MFC r197223: Fix a deadlock in the ULE scheduler.

[FreeBSD/releng/7.2.git] / sys / kern / sched_ule.c

/*-
 * 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_kdtrace.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/lock.h>
#include <sys/mutex.h>
#include <sys/proc.h>
#include <sys/resource.h>
#include <sys/resourcevar.h>
#include <sys/sched.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>
#ifdef KTRACE
#include <sys/uio.h>
#include <sys/ktrace.h>
#endif

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

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

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

#if !defined(__i386__) && !defined(__amd64__) && !defined(__arm__)
#error "This architecture is not currently compatible with ULE"
#endif

#define KTR_ULE 0

/*
 * Thread scheduler specific section.  All fields are protected
 * by the thread lock.
 */
struct td_sched {       
        TAILQ_ENTRY(td_sched) ts_procq; /* Run queue. */
        struct thread   *ts_thread;     /* Active associated thread. */
        struct runq     *ts_runq;       /* Run-queue we're queued on. */
        short           ts_flags;       /* TSF_* flags. */
        u_char          ts_rqindex;     /* Run queue index. */
        u_char          ts_cpu;         /* CPU that we have affinity for. */
        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 */
        /* The following variables are only used for pctcpu calculation */
        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 SMP
        int             ts_rltick;      /* Real last tick, for affinity. */
#endif
};
/* flags kept in ts_flags */
#define TSF_BOUND       0x0001          /* Thread can not migrate. */
#define TSF_XFERABLE    0x0002          /* Thread was added as transferable. */

static struct td_sched td_sched0;

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

/*
 * 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_TIMESHARE + SCHED_PRI_NHALF)
#define SCHED_PRI_MAX           (PRI_MAX_TIMESHARE - SCHED_PRI_NHALF)
#define SCHED_PRI_RANGE         (SCHED_PRI_MAX - SCHED_PRI_MIN)
#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:     Threshhold 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)

/*
 * 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 sched_interact = SCHED_INTERACT_THRESH;
static int realstathz;
static int tickincr;
static int sched_slice;
#ifdef PREEMPTION
#ifdef FULL_PREEMPTION
static int preempt_thresh = PRI_MAX_IDLE;
#else
static int preempt_thresh = PRI_MIN_KERN;
#endif
#else 
static int preempt_thresh = 0;
#endif

/*
 * 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 {
        struct mtx      *tdq_lock;              /* Pointer to group lock. */
        struct runq     tdq_realtime;           /* real-time run queue. */
        struct runq     tdq_timeshare;          /* timeshare run queue. */
        struct runq     tdq_idle;               /* Queue of IDLE threads. */
        int             tdq_load;               /* Aggregate load. */
        u_char          tdq_idx;                /* Current insert index. */
        u_char          tdq_ridx;               /* Current removal index. */
#ifdef SMP
        u_char          tdq_lowpri;             /* Lowest priority thread. */
        int             tdq_transferable;       /* Transferable thread count. */
        LIST_ENTRY(tdq) tdq_siblings;           /* Next in tdq group. */
        struct tdq_group *tdq_group;            /* Our processor group. */
#else
        int             tdq_sysload;            /* For loadavg, !ITHD load. */
#endif
} __aligned(64);


#ifdef SMP
/*
 * tdq groups are groups of processors which can cheaply share threads.  When
 * one processor in the group goes idle it will check the runqs of the other
 * processors in its group prior to halting and waiting for an interrupt.
 * These groups are suitable for SMT (Symetric Multi-Threading) and not NUMA.
 * In a numa environment we'd want an idle bitmap per group and a two tiered
 * load balancer.
 */
struct tdq_group {
        struct mtx      tdg_lock;       /* Protects all fields below. */
        int             tdg_cpus;       /* Count of CPUs in this tdq group. */
        cpumask_t       tdg_cpumask;    /* Mask of cpus in this group. */
        cpumask_t       tdg_idlemask;   /* Idle cpus in this group. */
        cpumask_t       tdg_mask;       /* Bit mask for first cpu. */
        int             tdg_load;       /* Total load of this group. */
        int     tdg_transferable;       /* Transferable load of this group. */
        LIST_HEAD(, tdq) tdg_members;   /* Linked list of all members. */
        char            tdg_name[16];   /* lock name. */
} __aligned(64);

#define SCHED_AFFINITY_DEFAULT  (max(1, hz / 300))
#define SCHED_AFFINITY(ts)      ((ts)->ts_rltick > ticks - affinity)

/*
 * Run-time tunables.
 */
static int rebalance = 1;
static int balance_interval = 128;      /* Default set in sched_initticks(). */
static int pick_pri = 1;
static int affinity;
static int tryself = 1;
static int steal_htt = 1;
static int steal_idle = 1;
static int steal_thresh = 2;
static int topology = 0;

/*
 * One thread queue per processor.
 */
static volatile cpumask_t tdq_idle;
static int tdg_maxid;
static struct tdq       tdq_cpu[MAXCPU];
static struct tdq_group tdq_groups[MAXCPU];
static struct tdq       *balance_tdq;
static int balance_group_ticks;
static int balance_ticks;

#define TDQ_SELF()      (&tdq_cpu[PCPU_GET(cpuid)])
#define TDQ_CPU(x)      (&tdq_cpu[(x)])
#define TDQ_ID(x)       ((int)((x) - tdq_cpu))
#define TDQ_GROUP(x)    (&tdq_groups[(x)])
#define TDG_ID(x)       ((int)((x) - tdq_groups))
#else   /* !SMP */
static struct tdq       tdq_cpu;
static struct mtx       tdq_lock;

#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)          ((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 *);

/* Operations on per processor queues */
static struct td_sched * tdq_choose(struct tdq *);
static void tdq_setup(struct tdq *);
static void tdq_load_add(struct tdq *, struct td_sched *);
static void tdq_load_rem(struct tdq *, struct td_sched *);
static __inline void tdq_runq_add(struct tdq *, struct td_sched *, int);
static __inline void tdq_runq_rem(struct tdq *, struct td_sched *);
void tdq_print(int cpu);
static void runq_print(struct runq *rq);
static void tdq_add(struct tdq *, struct thread *, int);
#ifdef SMP
static void tdq_move(struct tdq *, struct tdq *);
static int tdq_idled(struct tdq *);
static void tdq_notify(struct td_sched *);
static struct td_sched *tdq_steal(struct tdq *, int);
static struct td_sched *runq_steal(struct runq *, int);
static int sched_pickcpu(struct thread *, int);
static void sched_balance(void);
static void sched_balance_groups(void);
static void sched_balance_group(struct tdq_group *);
static void sched_balance_pair(struct tdq *, struct tdq *);
static inline struct tdq *sched_setcpu(struct td_sched *, int, int);
static inline struct mtx *thread_block_switch(struct thread *);
static inline void thread_unblock_switch(struct thread *, struct mtx *);
static struct mtx *sched_switch_migrate(struct tdq *, struct thread *, int);
#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);

