sched: Update the idle statistics in get_cpu_idle_time_us()

Right now, get_cpu_idle_time_us() only reports the idle
statistics upto the point the CPU entered last idle; not what is
valid right now.

This patch adds an update of the idle statistics to
get_cpu_idle_time_us(), so that calling this function always
returns statistics that are accurate at the point of the call.

This includes resetting the start of the idle time for
accounting purposes to avoid double accounting.
Signed-off-by: NArjan van de Ven <arjan@linux.intel.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: NRik van Riel <riel@redhat.com>
Acked-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: davej@redhat.com
LKML-Reference: <20100509082323.2d2f1945@infradead.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

kernel/time/tick-sched.c

@@ -161,6 +161,7 @@ static void update_ts_time_stats(struct tick_sched *ts, ktime_t 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;
 	}
 }
 
@@ -205,14 +206,18 @@ static ktime_t tick_nohz_start_idle(struct tick_sched *ts)
 u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time)
 {
 	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
+	ktime_t now;
 
 	if (!tick_nohz_enabled)
 		return -1;
 
+	now = ktime_get();
+	update_ts_time_stats(ts, now);
+
 	if (ts->idle_active)
 		*last_update_time = ktime_to_us(ts->idle_lastupdate);
 	else
-		*last_update_time = ktime_to_us(ktime_get());
+		*last_update_time = ktime_to_us(now);
 
 	return ktime_to_us(ts->idle_sleeptime);
 }