Rename msleep() to ssleep().

[dragonfly.git] / sys / kern / usched_bsd4.c

/*
 * Copyright (c) 1999 Peter Wemm <peter@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, 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 AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * $DragonFly: src/sys/kern/usched_bsd4.c,v 1.26 2008/11/01 23:31:19 dillon Exp $
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/lock.h>
#include <sys/queue.h>
#include <sys/proc.h>
#include <sys/rtprio.h>
#include <sys/uio.h>
#include <sys/sysctl.h>
#include <sys/resourcevar.h>
#include <sys/spinlock.h>
#include <machine/cpu.h>
#include <machine/smp.h>

#include <sys/thread2.h>
#include <sys/spinlock2.h>

/*
 * Priorities.  Note that with 32 run queues per scheduler each queue
 * represents four priority levels.
 */

#define MAXPRI                  128
#define PRIMASK                 (MAXPRI - 1)
#define PRIBASE_REALTIME        0
#define PRIBASE_NORMAL          MAXPRI
#define PRIBASE_IDLE            (MAXPRI * 2)
#define PRIBASE_THREAD          (MAXPRI * 3)
#define PRIBASE_NULL            (MAXPRI * 4)

#define NQS     32                      /* 32 run queues. */
#define PPQ     (MAXPRI / NQS)          /* priorities per queue */
#define PPQMASK (PPQ - 1)

/*
 * NICEPPQ      - number of nice units per priority queue
 * ESTCPURAMP   - number of scheduler ticks for estcpu to switch queues
 *
 * ESTCPUPPQ    - number of estcpu units per priority queue
 * ESTCPUMAX    - number of estcpu units
 * ESTCPUINCR   - amount we have to increment p_estcpu per scheduling tick at
 *                100% cpu.
 */
#define NICEPPQ         2
#define ESTCPURAMP      4
#define ESTCPUPPQ       512
#define ESTCPUMAX       (ESTCPUPPQ * NQS)
#define ESTCPUINCR      (ESTCPUPPQ / ESTCPURAMP)
#define PRIO_RANGE      (PRIO_MAX - PRIO_MIN + 1)

#define ESTCPULIM(v)    min((v), ESTCPUMAX)

TAILQ_HEAD(rq, lwp);

#define lwp_priority    lwp_usdata.bsd4.priority
#define lwp_rqindex     lwp_usdata.bsd4.rqindex
#define lwp_origcpu     lwp_usdata.bsd4.origcpu
#define lwp_estcpu      lwp_usdata.bsd4.estcpu
#define lwp_rqtype      lwp_usdata.bsd4.rqtype

static void bsd4_acquire_curproc(struct lwp *lp);
static void bsd4_release_curproc(struct lwp *lp);
static void bsd4_select_curproc(globaldata_t gd);
static void bsd4_setrunqueue(struct lwp *lp);
static void bsd4_schedulerclock(struct lwp *lp, sysclock_t period,
                                sysclock_t cpstamp);
static void bsd4_recalculate_estcpu(struct lwp *lp);
static void bsd4_resetpriority(struct lwp *lp);
static void bsd4_forking(struct lwp *plp, struct lwp *lp);
static void bsd4_exiting(struct lwp *plp, struct lwp *lp);
static void bsd4_yield(struct lwp *lp);

#ifdef SMP
static void need_user_resched_remote(void *dummy);
#endif
static struct lwp *chooseproc_locked(struct lwp *chklp);
static void bsd4_remrunqueue_locked(struct lwp *lp);
static void bsd4_setrunqueue_locked(struct lwp *lp);

struct usched usched_bsd4 = {
        { NULL },
        "bsd4", "Original DragonFly Scheduler",
        NULL,                   /* default registration */
        NULL,                   /* default deregistration */
        bsd4_acquire_curproc,
        bsd4_release_curproc,
        bsd4_setrunqueue,
        bsd4_schedulerclock,
        bsd4_recalculate_estcpu,
        bsd4_resetpriority,
        bsd4_forking,
        bsd4_exiting,
        NULL,                   /* setcpumask not supported */
        bsd4_yield
};

struct usched_bsd4_pcpu {
        struct thread helper_thread;
        short   rrcount;
        short   upri;
        struct lwp *uschedcp;
};

typedef struct usched_bsd4_pcpu *bsd4_pcpu_t;

/*
 * We have NQS (32) run queues per scheduling class.  For the normal
 * class, there are 128 priorities scaled onto these 32 queues.  New
 * processes are added to the last entry in each queue, and processes
 * are selected for running by taking them from the head and maintaining
 * a simple FIFO arrangement.  Realtime and Idle priority processes have
 * and explicit 0-31 priority which maps directly onto their class queue
 * index.  When a queue has something in it, the corresponding bit is
 * set in the queuebits variable, allowing a single read to determine
 * the state of all 32 queues and then a ffs() to find the first busy
 * queue.
 */
static struct rq bsd4_queues[NQS];
static struct rq bsd4_rtqueues[NQS];
static struct rq bsd4_idqueues[NQS];
static u_int32_t bsd4_queuebits;
static u_int32_t bsd4_rtqueuebits;
static u_int32_t bsd4_idqueuebits;
static cpumask_t bsd4_curprocmask = -1; /* currently running a user process */
static cpumask_t bsd4_rdyprocmask;      /* ready to accept a user process */
static int       bsd4_runqcount;
#ifdef SMP
static volatile int bsd4_scancpu;
#endif
static struct spinlock bsd4_spin;
static struct usched_bsd4_pcpu bsd4_pcpu[MAXCPU];