/*
 * Print the threads waiting on a run-queue.
 */
static void
runq_print(struct runq *rq)
{
        struct rqhead *rqh;
        struct td_sched *ts;
        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(ts, rqh, ts_procq) {
                                        printf("\t\t\ttd %p(%s) priority %d rqindex %d pri %d\n",
                                            ts->ts_thread, ts->ts_thread->td_proc->p_comm, ts->ts_thread->td_priority, ts->ts_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("\tlockptr         %p\n", TDQ_LOCKPTR(tdq));
        printf("\tload:           %d\n", tdq->tdq_load);
        printf("\ttimeshare idx:  %d\n", tdq->tdq_idx);
        printf("\ttimeshare ridx: %d\n", tdq->tdq_ridx);
        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);
#ifdef SMP
        printf("\tload transferable: %d\n", tdq->tdq_transferable);
        printf("\tlowest priority:   %d\n", tdq->tdq_lowpri);
        printf("\tgroup:             %d\n", TDG_ID(tdq->tdq_group));
        printf("\tLock name:         %s\n", tdq->tdq_group->tdg_name);
#endif
}

#define TS_RQ_PPQ       (((PRI_MAX_TIMESHARE - PRI_MIN_TIMESHARE) + 1) / RQ_NQS)
/*
 * 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 td_sched *ts, int flags)
{
        TDQ_LOCK_ASSERT(tdq, MA_OWNED);
        THREAD_LOCK_ASSERT(ts->ts_thread, MA_OWNED);
#ifdef SMP
        if (THREAD_CAN_MIGRATE(ts->ts_thread)) {
                tdq->tdq_transferable++;
                tdq->tdq_group->tdg_transferable++;
                ts->ts_flags |= TSF_XFERABLE;
        }
#endif
        if (ts->ts_runq == &tdq->tdq_timeshare) {
                u_char pri;

                pri = ts->ts_thread->td_priority;
                KASSERT(pri <= PRI_MAX_TIMESHARE && pri >= PRI_MIN_TIMESHARE,
                        ("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 = (pri - PRI_MIN_TIMESHARE) / TS_RQ_PPQ;
                        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, ts, pri, flags);
        } else
                runq_add(ts->ts_runq, ts, 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 td_sched *ts)
{
        TDQ_LOCK_ASSERT(tdq, MA_OWNED);
        KASSERT(ts->ts_runq != NULL,
            ("tdq_runq_remove: thread %p null ts_runq", ts->ts_thread));
#ifdef SMP
        if (ts->ts_flags & TSF_XFERABLE) {
                tdq->tdq_transferable--;
                tdq->tdq_group->tdg_transferable--;
                ts->ts_flags &= ~TSF_XFERABLE;
        }
#endif
        if (ts->ts_runq == &tdq->tdq_timeshare) {
                if (tdq->tdq_idx != tdq->tdq_ridx)
                        runq_remove_idx(ts->ts_runq, ts, &tdq->tdq_ridx);
                else
                        runq_remove_idx(ts->ts_runq, ts, NULL);
                /*
                 * For timeshare threads we update the priority here so
                 * the priority reflects the time we've been sleeping.
                 */
                ts->ts_ltick = ticks;
                sched_pctcpu_update(ts);
                sched_priority(ts->ts_thread);
        } else
                runq_remove(ts->ts_runq, ts);
}

/*
 * 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 td_sched *ts)
{
        int class;

        TDQ_LOCK_ASSERT(tdq, MA_OWNED);
        THREAD_LOCK_ASSERT(ts->ts_thread, MA_OWNED);
        class = PRI_BASE(ts->ts_thread->td_pri_class);
        tdq->tdq_load++;
        CTR2(KTR_SCHED, "cpu %d load: %d", TDQ_ID(tdq), tdq->tdq_load);
        if (class != PRI_ITHD &&
            (ts->ts_thread->td_proc->p_flag & P_NOLOAD) == 0)
#ifdef SMP
                tdq->tdq_group->tdg_load++;
#else
                tdq->tdq_sysload++;
#endif
}

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

        THREAD_LOCK_ASSERT(ts->ts_thread, MA_OWNED);
        TDQ_LOCK_ASSERT(tdq, MA_OWNED);
        class = PRI_BASE(ts->ts_thread->td_pri_class);
        if (class != PRI_ITHD &&
            (ts->ts_thread->td_proc->p_flag & P_NOLOAD) == 0)
#ifdef SMP
                tdq->tdq_group->tdg_load--;
#else
                tdq->tdq_sysload--;
#endif
        KASSERT(tdq->tdq_load != 0,
            ("tdq_load_rem: Removing with 0 load on queue %d", TDQ_ID(tdq)));
        tdq->tdq_load--;
        CTR1(KTR_SCHED, "load: %d", tdq->tdq_load);
        ts->ts_runq = NULL;
}

#ifdef SMP
/*
 * sched_balance is a simple CPU load balancing algorithm.  It operates by
 * finding the least loaded and most loaded cpu and equalizing their load
 * by migrating some processes.
 *
 * Dealing only with two CPUs at a time has two advantages.  Firstly, most
 * installations will only have 2 cpus.  Secondly, load balancing too much at
 * once can have an unpleasant effect on the system.  The scheduler rarely has
 * enough information to make perfect decisions.  So this algorithm chooses
 * simplicity and more gradual effects on load in larger systems.
 *
 */
static void
sched_balance()
{
        struct tdq_group *high;
        struct tdq_group *low;
        struct tdq_group *tdg;
        struct tdq *tdq;
        int cnt;
        int i;

        /*
         * Select a random time between .5 * balance_interval and
         * 1.5 * balance_interval.
         */
        balance_ticks = max(balance_interval / 2, 1);
        balance_ticks += random() % balance_interval;
        if (smp_started == 0 || rebalance == 0)
                return;
        tdq = TDQ_SELF();
        TDQ_UNLOCK(tdq);
        low = high = NULL;
        i = random() % (tdg_maxid + 1);
        for (cnt = 0; cnt <= tdg_maxid; cnt++) {
                tdg = TDQ_GROUP(i);
                /*
                 * Find the CPU with the highest load that has some
                 * threads to transfer.
                 */
                if ((high == NULL || tdg->tdg_load > high->tdg_load)
                    && tdg->tdg_transferable)
                        high = tdg;
                if (low == NULL || tdg->tdg_load < low->tdg_load)
                        low = tdg;
                if (++i > tdg_maxid)
                        i = 0;
        }
        if (low != NULL && high != NULL && high != low)
                sched_balance_pair(LIST_FIRST(&high->tdg_members),
                    LIST_FIRST(&low->tdg_members));
        TDQ_LOCK(tdq);
}

/*
 * Balance load between CPUs in a group.  Will only migrate within the group.
 */
static void
sched_balance_groups()
{
        struct tdq *tdq;
        int i;

        /*
         * Select a random time between .5 * balance_interval and
         * 1.5 * balance_interval.
         */
        balance_group_ticks = max(balance_interval / 2, 1);
        balance_group_ticks += random() % balance_interval;
        if (smp_started == 0 || rebalance == 0)
                return;
        tdq = TDQ_SELF();
        TDQ_UNLOCK(tdq);
        for (i = 0; i <= tdg_maxid; i++)
                sched_balance_group(TDQ_GROUP(i));
        TDQ_LOCK(tdq);
}

/*
 * Finds the greatest imbalance between two tdqs in a group.
 */
static void
sched_balance_group(struct tdq_group *tdg)
{
        struct tdq *tdq;
        struct tdq *high;
        struct tdq *low;
        int load;

        if (tdg->tdg_transferable == 0)
                return;
        low = NULL;
        high = NULL;
        LIST_FOREACH(tdq, &tdg->tdg_members, tdq_siblings) {
                load = tdq->tdq_load;
                if (high == NULL || load > high->tdq_load)
                        high = tdq;
                if (low == NULL || load < low->tdq_load)
                        low = tdq;
        }
        if (high != NULL && low != NULL && high != low)
                sched_balance_pair(high, low);
}

