rtld-elf: link udivmoddi4 from compiler_rt

[FreeBSD/FreeBSD.git] / sys / kern / sched_ule.c

/*-
 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
 *
 * Copyright (c) 2002-2007, Jeffrey Roberson <jeff@freebsd.org>
 * All rights reserved.
 *
 * 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 unmodified, 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.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR 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.
 */

/*
 * This file implements the ULE scheduler.  ULE supports independent CPU
 * run queues and fine grain locking.  It has superior interactive
 * performance under load even on uni-processor systems.
 *
 * etymology:
 *   ULE is the last three letters in schedule.  It owes its name to a
 * generic user created for a scheduling system by Paul Mikesell at
 * Isilon Systems and a general lack of creativity on the part of the author.
 */

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

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

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kdb.h>
#include <sys/kernel.h>
#include <sys/ktr.h>
#include <sys/limits.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/proc.h>
#include <sys/resource.h>
#include <sys/resourcevar.h>
#include <sys/sched.h>
#include <sys/sdt.h>
#include <sys/smp.h>
#include <sys/sx.h>
#include <sys/sysctl.h>
#include <sys/sysproto.h>
#include <sys/turnstile.h>
#include <sys/umtx.h>
#include <sys/vmmeter.h>
#include <sys/cpuset.h>
#include <sys/sbuf.h>

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

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

#include <machine/cpu.h>
#include <machine/smp.h>

#define KTR_ULE 0

#define TS_NAME_LEN (MAXCOMLEN + sizeof(" td ") + sizeof(__XSTRING(UINT_MAX)))
#define TDQ_NAME_LEN    (sizeof("sched lock ") + sizeof(__XSTRING(MAXCPU)))
#define TDQ_LOADNAME_LEN        (sizeof("CPU ") + sizeof(__XSTRING(MAXCPU)) - 1 + sizeof(" load"))

/*
 * Thread scheduler specific section.  All fields are protected
 * by the thread lock.
 */
struct td_sched {       
        struct runq     *ts_runq;       /* Run-queue we're queued on. */
        short           ts_flags;       /* TSF_* flags. */
        int             ts_cpu;         /* CPU that we have affinity for. */
        int             ts_rltick;      /* Real last tick, for affinity. */
        int             ts_slice;       /* Ticks of slice remaining. */
        u_int           ts_slptime;     /* Number of ticks we vol. slept */
        u_int           ts_runtime;     /* Number of ticks we were running */
        int             ts_ltick;       /* Last tick that we were running on */
        int             ts_ftick;       /* First tick that we were running on */
        int             ts_ticks;       /* Tick count */
#ifdef KTR
        char            ts_name[TS_NAME_LEN];
#endif
};
/* flags kept in ts_flags */
#define TSF_BOUND       0x0001          /* Thread can not migrate. */
#define TSF_XFERABLE    0x0002          /* Thread was added as transferable. */

#define THREAD_CAN_MIGRATE(td)  ((td)->td_pinned == 0)
#define THREAD_CAN_SCHED(td, cpu)       \
    CPU_ISSET((cpu), &(td)->td_cpuset->cs_mask)

_Static_assert(sizeof(struct thread) + sizeof(struct td_sched) <=
    sizeof(struct thread0_storage),
    "increase struct thread0_storage.t0st_sched size");

/*
 * Priority ranges used for interactive and non-interactive timeshare
 * threads.  The timeshare priorities are split up into four ranges.
 * The first range handles interactive threads.  The last three ranges
 * (NHALF, x, and NHALF) handle non-interactive threads with the outer
 * ranges supporting nice values.
 */
#define PRI_TIMESHARE_RANGE     (PRI_MAX_TIMESHARE - PRI_MIN_TIMESHARE + 1)
#define PRI_INTERACT_RANGE      ((PRI_TIMESHARE_RANGE - SCHED_PRI_NRESV) / 2)
#define PRI_BATCH_RANGE         (PRI_TIMESHARE_RANGE - PRI_INTERACT_RANGE)

#define PRI_MIN_INTERACT        PRI_MIN_TIMESHARE
#define PRI_MAX_INTERACT        (PRI_MIN_TIMESHARE + PRI_INTERACT_RANGE - 1)
#define PRI_MIN_BATCH           (PRI_MIN_TIMESHARE + PRI_INTERACT_RANGE)
#define PRI_MAX_BATCH           PRI_MAX_TIMESHARE

/*
 * Cpu percentage computation macros and defines.
 *
 * SCHED_TICK_SECS:     Number of seconds to average the cpu usage across.
 * SCHED_TICK_TARG:     Number of hz ticks to average the cpu usage across.
 * SCHED_TICK_MAX:      Maximum number of ticks before scaling back.
 * SCHED_TICK_SHIFT:    Shift factor to avoid rounding away results.
 * SCHED_TICK_HZ:       Compute the number of hz ticks for a given ticks count.
 * SCHED_TICK_TOTAL:    Gives the amount of time we've been recording ticks.
 */
#define SCHED_TICK_SECS         10
#define SCHED_TICK_TARG         (hz * SCHED_TICK_SECS)
#define SCHED_TICK_MAX          (SCHED_TICK_TARG + hz)
#define SCHED_TICK_SHIFT        10
#define SCHED_TICK_HZ(ts)       ((ts)->ts_ticks >> SCHED_TICK_SHIFT)
#define SCHED_TICK_TOTAL(ts)    (max((ts)->ts_ltick - (ts)->ts_ftick, hz))

/*
 * These macros determine priorities for non-interactive threads.  They are
 * assigned a priority based on their recent cpu utilization as expressed
 * by the ratio of ticks to the tick total.  NHALF priorities at the start
 * and end of the MIN to MAX timeshare range are only reachable with negative
 * or positive nice respectively.
 *
 * PRI_RANGE:   Priority range for utilization dependent priorities.
 * PRI_NRESV:   Number of nice values.
 * PRI_TICKS:   Compute a priority in PRI_RANGE from the ticks count and total.
 * PRI_NICE:    Determines the part of the priority inherited from nice.
 */
#define SCHED_PRI_NRESV         (PRIO_MAX - PRIO_MIN)
#define SCHED_PRI_NHALF         (SCHED_PRI_NRESV / 2)
#define SCHED_PRI_MIN           (PRI_MIN_BATCH + SCHED_PRI_NHALF)
#define SCHED_PRI_MAX           (PRI_MAX_BATCH - SCHED_PRI_NHALF)
#define SCHED_PRI_RANGE         (SCHED_PRI_MAX - SCHED_PRI_MIN + 1)
#define SCHED_PRI_TICKS(ts)                                             \
    (SCHED_TICK_HZ((ts)) /                                              \
    (roundup(SCHED_TICK_TOTAL((ts)), SCHED_PRI_RANGE) / SCHED_PRI_RANGE))
#define SCHED_PRI_NICE(nice)    (nice)

/*
 * These determine the interactivity of a process.  Interactivity differs from
 * cpu utilization in that it expresses the voluntary time slept vs time ran
 * while cpu utilization includes all time not running.  This more accurately
 * models the intent of the thread.
 *
 * SLP_RUN_MAX: Maximum amount of sleep time + run time we'll accumulate
 *              before throttling back.
 * SLP_RUN_FORK:        Maximum slp+run time to inherit at fork time.
 * INTERACT_MAX:        Maximum interactivity value.  Smaller is better.
 * INTERACT_THRESH:     Threshold for placement on the current runq.
 */
#define SCHED_SLP_RUN_MAX       ((hz * 5) << SCHED_TICK_SHIFT)
#define SCHED_SLP_RUN_FORK      ((hz / 2) << SCHED_TICK_SHIFT)
#define SCHED_INTERACT_MAX      (100)
#define SCHED_INTERACT_HALF     (SCHED_INTERACT_MAX / 2)
#define SCHED_INTERACT_THRESH   (30)

/*
 * These parameters determine the slice behavior for batch work.
 */
#define SCHED_SLICE_DEFAULT_DIVISOR     10      /* ~94 ms, 12 stathz ticks. */
#define SCHED_SLICE_MIN_DIVISOR         6       /* DEFAULT/MIN = ~16 ms. */

/* Flags kept in td_flags. */
#define TDF_SLICEEND    TDF_SCHED2      /* Thread time slice is over. */

/*
 * tickincr:            Converts a stathz tick into a hz domain scaled by
 *                      the shift factor.  Without the shift the error rate
 *                      due to rounding would be unacceptably high.
 * realstathz:          stathz is sometimes 0 and run off of hz.
 * sched_slice:         Runtime of each thread before rescheduling.
 * preempt_thresh:      Priority threshold for preemption and remote IPIs.
 */
static int __read_mostly sched_interact = SCHED_INTERACT_THRESH;
static int __read_mostly tickincr = 8 << SCHED_TICK_SHIFT;
static int __read_mostly realstathz = 127;      /* reset during boot. */
static int __read_mostly sched_slice = 10;      /* reset during boot. */
static int __read_mostly sched_slice_min = 1;   /* reset during boot. */
#ifdef PREEMPTION
#ifdef FULL_PREEMPTION
static int __read_mostly preempt_thresh = PRI_MAX_IDLE;
#else
static int __read_mostly preempt_thresh = PRI_MIN_KERN;
#endif
#else 
static int __read_mostly preempt_thresh = 0;
#endif
static int __read_mostly static_boost = PRI_MIN_BATCH;
static int __read_mostly sched_idlespins = 10000;
static int __read_mostly sched_idlespinthresh = -1;

/*
 * tdq - per processor runqs and statistics.  All fields are protected by the
 * tdq_lock.  The load and lowpri may be accessed without to avoid excess
 * locking in sched_pickcpu();
 */
struct tdq {
        /* 
         * Ordered to improve efficiency of cpu_search() and switch().
         * tdq_lock is padded to avoid false sharing with tdq_load and
         * tdq_cpu_idle.
         */
        struct mtx_padalign tdq_lock;           /* run queue lock. */
        struct cpu_group *tdq_cg;               /* Pointer to cpu topology. */
        volatile int    tdq_load;               /* Aggregate load. */
        volatile int    tdq_cpu_idle;           /* cpu_idle() is active. */
        int             tdq_sysload;            /* For loadavg, !ITHD load. */
        volatile int    tdq_transferable;       /* Transferable thread count. */
        volatile short  tdq_switchcnt;          /* Switches this tick. */
        volatile short  tdq_oldswitchcnt;       /* Switches last tick. */
        u_char          tdq_lowpri;             /* Lowest priority thread. */
        u_char          tdq_owepreempt;         /* Remote preemption pending. */
        u_char          tdq_idx;                /* Current insert index. */
        u_char          tdq_ridx;               /* Current removal index. */
        int             tdq_id;                 /* cpuid. */
        struct runq     tdq_realtime;           /* real-time run queue. */
        struct runq     tdq_timeshare;          /* timeshare run queue. */
        struct runq     tdq_idle;               /* Queue of IDLE threads. */
        char            tdq_name[TDQ_NAME_LEN];
#ifdef KTR
        char            tdq_loadname[TDQ_LOADNAME_LEN];
#endif
} __aligned(64);

/* Idle thread states and config. */
#define TDQ_RUNNING     1
#define TDQ_IDLE        2

#ifdef SMP
struct cpu_group __read_mostly *cpu_top;                /* CPU topology */

#define SCHED_AFFINITY_DEFAULT  (max(1, hz / 1000))
#define SCHED_AFFINITY(ts, t)   ((ts)->ts_rltick > ticks - ((t) * affinity))

/*
 * Run-time tunables.
 */
static int rebalance = 1;
static int balance_interval = 128;      /* Default set in sched_initticks(). */
static int __read_mostly affinity;
static int __read_mostly steal_idle = 1;
static int __read_mostly steal_thresh = 2;
static int __read_mostly always_steal = 0;
static int __read_mostly trysteal_limit = 2;

/*
 * One thread queue per processor.
 */
static struct tdq __read_mostly *balance_tdq;
static int balance_ticks;
DPCPU_DEFINE_STATIC(struct tdq, tdq);
DPCPU_DEFINE_STATIC(uint32_t, randomval);

#define TDQ_SELF()      ((struct tdq *)PCPU_GET(sched))
#define TDQ_CPU(x)      (DPCPU_ID_PTR((x), tdq))
#define TDQ_ID(x)       ((x)->tdq_id)
#else   /* !SMP */
static struct tdq       tdq_cpu;

#define TDQ_ID(x)       (0)
#define TDQ_SELF()      (&tdq_cpu)
#define TDQ_CPU(x)      (&tdq_cpu)
#endif

