kern_synch.c

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/*-
 * 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.
 * 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
 */

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

#include "opt_kdtrace.h"
#include "opt_ktrace.h"
#include "opt_sched.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/condvar.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/resourcevar.h>
#include <sys/sched.h>
#include <sys/sdt.h>
#include <sys/signalvar.h>
#include <sys/sleepqueue.h>
#include <sys/smp.h>
#include <sys/sx.h>
#include <sys/sysctl.h>
#include <sys/sysproto.h>
#include <sys/vmmeter.h>
#ifdef KTRACE
#include <sys/uio.h>
#include <sys/ktrace.h>
#endif

#include <machine/cpu.h>

#ifdef XEN
#include <vm/vm.h>
#include <vm/vm_param.h>
#include <vm/pmap.h>
#endif

#define KTDSTATE(td)                                                    \
        (((td)->td_inhibitors & TDI_SLEEPING) != 0 ? "sleep"  :         \
        ((td)->td_inhibitors & TDI_SUSPENDED) != 0 ? "suspended" :      \
        ((td)->td_inhibitors & TDI_SWAPPED) != 0 ? "swapped" :          \
        ((td)->td_inhibitors & TDI_LOCK) != 0 ? "blocked" :             \
        ((td)->td_inhibitors & TDI_IWAIT) != 0 ? "iwait" : "yielding")

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

int     hogticks;
static int pause_wchan;

static struct callout loadav_callout;

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) */
};

/* kernel uses `FSCALE', userland (SHOULD) use kern.fscale */
SYSCTL_INT(_kern, OID_AUTO, fscale, CTLFLAG_RD, SYSCTL_NULL_INT_PTR, FSCALE, "");

static void     loadav(void *arg);

SDT_PROVIDER_DECLARE(sched);
SDT_PROBE_DEFINE(sched, , , preempt);

/*
 * These probes reference Solaris features that are not implemented in FreeBSD.
 * Create the probes anyway for compatibility with existing D scripts; they'll
 * just never fire.
 */
SDT_PROBE_DEFINE(sched, , , cpucaps__sleep);
SDT_PROBE_DEFINE(sched, , , cpucaps__wakeup);
SDT_PROBE_DEFINE(sched, , , schedctl__nopreempt);
SDT_PROBE_DEFINE(sched, , , schedctl__preempt);
SDT_PROBE_DEFINE(sched, , , schedctl__yield);

void
sleepinit(void)
{

        hogticks = (hz / 10) * 2;       /* Default only. */
        init_sleepqueues();
}

/*
 * General sleep call.  Suspends the current thread until a wakeup is
 * performed on the specified identifier.  The thread will then be made
 * runnable with the specified priority.  Sleeps at most timo/hz seconds
 * (0 means no timeout).  If pri 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).
 *
 * The lock argument is unlocked before the caller is suspended, and
 * re-locked before _sleep() returns.  If priority includes the PDROP
 * flag the lock is not re-locked before returning.
 */
int
_sleep(void *ident, struct lock_object *lock, int priority,
    const char *wmesg, int timo)
{
        struct thread *td;
        struct proc *p;
        struct lock_class *class;
        int catch, flags, lock_state, pri, rval;
        WITNESS_SAVE_DECL(lock_witness);

        td = curthread;
        p = td->td_proc;
#ifdef KTRACE
        if (KTRPOINT(td, KTR_CSW))
                ktrcsw(1, 0, wmesg);
#endif
        WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock,
            "Sleeping on \"%s\"", wmesg);
        KASSERT(timo != 0 || mtx_owned(&Giant) || lock != NULL,
            ("sleeping without a lock"));
        KASSERT(p != NULL, ("msleep1"));
        KASSERT(ident != NULL && TD_IS_RUNNING(td), ("msleep"));
        if (priority & PDROP)
                KASSERT(lock != NULL && lock != &Giant.lock_object,
                    ("PDROP requires a non-Giant lock"));
        if (lock != NULL)
                class = LOCK_CLASS(lock);
        else
                class = NULL;

        if (cold || SCHEDULER_STOPPED()) {
                /*
                 * During autoconfiguration, just return;
                 * don't run any other threads or panic below,
                 * in case this is the idle thread and already asleep.
                 * XXX: this used to do "s = splhigh(); splx(safepri);
                 * splx(s);" to give interrupts a chance, but there is
                 * no way to give interrupts a chance now.
                 */
                if (lock != NULL && priority & PDROP)
                        class->lc_unlock(lock);
                return (0);
        }
        catch = priority & PCATCH;
        pri = priority & PRIMASK;

