tick-sched: add more debug information

To allow better diagnosis of tick-sched related, especially NOHZ
related problems, we need to know when the last wakeup via an irq
happened and when the CPU left the idle state.

Add two fields (idle_waketime, idle_exittime) to the tick_sched
structure and add them to the timer_list output.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

include/linux/tick.h

@@ -39,6 +39,8 @@ enum tick_nohz_mode {
  * @idle_calls:		Total number of idle calls
  * @idle_sleeps:	Number of idle calls, where the sched tick was stopped
  * @idle_entrytime:	Time when the idle call was entered
+ * @idle_waketime:	Time when the idle was interrupted
+ * @idle_exittime:	Time when the idle state was left
  * @idle_sleeptime:	Sum of the time slept in idle with sched tick stopped
  * @sleep_length:	Duration of the current idle sleep
  */
@@ -53,6 +55,8 @@ struct tick_sched {
 	unsigned long			idle_sleeps;
 	int				idle_active;
 	ktime_t				idle_entrytime;
+	ktime_t				idle_waketime;
+	ktime_t				idle_exittime;
 	ktime_t				idle_sleeptime;
 	ktime_t				idle_lastupdate;
 	ktime_t				sleep_length;

kernel/time/tick-sched.c

@@ -137,6 +137,7 @@ void tick_nohz_update_jiffies(void)
 
 	cpu_clear(cpu, nohz_cpu_mask);
 	now = ktime_get();
+	ts->idle_waketime = now;
 
 	local_irq_save(flags);
 	tick_do_update_jiffies64(now);
@@ -400,6 +401,7 @@ void tick_nohz_restart_sched_tick(void)
 	 * Cancel the scheduled timer and restore the tick
 	 */
 	ts->tick_stopped  = 0;
+	ts->idle_exittime = now;
 	hrtimer_cancel(&ts->sched_timer);
 	ts->sched_timer.expires = ts->idle_tick;
 

kernel/time/timer_list.c

@@ -166,6 +166,8 @@ static void print_cpu(struct seq_file *m, int cpu, u64 now)
 		P(idle_calls);
 		P(idle_sleeps);
 		P_ns(idle_entrytime);
+		P_ns(idle_waketime);
+		P_ns(idle_exittime);
 		P_ns(idle_sleeptime);
 		P(last_jiffies);
 		P(next_jiffies);