time.c

linux 内核源代码

static cycle_t rtc_read(void)
{
	return (cycle_t)get_rtc();
}

static cycle_t timebase_read(void)
{
	return (cycle_t)get_tb();
}

void update_vsyscall(struct timespec *wall_time, struct clocksource *clock)
{
	u64 t2x, stamp_xsec;

	if (clock != &clocksource_timebase)
		return;

	/* Make userspace gettimeofday spin until we're done. */
	++vdso_data->tb_update_count;
	smp_mb();

	/* XXX this assumes clock->shift == 22 */
	/* 4611686018 ~= 2^(20+64-22) / 1e9 */
	t2x = (u64) clock->mult * 4611686018ULL;
	stamp_xsec = (u64) xtime.tv_nsec * XSEC_PER_SEC;
	do_div(stamp_xsec, 1000000000);
	stamp_xsec += (u64) xtime.tv_sec * XSEC_PER_SEC;
	update_gtod(clock->cycle_last, stamp_xsec, t2x);
}

void update_vsyscall_tz(void)
{
	/* Make userspace gettimeofday spin until we're done. */
	++vdso_data->tb_update_count;
	smp_mb();
	vdso_data->tz_minuteswest = sys_tz.tz_minuteswest;
	vdso_data->tz_dsttime = sys_tz.tz_dsttime;
	smp_mb();
	++vdso_data->tb_update_count;
}

void __init clocksource_init(void)
{
	struct clocksource *clock;

	if (__USE_RTC())
		clock = &clocksource_rtc;
	else
		clock = &clocksource_timebase;

	clock->mult = clocksource_hz2mult(tb_ticks_per_sec, clock->shift);

	if (clocksource_register(clock)) {
		printk(KERN_ERR "clocksource: %s is already registered\n",
		       clock->name);
		return;
	}

	printk(KERN_INFO "clocksource: %s mult[%x] shift[%d] registered\n",
	       clock->name, clock->mult, clock->shift);
}

static int decrementer_set_next_event(unsigned long evt,
				      struct clock_event_device *dev)
{
	__get_cpu_var(decrementer_next_tb) = get_tb_or_rtc() + evt;
	set_dec(evt);
	return 0;
}

static void decrementer_set_mode(enum clock_event_mode mode,
				 struct clock_event_device *dev)
{
	if (mode != CLOCK_EVT_MODE_ONESHOT)
		decrementer_set_next_event(DECREMENTER_MAX, dev);
}

static void register_decrementer_clockevent(int cpu)
{
	struct clock_event_device *dec = &per_cpu(decrementers, cpu);

	*dec = decrementer_clockevent;
	dec->cpumask = cpumask_of_cpu(cpu);

	printk(KERN_DEBUG "clockevent: %s mult[%lx] shift[%d] cpu[%d]\n",
	       dec->name, dec->mult, dec->shift, cpu);

	clockevents_register_device(dec);
}

void init_decrementer_clockevent(void)
{
	int cpu = smp_processor_id();

	decrementer_clockevent.mult = div_sc(ppc_tb_freq, NSEC_PER_SEC,
					     decrementer_clockevent.shift);
	decrementer_clockevent.max_delta_ns =
		clockevent_delta2ns(DECREMENTER_MAX, &decrementer_clockevent);
	decrementer_clockevent.min_delta_ns =
		clockevent_delta2ns(2, &decrementer_clockevent);

	register_decrementer_clockevent(cpu);
}

void secondary_cpu_time_init(void)
{
	/* FIME: Should make unrelatred change to move snapshot_timebase
	 * call here ! */
	register_decrementer_clockevent(smp_processor_id());
}

/* This function is only called on the boot processor */
void __init time_init(void)
{
	unsigned long flags;
	struct div_result res;
	u64 scale, x;
	unsigned shift;

	if (__USE_RTC()) {
		/* 601 processor: dec counts down by 128 every 128ns */
		ppc_tb_freq = 1000000000;
		tb_last_jiffy = get_rtcl();
	} else {
		/* Normal PowerPC with timebase register */
		ppc_md.calibrate_decr();
		printk(KERN_DEBUG "time_init: decrementer frequency = %lu.%.6lu MHz\n",
		       ppc_tb_freq / 1000000, ppc_tb_freq % 1000000);
		printk(KERN_DEBUG "time_init: processor frequency   = %lu.%.6lu MHz\n",
		       ppc_proc_freq / 1000000, ppc_proc_freq % 1000000);
		tb_last_jiffy = get_tb();
	}

	tb_ticks_per_jiffy = ppc_tb_freq / HZ;
	tb_ticks_per_sec = ppc_tb_freq;
	tb_ticks_per_usec = ppc_tb_freq / 1000000;
	tb_to_us = mulhwu_scale_factor(ppc_tb_freq, 1000000);
	calc_cputime_factors();

