common/os/clock_realtime.c

	clock_realtime.c revision 7c478bd95313f5f23a4c958a745db2134aa03244
/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License, Version 1.0 only
 * (the "License").  You may not use this file except in compliance
 * with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */
/*
 * Copyright 2003 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

#pragma ident   "%Z%%M% %I% %E% SMI"

#include <sys/timer.h>
#include <sys/systm.h>
#include <sys/param.h>
#include <sys/kmem.h>
#include <sys/debug.h>

static clock_backend_t clock_realtime;

static int
clock_realtime_settime(timespec_t *ts)
{
    mutex_enter(&tod_lock);
    tod_set(*ts);
    set_hrestime(ts);
    mutex_exit(&tod_lock);

    return (0);
}

/*
 * We normally won't execute this path; libc will see CLOCK_REALTIME and
 * fast trap directly into gethrestime().
 */
static int
clock_realtime_gettime(timespec_t *ts)
{
    gethrestime(ts);

    return (0);
}

static int
clock_realtime_getres(timespec_t *ts)
{
    ts->tv_sec = 0;
    ts->tv_nsec = nsec_per_tick;

    return (0);
}

static void
clock_realtime_fire(void *arg)
{
    int cnt2nth;
    itimer_t *it = (itimer_t *)arg;
    timeout_id_t *tidp = it->it_arg;
    timespec_t now, interval2nth;
    timespec_t *val, *interval;
    proc_t *p = it->it_proc;
    clock_t ticks;

    /*
     * First call into the timer subsystem to get the signal going.
     */
    timer_fire(it);

    val = &it->it_itime.it_value;
    interval = &it->it_itime.it_interval;

    mutex_enter(&p->p_lock);

    if (!timerspecisset(interval)) {
        timerspecclear(val);
        *tidp = 0;
    } else {
        /*
         * If this is an interval timer, we need to determine a time
         * at which to go off in the future.  In the event that the
         * clock has been adjusted, we want to find our new interval
         * relatively quickly (and we don't want to simply take the
         * current time and add the interval; it would lead to
         * unnecessary jitter in the timer).  We therefore take steps
         * from the time we expected to go off into the future;
         * if the resulting time is still in the past, then we double
         * our step size and continue.  Once the resulting time is
         * in the future, we subtract our last step, change our step
         * size back to the original interval, and repeat until we
         * can get to a valid, future timeout in one step.  This
         * assures that we will get the minimum, valid timeout
         * value in a reasonable amount of wall time.
         */
        for (;;) {
            interval2nth = *interval;

            /*
             * We put a floor on interval2nth at nsec_per_tick.
             * If we don't do this, and the interval is shorter
             * than the time required to run through this logic,
             * we'll never catch up to the current time (which
             * is a moving target).
             */
            if (interval2nth.tv_sec == 0 &&
                interval2nth.tv_nsec < nsec_per_tick)
                interval2nth.tv_nsec = nsec_per_tick;

            for (cnt2nth = 0; ; cnt2nth++) {
                timespecadd(val, &interval2nth);
                gethrestime(&now);
                if (timerspeccmp(val, &now) > 0)
                    break;
                timespecadd(&interval2nth, &interval2nth);
            }
            if (cnt2nth == 0)
                break;
            timespecsub(val, &interval2nth);
        }

        ticks = timespectohz(val, now);
        *tidp = realtime_timeout(clock_realtime_fire, it, ticks);
    }
    mutex_exit(&p->p_lock);
}

/*
 * See the block comment in clock_realtime_timer_settime(), below.
 */
static void
clock_realtime_fire_first(void *arg)
{
    itimer_t *it = (itimer_t *)arg;
    timespec_t now;
    timespec_t *val = &it->it_itime.it_value;
    timeout_id_t *tidp = it->it_arg;
    proc_t *p = it->it_proc;

    gethrestime(&now);

    if ((val->tv_sec > now.tv_sec) ||
        (val->tv_sec == now.tv_sec && val->tv_nsec > now.tv_nsec)) {
        /*
         * We went off too early.  We'll go to bed for one more tick,
         * regardless of the actual difference; if the difference
         * is greater than one tick, then we must have seen an adjtime.
         */
        mutex_enter(&p->p_lock);
        *tidp = realtime_timeout(clock_realtime_fire, it, 1);
        mutex_exit(&p->p_lock);
        return;
    }

    clock_realtime_fire(arg);
}

/*ARGSUSED*/
static int
clock_realtime_timer_create(itimer_t *it, struct sigevent *ev)
{
    it->it_arg = kmem_zalloc(sizeof (timeout_id_t), KM_SLEEP);

    return (0);
}

static int
clock_realtime_timer_settime(itimer_t *it, int flags,
    const struct itimerspec *when)
{
    timeout_id_t tid, *tidp = it->it_arg;
    timespec_t now;
    proc_t *p = curproc;
    clock_t ticks;

    gethrestime(&now);

    mutex_enter(&p->p_lock);

    while ((tid = *tidp) != 0) {
        *tidp = 0;
        mutex_exit(&p->p_lock);
        (void) untimeout(tid);
        mutex_enter(&p->p_lock);
    }