        /*
         * If we are already on a sleep queue, then remove us from that
         * sleep queue first.  We have to do this to handle recursive
         * sleeps.
         */
        if (TD_ON_SLEEPQ(td))
                sleepq_remove(td, td->td_wchan);

        if (ident == &pause_wchan)
                flags = SLEEPQ_PAUSE;
        else
                flags = SLEEPQ_SLEEP;
        if (catch)
                flags |= SLEEPQ_INTERRUPTIBLE;
        if (priority & PBDRY)
                flags |= SLEEPQ_STOP_ON_BDRY;

        sleepq_lock(ident);
        CTR5(KTR_PROC, "sleep: thread %ld (pid %ld, %s) on %s (%p)",
            td->td_tid, p->p_pid, td->td_name, wmesg, ident);

        if (lock == &Giant.lock_object)
                mtx_assert(&Giant, MA_OWNED);
        DROP_GIANT();
        if (lock != NULL && lock != &Giant.lock_object &&
            !(class->lc_flags & LC_SLEEPABLE)) {
                WITNESS_SAVE(lock, lock_witness);
                lock_state = class->lc_unlock(lock);
        } else
                /* GCC needs to follow the Yellow Brick Road */
                lock_state = -1;

        /*
         * We put ourselves on the sleep queue and start our timeout
         * before calling thread_suspend_check, as we could stop there,
         * and a wakeup or a SIGCONT (or both) could occur while we were
         * stopped without resuming us.  Thus, we must be ready for sleep
         * when cursig() is called.  If the wakeup happens while we're
         * stopped, then td will no longer be on a sleep queue upon
         * return from cursig().
         */
        sleepq_add(ident, lock, wmesg, flags, 0);
        if (timo)
                sleepq_set_timeout(ident, timo);
        if (lock != NULL && class->lc_flags & LC_SLEEPABLE) {
                sleepq_release(ident);
                WITNESS_SAVE(lock, lock_witness);
                lock_state = class->lc_unlock(lock);
                sleepq_lock(ident);
        }
        if (timo && catch)
                rval = sleepq_timedwait_sig(ident, pri);
        else if (timo)
                rval = sleepq_timedwait(ident, pri);
        else if (catch)
                rval = sleepq_wait_sig(ident, pri);
        else {
                sleepq_wait(ident, pri);
                rval = 0;
        }
#ifdef KTRACE
        if (KTRPOINT(td, KTR_CSW))
                ktrcsw(0, 0, wmesg);
#endif
        PICKUP_GIANT();
        if (lock != NULL && lock != &Giant.lock_object && !(priority & PDROP)) {
                class->lc_lock(lock, lock_state);
                WITNESS_RESTORE(lock, lock_witness);
        }
        return (rval);
}

int
msleep_spin(void *ident, struct mtx *mtx, const char *wmesg, int timo)
{
        struct thread *td;
        struct proc *p;
        int rval;
        WITNESS_SAVE_DECL(mtx);

        td = curthread;
        p = td->td_proc;
        KASSERT(mtx != NULL, ("sleeping without a mutex"));
        KASSERT(p != NULL, ("msleep1"));
        KASSERT(ident != NULL && TD_IS_RUNNING(td), ("msleep"));

        if (cold || SCHEDULER_STOPPED()) {
                /*
                 * During autoconfiguration, just return;
                 * don't run any other threads or panic below,
                 * in case this is the idle thread and already asleep.
                 * XXX: this used to do "s = splhigh(); splx(safepri);
                 * splx(s);" to give interrupts a chance, but there is
                 * no way to give interrupts a chance now.
                 */
                return (0);
        }

        sleepq_lock(ident);
        CTR5(KTR_PROC, "msleep_spin: thread %ld (pid %ld, %s) on %s (%p)",
            td->td_tid, p->p_pid, td->td_name, wmesg, ident);

        DROP_GIANT();
        mtx_assert(mtx, MA_OWNED | MA_NOTRECURSED);
        WITNESS_SAVE(&mtx->lock_object, mtx);
        mtx_unlock_spin(mtx);

        /*
         * We put ourselves on the sleep queue and start our timeout.
         */
        sleepq_add(ident, &mtx->lock_object, wmesg, SLEEPQ_SLEEP, 0);
        if (timo)
                sleepq_set_timeout(ident, timo);