SYSCTL_INT(_debug, OID_AUTO, bsd4_runqcount, CTLFLAG_RD, &bsd4_runqcount, 0, "");
#ifdef INVARIANTS
static int usched_nonoptimal;
SYSCTL_INT(_debug, OID_AUTO, usched_nonoptimal, CTLFLAG_RW,
        &usched_nonoptimal, 0, "acquire_curproc() was not optimal");
static int usched_optimal;
SYSCTL_INT(_debug, OID_AUTO, usched_optimal, CTLFLAG_RW,
        &usched_optimal, 0, "acquire_curproc() was optimal");
#endif
static int usched_debug = -1;
SYSCTL_INT(_debug, OID_AUTO, scdebug, CTLFLAG_RW, &usched_debug, 0, "");
#ifdef SMP
static int remote_resched_nonaffinity;
static int remote_resched_affinity;
static int choose_affinity;
SYSCTL_INT(_debug, OID_AUTO, remote_resched_nonaffinity, CTLFLAG_RD,
        &remote_resched_nonaffinity, 0, "Number of remote rescheds");
SYSCTL_INT(_debug, OID_AUTO, remote_resched_affinity, CTLFLAG_RD,
        &remote_resched_affinity, 0, "Number of remote rescheds");
SYSCTL_INT(_debug, OID_AUTO, choose_affinity, CTLFLAG_RD,
        &choose_affinity, 0, "chooseproc() was smart");
#endif

static int usched_bsd4_rrinterval = (ESTCPUFREQ + 9) / 10;
SYSCTL_INT(_kern, OID_AUTO, usched_bsd4_rrinterval, CTLFLAG_RW,
        &usched_bsd4_rrinterval, 0, "");
static int usched_bsd4_decay = ESTCPUINCR / 2;
SYSCTL_INT(_kern, OID_AUTO, usched_bsd4_decay, CTLFLAG_RW,
        &usched_bsd4_decay, 0, "");

/*
 * Initialize the run queues at boot time.
 */
static void
rqinit(void *dummy)
{
        int i;

        spin_init(&bsd4_spin);
        for (i = 0; i < NQS; i++) {
                TAILQ_INIT(&bsd4_queues[i]);
                TAILQ_INIT(&bsd4_rtqueues[i]);
                TAILQ_INIT(&bsd4_idqueues[i]);
        }
        atomic_clear_int(&bsd4_curprocmask, 1);
}
SYSINIT(runqueue, SI_BOOT2_USCHED, SI_ORDER_FIRST, rqinit, NULL)

/*
 * BSD4_ACQUIRE_CURPROC
 *
 * This function is called when the kernel intends to return to userland.
 * It is responsible for making the thread the current designated userland
 * thread for this cpu, blocking if necessary.
 *
 * The kernel has already depressed our LWKT priority so we must not switch
 * until we have either assigned or disposed of the thread.
 *
 * WARNING! THIS FUNCTION IS ALLOWED TO CAUSE THE CURRENT THREAD TO MIGRATE
 * TO ANOTHER CPU!  Because most of the kernel assumes that no migration will
 * occur, this function is called only under very controlled circumstances.
 *
 * MPSAFE
 */
static void
bsd4_acquire_curproc(struct lwp *lp)
{
        globaldata_t gd;
        bsd4_pcpu_t dd;
        struct lwp *olp;

        crit_enter();
        bsd4_recalculate_estcpu(lp);

        /*
         * If a reschedule was requested give another thread the
         * driver's seat.
         */
        if (user_resched_wanted()) {
                clear_user_resched();
                bsd4_release_curproc(lp);
        }

        /*
         * Loop until we are the current user thread
         */
        do {
                /*
                 * Reload after a switch or setrunqueue/switch possibly
                 * moved us to another cpu.
                 */
                clear_lwkt_resched();
                gd = mycpu;
                dd = &bsd4_pcpu[gd->gd_cpuid];

                /*
                 * Become the currently scheduled user thread for this cpu
                 * if we can do so trivially.
                 *
                 * We can steal another thread's current thread designation
                 * on this cpu since if we are running that other thread
                 * must not be, so we can safely deschedule it.
                 */
                if (dd->uschedcp == lp) {
                        dd->upri = lp->lwp_priority;
                } else if (dd->uschedcp == NULL) {
                        atomic_set_int(&bsd4_curprocmask, gd->gd_cpumask);
                        dd->uschedcp = lp;
                        dd->upri = lp->lwp_priority;
                } else if (dd->upri > lp->lwp_priority) {
                        olp = dd->uschedcp;
                        dd->uschedcp = lp;
                        dd->upri = lp->lwp_priority;
                        lwkt_deschedule(olp->lwp_thread);
                        bsd4_setrunqueue(olp);
                } else {
                        lwkt_deschedule(lp->lwp_thread);
                        bsd4_setrunqueue(lp);
                        lwkt_switch();
                }

