FreeBSD/Linux Kernel Cross Reference
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: releng/9.0/sys/kern/sched_ule.c 225199 2011-08-26 18:00:07Z delphij $");
    
    #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>
    #include <sys/sbuf.h>
    
    #ifdef HWPMC_HOOKS
    #include <sys/pmckern.h>
    #endif
    
    #ifdef KDTRACE_HOOKS
    #include <sys/dtrace_bsd.h>
    int                             dtrace_vtime_active;
    dtrace_vtime_switch_func_t      dtrace_vtime_switch_func;
    #endif
    
    #include <machine/cpu.h>
    #include <machine/smp.h>
    
    #if defined(__sparc64__)
    #error "This architecture is not currently compatible with ULE"
    #endif
    
    #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. */
            u_char          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_incrtick;    /* Last tick that we incremented 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. */
   
   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)
   
   /*
    * 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_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)
   
   /*
    * 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 = 1;
   #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
   static int static_boost = PRI_MIN_BATCH;
   static int sched_idlespins = 10000;
   static int sched_idlespinthresh = 16;
   
   /*
    * 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(). */
           struct mtx      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. */
           int             tdq_transferable;       /* Transferable thread count. */
           short           tdq_switchcnt;          /* Switches this tick. */
           short           tdq_oldswitchcnt;       /* Switches last tick. */
           u_char          tdq_lowpri;             /* Lowest priority thread. */
           u_char          tdq_ipipending;         /* IPI pending. */
           u_char          tdq_idx;                /* Current insert index. */
           u_char          tdq_ridx;               /* Current removal index. */
           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 *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 affinity;
   static int steal_htt = 1;
   static int steal_idle = 1;
   static int steal_thresh = 2;
   
   /*
    * One thread queue per processor.
    */
   static struct tdq       tdq_cpu[MAXCPU];
   static struct tdq       *balance_tdq;
   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))
   #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)          (&(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 thread *tdq_choose(struct tdq *);
   static void tdq_setup(struct tdq *);
   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 int 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 struct mtx *sched_switch_migrate(struct tdq *, struct thread *, int);
   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);
   
   /*
    * 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);
   }
   
   #define TS_RQ_PPQ       (((PRI_MAX_BATCH - PRI_MIN_BATCH) + 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 thread *td, int flags)
   {
           struct td_sched *ts;
           u_char pri;
   
           TDQ_LOCK_ASSERT(tdq, MA_OWNED);
           THREAD_LOCK_ASSERT(td, MA_OWNED);
   
           pri = td->td_priority;
           ts = td->td_sched;
           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 = (pri - PRI_MIN_BATCH) / 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, 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->td_sched;
           TDQ_LOCK_ASSERT(tdq, 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_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);
   }
   
   /*
    * 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)
   {
   
           THREAD_LOCK_ASSERT(td, MA_OWNED);
           TDQ_LOCK_ASSERT(tdq, 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);
   }
   
   /*
    * 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
   struct cpu_search {
           cpuset_t cs_mask;
           u_int   cs_load;
           u_int   cs_cpu;
           int     cs_limit;       /* Min priority for low min load for high. */
   };
   
   #define CPU_SEARCH_LOWEST       0x1
   #define CPU_SEARCH_HIGHEST      0x2
   #define CPU_SEARCH_BOTH         (CPU_SEARCH_LOWEST|CPU_SEARCH_HIGHEST)
   
   #define CPUSET_FOREACH(cpu, mask)                               \
           for ((cpu) = 0; (cpu) <= mp_maxid; (cpu)++)             \
                   if (CPU_ISSET(cpu, &mask))
   
   static __inline int cpu_search(struct cpu_group *cg, struct cpu_search *low,
       struct cpu_search *high, const int match);
   int cpu_search_lowest(struct cpu_group *cg, struct cpu_search *low);
   int cpu_search_highest(struct cpu_group *cg, struct cpu_search *high);
   int cpu_search_both(struct cpu_group *cg, struct cpu_search *low,
       struct cpu_search *high);
   
