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SubjectRe: [PATCH 8/8] handle leap second via timer
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On Fri, 2008-03-14 at 19:40 +0100, zippel@linux-m68k.org wrote:
> plain text document attachment (leap_sec)
> Remove the leap second handling from second_overflow(), which doesn't
> has to check for it every second anymore. With CONFIG_NO_HZ this also
> makes sure the leap second is handled close to the full second.
> Additionally this makes it possible to abort a leap second properly
> by resetting the STA_INS/STA_DEL status bits.
>
> Signed-off-by: Roman Zippel <zippel@linux-m68k.org>

Looks interesting. Small comment below.


> -void second_overflow(void)
> +static enum hrtimer_restart ntp_leap_second(struct hrtimer *timer)
> {
> - s64 time_adj;
> + enum hrtimer_restart res = HRTIMER_NORESTART;
>
> - /* Bump the maxerror field */
> - time_maxerror += MAXFREQ / NSEC_PER_USEC;
> - if (time_maxerror > NTP_PHASE_LIMIT) {
> - time_maxerror = NTP_PHASE_LIMIT;
> - time_status |= STA_UNSYNC;
> - }
> + write_seqlock_irq(&xtime_lock);
>
> - /*
> - * Leap second processing. If in leap-insert state at the end of the
> - * day, the system clock is set back one second; if in leap-delete
> - * state, the system clock is set ahead one second. The microtime()
> - * routine or external clock driver will insure that reported time is
> - * always monotonic. The ugly divides should be replaced.
> - */
> switch (time_state) {
> case TIME_OK:
> - if (time_status & STA_INS)
> - time_state = TIME_INS;
> - else if (time_status & STA_DEL)
> - time_state = TIME_DEL;
> break;
> case TIME_INS:
> - if (xtime.tv_sec % 86400 == 0) {
> - xtime.tv_sec--;
> - wall_to_monotonic.tv_sec++;
> - time_state = TIME_OOP;
> - printk(KERN_NOTICE "Clock: inserting leap second "
> - "23:59:60 UTC\n");
> - }
> + xtime.tv_sec--;
> + wall_to_monotonic.tv_sec++;
> + time_state = TIME_OOP;
> + printk(KERN_NOTICE "Clock: "
> + "inserting leap second 23:59:60 UTC\n");
> + leap_timer.expires = ktime_add_ns(leap_timer.expires,
> + NSEC_PER_SEC);
> + res = HRTIMER_RESTART;
> break;
> case TIME_DEL:
> - if ((xtime.tv_sec + 1) % 86400 == 0) {
> - xtime.tv_sec++;
> - time_tai--;
> - wall_to_monotonic.tv_sec--;
> - time_state = TIME_WAIT;
> - printk(KERN_NOTICE "Clock: deleting leap second "
> - "23:59:59 UTC\n");
> - }
> + xtime.tv_sec++;
> + time_tai--;
> + wall_to_monotonic.tv_sec--;
> + time_state = TIME_WAIT;
> + printk(KERN_NOTICE "Clock: "
> + "deleting leap second 23:59:59 UTC\n");
> break;
> case TIME_OOP:
> time_tai++;
> time_state = TIME_WAIT;
> - break;
> + /* fall through */
> case TIME_WAIT:
> if (!(time_status & (STA_INS | STA_DEL)))
> time_state = TIME_OK;
> + break;
> + }
> + update_vsyscall(&xtime, clock);
> +

<snip>

> Index: linux-2.6/include/linux/clocksource.h
> ===================================================================
> --- linux-2.6.orig/include/linux/clocksource.h 2008-03-10 19:50:33.000000000 +0100
> +++ linux-2.6/include/linux/clocksource.h 2008-03-13 10:33:24.000000000 +0100
> @@ -93,6 +93,8 @@ struct clocksource {
> #endif
> };
>
> +extern struct clocksource *clock; /* current clocksource */
> +
> /*
> * Clock source flags bits::
> */

Instead of exporting the clocksource making it global, could you use a
timekeeping_insert/remove_second() style interface?

That would help remove the xtime/wall_to_monotonic references in ntp.c
as well, cleaning up things nicely.

thanks
-john




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