                /*
                 * Other threads at our current user priority have already
                 * put in their bids, but we must run any kernel threads
                 * at higher priorities, and we could lose our bid to
                 * another thread trying to return to user mode in the
                 * process.
                 *
                 * If we lose our bid we will be descheduled and put on
                 * the run queue.  When we are reactivated we will have
                 * another chance.
                 */
                if (lwkt_check_resched(lp->lwp_thread) > 1) {
                        lwkt_switch();
                        continue;
                }
        } while (dd->uschedcp != lp);

        crit_exit();
        KKASSERT((lp->lwp_flag & LWP_ONRUNQ) == 0);
}

/*
 * BSD4_RELEASE_CURPROC
 *
 * This routine detaches the current thread from the userland scheduler,
 * usually because the thread needs to run or block in the kernel (at
 * kernel priority) for a while.
 *
 * This routine is also responsible for selecting a new thread to
 * make the current thread.
 *
 * NOTE: This implementation differs from the dummy example in that
 * bsd4_select_curproc() is able to select the current process, whereas
 * dummy_select_curproc() is not able to select the current process.
 * This means we have to NULL out uschedcp.
 *
 * Additionally, note that we may already be on a run queue if releasing
 * via the lwkt_switch() in bsd4_setrunqueue().
 *
 * WARNING!  The MP lock may be in an unsynchronized state due to the
 * way get_mplock() works and the fact that this function may be called
 * from a passive release during a lwkt_switch().   try_mplock() will deal 
 * with this for us but you should be aware that td_mpcount may not be
 * useable.
 *
 * MPSAFE
 */
static void
bsd4_release_curproc(struct lwp *lp)
{
        globaldata_t gd = mycpu;
        bsd4_pcpu_t dd = &bsd4_pcpu[gd->gd_cpuid];

        if (dd->uschedcp == lp) {
                crit_enter();
                KKASSERT((lp->lwp_flag & LWP_ONRUNQ) == 0);
                dd->uschedcp = NULL;    /* don't let lp be selected */
                dd->upri = PRIBASE_NULL;
                atomic_clear_int(&bsd4_curprocmask, gd->gd_cpumask);
                bsd4_select_curproc(gd);
                crit_exit();
        }
}

/*
 * BSD4_SELECT_CURPROC
 *
 * Select a new current process for this cpu and clear any pending user
 * reschedule request.  The cpu currently has no current process.
 *
 * This routine is also responsible for equal-priority round-robining,
 * typically triggered from bsd4_schedulerclock().  In our dummy example
 * all the 'user' threads are LWKT scheduled all at once and we just
 * call lwkt_switch().
 *
 * The calling process is not on the queue and cannot be selected.
 *
 * MPSAFE
 */
static
void
bsd4_select_curproc(globaldata_t gd)
{
        bsd4_pcpu_t dd = &bsd4_pcpu[gd->gd_cpuid];
        struct lwp *nlp;
        int cpuid = gd->gd_cpuid;

        crit_enter_gd(gd);

        spin_lock_wr(&bsd4_spin);
        if ((nlp = chooseproc_locked(dd->uschedcp)) != NULL) {
                atomic_set_int(&bsd4_curprocmask, 1 << cpuid);
                dd->upri = nlp->lwp_priority;
                dd->uschedcp = nlp;
                spin_unlock_wr(&bsd4_spin);
#ifdef SMP
                lwkt_acquire(nlp->lwp_thread);
#endif
                lwkt_schedule(nlp->lwp_thread);
        } else if (bsd4_runqcount && (bsd4_rdyprocmask & (1 << cpuid))) {
                atomic_clear_int(&bsd4_rdyprocmask, 1 << cpuid);
                spin_unlock_wr(&bsd4_spin);
                lwkt_schedule(&dd->helper_thread);
        } else {
                spin_unlock_wr(&bsd4_spin);
        }
        crit_exit_gd(gd);
}

/*
 * BSD4_SETRUNQUEUE
 *
 * Place the specified lwp on the user scheduler's run queue.  This routine
 * must be called with the thread descheduled.  The lwp must be runnable.
 *
 * The thread may be the current thread as a special case.
 *
 * MPSAFE
 */
static void
bsd4_setrunqueue(struct lwp *lp)
{
        globaldata_t gd;
        bsd4_pcpu_t dd;
#ifdef SMP
        int cpuid;
        cpumask_t mask;
        cpumask_t tmpmask;
#endif

        /*
         * First validate the process state relative to the current cpu.
         * We don't need the spinlock for this, just a critical section.
         * We are in control of the process.
         */
        crit_enter();
        KASSERT(lp->lwp_stat == LSRUN, ("setrunqueue: lwp not LSRUN"));
        KASSERT((lp->lwp_flag & LWP_ONRUNQ) == 0,
            ("lwp %d/%d already on runq! flag %08x/%08x", lp->lwp_proc->p_pid,
             lp->lwp_tid, lp->lwp_proc->p_flag, lp->lwp_flag));
        KKASSERT((lp->lwp_thread->td_flags & TDF_RUNQ) == 0);

        /*
         * Note: gd and dd are relative to the target thread's last cpu,
         * NOT our current cpu.
         */
        gd = lp->lwp_thread->td_gd;
        dd = &bsd4_pcpu[gd->gd_cpuid];

        /*
         * This process is not supposed to be scheduled anywhere or assigned
         * as the current process anywhere.  Assert the condition.
         */
        KKASSERT(dd->uschedcp != lp);

