tick: Rename tick_check_idle() to tick_irq_enter()

This makes the code more symetric against the existing tick functions
called on irq exit: tick_irq_exit() and tick_nohz_irq_exit().

These function are also symetric as they mirror each other's action:
we start to account idle time on irq exit and we stop this accounting
on irq entry. Also the tick is stopped on irq exit and timekeeping
catches up with the tickless time elapsed until we reach irq entry.

This rename was suggested by Peter Zijlstra a long while ago but it
got forgotten in the mass.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Alex Shi <alex.shi@linaro.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Kevin Hilman <khilman@linaro.org>
Link: http://lkml.kernel.org/r/1387320692-28460-2-git-send-email-fweisbec@gmail.com
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 11348de..ca9cb35 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -318,7 +318,7 @@
 		 * here, as softirq will be serviced on return from interrupt.
 		 */
 		local_bh_disable();
-		tick_check_idle();
+		tick_irq_enter();
 		_local_bh_enable();
 	}
 
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 0ddd020..e4d0f09 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -1023,7 +1023,7 @@
 #endif
 }
 
-static inline void tick_check_nohz_this_cpu(void)
+static inline void tick_nohz_irq_enter(void)
 {
 	struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
 	ktime_t now;
@@ -1042,17 +1042,17 @@
 #else
 
 static inline void tick_nohz_switch_to_nohz(void) { }
-static inline void tick_check_nohz_this_cpu(void) { }
+static inline void tick_nohz_irq_enter(void) { }
 
 #endif /* CONFIG_NO_HZ_COMMON */
 
 /*
  * Called from irq_enter to notify about the possible interruption of idle()
  */
-void tick_check_idle(void)
+void tick_irq_enter(void)
 {
 	tick_check_oneshot_broadcast_this_cpu();
-	tick_check_nohz_this_cpu();
+	tick_nohz_irq_enter();
 }
 
 /*