#define TDQ_LOCK_ASSERT(t, type)        mtx_assert(TDQ_LOCKPTR((t)), (type))
#define TDQ_LOCK(t)             mtx_lock_spin(TDQ_LOCKPTR((t)))
#define TDQ_LOCK_FLAGS(t, f)    mtx_lock_spin_flags(TDQ_LOCKPTR((t)), (f))
#define TDQ_UNLOCK(t)           mtx_unlock_spin(TDQ_LOCKPTR((t)))
#define TDQ_LOCKPTR(t)          ((struct mtx *)(&(t)->tdq_lock))

static void sched_priority(struct thread *);
static void sched_thread_priority(struct thread *, u_char);
static int sched_interact_score(struct thread *);
static void sched_interact_update(struct thread *);
static void sched_interact_fork(struct thread *);
static void sched_pctcpu_update(struct td_sched *, int);

/* Operations on per processor queues */
static struct thread *tdq_choose(struct tdq *);
static void tdq_setup(struct tdq *, int i);
static void tdq_load_add(struct tdq *, struct thread *);
static void tdq_load_rem(struct tdq *, struct thread *);
static __inline void tdq_runq_add(struct tdq *, struct thread *, int);
static __inline void tdq_runq_rem(struct tdq *, struct thread *);
static inline int sched_shouldpreempt(int, int, int);
void tdq_print(int cpu);
static void runq_print(struct runq *rq);
static void tdq_add(struct tdq *, struct thread *, int);
#ifdef SMP
static struct thread *tdq_move(struct tdq *, struct tdq *);
static int tdq_idled(struct tdq *);
static void tdq_notify(struct tdq *, struct thread *);
static struct thread *tdq_steal(struct tdq *, int);
static struct thread *runq_steal(struct runq *, int);
static int sched_pickcpu(struct thread *, int);
static void sched_balance(void);
static int sched_balance_pair(struct tdq *, struct tdq *);
static inline struct tdq *sched_setcpu(struct thread *, int, int);
static inline void thread_unblock_switch(struct thread *, struct mtx *);
static int sysctl_kern_sched_topology_spec(SYSCTL_HANDLER_ARGS);
static int sysctl_kern_sched_topology_spec_internal(struct sbuf *sb, 
    struct cpu_group *cg, int indent);
#endif

static void sched_setup(void *dummy);
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);

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 *");

/*
 * Print the threads waiting on a run-queue.
 */
static void
runq_print(struct runq *rq)
{
        struct rqhead *rqh;
        struct thread *td;
        int pri;
        int j;
        int i;

        for (i = 0; i < RQB_LEN; i++) {
                printf("\t\trunq bits %d 0x%zx\n",
                    i, rq->rq_status.rqb_bits[i]);
                for (j = 0; j < RQB_BPW; j++)
                        if (rq->rq_status.rqb_bits[i] & (1ul << j)) {
                                pri = j + (i << RQB_L2BPW);
                                rqh = &rq->rq_queues[pri];
                                TAILQ_FOREACH(td, rqh, td_runq) {
                                        printf("\t\t\ttd %p(%s) priority %d rqindex %d pri %d\n",
                                            td, td->td_name, td->td_priority,
                                            td->td_rqindex, pri);
                                }
                        }
        }
}

/*
 * Print the status of a per-cpu thread queue.  Should be a ddb show cmd.
 */
void
tdq_print(int cpu)
{
        struct tdq *tdq;

        tdq = TDQ_CPU(cpu);

        printf("tdq %d:\n", TDQ_ID(tdq));
        printf("\tlock            %p\n", TDQ_LOCKPTR(tdq));
        printf("\tLock name:      %s\n", tdq->tdq_name);
        printf("\tload:           %d\n", tdq->tdq_load);
        printf("\tswitch cnt:     %d\n", tdq->tdq_switchcnt);
        printf("\told switch cnt: %d\n", tdq->tdq_oldswitchcnt);
        printf("\ttimeshare idx:  %d\n", tdq->tdq_idx);
        printf("\ttimeshare ridx: %d\n", tdq->tdq_ridx);
        printf("\tload transferable: %d\n", tdq->tdq_transferable);
        printf("\tlowest priority:   %d\n", tdq->tdq_lowpri);
        printf("\trealtime runq:\n");
        runq_print(&tdq->tdq_realtime);
        printf("\ttimeshare runq:\n");
        runq_print(&tdq->tdq_timeshare);
        printf("\tidle runq:\n");
        runq_print(&tdq->tdq_idle);
}

static inline int
sched_shouldpreempt(int pri, int cpri, int remote)
{
        /*
         * If the new priority is not better than the current priority there is
         * nothing to do.
         */
        if (pri >= cpri)
                return (0);
        /*
         * Always preempt idle.
         */
        if (cpri >= PRI_MIN_IDLE)
                return (1);
        /*
         * If preemption is disabled don't preempt others.
         */
        if (preempt_thresh == 0)
                return (0);
        /*
         * Preempt if we exceed the threshold.
         */
        if (pri <= preempt_thresh)
                return (1);
        /*
         * If we're interactive or better and there is non-interactive
         * or worse running preempt only remote processors.
         */
        if (remote && pri <= PRI_MAX_INTERACT && cpri > PRI_MAX_INTERACT)
                return (1);
        return (0);
}

/*
 * Add a thread to the actual run-queue.  Keeps transferable counts up to
 * date with what is actually on the run-queue.  Selects the correct
 * queue position for timeshare threads.
 */
static __inline void
tdq_runq_add(struct tdq *tdq, struct thread *td, int flags)
{
        struct td_sched *ts;
        u_char pri;

        TDQ_LOCK_ASSERT(tdq, MA_OWNED);
        THREAD_LOCK_BLOCKED_ASSERT(td, MA_OWNED);

        pri = td->td_priority;
        ts = td_get_sched(td);
        TD_SET_RUNQ(td);
        if (THREAD_CAN_MIGRATE(td)) {
                tdq->tdq_transferable++;
                ts->ts_flags |= TSF_XFERABLE;
        }
        if (pri < PRI_MIN_BATCH) {
                ts->ts_runq = &tdq->tdq_realtime;
        } else if (pri <= PRI_MAX_BATCH) {
                ts->ts_runq = &tdq->tdq_timeshare;
                KASSERT(pri <= PRI_MAX_BATCH && pri >= PRI_MIN_BATCH,
                        ("Invalid priority %d on timeshare runq", pri));
                /*
                 * This queue contains only priorities between MIN and MAX
                 * realtime.  Use the whole queue to represent these values.
                 */
                if ((flags & (SRQ_BORROWING|SRQ_PREEMPTED)) == 0) {
                        pri = RQ_NQS * (pri - PRI_MIN_BATCH) / PRI_BATCH_RANGE;
                        pri = (pri + tdq->tdq_idx) % RQ_NQS;
                        /*
                         * This effectively shortens the queue by one so we
                         * can have a one slot difference between idx and
                         * ridx while we wait for threads to drain.
                         */
                        if (tdq->tdq_ridx != tdq->tdq_idx &&
                            pri == tdq->tdq_ridx)
                                pri = (unsigned char)(pri - 1) % RQ_NQS;
                } else
                        pri = tdq->tdq_ridx;
                runq_add_pri(ts->ts_runq, td, pri, flags);
                return;
        } else
                ts->ts_runq = &tdq->tdq_idle;
        runq_add(ts->ts_runq, td, flags);
}

/* 
 * Remove a thread from a run-queue.  This typically happens when a thread
 * is selected to run.  Running threads are not on the queue and the
 * transferable count does not reflect them.
 */
static __inline void
tdq_runq_rem(struct tdq *tdq, struct thread *td)
{
        struct td_sched *ts;

        ts = td_get_sched(td);
        TDQ_LOCK_ASSERT(tdq, MA_OWNED);
        THREAD_LOCK_BLOCKED_ASSERT(td, MA_OWNED);
        KASSERT(ts->ts_runq != NULL,
            ("tdq_runq_remove: thread %p null ts_runq", td));
        if (ts->ts_flags & TSF_XFERABLE) {
                tdq->tdq_transferable--;
                ts->ts_flags &= ~TSF_XFERABLE;
        }
        if (ts->ts_runq == &tdq->tdq_timeshare) {
                if (tdq->tdq_idx != tdq->tdq_ridx)
                        runq_remove_idx(ts->ts_runq, td, &tdq->tdq_ridx);
                else
                        runq_remove_idx(ts->ts_runq, td, NULL);
        } else
                runq_remove(ts->ts_runq, td);
}

/*
 * Load is maintained for all threads RUNNING and ON_RUNQ.  Add the load
 * for this thread to the referenced thread queue.
 */
static void
tdq_load_add(struct tdq *tdq, struct thread *td)
{

        TDQ_LOCK_ASSERT(tdq, MA_OWNED);
        THREAD_LOCK_BLOCKED_ASSERT(td, MA_OWNED);

        tdq->tdq_load++;
        if ((td->td_flags & TDF_NOLOAD) == 0)
                tdq->tdq_sysload++;
        KTR_COUNTER0(KTR_SCHED, "load", tdq->tdq_loadname, tdq->tdq_load);
        SDT_PROBE2(sched, , , load__change, (int)TDQ_ID(tdq), tdq->tdq_load);
}

/*
 * Remove the load from a thread that is transitioning to a sleep state or
 * exiting.
 */
static void
tdq_load_rem(struct tdq *tdq, struct thread *td)
{

        TDQ_LOCK_ASSERT(tdq, MA_OWNED);
        THREAD_LOCK_BLOCKED_ASSERT(td, MA_OWNED);
        KASSERT(tdq->tdq_load != 0,
            ("tdq_load_rem: Removing with 0 load on queue %d", TDQ_ID(tdq)));

        tdq->tdq_load--;
        if ((td->td_flags & TDF_NOLOAD) == 0)
                tdq->tdq_sysload--;
        KTR_COUNTER0(KTR_SCHED, "load", tdq->tdq_loadname, tdq->tdq_load);
        SDT_PROBE2(sched, , , load__change, (int)TDQ_ID(tdq), tdq->tdq_load);
}

/*
 * Bound timeshare latency by decreasing slice size as load increases.  We
 * consider the maximum latency as the sum of the threads waiting to run
 * aside from curthread and target no more than sched_slice latency but
 * no less than sched_slice_min runtime.
 */
static inline int
tdq_slice(struct tdq *tdq)
{
        int load;

        /*
         * It is safe to use sys_load here because this is called from
         * contexts where timeshare threads are running and so there
         * cannot be higher priority load in the system.
         */
        load = tdq->tdq_sysload - 1;
        if (load >= SCHED_SLICE_MIN_DIVISOR)
                return (sched_slice_min);
        if (load <= 1)
                return (sched_slice);
        return (sched_slice / load);
}

/*
 * Set lowpri to its exact value by searching the run-queue and
 * evaluating curthread.  curthread may be passed as an optimization.
 */
static void
tdq_setlowpri(struct tdq *tdq, struct thread *ctd)
{
        struct thread *td;

        TDQ_LOCK_ASSERT(tdq, MA_OWNED);
        if (ctd == NULL)
                ctd = pcpu_find(TDQ_ID(tdq))->pc_curthread;
        td = tdq_choose(tdq);
        if (td == NULL || td->td_priority > ctd->td_priority)
                tdq->tdq_lowpri = ctd->td_priority;
        else
                tdq->tdq_lowpri = td->td_priority;
}

#ifdef SMP
/*
 * We need some randomness. Implement a classic Linear Congruential
 * Generator X_{n+1}=(aX_n+c) mod m. These values are optimized for
 * m = 2^32, a = 69069 and c = 5. We only return the upper 16 bits
 * of the random state (in the low bits of our answer) to keep
 * the maximum randomness.
 */
static uint32_t
sched_random(void)
{
        uint32_t *rndptr;

        rndptr = DPCPU_PTR(randomval);
        *rndptr = *rndptr * 69069 + 5;

        return (*rndptr >> 16);
}

struct cpu_search {
        cpuset_t cs_mask;
        u_int   cs_prefer;
        int     cs_pri;         /* Min priority for low. */
        int     cs_limit;       /* Max load for low, min load for high. */
        int     cs_cpu;
        int     cs_load;
};

#define CPU_SEARCH_LOWEST       0x1
#define CPU_SEARCH_HIGHEST      0x2
#define CPU_SEARCH_BOTH         (CPU_SEARCH_LOWEST|CPU_SEARCH_HIGHEST)

static __always_inline int cpu_search(const struct cpu_group *cg,
    struct cpu_search *low, struct cpu_search *high, const int match);
int __noinline cpu_search_lowest(const struct cpu_group *cg,
    struct cpu_search *low);
int __noinline cpu_search_highest(const struct cpu_group *cg,
    struct cpu_search *high);
int __noinline cpu_search_both(const struct cpu_group *cg,
    struct cpu_search *low, struct cpu_search *high);