#ifndef SMP
        /*
         * If we are not SMP we do not have a scheduler helper to kick
         * and must directly activate the process if none are scheduled.
         *
         * This is really only an issue when bootstrapping init since
         * the caller in all other cases will be a user process, and
         * even if released (dd->uschedcp == NULL), that process will
         * kickstart the scheduler when it returns to user mode from
         * the kernel.
         */
        if (dd->uschedcp == NULL) {
                atomic_set_int(&bsd4_curprocmask, gd->gd_cpumask);
                dd->uschedcp = lp;
                dd->upri = lp->lwp_priority;
                lwkt_schedule(lp->lwp_thread);
                crit_exit();
                return;
        }
#endif

#ifdef SMP
        /*
         * XXX fixme.  Could be part of a remrunqueue/setrunqueue
         * operation when the priority is recalculated, so TDF_MIGRATING
         * may already be set.
         */
        if ((lp->lwp_thread->td_flags & TDF_MIGRATING) == 0)
                lwkt_giveaway(lp->lwp_thread);
#endif

        /*
         * We lose control of lp the moment we release the spinlock after
         * having placed lp on the queue.  i.e. another cpu could pick it
         * up and it could exit, or its priority could be further adjusted,
         * or something like that.
         */
        spin_lock_wr(&bsd4_spin);
        bsd4_setrunqueue_locked(lp);

#ifdef SMP
        /*
         * Kick the scheduler helper on one of the other cpu's
         * and request a reschedule if appropriate.
         */
        cpuid = (bsd4_scancpu & 0xFFFF) % ncpus;
        ++bsd4_scancpu;
        mask = ~bsd4_curprocmask & bsd4_rdyprocmask &
                lp->lwp_cpumask & smp_active_mask;
        spin_unlock_wr(&bsd4_spin);

        while (mask) {
                tmpmask = ~((1 << cpuid) - 1);
                if (mask & tmpmask)
                        cpuid = bsfl(mask & tmpmask);
                else
                        cpuid = bsfl(mask);
                gd = globaldata_find(cpuid);
                dd = &bsd4_pcpu[cpuid];

                if ((dd->upri & ~PPQMASK) > (lp->lwp_priority & ~PPQMASK)) {
                        if (gd == mycpu)
                                need_user_resched_remote(NULL);
                        else
                                lwkt_send_ipiq(gd, need_user_resched_remote, NULL);
                        break;
                }
                mask &= ~(1 << cpuid);
        }
#else
        /*
         * Request a reschedule if appropriate.
         */
        spin_unlock_wr(&bsd4_spin);
        if ((dd->upri & ~PPQMASK) > (lp->lwp_priority & ~PPQMASK)) {
                need_user_resched();
        }
#endif
        crit_exit();
}

/*
 * This routine is called from a systimer IPI.  It MUST be MP-safe and
 * the BGL IS NOT HELD ON ENTRY.  This routine is called at ESTCPUFREQ on
 * each cpu.
 *
 * Because this is effectively a 'fast' interrupt, we cannot safely
 * use spinlocks unless gd_spinlock_rd is NULL and gd_spinlocks_wr is 0,
 * even if the spinlocks are 'non conflicting'.  This is due to the way
 * spinlock conflicts against cached read locks are handled.
 *
 * MPSAFE
 */
static
void
bsd4_schedulerclock(struct lwp *lp, sysclock_t period, sysclock_t cpstamp)
{
        globaldata_t gd = mycpu;
        bsd4_pcpu_t dd = &bsd4_pcpu[gd->gd_cpuid];

        /*
         * Do we need to round-robin?  We round-robin 10 times a second.
         * This should only occur for cpu-bound batch processes.
         */
        if (++dd->rrcount >= usched_bsd4_rrinterval) {
                dd->rrcount = 0;
                need_user_resched();
        }

        /*
         * As the process accumulates cpu time p_estcpu is bumped and may
         * push the process into another scheduling queue.  It typically
         * takes 4 ticks to bump the queue.
         */
        lp->lwp_estcpu = ESTCPULIM(lp->lwp_estcpu + ESTCPUINCR);

        /*
         * Reducing p_origcpu over time causes more of our estcpu to be
         * returned to the parent when we exit.  This is a small tweak
         * for the batch detection heuristic.
         */
        if (lp->lwp_origcpu)
                --lp->lwp_origcpu;

        /*
         * We can only safely call bsd4_resetpriority(), which uses spinlocks,
         * if we aren't interrupting a thread that is using spinlocks.
         * Otherwise we can deadlock with another cpu waiting for our read
         * spinlocks to clear.
         */
        if (gd->gd_spinlock_rd == NULL && gd->gd_spinlocks_wr == 0)
                bsd4_resetpriority(lp);
        else
                need_user_resched();
}

/*
 * Called from acquire and from kern_synch's one-second timer (one of the
 * callout helper threads) with a critical section held. 
 *
 * Decay p_estcpu based on the number of ticks we haven't been running
 * and our p_nice.  As the load increases each process observes a larger
 * number of idle ticks (because other processes are running in them).
 * This observation leads to a larger correction which tends to make the
 * system more 'batchy'.
 *
 * Note that no recalculation occurs for a process which sleeps and wakes
 * up in the same tick.  That is, a system doing thousands of context
 * switches per second will still only do serious estcpu calculations
 * ESTCPUFREQ times per second.
 *
 * MPSAFE
 */
static
void 
bsd4_recalculate_estcpu(struct lwp *lp)
{
        globaldata_t gd = mycpu;
        sysclock_t cpbase;
        int loadfac;
        int ndecay;
        int nticks;
        int nleft;

