2 files changed, 30 insertions, 2 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 651c899a9b74..a6f6869fdefb 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -541,6 +541,11 @@ struct rq {
         unsigned long long rq_cpu_time;
         /* could above be rq->cfs_rq.exec_clock + rq->rt_rq.rt_runtime ? */
 
+        u64 skip_clock_max;
+        u64 skip_clock_recent_max;
+        u64 skip_clock_set;
+        unsigned int skip_clock_count;
+
         /* sys_sched_yield() stats */
         unsigned int yld_count;
 
@@ -639,6 +644,22 @@ static inline struct task_group *task_group(struct task_struct *p)
 static u64 irq_time_cpu(int cpu);
 static void sched_irq_time_avg_update(struct rq *rq, u64 irq_time);
 
+static void clear_skip_clock_update(struct rq *rq)
+{
+#ifdef CONFIG_SCHEDSTATS
+        if (unlikely(rq->skip_clock_update)) {
+                u64 skipped = sched_clock_cpu(cpu_of(rq)) - rq->skip_clock_set;
+                rq->skip_clock_max = max(rq->skip_clock_max, skipped);
+                /* reset infrequently to expose changes */
+                if (!(++rq->skip_clock_count % 10000))
+                        rq->skip_clock_recent_max = 0;
+                rq->skip_clock_recent_max = max(rq->skip_clock_recent_max,
+                                                skipped);
+        }
+#endif
+        rq->skip_clock_update = 0;
+}
+
 inline void update_rq_clock(struct rq *rq)
 {
         if (!rq->skip_clock_update) {
@@ -652,7 +673,7 @@ inline void update_rq_clock(struct rq *rq)
 
                 sched_irq_time_avg_update(rq, irq_time);
         }
-        rq->skip_clock_update = 0;
+        clear_skip_clock_update(rq);
 }
 
 /*
@@ -2130,8 +2151,11 @@ static void check_preempt_curr(struct rq *rq, struct task_struct *p, int flags)
          * A queue event has occurred, and we're going to schedule.  In
          * this case, we can save a useless back to back clock update.
          */
-        if (rq->curr->se.on_rq && test_tsk_need_resched(rq->curr))
+        if (rq->curr->se.on_rq && test_tsk_need_resched(rq->curr)) {
+                schedstat_set(rq->skip_clock_set,
+                              sched_clock_cpu(cpu_of(rq)));
                 rq->skip_clock_update = 1;
+        }
 }
 
 #ifdef CONFIG_SMP
diff --git a/kernel/sched_debug.c b/kernel/sched_debug.c
index 2e1b0d17dd9b..8924be259506 100644
--- a/kernel/sched_debug.c
+++ b/kernel/sched_debug.c
@@ -298,6 +298,10 @@ static void print_cpu(struct seq_file *m, int cpu)
 
         P(bkl_count);
 
+        P(skip_clock_count);
+        P64(skip_clock_recent_max);
+        P64(skip_clock_max);
+
 #undef P
 #endif
         print_cfs_stats(m, cpu);