   /*
    * This routine compares according to the match argument and should be
    * reduced in actual instantiations via constant propagation and dead code
    * elimination.
    */ 
   static __inline int
   cpu_compare(int cpu, struct cpu_search *low, struct cpu_search *high,
       const int match)
   {
           struct tdq *tdq;
   
           tdq = TDQ_CPU(cpu);
           if (match & CPU_SEARCH_LOWEST)
                   if (CPU_ISSET(cpu, &low->cs_mask) &&
                       tdq->tdq_load < low->cs_load &&
                       tdq->tdq_lowpri > low->cs_limit) {
                           low->cs_cpu = cpu;
                           low->cs_load = tdq->tdq_load;
                   }
           if (match & CPU_SEARCH_HIGHEST)
                   if (CPU_ISSET(cpu, &high->cs_mask) &&
                       tdq->tdq_load >= high->cs_limit && 
                       tdq->tdq_load > high->cs_load &&
                       tdq->tdq_transferable) {
                           high->cs_cpu = cpu;
                           high->cs_load = tdq->tdq_load;
                   }
           return (tdq->tdq_load);
   }
   
   /*
    * 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 busses.
    *
    * 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 __inline int
   cpu_search(struct cpu_group *cg, struct cpu_search *low,
       struct cpu_search *high, const int match)
   {
           int total;
   
           total = 0;
           if (cg->cg_children) {
                   struct cpu_search lgroup;
                   struct cpu_search hgroup;
                   struct cpu_group *child;
                   u_int lload;
                   int hload;
                   int load;
                   int i;
   
                   lload = -1;
                   hload = -1;
                   for (i = 0; i < cg->cg_children; i++) {
                           child = &cg->cg_child[i];
                           if (match & CPU_SEARCH_LOWEST) {
                                   lgroup = *low;
                                   lgroup.cs_load = -1;
                           }
                           if (match & CPU_SEARCH_HIGHEST) {
                                   hgroup = *high;
                                   lgroup.cs_load = 0;
                           }
                           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;
                           }
                           total += load;
                           if (match & CPU_SEARCH_LOWEST)
                                   if (load < lload || low->cs_cpu == -1) {
                                           *low = lgroup;
                                           lload = load;
                                   }
                           if (match & CPU_SEARCH_HIGHEST) 
                                   if (load > hload || high->cs_cpu == -1) {
                                           hload = load;
                                           *high = hgroup;
                                   }
                   }
           } else {
                   int cpu;
   
                   CPUSET_FOREACH(cpu, cg->cg_mask)
                           total += cpu_compare(cpu, low, high, match);
           }
           return (total);
   }
   
   /*
    * cpu_search instantiations must pass constants to maintain the inline
    * optimization.
    */
   int
   cpu_search_lowest(struct cpu_group *cg, struct cpu_search *low)
   {
           return cpu_search(cg, low, NULL, CPU_SEARCH_LOWEST);
   }
   
   int
   cpu_search_highest(struct cpu_group *cg, struct cpu_search *high)
   {
           return cpu_search(cg, NULL, high, CPU_SEARCH_HIGHEST);
   }
   
   int
   cpu_search_both(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(struct cpu_group *cg, cpuset_t mask, int pri)
   {
           struct cpu_search low;
   
           low.cs_cpu = -1;
           low.cs_load = -1;
           low.cs_mask = mask;
           low.cs_limit = pri;
           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(struct cpu_group *cg, cpuset_t mask, int minload)
   {
           struct cpu_search high;
   
           high.cs_cpu = -1;
           high.cs_load = 0;
           high.cs_mask = mask;
           high.cs_limit = minload;
           cpu_search_highest(cg, &high);
           return high.cs_cpu;
   }
   
   /*
    * Simultaneously find the highest and lowest loaded cpu reachable via
    * cg.
    */
   static inline void 
   sched_both(struct cpu_group *cg, cpuset_t mask, int *lowcpu, int *highcpu)
   {
           struct cpu_search high;
           struct cpu_search low;
   
           low.cs_cpu = -1;
           low.cs_limit = -1;
           low.cs_load = -1;
           low.cs_mask = mask;
           high.cs_load = 0;
           high.cs_cpu = -1;
           high.cs_limit = -1;
           high.cs_mask = mask;
           cpu_search_both(cg, &low, &high);
           *lowcpu = low.cs_cpu;
           *highcpu = high.cs_cpu;
           return;
   }
   
   static void
   sched_balance_group(struct cpu_group *cg)
   {
           cpuset_t mask;
           int high;
           int low;
           int i;
   
