Merge from vendor branch GCC:

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

/*-
 * Copyright (c) 1982, 1986, 1990, 1991, 1993
 *      The Regents of the University of California.  All rights reserved.
 * (c) UNIX System Laboratories, Inc.
 * All or some portions of this file are derived from material licensed
 * to the University of California by American Telephone and Telegraph
 * Co. or Unix System Laboratories, Inc. and are reproduced herein with
 * the permission of UNIX System Laboratories, Inc.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *      @(#)kern_synch.c        8.9 (Berkeley) 5/19/95
 * $FreeBSD: src/sys/kern/kern_synch.c,v 1.87.2.6 2002/10/13 07:29:53 kbyanc Exp $
 * $DragonFly: src/sys/kern/kern_synch.c,v 1.71 2007/01/14 07:59:03 dillon Exp $
 */

#include "opt_ktrace.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/proc.h>
#include <sys/kernel.h>
#include <sys/signalvar.h>
#include <sys/resourcevar.h>
#include <sys/vmmeter.h>
#include <sys/sysctl.h>
#include <sys/lock.h>
#ifdef KTRACE
#include <sys/uio.h>
#include <sys/ktrace.h>
#endif
#include <sys/xwait.h>
#include <sys/ktr.h>

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

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

TAILQ_HEAD(tslpque, thread);

static void sched_setup (void *dummy);
SYSINIT(sched_setup, SI_SUB_KICK_SCHEDULER, SI_ORDER_FIRST, sched_setup, NULL)

int     hogticks;
int     lbolt;
int     lbolt_syncer;
int     sched_quantum;          /* Roundrobin scheduling quantum in ticks. */
int     ncpus;
int     ncpus2, ncpus2_shift, ncpus2_mask;
int     safepri;

static struct callout loadav_callout;
static struct callout schedcpu_callout;
MALLOC_DEFINE(M_TSLEEP, "tslpque", "tsleep queues");

#if !defined(KTR_TSLEEP)
#define KTR_TSLEEP      KTR_ALL
#endif
KTR_INFO_MASTER(tsleep);
KTR_INFO(KTR_TSLEEP, tsleep, tsleep_beg, 0, "tsleep enter", 0);
KTR_INFO(KTR_TSLEEP, tsleep, tsleep_end, 0, "tsleep exit", 0);
KTR_INFO(KTR_TSLEEP, tsleep, wakeup_beg, 0, "wakeup enter", 0);
KTR_INFO(KTR_TSLEEP, tsleep, wakeup_end, 0, "wakeup exit", 0);
#define logtsleep(name) KTR_LOG(tsleep_ ## name)

struct loadavg averunnable =
        { {0, 0, 0}, FSCALE };  /* load average, of runnable procs */
/*
 * Constants for averages over 1, 5, and 15 minutes
 * when sampling at 5 second intervals.
 */
static fixpt_t cexp[3] = {
        0.9200444146293232 * FSCALE,    /* exp(-1/12) */
        0.9834714538216174 * FSCALE,    /* exp(-1/60) */
        0.9944598480048967 * FSCALE,    /* exp(-1/180) */
};

static void     endtsleep (void *);
static void     unsleep_and_wakeup_thread(struct thread *td);
static void     loadav (void *arg);
static void     schedcpu (void *arg);

/*
 * Adjust the scheduler quantum.  The quantum is specified in microseconds.
 * Note that 'tick' is in microseconds per tick.
 */
static int
sysctl_kern_quantum(SYSCTL_HANDLER_ARGS)
{
        int error, new_val;

        new_val = sched_quantum * tick;
        error = sysctl_handle_int(oidp, &new_val, 0, req);
        if (error != 0 || req->newptr == NULL)
                return (error);
        if (new_val < tick)
                return (EINVAL);
        sched_quantum = new_val / tick;
        hogticks = 2 * sched_quantum;
        return (0);
}

SYSCTL_PROC(_kern, OID_AUTO, quantum, CTLTYPE_INT|CTLFLAG_RW,
        0, sizeof sched_quantum, sysctl_kern_quantum, "I", "");

