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>

3 files changed, 8 insertions, 0 deletions

diff --git a/include/linux/tick.h b/include/linux/tick.h
index 0fadf95debe1..a881c652f7e9 100644
--- a/include/linux/tick.h
+++ b/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;
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 63f24b550695..88267f0a8471 100644
--- a/kernel/time/tick-sched.c
+++ b/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;
 
diff --git a/kernel/time/timer_list.c b/kernel/time/timer_list.c
index 12c5f4cb6b8c..d3d94c1a0fd2 100644
--- a/kernel/time/timer_list.c
+++ b/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);