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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>
This commit is contained in:
John Stultz 2011-08-10 11:31:03 -07:00
parent 54da23b720
commit dce75a8c71
2 changed files with 38 additions and 1 deletions
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2
include/linux/alarmtimer.h
View File

@ -42,4 +42,6 @@ void alarm_init(struct alarm *alarm, enum alarmtimer_type type,
void alarm_start(struct alarm *alarm, ktime_t start, ktime_t period);
void alarm_cancel(struct alarm *alarm);
u64 alarm_forward(struct alarm *alarm, ktime_t now, ktime_t interval);
#endif

37
kernel/time/alarmtimer.c
View File

@ -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;