        /*
         * We have to subtract periodic to get the last schedclock
         * timeout time, otherwise we would get the upcoming timeout.
         * Keep in mind that a process can migrate between cpus and
         * while the scheduler clock should be very close, boundary
         * conditions could lead to a small negative delta.
         */
        cpbase = gd->gd_schedclock.time - gd->gd_schedclock.periodic;

        if (lp->lwp_slptime > 1) {
                /*
                 * Too much time has passed, do a coarse correction.
                 */
                lp->lwp_estcpu = lp->lwp_estcpu >> 1;
                bsd4_resetpriority(lp);
                lp->lwp_cpbase = cpbase;
                lp->lwp_cpticks = 0;
        } else if (lp->lwp_cpbase != cpbase) {
                /*
                 * Adjust estcpu if we are in a different tick.  Don't waste
                 * time if we are in the same tick. 
                 * 
                 * First calculate the number of ticks in the measurement
                 * interval.  The nticks calculation can wind up 0 due to
                 * a bug in the handling of lwp_slptime  (as yet not found),
                 * so make sure we do not get a divide by 0 panic.
                 */
                nticks = (cpbase - lp->lwp_cpbase) / gd->gd_schedclock.periodic;
                if (nticks <= 0)
                        nticks = 1;
                updatepcpu(lp, lp->lwp_cpticks, nticks);

                if ((nleft = nticks - lp->lwp_cpticks) < 0)
                        nleft = 0;
                if (usched_debug == lp->lwp_proc->p_pid) {
                        kprintf("pid %d tid %d estcpu %d cpticks %d nticks %d nleft %d",
                                lp->lwp_proc->p_pid, lp->lwp_tid, lp->lwp_estcpu,
                                lp->lwp_cpticks, nticks, nleft);
                }

                /*
                 * Calculate a decay value based on ticks remaining scaled
                 * down by the instantanious load and p_nice.
                 */
                if ((loadfac = bsd4_runqcount) < 2)
                        loadfac = 2;
                ndecay = nleft * usched_bsd4_decay * 2 * 
                        (PRIO_MAX * 2 - lp->lwp_proc->p_nice) / (loadfac * PRIO_MAX * 2);

                /*
                 * Adjust p_estcpu.  Handle a border case where batch jobs
                 * can get stalled long enough to decay to zero when they
                 * shouldn't.
                 */
                if (lp->lwp_estcpu > ndecay * 2)
                        lp->lwp_estcpu -= ndecay;
                else
                        lp->lwp_estcpu >>= 1;

                if (usched_debug == lp->lwp_proc->p_pid)
                        kprintf(" ndecay %d estcpu %d\n", ndecay, lp->lwp_estcpu);
                bsd4_resetpriority(lp);
                lp->lwp_cpbase = cpbase;
                lp->lwp_cpticks = 0;
        }
}

/*
 * Compute the priority of a process when running in user mode.
 * Arrange to reschedule if the resulting priority is better
 * than that of the current process.
 *
 * This routine may be called with any process.
 *
 * This routine is called by fork1() for initial setup with the process
 * of the run queue, and also may be called normally with the process on or
 * off the run queue.
 *
 * MPSAFE
 */
static void
bsd4_resetpriority(struct lwp *lp)
{
        bsd4_pcpu_t dd;
        int newpriority;
        u_short newrqtype;
        int reschedcpu;

        /*
         * Calculate the new priority and queue type
         */
        crit_enter();
        spin_lock_wr(&bsd4_spin);

        newrqtype = lp->lwp_rtprio.type;

        switch(newrqtype) {
        case RTP_PRIO_REALTIME:
        case RTP_PRIO_FIFO:
                newpriority = PRIBASE_REALTIME +
                             (lp->lwp_rtprio.prio & PRIMASK);
                break;
        case RTP_PRIO_NORMAL:
                newpriority = (lp->lwp_proc->p_nice - PRIO_MIN) * PPQ / NICEPPQ;
                newpriority += lp->lwp_estcpu * PPQ / ESTCPUPPQ;
                newpriority = newpriority * MAXPRI / (PRIO_RANGE * PPQ /
                              NICEPPQ + ESTCPUMAX * PPQ / ESTCPUPPQ);
                newpriority = PRIBASE_NORMAL + (newpriority & PRIMASK);
                break;
        case RTP_PRIO_IDLE:
                newpriority = PRIBASE_IDLE + (lp->lwp_rtprio.prio & PRIMASK);
                break;
        case RTP_PRIO_THREAD:
                newpriority = PRIBASE_THREAD + (lp->lwp_rtprio.prio & PRIMASK);
                break;
        default:
                panic("Bad RTP_PRIO %d", newrqtype);
                /* NOT REACHED */
        }

        /*
         * The newpriority incorporates the queue type so do a simple masked
         * check to determine if the process has moved to another queue.  If
         * it has, and it is currently on a run queue, then move it.
         */
        if ((lp->lwp_priority ^ newpriority) & ~PPQMASK) {
                lp->lwp_priority = newpriority;
                if (lp->lwp_flag & LWP_ONRUNQ) {
                        bsd4_remrunqueue_locked(lp);
                        lp->lwp_rqtype = newrqtype;
                        lp->lwp_rqindex = (newpriority & PRIMASK) / PPQ;
                        bsd4_setrunqueue_locked(lp);
                        reschedcpu = lp->lwp_thread->td_gd->gd_cpuid;
                } else {
                        lp->lwp_rqtype = newrqtype;
                        lp->lwp_rqindex = (newpriority & PRIMASK) / PPQ;
                        reschedcpu = -1;
                }
        } else {
                lp->lwp_priority = newpriority;
                reschedcpu = -1;
        }
        spin_unlock_wr(&bsd4_spin);