           CPU_FILL(&mask);
           for (;;) {
                   sched_both(cg, mask, &low, &high);
                   if (low == high || low == -1 || high == -1)
                           break;
                   if (sched_balance_pair(TDQ_CPU(high), TDQ_CPU(low)))
                           break;
                   /*
                    * If we failed to move any threads determine which cpu
                    * to kick out of the set and try again.
                    */
                   if (TDQ_CPU(high)->tdq_transferable == 0)
                           CPU_CLR(high, &mask);
                   else
                           CPU_CLR(low, &mask);
           }
   
           for (i = 0; i < cg->cg_children; i++)
                   sched_balance_group(&cg->cg_child[i]);
   }
   
   static void
   sched_balance(void)
   {
           struct tdq *tdq;
   
           /*
            * 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);
           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)
   {
           int transferable;
           int high_load;
           int low_load;
           int moved;
           int move;
           int diff;
           int i;
   
           tdq_lock_pair(high, low);
           transferable = high->tdq_transferable;
           high_load = high->tdq_load;
           low_load = low->tdq_load;
           moved = 0;
           /*
            * 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++)
                           moved += tdq_move(high, low);
                   /*
                    * IPI the target cpu to force it to reschedule with the new
                    * workload.
                    */
                   ipi_cpu(TDQ_ID(low), IPI_PREEMPT);
           }
           tdq_unlock_pair(high, low);
           return (moved);
   }
   
   /*
    * Move a thread from one thread queue to another.
    */
   static int
   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);
           td = tdq_steal(tdq, cpu);
           if (td == NULL)
                   return (0);
           ts = td->td_sched;
           /*
            * 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);
           return (1);
   }
   
   /*
    * 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 thresh;
           int cpu;
   
           if (smp_started == 0 || steal_idle == 0)
                   return (1);
           CPU_FILL(&mask);
           CPU_CLR(PCPU_GET(cpuid), &mask);
           /* We don't want to be preempted while we're iterating. */
           spinlock_enter();
           for (cg = tdq->tdq_cg; cg != NULL; ) {
                   if ((cg->cg_flags & CG_FLAG_THREAD) == 0)
                           thresh = steal_thresh;
                   else
                           thresh = 1;
                   cpu = sched_highest(cg, mask, thresh);
                   if (cpu == -1) {
                           cg = cg->cg_parent;
                           continue;
                   }
                   steal = TDQ_CPU(cpu);
                   CPU_CLR(cpu, &mask);
                   tdq_lock_pair(tdq, steal);
                   if (steal->tdq_load < thresh || steal->tdq_transferable == 0) {
                           tdq_unlock_pair(tdq, steal);
                           continue;
                   }
                   /*
                    * If a thread was added while interrupts were disabled don't
                    * steal one here.  If we fail to acquire one due to affinity
                    * restrictions loop again with this cpu removed from the
                    * set.
                    */
                   if (tdq->tdq_load == 0 && tdq_move(steal, tdq) == 0) {
                           tdq_unlock_pair(tdq, steal);
                           continue;
                   }
                   spinlock_exit();
                   TDQ_UNLOCK(steal);
                   mi_switch(SW_VOL | SWT_IDLE, NULL);
                   thread_unlock(curthread);
   
                   return (0);
           }
           spinlock_exit();
           return (1);
   }
   
   /*
    * 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_ipipending)
                   return;
           cpu = td->td_sched->ts_cpu;
           pri = td->td_priority;
           ctd = pcpu_find(cpu)->pc_curthread;
           if (!sched_shouldpreempt(pri, ctd->td_priority, 1))
                   return;
           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;
           }
           tdq->tdq_ipipending = 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;
          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(td, rqh, td_runq) {
                          if (first && THREAD_CAN_MIGRATE(td) &&
                              THREAD_CAN_SCHED(td, cpu))
                                  return (td);
                          first = 1;
                  }
          }
          if (start != 0) {
                  start = 0;
                  goto again;
          }
  