	/*
	 * Calculate the length of each tick in ns.  It will not be
	 * exactly 1e9/HZ unless ppc_tb_freq is divisible by HZ.
	 * We compute 1e9 * tb_ticks_per_jiffy / ppc_tb_freq,
	 * rounded up.
	 */
	x = (u64) NSEC_PER_SEC * tb_ticks_per_jiffy + ppc_tb_freq - 1;
	do_div(x, ppc_tb_freq);
	tick_nsec = x;
	last_tick_len = x << TICKLEN_SCALE;

	/*
	 * Compute ticklen_to_xs, which is a factor which gets multiplied
	 * by (last_tick_len << TICKLEN_SHIFT) to get a tb_to_xs value.
	 * It is computed as:
	 * ticklen_to_xs = 2^N / (tb_ticks_per_jiffy * 1e9)
	 * where N = 64 + 20 - TICKLEN_SCALE - TICKLEN_SHIFT
	 * which turns out to be N = 51 - SHIFT_HZ.
	 * This gives the result as a 0.64 fixed-point fraction.
	 * That value is reduced by an offset amounting to 1 xsec per
	 * 2^31 timebase ticks to avoid problems with time going backwards
	 * by 1 xsec when we do timer_recalc_offset due to losing the
	 * fractional xsec.  That offset is equal to ppc_tb_freq/2^51
	 * since there are 2^20 xsec in a second.
	 */
	div128_by_32((1ULL << 51) - ppc_tb_freq, 0,
		     tb_ticks_per_jiffy << SHIFT_HZ, &res);
	div128_by_32(res.result_high, res.result_low, NSEC_PER_SEC, &res);
	ticklen_to_xs = res.result_low;

	/* Compute tb_to_xs from tick_nsec */
	tb_to_xs = mulhdu(last_tick_len << TICKLEN_SHIFT, ticklen_to_xs);

	/*
	 * Compute scale factor for sched_clock.
	 * The calibrate_decr() function has set tb_ticks_per_sec,
	 * which is the timebase frequency.
	 * We compute 1e9 * 2^64 / tb_ticks_per_sec and interpret
	 * the 128-bit result as a 64.64 fixed-point number.
	 * We then shift that number right until it is less than 1.0,
	 * giving us the scale factor and shift count to use in
	 * sched_clock().
	 */
	div128_by_32(1000000000, 0, tb_ticks_per_sec, &res);
	scale = res.result_low;
	for (shift = 0; res.result_high != 0; ++shift) {
		scale = (scale >> 1) | (res.result_high << 63);
		res.result_high >>= 1;
	}
	tb_to_ns_scale = scale;
	tb_to_ns_shift = shift;
	/* Save the current timebase to pretty up CONFIG_PRINTK_TIME */
	boot_tb = get_tb_or_rtc();

	write_seqlock_irqsave(&xtime_lock, flags);

	/* If platform provided a timezone (pmac), we correct the time */
        if (timezone_offset) {
		sys_tz.tz_minuteswest = -timezone_offset / 60;
		sys_tz.tz_dsttime = 0;
        }

	do_gtod.varp = &do_gtod.vars[0];
	do_gtod.var_idx = 0;
	do_gtod.varp->tb_orig_stamp = tb_last_jiffy;
	__get_cpu_var(last_jiffy) = tb_last_jiffy;
	do_gtod.varp->stamp_xsec = (u64) xtime.tv_sec * XSEC_PER_SEC;
	do_gtod.tb_ticks_per_sec = tb_ticks_per_sec;
	do_gtod.varp->tb_to_xs = tb_to_xs;
	do_gtod.tb_to_us = tb_to_us;

	vdso_data->tb_orig_stamp = tb_last_jiffy;
	vdso_data->tb_update_count = 0;
	vdso_data->tb_ticks_per_sec = tb_ticks_per_sec;
	vdso_data->stamp_xsec = (u64) xtime.tv_sec * XSEC_PER_SEC;
	vdso_data->tb_to_xs = tb_to_xs;

	time_freq = 0;

	write_sequnlock_irqrestore(&xtime_lock, flags);