/*
 * Search the tree of cpu_groups for the lowest or highest loaded cpu
 * according to the match argument.  This routine actually compares the
 * load on all paths through the tree and finds the least loaded cpu on
 * the least loaded path, which may differ from the least loaded cpu in
 * the system.  This balances work among caches and buses.
 *
 * This inline is instantiated in three forms below using constants for the
 * match argument.  It is reduced to the minimum set for each case.  It is
 * also recursive to the depth of the tree.
 */
static __always_inline int
cpu_search(const struct cpu_group *cg, struct cpu_search *low,
    struct cpu_search *high, const int match)
{
        struct cpu_search lgroup;
        struct cpu_search hgroup;
        cpuset_t cpumask;
        struct cpu_group *child;
        struct tdq *tdq;
        int cpu, i, hload, lload, load, total, rnd;

        total = 0;
        cpumask = cg->cg_mask;
        if (match & CPU_SEARCH_LOWEST) {
                lload = INT_MAX;
                lgroup = *low;
        }
        if (match & CPU_SEARCH_HIGHEST) {
                hload = INT_MIN;
                hgroup = *high;
        }

        /* Iterate through the child CPU groups and then remaining CPUs. */
        for (i = cg->cg_children, cpu = mp_maxid; ; ) {
                if (i == 0) {
#ifdef HAVE_INLINE_FFSL
                        cpu = CPU_FFS(&cpumask) - 1;
#else
                        while (cpu >= 0 && !CPU_ISSET(cpu, &cpumask))
                                cpu--;
#endif
                        if (cpu < 0)
                                break;
                        child = NULL;
                } else
                        child = &cg->cg_child[i - 1];

                if (match & CPU_SEARCH_LOWEST)
                        lgroup.cs_cpu = -1;
                if (match & CPU_SEARCH_HIGHEST)
                        hgroup.cs_cpu = -1;
                if (child) {                    /* Handle child CPU group. */
                        CPU_ANDNOT(&cpumask, &child->cg_mask);
                        switch (match) {
                        case CPU_SEARCH_LOWEST:
                                load = cpu_search_lowest(child, &lgroup);
                                break;
                        case CPU_SEARCH_HIGHEST:
                                load = cpu_search_highest(child, &hgroup);
                                break;
                        case CPU_SEARCH_BOTH:
                                load = cpu_search_both(child, &lgroup, &hgroup);
                                break;
                        }
                } else {                        /* Handle child CPU. */
                        CPU_CLR(cpu, &cpumask);
                        tdq = TDQ_CPU(cpu);
                        load = tdq->tdq_load * 256;
                        rnd = sched_random() % 32;
                        if (match & CPU_SEARCH_LOWEST) {
                                if (cpu == low->cs_prefer)
                                        load -= 64;
                                /* If that CPU is allowed and get data. */
                                if (tdq->tdq_lowpri > lgroup.cs_pri &&
                                    tdq->tdq_load <= lgroup.cs_limit &&
                                    CPU_ISSET(cpu, &lgroup.cs_mask)) {
                                        lgroup.cs_cpu = cpu;
                                        lgroup.cs_load = load - rnd;
                                }
                        }
                        if (match & CPU_SEARCH_HIGHEST)
                                if (tdq->tdq_load >= hgroup.cs_limit &&
                                    tdq->tdq_transferable &&
                                    CPU_ISSET(cpu, &hgroup.cs_mask)) {
                                        hgroup.cs_cpu = cpu;
                                        hgroup.cs_load = load - rnd;
                                }
                }
                total += load;

                /* We have info about child item. Compare it. */
                if (match & CPU_SEARCH_LOWEST) {
                        if (lgroup.cs_cpu >= 0 &&
                            (load < lload ||
                             (load == lload && lgroup.cs_load < low->cs_load))) {
                                lload = load;
                                low->cs_cpu = lgroup.cs_cpu;
                                low->cs_load = lgroup.cs_load;
                        }
                }
                if (match & CPU_SEARCH_HIGHEST)
                        if (hgroup.cs_cpu >= 0 &&
                            (load > hload ||
                             (load == hload && hgroup.cs_load > high->cs_load))) {
                                hload = load;
                                high->cs_cpu = hgroup.cs_cpu;
                                high->cs_load = hgroup.cs_load;
                        }
                if (child) {
                        i--;
                        if (i == 0 && CPU_EMPTY(&cpumask))
                                break;
                }
#ifndef HAVE_INLINE_FFSL
                else
                        cpu--;
#endif
        }
        return (total);
}

/*
 * cpu_search instantiations must pass constants to maintain the inline
 * optimization.
 */
int
cpu_search_lowest(const struct cpu_group *cg, struct cpu_search *low)
{
        return cpu_search(cg, low, NULL, CPU_SEARCH_LOWEST);
}

int
cpu_search_highest(const struct cpu_group *cg, struct cpu_search *high)
{
        return cpu_search(cg, NULL, high, CPU_SEARCH_HIGHEST);
}

int
cpu_search_both(const struct cpu_group *cg, struct cpu_search *low,
    struct cpu_search *high)
{
        return cpu_search(cg, low, high, CPU_SEARCH_BOTH);
}

/*
 * Find the cpu with the least load via the least loaded path that has a
 * lowpri greater than pri  pri.  A pri of -1 indicates any priority is
 * acceptable.
 */
static inline int
sched_lowest(const struct cpu_group *cg, cpuset_t mask, int pri, int maxload,
    int prefer)
{
        struct cpu_search low;

        low.cs_cpu = -1;
        low.cs_prefer = prefer;
        low.cs_mask = mask;
        low.cs_pri = pri;
        low.cs_limit = maxload;
        cpu_search_lowest(cg, &low);
        return low.cs_cpu;
}

/*
 * Find the cpu with the highest load via the highest loaded path.
 */
static inline int
sched_highest(const struct cpu_group *cg, cpuset_t mask, int minload)
{
        struct cpu_search high;

        high.cs_cpu = -1;
        high.cs_mask = mask;
        high.cs_limit = minload;
        cpu_search_highest(cg, &high);
        return high.cs_cpu;
}

static void
sched_balance_group(struct cpu_group *cg)
{
        struct tdq *tdq;
        cpuset_t hmask, lmask;
        int high, low, anylow;

        CPU_FILL(&hmask);
        for (;;) {
                high = sched_highest(cg, hmask, 2);
                /* Stop if there is no more CPU with transferrable threads. */
                if (high == -1)
                        break;
                CPU_CLR(high, &hmask);
                CPU_COPY(&hmask, &lmask);
                /* Stop if there is no more CPU left for low. */
                if (CPU_EMPTY(&lmask))
                        break;
                anylow = 1;
                tdq = TDQ_CPU(high);
nextlow:
                low = sched_lowest(cg, lmask, -1, tdq->tdq_load - 1, high);
                /* Stop if we looked well and found no less loaded CPU. */
                if (anylow && low == -1)
                        break;
                /* Go to next high if we found no less loaded CPU. */
                if (low == -1)
                        continue;
                /* Transfer thread from high to low. */
                if (sched_balance_pair(tdq, TDQ_CPU(low))) {
                        /* CPU that got thread can no longer be a donor. */
                        CPU_CLR(low, &hmask);
                } else {
                        /*
                         * If failed, then there is no threads on high
                         * that can run on this low. Drop low from low
                         * mask and look for different one.
                         */
                        CPU_CLR(low, &lmask);
                        anylow = 0;
                        goto nextlow;
                }
        }
}

static void
sched_balance(void)
{
        struct tdq *tdq;

        balance_ticks = max(balance_interval / 2, 1) +
            (sched_random() % balance_interval);
        tdq = TDQ_SELF();
        TDQ_UNLOCK(tdq);
        sched_balance_group(cpu_top);
        TDQ_LOCK(tdq);
}

/*
 * Lock two thread queues using their address to maintain lock order.
 */
static void
tdq_lock_pair(struct tdq *one, struct tdq *two)
{
        if (one < two) {
                TDQ_LOCK(one);
                TDQ_LOCK_FLAGS(two, MTX_DUPOK);
        } else {
                TDQ_LOCK(two);
                TDQ_LOCK_FLAGS(one, MTX_DUPOK);
        }
}

/*
 * Unlock two thread queues.  Order is not important here.
 */
static void
tdq_unlock_pair(struct tdq *one, struct tdq *two)
{
        TDQ_UNLOCK(one);
        TDQ_UNLOCK(two);
}

/*
 * Transfer load between two imbalanced thread queues.
 */
static int
sched_balance_pair(struct tdq *high, struct tdq *low)
{
        struct thread *td;
        int cpu;

        tdq_lock_pair(high, low);
        td = NULL;
        /*
         * Transfer a thread from high to low.
         */
        if (high->tdq_transferable != 0 && high->tdq_load > low->tdq_load &&
            (td = tdq_move(high, low)) != NULL) {
                /*
                 * In case the target isn't the current cpu notify it of the
                 * new load, possibly sending an IPI to force it to reschedule.
                 */
                cpu = TDQ_ID(low);
                if (cpu != PCPU_GET(cpuid))
                        tdq_notify(low, td);
        }
        tdq_unlock_pair(high, low);
        return (td != NULL);
}

/*
 * Move a thread from one thread queue to another.
 */
static struct thread *
tdq_move(struct tdq *from, struct tdq *to)
{
        struct thread *td;
        struct tdq *tdq;
        int cpu;

        TDQ_LOCK_ASSERT(from, MA_OWNED);
        TDQ_LOCK_ASSERT(to, MA_OWNED);

        tdq = from;
        cpu = TDQ_ID(to);
        td = tdq_steal(tdq, cpu);
        if (td == NULL)
                return (NULL);

        /*
         * Although the run queue is locked the thread may be
         * blocked.  We can not set the lock until it is unblocked.
         */
        thread_lock_block_wait(td);
        sched_rem(td);
        THREAD_LOCKPTR_ASSERT(td, TDQ_LOCKPTR(from));
        td->td_lock = TDQ_LOCKPTR(to);
        td_get_sched(td)->ts_cpu = cpu;
        tdq_add(to, td, SRQ_YIELDING);

        return (td);
}

/*
 * This tdq has idled.  Try to steal a thread from another cpu and switch
 * to it.
 */
static int
tdq_idled(struct tdq *tdq)
{
        struct cpu_group *cg;
        struct tdq *steal;
        cpuset_t mask;
        int cpu, switchcnt;

        if (smp_started == 0 || steal_idle == 0 || tdq->tdq_cg == NULL)
                return (1);
        CPU_FILL(&mask);
        CPU_CLR(PCPU_GET(cpuid), &mask);
    restart:
        switchcnt = tdq->tdq_switchcnt + tdq->tdq_oldswitchcnt;
        for (cg = tdq->tdq_cg; ; ) {
                cpu = sched_highest(cg, mask, steal_thresh);
                /*
                 * We were assigned a thread but not preempted.  Returning
                 * 0 here will cause our caller to switch to it.
                 */
                if (tdq->tdq_load)
                        return (0);
                if (cpu == -1) {
                        cg = cg->cg_parent;
                        if (cg == NULL)
                                return (1);
                        continue;
                }
                steal = TDQ_CPU(cpu);
                /*
                 * The data returned by sched_highest() is stale and
                 * the chosen CPU no longer has an eligible thread.
                 *
                 * Testing this ahead of tdq_lock_pair() only catches
                 * this situation about 20% of the time on an 8 core
                 * 16 thread Ryzen 7, but it still helps performance.
                 */
                if (steal->tdq_load < steal_thresh ||
                    steal->tdq_transferable == 0)
                        goto restart;
                tdq_lock_pair(tdq, steal);
                /*
                 * We were assigned a thread while waiting for the locks.
                 * Switch to it now instead of stealing a thread.
                 */
                if (tdq->tdq_load)
                        break;
                /*
                 * The data returned by sched_highest() is stale and
                 * the chosen CPU no longer has an eligible thread, or
                 * we were preempted and the CPU loading info may be out
                 * of date.  The latter is rare.  In either case restart
                 * the search.
                 */
                if (steal->tdq_load < steal_thresh ||
                    steal->tdq_transferable == 0 ||
                    switchcnt != tdq->tdq_switchcnt + tdq->tdq_oldswitchcnt) {
                        tdq_unlock_pair(tdq, steal);
                        goto restart;
                }
                /*
                 * Steal the thread and switch to it.
                 */
                if (tdq_move(steal, tdq) != NULL)
                        break;
                /*
                 * We failed to acquire a thread even though it looked
                 * like one was available.  This could be due to affinity
                 * restrictions or for other reasons.  Loop again after
                 * removing this CPU from the set.  The restart logic
                 * above does not restore this CPU to the set due to the
                 * likelyhood of failing here again.
                 */
                CPU_CLR(cpu, &mask);
                tdq_unlock_pair(tdq, steal);
        }
        TDQ_UNLOCK(steal);
        mi_switch(SW_VOL | SWT_IDLE);
        return (0);
}