/*
 * 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 void
sched_balance_pair(struct tdq *high, struct tdq *low)
{
        int transferable;
        int high_load;
        int low_load;
        int move;
        int diff;
        int i;

        tdq_lock_pair(high, low);
        /*
         * If we're transfering within a group we have to use this specific
         * tdq's transferable count, otherwise we can steal from other members
         * of the group.
         */
        if (high->tdq_group == low->tdq_group) {
                transferable = high->tdq_transferable;
                high_load = high->tdq_load;
                low_load = low->tdq_load;
        } else {
                transferable = high->tdq_group->tdg_transferable;
                high_load = high->tdq_group->tdg_load;
                low_load = low->tdq_group->tdg_load;
        }
        /*
         * Determine what the imbalance is and then adjust that to how many
         * threads we actually have to give up (transferable).
         */
        if (transferable != 0) {
                diff = high_load - low_load;
                move = diff / 2;
                if (diff & 0x1)
                        move++;
                move = min(move, transferable);
                for (i = 0; i < move; i++)
                        tdq_move(high, low);
                /*
                 * IPI the target cpu to force it to reschedule with the new
                 * workload.
                 */
                ipi_selected(1 << TDQ_ID(low), IPI_PREEMPT);
        }
        tdq_unlock_pair(high, low);
        return;
}

/*
 * Move a thread from one thread queue to another.
 */
static void
tdq_move(struct tdq *from, struct tdq *to)
{
        struct td_sched *ts;
        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);
        ts = tdq_steal(tdq, cpu);
        if (ts == NULL) {
                struct tdq_group *tdg;

                tdg = tdq->tdq_group;
                LIST_FOREACH(tdq, &tdg->tdg_members, tdq_siblings) {
                        if (tdq == from || tdq->tdq_transferable == 0)
                                continue;
                        ts = tdq_steal(tdq, cpu);
                        break;
                }
                if (ts == NULL)
                        return;
        }
        if (tdq == to)
                return;
        td = ts->ts_thread;
        /*
         * Although the run queue is locked the thread may be blocked.  Lock
         * it to clear this and acquire the run-queue lock.
         */
        thread_lock(td);
        /* Drop recursive lock on from acquired via thread_lock(). */
        TDQ_UNLOCK(from);
        sched_rem(td);
        ts->ts_cpu = cpu;
        td->td_lock = TDQ_LOCKPTR(to);
        tdq_add(to, td, SRQ_YIELDING);
}

/*
 * This tdq has idled.  Try to steal a thread from another cpu and switch
 * to it.
 */
static int
tdq_idled(struct tdq *tdq)
{
        struct tdq_group *tdg;
        struct tdq *steal;
        int highload;
        int highcpu;
        int cpu;

        if (smp_started == 0 || steal_idle == 0)
                return (1);
        /* We don't want to be preempted while we're iterating over tdqs */
        spinlock_enter();
        tdg = tdq->tdq_group;
        /*
         * If we're in a cpu group, try and steal threads from another cpu in
         * the group before idling.  In a HTT group all cpus share the same
         * run-queue lock, however, we still need a recursive lock to
         * call tdq_move().
         */
        if (steal_htt && tdg->tdg_cpus > 1 && tdg->tdg_transferable) {
                TDQ_LOCK(tdq);
                LIST_FOREACH(steal, &tdg->tdg_members, tdq_siblings) {
                        if (steal == tdq || steal->tdq_transferable == 0)
                                continue;
                        TDQ_LOCK(steal);
                        goto steal;
                }
                TDQ_UNLOCK(tdq);
        }
        /*
         * Find the least loaded CPU with a transferable thread and attempt
         * to steal it.  We make a lockless pass and then verify that the
         * thread is still available after locking.
         */
        for (;;) {
                highcpu = 0;
                highload = 0;
                for (cpu = 0; cpu <= mp_maxid; cpu++) {
                        if (CPU_ABSENT(cpu))
                                continue;
                        steal = TDQ_CPU(cpu);
                        if (steal->tdq_transferable == 0)
                                continue;
                        if (steal->tdq_load < highload)
                                continue;
                        highload = steal->tdq_load;
                        highcpu = cpu;
                }
                if (highload < steal_thresh)
                        break;
                steal = TDQ_CPU(highcpu);
                if (steal == tdq)
                        break;
                tdq_lock_pair(tdq, steal);
                if (steal->tdq_load >= steal_thresh && steal->tdq_transferable)
                        goto steal;
                tdq_unlock_pair(tdq, steal);
        }
        spinlock_exit();
        return (1);
steal:
        spinlock_exit();
        tdq_move(steal, tdq);
        TDQ_UNLOCK(steal);
        mi_switch(SW_VOL, NULL);
        thread_unlock(curthread);

        return (0);
}

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

        cpu = ts->ts_cpu;
        pri = ts->ts_thread->td_priority;
        pcpu = pcpu_find(cpu);
        ctd = pcpu->pc_curthread;
        cpri = ctd->td_priority;

        /*
         * If our priority is not better than the current priority there is
         * nothing to do.
         */
        if (pri > cpri)
                return;
        /*
         * Always IPI idle.
         */
        if (cpri > PRI_MIN_IDLE)
                goto sendipi;
        /*
         * If we're realtime or better and there is timeshare or worse running
         * send an IPI.
         */
        if (pri < PRI_MAX_REALTIME && cpri > PRI_MAX_REALTIME)
                goto sendipi;
        /*
         * Otherwise only IPI if we exceed the threshold.
         */
        if (pri > preempt_thresh)
                return;
sendipi:
        ipi_selected(1 << cpu, IPI_PREEMPT);
}

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

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

        return (NULL);
}

/*
 * Steals load from a standard linear queue.
 */
static struct td_sched *
runq_steal(struct runq *rq, int cpu)
{
        struct rqhead *rqh;
        struct rqbits *rqb;
        struct td_sched *ts;
        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(ts, rqh, ts_procq)
                                if (THREAD_CAN_MIGRATE(ts->ts_thread) &&
                                    THREAD_CAN_SCHED(ts->ts_thread, cpu))
                                        return (ts);
                }
        }
        return (NULL);
}

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

        TDQ_LOCK_ASSERT(tdq, MA_OWNED);
        if ((ts = runq_steal(&tdq->tdq_realtime, cpu)) != NULL)
                return (ts);
        if ((ts = runq_steal_from(&tdq->tdq_timeshare,
            cpu, tdq->tdq_ridx)) != NULL)
                return (ts);
        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 td_sched *ts, int cpu, int flags)
{
        struct thread *td;
        struct tdq *tdq;

        THREAD_LOCK_ASSERT(ts->ts_thread, MA_OWNED);

        tdq = TDQ_CPU(cpu);
        td = ts->ts_thread;
        ts->ts_cpu = cpu;

        /* If the lock matches just return the queue. */
        if (td->td_lock == TDQ_LOCKPTR(tdq))
                return (tdq);
#ifdef notyet
        /*
         * If the thread isn't running its lockptr is a
         * turnstile or a sleepqueue.  We can just lock_set without
         * blocking.
         */
        if (TD_CAN_RUN(td)) {
                TDQ_LOCK(tdq);
                thread_lock_set(td, TDQ_LOCKPTR(tdq));
                return (tdq);
        }
#endif
        /*
         * The hard case, migration, we need to block the thread first to
         * prevent order reversals with other cpus locks.
         */
        thread_lock_block(td);
        TDQ_LOCK(tdq);
        thread_lock_unblock(td, TDQ_LOCKPTR(tdq));
        return (tdq);
}

