clockevents: Make minimum delay adjustments configurable

The automatic increase of the min_delta_ns of a clockevents device
should be done in the clockevents code as the minimum delay is an
attribute of the clockevents device.

In addition not all architectures want the automatic adjustment, on a
massively virtualized system it can happen that the programming of a
clock event fails several times in a row because the virtual cpu has
been rescheduled quickly enough. In that case the minimum delay will
erroneously be increased with no way back. The new config symbol
GENERIC_CLOCKEVENTS_MIN_ADJUST is used to enable the automatic
adjustment. The config option is selected only for x86.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: john stultz <johnstul@us.ibm.com>
Link: http://lkml.kernel.org/r/20110823133142.494157493@de.ibm.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 4 insertions, 73 deletions

diff --git a/kernel/time/tick-oneshot.c b/kernel/time/tick-oneshot.c
index 2d04411a5f0..824109060a3 100644
--- a/kernel/time/tick-oneshot.c
+++ b/kernel/time/tick-oneshot.c
@@ -21,74 +21,6 @@
 
 #include "tick-internal.h"
 
-/* Limit min_delta to a jiffie */
-#define MIN_DELTA_LIMIT		(NSEC_PER_SEC / HZ)
-
-static int tick_increase_min_delta(struct clock_event_device *dev)
-{
-	/* Nothing to do if we already reached the limit */
-	if (dev->min_delta_ns >= MIN_DELTA_LIMIT)
-		return -ETIME;
-
-	if (dev->min_delta_ns < 5000)
-		dev->min_delta_ns = 5000;
-	else
-		dev->min_delta_ns += dev->min_delta_ns >> 1;
-
-	if (dev->min_delta_ns > MIN_DELTA_LIMIT)
-		dev->min_delta_ns = MIN_DELTA_LIMIT;
-
-	printk(KERN_WARNING "CE: %s increased min_delta_ns to %llu nsec\n",
-	       dev->name ? dev->name : "?",
-	       (unsigned long long) dev->min_delta_ns);
-	return 0;
-}
-
-/**
- * tick_program_event internal worker function
- */
-int tick_dev_program_event(struct clock_event_device *dev, ktime_t expires,
-			   int force)
-{
-	ktime_t now = ktime_get();
-	int i;
-
-	for (i = 0;;) {
-		int ret = clockevents_program_event(dev, expires, now);
-
-		if (!ret || !force)
-			return ret;
-
-		dev->retries++;
-		/*
-		 * We tried 3 times to program the device with the given
-		 * min_delta_ns. If that's not working then we increase it
-		 * and emit a warning.
-		 */
-		if (++i > 2) {
-			/* Increase the min. delta and try again */
-			if (tick_increase_min_delta(dev)) {
-				/*
-				 * Get out of the loop if min_delta_ns
-				 * hit the limit already. That's
-				 * better than staying here forever.
-				 *
-				 * We clear next_event so we have a
-				 * chance that the box survives.
-				 */
-				printk(KERN_WARNING
-				       "CE: Reprogramming failure. Giving up\n");
-				dev->next_event.tv64 = KTIME_MAX;
-				return -ETIME;
-			}
-			i = 0;
-		}
-
-		now = ktime_get();
-		expires = ktime_add_ns(now, dev->min_delta_ns);
-	}
-}
-
 /**
  * tick_program_event
  */
@@ -96,7 +28,7 @@ int tick_program_event(ktime_t expires, int force)
 {
 	struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);
 
-	return tick_dev_program_event(dev, expires, force);
+	return clockevents_program_event(dev, expires, force);
 }
 
 /**
@@ -104,11 +36,10 @@ int tick_program_event(ktime_t expires, int force)
  */
 void tick_resume_oneshot(void)
 {
-	struct tick_device *td = &__get_cpu_var(tick_cpu_device);
-	struct clock_event_device *dev = td->evtdev;
+	struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);
 
 	clockevents_set_mode(dev, CLOCK_EVT_MODE_ONESHOT);
-	tick_program_event(ktime_get(), 1);
+	clockevents_program_event(dev, ktime_get(), true);
 }
 
 /**
@@ -120,7 +51,7 @@ void tick_setup_oneshot(struct clock_event_device *newdev,
 {
 	newdev->event_handler = handler;
 	clockevents_set_mode(newdev, CLOCK_EVT_MODE_ONESHOT);
-	tick_dev_program_event(newdev, next_event, 1);
+	clockevents_program_event(newdev, next_event, true);
 }
 
 /**