time sharing user priority. */
        if (td->td_priority < PRI_MIN_TIMESHARE ||
            td->td_priority > PRI_MAX_TIMESHARE)
                return;

        /* XXX the whole needresched thing is broken, but not silly. */
        maybe_resched(td);

        sched_prio(td, td->td_user_pri);
}

/* ARGSUSED */
static void
sched_setup(void *dummy)
{

        setup_runqs();

        /* Account for thread0. */
        sched_load_add();
}

/*
 * This routine determines time constants after stathz and hz are setup.
 */
static void
sched_initticks(void *dummy)
{

        realstathz = stathz ? stathz : hz;
        sched_slice = realstathz / 10;  /* ~100ms */
        hogticks = imax(1, (2 * hz * sched_slice + realstathz / 2) /
            realstathz);
}

/* External interfaces start here */

/*
 * Very early in the boot some setup of scheduler-specific
 * parts of proc0 and of some scheduler resources needs to be done.
 * Called from:
 *  proc0_init()
 */
void
schedinit(void)
{
        /*
         * Set up the scheduler specific parts of proc0.
         */
        proc0.p_sched = NULL; /* XXX */
        thread0.td_sched = &td_sched0;
        thread0.td_lock = &sched_lock;
        td_sched0.ts_slice = sched_slice;
        mtx_init(&sched_lock, "sched lock", NULL, MTX_SPIN | MTX_RECURSE);
}

int
sched_runnable(void)
{
#ifdef SMP
        return runq_check(&runq) + runq_check(&runq_pcpu[PCPU_GET(cpuid)]);
#else
        return runq_check(&runq);
#endif
}

int
sched_rr_interval(void)
{

        /* Convert sched_slice from stathz to hz. */
        return (imax(1, (sched_slice * hz + realstathz / 2) / realstathz));
}

/*
 * We adjust the priority of the current process.  The priority of
 * a process gets worse as it accumulates CPU time.  The cpu usage
 * estimator (td_estcpu) is increased here.  resetpriority() will
 * compute a different priority each time td_estcpu increases by
 * INVERSE_ESTCPU_WEIGHT
 * (until MAXPRI is reached).  The cpu usage estimator ramps up
 * quite quickly when the process is running (linearly), and decays
 * away exponentially, at a rate which is proportionally slower when
 * the system is busy.  The basic principle is that the system will
 * 90% forget that the process used a lot of CPU time in 5 * loadav
 * seconds.  This causes the system to favor processes which haven't
 * run much recently, and to round-robin among other processes.
 */
void
sched_clock(struct thread *td)
{
        struct pcpuidlestat *stat;
        struct td_sched *ts;

        THREAD_LOCK_ASSERT(td, MA_OWNED);
        ts = td->td_sched;

        ts->ts_cpticks++;
        td->td_estcpu = ESTCPULIM(td->td_estcpu + 1);
        if ((td->td_estcpu % INVERSE_ESTCPU_WEIGHT) == 0) {
                resetpriority(td);
                resetpriority_thread(td);
        }

        /*
         * Force a context switch if the current thread has used up a full
         * time slice (default is 100ms).
         */
        if (!TD_IS_IDLETHREAD(td) && --ts->ts_slice <= 0) {
                ts->ts_slice = sched_slice;
                td->td_flags |= TDF_NEEDRESCHED | TDF_SLICEEND;
        }

        stat = DPCPU_PTR(idlestat);
        stat->oldidlecalls = stat->idlecalls;
        stat->idlecalls = 0;
}

/*
 * Charge child's scheduling CPU usage to parent.
 */
void
sched_exit(struct proc *p, struct thread *td)
{

        KTR_STATE1(KTR_SCHED, "thread", sched_tdname(td), "proc exit",
            "prio:%d", td->td_priority);

        PROC_LOCK_ASSERT(p, MA_OWNED);
        sched_exit_thread(FIRST_THREAD_IN_PROC(p), td);
}

void
sched_exit_thread(struct thread *td, struct thread *child)
{

        KTR_STATE1(KTR_SCHED, "thread", sched_tdname(child), "exit",
            "prio:%d", child->td_priority);
        thread_lock(td);
        td->td_estcpu = ESTCPULIM(td->td_estcpu + child->td_estcpu);
        thread_unlock(td);
        thread_lock(child);
        if ((child->td_flags & TDF_NOLOAD) == 0)
                sched_load_rem();
        thread_unlock(child);
}

void
sched_fork(struct thread *td, struct thread *childtd)
{
        sched_fork_thread(td, childtd);
}

void
sched_fork_thread(struct thread *td, struct thread *childtd)
{
        struct td_sched *ts;

        childtd->td_estcpu = td->td_estcpu;
        childtd->td_lock = &sched_lock;
        childtd->td_cpuset = cpuset_ref(td->td_cpuset);
        childtd->td_priority = childtd->td_base_pri;
        ts = childtd->td_sched;
        bzero(ts, sizeof(*ts));
        ts->ts_flags |= (td->td_sched->ts_flags & TSF_AFFINITY);
        ts->ts_slice = 1;
}

void
sched_nice(struct proc *p, int nice)
{
        struct thread *td;