/*
 * Find the thread queue running the lowest priority thread.
 */
static int
tdq_lowestpri(struct thread *td)
{
        struct tdq *tdq;
        int lowpri;
        int lowcpu;
        int lowload;
        int load;
        int cpu;
        int pri;

        lowload = 0;
        lowpri = lowcpu = 0;
        for (cpu = 0; cpu <= mp_maxid; cpu++) {
                if (CPU_ABSENT(cpu))
                        continue;
                if (!THREAD_CAN_SCHED(td, cpu))
                        continue;
                tdq = TDQ_CPU(cpu);
                pri = tdq->tdq_lowpri;
                load = TDQ_CPU(cpu)->tdq_load;
                CTR4(KTR_ULE,
                    "cpu %d pri %d lowcpu %d lowpri %d",
                    cpu, pri, lowcpu, lowpri);
                if (pri < lowpri)
                        continue;
                if (lowpri && lowpri == pri && load > lowload)
                        continue;
                lowpri = pri;
                lowcpu = cpu;
                lowload = load;
        }

        return (lowcpu);
}

/*
 * Find the thread queue with the least load.
 */
static int
tdq_lowestload(struct thread *td)
{
        struct tdq *tdq;
        int lowload;
        int lowpri;
        int lowcpu;
        int load;
        int cpu;
        int pri;

        lowcpu = 0;
        lowload = TDQ_CPU(0)->tdq_load;
        lowpri = TDQ_CPU(0)->tdq_lowpri;
        for (cpu = 1; cpu <= mp_maxid; cpu++) {
                if (CPU_ABSENT(cpu))
                        continue;
                if (!THREAD_CAN_SCHED(td, cpu))
                        continue;
                tdq = TDQ_CPU(cpu);
                load = tdq->tdq_load;
                pri = tdq->tdq_lowpri;
                CTR4(KTR_ULE, "cpu %d load %d lowcpu %d lowload %d",
                    cpu, load, lowcpu, lowload);
                if (load > lowload)
                        continue;
                if (load == lowload && pri < lowpri)
                        continue;
                lowcpu = cpu;
                lowload = load;
                lowpri = pri;
        }

        return (lowcpu);
}

/*
 * Pick the destination cpu for sched_add().  Respects affinity and makes
 * a determination based on load or priority of available processors.
 */
static int
sched_pickcpu(struct thread *td, int flags)
{
        struct tdq *tdq;
        struct td_sched *ts;
        cpumask_t mask;
        int self;
        int pri;
        int cpu;

        self = PCPU_GET(cpuid);
        ts = td->td_sched;
        if (smp_started == 0)
                return (self);
        /*
         * Don't migrate a running thread from sched_switch().
         */
        if (flags & SRQ_OURSELF) {
                CTR1(KTR_ULE, "YIELDING %d",
                    curthread->td_priority);
                return (self);
        }
        pri = ts->ts_thread->td_priority;
        cpu = ts->ts_cpu;
        if (THREAD_CAN_SCHED(td, cpu)) {
                /*
                 * Regardless of affinity, if the last cpu is idle
                 * send it there.
                 */
                tdq = TDQ_CPU(cpu);
                if (tdq->tdq_lowpri > PRI_MIN_IDLE) {
                        CTR5(KTR_ULE,
                    "ts_cpu %d idle, ltick %d ticks %d pri %d curthread %d",
                            ts->ts_cpu, ts->ts_rltick, ticks, pri,
                            tdq->tdq_lowpri);
                        return (ts->ts_cpu);
                }
                /*
                 * If we have affinity, try to place it on the cpu we
                 * last ran on.
                 */
                if (SCHED_AFFINITY(ts) && tdq->tdq_lowpri > pri) {
                        CTR5(KTR_ULE,
                    "affinity for %d, ltick %d ticks %d pri %d curthread %d",
                            ts->ts_cpu, ts->ts_rltick, ticks, pri,
                            tdq->tdq_lowpri);
                        return (ts->ts_cpu);
                }
        }

        /*
         * Look for an idle group.
         */
        CTR1(KTR_ULE, "tdq_idle %X", tdq_idle);
        mask = tdq_idle;
        while ((cpu = ffs(mask)) != 0) {
                --cpu;
                if (THREAD_CAN_SCHED(td, cpu))
                        return (cpu);
                mask &= ~(1 << cpu);
        }
        /*
         * If there are no idle cores see if we can run the thread locally.
         * This may improve locality among sleepers and wakers when there
         * is shared data.
         */
        if (tryself && THREAD_CAN_SCHED(td, self) &&
            pri < curthread->td_priority) {
                CTR1(KTR_ULE, "tryself %d",
                    curthread->td_priority);
                return (self);
        }
        /*
         * Now search for the cpu running the lowest priority thread with
         * the least load.
         */
        if (pick_pri)
                cpu = tdq_lowestpri(td);
        else
                cpu = tdq_lowestload(td);
        return (cpu);
}

#endif  /* SMP */

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

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

        ts = runq_choose(&tdq->tdq_idle);
        if (ts != NULL) {
                KASSERT(ts->ts_thread->td_priority >= PRI_MIN_IDLE,
                    ("tdq_choose: Invalid priority on idle queue %d",
                    ts->ts_thread->td_priority));
                return (ts);
        }

        return (NULL);
}

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

        if (bootverbose)
                printf("ULE: setup cpu %d\n", TDQ_ID(tdq));
        runq_init(&tdq->tdq_realtime);
        runq_init(&tdq->tdq_timeshare);
        runq_init(&tdq->tdq_idle);
        tdq->tdq_load = 0;
}

#ifdef SMP
static void
tdg_setup(struct tdq_group *tdg)
{
        if (bootverbose)
                printf("ULE: setup cpu group %d\n", TDG_ID(tdg));
        snprintf(tdg->tdg_name, sizeof(tdg->tdg_name),
            "sched lock %d", (int)TDG_ID(tdg));
        mtx_init(&tdg->tdg_lock, tdg->tdg_name, "sched lock",
            MTX_SPIN | MTX_RECURSE);
        LIST_INIT(&tdg->tdg_members);
        tdg->tdg_load = 0;
        tdg->tdg_transferable = 0;
        tdg->tdg_cpus = 0;
        tdg->tdg_mask = 0;
        tdg->tdg_cpumask = 0;
        tdg->tdg_idlemask = 0;
}

static void
tdg_add(struct tdq_group *tdg, struct tdq *tdq)
{
        if (tdg->tdg_mask == 0)
                tdg->tdg_mask |= 1 << TDQ_ID(tdq);
        tdg->tdg_cpumask |= 1 << TDQ_ID(tdq);
        tdg->tdg_cpus++;
        tdq->tdq_group = tdg;
        tdq->tdq_lock = &tdg->tdg_lock;
        LIST_INSERT_HEAD(&tdg->tdg_members, tdq, tdq_siblings);
        if (bootverbose)
                printf("ULE: adding cpu %d to group %d: cpus %d mask 0x%X\n",
                    TDQ_ID(tdq), TDG_ID(tdg), tdg->tdg_cpus, tdg->tdg_cpumask);
}

static void
sched_setup_topology(void)
{
        struct tdq_group *tdg;
        struct cpu_group *cg;
        int balance_groups;
        struct tdq *tdq;
        int i;
        int j;