	/* Register the clocksource, if we're not running on iSeries */
	if (!firmware_has_feature(FW_FEATURE_ISERIES))
		clocksource_init();

	init_decrementer_clockevent();
}


#define FEBRUARY	2
#define	STARTOFTIME	1970
#define SECDAY		86400L
#define SECYR		(SECDAY * 365)
#define	leapyear(year)		((year) % 4 == 0 && \
				 ((year) % 100 != 0 || (year) % 400 == 0))
#define	days_in_year(a) 	(leapyear(a) ? 366 : 365)
#define	days_in_month(a) 	(month_days[(a) - 1])

static int month_days[12] = {
	31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
};

/*
 * This only works for the Gregorian calendar - i.e. after 1752 (in the UK)
 */
void GregorianDay(struct rtc_time * tm)
{
	int leapsToDate;
	int lastYear;
	int day;
	int MonthOffset[] = { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334 };

	lastYear = tm->tm_year - 1;

	/*
	 * Number of leap corrections to apply up to end of last year
	 */
	leapsToDate = lastYear / 4 - lastYear / 100 + lastYear / 400;

	/*
	 * This year is a leap year if it is divisible by 4 except when it is
	 * divisible by 100 unless it is divisible by 400
	 *
	 * e.g. 1904 was a leap year, 1900 was not, 1996 is, and 2000 was
	 */
	day = tm->tm_mon > 2 && leapyear(tm->tm_year);

	day += lastYear*365 + leapsToDate + MonthOffset[tm->tm_mon-1] +
		   tm->tm_mday;

	tm->tm_wday = day % 7;
}

void to_tm(int tim, struct rtc_time * tm)
{
	register int    i;
	register long   hms, day;

	day = tim / SECDAY;
	hms = tim % SECDAY;

	/* Hours, minutes, seconds are easy */
	tm->tm_hour = hms / 3600;
	tm->tm_min = (hms % 3600) / 60;
	tm->tm_sec = (hms % 3600) % 60;

	/* Number of years in days */
	for (i = STARTOFTIME; day >= days_in_year(i); i++)
		day -= days_in_year(i);
	tm->tm_year = i;

	/* Number of months in days left */
	if (leapyear(tm->tm_year))
		days_in_month(FEBRUARY) = 29;
	for (i = 1; day >= days_in_month(i); i++)
		day -= days_in_month(i);
	days_in_month(FEBRUARY) = 28;
	tm->tm_mon = i;

	/* Days are what is left over (+1) from all that. */
	tm->tm_mday = day + 1;

	/*
	 * Determine the day of week
	 */
	GregorianDay(tm);
}

/* Auxiliary function to compute scaling factors */
/* Actually the choice of a timebase running at 1/4 the of the bus
 * frequency giving resolution of a few tens of nanoseconds is quite nice.
 * It makes this computation very precise (27-28 bits typically) which
 * is optimistic considering the stability of most processor clock
 * oscillators and the precision with which the timebase frequency
 * is measured but does not harm.
 */
unsigned mulhwu_scale_factor(unsigned inscale, unsigned outscale)
{
        unsigned mlt=0, tmp, err;
        /* No concern for performance, it's done once: use a stupid
         * but safe and compact method to find the multiplier.
         */
  
        for (tmp = 1U<<31; tmp != 0; tmp >>= 1) {
                if (mulhwu(inscale, mlt|tmp) < outscale)
			mlt |= tmp;
        }
  
        /* We might still be off by 1 for the best approximation.
         * A side effect of this is that if outscale is too large
         * the returned value will be zero.
         * Many corner cases have been checked and seem to work,
         * some might have been forgotten in the test however.
         */
  
        err = inscale * (mlt+1);
        if (err <= inscale/2)
		mlt++;
        return mlt;
}

/*
 * Divide a 128-bit dividend by a 32-bit divisor, leaving a 128 bit
 * result.
 */
void div128_by_32(u64 dividend_high, u64 dividend_low,
		  unsigned divisor, struct div_result *dr)
{
	unsigned long a, b, c, d;
	unsigned long w, x, y, z;
	u64 ra, rb, rc;

	a = dividend_high >> 32;
	b = dividend_high & 0xffffffff;
	c = dividend_low >> 32;
	d = dividend_low & 0xffffffff;

	w = a / divisor;
	ra = ((u64)(a - (w * divisor)) << 32) + b;

	rb = ((u64) do_div(ra, divisor) << 32) + c;
	x = ra;

	rc = ((u64) do_div(rb, divisor) << 32) + d;
	y = rb;

	do_div(rc, divisor);
	z = rc;

	dr->result_high = ((u64)w << 32) + x;
	dr->result_low  = ((u64)y << 32) + z;

}