        /*
         * Determine if we need to reschedule the target cpu.  This only
         * occurs if the LWP is already on a scheduler queue, which means
         * that idle cpu notification has already occured.  At most we
         * need only issue a need_user_resched() on the appropriate cpu.
         *
         * The LWP may be owned by a CPU different from the current one,
         * in which case dd->uschedcp may be modified without an MP lock
         * or a spinlock held.  The worst that happens is that the code
         * below causes a spurious need_user_resched() on the target CPU
         * and dd->pri to be wrong for a short period of time, both of
         * which are harmless.
         */
        if (reschedcpu >= 0) {
                dd = &bsd4_pcpu[reschedcpu];
                if ((dd->upri & ~PRIMASK) > (lp->lwp_priority & ~PRIMASK)) {
                        dd->upri = lp->lwp_priority;
#ifdef SMP
                        if (reschedcpu == mycpu->gd_cpuid) {
                                need_user_resched();
                        } else {
                                lwkt_send_ipiq(lp->lwp_thread->td_gd,
                                               need_user_resched_remote, NULL);
                        }
#else
                        need_user_resched();
#endif
                }
        }
        crit_exit();
}

static
void
bsd4_yield(struct lwp *lp) 
{
#if 0
        /* FUTURE (or something similar) */
        switch(lp->lwp_rqtype) {
        case RTP_PRIO_NORMAL:
                lp->lwp_estcpu = ESTCPULIM(lp->lwp_estcpu + ESTCPUINCR);
                break;
        default:
                break;
        }
#endif
        need_user_resched();
}

/*
 * Called from fork1() when a new child process is being created.
 *
 * Give the child process an initial estcpu that is more batch then
 * its parent and dock the parent for the fork (but do not
 * reschedule the parent).   This comprises the main part of our batch
 * detection heuristic for both parallel forking and sequential execs.
 *
 * Interactive processes will decay the boosted estcpu quickly while batch
 * processes will tend to compound it.
 * XXX lwp should be "spawning" instead of "forking"
 *
 * MPSAFE
 */
static void
bsd4_forking(struct lwp *plp, struct lwp *lp)
{
        lp->lwp_estcpu = ESTCPULIM(plp->lwp_estcpu + ESTCPUPPQ);
        lp->lwp_origcpu = lp->lwp_estcpu;
        plp->lwp_estcpu = ESTCPULIM(plp->lwp_estcpu + ESTCPUPPQ);
}

/*
 * Called when the parent reaps a child.   Propogate cpu use by the child
 * back to the parent.
 *
 * MPSAFE
 */
static void
bsd4_exiting(struct lwp *plp, struct lwp *lp)
{
        int delta;

        if (plp->lwp_proc->p_pid != 1) {
                delta = lp->lwp_estcpu - lp->lwp_origcpu;
                if (delta > 0)
                        plp->lwp_estcpu = ESTCPULIM(plp->lwp_estcpu + delta);
        }
}


/*
 * chooseproc() is called when a cpu needs a user process to LWKT schedule,
 * it selects a user process and returns it.  If chklp is non-NULL and chklp
 * has a better or equal priority then the process that would otherwise be
 * chosen, NULL is returned.
 *
 * Until we fix the RUNQ code the chklp test has to be strict or we may
 * bounce between processes trying to acquire the current process designation.
 *
 * MPSAFE - must be called with bsd4_spin exclusive held.  The spinlock is
 *          left intact through the entire routine.
 */
static
struct lwp *
chooseproc_locked(struct lwp *chklp)
{
        struct lwp *lp;
        struct rq *q;
        u_int32_t *which, *which2;
        u_int32_t pri;
        u_int32_t rtqbits;
        u_int32_t tsqbits;
        u_int32_t idqbits;
        cpumask_t cpumask;

        rtqbits = bsd4_rtqueuebits;
        tsqbits = bsd4_queuebits;
        idqbits = bsd4_idqueuebits;
        cpumask = mycpu->gd_cpumask;

#ifdef SMP
again:
#endif
        if (rtqbits) {
                pri = bsfl(rtqbits);
                q = &bsd4_rtqueues[pri];
                which = &bsd4_rtqueuebits;
                which2 = &rtqbits;
        } else if (tsqbits) {
                pri = bsfl(tsqbits);
                q = &bsd4_queues[pri];
                which = &bsd4_queuebits;
                which2 = &tsqbits;
        } else if (idqbits) {
                pri = bsfl(idqbits);
                q = &bsd4_idqueues[pri];
                which = &bsd4_idqueuebits;
                which2 = &idqbits;
        } else {
                return NULL;
        }
        lp = TAILQ_FIRST(q);
        KASSERT(lp, ("chooseproc: no lwp on busy queue"));

#ifdef SMP
        while ((lp->lwp_cpumask & cpumask) == 0) {
                lp = TAILQ_NEXT(lp, lwp_procq);
                if (lp == NULL) {
                        *which2 &= ~(1 << pri);
                        goto again;
                }
        }
#endif

