sched: Eliminate the ts->idle_lastupdate field

Now that the only user of ts->idle_lastupdate is
update_ts_time_stats(), the entire field can be eliminated.

In update_ts_time_stats(), idle_lastupdate is first set to
"now", and a few lines later, the only user is an if() statement
that assigns a variable either to "now" or to
ts->idle_lastupdate, which has the value of "now" at that point.

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Rik van Riel <riel@redhat.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: davej@redhat.com
LKML-Reference: <20100509082439.2fab0b4f@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

include/linux/tick.h

@@ -60,7 +60,6 @@ struct tick_sched {
 	ktime_t				idle_waketime;
 	ktime_t				idle_exittime;
 	ktime_t				idle_sleeptime;
-	ktime_t				idle_lastupdate;
 	ktime_t				sleep_length;
 	unsigned long			last_jiffies;
 	unsigned long			next_jiffies;

kernel/time/tick-sched.c

@@ -158,16 +158,13 @@ update_ts_time_stats(struct tick_sched *ts, ktime_t now, u64 *last_update_time)
 {
 	ktime_t delta;
 
-	ts->idle_lastupdate = now;
 	if (ts->idle_active) {
 		delta = ktime_sub(now, ts->idle_entrytime);
 		ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
 		ts->idle_entrytime = now;
 	}
 
-	if (ts->idle_active && last_update_time)
-		*last_update_time = ktime_to_us(ts->idle_lastupdate);
-	else
+	if (last_update_time)
 		*last_update_time = ktime_to_us(now);
 
 }