3 files changed, 56 insertions, 2 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index c5d3f847ca8d..33a8f42041fa 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1573,13 +1573,28 @@ static inline void sched_clock_idle_sleep_event(void)
 static inline void sched_clock_idle_wakeup_event(u64 delta_ns)
 {
 }
-#else
+
+#ifdef CONFIG_NO_HZ
+static inline void sched_clock_tick_stop(int cpu)
+{
+}
+
+static inline void sched_clock_tick_start(int cpu)
+{
+}
+#endif
+
+#else /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */
 extern void sched_clock_init(void);
 extern u64 sched_clock_cpu(int cpu);
 extern void sched_clock_tick(void);
 extern void sched_clock_idle_sleep_event(void);
 extern void sched_clock_idle_wakeup_event(u64 delta_ns);
+#ifdef CONFIG_NO_HZ
+extern void sched_clock_tick_stop(int cpu);
+extern void sched_clock_tick_start(int cpu);
 #endif
+#endif /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */
 
 /*
  * For kernel-internal use: high-speed (but slightly incorrect) per-cpu
diff --git a/kernel/sched_clock.c b/kernel/sched_clock.c
index 42b81fa38cbd..97159e225a77 100644
--- a/kernel/sched_clock.c
+++ b/kernel/sched_clock.c
@@ -45,6 +45,9 @@ struct sched_clock_data {
         u64                     tick_raw;
         u64                     tick_gtod;
         u64                     clock;
+#ifdef CONFIG_NO_HZ
+        int                     check_max;
+#endif
 };
 
 static DEFINE_PER_CPU_SHARED_ALIGNED(struct sched_clock_data, sched_clock_data);
@@ -76,11 +79,45 @@ void sched_clock_init(void)
                 scd->tick_raw = 0;
                 scd->tick_gtod = ktime_now;
                 scd->clock = ktime_now;
+#ifdef CONFIG_NO_HZ
+                scd->check_max = 1;
+#endif
         }
 
         sched_clock_running = 1;
 }
 
+#ifdef CONFIG_NO_HZ
+/*
+ * The dynamic ticks makes the delta jiffies inaccurate. This
+ * prevents us from checking the maximum time update.
+ * Disable the maximum check during stopped ticks.
+ */
+void sched_clock_tick_stop(int cpu)
+{
+        struct sched_clock_data *scd = cpu_sdc(cpu);
+
+        scd->check_max = 0;
+}
+
+void sched_clock_tick_start(int cpu)
+{
+        struct sched_clock_data *scd = cpu_sdc(cpu);
+
+        scd->check_max = 1;
+}
+
+static int check_max(struct sched_clock_data *scd)
+{
+        return scd->check_max;
+}
+#else
+static int check_max(struct sched_clock_data *scd)
+{
+        return 1;
+}
+#endif /* CONFIG_NO_HZ */
+
 /*
  * update the percpu scd from the raw @now value
  *
@@ -112,7 +149,7 @@ static void __update_sched_clock(struct sched_clock_data *scd, u64 now)
          */
         max_clock = scd->tick_gtod + (2 + delta_jiffies) * TICK_NSEC;
 
-        if (unlikely(clock + delta > max_clock)) {
+        if (unlikely(clock + delta > max_clock) && check_max(scd)) {
                 if (clock < max_clock)
                         clock = max_clock;
                 else
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index b854a895591e..d63008b09a4c 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -276,6 +276,7 @@ void tick_nohz_stop_sched_tick(void)
                         ts->tick_stopped = 1;
                         ts->idle_jiffies = last_jiffies;
                         rcu_enter_nohz();
+                        sched_clock_tick_stop(cpu);
                 }
 
                 /*
@@ -375,6 +376,7 @@ void tick_nohz_restart_sched_tick(void)
         select_nohz_load_balancer(0);
         now = ktime_get();
         tick_do_update_jiffies64(now);
+        sched_clock_tick_start(cpu);
         cpu_clear(cpu, nohz_cpu_mask);
 
         /*