        /*
         * If the passed lwp <chklp> is reasonably close to the selected
         * lwp <lp>, return NULL (indicating that <chklp> should be kept).
         * 
         * Note that we must error on the side of <chklp> to avoid bouncing
         * between threads in the acquire code.
         */
        if (chklp) {
                if (chklp->lwp_priority < lp->lwp_priority + PPQ)
                        return(NULL);
        }

#ifdef SMP
        /*
         * If the chosen lwp does not reside on this cpu spend a few
         * cycles looking for a better candidate at the same priority level.
         * This is a fallback check, setrunqueue() tries to wakeup the
         * correct cpu and is our front-line affinity.
         */
        if (lp->lwp_thread->td_gd != mycpu &&
            (chklp = TAILQ_NEXT(lp, lwp_procq)) != NULL
        ) {
                if (chklp->lwp_thread->td_gd == mycpu) {
                        ++choose_affinity;
                        lp = chklp;
                }
        }
#endif

        TAILQ_REMOVE(q, lp, lwp_procq);
        --bsd4_runqcount;
        if (TAILQ_EMPTY(q))
                *which &= ~(1 << pri);
        KASSERT((lp->lwp_flag & LWP_ONRUNQ) != 0, ("not on runq6!"));
        lp->lwp_flag &= ~LWP_ONRUNQ;
        return lp;
}

#ifdef SMP

/*
 * Called via an ipi message to reschedule on another cpu.  If no
 * user thread is active on the target cpu we wake the scheduler
 * helper thread up to help schedule one.
 *
 * MPSAFE
 */
static
void
need_user_resched_remote(void *dummy)
{
        globaldata_t gd = mycpu;
        bsd4_pcpu_t  dd = &bsd4_pcpu[gd->gd_cpuid];

        if (dd->uschedcp == NULL && (bsd4_rdyprocmask & gd->gd_cpumask)) {
                atomic_clear_int(&bsd4_rdyprocmask, gd->gd_cpumask);
                lwkt_schedule(&dd->helper_thread);
        } else {
                need_user_resched();
        }
}

#endif

/*
 * bsd4_remrunqueue_locked() removes a given process from the run queue
 * that it is on, clearing the queue busy bit if it becomes empty.
 *
 * Note that user process scheduler is different from the LWKT schedule.
 * The user process scheduler only manages user processes but it uses LWKT
 * underneath, and a user process operating in the kernel will often be
 * 'released' from our management.
 *
 * MPSAFE - bsd4_spin must be held exclusively on call
 */
static void
bsd4_remrunqueue_locked(struct lwp *lp)
{
        struct rq *q;
        u_int32_t *which;
        u_int8_t pri;

        KKASSERT(lp->lwp_flag & LWP_ONRUNQ);
        lp->lwp_flag &= ~LWP_ONRUNQ;
        --bsd4_runqcount;
        KKASSERT(bsd4_runqcount >= 0);

        pri = lp->lwp_rqindex;
        switch(lp->lwp_rqtype) {
        case RTP_PRIO_NORMAL:
                q = &bsd4_queues[pri];
                which = &bsd4_queuebits;
                break;
        case RTP_PRIO_REALTIME:
        case RTP_PRIO_FIFO:
                q = &bsd4_rtqueues[pri];
                which = &bsd4_rtqueuebits;
                break;
        case RTP_PRIO_IDLE:
                q = &bsd4_idqueues[pri];
                which = &bsd4_idqueuebits;
                break;
        default:
                panic("remrunqueue: invalid rtprio type");
                /* NOT REACHED */
        }
        TAILQ_REMOVE(q, lp, lwp_procq);
        if (TAILQ_EMPTY(q)) {
                KASSERT((*which & (1 << pri)) != 0,
                        ("remrunqueue: remove from empty queue"));
                *which &= ~(1 << pri);
        }
}

/*
 * bsd4_setrunqueue_locked()
 *
 * Add a process whos rqtype and rqindex had previously been calculated
 * onto the appropriate run queue.   Determine if the addition requires
 * a reschedule on a cpu and return the cpuid or -1.
 *
 * NOTE: Lower priorities are better priorities.
 *
 * MPSAFE - bsd4_spin must be held exclusively on call
 */
static void
bsd4_setrunqueue_locked(struct lwp *lp)
{
        struct rq *q;
        u_int32_t *which;
        int pri;

        KKASSERT((lp->lwp_flag & LWP_ONRUNQ) == 0);
        lp->lwp_flag |= LWP_ONRUNQ;
        ++bsd4_runqcount;

        pri = lp->lwp_rqindex;

        switch(lp->lwp_rqtype) {
        case RTP_PRIO_NORMAL:
                q = &bsd4_queues[pri];
                which = &bsd4_queuebits;
                break;
        case RTP_PRIO_REALTIME:
        case RTP_PRIO_FIFO:
                q = &bsd4_rtqueues[pri];
                which = &bsd4_rtqueuebits;
                break;
        case RTP_PRIO_IDLE:
                q = &bsd4_idqueues[pri];
                which = &bsd4_idqueuebits;
                break;
        default:
                panic("remrunqueue: invalid rtprio type");
                /* NOT REACHED */
        }