        PROC_LOCK_ASSERT(p, MA_OWNED);
        p->p_nice = nice;
        FOREACH_THREAD_IN_PROC(p, td) {
                thread_lock(td);
                resetpriority(td);
                resetpriority_thread(td);
                thread_unlock(td);
        }
}

void
sched_class(struct thread *td, int class)
{
        THREAD_LOCK_ASSERT(td, MA_OWNED);
        td->td_pri_class = class;
}

/*
 * Adjust the priority of a thread.
 */
static void
sched_priority(struct thread *td, u_char prio)
{


        KTR_POINT3(KTR_SCHED, "thread", sched_tdname(td), "priority change",
            "prio:%d", td->td_priority, "new prio:%d", prio, KTR_ATTR_LINKED,
            sched_tdname(curthread));
        SDT_PROBE3(sched, , , change__pri, td, td->td_proc, prio);
        if (td != curthread && prio > td->td_priority) {
                KTR_POINT3(KTR_SCHED, "thread", sched_tdname(curthread),
                    "lend prio", "prio:%d", td->td_priority, "new prio:%d",
                    prio, KTR_ATTR_LINKED, sched_tdname(td));
                SDT_PROBE4(sched, , , lend__pri, td, td->td_proc, prio, 
                    curthread);
        }
        THREAD_LOCK_ASSERT(td, MA_OWNED);
        if (td->td_priority == prio)
                return;
        td->td_priority = prio;
        if (TD_ON_RUNQ(td) && td->td_rqindex != (prio / RQ_PPQ)) {
                sched_rem(td);
                sched_add(td, SRQ_BORING);
        }
}

/*
 * Update a thread's priority when it is lent another thread's
 * priority.
 */
void
sched_lend_prio(struct thread *td, u_char prio)
{

        td->td_flags |= TDF_BORROWING;
        sched_priority(td, prio);
}

/*
 * Restore a thread's priority when priority propagation is
 * over.  The prio argument is the minimum priority the thread
 * needs to have to satisfy other possible priority lending
 * requests.  If the thread's regulary priority is less
 * important than prio the thread will keep a priority boost
 * of prio.
 */
void
sched_unlend_prio(struct thread *td, u_char prio)
{
        u_char base_pri;

        if (td->td_base_pri >= PRI_MIN_TIMESHARE &&
            td->td_base_pri <= PRI_MAX_TIMESHARE)
                base_pri = td->td_user_pri;
        else
                base_pri = td->td_base_pri;
        if (prio >= base_pri) {
                td->td_flags &= ~TDF_BORROWING;
                sched_prio(td, base_pri);
        } else
                sched_lend_prio(td, prio);
}

void
sched_prio(struct thread *td, u_char prio)
{
        u_char oldprio;

        /* First, update the base priority. */
        td->td_base_pri = prio;

        /*
         * If the thread is borrowing another thread's priority, don't ever
         * lower the priority.
         */
        if (td->td_flags & TDF_BORROWING && td->td_priority < prio)
                return;

        /* Change the real priority. */
        oldprio = td->td_priority;
        sched_priority(td, prio);

        /*
         * If the thread is on a turnstile, then let the turnstile update
         * its state.
         */
        if (TD_ON_LOCK(td) && oldprio != prio)
                turnstile_adjust(td, oldprio);
}

void
sched_user_prio(struct thread *td, u_char prio)
{

        THREAD_LOCK_ASSERT(td, MA_OWNED);
        td->td_base_user_pri = prio;
        if (td->td_lend_user_pri <= prio)
                return;
        td->td_user_pri = prio;
}

void
sched_lend_user_prio(struct thread *td, u_char prio)
{

        THREAD_LOCK_ASSERT(td, MA_OWNED);
        td->td_lend_user_pri = prio;
        td->td_user_pri = min(prio, td->td_base_user_pri);
        if (td->td_priority > td->td_user_pri)
                sched_prio(td, td->td_user_pri);
        else if (td->td_priority != td->td_user_pri)
                td->td_flags |= TDF_NEEDRESCHED;
}