/*
 * If `ccpu' is not equal to `exp(-1/20)' and you still want to use the
 * faster/more-accurate formula, you'll have to estimate CCPU_SHIFT below
 * and possibly adjust FSHIFT in "param.h" so that (FSHIFT >= CCPU_SHIFT).
 *
 * To estimate CCPU_SHIFT for exp(-1/20), the following formula was used:
 *     1 - exp(-1/20) ~= 0.0487 ~= 0.0488 == 1 (fixed pt, *11* bits).
 *
 * If you don't want to bother with the faster/more-accurate formula, you
 * can set CCPU_SHIFT to (FSHIFT + 1) which will use a slower/less-accurate
 * (more general) method of calculating the %age of CPU used by a process.
 *
 * decay 95% of `p_pctcpu' in 60 seconds; see CCPU_SHIFT before changing 
 */
#define CCPU_SHIFT      11

static fixpt_t ccpu = 0.95122942450071400909 * FSCALE; /* exp(-1/20) */
SYSCTL_INT(_kern, OID_AUTO, ccpu, CTLFLAG_RD, &ccpu, 0, "");

/*
 * kernel uses `FSCALE', userland (SHOULD) use kern.fscale 
 */
int     fscale __unused = FSCALE;       /* exported to systat */
SYSCTL_INT(_kern, OID_AUTO, fscale, CTLFLAG_RD, 0, FSCALE, "");

/*
 * Recompute process priorities, once a second.
 *
 * Since the userland schedulers are typically event oriented, if the
 * estcpu calculation at wakeup() time is not sufficient to make a
 * process runnable relative to other processes in the system we have
 * a 1-second recalc to help out.
 *
 * This code also allows us to store sysclock_t data in the process structure
 * without fear of an overrun, since sysclock_t are guarenteed to hold 
 * several seconds worth of count.
 *
 * WARNING!  callouts can preempt normal threads.  However, they will not
 * preempt a thread holding a spinlock so we *can* safely use spinlocks.
 */
static int schedcpu_stats(struct proc *p, void *data __unused);
static int schedcpu_resource(struct proc *p, void *data __unused);

static void
schedcpu(void *arg)
{
        allproc_scan(schedcpu_stats, NULL);
        allproc_scan(schedcpu_resource, NULL);
        wakeup((caddr_t)&lbolt);
        wakeup((caddr_t)&lbolt_syncer);
        callout_reset(&schedcpu_callout, hz, schedcpu, NULL);
}

/*
 * General process statistics once a second
 */
static int
schedcpu_stats(struct proc *p, void *data __unused)
{
        crit_enter();
        p->p_swtime++;
        if (p->p_stat == SSLEEP)
                p->p_slptime++;

        /*
         * Only recalculate processes that are active or have slept
         * less then 2 seconds.  The schedulers understand this.
         */
        if (p->p_slptime <= 1) {
                p->p_usched->recalculate(&p->p_lwp);
        } else {
                p->p_pctcpu = (p->p_pctcpu * ccpu) >> FSHIFT;
        }
        crit_exit();
        return(0);
}

/*
 * Resource checks.  XXX break out since ksignal/killproc can block,
 * limiting us to one process killed per second.  There is probably
 * a better way.
 */
static int
schedcpu_resource(struct proc *p, void *data __unused)
{
        u_int64_t ttime;

        crit_enter();
        if (p->p_stat == SIDL || 
            (p->p_flag & P_ZOMBIE) ||
            p->p_limit == NULL || 
            p->p_thread == NULL
        ) {
                crit_exit();
                return(0);
        }

        ttime = p->p_thread->td_sticks + p->p_thread->td_uticks;

        switch(plimit_testcpulimit(p->p_limit, ttime)) {
        case PLIMIT_TESTCPU_KILL:
                killproc(p, "exceeded maximum CPU limit");
                break;
        case PLIMIT_TESTCPU_XCPU:
                if ((p->p_flag & P_XCPU) == 0) {
                        p->p_flag |= P_XCPU;
                        ksignal(p, SIGXCPU);
                }
                break;
        default:
                break;
        }
        crit_exit();
        return(0);
}