          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;
  
          THREAD_LOCK_ASSERT(td, MA_OWNED);
          tdq = TDQ_CPU(cpu);
          td->td_sched->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.
           */
          spinlock_enter();
          thread_lock_block(td);
          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;
          struct td_sched *ts;
          struct tdq *tdq;
          cpuset_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) || !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 && ts->ts_cpu != self) {
                  SCHED_STAT_INC(pickcpu_intrbind);
                  ts->ts_cpu = self;
          }
          /*
           * If the thread can run on the last cpu and the affinity has not
           * expired or it is idle run it there.
           */
          pri = td->td_priority;
          tdq = TDQ_CPU(ts->ts_cpu);
          if (THREAD_CAN_SCHED(td, ts->ts_cpu)) {
                  if (tdq->tdq_lowpri > PRI_MIN_IDLE) {
                          SCHED_STAT_INC(pickcpu_idle_affinity);
                          return (ts->ts_cpu);
                  }
                  if (SCHED_AFFINITY(ts, CG_SHARE_L2) && tdq->tdq_lowpri > pri) {
                          SCHED_STAT_INC(pickcpu_affinity);
                          return (ts->ts_cpu);
                  }
          }
          /*
           * Search for the highest level in the tree that still has affinity.
           */
          cg = NULL;
          for (cg = tdq->tdq_cg; cg != NULL; cg = cg->cg_parent)
                  if (SCHED_AFFINITY(ts, cg->cg_level))
                          break;
          cpu = -1;
          mask = td->td_cpuset->cs_mask;
          if (cg)
                  cpu = sched_lowest(cg, mask, pri);
          if (cpu == -1)
                  cpu = sched_lowest(cpu_top, mask, -1);
          /*
           * Compare the lowest loaded cpu to current cpu.
           */
          if (THREAD_CAN_SCHED(td, self) && TDQ_CPU(self)->tdq_lowpri > pri &&
              TDQ_CPU(cpu)->tdq_lowpri < PRI_MIN_IDLE) {
                  SCHED_STAT_INC(pickcpu_local);
                  cpu = self;
          } else
                  SCHED_STAT_INC(pickcpu_lowest);
          if (cpu != ts->ts_cpu)
                  SCHED_STAT_INC(pickcpu_migration);
          KASSERT(cpu != -1, ("sched_pickcpu: Failed to find a cpu."));
          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)
  {
  
          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);
          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 | MTX_RECURSE);
  #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 = TDQ_CPU(i);
                  tdq_setup(tdq);
                  tdq->tdq_cg = smp_topo_find(cpu_top, i);
                  if (tdq->tdq_cg == NULL)
                          panic("Can't find cpu group for %d\n", i);
          }
          balance_tdq = TDQ_SELF();
          sched_balance();
  }
  #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_setup_smp();
  #else
          tdq_setup(tdq);
  #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, &thread0);
          tdq->tdq_lowpri = thread0.td_priority;
          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 (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->td_sched->ts_ticks)
                          pri += SCHED_PRI_TICKS(td->td_sched);
                  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->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_slice = sched_slice;
  }
  
  /*
   * 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;
          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));
          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));
          } 
          ts = td->td_sched;
          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);
                  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;
  }
  
  /*
   * 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
          tdq_load_rem(tdq, td);
          /*
           * 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_lock_block(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.
           */
          tdq_lock_pair(tdn, tdq);
          tdq_add(tdn, td, flags);
          tdq_notify(tdn, td);
          TDQ_UNLOCK(tdn);
          spinlock_exit();
  #endif
          return (TDQ_LOCKPTR(tdn));
  }
  