void
sched_sleep(struct thread *td, int pri)
{

        THREAD_LOCK_ASSERT(td, MA_OWNED);
        td->td_slptick = ticks;
        td->td_sched->ts_slptime = 0;
        if (pri != 0 && PRI_BASE(td->td_pri_class) == PRI_TIMESHARE)
                sched_prio(td, pri);
        if (TD_IS_SUSPENDED(td) || pri >= PSOCK)
                td->td_flags |= TDF_CANSWAP;
}

void
sched_switch(struct thread *td, struct thread *newtd, int flags)
{
        struct mtx *tmtx;
        struct td_sched *ts;
        struct proc *p;
        int preempted;

        tmtx = NULL;
        ts = td->td_sched;
        p = td->td_proc;

        THREAD_LOCK_ASSERT(td, MA_OWNED);

        /* 
         * Switch to the sched lock to fix things up and pick
         * a new thread.
         * Block the td_lock in order to avoid breaking the critical path.
         */
        if (td->td_lock != &sched_lock) {
                mtx_lock_spin(&sched_lock);
                tmtx = thread_lock_block(td);
        }

        if ((td->td_flags & TDF_NOLOAD) == 0)
                sched_load_rem();

        td->td_lastcpu = td->td_oncpu;
        preempted = !((td->td_flags & TDF_SLICEEND) ||
            (flags & SWT_RELINQUISH));
        td->td_flags &= ~(TDF_NEEDRESCHED | TDF_SLICEEND);
        td->td_owepreempt = 0;
        td->td_oncpu = NOCPU;

        /*
         * At the last moment, if this thread is still marked RUNNING,
         * then put it back on the run queue as it has not been suspended
         * or stopped or any thing else similar.  We never put the idle
         * threads on the run queue, however.
         */
        if (td->td_flags & TDF_IDLETD) {
                TD_SET_CAN_RUN(td);
#ifdef SMP
                CPU_CLR(PCPU_GET(cpuid), &idle_cpus_mask);
#endif
        } else {
                if (TD_IS_RUNNING(td)) {
                        /* Put us back on the run queue. */
                        sched_add(td, preempted ?
                            SRQ_OURSELF|SRQ_YIELDING|SRQ_PREEMPTED :
                            SRQ_OURSELF|SRQ_YIELDING);
                }
        }
        if (newtd) {
                /*
                 * The thread we are about to run needs to be counted
                 * as if it had been added to the run queue and selected.
                 * It came from:
                 * * A preemption
                 * * An upcall
                 * * A followon
                 */
                KASSERT((newtd->td_inhibitors == 0),
                        ("trying to run inhibited thread"));
                newtd->td_flags |= TDF_DIDRUN;
                TD_SET_RUNNING(newtd);
                if ((newtd->td_flags & TDF_NOLOAD) == 0)
                        sched_load_add();
        } else {
                newtd = choosethread();
                MPASS(newtd->td_lock == &sched_lock);
        }

        if (td != newtd) {
#ifdef  HWPMC_HOOKS
                if (PMC_PROC_IS_USING_PMCS(td->td_proc))
                        PMC_SWITCH_CONTEXT(td, PMC_FN_CSW_OUT);
#endif

                SDT_PROBE2(sched, , , off__cpu, newtd, newtd->td_proc);

                /* I feel sleepy */
                lock_profile_release_lock(&sched_lock.lock_object);
#ifdef KDTRACE_HOOKS
                /*
                 * If DTrace has set the active vtime enum to anything
                 * other than INACTIVE (0), then it should have set the
                 * function to call.
                 */
                if (dtrace_vtime_active)
                        (*dtrace_vtime_switch_func)(newtd);
#endif

                cpu_switch(td, newtd, tmtx != NULL ? tmtx : td->td_lock);
                lock_profile_obtain_lock_success(&sched_lock.lock_object,
                    0, 0, __FILE__, __LINE__);
                /*
                 * Where am I?  What year is it?
                 * We are in the same thread that went to sleep above,
                 * but any amount of time may have passed. All our context
                 * will still be available as will local variables.
                 * PCPU values however may have changed as we may have
                 * changed CPU so don't trust cached values of them.
                 * New threads will go to fork_exit() instead of here
                 * so if you change things here you may need to change
                 * things there too.
                 *
                 * If the thread above was exiting it will never wake
                 * up again here, so either it has saved everything it
                 * needed to, or the thread_wait() or wait() will
                 * need to reap it.
                 */