/*
 * This is only used by ps.  Generate a cpu percentage use over
 * a period of one second.
 *
 * MPSAFE
 */
void
updatepcpu(struct lwp *lp, int cpticks, int ttlticks)
{
        fixpt_t acc;
        int remticks;

        acc = (cpticks << FSHIFT) / ttlticks;
        if (ttlticks >= ESTCPUFREQ) {
                lp->lwp_pctcpu = acc;
        } else {
                remticks = ESTCPUFREQ - ttlticks;
                lp->lwp_pctcpu = (acc * ttlticks + lp->lwp_pctcpu * remticks) /
                                ESTCPUFREQ;
        }
}

/*
 * We're only looking at 7 bits of the address; everything is
 * aligned to 4, lots of things are aligned to greater powers
 * of 2.  Shift right by 8, i.e. drop the bottom 256 worth.
 */
#define TABLESIZE       128
#define LOOKUP(x)       (((intptr_t)(x) >> 8) & (TABLESIZE - 1))

static cpumask_t slpque_cpumasks[TABLESIZE];

/*
 * General scheduler initialization.  We force a reschedule 25 times
 * a second by default.  Note that cpu0 is initialized in early boot and
 * cannot make any high level calls.
 *
 * Each cpu has its own sleep queue.
 */
void
sleep_gdinit(globaldata_t gd)
{
        static struct tslpque slpque_cpu0[TABLESIZE];
        int i;

        if (gd->gd_cpuid == 0) {
                sched_quantum = (hz + 24) / 25;
                hogticks = 2 * sched_quantum;

                gd->gd_tsleep_hash = slpque_cpu0;
        } else {
                gd->gd_tsleep_hash = kmalloc(sizeof(slpque_cpu0), 
                                            M_TSLEEP, M_WAITOK | M_ZERO);
        }
        for (i = 0; i < TABLESIZE; ++i)
                TAILQ_INIT(&gd->gd_tsleep_hash[i]);
}

/*
 * General sleep call.  Suspends the current process until a wakeup is
 * performed on the specified identifier.  The process will then be made
 * runnable with the specified priority.  Sleeps at most timo/hz seconds
 * (0 means no timeout).  If flags includes PCATCH flag, signals are checked
 * before and after sleeping, else signals are not checked.  Returns 0 if
 * awakened, EWOULDBLOCK if the timeout expires.  If PCATCH is set and a
 * signal needs to be delivered, ERESTART is returned if the current system
 * call should be restarted if possible, and EINTR is returned if the system
 * call should be interrupted by the signal (return EINTR).
 *
 * Note that if we are a process, we release_curproc() before messing with
 * the LWKT scheduler.
 *
 * During autoconfiguration or after a panic, a sleep will simply
 * lower the priority briefly to allow interrupts, then return.
 */
int
tsleep(void *ident, int flags, const char *wmesg, int timo)
{
        struct thread *td = curthread;
        struct proc *p = td->td_proc;           /* may be NULL */
        globaldata_t gd;
        int sig;
        int catch;
        int id;
        int error;
        int oldpri;
        struct callout thandle;

        /*
         * NOTE: removed KTRPOINT, it could cause races due to blocking
         * even in stable.  Just scrap it for now.
         */
        if (cold || panicstr) {
                /*
                 * After a panic, or during autoconfiguration,
                 * just give interrupts a chance, then just return;
                 * don't run any other procs or panic below,
                 * in case this is the idle process and already asleep.
                 */
                splz();
                oldpri = td->td_pri & TDPRI_MASK;
                lwkt_setpri_self(safepri);
                lwkt_switch();
                lwkt_setpri_self(oldpri);
                return (0);
        }
        logtsleep(tsleep_beg);
        gd = td->td_gd;
        KKASSERT(td != &gd->gd_idlethread);     /* you must be kidding! */

        /*
         * NOTE: all of this occurs on the current cpu, including any
         * callout-based wakeups, so a critical section is a sufficient
         * interlock.
         *
         * The entire sequence through to where we actually sleep must
         * run without breaking the critical section.
         */
        id = LOOKUP(ident);
        catch = flags & PCATCH;
        error = 0;
        sig = 0;

        crit_enter_quick(td);

