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clocksource: Get rid of the hardcoded 5 seconds sleep time limit

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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>
Cc: John Stultz <john.stultz@linaro.org>
Reviewed-by: Ingo Molnar <mingo@elte.hu>
Link: http://lkml.kernel.org/r/%3C20110518210136.109811585%40linutronix.de%3E
This commit is contained in:
Thomas Gleixner 2011-05-18 21:33:40 +00:00
parent 369db4c952
commit 724ed53e8a
1 changed files with 19 additions and 19 deletions
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38
kernel/time/clocksource.c
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@ -626,19 +626,6 @@ static void clocksource_enqueue(struct clocksource *cs)
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 clocksource *cs)
*/
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);