x86_64: prepare idle loop for dynamic ticks

Add tick_nohz_{stop,restart}_sched_tick to idle loop in prepartion for turning
on dynticks.  These are just noops until NO_HZ is enabled.

Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>

arch/x86/kernel/process_64.c

@@ -38,6 +38,7 @@
 #include <linux/notifier.h>
 #include <linux/kprobes.h>
 #include <linux/kdebug.h>
+#include <linux/tick.h>
 
 #include <asm/uaccess.h>
 #include <asm/pgtable.h>
@@ -208,6 +209,8 @@ void cpu_idle (void)
 			if (__get_cpu_var(cpu_idle_state))
 				__get_cpu_var(cpu_idle_state) = 0;
 
+			tick_nohz_stop_sched_tick();
+
 			rmb();
 			idle = pm_idle;
 			if (!idle)
@@ -228,6 +231,7 @@ void cpu_idle (void)
 			__exit_idle();
 		}
 
+		tick_nohz_restart_sched_tick();
 		preempt_enable_no_resched();
 		schedule();
 		preempt_disable();