        topology = 1;
        balance_groups = 0;
        for (i = 0; i < smp_topology->ct_count; i++) {
                cg = &smp_topology->ct_group[i];
                tdg = &tdq_groups[i];
                /*
                 * Initialize the group.
                 */
                tdg_setup(tdg);
                /*
                 * Find all of the group members and add them.
                 */
                for (j = 0; j < MAXCPU; j++) { 
                        if ((cg->cg_mask & (1 << j)) != 0) {
                                tdq = TDQ_CPU(j);
                                tdq_setup(tdq);
                                tdg_add(tdg, tdq);
                        }
                }
                if (tdg->tdg_cpus > 1)
                        balance_groups = 1;
        }
        tdg_maxid = smp_topology->ct_count - 1;
        if (balance_groups)
                sched_balance_groups();
}

static void
sched_setup_smp(void)
{
        struct tdq_group *tdg;
        struct tdq *tdq;
        int cpus;
        int i;

        for (cpus = 0, i = 0; i < MAXCPU; i++) {
                if (CPU_ABSENT(i))
                        continue;
                tdq = &tdq_cpu[i];
                tdg = &tdq_groups[i];
                /*
                 * Setup a tdq group with one member.
                 */
                tdg_setup(tdg);
                tdq_setup(tdq);
                tdg_add(tdg, tdq);
                cpus++;
        }
        tdg_maxid = cpus - 1;
}

/*
 * Fake a topology with one group containing all CPUs.
 */
static void
sched_fake_topo(void)
{
#ifdef SCHED_FAKE_TOPOLOGY
        static struct cpu_top top;
        static struct cpu_group group;

        top.ct_count = 1;
        top.ct_group = &group;
        group.cg_mask = all_cpus;
        group.cg_count = mp_ncpus;
        group.cg_children = 0;
        smp_topology = &top;
#endif
}
#endif

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

        tdq = TDQ_SELF();
#ifdef SMP
        sched_fake_topo();
        /*
         * Setup tdqs based on a topology configuration or vanilla SMP based
         * on mp_maxid.
         */
        if (smp_topology == NULL)
                sched_setup_smp();
        else 
                sched_setup_topology();
        balance_tdq = tdq;
        sched_balance();
#else
        tdq_setup(tdq);
        mtx_init(&tdq_lock, "sched lock", "sched lock", MTX_SPIN | MTX_RECURSE);
        tdq->tdq_lock = &tdq_lock;
#endif
        /*
         * To avoid divide-by-zero, we set realstathz a dummy value
         * in case which sched_clock() called before sched_initticks().
         */
        realstathz = hz;
        sched_slice = (realstathz/10);  /* ~100ms */
        tickincr = 1 << SCHED_TICK_SHIFT;

        /* Add thread0's load since it's running. */
        TDQ_LOCK(tdq);
        thread0.td_lock = TDQ_LOCKPTR(TDQ_SELF());
        tdq_load_add(tdq, &td_sched0);
        TDQ_UNLOCK(tdq);
}

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

        realstathz = stathz ? stathz : hz;
        sched_slice = (realstathz/10);  /* ~100ms */

        /*
         * 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;
        /*
         * Set steal thresh to roughly log2(mp_ncpu) but no greater than 4. 
         * This prevents excess thrashing on large machines and excess idle 
         * on smaller machines.
         */
        steal_thresh = min(fls(mp_ncpus) - 1, 3);
        affinity = SCHED_AFFINITY_DEFAULT;
#endif
}


/*
 * 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.
 */
static int
sched_interact_score(struct thread *td)
{
        struct td_sched *ts;
        int div;

        ts = td->td_sched;
        /*
         * 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 (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_REALTIME;
                pri += ((PRI_MAX_REALTIME - PRI_MIN_REALTIME) / sched_interact)
                    * score;
                KASSERT(pri >= PRI_MIN_REALTIME && pri <= PRI_MAX_REALTIME,
                    ("sched_priority: invalid interactive priority %d score %d",
                    pri, score));
        } else {
                pri = SCHED_PRI_MIN;
                if (td->td_sched->ts_ticks)
                        pri += SCHED_PRI_TICKS(td->td_sched);
                pri += SCHED_PRI_NICE(td->td_proc->p_nice);
                KASSERT(pri >= PRI_MIN_TIMESHARE && pri <= PRI_MAX_TIMESHARE,
                    ("sched_priority: invalid priority %d: nice %d, " 
                    "ticks %d ftick %d ltick %d tick pri %d",
                    pri, td->td_proc->p_nice, td->td_sched->ts_ticks,
                    td->td_sched->ts_ftick, td->td_sched->ts_ltick,
                    SCHED_PRI_TICKS(td->td_sched)));
        }
        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->td_sched;
        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)
{
        int ratio;
        int sum;

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

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

        /*
         * Set up the scheduler specific parts of proc0.
         */
        proc0.p_sched = NULL; /* XXX */
        thread0.td_sched = &td_sched0;
        td_sched0.ts_ltick = ticks;
        td_sched0.ts_ftick = ticks;
        td_sched0.ts_thread = &thread0;
}

/*
 * 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 to hz */
        return (hz/(realstathz/sched_slice));
}

/*
 * 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)
{

        if (ts->ts_ticks == 0)
                return;
        if (ticks - (hz / 10) < ts->ts_ltick &&
            SCHED_TICK_TOTAL(ts) < SCHED_TICK_MAX)
                return;
        /*
         * Adjust counters and watermark for pctcpu calc.
         */
        if (ts->ts_ltick > ticks - SCHED_TICK_TARG)
                ts->ts_ticks = (ts->ts_ticks / (ticks - ts->ts_ftick)) *
                            SCHED_TICK_TARG;
        else
                ts->ts_ticks = 0;
        ts->ts_ltick = ticks;
        ts->ts_ftick = ts->ts_ltick - SCHED_TICK_TARG;
}

/*
 * 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;

        CTR6(KTR_SCHED, "sched_prio: %p(%s) prio %d newprio %d by %p(%s)",
            td, td->td_proc->p_comm, td->td_priority, prio, curthread,
            curthread->td_proc->p_comm);
        ts = td->td_sched;
        THREAD_LOCK_ASSERT(td, MA_OWNED);
        if (td->td_priority == prio)
                return;

        if (TD_ON_RUNQ(td) && prio < td->td_priority) {
                /*
                 * 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.
                 */
                sched_rem(td);
                td->td_priority = prio;
                sched_add(td, SRQ_BORROWING);
        } else {
#ifdef SMP
                struct tdq *tdq;

                tdq = TDQ_CPU(ts->ts_cpu);
                if (prio < tdq->tdq_lowpri)
                        tdq->tdq_lowpri = prio;
#endif
                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)
{
        u_char oldprio;

        td->td_base_user_pri = prio;
        if (td->td_flags & TDF_UBORROWING && td->td_user_pri <= prio)
                return;
        oldprio = td->td_user_pri;
        td->td_user_pri = prio;
}

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

        THREAD_LOCK_ASSERT(td, MA_OWNED);
        td->td_flags |= TDF_UBORROWING;
        oldprio = td->td_user_pri;
        td->td_user_pri = prio;
}

void
sched_unlend_user_prio(struct thread *td, u_char prio)
{
        u_char base_pri;

        THREAD_LOCK_ASSERT(td, MA_OWNED);
        base_pri = td->td_base_user_pri;
        if (prio >= base_pri) {
                td->td_flags &= ~TDF_UBORROWING;
                sched_user_prio(td, base_pri);
        } else {
                sched_lend_user_prio(td, prio);
        }
}