                SDT_PROBE0(sched, , , on__cpu);
#ifdef  HWPMC_HOOKS
                if (PMC_PROC_IS_USING_PMCS(td->td_proc))
                        PMC_SWITCH_CONTEXT(td, PMC_FN_CSW_IN);
#endif
        } else
                SDT_PROBE0(sched, , , remain__cpu);

#ifdef SMP
        if (td->td_flags & TDF_IDLETD)
                CPU_SET(PCPU_GET(cpuid), &idle_cpus_mask);
#endif
        sched_lock.mtx_lock = (uintptr_t)td;
        td->td_oncpu = PCPU_GET(cpuid);
        MPASS(td->td_lock == &sched_lock);
}

void
sched_wakeup(struct thread *td)
{
        struct td_sched *ts;

        THREAD_LOCK_ASSERT(td, MA_OWNED);
        ts = td->td_sched;
        td->td_flags &= ~TDF_CANSWAP;
        if (ts->ts_slptime > 1) {
                updatepri(td);
                resetpriority(td);
        }
        td->td_slptick = 0;
        ts->ts_slptime = 0;
        ts->ts_slice = sched_slice;
        sched_add(td, SRQ_BORING);
}

#ifdef SMP
static int
forward_wakeup(int cpunum)
{
        struct pcpu *pc;
        cpuset_t dontuse, map, map2;
        u_int id, me;
        int iscpuset;

        mtx_assert(&sched_lock, MA_OWNED);

        CTR0(KTR_RUNQ, "forward_wakeup()");

        if ((!forward_wakeup_enabled) ||
             (forward_wakeup_use_mask == 0 && forward_wakeup_use_loop == 0))
                return (0);
        if (!smp_started || cold || panicstr)
                return (0);

        forward_wakeups_requested++;

        /*
         * Check the idle mask we received against what we calculated
         * before in the old version.
         */
        me = PCPU_GET(cpuid);

        /* Don't bother if we should be doing it ourself. */
        if (CPU_ISSET(me, &idle_cpus_mask) &&
            (cpunum == NOCPU || me == cpunum))
                return (0);

        CPU_SETOF(me, &dontuse);
        CPU_OR(&dontuse, &stopped_cpus);
        CPU_OR(&dontuse, &hlt_cpus_mask);
        CPU_ZERO(&map2);
        if (forward_wakeup_use_loop) {
                STAILQ_FOREACH(pc, &cpuhead, pc_allcpu) {
                        id = pc->pc_cpuid;
                        if (!CPU_ISSET(id, &dontuse) &&
                            pc->pc_curthread == pc->pc_idlethread) {
                                CPU_SET(id, &map2);
                        }
                }
        }

        if (forward_wakeup_use_mask) {
                map = idle_cpus_mask;
                CPU_NAND(&map, &dontuse);

                /* If they are both on, compare and use loop if different. */
                if (forward_wakeup_use_loop) {
                        if (CPU_CMP(&map, &map2)) {
                                printf("map != map2, loop method preferred\n");
                                map = map2;
                        }
                }
        } else {
                map = map2;
        }

        /* If we only allow a specific CPU, then mask off all the others. */
        if (cpunum != NOCPU) {
                KASSERT((cpunum <= mp_maxcpus),("forward_wakeup: bad cpunum."));
                iscpuset = CPU_ISSET(cpunum, &map);
                if (iscpuset == 0)
                        CPU_ZERO(&map);
                else
                        CPU_SETOF(cpunum, &map);
        }
        if (!CPU_EMPTY(&map)) {
                forward_wakeups_delivered++;
                STAILQ_FOREACH(pc, &cpuhead, pc_allcpu) {
                        id = pc->pc_cpuid;
                        if (!CPU_ISSET(id, &map))
                                continue;
                        if (cpu_idle_wakeup(pc->pc_cpuid))
                                CPU_CLR(id, &map);
                }
                if (!CPU_EMPTY(&map))
                        ipi_selected(map, IPI_AST);
                return (1);
        }
        if (cpunum == NOCPU)
                printf("forward_wakeup: Idle processor not found\n");
        return (0);
}

static void
kick_other_cpu(int pri, int cpuid)
{
        struct pcpu *pcpu;
        int cpri;

        pcpu = pcpu_find(cpuid);
        if (CPU_ISSET(cpuid, &idle_cpus_mask)) {
                forward_wakeups_delivered++;
                if (!cpu_idle_wakeup(cpuid))
                        ipi_cpu(cpuid, IPI_AST);
                return;
        }

        cpri = pcpu->pc_curthread->td_priority;
        if (pri >= cpri)
                return;