        KASSERT(ident != NULL, ("tsleep: no ident"));
        KASSERT(p == NULL || p->p_stat == SRUN, ("tsleep %p %s %d",
                ident, wmesg, p->p_stat));

        /*
         * Setup for the current process (if this is a process). 
         */
        if (p) {
                if (catch) {
                        /*
                         * Early termination if PCATCH was set and a
                         * signal is pending, interlocked with the
                         * critical section.
                         *
                         * Early termination only occurs when tsleep() is
                         * entered while in a normal SRUN state.
                         */
                        if ((sig = CURSIG(p)) != 0)
                                goto resume;

                        /*
                         * Early termination if PCATCH was set and a
                         * mailbox signal was possibly delivered prior to
                         * the system call even being made, in order to
                         * allow the user to interlock without having to
                         * make additional system calls.
                         */
                        if (p->p_flag & P_MAILBOX)
                                goto resume;

                        /*
                         * Causes ksignal to wake us up when.
                         */
                        p->p_flag |= P_SINTR;
                }

                /*
                 * Make sure the current process has been untangled from
                 * the userland scheduler and initialize slptime to start
                 * counting.
                 */
                if (flags & PNORESCHED)
                        td->td_flags |= TDF_NORESCHED;
                p->p_usched->release_curproc(&p->p_lwp);
                p->p_slptime = 0;
        }

        /*
         * Move our thread to the correct queue and setup our wchan, etc.
         */
        lwkt_deschedule_self(td);
        td->td_flags |= TDF_TSLEEPQ;
        TAILQ_INSERT_TAIL(&gd->gd_tsleep_hash[id], td, td_threadq);
        atomic_set_int(&slpque_cpumasks[id], gd->gd_cpumask);

        td->td_wchan = ident;
        td->td_wmesg = wmesg;
        td->td_wdomain = flags & PDOMAIN_MASK;

        /*
         * Setup the timeout, if any
         */
        if (timo) {
                callout_init(&thandle);
                callout_reset(&thandle, timo, endtsleep, td);
        }

        /*
         * Beddy bye bye.
         */
        if (p) {
                /*
                 * Ok, we are sleeping.  Place us in the SSLEEP state.
                 */
                KKASSERT((p->p_flag & P_ONRUNQ) == 0);
                p->p_stat = SSLEEP;
                p->p_lwp.lwp_ru.ru_nvcsw++;
                lwkt_switch();

                /*
                 * And when we are woken up, put us back in SRUN.  If we
                 * slept for over a second, recalculate our estcpu.
                 */
                p->p_stat = SRUN;
                if (p->p_slptime)
                        p->p_usched->recalculate(&p->p_lwp);
                p->p_slptime = 0;
        } else {
                lwkt_switch();
        }

        /* 
         * Make sure we haven't switched cpus while we were asleep.  It's
         * not supposed to happen.  Cleanup our temporary flags.
         */
        KKASSERT(gd == td->td_gd);
        td->td_flags &= ~TDF_NORESCHED;

        /*
         * Cleanup the timeout.
         */
        if (timo) {
                if (td->td_flags & TDF_TIMEOUT) {
                        td->td_flags &= ~TDF_TIMEOUT;
                        if (sig == 0)
                                error = EWOULDBLOCK;
                } else {
                        callout_stop(&thandle);
                }
        }

        /*
         * Since td_threadq is used both for our run queue AND for the
         * tsleep hash queue, we can't still be on it at this point because
         * we've gotten cpu back.
         */
        KASSERT((td->td_flags & TDF_TSLEEPQ) == 0, ("tsleep: impossible thread flags %08x", td->td_flags));
        td->td_wchan = NULL;
        td->td_wmesg = NULL;
        td->td_wdomain = 0;