  /*
   * Variadic version of 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, 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);
          KASSERT(newtd == NULL, ("sched_switch: Unsupported newtd argument"));
  
          cpuid = PCPU_GET(cpuid);
          tdq = TDQ_CPU(cpuid);
          ts = td->td_sched;
          mtx = td->td_lock;
          ts->ts_rltick = ticks;
          td->td_lastcpu = td->td_oncpu;
          td->td_oncpu = NOCPU;
          if (!(flags & SW_PREEMPT))
                  td->td_flags &= ~TDF_NEEDRESCHED;
          td->td_owepreempt = 0;
          tdq->tdq_switchcnt++;
          /*
           * 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));
                  srqflag = (flags & SW_PREEMPT) ?
                      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 {
                          KASSERT(THREAD_CAN_MIGRATE(td) ||
                              (ts->ts_flags & TSF_BOUND) != 0,
                              ("Thread %p shouldn't migrate", td));
                          mtx = sched_switch_migrate(tdq, td, srqflag);
                  }
          } else {
                  /* This thread must be going to sleep. */
                  TDQ_LOCK(tdq);
                  mtx = thread_lock_block(td);
                  tdq_load_rem(tdq, td);
          }
          /*
           * 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();
          /*
           * 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
                  lock_profile_release_lock(&TDQ_LOCKPTR(tdq)->lock_object);
                  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);
                  lock_profile_obtain_lock_success(
                      &TDQ_LOCKPTR(tdq)->lock_object, 0, 0, __FILE__, __LINE__);
  #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.
           */
          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);
  
          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.
   */
  void
  sched_wakeup(struct thread *td)
  {
          struct td_sched *ts;
          int slptick;
  
          THREAD_LOCK_ASSERT(td, MA_OWNED);
          ts = td->td_sched;
          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) {
                  u_int hzticks;
  
                  hzticks = (ticks - slptick) << SCHED_TICK_SHIFT;
                  ts->ts_slptime += hzticks;
                  sched_interact_update(td);
                  sched_pctcpu_update(ts);
          }
          /* 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;
  
          THREAD_LOCK_ASSERT(td, MA_OWNED);
          /*
           * Initialize child.
           */
          ts = td->td_sched;
          ts2 = child->td_sched;
          child->td_lock = TDQ_LOCKPTR(TDQ_SELF());
          child->td_cpuset = cpuset_ref(td->td_cpuset);
          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_incrtick = ts->ts_incrtick;
          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;
          ts2->ts_slice = 1;      /* Attempt to quickly learn interactivity. */
  #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->td_sched->ts_runtime += child->td_sched->ts_runtime;
          sched_interact_update(td);
          sched_priority(td);
          thread_unlock(td);
  }
  
  void
  sched_preempt(struct thread *td)
  {
          struct tdq *tdq;
  
          thread_lock(td);
          tdq = TDQ_SELF();
          TDQ_LOCK_ASSERT(tdq, MA_OWNED);
          tdq->tdq_ipipending = 0;
          if (td->td_priority > tdq->tdq_lowpri) {
                  int flags;
  
                  flags = SW_INVOL | SW_PREEMPT;
                  if (td->td_critnest > 1)
                          td->td_owepreempt = 1;
                  else if (TD_IS_IDLETHREAD(td))
                          mi_switch(flags | SWT_REMOTEWAKEIDLE, NULL);
                  else
                          mi_switch(flags | SWT_REMOTEPREEMPT, NULL);
          }
          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;
                  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)
  {
          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();
          }
  #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->td_sched;
          if (td->td_pri_class & PRI_FIFO_BIT)
                  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->td_sched->ts_runtime += tickincr;
                  sched_interact_update(td);
                  sched_priority(td);
          }
          /*
           * We used up one time slice.
           */
          if (--ts->ts_slice > 0)
                  return;
          /*
           * We're out of time, force a requeue at userret().
           */
          ts->ts_slice = sched_slice;
          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(int cnt)
  {
          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_incrtick == ticks)
                  return;
          /* Adjust ticks for pctcpu */
          ts->ts_ticks += cnt << SCHED_TICK_SHIFT;
          ts->ts_ltick = ticks;
          ts->ts_incrtick = ticks;
          /*
           * Update if we've exceeded our desired tick threshold 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)
  {
          struct thread *td;
          struct tdq *tdq;
  
          tdq = TDQ_SELF();
          TDQ_LOCK_ASSERT(tdq, MA_OWNED);
          td = tdq_choose(tdq);
          if (td) {
                  td->td_sched->ts_ltick = ticks;
                  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 (panicstr != NULL || 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);
          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.
   */
  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));
          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);
                  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;
  