#if defined(IPI_PREEMPTION) && defined(PREEMPTION)
#if !defined(FULL_PREEMPTION)
        if (pri <= PRI_MAX_ITHD)
#endif /* ! FULL_PREEMPTION */
        {
                ipi_cpu(cpuid, IPI_PREEMPT);
                return;
        }
#endif /* defined(IPI_PREEMPTION) && defined(PREEMPTION) */

        pcpu->pc_curthread->td_flags |= TDF_NEEDRESCHED;
        ipi_cpu(cpuid, IPI_AST);
        return;
}
#endif /* SMP */

#ifdef SMP
static int
sched_pickcpu(struct thread *td)
{
        int best, cpu;

        mtx_assert(&sched_lock, MA_OWNED);

        if (THREAD_CAN_SCHED(td, td->td_lastcpu))
                best = td->td_lastcpu;
        else
                best = NOCPU;
        CPU_FOREACH(cpu) {
                if (!THREAD_CAN_SCHED(td, cpu))
                        continue;
        
                if (best == NOCPU)
                        best = cpu;
                else if (runq_length[cpu] < runq_length[best])
                        best = cpu;
        }
        KASSERT(best != NOCPU, ("no valid CPUs"));

        return (best);
}
#endif

void
sched_add(struct thread *td, int flags)
#ifdef SMP
{
        cpuset_t tidlemsk;
        struct td_sched *ts;
        u_int cpu, cpuid;
        int forwarded = 0;
        int single_cpu = 0;

        ts = td->td_sched;
        THREAD_LOCK_ASSERT(td, MA_OWNED);
        KASSERT((td->td_inhibitors == 0),
            ("sched_add: trying to run inhibited thread"));
        KASSERT((TD_CAN_RUN(td) || TD_IS_RUNNING(td)),
            ("sched_add: bad thread state"));
        KASSERT(td->td_flags & TDF_INMEM,
            ("sched_add: thread swapped out"));

        KTR_STATE2(KTR_SCHED, "thread", sched_tdname(td), "runq add",
            "prio:%d", td->td_priority, KTR_ATTR_LINKED,
            sched_tdname(curthread));
        KTR_POINT1(KTR_SCHED, "thread", sched_tdname(curthread), "wokeup",
            KTR_ATTR_LINKED, sched_tdname(td));
        SDT_PROBE4(sched, , , enqueue, td, td->td_proc, NULL, 
            flags & SRQ_PREEMPTED);


        /*
         * Now that the thread is moving to the run-queue, set the lock
         * to the scheduler's lock.
         */
        if (td->td_lock != &sched_lock) {
                mtx_lock_spin(&sched_lock);
                thread_lock_set(td, &sched_lock);
        }
        TD_SET_RUNQ(td);

        /*
         * If SMP is started and the thread is pinned or otherwise limited to
         * a specific set of CPUs, queue the thread to a per-CPU run queue.
         * Otherwise, queue the thread to the global run queue.
         *
         * If SMP has not yet been started we must use the global run queue
         * as per-CPU state may not be initialized yet and we may crash if we
         * try to access the per-CPU run queues.
         */
        if (smp_started && (td->td_pinned != 0 || td->td_flags & TDF_BOUND ||
            ts->ts_flags & TSF_AFFINITY)) {
                if (td->td_pinned != 0)
                        cpu = td->td_lastcpu;
                else if (td->td_flags & TDF_BOUND) {
                        /* Find CPU from bound runq. */
                        KASSERT(SKE_RUNQ_PCPU(ts),
                            ("sched_add: bound td_sched not on cpu runq"));
                        cpu = ts->ts_runq - &runq_pcpu[0];
                } else
                        /* Find a valid CPU for our cpuset */
                        cpu = sched_pickcpu(td);
                ts->ts_runq = &runq_pcpu[cpu];
                single_cpu = 1;
                CTR3(KTR_RUNQ,
                    "sched_add: Put td_sched:%p(td:%p) on cpu%d runq", ts, td,
                    cpu);
        } else {
                CTR2(KTR_RUNQ,
                    "sched_add: adding td_sched:%p (td:%p) to gbl runq", ts,
                    td);
                cpu = NOCPU;
                ts->ts_runq = &runq;
        }

        cpuid = PCPU_GET(cpuid);
        if (single_cpu && cpu != cpuid) {
                kick_other_cpu(td->td_priority, cpu);
        } else {
                if (!single_cpu) {
                        tidlemsk = idle_cpus_mask;
                        CPU_NAND(&tidlemsk, &hlt_cpus_mask);
                        CPU_CLR(cpuid, &tidlemsk);