/*
 * Add the thread passed as 'newtd' to the run queue before selecting
 * the next thread to run.  This is only used for KSE.
 */
static void
sched_switchin(struct tdq *tdq, struct thread *td)
{
#ifdef SMP
        spinlock_enter();
        TDQ_UNLOCK(tdq);
        thread_lock(td);
        spinlock_exit();
        sched_setcpu(td->td_sched, TDQ_ID(tdq), SRQ_YIELDING);
#else
        td->td_lock = TDQ_LOCKPTR(tdq);
#endif
        tdq_add(tdq, td, SRQ_YIELDING);
        MPASS(td->td_lock == TDQ_LOCKPTR(tdq));
}

/*
 * Block a thread for switching.  Similar to thread_block() but does not
 * bump the spin count.
 */
static inline struct mtx *
thread_block_switch(struct thread *td)
{
        struct mtx *lock;

        THREAD_LOCK_ASSERT(td, MA_OWNED);
        lock = td->td_lock;
        td->td_lock = &blocked_lock;
        mtx_unlock_spin(lock);

        return (lock);
}

/*
 * 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;

        tdn = TDQ_CPU(td->td_sched->ts_cpu);
#ifdef SMP
        /*
         * Do the lock dance required to avoid LOR.  We grab an extra
         * spinlock nesting to prevent preemption while we're
         * not holding either run-queue lock.
         */
        spinlock_enter();
        thread_block_switch(td);        /* This releases the lock on tdq. */

        /*
         * Acquire both run-queue locks before placing the thread on the new
         * run-queue to avoid deadlocks created by placing a thread with a
         * blocked lock on the run-queue of a remote processor.  The deadlock
         * occurs when a third processor attempts to lock the two queues in
         * question while the target processor is spinning with its own
         * run-queue lock held while waiting for the blocked lock to clear.
         */
        if (TDQ_LOCKPTR(tdn) == TDQ_LOCKPTR(tdq)) {
                TDQ_LOCK(tdq);
                tdq_add(tdn, td, flags);
                tdq_notify(td->td_sched);
        } else {
                tdq_lock_pair(tdn, tdq);
                tdq_add(tdn, td, flags);
                tdq_notify(td->td_sched);
                TDQ_UNLOCK(tdn);
        }
        spinlock_exit();
#endif
        return (TDQ_LOCKPTR(tdn));
}

/*
 * Release a thread that was blocked with thread_block_switch().
 */
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, struct thread *newtd, int flags)
{
        struct tdq *tdq;
        struct td_sched *ts;
        struct mtx *mtx;
        int srqflag;
        int cpuid;

        THREAD_LOCK_ASSERT(td, MA_OWNED);

        cpuid = PCPU_GET(cpuid);
        tdq = TDQ_CPU(cpuid);
        ts = td->td_sched;
        mtx = td->td_lock;
#ifdef SMP
        ts->ts_rltick = ticks;
        if (newtd && newtd->td_priority < tdq->tdq_lowpri)
                tdq->tdq_lowpri = newtd->td_priority;
#endif
        td->td_lastcpu = td->td_oncpu;
        td->td_oncpu = NOCPU;
        td->td_flags &= ~TDF_NEEDRESCHED;
        td->td_owepreempt = 0;
        /*
         * The lock pointer in an idle thread should never change.  Reset it
         * to CAN_RUN as well.
         */
        if (TD_IS_IDLETHREAD(td)) {
                MPASS(td->td_lock == TDQ_LOCKPTR(tdq));
                TD_SET_CAN_RUN(td);
        } else if (TD_IS_RUNNING(td)) {
                MPASS(td->td_lock == TDQ_LOCKPTR(tdq));
                tdq_load_rem(tdq, ts);
                srqflag = (flags & SW_PREEMPT) ?
                    SRQ_OURSELF|SRQ_YIELDING|SRQ_PREEMPTED :
                    SRQ_OURSELF|SRQ_YIELDING;
                if (ts->ts_cpu == cpuid)
                        tdq_add(tdq, td, srqflag);
                else
                        mtx = sched_switch_migrate(tdq, td, srqflag);
        } else {
                /* This thread must be going to sleep. */
                TDQ_LOCK(tdq);
                mtx = thread_block_switch(td);
                tdq_load_rem(tdq, ts);
        }
        /*
         * 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);
        /*
         * If KSE assigned a new thread just add it here and let choosethread
         * select the best one.
         */
        if (newtd != NULL)
                sched_switchin(tdq, newtd);
        newtd = choosethread();
        /*
         * 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
                TDQ_LOCKPTR(tdq)->mtx_lock = (uintptr_t)newtd;

#ifdef KDTRACE_HOOKS
                /*
                 * If DTrace has set the active vtime enum to anything
                 * other than INACTIVE (0), then it should have set the
                 * function to call.
                 */
                if (dtrace_vtime_active)
                        (*dtrace_vtime_switch_func)(newtd);
#endif
                cpu_switch(td, newtd, mtx);
                /*
                 * We may return from cpu_switch on a different cpu.  However,
                 * we always return with td_lock pointing to the current cpu's
                 * run queue lock.
                 */
                cpuid = PCPU_GET(cpuid);
                tdq = TDQ_CPU(cpuid);
#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);
        /*
         * Assert that all went well and return.
         */
#ifdef SMP
        /* We should always get here with the lowest priority td possible */
        tdq->tdq_lowpri = td->td_priority;
#endif
        TDQ_LOCK_ASSERT(tdq, MA_OWNED|MA_NOTRECURSED);
        MPASS(td->td_lock == TDQ_LOCKPTR(tdq));
        td->td_oncpu = cpuid;
}

/*
 * 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);
        PROC_SLOCK_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)
{

        THREAD_LOCK_ASSERT(td, MA_OWNED);

        td->td_slptick = ticks;
}

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

        THREAD_LOCK_ASSERT(td, MA_OWNED);
        ts = td->td_sched;
        /*
         * 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) {
                u_int hzticks;

                hzticks = (ticks - slptick) << SCHED_TICK_SHIFT;
                ts->ts_slptime += hzticks;
                sched_interact_update(td);
                sched_pctcpu_update(ts);
                sched_priority(td);
        }
        /* Reset the slice value after we sleep. */
        ts->ts_slice = sched_slice;
        sched_add(td, SRQ_BORING);
}

/*
 * 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_fork_thread(td, child);
        /*
         * Penalize the parent and child for forking.
         */
        sched_interact_fork(child);
        sched_priority(child);
        td->td_sched->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;

        /*
         * Initialize child.
         */
        THREAD_LOCK_ASSERT(td, MA_OWNED);
        sched_newthread(child);
        child->td_lock = TDQ_LOCKPTR(TDQ_SELF());
        child->td_cpuset = cpuset_ref(td->td_cpuset);
        ts = td->td_sched;
        ts2 = child->td_sched;
        ts2->ts_cpu = ts->ts_cpu;
        ts2->ts_runq = NULL;
        /*
         * Grab our parents cpu estimation information and priority.
         */
        ts2->ts_ticks = ts->ts_ticks;
        ts2->ts_ltick = ts->ts_ltick;
        ts2->ts_ftick = ts->ts_ftick;
        child->td_user_pri = td->td_user_pri;
        child->td_base_user_pri = td->td_base_user_pri;
        /*
         * And update interactivity score.
         */
        ts2->ts_slptime = ts->ts_slptime;
        ts2->ts_runtime = ts->ts_runtime;
        ts2->ts_slice = 1;      /* Attempt to quickly learn interactivity. */
}