/*
 * Notify a remote cpu of new work.  Sends an IPI if criteria are met.
 */
static void
tdq_notify(struct tdq *tdq, struct thread *td)
{
        struct thread *ctd;
        int pri;
        int cpu;

        if (tdq->tdq_owepreempt)
                return;
        cpu = td_get_sched(td)->ts_cpu;
        pri = td->td_priority;
        ctd = pcpu_find(cpu)->pc_curthread;
        if (!sched_shouldpreempt(pri, ctd->td_priority, 1))
                return;

        /*
         * Make sure that our caller's earlier update to tdq_load is
         * globally visible before we read tdq_cpu_idle.  Idle thread
         * accesses both of them without locks, and the order is important.
         */
        atomic_thread_fence_seq_cst();

        if (TD_IS_IDLETHREAD(ctd)) {
                /*
                 * If the MD code has an idle wakeup routine try that before
                 * falling back to IPI.
                 */
                if (!tdq->tdq_cpu_idle || cpu_idle_wakeup(cpu))
                        return;
        }

        /*
         * The run queues have been updated, so any switch on the remote CPU
         * will satisfy the preemption request.
         */
        tdq->tdq_owepreempt = 1;
        ipi_cpu(cpu, IPI_PREEMPT);
}

/*
 * Steals load from a timeshare queue.  Honors the rotating queue head
 * index.
 */
static struct thread *
runq_steal_from(struct runq *rq, int cpu, u_char start)
{
        struct rqbits *rqb;
        struct rqhead *rqh;
        struct thread *td, *first;
        int bit;
        int i;

        rqb = &rq->rq_status;
        bit = start & (RQB_BPW -1);
        first = NULL;
again:
        for (i = RQB_WORD(start); i < RQB_LEN; bit = 0, i++) {
                if (rqb->rqb_bits[i] == 0)
                        continue;
                if (bit == 0)
                        bit = RQB_FFS(rqb->rqb_bits[i]);
                for (; bit < RQB_BPW; bit++) {
                        if ((rqb->rqb_bits[i] & (1ul << bit)) == 0)
                                continue;
                        rqh = &rq->rq_queues[bit + (i << RQB_L2BPW)];
                        TAILQ_FOREACH(td, rqh, td_runq) {
                                if (first && THREAD_CAN_MIGRATE(td) &&
                                    THREAD_CAN_SCHED(td, cpu))
                                        return (td);
                                first = td;
                        }
                }
        }
        if (start != 0) {
                start = 0;
                goto again;
        }

        if (first && THREAD_CAN_MIGRATE(first) &&
            THREAD_CAN_SCHED(first, cpu))
                return (first);
        return (NULL);
}

/*
 * Steals load from a standard linear queue.
 */
static struct thread *
runq_steal(struct runq *rq, int cpu)
{
        struct rqhead *rqh;
        struct rqbits *rqb;
        struct thread *td;
        int word;
        int bit;

        rqb = &rq->rq_status;
        for (word = 0; word < RQB_LEN; word++) {
                if (rqb->rqb_bits[word] == 0)
                        continue;
                for (bit = 0; bit < RQB_BPW; bit++) {
                        if ((rqb->rqb_bits[word] & (1ul << bit)) == 0)
                                continue;
                        rqh = &rq->rq_queues[bit + (word << RQB_L2BPW)];
                        TAILQ_FOREACH(td, rqh, td_runq)
                                if (THREAD_CAN_MIGRATE(td) &&
                                    THREAD_CAN_SCHED(td, cpu))
                                        return (td);
                }
        }
        return (NULL);
}

/*
 * Attempt to steal a thread in priority order from a thread queue.
 */
static struct thread *
tdq_steal(struct tdq *tdq, int cpu)
{
        struct thread *td;

        TDQ_LOCK_ASSERT(tdq, MA_OWNED);
        if ((td = runq_steal(&tdq->tdq_realtime, cpu)) != NULL)
                return (td);
        if ((td = runq_steal_from(&tdq->tdq_timeshare,
            cpu, tdq->tdq_ridx)) != NULL)
                return (td);
        return (runq_steal(&tdq->tdq_idle, cpu));
}

/*
 * Sets the thread lock and ts_cpu to match the requested cpu.  Unlocks the
 * current lock and returns with the assigned queue locked.
 */
static inline struct tdq *
sched_setcpu(struct thread *td, int cpu, int flags)
{

        struct tdq *tdq;
        struct mtx *mtx;

        THREAD_LOCK_ASSERT(td, MA_OWNED);
        tdq = TDQ_CPU(cpu);
        td_get_sched(td)->ts_cpu = cpu;
        /*
         * If the lock matches just return the queue.
         */
        if (td->td_lock == TDQ_LOCKPTR(tdq)) {
                KASSERT((flags & SRQ_HOLD) == 0,
                    ("sched_setcpu: Invalid lock for SRQ_HOLD"));
                return (tdq);
        }

        /*
         * The hard case, migration, we need to block the thread first to
         * prevent order reversals with other cpus locks.
         */
        spinlock_enter();
        mtx = thread_lock_block(td);
        if ((flags & SRQ_HOLD) == 0)
                mtx_unlock_spin(mtx);
        TDQ_LOCK(tdq);
        thread_lock_unblock(td, TDQ_LOCKPTR(tdq));
        spinlock_exit();
        return (tdq);
}

SCHED_STAT_DEFINE(pickcpu_intrbind, "Soft interrupt binding");
SCHED_STAT_DEFINE(pickcpu_idle_affinity, "Picked idle cpu based on affinity");
SCHED_STAT_DEFINE(pickcpu_affinity, "Picked cpu based on affinity");
SCHED_STAT_DEFINE(pickcpu_lowest, "Selected lowest load");
SCHED_STAT_DEFINE(pickcpu_local, "Migrated to current cpu");
SCHED_STAT_DEFINE(pickcpu_migration, "Selection may have caused migration");

static int
sched_pickcpu(struct thread *td, int flags)
{
        struct cpu_group *cg, *ccg;
        struct td_sched *ts;
        struct tdq *tdq;
        cpuset_t mask;
        int cpu, pri, self, intr;

        self = PCPU_GET(cpuid);
        ts = td_get_sched(td);
        KASSERT(!CPU_ABSENT(ts->ts_cpu), ("sched_pickcpu: Start scheduler on "
            "absent CPU %d for thread %s.", ts->ts_cpu, td->td_name));
        if (smp_started == 0)
                return (self);
        /*
         * Don't migrate a running thread from sched_switch().
         */
        if ((flags & SRQ_OURSELF) || !THREAD_CAN_MIGRATE(td))
                return (ts->ts_cpu);
        /*
         * Prefer to run interrupt threads on the processors that generate
         * the interrupt.
         */
        if (td->td_priority <= PRI_MAX_ITHD && THREAD_CAN_SCHED(td, self) &&
            curthread->td_intr_nesting_level) {
                tdq = TDQ_SELF();
                if (tdq->tdq_lowpri >= PRI_MIN_IDLE) {
                        SCHED_STAT_INC(pickcpu_idle_affinity);
                        return (self);
                }
                ts->ts_cpu = self;
                intr = 1;
                cg = tdq->tdq_cg;
                goto llc;
        } else {
                intr = 0;
                tdq = TDQ_CPU(ts->ts_cpu);
                cg = tdq->tdq_cg;
        }
        /*
         * If the thread can run on the last cpu and the affinity has not
         * expired and it is idle, run it there.
         */
        if (THREAD_CAN_SCHED(td, ts->ts_cpu) &&
            tdq->tdq_lowpri >= PRI_MIN_IDLE &&
            SCHED_AFFINITY(ts, CG_SHARE_L2)) {
                if (cg->cg_flags & CG_FLAG_THREAD) {
                        /* Check all SMT threads for being idle. */
                        for (cpu = CPU_FFS(&cg->cg_mask) - 1; ; cpu++) {
                                if (CPU_ISSET(cpu, &cg->cg_mask) &&
                                    TDQ_CPU(cpu)->tdq_lowpri < PRI_MIN_IDLE)
                                        break;
                                if (cpu >= mp_maxid) {
                                        SCHED_STAT_INC(pickcpu_idle_affinity);
                                        return (ts->ts_cpu);
                                }
                        }
                } else {
                        SCHED_STAT_INC(pickcpu_idle_affinity);
                        return (ts->ts_cpu);
                }
        }
llc:
        /*
         * Search for the last level cache CPU group in the tree.
         * Skip SMT, identical groups and caches with expired affinity.
         * Interrupt threads affinity is explicit and never expires.
         */
        for (ccg = NULL; cg != NULL; cg = cg->cg_parent) {
                if (cg->cg_flags & CG_FLAG_THREAD)
                        continue;
                if (cg->cg_children == 1 || cg->cg_count == 1)
                        continue;
                if (cg->cg_level == CG_SHARE_NONE ||
                    (!intr && !SCHED_AFFINITY(ts, cg->cg_level)))
                        continue;
                ccg = cg;
        }
        /* Found LLC shared by all CPUs, so do a global search. */
        if (ccg == cpu_top)
                ccg = NULL;
        cpu = -1;
        mask = td->td_cpuset->cs_mask;
        pri = td->td_priority;
        /*
         * Try hard to keep interrupts within found LLC.  Search the LLC for
         * the least loaded CPU we can run now.  For NUMA systems it should
         * be within target domain, and it also reduces scheduling overhead.
         */
        if (ccg != NULL && intr) {
                cpu = sched_lowest(ccg, mask, pri, INT_MAX, ts->ts_cpu);
                if (cpu >= 0)
                        SCHED_STAT_INC(pickcpu_intrbind);
        } else
        /* Search the LLC for the least loaded idle CPU we can run now. */
        if (ccg != NULL) {
                cpu = sched_lowest(ccg, mask, max(pri, PRI_MAX_TIMESHARE),
                    INT_MAX, ts->ts_cpu);
                if (cpu >= 0)
                        SCHED_STAT_INC(pickcpu_affinity);
        }
        /* Search globally for the least loaded CPU we can run now. */
        if (cpu < 0) {
                cpu = sched_lowest(cpu_top, mask, pri, INT_MAX, ts->ts_cpu);
                if (cpu >= 0)
                        SCHED_STAT_INC(pickcpu_lowest);
        }
        /* Search globally for the least loaded CPU. */
        if (cpu < 0) {
                cpu = sched_lowest(cpu_top, mask, -1, INT_MAX, ts->ts_cpu);
                if (cpu >= 0)
                        SCHED_STAT_INC(pickcpu_lowest);
        }
        KASSERT(cpu >= 0, ("sched_pickcpu: Failed to find a cpu."));
        KASSERT(!CPU_ABSENT(cpu), ("sched_pickcpu: Picked absent CPU %d.", cpu));
        /*
         * Compare the lowest loaded cpu to current cpu.
         */
        tdq = TDQ_CPU(cpu);
        if (THREAD_CAN_SCHED(td, self) && TDQ_SELF()->tdq_lowpri > pri &&
            tdq->tdq_lowpri < PRI_MIN_IDLE &&
            TDQ_SELF()->tdq_load <= tdq->tdq_load + 1) {
                SCHED_STAT_INC(pickcpu_local);
                cpu = self;
        }
        if (cpu != ts->ts_cpu)
                SCHED_STAT_INC(pickcpu_migration);
        return (cpu);
}
#endif

/*
 * Pick the highest priority task we have and return it.
 */
static struct thread *
tdq_choose(struct tdq *tdq)
{
        struct thread *td;

        TDQ_LOCK_ASSERT(tdq, MA_OWNED);
        td = runq_choose(&tdq->tdq_realtime);
        if (td != NULL)
                return (td);
        td = runq_choose_from(&tdq->tdq_timeshare, tdq->tdq_ridx);
        if (td != NULL) {
                KASSERT(td->td_priority >= PRI_MIN_BATCH,
                    ("tdq_choose: Invalid priority on timeshare queue %d",
                    td->td_priority));
                return (td);
        }
        td = runq_choose(&tdq->tdq_idle);
        if (td != NULL) {
                KASSERT(td->td_priority >= PRI_MIN_IDLE,
                    ("tdq_choose: Invalid priority on idle queue %d",
                    td->td_priority));
                return (td);
        }

        return (NULL);
}

/*
 * Initialize a thread queue.
 */
static void
tdq_setup(struct tdq *tdq, int id)
{

        if (bootverbose)
                printf("ULE: setup cpu %d\n", id);
        runq_init(&tdq->tdq_realtime);
        runq_init(&tdq->tdq_timeshare);
        runq_init(&tdq->tdq_idle);
        tdq->tdq_id = id;
        snprintf(tdq->tdq_name, sizeof(tdq->tdq_name),
            "sched lock %d", (int)TDQ_ID(tdq));
        mtx_init(&tdq->tdq_lock, tdq->tdq_name, "sched lock", MTX_SPIN);
#ifdef KTR
        snprintf(tdq->tdq_loadname, sizeof(tdq->tdq_loadname),
            "CPU %d load", (int)TDQ_ID(tdq));
#endif
}

