sched: make !hrtick faster

it is safe to ignore timers and flags when the feature is disabled.
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

kernel/sched.c

@@ -4134,7 +4134,7 @@ asmlinkage void __sched schedule(void)
 	struct task_struct *prev, *next;
 	unsigned long *switch_count;
 	struct rq *rq;
-	int cpu;
+	int cpu, hrtick = sched_feat(HRTICK);
 
 need_resched:
 	preempt_disable();
@@ -4149,7 +4149,8 @@ asmlinkage void __sched schedule(void)
 
 	schedule_debug(prev);
 
-	hrtick_clear(rq);
+	if (hrtick)
+		hrtick_clear(rq);
 
 	/*
 	 * Do the rq-clock update outside the rq lock:
@@ -4197,7 +4198,8 @@ asmlinkage void __sched schedule(void)
 	} else
 		spin_unlock_irq(&rq->lock);
 
-	hrtick_set(rq);
+	if (hrtick)
+		hrtick_set(rq);
 
 	if (unlikely(reacquire_kernel_lock(current) < 0))
 		goto need_resched_nonpreemptible;