[2/4] ARM: OMAP: sched_clock() corrected
diff mbox

Message ID 20090304182753.27331.99951.stgit@localhost
State RFC
Delegated to: Tony Lindgren
Headers show

Commit Message

Tony Lindgren March 4, 2009, 6:27 p.m. UTC
From: Aaro Koskinen <Aaro.Koskinen@nokia.com>

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>
---
 arch/arm/plat-omap/common.c |   14 +++++---------
 1 files changed, 5 insertions(+), 9 deletions(-)


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Patch
diff mbox

diff --git a/arch/arm/plat-omap/common.c b/arch/arm/plat-omap/common.c
index 0843b88..6825fbb 100644
--- a/arch/arm/plat-omap/common.c
+++ b/arch/arm/plat-omap/common.c
@@ -200,20 +200,16 @@  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)