        /*
         * Figure out the correct error return.  If interrupted by a
         * signal we want to return EINTR or ERESTART.  
         *
         * If P_MAILBOX is set no automatic system call restart occurs
         * and we return EINTR.  P_MAILBOX is meant to be used as an
         * interlock, the user must poll it prior to any system call
         * that it wishes to interlock a mailbox signal against since
         * the flag is cleared on *any* system call that sleeps.
         */
resume:
        if (p) {
                if (catch && error == 0) {
                        if ((p->p_flag & P_MAILBOX) && sig == 0) {
                                error = EINTR;
                        } else if ((sig != 0 || (sig = CURSIG(p)))) {
                                if (SIGISMEMBER(p->p_sigacts->ps_sigintr, sig))
                                        error = EINTR;
                                else
                                        error = ERESTART;
                        }
                }
                p->p_flag &= ~(P_BREAKTSLEEP | P_SINTR | P_MAILBOX);
        }
        logtsleep(tsleep_end);
        crit_exit_quick(td);
        return (error);
}

/*
 * This is a dandy function that allows us to interlock tsleep/wakeup
 * operations with unspecified upper level locks, such as lockmgr locks,
 * simply by holding a critical section.  The sequence is:
 *
 *      (enter critical section)
 *      (acquire upper level lock)
 *      tsleep_interlock(blah)
 *      (release upper level lock)
 *      tsleep(blah, ...)
 *      (exit critical section)
 *
 * Basically this function sets our cpumask for the ident which informs
 * other cpus that our cpu 'might' be waiting (or about to wait on) the
 * hash index related to the ident.  The critical section prevents another
 * cpu's wakeup() from being processed on our cpu until we are actually
 * able to enter the tsleep().  Thus, no race occurs between our attempt
 * to release a resource and sleep, and another cpu's attempt to acquire
 * a resource and call wakeup.
 *
 * There isn't much of a point to this function unless you call it while
 * holding a critical section.
 */
static __inline void
_tsleep_interlock(globaldata_t gd, void *ident)
{
        int id = LOOKUP(ident);

        atomic_set_int(&slpque_cpumasks[id], gd->gd_cpumask);
}

void
tsleep_interlock(void *ident)
{
        _tsleep_interlock(mycpu, ident);
}

/*
 * Interlocked spinlock sleep.  An exclusively held spinlock must
 * be passed to msleep().  The function will atomically release the
 * spinlock and tsleep on the ident, then reacquire the spinlock and
 * return.
 *
 * This routine is fairly important along the critical path, so optimize it
 * heavily.
 */
int
msleep(void *ident, struct spinlock *spin, int flags,
       const char *wmesg, int timo)
{
        globaldata_t gd = mycpu;
        int error;

        crit_enter_gd(gd);
        _tsleep_interlock(gd, ident);
        spin_unlock_wr_quick(gd, spin);
        error = tsleep(ident, flags, wmesg, timo);
        spin_lock_wr_quick(gd, spin);
        crit_exit_gd(gd);

        return (error);
}

/*
 * Implement the timeout for tsleep.
 *
 * We set P_BREAKTSLEEP to indicate that an event has occured, but
 * we only call setrunnable if the process is not stopped.
 *
 * This type of callout timeout is scheduled on the same cpu the process
 * is sleeping on.  Also, at the moment, the MP lock is held.
 */
static void
endtsleep(void *arg)
{
        thread_t td = arg;
        struct proc *p;

        ASSERT_MP_LOCK_HELD(curthread);
        crit_enter();

        /*
         * cpu interlock.  Thread flags are only manipulated on
         * the cpu owning the thread.  proc flags are only manipulated
         * by the older of the MP lock.  We have both.
         */
        if (td->td_flags & TDF_TSLEEPQ) {
                td->td_flags |= TDF_TIMEOUT;

                if ((p = td->td_proc) != NULL) {
                        p->p_flag |= P_BREAKTSLEEP;
                        if ((p->p_flag & P_STOPPED) == 0)
                                setrunnable(p);
                } else {
                        unsleep_and_wakeup_thread(td);
                }
        }
        crit_exit();
}

/*
 * Unsleep and wakeup a thread.  This function runs without the MP lock
 * which means that it can only manipulate thread state on the owning cpu,
 * and cannot touch the process state at all.
 */
static
void
unsleep_and_wakeup_thread(struct thread *td)
{
        globaldata_t gd = mycpu;
        int id;

