sched: monitor clock underflows in /proc/sched_debug

We monitor clock overflows, let's also monitor clock underflows.

Signed-off-by: Guillaume Chazarain <guichaz@yahoo.fr>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 5 insertions, 2 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 3995d1679858..4d3a5a700866 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -465,7 +465,7 @@ struct rq {
         u64 clock, prev_clock_raw;
         s64 clock_max_delta;
 
-        unsigned int clock_warps, clock_overflows;
+        unsigned int clock_warps, clock_overflows, clock_underflows;
         u64 idle_clock;
         unsigned int clock_deep_idle_events;
         u64 tick_timestamp;
@@ -3736,8 +3736,10 @@ void scheduler_tick(void)
         /*
          * Let rq->clock advance by at least TICK_NSEC:
          */
-        if (unlikely(rq->clock < next_tick))
+        if (unlikely(rq->clock < next_tick)) {
                 rq->clock = next_tick;
+                rq->clock_underflows++;
+        }
         rq->tick_timestamp = rq->clock;
         update_cpu_load(rq);
         curr->sched_class->task_tick(rq, curr, 0);
diff --git a/kernel/sched_debug.c b/kernel/sched_debug.c
index 80fbbfc04290..9e5de098d471 100644
--- a/kernel/sched_debug.c
+++ b/kernel/sched_debug.c
@@ -179,6 +179,7 @@ static void print_cpu(struct seq_file *m, int cpu)
         PN(prev_clock_raw);
         P(clock_warps);
         P(clock_overflows);
+        P(clock_underflows);
         P(clock_deep_idle_events);
         PN(clock_max_delta);
         P(cpu_load[0]);