    /*
     * The timeout has been removed; it is safe to update it_itime.
     */
    it->it_itime = *when;

    if (timerspecisset(&it->it_itime.it_value)) {
        if (!(flags & TIMER_ABSTIME))
            timespecadd(&it->it_itime.it_value, &now);

        ticks = timespectohz(&it->it_itime.it_value, now);

        /*
         * gethrestime() works by reading hres_last_tick, and
         * adding in the current time delta (that is, the amount of
         * time which has passed since the last tick of the clock).
         * As a result, the time returned in "now", above, represents
         * an hrestime sometime after lbolt was last bumped.
         * The "ticks" we've been returned from timespectohz(), then,
         * reflects the number of times the clock will tick between
         * "now" and our desired execution time.
         *
         * However, when we call into realtime_timeout(), below,
         * "ticks" will be interpreted against lbolt.  That is,
         * if we specify 1 tick, we will be registering a callout
         * for the next tick of the clock -- which may occur in
         * less than (1 / hz) seconds.  More generally, we are
         * registering a callout for "ticks" of the clock, which
         * may be less than ("ticks" / hz) seconds (but not more than
         * (1 / hz) seconds less).  In other words, we may go off
         * early.
         *
         * This is only a problem for the initial firing of the
         * timer, so we have the initial firing go through a
         * different handler which implements a nanosleep-esque
         * algorithm.
         */
        *tidp = realtime_timeout(clock_realtime_fire_first, it, ticks);
    }

    mutex_exit(&p->p_lock);

    return (0);
}

static int
clock_realtime_timer_gettime(itimer_t *it, struct itimerspec *when)
{
    timespec_t now;
    proc_t *p = curproc;

    /*
     * We always keep it_itime up to date, so we just need to snapshot
     * the time under p_lock, and clean it up.
     */
    mutex_enter(&p->p_lock);
    gethrestime(&now);
    *when = it->it_itime;
    mutex_exit(&p->p_lock);

    if (!timerspecisset(&when->it_value))
        return (0);

    if (timerspeccmp(&when->it_value, &now) < 0) {
        /*
         * If this timer should have already gone off, set it_value
         * to 0.
         */
        timerspecclear(&when->it_value);
    } else {
        timespecsub(&when->it_value, &now);
    }

    return (0);
}

static int
clock_realtime_timer_delete(itimer_t *it)
{
    proc_t *p = curproc;
    timeout_id_t tid, *tidp = it->it_arg;

    mutex_enter(&p->p_lock);

    while ((tid = *tidp) != 0) {
        *tidp = 0;
        mutex_exit(&p->p_lock);
        (void) untimeout(tid);
        mutex_enter(&p->p_lock);
    }

    mutex_exit(&p->p_lock);

    kmem_free(tidp, sizeof (timeout_id_t));

    return (0);
}

/*ARGSUSED*/
void
clock_realtime_timer_lwpbind(itimer_t *it)
{
}

void
clock_realtime_init()
{
    clock_backend_t *be = &clock_realtime;
    struct sigevent *ev = &be->clk_default;

    ev->sigev_signo = SIGALRM;
    ev->sigev_notify = SIGEV_SIGNAL;
    ev->sigev_value.sival_ptr = NULL;

    be->clk_clock_settime = clock_realtime_settime;
    be->clk_clock_gettime = clock_realtime_gettime;
    be->clk_clock_getres = clock_realtime_getres;
    be->clk_timer_gettime = clock_realtime_timer_gettime;
    be->clk_timer_settime = clock_realtime_timer_settime;
    be->clk_timer_delete = clock_realtime_timer_delete;
    be->clk_timer_lwpbind = clock_realtime_timer_lwpbind;
    be->clk_timer_create = clock_realtime_timer_create;
    clock_add_backend(CLOCK_REALTIME, &clock_realtime);
    /*
     * For binary compatibility with old statically linked
     * applications, we make the behavior of __CLOCK_REALTIME0
     * the same as CLOCK_REALTIME.
     */
    clock_add_backend(__CLOCK_REALTIME0, &clock_realtime);
}