          KTR_STATE1(KTR_SCHED, "thread", sched_tdname(td), "runq rem",
              "prio:%d", td->td_priority);
          tdq = TDQ_CPU(td->td_sched->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->td_sched;
          if (ts == NULL)
                  return (0);
  
          THREAD_LOCK_ASSERT(td, MA_OWNED);
          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;
          }
  
          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->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;
          /*
           * 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->td_sched;
          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, NULL);
  }
  
  /*
   * 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->td_sched;
          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->td_sched->ts_flags & TSF_BOUND);
  }
  
  /*
   * Basic yield call.
   */
  void
  sched_relinquish(struct thread *td)
  {
          thread_lock(td);
          mi_switch(SW_VOL | SWT_RELINQUISH, NULL);
          thread_unlock(td);
  }
  
  /*
   * 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 switchcnt;
          int i;
  
          mtx_assert(&Giant, MA_NOTOWNED);
          td = curthread;
          tdq = TDQ_SELF();
          for (;;) {
  #ifdef SMP
                  if (tdq_idled(tdq) == 0)
                          continue;
  #endif
                  switchcnt = tdq->tdq_switchcnt + tdq->tdq_oldswitchcnt;
                  /*
                   * 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();
                          }
                  }
                  switchcnt = tdq->tdq_switchcnt + tdq->tdq_oldswitchcnt;
                  if (tdq->tdq_load == 0) {
                          tdq->tdq_cpu_idle = 1;
                          if (tdq->tdq_load == 0) {
                                  cpu_idle(switchcnt > sched_idlespinthresh * 4);
                                  tdq->tdq_switchcnt++;
                          }
                          tdq->tdq_cpu_idle = 0;
                  }
                  if (tdq->tdq_load) {
                          thread_lock(td);
                          mi_switch(SW_VOL | SWT_IDLE, NULL);
                          thread_unlock(td);
                  }
          }
  }
  
  /*
   * 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);
                  lock_profile_release_lock(&TDQ_LOCKPTR(tdq)->lock_object);
          }
          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);
          lock_profile_obtain_lock_success(
              &TDQ_LOCKPTR(tdq)->lock_object, 0, 0, __FILE__, __LINE__);
  }
  
  /*
   * Create on first use to catch odd startup conditons.
   */
  char *
  sched_tdname(struct thread *td)
  {
  #ifdef KTR
          struct td_sched *ts;
  
          ts = td->td_sched;
          if (ts->ts_name[0] == '\0')
                  snprintf(ts->ts_name, sizeof(ts->ts_name),
                      "%s tid %d", td->td_name, td->td_tid);
          return (ts->ts_name);
  #else
          return (td->td_name);
  #endif
  }
  
  #ifdef 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(NULL, NULL, 500, SBUF_AUTOEXTEND);
          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) {
                  sbuf_finish(topo);
                  err = SYSCTL_OUT(req, sbuf_data(topo), sbuf_len(topo));
          }
          sbuf_delete(topo);
          return (err);
  }
  
  #endif
  
  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");
  SYSCTL_INT(_kern_sched, OID_AUTO, static_boost, CTLFLAG_RW, &static_boost,
       0,"Controls whether static kernel priorities are assigned to sleeping threads.");
  SYSCTL_INT(_kern_sched, OID_AUTO, idlespins, CTLFLAG_RW, &sched_idlespins,
       0,"Number of times idle will spin waiting for new work.");
  SYSCTL_INT(_kern_sched, OID_AUTO, idlespinthresh, CTLFLAG_RW, &sched_idlespinthresh,
       0,"Threshold before we will permit idle 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 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");
  
  /* Retrieve SMP topology */
  SYSCTL_PROC(_kern_sched, OID_AUTO, topology_spec, CTLTYPE_STRING |
      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, "");

Cache object: 63feb88782eb660ade248eeee533e881