        /*
         * Can't call ktrace with any spin locks held so it can lock the
         * ktrace_mtx lock, and WITNESS_WARN considers it an error to hold
         * any spin lock.  Thus, we have to drop the sleepq spin lock while
         * we handle those requests.  This is safe since we have placed our
         * thread on the sleep queue already.
         */
#ifdef KTRACE
        if (KTRPOINT(td, KTR_CSW)) {
                sleepq_release(ident);
                ktrcsw(1, 0, wmesg);
                sleepq_lock(ident);
        }
#endif
#ifdef WITNESS
        sleepq_release(ident);
        WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, "Sleeping on \"%s\"",
            wmesg);
        sleepq_lock(ident);
#endif
        if (timo)
                rval = sleepq_timedwait(ident, 0);
        else {
                sleepq_wait(ident, 0);
                rval = 0;
        }
#ifdef KTRACE
        if (KTRPOINT(td, KTR_CSW))
                ktrcsw(0, 0, wmesg);
#endif
        PICKUP_GIANT();
        mtx_lock_spin(mtx);
        WITNESS_RESTORE(&mtx->lock_object, mtx);
        return (rval);
}

/*
 * pause() delays the calling thread by the given number of system ticks.
 * During cold bootup, pause() uses the DELAY() function instead of
 * the tsleep() function to do the waiting. The "timo" argument must be
 * greater than or equal to zero. A "timo" value of zero is equivalent
 * to a "timo" value of one.
 */
int
pause(const char *wmesg, int timo)
{
        KASSERT(timo >= 0, ("pause: timo must be >= 0"));

        /* silently convert invalid timeouts */
        if (timo < 1)
                timo = 1;

        if (cold) {
                /*
                 * We delay one HZ at a time to avoid overflowing the
                 * system specific DELAY() function(s):
                 */
                while (timo >= hz) {
                        DELAY(1000000);
                        timo -= hz;
                }
                if (timo > 0)
                        DELAY(timo * tick);
                return (0);
        }
        return (tsleep(&pause_wchan, 0, wmesg, timo));
}

/*
 * Make all threads sleeping on the specified identifier runnable.
 */
void
wakeup(void *ident)
{
        int wakeup_swapper;

        sleepq_lock(ident);
        wakeup_swapper = sleepq_broadcast(ident, SLEEPQ_SLEEP, 0, 0);
        sleepq_release(ident);
        if (wakeup_swapper) {
                KASSERT(ident != &proc0,
                    ("wakeup and wakeup_swapper and proc0"));
                kick_proc0();
        }
}

/*
 * Make a thread sleeping on the specified identifier runnable.
 * May wake more than one thread if a target thread is currently
 * swapped out.
 */
void
wakeup_one(void *ident)
{
        int wakeup_swapper;

        sleepq_lock(ident);
        wakeup_swapper = sleepq_signal(ident, SLEEPQ_SLEEP, 0, 0);
        sleepq_release(ident);
        if (wakeup_swapper)
                kick_proc0();
}

static void
kdb_switch(void)
{
        thread_unlock(curthread);
        kdb_backtrace();
        kdb_reenter();
        panic("%s: did not reenter debugger", __func__);
}

/*
 * The machine independent parts of context switching.
 */
void
mi_switch(int flags, struct thread *newtd)
{
        uint64_t runtime, new_switchtime;
        struct thread *td;
        struct proc *p;

        td = curthread;                 /* XXX */
        THREAD_LOCK_ASSERT(td, MA_OWNED | MA_NOTRECURSED);
        p = td->td_proc;                /* XXX */
        KASSERT(!TD_ON_RUNQ(td), ("mi_switch: called by old code"));
#ifdef INVARIANTS
        if (!TD_ON_LOCK(td) && !TD_IS_RUNNING(td))
                mtx_assert(&Giant, MA_NOTOWNED);
#endif
        KASSERT(td->td_critnest == 1 || panicstr,
            ("mi_switch: switch in a critical section"));
        KASSERT((flags & (SW_INVOL | SW_VOL)) != 0,
            ("mi_switch: switch must be voluntary or involuntary"));
        KASSERT(newtd != curthread, ("mi_switch: preempting back to ourself"));

