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    Subject[patch 2/7] clocksource: Get rid of the hardcoded 5 seconds sleep time limit
    Slow clocksources can have a way longer sleep time than 5 seconds and
    even fast ones can easily cope with 600 seconds and still maintain
    proper accuracy.

    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    ---
    kernel/time/clocksource.c | 38 +++++++++++++++++++-------------------
    1 file changed, 19 insertions(+), 19 deletions(-)

    Index: linux-2.6-tip/kernel/time/clocksource.c
    ===================================================================
    --- linux-2.6-tip.orig/kernel/time/clocksource.c
    +++ linux-2.6-tip/kernel/time/clocksource.c
    @@ -626,19 +626,6 @@ static void clocksource_enqueue(struct c
    list_add(&cs->list, entry);
    }

    -
    -/*
    - * Maximum time we expect to go between ticks. This includes idle
    - * tickless time. It provides the trade off between selecting a
    - * mult/shift pair that is very precise but can only handle a short
    - * period of time, vs. a mult/shift pair that can handle long periods
    - * of time but isn't as precise.
    - *
    - * This is a subsystem constant, and actual hardware limitations
    - * may override it (ie: clocksources that wrap every 3 seconds).
    - */
    -#define MAX_UPDATE_LENGTH 5 /* Seconds */
    -
    /**
    * __clocksource_updatefreq_scale - Used update clocksource with new freq
    * @t: clocksource to be registered
    @@ -652,15 +639,28 @@ static void clocksource_enqueue(struct c
    */
    void __clocksource_updatefreq_scale(struct clocksource *cs, u32 scale, u32 freq)
    {
    + unsigned long sec;
    +
    /*
    - * Ideally we want to use some of the limits used in
    - * clocksource_max_deferment, to provide a more informed
    - * MAX_UPDATE_LENGTH. But for now this just gets the
    - * register interface working properly.
    + * Calc the maximum number of seconds which we can run before
    + * wrapping around. For clocksources which have a mask > 32bit
    + * we need to limit the max sleep time to have a good
    + * conversion precision. 10 minutes is still a reasonable
    + * amount. That results in a shift value of 24 for a
    + * clocksource with mask >= 40bit and f >= 4GHz. That maps to
    + * ~ 0.06ppm granularity for NTP. We apply the same 12.5%
    + * margin as we do in clocksource_max_deferment()
    */
    + sec = (cs->mask - (cs->mask >> 5));
    + do_div(sec, freq);
    + do_div(sec, scale);
    + if (!sec)
    + sec = 1;
    + else if (sec > 600 && cs->mask > UINT_MAX)
    + sec = 600;
    +
    clocks_calc_mult_shift(&cs->mult, &cs->shift, freq,
    - NSEC_PER_SEC/scale,
    - MAX_UPDATE_LENGTH*scale);
    + NSEC_PER_SEC / scale, sec * scale);
    cs->max_idle_ns = clocksource_max_deferment(cs);
    }
    EXPORT_SYMBOL_GPL(__clocksource_updatefreq_scale);



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