                        if (!CPU_ISSET(cpuid, &idle_cpus_mask) &&
                            ((flags & SRQ_INTR) == 0) &&
                            !CPU_EMPTY(&tidlemsk))
                                forwarded = forward_wakeup(cpu);
                }

                if (!forwarded) {
                        if ((flags & SRQ_YIELDING) == 0 && maybe_preempt(td))
                                return;
                        else
                                maybe_resched(td);
                }
        }

        if ((td->td_flags & TDF_NOLOAD) == 0)
                sched_load_add();
        runq_add(ts->ts_runq, td, flags);
        if (cpu != NOCPU)
                runq_length[cpu]++;
}
#else /* SMP */
{
        struct td_sched *ts;

        ts = td->td_sched;
        THREAD_LOCK_ASSERT(td, MA_OWNED);
        KASSERT((td->td_inhibitors == 0),
            ("sched_add: trying to run inhibited thread"));
        KASSERT((TD_CAN_RUN(td) || TD_IS_RUNNING(td)),
            ("sched_add: bad thread state"));
        KASSERT(td->td_flags & TDF_INMEM,
            ("sched_add: thread swapped out"));
        KTR_STATE2(KTR_SCHED, "thread", sched_tdname(td), "runq add",
            "prio:%d", td->td_priority, KTR_ATTR_LINKED,
            sched_tdname(curthread));
        KTR_POINT1(KTR_SCHED, "thread", sched_tdname(curthread), "wokeup",
            KTR_ATTR_LINKED, sched_tdname(td));
        SDT_PROBE4(sched, , , enqueue, td, td->td_proc, NULL, 
            flags & SRQ_PREEMPTED);

        /*
         * Now that the thread is moving to the run-queue, set the lock
         * to the scheduler's lock.
         */
        if (td->td_lock != &sched_lock) {
                mtx_lock_spin(&sched_lock);
                thread_lock_set(td, &sched_lock);
        }
        TD_SET_RUNQ(td);
        CTR2(KTR_RUNQ, "sched_add: adding td_sched:%p (td:%p) to runq", ts, td);
        ts->ts_runq = &runq;

        /*
         * If we are yielding (on the way out anyhow) or the thread
         * being saved is US, then don't try be smart about preemption
         * or kicking off another CPU as it won't help and may hinder.
         * In the YIEDLING case, we are about to run whoever is being
         * put in the queue anyhow, and in the OURSELF case, we are
         * puting ourself on the run queue which also only happens
         * when we are about to yield.
         */
        if ((flags & SRQ_YIELDING) == 0) {
                if (maybe_preempt(td))
                        return;
        }
        if ((td->td_flags & TDF_NOLOAD) == 0)
                sched_load_add();
        runq_add(ts->ts_runq, td, flags);
        maybe_resched(td);
}
#endif /* SMP */

void
sched_rem(struct thread *td)
{
        struct td_sched *ts;

        ts = td->td_sched;
        KASSERT(td->td_flags & TDF_INMEM,
            ("sched_rem: thread swapped out"));
        KASSERT(TD_ON_RUNQ(td),
            ("sched_rem: thread not on run queue"));
        mtx_assert(&sched_lock, MA_OWNED);
        KTR_STATE2(KTR_SCHED, "thread", sched_tdname(td), "runq rem",
            "prio:%d", td->td_priority, KTR_ATTR_LINKED,
            sched_tdname(curthread));
        SDT_PROBE3(sched, , , dequeue, td, td->td_proc, NULL);

        if ((td->td_flags & TDF_NOLOAD) == 0)
                sched_load_rem();
#ifdef SMP
        if (ts->ts_runq != &runq)
                runq_length[ts->ts_runq - runq_pcpu]--;
#endif
        runq_remove(ts->ts_runq, td);
        TD_SET_CAN_RUN(td);
}

/*
 * Select threads to run.  Note that running threads still consume a
 * slot.
 */
struct thread *
sched_choose(void)
{
        struct thread *td;
        struct runq *rq;

        mtx_assert(&sched_lock,  MA_OWNED);
#ifdef SMP
        struct thread *tdcpu;

        rq = &runq;
        td = runq_choose_fuzz(&runq, runq_fuzz);
        tdcpu = runq_choose(&runq_pcpu[PCPU_GET(cpuid)]);

        if (td == NULL ||
            (tdcpu != NULL &&
             tdcpu->td_priority < td->td_priority)) {
                CTR2(KTR_RUNQ, "choosing td %p from pcpu runq %d", tdcpu,
                     PCPU_GET(cpuid));
                td = tdcpu;
                rq = &runq_pcpu[PCPU_GET(cpuid)];
        } else {
                CTR1(KTR_RUNQ, "choosing td_sched %p from main runq", td);
        }

