alarmtimers: Add alarm_forward functionality

In order to avoid wasting time expiring and re-adding very high freq
periodic alarmtimers, introduce alarm_forward() which is similar to
hrtimer_forward and moves the timer to the next future expiration time
and returns the number of overruns.

CC: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: John Stultz <john.stultz@linaro.org>

1 files changed, 36 insertions, 1 deletions

diff --git a/kernel/time/alarmtimer.c b/kernel/time/alarmtimer.c
index 55e634ea6054..f03b04291b6f 100644
--- a/kernel/time/alarmtimer.c
+++ b/kernel/time/alarmtimer.c
@@ -347,6 +347,41 @@ void alarm_cancel(struct alarm *alarm)
 }
 
 
+
+u64 alarm_forward(struct alarm *alarm, ktime_t now, ktime_t interval)
+{
+        u64 overrun = 1;
+        ktime_t delta;
+
+        delta = ktime_sub(now, alarm->node.expires);
+
+        if (delta.tv64 < 0)
+                return 0;
+
+        if (unlikely(delta.tv64 >= interval.tv64)) {
+                s64 incr = ktime_to_ns(interval);
+
+                overrun = ktime_divns(delta, incr);
+
+                alarm->node.expires = ktime_add_ns(alarm->node.expires,
+                                                        incr*overrun);
+
+                if (alarm->node.expires.tv64 > now.tv64)
+                        return overrun;
+                /*
+                 * This (and the ktime_add() below) is the
+                 * correction for exact:
+                 */
+                overrun++;
+        }
+
+        alarm->node.expires = ktime_add(alarm->node.expires, interval);
+        return overrun;
+}
+
+
+
+
 /**
  * clock2alarm - helper that converts from clockid to alarmtypes
  * @clockid: clockid.
@@ -376,7 +411,7 @@ static enum alarmtimer_restart alarm_handle_timer(struct alarm *alarm,
 
         /* Re-add periodic timers */
         if (alarm->period.tv64) {
-                alarm->node.expires = ktime_add(now, alarm->period);
+                ptr->it_overrun += alarm_forward(alarm, now, alarm->period);
                 return ALARMTIMER_RESTART;
         }
         return ALARMTIMER_NORESTART;