#ifdef SMP
        if (td->td_gd != gd) {
                lwkt_send_ipiq(td->td_gd, (ipifunc1_t)unsleep_and_wakeup_thread, td);
                return;
        }
#endif
        crit_enter();
        if (td->td_flags & TDF_TSLEEPQ) {
                td->td_flags &= ~TDF_TSLEEPQ;
                id = LOOKUP(td->td_wchan);
                TAILQ_REMOVE(&gd->gd_tsleep_hash[id], td, td_threadq);
                if (TAILQ_FIRST(&gd->gd_tsleep_hash[id]) == NULL)
                        atomic_clear_int(&slpque_cpumasks[id], gd->gd_cpumask);
                lwkt_schedule(td);
        }
        crit_exit();
}

/*
 * Make all processes sleeping on the specified identifier runnable.
 * count may be zero or one only.
 *
 * The domain encodes the sleep/wakeup domain AND the first cpu to check
 * (which is always the current cpu).  As we iterate across cpus
 *
 * This call may run without the MP lock held.  We can only manipulate thread
 * state on the cpu owning the thread.  We CANNOT manipulate process state
 * at all.
 */
static void
_wakeup(void *ident, int domain)
{
        struct tslpque *qp;
        struct thread *td;
        struct thread *ntd;
        globaldata_t gd;
#ifdef SMP
        cpumask_t mask;
        cpumask_t tmask;
        int startcpu;
        int nextcpu;
#endif
        int id;

        crit_enter();
        logtsleep(wakeup_beg);
        gd = mycpu;
        id = LOOKUP(ident);
        qp = &gd->gd_tsleep_hash[id];
restart:
        for (td = TAILQ_FIRST(qp); td != NULL; td = ntd) {
                ntd = TAILQ_NEXT(td, td_threadq);
                if (td->td_wchan == ident && 
                    td->td_wdomain == (domain & PDOMAIN_MASK)
                ) {
                        KKASSERT(td->td_flags & TDF_TSLEEPQ);
                        td->td_flags &= ~TDF_TSLEEPQ;
                        TAILQ_REMOVE(qp, td, td_threadq);
                        if (TAILQ_FIRST(qp) == NULL) {
                                atomic_clear_int(&slpque_cpumasks[id],
                                                 gd->gd_cpumask);
                        }
                        lwkt_schedule(td);
                        if (domain & PWAKEUP_ONE)
                                goto done;
                        goto restart;
                }
        }

#ifdef SMP
        /*
         * We finished checking the current cpu but there still may be
         * more work to do.  Either wakeup_one was requested and no matching
         * thread was found, or a normal wakeup was requested and we have
         * to continue checking cpus.
         *
         * The cpu that started the wakeup sequence is encoded in the domain.
         * We use this information to determine which cpus still need to be
         * checked, locate a candidate cpu, and chain the wakeup 
         * asynchronously with an IPI message. 
         *
         * It should be noted that this scheme is actually less expensive then
         * the old scheme when waking up multiple threads, since we send 
         * only one IPI message per target candidate which may then schedule
         * multiple threads.  Before we could have wound up sending an IPI
         * message for each thread on the target cpu (!= current cpu) that
         * needed to be woken up.
         *
         * NOTE: Wakeups occuring on remote cpus are asynchronous.  This
         * should be ok since we are passing idents in the IPI rather then
         * thread pointers.
         */
        if ((domain & PWAKEUP_MYCPU) == 0 && 
            (mask = slpque_cpumasks[id]) != 0
        ) {
                /*
                 * Look for a cpu that might have work to do.  Mask out cpus
                 * which have already been processed.
                 *
                 * 31xxxxxxxxxxxxxxxxxxxxxxxxxxxxx0
                 *        ^        ^           ^
                 *      start   currentcpu    start
                 *      case2                 case1
                 *        *        *           *
                 * 11111111111111110000000000000111     case1
                 * 00000000111111110000000000000000     case2
                 *
                 * case1:  We started at start_case1 and processed through
                 *         to the current cpu.  We have to check any bits
                 *         after the current cpu, then check bits before 
                 *         the starting cpu.
                 *
                 * case2:  We have already checked all the bits from
                 *         start_case2 to the end, and from 0 to the current
                 *         cpu.  We just have the bits from the current cpu
                 *         to start_case2 left to check.
                 */
                startcpu = PWAKEUP_DECODE(domain);
                if (gd->gd_cpuid >= startcpu) {
                        /*
                         * CASE1
                         */
                        tmask = mask & ~((gd->gd_cpumask << 1) - 1);
                        if (mask & tmask) {
                                nextcpu = bsfl(mask & tmask);
                                lwkt_send_ipiq2(globaldata_find(nextcpu), 
                                                _wakeup, ident, domain);
                        } else {
                                tmask = (1 << startcpu) - 1;
                                if (mask & tmask) {
                                        nextcpu = bsfl(mask & tmask);
                                        lwkt_send_ipiq2(
                                                    globaldata_find(nextcpu),
                                                    _wakeup, ident, domain);
                                }
                        }
                } else {
                        /*
                         * CASE2
                         */
                        tmask = ~((gd->gd_cpumask << 1) - 1) &
                                 ((1 << startcpu) - 1);
                        if (mask & tmask) {
                                nextcpu = bsfl(mask & tmask);
                                lwkt_send_ipiq2(globaldata_find(nextcpu), 
                                                _wakeup, ident, domain);
                        }
                }
        }
#endif
done:
        logtsleep(wakeup_end);
        crit_exit();
}