/*
 * 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;

#ifdef SMP
        /*
         * On SMP if we're on the RUNQ we must adjust the transferable
         * count because could be changing to or from an interrupt
         * class.
         */
        if (TD_ON_RUNQ(td)) {
                struct tdq *tdq;

                tdq = TDQ_CPU(td->td_sched->ts_cpu);
                if (THREAD_CAN_MIGRATE(td)) {
                        tdq->tdq_transferable--;
                        tdq->tdq_group->tdg_transferable--;
                }
                td->td_pri_class = class;
                if (THREAD_CAN_MIGRATE(td)) {
                        tdq->tdq_transferable++;
                        tdq->tdq_group->tdg_transferable++;
                }
        }
#endif
        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;
        
        CTR3(KTR_SCHED, "sched_exit: %p(%s) prio %d",
            child, child->td_proc->p_comm, child->td_priority);

        PROC_SLOCK_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)
{

        CTR3(KTR_SCHED, "sched_exit_thread: %p(%s) prio %d",
            child, child->td_proc->p_comm, child->td_priority);

#ifdef KSE
        /*
         * KSE forks and exits so often that this penalty causes short-lived
         * threads to always be non-interactive.  This causes mozilla to
         * crawl under load.
         */
        if ((td->td_pflags & TDP_SA) && td->td_proc == child->td_proc)
                return;
#endif
        /*
         * 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->td_sched->ts_runtime += child->td_sched->ts_runtime;
        sched_interact_update(td);
        sched_priority(td);
        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(struct thread *td)
{
        /*
         * XXX we cheat slightly on the locking here to avoid locking in  
         * the usual case.  Setting td_priority here is essentially an
         * incomplete workaround for not setting it properly elsewhere.
         * Now that some interrupt handlers are threads, not setting it
         * properly elsewhere can clobber it in the window between setting
         * it here and returning to user mode, so don't waste time setting
         * it perfectly here.
         */
        KASSERT((td->td_flags & TDF_BORROWING) == 0,
            ("thread with borrowed priority returning to userland"));
        if (td->td_priority != td->td_user_pri) {
                thread_lock(td);
                td->td_priority = td->td_user_pri;
                td->td_base_pri = td->td_user_pri;
                thread_unlock(td);
        }
}

/*
 * Handle a stathz tick.  This is really only relevant for timeshare
 * threads.
 */
void
sched_clock(struct thread *td)
{
        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) {
                if (balance_ticks && --balance_ticks == 0)
                        sched_balance();
                if (balance_group_ticks && --balance_group_ticks == 0)
                        sched_balance_groups();
        }
#endif
        /*
         * 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->td_sched;
        if (td->td_pri_class & PRI_FIFO_BIT)
                return;
        if (td->td_pri_class == PRI_TIMESHARE) {
                /*
                 * We used a tick; charge it to the thread so
                 * that we can compute our interactivity.
                 */
                td->td_sched->ts_runtime += tickincr;
                sched_interact_update(td);
        }
        /*
         * We used up one time slice.
         */
        if (--ts->ts_slice > 0)
                return;
        /*
         * We're out of time, recompute priorities and requeue.
         */
        sched_priority(td);
        td->td_flags |= TDF_NEEDRESCHED;
}

/*
 * Called once per hz tick.  Used for cpu utilization information.  This
 * is easier than trying to scale based on stathz.
 */
void
sched_tick(void)
{
        struct td_sched *ts;

        ts = curthread->td_sched;
        /*
         * Ticks is updated asynchronously on a single cpu.  Check here to
         * avoid incrementing ts_ticks multiple times in a single tick.
         */
        if (ts->ts_ltick == ticks)
                return;
        /* Adjust ticks for pctcpu */
        ts->ts_ticks += 1 << SCHED_TICK_SHIFT;
        ts->ts_ltick = ticks;
        /*
         * Update if we've exceeded our desired tick threshhold by over one
         * second.
         */
        if (ts->ts_ftick + SCHED_TICK_MAX < ts->ts_ltick)
                sched_pctcpu_update(ts);
}

/*
 * 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)
{
#ifdef SMP
        struct tdq_group *tdg;
#endif
        struct td_sched *ts;
        struct tdq *tdq;

        tdq = TDQ_SELF();
        TDQ_LOCK_ASSERT(tdq, MA_OWNED);
        ts = tdq_choose(tdq);
        if (ts) {
                tdq_runq_rem(tdq, ts);
                return (ts->ts_thread);
        }
#ifdef SMP
        /*
         * We only set the idled bit when all of the cpus in the group are
         * idle.  Otherwise we could get into a situation where a thread bounces
         * back and forth between two idle cores on seperate physical CPUs.
         */
        tdg = tdq->tdq_group;
        tdg->tdg_idlemask |= PCPU_GET(cpumask);
        if (tdg->tdg_idlemask == tdg->tdg_cpumask)
                atomic_set_int(&tdq_idle, tdg->tdg_mask);
        tdq->tdq_lowpri = PRI_MAX_IDLE;
#endif
        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;

        ctd = curthread;
        pri = td->td_priority;
        cpri = ctd->td_priority;
        if (td->td_priority < ctd->td_priority)
                curthread->td_flags |= TDF_NEEDRESCHED;
        if (panicstr != NULL || pri >= cpri || cold || TD_IS_INHIBITED(ctd))
                return;
        /*
         * Always preempt IDLE threads.  Otherwise only if the preempting
         * thread is an ithread.
         */
        if (pri > preempt_thresh && cpri < PRI_MIN_IDLE)
                return;
        ctd->td_owepreempt = 1;
        return;
}

/*
 * Add a thread to a thread queue.  Initializes priority, slice, runq, and
 * add it to the appropriate queue.  This is the internal function called
 * when the tdq is predetermined.
 */
void
tdq_add(struct tdq *tdq, struct thread *td, int flags)
{
        struct td_sched *ts;
        int class;
#ifdef SMP
        int cpumask;
#endif

        TDQ_LOCK_ASSERT(tdq, 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"));

        ts = td->td_sched;
        class = PRI_BASE(td->td_pri_class);
        TD_SET_RUNQ(td);
        if (ts->ts_slice == 0)
                ts->ts_slice = sched_slice;
        /*
         * Pick the run queue based on priority.
         */
        if (td->td_priority <= PRI_MAX_REALTIME)
                ts->ts_runq = &tdq->tdq_realtime;
        else if (td->td_priority <= PRI_MAX_TIMESHARE)
                ts->ts_runq = &tdq->tdq_timeshare;
        else
                ts->ts_runq = &tdq->tdq_idle;
#ifdef SMP
        cpumask = 1 << ts->ts_cpu;
        /*
         * If we had been idle, clear our bit in the group and potentially
         * the global bitmap.
         */
        if ((class != PRI_IDLE && class != PRI_ITHD) &&
            (tdq->tdq_group->tdg_idlemask & cpumask) != 0) {
                /*
                 * Check to see if our group is unidling, and if so, remove it
                 * from the global idle mask.
                 */
                if (tdq->tdq_group->tdg_idlemask ==
                    tdq->tdq_group->tdg_cpumask)
                        atomic_clear_int(&tdq_idle, tdq->tdq_group->tdg_mask);
                /*
                 * Now remove ourselves from the group specific idle mask.
                 */
                tdq->tdq_group->tdg_idlemask &= ~cpumask;
        }
        if (td->td_priority < tdq->tdq_lowpri)
                tdq->tdq_lowpri = td->td_priority;
#endif
        tdq_runq_add(tdq, ts, flags);
        tdq_load_add(tdq, ts);
}