        /*
         * Add to the correct queue and set the appropriate bit.  If no
         * lower priority (i.e. better) processes are in the queue then
         * we want a reschedule, calculate the best cpu for the job.
         *
         * Always run reschedules on the LWPs original cpu.
         */
        TAILQ_INSERT_TAIL(q, lp, lwp_procq);
        *which |= 1 << pri;
}

#ifdef SMP

/*
 * For SMP systems a user scheduler helper thread is created for each
 * cpu and is used to allow one cpu to wakeup another for the purposes of
 * scheduling userland threads from setrunqueue().  UP systems do not
 * need the helper since there is only one cpu.  We can't use the idle
 * thread for this because we need to hold the MP lock.  Additionally,
 * doing things this way allows us to HLT idle cpus on MP systems.
 *
 * MPSAFE
 */
static void
sched_thread(void *dummy)
{
    globaldata_t gd;
    bsd4_pcpu_t  dd;
    struct lwp *nlp;
    cpumask_t cpumask;
    int cpuid;
#if 0
    cpumask_t tmpmask;
    int tmpid;
#endif

    gd = mycpu;
    cpuid = gd->gd_cpuid;       /* doesn't change */
    cpumask = gd->gd_cpumask;   /* doesn't change */
    dd = &bsd4_pcpu[cpuid];

    /*
     * The scheduler thread does not need to hold the MP lock.  Since we
     * are woken up only when no user processes are scheduled on a cpu, we
     * can run at an ultra low priority.
     */
    rel_mplock();
    lwkt_setpri_self(TDPRI_USER_SCHEDULER);

    for (;;) {
        /*
         * We use the LWKT deschedule-interlock trick to avoid racing
         * bsd4_rdyprocmask.  This means we cannot block through to the
         * manual lwkt_switch() call we make below.
         */
        crit_enter_gd(gd);
        lwkt_deschedule_self(gd->gd_curthread);
        spin_lock_wr(&bsd4_spin);
        atomic_set_int(&bsd4_rdyprocmask, cpumask);

        clear_user_resched();   /* This satisfied the reschedule request */
        dd->rrcount = 0;        /* Reset the round-robin counter */

        if ((bsd4_curprocmask & cpumask) == 0) {
                /*
                 * No thread is currently scheduled.
                 */
                KKASSERT(dd->uschedcp == NULL);
                if ((nlp = chooseproc_locked(NULL)) != NULL) {
                        atomic_set_int(&bsd4_curprocmask, cpumask);
                        dd->upri = nlp->lwp_priority;
                        dd->uschedcp = nlp;
                        spin_unlock_wr(&bsd4_spin);
                        lwkt_acquire(nlp->lwp_thread);
                        lwkt_schedule(nlp->lwp_thread);
                } else {
                        spin_unlock_wr(&bsd4_spin);
                }
#if 0
        /*
         * Disabled for now, this can create an infinite loop.
         */
        } else if (bsd4_runqcount) {
                /*
                 * Someone scheduled us but raced.  In order to not lose
                 * track of the fact that there may be a LWP ready to go,
                 * forward the request to another cpu if available.
                 *
                 * Rotate through cpus starting with cpuid + 1.  Since cpuid
                 * is already masked out by gd_other_cpus, just use ~cpumask.
                 */
                tmpmask = bsd4_rdyprocmask & mycpu->gd_other_cpus &
                          ~bsd4_curprocmask;
                if (tmpmask) {
                        if (tmpmask & ~(cpumask - 1))
                                tmpid = bsfl(tmpmask & ~(cpumask - 1));
                        else
                                tmpid = bsfl(tmpmask);
                        bsd4_scancpu = tmpid;
                        atomic_clear_int(&bsd4_rdyprocmask, 1 << tmpid);
                        spin_unlock_wr(&bsd4_spin);
                        lwkt_schedule(&bsd4_pcpu[tmpid].helper_thread);
                } else {
                        spin_unlock_wr(&bsd4_spin);
                }
#endif
        } else {
                /*
                 * The runq is empty.
                 */
                spin_unlock_wr(&bsd4_spin);
        }
        crit_exit_gd(gd);
        lwkt_switch();
    }
}

/*
 * Setup our scheduler helpers.  Note that curprocmask bit 0 has already
 * been cleared by rqinit() and we should not mess with it further.
 */
static void
sched_thread_cpu_init(void)
{
    int i;

    if (bootverbose)
        kprintf("start scheduler helpers on cpus:");

    for (i = 0; i < ncpus; ++i) {
        bsd4_pcpu_t dd = &bsd4_pcpu[i];
        cpumask_t mask = 1 << i;

        if ((mask & smp_active_mask) == 0)
            continue;

        if (bootverbose)
            kprintf(" %d", i);

        lwkt_create(sched_thread, NULL, NULL, &dd->helper_thread, 
                    TDF_STOPREQ, i, "usched %d", i);

        /*
         * Allow user scheduling on the target cpu.  cpu #0 has already
         * been enabled in rqinit().
         */
        if (i)
            atomic_clear_int(&bsd4_curprocmask, mask);
        atomic_set_int(&bsd4_rdyprocmask, mask);
        dd->upri = PRIBASE_NULL;
    }
    if (bootverbose)
        kprintf("\n");
}
SYSINIT(uschedtd, SI_BOOT2_USCHED, SI_ORDER_SECOND,
        sched_thread_cpu_init, NULL)

#endif