#ifdef SMP
static void
sched_setup_smp(void)
{
        struct tdq *tdq;
        int i;

        cpu_top = smp_topo();
        CPU_FOREACH(i) {
                tdq = DPCPU_ID_PTR(i, tdq);
                tdq_setup(tdq, i);
                tdq->tdq_cg = smp_topo_find(cpu_top, i);
                if (tdq->tdq_cg == NULL)
                        panic("Can't find cpu group for %d\n", i);
        }
        PCPU_SET(sched, DPCPU_PTR(tdq));
        balance_tdq = TDQ_SELF();
}
#endif

/*
 * Setup the thread queues and initialize the topology based on MD
 * information.
 */
static void
sched_setup(void *dummy)
{
        struct tdq *tdq;

#ifdef SMP
        sched_setup_smp();
#else
        tdq_setup(TDQ_SELF(), 0);
#endif
        tdq = TDQ_SELF();

        /* Add thread0's load since it's running. */
        TDQ_LOCK(tdq);
        thread0.td_lock = TDQ_LOCKPTR(tdq);
        tdq_load_add(tdq, &thread0);
        tdq->tdq_lowpri = thread0.td_priority;
        TDQ_UNLOCK(tdq);
}

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

        realstathz = stathz ? stathz : hz;
        sched_slice = realstathz / SCHED_SLICE_DEFAULT_DIVISOR;
        sched_slice_min = sched_slice / SCHED_SLICE_MIN_DIVISOR;
        hogticks = imax(1, (2 * hz * sched_slice + realstathz / 2) /
            realstathz);

        /*
         * tickincr is shifted out by 10 to avoid rounding errors due to
         * hz not being evenly divisible by stathz on all platforms.
         */
        incr = (hz << SCHED_TICK_SHIFT) / realstathz;
        /*
         * This does not work for values of stathz that are more than
         * 1 << SCHED_TICK_SHIFT * hz.  In practice this does not happen.
         */
        if (incr == 0)
                incr = 1;
        tickincr = incr;
#ifdef SMP
        /*
         * Set the default balance interval now that we know
         * what realstathz is.
         */
        balance_interval = realstathz;
        balance_ticks = balance_interval;
        affinity = SCHED_AFFINITY_DEFAULT;
#endif
        if (sched_idlespinthresh < 0)
                sched_idlespinthresh = 2 * max(10000, 6 * hz) / realstathz;
}

/*
 * This is the core of the interactivity algorithm.  Determines a score based
 * on past behavior.  It is the ratio of sleep time to run time scaled to
 * a [0, 100] integer.  This is the voluntary sleep time of a process, which
 * differs from the cpu usage because it does not account for time spent
 * waiting on a run-queue.  Would be prettier if we had floating point.
 *
 * When a thread's sleep time is greater than its run time the
 * calculation is:
 *
 *                           scaling factor 
 * interactivity score =  ---------------------
 *                        sleep time / run time
 *
 *
 * When a thread's run time is greater than its sleep time the
 * calculation is:
 *
 *                           scaling factor 
 * interactivity score =  ---------------------    + scaling factor
 *                        run time / sleep time
 */
static int
sched_interact_score(struct thread *td)
{
        struct td_sched *ts;
        int div;

        ts = td_get_sched(td);
        /*
         * The score is only needed if this is likely to be an interactive
         * task.  Don't go through the expense of computing it if there's
         * no chance.
         */
        if (sched_interact <= SCHED_INTERACT_HALF &&
                ts->ts_runtime >= ts->ts_slptime)
                        return (SCHED_INTERACT_HALF);

        if (ts->ts_runtime > ts->ts_slptime) {
                div = max(1, ts->ts_runtime / SCHED_INTERACT_HALF);
                return (SCHED_INTERACT_HALF +
                    (SCHED_INTERACT_HALF - (ts->ts_slptime / div)));
        }
        if (ts->ts_slptime > ts->ts_runtime) {
                div = max(1, ts->ts_slptime / SCHED_INTERACT_HALF);
                return (ts->ts_runtime / div);
        }
        /* runtime == slptime */
        if (ts->ts_runtime)
                return (SCHED_INTERACT_HALF);

        /*
         * This can happen if slptime and runtime are 0.
         */
        return (0);

}

/*
 * Scale the scheduling priority according to the "interactivity" of this
 * process.
 */
static void
sched_priority(struct thread *td)
{
        int score;
        int pri;

        if (PRI_BASE(td->td_pri_class) != PRI_TIMESHARE)
                return;
        /*
         * If the score is interactive we place the thread in the realtime
         * queue with a priority that is less than kernel and interrupt
         * priorities.  These threads are not subject to nice restrictions.
         *
         * Scores greater than this are placed on the normal timeshare queue
         * where the priority is partially decided by the most recent cpu
         * utilization and the rest is decided by nice value.
         *
         * The nice value of the process has a linear effect on the calculated
         * score.  Negative nice values make it easier for a thread to be
         * considered interactive.
         */
        score = imax(0, sched_interact_score(td) + td->td_proc->p_nice);
        if (score < sched_interact) {
                pri = PRI_MIN_INTERACT;
                pri += ((PRI_MAX_INTERACT - PRI_MIN_INTERACT + 1) /
                    sched_interact) * score;
                KASSERT(pri >= PRI_MIN_INTERACT && pri <= PRI_MAX_INTERACT,
                    ("sched_priority: invalid interactive priority %d score %d",
                    pri, score));
        } else {
                pri = SCHED_PRI_MIN;
                if (td_get_sched(td)->ts_ticks)
                        pri += min(SCHED_PRI_TICKS(td_get_sched(td)),
                            SCHED_PRI_RANGE - 1);
                pri += SCHED_PRI_NICE(td->td_proc->p_nice);
                KASSERT(pri >= PRI_MIN_BATCH && pri <= PRI_MAX_BATCH,
                    ("sched_priority: invalid priority %d: nice %d, " 
                    "ticks %d ftick %d ltick %d tick pri %d",
                    pri, td->td_proc->p_nice, td_get_sched(td)->ts_ticks,
                    td_get_sched(td)->ts_ftick, td_get_sched(td)->ts_ltick,
                    SCHED_PRI_TICKS(td_get_sched(td))));
        }
        sched_user_prio(td, pri);

        return;
}

/*
 * This routine enforces a maximum limit on the amount of scheduling history
 * kept.  It is called after either the slptime or runtime is adjusted.  This
 * function is ugly due to integer math.
 */
static void
sched_interact_update(struct thread *td)
{
        struct td_sched *ts;
        u_int sum;

        ts = td_get_sched(td);
        sum = ts->ts_runtime + ts->ts_slptime;
        if (sum < SCHED_SLP_RUN_MAX)
                return;
        /*
         * This only happens from two places:
         * 1) We have added an unusual amount of run time from fork_exit.
         * 2) We have added an unusual amount of sleep time from sched_sleep().
         */
        if (sum > SCHED_SLP_RUN_MAX * 2) {
                if (ts->ts_runtime > ts->ts_slptime) {
                        ts->ts_runtime = SCHED_SLP_RUN_MAX;
                        ts->ts_slptime = 1;
                } else {
                        ts->ts_slptime = SCHED_SLP_RUN_MAX;
                        ts->ts_runtime = 1;
                }
                return;
        }
        /*
         * If we have exceeded by more than 1/5th then the algorithm below
         * will not bring us back into range.  Dividing by two here forces
         * us into the range of [4/5 * SCHED_INTERACT_MAX, SCHED_INTERACT_MAX]
         */
        if (sum > (SCHED_SLP_RUN_MAX / 5) * 6) {
                ts->ts_runtime /= 2;
                ts->ts_slptime /= 2;
                return;
        }
        ts->ts_runtime = (ts->ts_runtime / 5) * 4;
        ts->ts_slptime = (ts->ts_slptime / 5) * 4;
}

/*
 * Scale back the interactivity history when a child thread is created.  The
 * history is inherited from the parent but the thread may behave totally
 * differently.  For example, a shell spawning a compiler process.  We want
 * to learn that the compiler is behaving badly very quickly.
 */
static void
sched_interact_fork(struct thread *td)
{
        struct td_sched *ts;
        int ratio;
        int sum;

        ts = td_get_sched(td);
        sum = ts->ts_runtime + ts->ts_slptime;
        if (sum > SCHED_SLP_RUN_FORK) {
                ratio = sum / SCHED_SLP_RUN_FORK;
                ts->ts_runtime /= ratio;
                ts->ts_slptime /= ratio;
        }
}

/*
 * Called from proc0_init() to setup the scheduler fields.
 */
void
schedinit(void)
{
        struct td_sched *ts0;

        /*
         * Set up the scheduler specific parts of thread0.
         */
        ts0 = td_get_sched(&thread0);
        ts0->ts_ltick = ticks;
        ts0->ts_ftick = ticks;
        ts0->ts_slice = 0;
        ts0->ts_cpu = curcpu;   /* set valid CPU number */
}

/*
 * This is only somewhat accurate since given many processes of the same
 * priority they will switch when their slices run out, which will be
 * at most sched_slice stathz ticks.
 */
int
sched_rr_interval(void)
{

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

/*
 * Update the percent cpu tracking information when it is requested or
 * the total history exceeds the maximum.  We keep a sliding history of
 * tick counts that slowly decays.  This is less precise than the 4BSD
 * mechanism since it happens with less regular and frequent events.
 */
static void
sched_pctcpu_update(struct td_sched *ts, int run)
{
        int t = ticks;

        /*
         * The signed difference may be negative if the thread hasn't run for
         * over half of the ticks rollover period.
         */
        if ((u_int)(t - ts->ts_ltick) >= SCHED_TICK_TARG) {
                ts->ts_ticks = 0;
                ts->ts_ftick = t - SCHED_TICK_TARG;
        } else if (t - ts->ts_ftick >= SCHED_TICK_MAX) {
                ts->ts_ticks = (ts->ts_ticks / (ts->ts_ltick - ts->ts_ftick)) *
                    (ts->ts_ltick - (t - SCHED_TICK_TARG));
                ts->ts_ftick = t - SCHED_TICK_TARG;
        }
        if (run)
                ts->ts_ticks += (t - ts->ts_ltick) << SCHED_TICK_SHIFT;
        ts->ts_ltick = t;
}

/*
 * Adjust the priority of a thread.  Move it to the appropriate run-queue
 * if necessary.  This is the back-end for several priority related
 * functions.
 */
static void
sched_thread_priority(struct thread *td, u_char prio)
{
        struct td_sched *ts;
        struct tdq *tdq;
        int oldpri;

        KTR_POINT3(KTR_SCHED, "thread", sched_tdname(td), "prio",
            "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);
        } 
        ts = td_get_sched(td);
        THREAD_LOCK_ASSERT(td, MA_OWNED);
        if (td->td_priority == prio)
                return;
        /*
         * If the priority has been elevated due to priority
         * propagation, we may have to move ourselves to a new
         * queue.  This could be optimized to not re-add in some
         * cases.
         */
        if (TD_ON_RUNQ(td) && prio < td->td_priority) {
                sched_rem(td);
                td->td_priority = prio;
                sched_add(td, SRQ_BORROWING | SRQ_HOLDTD);
                return;
        }
        /*
         * If the thread is currently running we may have to adjust the lowpri
         * information so other cpus are aware of our current priority.
         */
        if (TD_IS_RUNNING(td)) {
                tdq = TDQ_CPU(ts->ts_cpu);
                oldpri = td->td_priority;
                td->td_priority = prio;
                if (prio < tdq->tdq_lowpri)
                        tdq->tdq_lowpri = prio;
                else if (tdq->tdq_lowpri == oldpri)
                        tdq_setlowpri(tdq, td);
                return;
        }
        td->td_priority = prio;
}

/*
 * 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_thread_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 regular 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_thread_priority(td, base_pri);
        } else
                sched_lend_prio(td, prio);
}

/*
 * Standard entry for setting the priority to an absolute value.
 */
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_thread_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);
}