/*
 * Select the target thread queue and add a thread to it.  Request
 * preemption or IPI a remote processor if required.
 */
void
sched_add(struct thread *td, int flags)
{
        struct td_sched *ts;
        struct tdq *tdq;
#ifdef SMP
        int cpuid;
        int cpu;
#endif
        CTR5(KTR_SCHED, "sched_add: %p(%s) prio %d by %p(%s)",
            td, td->td_proc->p_comm, td->td_priority, curthread,
            curthread->td_proc->p_comm);
        THREAD_LOCK_ASSERT(td, MA_OWNED);
        ts = td->td_sched;
        /*
         * 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
        cpuid = PCPU_GET(cpuid);
        /*
         * Pick the destination cpu and if it isn't ours transfer to the
         * target cpu.
         */
        if (td->td_priority <= PRI_MAX_ITHD && THREAD_CAN_MIGRATE(td) &&
            curthread->td_intr_nesting_level)
                ts->ts_cpu = cpuid;
        if (!THREAD_CAN_MIGRATE(td))
                cpu = ts->ts_cpu;
        else
                cpu = sched_pickcpu(td, flags);
        tdq = sched_setcpu(ts, cpu, flags);
        tdq_add(tdq, td, flags);
        if (cpu != cpuid) {
                tdq_notify(ts);
                return;
        }
#else
        tdq = TDQ_SELF();
        TDQ_LOCK(tdq);
        /*
         * Now that the thread is moving to the run-queue, set the lock
         * to the scheduler's lock.
         */
        thread_lock_set(td, TDQ_LOCKPTR(tdq));
        tdq_add(tdq, td, flags);
#endif
        if (!(flags & SRQ_YIELDING))
                sched_setpreempt(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;
        struct td_sched *ts;

        CTR5(KTR_SCHED, "sched_rem: %p(%s) prio %d by %p(%s)",
            td, td->td_proc->p_comm, td->td_priority, curthread,
            curthread->td_proc->p_comm);
        ts = td->td_sched;
        tdq = TDQ_CPU(ts->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, ts);
        tdq_load_rem(tdq, ts);
        TD_SET_CAN_RUN(td);
}

/*
 * 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->td_sched;
        if (ts == NULL)
                return (0);

        thread_lock(td);
        if (ts->ts_ticks) {
                int rtick;

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

        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;
        int cpu;

        THREAD_LOCK_ASSERT(td, MA_OWNED);
        ts = td->td_sched;
        if (THREAD_CAN_SCHED(td, ts->ts_cpu))
                return;
        if (TD_ON_RUNQ(td)) {
                sched_rem(td);
                sched_add(td, SRQ_BORING);
                return;
        }
        if (!TD_IS_RUNNING(td))
                return;
        td->td_flags |= TDF_NEEDRESCHED;
        if (!THREAD_CAN_MIGRATE(td))
                return;
        /*
         * Assign the new cpu and force a switch before returning to
         * userspace.  If the target thread is not running locally send
         * an ipi to force the issue.
         */
        cpu = ts->ts_cpu;
        ts->ts_cpu = sched_pickcpu(td, 0);
        if (cpu != PCPU_GET(cpuid))
                ipi_selected(1 << 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);
        ts = td->td_sched;
        if (ts->ts_flags & TSF_BOUND)
                sched_unbind(td);
        ts->ts_flags |= TSF_BOUND;
#ifdef SMP
        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, NULL);
#endif
}

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

        THREAD_LOCK_ASSERT(td, MA_OWNED);
        ts = td->td_sched;
        if ((ts->ts_flags & TSF_BOUND) == 0)
                return;
        ts->ts_flags &= ~TSF_BOUND;
#ifdef SMP
        sched_unpin();
#endif
}

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

/*
 * Basic yield call.
 */
void
sched_relinquish(struct thread *td)
{
        thread_lock(td);
        SCHED_STAT_INC(switch_relinquish);
        mi_switch(SW_VOL, NULL);
        thread_unlock(td);
}

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

        total = 0;
        for (i = 0; i <= tdg_maxid; i++)
                total += TDQ_GROUP(i)->tdg_load;
        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));
}

/*
 * The actual idle process.
 */
void
sched_idletd(void *dummy)
{
        struct thread *td;
        struct tdq *tdq;

        td = curthread;
        tdq = TDQ_SELF();
        mtx_assert(&Giant, MA_NOTOWNED);
        /* ULE relies on preemption for idle interruption. */
        for (;;) {
#ifdef SMP
                if (tdq_idled(tdq))
                        cpu_idle();
#else
                cpu_idle();
#endif
        }
}

/*
 * 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;

        tdq = TDQ_SELF();
        if (td == NULL) {
                /* Correct spinlock nesting and acquire the correct lock. */
                TDQ_LOCK(tdq);
                spinlock_exit();
        } else {
                MPASS(td->td_lock == TDQ_LOCKPTR(tdq));
                tdq_load_rem(tdq, td->td_sched);
        }
        KASSERT(curthread->td_md.md_spinlock_count == 1, ("invalid count"));
        newtd = choosethread();
        TDQ_LOCKPTR(tdq)->mtx_lock = (uintptr_t)newtd;
        PCPU_SET(switchtime, cpu_ticks());
        PCPU_SET(switchticks, ticks);
        cpu_throw(td, newtd);           /* doesn't return */
}

/*
 * 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 td_sched *ts;
        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.
         */
        cpuid = PCPU_GET(cpuid);
        tdq = TDQ_CPU(cpuid);
        ts = td->td_sched;
        if (TD_IS_IDLETHREAD(td))
                td->td_lock = TDQ_LOCKPTR(tdq);
        MPASS(td->td_lock == TDQ_LOCKPTR(tdq));
        td->td_oncpu = cpuid;
        TDQ_LOCK_ASSERT(tdq, MA_OWNED | MA_NOTRECURSED);
}

static SYSCTL_NODE(_kern, OID_AUTO, sched, CTLFLAG_RW, 0,
    "Scheduler");
SYSCTL_STRING(_kern_sched, OID_AUTO, name, CTLFLAG_RD, "ULE", 0,
    "Scheduler name");
SYSCTL_INT(_kern_sched, OID_AUTO, slice, CTLFLAG_RW, &sched_slice, 0,
    "Slice size for timeshare threads");
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,"Min priority for preemption, lower priorities have greater precedence");
#ifdef SMP
SYSCTL_INT(_kern_sched, OID_AUTO, pick_pri, CTLFLAG_RW, &pick_pri, 0,
    "Pick the target cpu based on priority rather than load.");
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, tryself, CTLFLAG_RW, &tryself, 0, "");
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 frequency in stathz ticks to run the long-term balancer");
SYSCTL_INT(_kern_sched, OID_AUTO, steal_htt, CTLFLAG_RW, &steal_htt, 0,
    "Steals work from another hyper-threaded core on idle");
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, topology, CTLFLAG_RD, &topology, 0,
    "True when a topology has been specified by the MD code.");
#endif

/* ps compat.  All cpu percentages from ULE are weighted. */
static int ccpu = 0;
SYSCTL_INT(_kern, OID_AUTO, ccpu, CTLFLAG_RD, &ccpu, 0, "");


#define KERN_SWITCH_INCLUDE 1
#include "kern/kern_switch.c"