/*
 * Wakeup all threads tsleep()ing on the specified ident, on all cpus
 */
void
wakeup(void *ident)
{
    _wakeup(ident, PWAKEUP_ENCODE(0, mycpu->gd_cpuid));
}

/*
 * Wakeup one thread tsleep()ing on the specified ident, on any cpu.
 */
void
wakeup_one(void *ident)
{
    /* XXX potentially round-robin the first responding cpu */
    _wakeup(ident, PWAKEUP_ENCODE(0, mycpu->gd_cpuid) | PWAKEUP_ONE);
}

/*
 * Wakeup threads tsleep()ing on the specified ident on the current cpu
 * only.
 */
void
wakeup_mycpu(void *ident)
{
    _wakeup(ident, PWAKEUP_MYCPU);
}

/*
 * Wakeup one thread tsleep()ing on the specified ident on the current cpu
 * only.
 */
void
wakeup_mycpu_one(void *ident)
{
    /* XXX potentially round-robin the first responding cpu */
    _wakeup(ident, PWAKEUP_MYCPU|PWAKEUP_ONE);
}

/*
 * Wakeup all thread tsleep()ing on the specified ident on the specified cpu
 * only.
 */
void
wakeup_oncpu(globaldata_t gd, void *ident)
{
#ifdef SMP
    if (gd == mycpu) {
        _wakeup(ident, PWAKEUP_MYCPU);
    } else {
        lwkt_send_ipiq2(gd, _wakeup, ident, PWAKEUP_MYCPU);
    }
#else
    _wakeup(ident, PWAKEUP_MYCPU);
#endif
}

/*
 * Wakeup one thread tsleep()ing on the specified ident on the specified cpu
 * only.
 */
void
wakeup_oncpu_one(globaldata_t gd, void *ident)
{
#ifdef SMP
    if (gd == mycpu) {
        _wakeup(ident, PWAKEUP_MYCPU | PWAKEUP_ONE);
    } else {
        lwkt_send_ipiq2(gd, _wakeup, ident, PWAKEUP_MYCPU | PWAKEUP_ONE);
    }
#else
    _wakeup(ident, PWAKEUP_MYCPU | PWAKEUP_ONE);
#endif
}

/*
 * Wakeup all threads waiting on the specified ident that slept using
 * the specified domain, on all cpus.
 */
void
wakeup_domain(void *ident, int domain)
{
    _wakeup(ident, PWAKEUP_ENCODE(domain, mycpu->gd_cpuid));
}

/*
 * Wakeup one thread waiting on the specified ident that slept using
 * the specified  domain, on any cpu.
 */
void
wakeup_domain_one(void *ident, int domain)
{
    /* XXX potentially round-robin the first responding cpu */
    _wakeup(ident, PWAKEUP_ENCODE(domain, mycpu->gd_cpuid) | PWAKEUP_ONE);
}

