context_tracking: Ground setup for static key use

Prepare for using a static key in the context tracking subsystem.
This will help optimizing the off case on its many users:

* user_enter, user_exit, exception_enter, exception_exit, guest_enter,
  guest_exit, vtime_*()

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Li Zhong <zhong@linux.vnet.ibm.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Kevin Hilman <khilman@linaro.org>

1 files changed, 17 insertions, 6 deletions

diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
index 72bcb2570d3e..839d377d0da5 100644
--- a/kernel/context_tracking.c
+++ b/kernel/context_tracking.c
@@ -20,15 +20,16 @@
 #include <linux/hardirq.h>
 #include <linux/export.h>
 
-DEFINE_PER_CPU(struct context_tracking, context_tracking) = {
-#ifdef CONFIG_CONTEXT_TRACKING_FORCE
-        .active = true,
-#endif
-};
+struct static_key context_tracking_enabled = STATIC_KEY_INIT_FALSE;
+
+DEFINE_PER_CPU(struct context_tracking, context_tracking);
 
 void context_tracking_cpu_set(int cpu)
 {
-        per_cpu(context_tracking.active, cpu) = true;
+        if (!per_cpu(context_tracking.active, cpu)) {
+                per_cpu(context_tracking.active, cpu) = true;
+                static_key_slow_inc(&context_tracking_enabled);
+        }
 }
 
 /**
@@ -202,3 +203,13 @@ void context_tracking_task_switch(struct task_struct *prev,
         clear_tsk_thread_flag(prev, TIF_NOHZ);
         set_tsk_thread_flag(next, TIF_NOHZ);
 }
+
+#ifdef CONFIG_CONTEXT_TRACKING_FORCE
+void __init context_tracking_init(void)
+{
+        int cpu;
+
+        for_each_possible_cpu(cpu)
+                context_tracking_cpu_set(cpu);
+}
+#endif