#else
        rq = &runq;
        td = runq_choose(&runq);
#endif

        if (td) {
#ifdef SMP
                if (td == tdcpu)
                        runq_length[PCPU_GET(cpuid)]--;
#endif
                runq_remove(rq, td);
                td->td_flags |= TDF_DIDRUN;

                KASSERT(td->td_flags & TDF_INMEM,
                    ("sched_choose: thread swapped out"));
                return (td);
        }
        return (PCPU_GET(idlethread));
}

void
sched_preempt(struct thread *td)
{

        SDT_PROBE2(sched, , , surrender, td, td->td_proc);
        thread_lock(td);
        if (td->td_critnest > 1)
                td->td_owepreempt = 1;
        else
                mi_switch(SW_INVOL | SW_PREEMPT | SWT_PREEMPT, NULL);
        thread_unlock(td);
}

void
sched_userret(struct thread *td)
{
        /*
         * XXX we cheat slightly on the locking here to avoid locking in
         * the usual case.  Setting td_priority here is essentially an
         * incomplete workaround for not setting it properly elsewhere.
         * Now that some interrupt handlers are threads, not setting it
         * properly elsewhere can clobber it in the window between setting
         * it here and returning to user mode, so don't waste time setting
         * it perfectly here.
         */
        KASSERT((td->td_flags & TDF_BORROWING) == 0,
            ("thread with borrowed priority returning to userland"));
        if (td->td_priority != td->td_user_pri) {
                thread_lock(td);
                td->td_priority = td->td_user_pri;
                td->td_base_pri = td->td_user_pri;
                thread_unlock(td);
        }
}

void
sched_bind(struct thread *td, int cpu)
{
        struct td_sched *ts;

        THREAD_LOCK_ASSERT(td, MA_OWNED|MA_NOTRECURSED);
        KASSERT(td == curthread, ("sched_bind: can only bind curthread"));

        ts = td->td_sched;

        td->td_flags |= TDF_BOUND;
#ifdef SMP
        ts->ts_runq = &runq_pcpu[cpu];
        if (PCPU_GET(cpuid) == cpu)
                return;

        mi_switch(SW_VOL, NULL);
#endif
}

void
sched_unbind(struct thread* td)
{
        THREAD_LOCK_ASSERT(td, MA_OWNED);
        KASSERT(td == curthread, ("sched_unbind: can only bind curthread"));
        td->td_flags &= ~TDF_BOUND;
}

int
sched_is_bound(struct thread *td)
{
        THREAD_LOCK_ASSERT(td, MA_OWNED);
        return (td->td_flags & TDF_BOUND);
}

void
sched_relinquish(struct thread *td)
{
        thread_lock(td);
        mi_switch(SW_VOL | SWT_RELINQUISH, NULL);
        thread_unlock(td);
}

int
sched_load(void)
{
        return (sched_tdcnt);
}

int
sched_sizeof_proc(void)
{
        return (sizeof(struct proc));
}

int
sched_sizeof_thread(void)
{
        return (sizeof(struct thread) + sizeof(struct td_sched));
}

fixpt_t
sched_pctcpu(struct thread *td)
{
        struct td_sched *ts;

        THREAD_LOCK_ASSERT(td, MA_OWNED);
        ts = td->td_sched;
        return (ts->ts_pctcpu);
}

#ifdef RACCT
/*
 * Calculates the contribution to the thread cpu usage for the latest
 * (unfinished) second.
 */
fixpt_t
sched_pctcpu_delta(struct thread *td)
{
        struct td_sched *ts;
        fixpt_t delta;
        int realstathz;

        THREAD_LOCK_ASSERT(td, MA_OWNED);
        ts = td->td_sched;
        delta = 0;
        realstathz = stathz ? stathz : hz;
        if (ts->ts_cpticks != 0) {
#if     (FSHIFT >= CCPU_SHIFT)
                delta = (realstathz == 100)
                    ? ((fixpt_t) ts->ts_cpticks) <<
                    (FSHIFT - CCPU_SHIFT) :
                    100 * (((fixpt_t) ts->ts_cpticks)
                    << (FSHIFT - CCPU_SHIFT)) / realstathz;
#else
                delta = ((FSCALE - ccpu) *
                    (ts->ts_cpticks *
                    FSCALE / realstathz)) >> FSHIFT;
#endif
        }

        return (delta);
}
#endif

void
sched_tick(int cnt)
{
}

/*
 * The actual idle process.
 */
void
sched_idletd(void *dummy)
{
        struct pcpuidlestat *stat;