/*
 * Set the base user priority, does not effect current running priority.
 */
void
sched_user_prio(struct thread *td, u_char prio)
{

        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;
}

/*
 * Like the above but first check if there is anything to do.
 */
void
sched_lend_user_prio_cond(struct thread *td, u_char prio)
{

        if (td->td_lend_user_pri != prio)
                goto lend;
        if (td->td_user_pri != min(prio, td->td_base_user_pri))
                goto lend;
        if (td->td_priority != td->td_user_pri)
                goto lend;
        return;

lend:
        thread_lock(td);
        sched_lend_user_prio(td, prio);
        thread_unlock(td);
}

#ifdef SMP
/*
 * This tdq is about to idle.  Try to steal a thread from another CPU before
 * choosing the idle thread.
 */
static void
tdq_trysteal(struct tdq *tdq)
{
        struct cpu_group *cg;
        struct tdq *steal;
        cpuset_t mask;
        int cpu, i;

        if (smp_started == 0 || trysteal_limit == 0 || tdq->tdq_cg == NULL)
                return;
        CPU_FILL(&mask);
        CPU_CLR(PCPU_GET(cpuid), &mask);
        /* We don't want to be preempted while we're iterating. */
        spinlock_enter();
        TDQ_UNLOCK(tdq);
        for (i = 1, cg = tdq->tdq_cg; ; ) {
                cpu = sched_highest(cg, mask, steal_thresh);
                /*
                 * If a thread was added while interrupts were disabled don't
                 * steal one here.
                 */
                if (tdq->tdq_load > 0) {
                        TDQ_LOCK(tdq);
                        break;
                }
                if (cpu == -1) {
                        i++;
                        cg = cg->cg_parent;
                        if (cg == NULL || i > trysteal_limit) {
                                TDQ_LOCK(tdq);
                                break;
                        }
                        continue;
                }
                steal = TDQ_CPU(cpu);
                /*
                 * The data returned by sched_highest() is stale and
                 * the chosen CPU no longer has an eligible thread.
                 */
                if (steal->tdq_load < steal_thresh ||
                    steal->tdq_transferable == 0)
                        continue;
                tdq_lock_pair(tdq, steal);
                /*
                 * If we get to this point, unconditonally exit the loop
                 * to bound the time spent in the critcal section.
                 *
                 * If a thread was added while interrupts were disabled don't
                 * steal one here.
                 */
                if (tdq->tdq_load > 0) {
                        TDQ_UNLOCK(steal);
                        break;
                }
                /*
                 * The data returned by sched_highest() is stale and
                 * the chosen CPU no longer has an eligible thread.
                 */
                if (steal->tdq_load < steal_thresh ||
                    steal->tdq_transferable == 0) {
                        TDQ_UNLOCK(steal);
                        break;
                }
                /*
                 * If we fail to acquire one due to affinity restrictions,
                 * bail out and let the idle thread to a more complete search
                 * outside of a critical section.
                 */
                if (tdq_move(steal, tdq) == NULL) {
                        TDQ_UNLOCK(steal);
                        break;
                }
                TDQ_UNLOCK(steal);
                break;
        }
        spinlock_exit();
}
#endif

/*
 * Handle migration from sched_switch().  This happens only for
 * cpu binding.
 */
static struct mtx *
sched_switch_migrate(struct tdq *tdq, struct thread *td, int flags)
{
        struct tdq *tdn;

        KASSERT(THREAD_CAN_MIGRATE(td) ||
            (td_get_sched(td)->ts_flags & TSF_BOUND) != 0,
            ("Thread %p shouldn't migrate", td));
        KASSERT(!CPU_ABSENT(td_get_sched(td)->ts_cpu), ("sched_switch_migrate: "
            "thread %s queued on absent CPU %d.", td->td_name,
            td_get_sched(td)->ts_cpu));
        tdn = TDQ_CPU(td_get_sched(td)->ts_cpu);
#ifdef SMP
        tdq_load_rem(tdq, td);
        /*
         * Do the lock dance required to avoid LOR.  We have an 
         * extra spinlock nesting from sched_switch() which will
         * prevent preemption while we're holding neither run-queue lock.
         */
        TDQ_UNLOCK(tdq);
        TDQ_LOCK(tdn);
        tdq_add(tdn, td, flags);
        tdq_notify(tdn, td);
        TDQ_UNLOCK(tdn);
        TDQ_LOCK(tdq);
#endif
        return (TDQ_LOCKPTR(tdn));
}

/*
 * thread_lock_unblock() that does not assume td_lock is blocked.
 */
static inline void
thread_unblock_switch(struct thread *td, struct mtx *mtx)
{
        atomic_store_rel_ptr((volatile uintptr_t *)&td->td_lock,
            (uintptr_t)mtx);
}

/*
 * Switch threads.  This function has to handle threads coming in while
 * blocked for some reason, running, or idle.  It also must deal with
 * migrating a thread from one queue to another as running threads may
 * be assigned elsewhere via binding.
 */
void
sched_switch(struct thread *td, int flags)
{
        struct thread *newtd;
        struct tdq *tdq;
        struct td_sched *ts;
        struct mtx *mtx;
        int srqflag;
        int cpuid, preempted;

        THREAD_LOCK_ASSERT(td, MA_OWNED);

        cpuid = PCPU_GET(cpuid);
        tdq = TDQ_SELF();
        ts = td_get_sched(td);
        sched_pctcpu_update(ts, 1);
        ts->ts_rltick = ticks;
        td->td_lastcpu = td->td_oncpu;
        preempted = (td->td_flags & TDF_SLICEEND) == 0 &&
            (flags & SW_PREEMPT) != 0;
        td->td_flags &= ~(TDF_NEEDRESCHED | TDF_SLICEEND);
        td->td_owepreempt = 0;
        tdq->tdq_owepreempt = 0;
        if (!TD_IS_IDLETHREAD(td))
                tdq->tdq_switchcnt++;

        /*
         * Always block the thread lock so we can drop the tdq lock early.
         */
        mtx = thread_lock_block(td);
        spinlock_enter();
        if (TD_IS_IDLETHREAD(td)) {
                MPASS(mtx == TDQ_LOCKPTR(tdq));
                TD_SET_CAN_RUN(td);
        } else if (TD_IS_RUNNING(td)) {
                MPASS(mtx == TDQ_LOCKPTR(tdq));
                srqflag = preempted ?
                    SRQ_OURSELF|SRQ_YIELDING|SRQ_PREEMPTED :
                    SRQ_OURSELF|SRQ_YIELDING;
#ifdef SMP
                if (THREAD_CAN_MIGRATE(td) && !THREAD_CAN_SCHED(td, ts->ts_cpu))
                        ts->ts_cpu = sched_pickcpu(td, 0);
#endif
                if (ts->ts_cpu == cpuid)
                        tdq_runq_add(tdq, td, srqflag);
                else
                        mtx = sched_switch_migrate(tdq, td, srqflag);
        } else {
                /* This thread must be going to sleep. */
                if (mtx != TDQ_LOCKPTR(tdq)) {
                        mtx_unlock_spin(mtx);
                        TDQ_LOCK(tdq);
                }
                tdq_load_rem(tdq, td);
#ifdef SMP
                if (tdq->tdq_load == 0)
                        tdq_trysteal(tdq);
#endif
        }

#if (KTR_COMPILE & KTR_SCHED) != 0
        if (TD_IS_IDLETHREAD(td))
                KTR_STATE1(KTR_SCHED, "thread", sched_tdname(td), "idle",
                    "prio:%d", td->td_priority);
        else
                KTR_STATE3(KTR_SCHED, "thread", sched_tdname(td), KTDSTATE(td),
                    "prio:%d", td->td_priority, "wmesg:\"%s\"", td->td_wmesg,
                    "lockname:\"%s\"", td->td_lockname);
#endif

        /*
         * We enter here with the thread blocked and assigned to the
         * appropriate cpu run-queue or sleep-queue and with the current
         * thread-queue locked.
         */
        TDQ_LOCK_ASSERT(tdq, MA_OWNED | MA_NOTRECURSED);
        newtd = choosethread();
        sched_pctcpu_update(td_get_sched(newtd), 0);
        TDQ_UNLOCK(tdq);

        /*
         * Call the MD code to switch contexts if necessary.
         */
        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);

#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
                td->td_oncpu = NOCPU;
                cpu_switch(td, newtd, mtx);
                cpuid = td->td_oncpu = PCPU_GET(cpuid);

                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 {
                thread_unblock_switch(td, mtx);
                SDT_PROBE0(sched, , , remain__cpu);
        }
        KASSERT(curthread->td_md.md_spinlock_count == 1,
            ("invalid count %d", curthread->td_md.md_spinlock_count));

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

/*
 * Adjust thread priorities as a result of a nice request.
 */
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);
                sched_priority(td);
                sched_prio(td, td->td_base_user_pri);
                thread_unlock(td);
        }
}

/*
 * Record the sleep time for the interactivity scorer.
 */
void
sched_sleep(struct thread *td, int prio)
{

        THREAD_LOCK_ASSERT(td, MA_OWNED);

        td->td_slptick = ticks;
        if (TD_IS_SUSPENDED(td) || prio >= PSOCK)
                td->td_flags |= TDF_CANSWAP;
        if (PRI_BASE(td->td_pri_class) != PRI_TIMESHARE)
                return;
        if (static_boost == 1 && prio)
                sched_prio(td, prio);
        else if (static_boost && td->td_priority > static_boost)
                sched_prio(td, static_boost);
}

/*
 * Schedule a thread to resume execution and record how long it voluntarily
 * slept.  We also update the pctcpu, interactivity, and priority.
 *
 * Requires the thread lock on entry, drops on exit.
 */
void
sched_wakeup(struct thread *td, int srqflags)
{
        struct td_sched *ts;
        int slptick;

        THREAD_LOCK_ASSERT(td, MA_OWNED);
        ts = td_get_sched(td);
        td->td_flags &= ~TDF_CANSWAP;

        /*
         * If we slept for more than a tick update our interactivity and
         * priority.
         */
        slptick = td->td_slptick;
        td->td_slptick = 0;
        if (slptick && slptick != ticks) {
                ts->ts_slptime += (ticks - slptick) << SCHED_TICK_SHIFT;
                sched_interact_update(td);
                sched_pctcpu_update(ts, 0);
        }
        /*
         * Reset the slice value since we slept and advanced the round-robin.
         */
        ts->ts_slice = 0;
        sched_add(td, SRQ_BORING | srqflags);
}

/*
 * Penalize the parent for creating a new child and initialize the child's
 * priority.
 */
void
sched_fork(struct thread *td, struct thread *child)
{
        THREAD_LOCK_ASSERT(td, MA_OWNED);
        sched_pctcpu_update(td_get_sched(td), 1);
        sched_fork_thread(td, child);
        /*
         * Penalize the parent and child for forking.
         */
        sched_interact_fork(child);
        sched_priority(child);
        td_get_sched(td)->ts_runtime += tickincr;
        sched_interact_update(td);
        sched_priority(td);
}

/*
 * Fork a new thread, may be within the same process.
 */
void
sched_fork_thread(struct thread *td, struct thread *child)
{
        struct td_sched *ts;
        struct td_sched *ts2;
        struct tdq *tdq;

        tdq = TDQ_SELF();
        THREAD_LOCK_ASSERT(td, MA_OWNED);
        /*
         * Initialize child.
         */
        ts = td_get_sched(td);
        ts2 = td_get_sched(child);
        child->td_oncpu = NOCPU;
        child->td_lastcpu = NOCPU;
        child->td_lock = TDQ_LOCKPTR(tdq);
        child->td_cpuset = cpuset_ref(td->td_cpuset);
        child->td_domain.dr_policy = td->td_cpuset->cs_domain;
        ts2->ts_cpu = ts->ts_cpu;
        ts2->ts_flags = 0;
        /*
         * Grab our parents cpu estimation information.
         */
        ts2->ts_ticks = ts->ts_ticks;
        ts2->ts_ltick = ts->ts_ltick;
        ts2->ts_ftick = ts->ts_ftick;
        /*
         * Do not inherit any borrowed priority from the parent.
         */
        child->td_priority = child->td_base_pri;
        /*
         * And update interactivity score.
         */
        ts2->ts_slptime = ts->ts_slptime;
        ts2->ts_runtime = ts->ts_runtime;
        /* Attempt to quickly learn interactivity. */
        ts2->ts_slice = tdq_slice(tdq) - sched_slice_min;
#ifdef KTR
        bzero(ts2->ts_name, sizeof(ts2->ts_name));
#endif
}

/*
 * Adjust the priority class of a thread.
 */
void
sched_class(struct thread *td, int class)
{

