Commit 80ea3bac authored Mar 04, 2009 by Aaro Koskinen Committed by Tony Lindgren Mar 04, 2009

ARM: OMAP: sched_clock() corrected



After my OMAP3 board has been running for a while, I'm seeing weird
latency traces like this:

      sh-1574    0d.h2  153us : do_timer (tick_do_update_jiffies64)
      sh-1574    0d.h2  153us : update_wall_time (do_timer)
      sh-1574    0d.h2  153us!: omap_32k_read (update_wall_time)
      sh-1574    0d.h2 1883us : update_xtime_cache (update_wall_time)
      sh-1574    0d.h2 1883us : clocksource_get_next (update_wall_time)
      sh-1574    0d.h2 1883us+: _spin_lock_irqsave (clocksource_get_next)

and after a while:

      sh-17818   0d.h3  153us : do_timer (tick_do_update_jiffies64)
      sh-17818   0d.h3  153us : update_wall_time (do_timer)
      sh-17818   0d.h3  153us!: omap_32k_read (update_wall_time)
      sh-17818   0d.h3 1915us : update_xtime_cache (update_wall_time)
      sh-17818   0d.h3 1915us+: clocksource_get_next (update_wall_time)
      sh-17818   0d.h3 1945us : _spin_lock_irqsave (clocksource_get_next)

Turns out that sched_clock() is using cyc2ns(), which returns NTP
adjusted time. The sched_clock() frequency should not be adjusted. The
patch deletes omap_32k_ticks_to_nsecs() and rewrites sched_clock()
to do the conversion using the constant multiplier.

Signed-off-by: Aaro Koskinen <Aaro.Koskinen@nokia.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>

parent 87d99d6f

arch/arm/plat-omap/common.c

+5 −9

Original line number	Diff line number	Diff line
		@@ -199,21 +199,17 @@ static struct clocksource clocksource_32k = {
		.flags = CLOCK_SOURCE_IS_CONTINUOUS,
		};

		/*
		* Rounds down to nearest nsec.
		*/
		unsigned long long omap_32k_ticks_to_nsecs(unsigned long ticks_32k)
		{
		return cyc2ns(&clocksource_32k, ticks_32k);
		}

		/*
		* Returns current time from boot in nsecs. It's OK for this to wrap
		* around for now, as it's just a relative time stamp.
		*/
		unsigned long long sched_clock(void)
		{
		return omap_32k_ticks_to_nsecs(omap_32k_read());
		unsigned long long ret;

		ret = (unsigned long long)omap_32k_read();
		ret = (ret * clocksource_32k.mult_orig) >> clocksource_32k.shift;
		return ret;
		}

		static int __init omap_init_clocksource_32k(void)