        /*
         * Don't perform context switches from the debugger.
         */
        if (kdb_active)
                kdb_switch();
        if (SCHEDULER_STOPPED())
                return;
        if (flags & SW_VOL) {
                td->td_ru.ru_nvcsw++;
                td->td_swvoltick = ticks;
        } else
                td->td_ru.ru_nivcsw++;
#ifdef SCHED_STATS
        SCHED_STAT_INC(sched_switch_stats[flags & SW_TYPE_MASK]);
#endif
        /*
         * Compute the amount of time during which the current
         * thread was running, and add that to its total so far.
         */
        new_switchtime = cpu_ticks();
        runtime = new_switchtime - PCPU_GET(switchtime);
        td->td_runtime += runtime;
        td->td_incruntime += runtime;
        PCPU_SET(switchtime, new_switchtime);
        td->td_generation++;    /* bump preempt-detect counter */
        PCPU_INC(cnt.v_swtch);
        PCPU_SET(switchticks, ticks);
        CTR4(KTR_PROC, "mi_switch: old thread %ld (td_sched %p, pid %ld, %s)",
            td->td_tid, td->td_sched, p->p_pid, td->td_name);
#if (KTR_COMPILE & KTR_SCHED) != 0
        if (TD_IS_IDLETHREAD(td))
                KTR_STATE1(KTR_SCHED, "thread", sched_tdname(td), "idle",
                    "prio:%d", td->td_priority);
        else
                KTR_STATE3(KTR_SCHED, "thread", sched_tdname(td), KTDSTATE(td),
                    "prio:%d", td->td_priority, "wmesg:\"%s\"", td->td_wmesg,
                    "lockname:\"%s\"", td->td_lockname);
#endif
        SDT_PROBE0(sched, , , preempt);
#ifdef XEN
        PT_UPDATES_FLUSH();
#endif
        sched_switch(td, newtd, flags);
        KTR_STATE1(KTR_SCHED, "thread", sched_tdname(td), "running",
            "prio:%d", td->td_priority);

        CTR4(KTR_PROC, "mi_switch: new thread %ld (td_sched %p, pid %ld, %s)",
            td->td_tid, td->td_sched, p->p_pid, td->td_name);

        /* 
         * If the last thread was exiting, finish cleaning it up.
         */
        if ((td = PCPU_GET(deadthread))) {
                PCPU_SET(deadthread, NULL);
                thread_stash(td);
        }
}

/*
 * Change thread state to be runnable, placing it on the run queue if
 * it is in memory.  If it is swapped out, return true so our caller
 * will know to awaken the swapper.
 */
int
setrunnable(struct thread *td)
{

        THREAD_LOCK_ASSERT(td, MA_OWNED);
        KASSERT(td->td_proc->p_state != PRS_ZOMBIE,
            ("setrunnable: pid %d is a zombie", td->td_proc->p_pid));
        switch (td->td_state) {
        case TDS_RUNNING:
        case TDS_RUNQ:
                return (0);
        case TDS_INHIBITED:
                /*
                 * If we are only inhibited because we are swapped out
                 * then arange to swap in this process. Otherwise just return.
                 */
                if (td->td_inhibitors != TDI_SWAPPED)
                        return (0);
                /* FALLTHROUGH */
        case TDS_CAN_RUN:
                break;
        default:
                printf("state is 0x%x", td->td_state);
                panic("setrunnable(2)");
        }
        if ((td->td_flags & TDF_INMEM) == 0) {
                if ((td->td_flags & TDF_SWAPINREQ) == 0) {
                        td->td_flags |= TDF_SWAPINREQ;
                        return (1);
                }
        } else
                sched_wakeup(td);
        return (0);
}

/*
 * Compute a tenex style load average of a quantity on
 * 1, 5 and 15 minute intervals.
 */
static void
loadav(void *arg)
{
        int i, nrun;
        struct loadavg *avg;

        nrun = sched_load();
        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)(random() % (hz * 2 + 1)),
            loadav, NULL);
}

/* ARGSUSED */
static void
synch_setup(void *dummy)
{
        callout_init(&loadav_callout, CALLOUT_MPSAFE);

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

int
should_yield(void)
{

        return ((u_int)ticks - (u_int)curthread->td_swvoltick >= hogticks);
}

void
maybe_yield(void)
{

        if (should_yield())
                kern_yield(PRI_USER);
}

void
kern_yield(int prio)
{
        struct thread *td;

        td = curthread;
        DROP_GIANT();
        thread_lock(td);
        if (prio == PRI_USER)
                prio = td->td_user_pri;
        if (prio >= 0)
                sched_prio(td, prio);
        mi_switch(SW_VOL | SWT_RELINQUISH, NULL);
        thread_unlock(td);
        PICKUP_GIANT();
}

/*
 * General purpose yield system call.
 */
int
sys_yield(struct thread *td, struct yield_args *uap)
{

        thread_lock(td);
        if (PRI_BASE(td->td_pri_class) == PRI_TIMESHARE)
                sched_prio(td, PRI_MAX_TIMESHARE);
        mi_switch(SW_VOL | SWT_RELINQUISH, NULL);
        thread_unlock(td);
        td->td_retval[0] = 0;
        return (0);
}