        THREAD_LOCK_ASSERT(td, MA_OWNED);
        if (td->td_pri_class == class)
                return;
        td->td_pri_class = class;
}

/*
 * Return some of the child's priority and interactivity to the parent.
 */
void
sched_exit(struct proc *p, struct thread *child)
{
        struct thread *td;

        KTR_STATE1(KTR_SCHED, "thread", sched_tdname(child), "proc exit",
            "prio:%d", child->td_priority);
        PROC_LOCK_ASSERT(p, MA_OWNED);
        td = FIRST_THREAD_IN_PROC(p);
        sched_exit_thread(td, child);
}

/*
 * Penalize another thread for the time spent on this one.  This helps to
 * worsen the priority and interactivity of processes which schedule batch
 * jobs such as make.  This has little effect on the make process itself but
 * causes new processes spawned by it to receive worse scores immediately.
 */
void
sched_exit_thread(struct thread *td, struct thread *child)
{

        KTR_STATE1(KTR_SCHED, "thread", sched_tdname(child), "thread exit",
            "prio:%d", child->td_priority);
        /*
         * Give the child's runtime to the parent without returning the
         * sleep time as a penalty to the parent.  This causes shells that
         * launch expensive things to mark their children as expensive.
         */
        thread_lock(td);
        td_get_sched(td)->ts_runtime += td_get_sched(child)->ts_runtime;
        sched_interact_update(td);
        sched_priority(td);
        thread_unlock(td);
}

void
sched_preempt(struct thread *td)
{
        struct tdq *tdq;
        int flags;

        SDT_PROBE2(sched, , , surrender, td, td->td_proc);

        thread_lock(td);
        tdq = TDQ_SELF();
        TDQ_LOCK_ASSERT(tdq, MA_OWNED);
        if (td->td_priority > tdq->tdq_lowpri) {
                if (td->td_critnest == 1) {
                        flags = SW_INVOL | SW_PREEMPT;
                        flags |= TD_IS_IDLETHREAD(td) ? SWT_REMOTEWAKEIDLE :
                            SWT_REMOTEPREEMPT;
                        mi_switch(flags);
                        /* Switch dropped thread lock. */
                        return;
                }
                td->td_owepreempt = 1;
        } else {
                tdq->tdq_owepreempt = 0;
        }
        thread_unlock(td);
}

/*
 * Fix priorities on return to user-space.  Priorities may be elevated due
 * to static priorities in msleep() or similar.
 */
void
sched_userret_slowpath(struct thread *td)
{

        thread_lock(td);
        td->td_priority = td->td_user_pri;
        td->td_base_pri = td->td_user_pri;
        tdq_setlowpri(TDQ_SELF(), td);
        thread_unlock(td);
}

/*
 * Handle a stathz tick.  This is really only relevant for timeshare
 * threads.
 */
void
sched_clock(struct thread *td, int cnt)
{
        struct tdq *tdq;
        struct td_sched *ts;

        THREAD_LOCK_ASSERT(td, MA_OWNED);
        tdq = TDQ_SELF();
#ifdef SMP
        /*
         * We run the long term load balancer infrequently on the first cpu.
         */
        if (balance_tdq == tdq && smp_started != 0 && rebalance != 0 &&
            balance_ticks != 0) {
                balance_ticks -= cnt;
                if (balance_ticks <= 0)
                        sched_balance();
        }
#endif
        /*
         * Save the old switch count so we have a record of the last ticks
         * activity.   Initialize the new switch count based on our load.
         * If there is some activity seed it to reflect that.
         */
        tdq->tdq_oldswitchcnt = tdq->tdq_switchcnt;
        tdq->tdq_switchcnt = tdq->tdq_load;
        /*
         * Advance the insert index once for each tick to ensure that all
         * threads get a chance to run.
         */
        if (tdq->tdq_idx == tdq->tdq_ridx) {
                tdq->tdq_idx = (tdq->tdq_idx + 1) % RQ_NQS;
                if (TAILQ_EMPTY(&tdq->tdq_timeshare.rq_queues[tdq->tdq_ridx]))
                        tdq->tdq_ridx = tdq->tdq_idx;
        }
        ts = td_get_sched(td);
        sched_pctcpu_update(ts, 1);
        if ((td->td_pri_class & PRI_FIFO_BIT) || TD_IS_IDLETHREAD(td))
                return;

        if (PRI_BASE(td->td_pri_class) == PRI_TIMESHARE) {
                /*
                 * We used a tick; charge it to the thread so
                 * that we can compute our interactivity.
                 */
                td_get_sched(td)->ts_runtime += tickincr * cnt;
                sched_interact_update(td);
                sched_priority(td);
        }

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

u_int
sched_estcpu(struct thread *td __unused)
{

        return (0);
}

/*
 * Return whether the current CPU has runnable tasks.  Used for in-kernel
 * cooperative idle threads.
 */
int
sched_runnable(void)
{
        struct tdq *tdq;
        int load;

        load = 1;

        tdq = TDQ_SELF();
        if ((curthread->td_flags & TDF_IDLETD) != 0) {
                if (tdq->tdq_load > 0)
                        goto out;
        } else
                if (tdq->tdq_load - 1 > 0)
                        goto out;
        load = 0;
out:
        return (load);
}

/*
 * Choose the highest priority thread to run.  The thread is removed from
 * the run-queue while running however the load remains.  For SMP we set
 * the tdq in the global idle bitmask if it idles here.
 */
struct thread *
sched_choose(void)
{
        struct thread *td;
        struct tdq *tdq;

        tdq = TDQ_SELF();
        TDQ_LOCK_ASSERT(tdq, MA_OWNED);
        td = tdq_choose(tdq);
        if (td) {
                tdq_runq_rem(tdq, td);
                tdq->tdq_lowpri = td->td_priority;
                return (td);
        }
        tdq->tdq_lowpri = PRI_MAX_IDLE;
        return (PCPU_GET(idlethread));
}

/*
 * Set owepreempt if necessary.  Preemption never happens directly in ULE,
 * we always request it once we exit a critical section.
 */
static inline void
sched_setpreempt(struct thread *td)
{
        struct thread *ctd;
        int cpri;
        int pri;

        THREAD_LOCK_ASSERT(curthread, MA_OWNED);

        ctd = curthread;
        pri = td->td_priority;
        cpri = ctd->td_priority;
        if (pri < cpri)
                ctd->td_flags |= TDF_NEEDRESCHED;
        if (KERNEL_PANICKED() || pri >= cpri || cold || TD_IS_INHIBITED(ctd))
                return;
        if (!sched_shouldpreempt(pri, cpri, 0))
                return;
        ctd->td_owepreempt = 1;
}

/*
 * Add a thread to a thread queue.  Select the appropriate runq and add the
 * thread to it.  This is the internal function called when the tdq is
 * predetermined.
 */
void
tdq_add(struct tdq *tdq, struct thread *td, int flags)
{

        TDQ_LOCK_ASSERT(tdq, MA_OWNED);
        THREAD_LOCK_BLOCKED_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"));

        if (td->td_priority < tdq->tdq_lowpri)
                tdq->tdq_lowpri = td->td_priority;
        tdq_runq_add(tdq, td, flags);
        tdq_load_add(tdq, td);
}

/*
 * Select the target thread queue and add a thread to it.  Request
 * preemption or IPI a remote processor if required.
 *
 * Requires the thread lock on entry, drops on exit.
 */
void
sched_add(struct thread *td, int flags)
{
        struct tdq *tdq;
#ifdef SMP
        int cpu;
#endif

        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);
        THREAD_LOCK_ASSERT(td, MA_OWNED);
        /*
         * Recalculate the priority before we select the target cpu or
         * run-queue.
         */
        if (PRI_BASE(td->td_pri_class) == PRI_TIMESHARE)
                sched_priority(td);
#ifdef SMP
        /*
         * Pick the destination cpu and if it isn't ours transfer to the
         * target cpu.
         */
        cpu = sched_pickcpu(td, flags);
        tdq = sched_setcpu(td, cpu, flags);
        tdq_add(tdq, td, flags);
        if (cpu != PCPU_GET(cpuid))
                tdq_notify(tdq, td);
        else if (!(flags & SRQ_YIELDING))
                sched_setpreempt(td);
#else
        tdq = TDQ_SELF();
        /*
         * Now that the thread is moving to the run-queue, set the lock
         * to the scheduler's lock.
         */
        if (td->td_lock != TDQ_LOCKPTR(tdq)) {
                TDQ_LOCK(tdq);
                if ((flags & SRQ_HOLD) != 0)
                        td->td_lock = TDQ_LOCKPTR(tdq);
                else
                        thread_lock_set(td, TDQ_LOCKPTR(tdq));
        }
        tdq_add(tdq, td, flags);
        if (!(flags & SRQ_YIELDING))
                sched_setpreempt(td);
#endif
        if (!(flags & SRQ_HOLDTD))
                thread_unlock(td);
}

/*
 * Remove a thread from a run-queue without running it.  This is used
 * when we're stealing a thread from a remote queue.  Otherwise all threads
 * exit by calling sched_exit_thread() and sched_throw() themselves.
 */
void
sched_rem(struct thread *td)
{
        struct tdq *tdq;

        KTR_STATE1(KTR_SCHED, "thread", sched_tdname(td), "runq rem",
            "prio:%d", td->td_priority);
        SDT_PROBE3(sched, , , dequeue, td, td->td_proc, NULL);
        tdq = TDQ_CPU(td_get_sched(td)->ts_cpu);
        TDQ_LOCK_ASSERT(tdq, MA_OWNED);
        MPASS(td->td_lock == TDQ_LOCKPTR(tdq));
        KASSERT(TD_ON_RUNQ(td),
            ("sched_rem: thread not on run queue"));
        tdq_runq_rem(tdq, td);
        tdq_load_rem(tdq, td);
        TD_SET_CAN_RUN(td);
        if (td->td_priority == tdq->tdq_lowpri)
                tdq_setlowpri(tdq, NULL);
}

/*
 * Fetch cpu utilization information.  Updates on demand.
 */
fixpt_t
sched_pctcpu(struct thread *td)
{
        fixpt_t pctcpu;
        struct td_sched *ts;

        pctcpu = 0;
        ts = td_get_sched(td);

        THREAD_LOCK_ASSERT(td, MA_OWNED);
        sched_pctcpu_update(ts, TD_IS_RUNNING(td));
        if (ts->ts_ticks) {
                int rtick;

                /* How many rtick per second ? */
                rtick = min(SCHED_TICK_HZ(ts) / SCHED_TICK_SECS, hz);
                pctcpu = (FSCALE * ((FSCALE * rtick)/hz)) >> FSHIFT;
        }

        return (pctcpu);
}

/*
 * Enforce affinity settings for a thread.  Called after adjustments to
 * cpumask.
 */
void
sched_affinity(struct thread *td)
{
#ifdef SMP
        struct td_sched *ts;

        THREAD_LOCK_ASSERT(td, MA_OWNED);
        ts = td_get_sched(td);
        if (THREAD_CAN_SCHED(td, ts->ts_cpu))
                return;
        if (TD_ON_RUNQ(td)) {
                sched_rem(td);
                sched_add(td, SRQ_BORING | SRQ_HOLDTD);
                return;
        }
        if (!TD_IS_RUNNING(td))
                return;
        /*
         * Force a switch before returning to userspace.  If the
         * target thread is not running locally send an ipi to force
         * the issue.
         */
        td->td_flags |= TDF_NEEDRESCHED;
        if (td != curthread)
                ipi_cpu(ts->ts_cpu, IPI_PREEMPT);
#endif
}

/*
 * Bind a thread to a target cpu.
 */
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_get_sched(td);
        if (ts->ts_flags & TSF_BOUND)
                sched_unbind(td);
        KASSERT(THREAD_CAN_MIGRATE(td), ("%p must be migratable", td));
        ts->ts_flags |= TSF_BOUND;
        sched_pin();
        if (PCPU_GET(cpuid) == cpu)
                return;
        ts->ts_cpu = cpu;
        /* When we return from mi_switch we'll be on the correct cpu. */
        mi_switch(SW_VOL);
        thread_lock(td);
}

/*
 * Release a bound thread.
 */
void
sched_unbind(struct thread *td)
{
        struct td_sched *ts;

        THREAD_LOCK_ASSERT(td, MA_OWNED);
        KASSERT(td == curthread, ("sched_unbind: can only bind curthread"));
        ts = td_get_sched(td);
        if ((ts->ts_flags & TSF_BOUND) == 0)
                return;
        ts->ts_flags &= ~TSF_BOUND;
        sched_unpin();
}

int
sched_is_bound(struct thread *td)
{
        THREAD_LOCK_ASSERT(td, MA_OWNED);
        return (td_get_sched(td)->ts_flags & TSF_BOUND);
}

