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Commit 724ed53e authored by Thomas Gleixner's avatar Thomas Gleixner
Browse files

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: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: John Stultz <john.stultz@linaro.org>
Reviewed-by: default avatarIngo Molnar <mingo@elte.hu>
Link: http://lkml.kernel.org/r/%3C20110518210136.109811585%40linutronix.de%3E
parent 369db4c9

kernel/time/clocksource.c

+19 −19
Original line number Diff line number Diff line
@@ -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);