time.c

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/*
 * Copyright (C) 2000 - 2007 Jeff Dike (jdike{addtoit,linux.intel}.com)
 * Licensed under the GPL
 */

#include <stddef.h>
#include <errno.h>
#include <signal.h>
#include <time.h>
#include <sys/time.h>
#include <kern_util.h>
#include <os.h>
#include "internal.h"

int set_interval(void)
{
    int usec = UM_USEC_PER_SEC / UM_HZ;
    struct itimerval interval = ((struct itimerval) { { 0, usec },
                              { 0, usec } });

    if (setitimer(ITIMER_VIRTUAL, &interval, NULL) == -1)
        return -errno;

    return 0;
}

int timer_one_shot(int ticks)
{
    unsigned long usec = ticks * UM_USEC_PER_SEC / UM_HZ;
    unsigned long sec = usec / UM_USEC_PER_SEC;
    struct itimerval interval;

    usec %= UM_USEC_PER_SEC;
    interval = ((struct itimerval) { { 0, 0 }, { sec, usec } });

    if (setitimer(ITIMER_VIRTUAL, &interval, NULL) == -1)
        return -errno;

    return 0;
}

static inline long long timeval_to_ns(const struct timeval *tv)
{
    return ((long long) tv->tv_sec * UM_NSEC_PER_SEC) +
        tv->tv_usec * UM_NSEC_PER_USEC;
}

long long disable_timer(void)
{
    struct itimerval time = ((struct itimerval) { { 0, 0 }, { 0, 0 } });
    long long remain, max = UM_NSEC_PER_SEC / UM_HZ;

    if (setitimer(ITIMER_VIRTUAL, &time, &time) < 0)
        printk(UM_KERN_ERR "disable_timer - setitimer failed, "
               "errno = %d\n", errno);

    remain = timeval_to_ns(&time.it_value);
    if (remain > max)
        remain = max;

    return remain;
}

long long os_nsecs(void)
{
    struct timeval tv;

    gettimeofday(&tv, NULL);
    return timeval_to_ns(&tv);
}

#ifdef UML_CONFIG_NO_HZ
static int after_sleep_interval(struct timespec *ts)
{
    return 0;
}

static void deliver_alarm(void)
{
    alarm_handler(SIGVTALRM, NULL, NULL);
}

static unsigned long long sleep_time(unsigned long long nsecs)
{
    return nsecs;
}

#else
unsigned long long last_tick;
unsigned long long skew;

static void deliver_alarm(void)
{
    unsigned long long this_tick = os_nsecs();
    int one_tick = UM_NSEC_PER_SEC / UM_HZ;

    /* Protection against the host's time going backwards */
    if ((last_tick != 0) && (this_tick < last_tick))
        this_tick = last_tick;

    if (last_tick == 0)
        last_tick = this_tick - one_tick;

    skew += this_tick - last_tick;

    while (skew >= one_tick) {
        alarm_handler(SIGVTALRM, NULL, NULL);
        skew -= one_tick;
    }

    last_tick = this_tick;
}

static unsigned long long sleep_time(unsigned long long nsecs)
{
    return nsecs > skew ? nsecs - skew : 0;
}

static inline long long timespec_to_us(const struct timespec *ts)
{
    return ((long long) ts->tv_sec * UM_USEC_PER_SEC) +
        ts->tv_nsec / UM_NSEC_PER_USEC;
}

static int after_sleep_interval(struct timespec *ts)
{
    int usec = UM_USEC_PER_SEC / UM_HZ;
    long long start_usecs = timespec_to_us(ts);
    struct timeval tv;
    struct itimerval interval;

    /*
     * It seems that rounding can increase the value returned from
     * setitimer to larger than the one passed in.  Over time,
     * this will cause the remaining time to be greater than the
     * tick interval.  If this happens, then just reduce the first
     * tick to the interval value.
     */
    if (start_usecs > usec)
        start_usecs = usec;

    start_usecs -= skew / UM_NSEC_PER_USEC;
    if (start_usecs < 0)
        start_usecs = 0;

    tv = ((struct timeval) { .tv_sec  = start_usecs / UM_USEC_PER_SEC,
                 .tv_usec = start_usecs % UM_USEC_PER_SEC });
    interval = ((struct itimerval) { { 0, usec }, tv });

    if (setitimer(ITIMER_VIRTUAL, &interval, NULL) == -1)
        return -errno;

    return 0;
}
#endif

void idle_sleep(unsigned long long nsecs)
{
    struct timespec ts;

    /*
     * nsecs can come in as zero, in which case, this starts a
     * busy loop.  To prevent this, reset nsecs to the tick
     * interval if it is zero.
     */
    if (nsecs == 0)
        nsecs = UM_NSEC_PER_SEC / UM_HZ;

    nsecs = sleep_time(nsecs);
    ts = ((struct timespec) { .tv_sec   = nsecs / UM_NSEC_PER_SEC,
                  .tv_nsec  = nsecs % UM_NSEC_PER_SEC });

    if (nanosleep(&ts, &ts) == 0)
        deliver_alarm();
    after_sleep_interval(&ts);
}