/*
 * Basic yield call.
 */
void
sched_relinquish(struct thread *td)
{
        thread_lock(td);
        mi_switch(SW_VOL | SWT_RELINQUISH);
}

/*
 * Return the total system load.
 */
int
sched_load(void)
{
#ifdef SMP
        int total;
        int i;

        total = 0;
        CPU_FOREACH(i)
                total += TDQ_CPU(i)->tdq_sysload;
        return (total);
#else
        return (TDQ_SELF()->tdq_sysload);
#endif
}

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

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

#ifdef SMP
#define TDQ_IDLESPIN(tdq)                                               \
    ((tdq)->tdq_cg != NULL && ((tdq)->tdq_cg->cg_flags & CG_FLAG_THREAD) == 0)
#else
#define TDQ_IDLESPIN(tdq)       1
#endif

/*
 * The actual idle process.
 */
void
sched_idletd(void *dummy)
{
        struct thread *td;
        struct tdq *tdq;
        int oldswitchcnt, switchcnt;
        int i;

        mtx_assert(&Giant, MA_NOTOWNED);
        td = curthread;
        tdq = TDQ_SELF();
        THREAD_NO_SLEEPING();
        oldswitchcnt = -1;
        for (;;) {
                if (tdq->tdq_load) {
                        thread_lock(td);
                        mi_switch(SW_VOL | SWT_IDLE);
                }
                switchcnt = tdq->tdq_switchcnt + tdq->tdq_oldswitchcnt;
#ifdef SMP
                if (always_steal || switchcnt != oldswitchcnt) {
                        oldswitchcnt = switchcnt;
                        if (tdq_idled(tdq) == 0)
                                continue;
                }
                switchcnt = tdq->tdq_switchcnt + tdq->tdq_oldswitchcnt;
#else
                oldswitchcnt = switchcnt;
#endif
                /*
                 * If we're switching very frequently, spin while checking
                 * for load rather than entering a low power state that 
                 * may require an IPI.  However, don't do any busy
                 * loops while on SMT machines as this simply steals
                 * cycles from cores doing useful work.
                 */
                if (TDQ_IDLESPIN(tdq) && switchcnt > sched_idlespinthresh) {
                        for (i = 0; i < sched_idlespins; i++) {
                                if (tdq->tdq_load)
                                        break;
                                cpu_spinwait();
                        }
                }

                /* If there was context switch during spin, restart it. */
                switchcnt = tdq->tdq_switchcnt + tdq->tdq_oldswitchcnt;
                if (tdq->tdq_load != 0 || switchcnt != oldswitchcnt)
                        continue;

                /* Run main MD idle handler. */
                tdq->tdq_cpu_idle = 1;
                /*
                 * Make sure that tdq_cpu_idle update is globally visible
                 * before cpu_idle() read tdq_load.  The order is important
                 * to avoid race with tdq_notify.
                 */
                atomic_thread_fence_seq_cst();
                /*
                 * Checking for again after the fence picks up assigned
                 * threads often enough to make it worthwhile to do so in
                 * order to avoid calling cpu_idle().
                 */
                if (tdq->tdq_load != 0) {
                        tdq->tdq_cpu_idle = 0;
                        continue;
                }
                cpu_idle(switchcnt * 4 > sched_idlespinthresh);
                tdq->tdq_cpu_idle = 0;

                /*
                 * Account thread-less hardware interrupts and
                 * other wakeup reasons equal to context switches.
                 */
                switchcnt = tdq->tdq_switchcnt + tdq->tdq_oldswitchcnt;
                if (switchcnt != oldswitchcnt)
                        continue;
                tdq->tdq_switchcnt++;
                oldswitchcnt++;
        }
}

/*
 * A CPU is entering for the first time or a thread is exiting.
 */
void
sched_throw(struct thread *td)
{
        struct thread *newtd;
        struct tdq *tdq;

        if (__predict_false(td == NULL)) {
#ifdef SMP
                PCPU_SET(sched, DPCPU_PTR(tdq));
#endif
                /* Correct spinlock nesting and acquire the correct lock. */
                tdq = TDQ_SELF();
                TDQ_LOCK(tdq);
                spinlock_exit();
                PCPU_SET(switchtime, cpu_ticks());
                PCPU_SET(switchticks, ticks);
                PCPU_GET(idlethread)->td_lock = TDQ_LOCKPTR(tdq);
        } else {
                tdq = TDQ_SELF();
                THREAD_LOCK_ASSERT(td, MA_OWNED);
                THREAD_LOCKPTR_ASSERT(td, TDQ_LOCKPTR(tdq));
                tdq_load_rem(tdq, td);
                td->td_lastcpu = td->td_oncpu;
                td->td_oncpu = NOCPU;
                thread_lock_block(td);
        }
        newtd = choosethread();
        spinlock_enter();
        TDQ_UNLOCK(tdq);
        KASSERT(curthread->td_md.md_spinlock_count == 1,
            ("invalid count %d", curthread->td_md.md_spinlock_count));
        /* doesn't return */
        if (__predict_false(td == NULL))
                cpu_throw(td, newtd);           /* doesn't return */
        else
                cpu_switch(td, newtd, TDQ_LOCKPTR(tdq));
}

/*
 * This is called from fork_exit().  Just acquire the correct locks and
 * let fork do the rest of the work.
 */
void
sched_fork_exit(struct thread *td)
{
        struct tdq *tdq;
        int cpuid;

        /*
         * Finish setting up thread glue so that it begins execution in a
         * non-nested critical section with the scheduler lock held.
         */
        KASSERT(curthread->td_md.md_spinlock_count == 1,
            ("invalid count %d", curthread->td_md.md_spinlock_count));
        cpuid = PCPU_GET(cpuid);
        tdq = TDQ_SELF();
        TDQ_LOCK(tdq);
        spinlock_exit();
        MPASS(td->td_lock == TDQ_LOCKPTR(tdq));
        td->td_oncpu = cpuid;
        KTR_STATE1(KTR_SCHED, "thread", sched_tdname(td), "running",
            "prio:%d", td->td_priority);
        SDT_PROBE0(sched, , , on__cpu);
}

/*
 * Create on first use to catch odd startup conditons.
 */
char *
sched_tdname(struct thread *td)
{
#ifdef KTR
        struct td_sched *ts;

        ts = td_get_sched(td);
        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_get_sched(td);
        ts->ts_name[0] = '\0';
}
#endif

#ifdef SMP

/*
 * Build the CPU topology dump string. Is recursively called to collect
 * the topology tree.
 */
static int
sysctl_kern_sched_topology_spec_internal(struct sbuf *sb, struct cpu_group *cg,
    int indent)
{
        char cpusetbuf[CPUSETBUFSIZ];
        int i, first;

        sbuf_printf(sb, "%*s<group level=\"%d\" cache-level=\"%d\">\n", indent,
            "", 1 + indent / 2, cg->cg_level);
        sbuf_printf(sb, "%*s <cpu count=\"%d\" mask=\"%s\">", indent, "",
            cg->cg_count, cpusetobj_strprint(cpusetbuf, &cg->cg_mask));
        first = TRUE;
        for (i = 0; i < MAXCPU; i++) {
                if (CPU_ISSET(i, &cg->cg_mask)) {
                        if (!first)
                                sbuf_printf(sb, ", ");
                        else
                                first = FALSE;
                        sbuf_printf(sb, "%d", i);
                }
        }
        sbuf_printf(sb, "</cpu>\n");

        if (cg->cg_flags != 0) {
                sbuf_printf(sb, "%*s <flags>", indent, "");
                if ((cg->cg_flags & CG_FLAG_HTT) != 0)
                        sbuf_printf(sb, "<flag name=\"HTT\">HTT group</flag>");
                if ((cg->cg_flags & CG_FLAG_THREAD) != 0)
                        sbuf_printf(sb, "<flag name=\"THREAD\">THREAD group</flag>");
                if ((cg->cg_flags & CG_FLAG_SMT) != 0)
                        sbuf_printf(sb, "<flag name=\"SMT\">SMT group</flag>");
                sbuf_printf(sb, "</flags>\n");
        }

        if (cg->cg_children > 0) {
                sbuf_printf(sb, "%*s <children>\n", indent, "");
                for (i = 0; i < cg->cg_children; i++)
                        sysctl_kern_sched_topology_spec_internal(sb, 
                            &cg->cg_child[i], indent+2);
                sbuf_printf(sb, "%*s </children>\n", indent, "");
        }
        sbuf_printf(sb, "%*s</group>\n", indent, "");
        return (0);
}

/*
 * Sysctl handler for retrieving topology dump. It's a wrapper for
 * the recursive sysctl_kern_smp_topology_spec_internal().
 */
static int
sysctl_kern_sched_topology_spec(SYSCTL_HANDLER_ARGS)
{
        struct sbuf *topo;
        int err;

        KASSERT(cpu_top != NULL, ("cpu_top isn't initialized"));

        topo = sbuf_new_for_sysctl(NULL, NULL, 512, req);
        if (topo == NULL)
                return (ENOMEM);

        sbuf_printf(topo, "<groups>\n");
        err = sysctl_kern_sched_topology_spec_internal(topo, cpu_top, 1);
        sbuf_printf(topo, "</groups>\n");

        if (err == 0) {
                err = sbuf_finish(topo);
        }
        sbuf_delete(topo);
        return (err);
}

#endif

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);
        sched_slice_min = sched_slice / SCHED_SLICE_MIN_DIVISOR;
        hogticks = imax(1, (2 * hz * sched_slice + realstathz / 2) /
            realstathz);
        return (0);
}

SYSCTL_NODE(_kern, OID_AUTO, sched, CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
    "Scheduler");
SYSCTL_STRING(_kern_sched, OID_AUTO, name, CTLFLAG_RD, "ULE", 0,
    "Scheduler name");
SYSCTL_PROC(_kern_sched, OID_AUTO, quantum,
    CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_MPSAFE, 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");
SYSCTL_INT(_kern_sched, OID_AUTO, interact, CTLFLAG_RW, &sched_interact, 0,
    "Interactivity score threshold");
SYSCTL_INT(_kern_sched, OID_AUTO, preempt_thresh, CTLFLAG_RW,
    &preempt_thresh, 0,
    "Maximal (lowest) priority for preemption");
SYSCTL_INT(_kern_sched, OID_AUTO, static_boost, CTLFLAG_RW, &static_boost, 0,
    "Assign static kernel priorities to sleeping threads");
SYSCTL_INT(_kern_sched, OID_AUTO, idlespins, CTLFLAG_RW, &sched_idlespins, 0,
    "Number of times idle thread will spin waiting for new work");
SYSCTL_INT(_kern_sched, OID_AUTO, idlespinthresh, CTLFLAG_RW,
    &sched_idlespinthresh, 0,
    "Threshold before we will permit idle thread spinning");
#ifdef SMP
SYSCTL_INT(_kern_sched, OID_AUTO, affinity, CTLFLAG_RW, &affinity, 0,
    "Number of hz ticks to keep thread affinity for");
SYSCTL_INT(_kern_sched, OID_AUTO, balance, CTLFLAG_RW, &rebalance, 0,
    "Enables the long-term load balancer");
SYSCTL_INT(_kern_sched, OID_AUTO, balance_interval, CTLFLAG_RW,
    &balance_interval, 0,
    "Average period in stathz ticks to run the long-term balancer");
SYSCTL_INT(_kern_sched, OID_AUTO, steal_idle, CTLFLAG_RW, &steal_idle, 0,
    "Attempts to steal work from other cores before idling");
SYSCTL_INT(_kern_sched, OID_AUTO, steal_thresh, CTLFLAG_RW, &steal_thresh, 0,
    "Minimum load on remote CPU before we'll steal");
SYSCTL_INT(_kern_sched, OID_AUTO, trysteal_limit, CTLFLAG_RW, &trysteal_limit,
    0, "Topological distance limit for stealing threads in sched_switch()");
SYSCTL_INT(_kern_sched, OID_AUTO, always_steal, CTLFLAG_RW, &always_steal, 0,
    "Always run the stealer from the idle thread");
SYSCTL_PROC(_kern_sched, OID_AUTO, topology_spec, CTLTYPE_STRING |
    CTLFLAG_MPSAFE | CTLFLAG_RD, NULL, 0, sysctl_kern_sched_topology_spec, "A",
    "XML dump of detected CPU topology");
#endif

/* ps compat.  All cpu percentages from ULE are weighted. */
static int ccpu = 0;
SYSCTL_INT(_kern, OID_AUTO, ccpu, CTLFLAG_RD, &ccpu, 0,
    "Decay factor used for updating %CPU in 4BSD scheduler");