        THREAD_NO_SLEEPING();
        stat = DPCPU_PTR(idlestat);
        for (;;) {
                mtx_assert(&Giant, MA_NOTOWNED);

                while (sched_runnable() == 0) {
                        cpu_idle(stat->idlecalls + stat->oldidlecalls > 64);
                        stat->idlecalls++;
                }

                mtx_lock_spin(&sched_lock);
                mi_switch(SW_VOL | SWT_IDLE, NULL);
                mtx_unlock_spin(&sched_lock);
        }
}

/*
 * A CPU is entering for the first time or a thread is exiting.
 */
void
sched_throw(struct thread *td)
{
        /*
         * Correct spinlock nesting.  The idle thread context that we are
         * borrowing was created so that it would start out with a single
         * spin lock (sched_lock) held in fork_trampoline().  Since we've
         * explicitly acquired locks in this function, the nesting count
         * is now 2 rather than 1.  Since we are nested, calling
         * spinlock_exit() will simply adjust the counts without allowing
         * spin lock using code to interrupt us.
         */
        if (td == NULL) {
                mtx_lock_spin(&sched_lock);
                spinlock_exit();
                PCPU_SET(switchtime, cpu_ticks());
                PCPU_SET(switchticks, ticks);
        } else {
                lock_profile_release_lock(&sched_lock.lock_object);
                MPASS(td->td_lock == &sched_lock);
        }
        mtx_assert(&sched_lock, MA_OWNED);
        KASSERT(curthread->td_md.md_spinlock_count == 1, ("invalid count"));
        cpu_throw(td, choosethread());  /* doesn't return */
}

void
sched_fork_exit(struct thread *td)
{

        /*
         * Finish setting up thread glue so that it begins execution in a
         * non-nested critical section with sched_lock held but not recursed.
         */
        td->td_oncpu = PCPU_GET(cpuid);
        sched_lock.mtx_lock = (uintptr_t)td;
        lock_profile_obtain_lock_success(&sched_lock.lock_object,
            0, 0, __FILE__, __LINE__);
        THREAD_LOCK_ASSERT(td, MA_OWNED | MA_NOTRECURSED);
}

char *
sched_tdname(struct thread *td)
{
#ifdef KTR
        struct td_sched *ts;

        ts = td->td_sched;
        if (ts->ts_name[0] == '\0')
                snprintf(ts->ts_name, sizeof(ts->ts_name),
                    "%s tid %d", td->td_name, td->td_tid);
        return (ts->ts_name);
#else   
        return (td->td_name);
#endif
}

#ifdef KTR
void
sched_clear_tdname(struct thread *td)
{
        struct td_sched *ts;

        ts = td->td_sched;
        ts->ts_name[0] = '\0';
}
#endif

void
sched_affinity(struct thread *td)
{
#ifdef SMP
        struct td_sched *ts;
        int cpu;

        THREAD_LOCK_ASSERT(td, MA_OWNED);       

        /*
         * Set the TSF_AFFINITY flag if there is at least one CPU this
         * thread can't run on.
         */
        ts = td->td_sched;
        ts->ts_flags &= ~TSF_AFFINITY;
        CPU_FOREACH(cpu) {
                if (!THREAD_CAN_SCHED(td, cpu)) {
                        ts->ts_flags |= TSF_AFFINITY;
                        break;
                }
        }

        /*
         * If this thread can run on all CPUs, nothing else to do.
         */
        if (!(ts->ts_flags & TSF_AFFINITY))
                return;

        /* Pinned threads and bound threads should be left alone. */
        if (td->td_pinned != 0 || td->td_flags & TDF_BOUND)
                return;

        switch (td->td_state) {
        case TDS_RUNQ:
                /*
                 * If we are on a per-CPU runqueue that is in the set,
                 * then nothing needs to be done.
                 */
                if (ts->ts_runq != &runq &&
                    THREAD_CAN_SCHED(td, ts->ts_runq - runq_pcpu))
                        return;

                /* Put this thread on a valid per-CPU runqueue. */
                sched_rem(td);
                sched_add(td, SRQ_BORING);
                break;
        case TDS_RUNNING:
                /*
                 * See if our current CPU is in the set.  If not, force a
                 * context switch.
                 */
                if (THREAD_CAN_SCHED(td, td->td_oncpu))
                        return;

                td->td_flags |= TDF_NEEDRESCHED;
                if (td != curthread)
                        ipi_cpu(cpu, IPI_AST);
                break;
        default:
                break;
        }
#endif
}