/*
 * setrunnable()
 *
 * Make a process runnable.  The MP lock must be held on call.  This only
 * has an effect if we are in SSLEEP.  We only break out of the
 * tsleep if P_BREAKTSLEEP is set, otherwise we just fix-up the state.
 *
 * NOTE: With the MP lock held we can only safely manipulate the process
 * structure.  We cannot safely manipulate the thread structure.
 */
void
setrunnable(struct proc *p)
{
        crit_enter();
        ASSERT_MP_LOCK_HELD(curthread);
        p->p_flag &= ~P_STOPPED;
        if (p->p_stat == SSLEEP && (p->p_flag & P_BREAKTSLEEP)) {
                unsleep_and_wakeup_thread(p->p_thread);
        }
        crit_exit();
}

/*
 * The process is stopped due to some condition, usually because P_STOPPED
 * is set but also possibly due to being traced.  
 *
 * NOTE!  If the caller sets P_STOPPED, the caller must also clear P_WAITED
 * because the parent may check the child's status before the child actually
 * gets to this routine.
 *
 * This routine is called with the current process only, typically just
 * before returning to userland.
 *
 * Setting P_BREAKTSLEEP before entering the tsleep will cause a passive
 * SIGCONT to break out of the tsleep.
 */
void
tstop(struct proc *p)
{
        wakeup((caddr_t)p->p_pptr);
        p->p_flag |= P_BREAKTSLEEP;
        tsleep(p, 0, "stop", 0);
}

/*
 * Yield / synchronous reschedule.  This is a bit tricky because the trap
 * code might have set a lazy release on the switch function.   Setting
 * P_PASSIVE_ACQ will ensure that the lazy release executes when we call
 * switch, and that we are given a greater chance of affinity with our
 * current cpu.
 *
 * We call lwkt_setpri_self() to rotate our thread to the end of the lwkt
 * run queue.  lwkt_switch() will also execute any assigned passive release
 * (which usually calls release_curproc()), allowing a same/higher priority
 * process to be designated as the current process.  
 *
 * While it is possible for a lower priority process to be designated,
 * it's call to lwkt_maybe_switch() in acquire_curproc() will likely
 * round-robin back to us and we will be able to re-acquire the current
 * process designation.
 */
void
uio_yield(void)
{
        struct thread *td = curthread;
        struct proc *p = td->td_proc;

        lwkt_setpri_self(td->td_pri & TDPRI_MASK);
        if (p) {
                p->p_flag |= P_PASSIVE_ACQ;
                lwkt_switch();
                p->p_flag &= ~P_PASSIVE_ACQ;
        } else {
                lwkt_switch();
        }
}

/*
 * Compute a tenex style load average of a quantity on
 * 1, 5 and 15 minute intervals.
 */
static int loadav_count_runnable(struct proc *p, void *data);

static void
loadav(void *arg)
{
        struct loadavg *avg;
        int i, nrun;

        nrun = 0;
        allproc_scan(loadav_count_runnable, &nrun);
        avg = &averunnable;
        for (i = 0; i < 3; i++) {
                avg->ldavg[i] = (cexp[i] * avg->ldavg[i] +
                    nrun * FSCALE * (FSCALE - cexp[i])) >> FSHIFT;
        }

        /*
         * Schedule the next update to occur after 5 seconds, but add a
         * random variation to avoid synchronisation with processes that
         * run at regular intervals.
         */
        callout_reset(&loadav_callout, hz * 4 + (int)(krandom() % (hz * 2 + 1)),
                      loadav, NULL);
}

static int
loadav_count_runnable(struct proc *p, void *data)
{
        int *nrunp = data;
        thread_t td;

        switch (p->p_stat) {
        case SRUN:
                if ((td = p->p_thread) == NULL)
                        break;
                if (td->td_flags & TDF_BLOCKED)
                        break;
                /* fall through */
        case SIDL:
                ++*nrunp;
                break;
        default:
                break;
        }
        return(0);
}

/* ARGSUSED */
static void
sched_setup(void *dummy)
{
        callout_init(&loadav_callout);
        callout_init(&schedcpu_callout);

        /* Kick off timeout driven events by calling first time. */
        schedcpu(NULL);
        loadav(NULL);
}