* Aaro Koskinen <Aaro.Koskinen@xxxxxxxxx> [090217 10:27]:
> 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.
Nice catch! Applying to linux-omap and omap-fixes.
Tony
> Signed-off-by: Aaro Koskinen <Aaro.Koskinen@xxxxxxxxx>
> ---
> arch/arm/plat-omap/common.c | 14 +++++---------
> 1 files changed, 5 insertions(+), 9 deletions(-)
>
> diff --git a/arch/arm/plat-omap/common.c b/arch/arm/plat-omap/common.c
> index 8c53125..2866612 100644
> --- a/arch/arm/plat-omap/common.c
> +++ b/arch/arm/plat-omap/common.c
> @@ -220,20 +220,16 @@ static struct clocksource clocksource_32k = {
> };
>
> /*
> - * 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)
> --
> 1.5.4.3
>
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