2 files changed, 35 insertions, 8 deletions

diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c
index 59371549ddf0..c9b34c4e3ecc 100644
--- a/kernel/sched/clock.c
+++ b/kernel/sched/clock.c
@@ -58,6 +58,7 @@
 #include <linux/percpu.h>
 #include <linux/ktime.h>
 #include <linux/sched.h>
+#include <linux/static_key.h>
 
 /*
  * Scheduler clock - returns current time in nanosec units.
@@ -74,7 +75,27 @@ EXPORT_SYMBOL_GPL(sched_clock);
 __read_mostly int sched_clock_running;
 
 #ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
-__read_mostly int sched_clock_stable;
+static struct static_key __sched_clock_stable = STATIC_KEY_INIT;
+
+int sched_clock_stable(void)
+{
+        if (static_key_false(&__sched_clock_stable))
+                return false;
+        return true;
+}
+
+void set_sched_clock_stable(void)
+{
+        if (!sched_clock_stable())
+                static_key_slow_dec(&__sched_clock_stable);
+}
+
+void clear_sched_clock_stable(void)
+{
+        /* XXX worry about clock continuity */
+        if (sched_clock_stable())
+                static_key_slow_inc(&__sched_clock_stable);
+}
 
 struct sched_clock_data {
         u64                     tick_raw;
@@ -234,7 +255,7 @@ u64 sched_clock_cpu(int cpu)
         struct sched_clock_data *scd;
         u64 clock;
 
-        if (sched_clock_stable)
+        if (sched_clock_stable())
                 return sched_clock();
 
         if (unlikely(!sched_clock_running))
@@ -257,7 +278,7 @@ void sched_clock_tick(void)
         struct sched_clock_data *scd;
         u64 now, now_gtod;
 
-        if (sched_clock_stable)
+        if (sched_clock_stable())
                 return;
 
         if (unlikely(!sched_clock_running))
@@ -308,7 +329,10 @@ EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);
  */
 u64 cpu_clock(int cpu)
 {
-        return sched_clock_cpu(cpu);
+        if (static_key_false(&__sched_clock_stable))
+                return sched_clock_cpu(cpu);
+
+        return sched_clock();
 }
 
 /*
@@ -320,7 +344,10 @@ u64 cpu_clock(int cpu)
  */
 u64 local_clock(void)
 {
-        return sched_clock_cpu(raw_smp_processor_id());
+        if (static_key_false(&__sched_clock_stable))
+                return sched_clock_cpu(raw_smp_processor_id());
+
+        return sched_clock();
 }
 
 #else /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */
@@ -340,12 +367,12 @@ u64 sched_clock_cpu(int cpu)
 
 u64 cpu_clock(int cpu)
 {
-        return sched_clock_cpu(cpu);
+        return sched_clock();
 }
 
 u64 local_clock(void)
 {
-        return sched_clock_cpu(0);
+        return sched_clock();
 }
 
 #endif /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */
diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 374fe04a5e6e..dd52e7ffb10e 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -371,7 +371,7 @@ static void sched_debug_header(struct seq_file *m)
         PN(cpu_clk);
         P(jiffies);
 #ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
-        P(sched_clock_stable);
+        P(sched_clock_stable());
 #endif
 #undef PN
 #undef P