sched: debug: update exec_clock only when SCHED_DEBUG

micro-optimization: update cfs_rq->exec_clock only if
CONFIG_SCHED_DEBUG=y.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Mike Galbraith <efault@gmx.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>

kernel/sched_fair.c

@@ -301,7 +301,7 @@ __update_curr(struct cfs_rq *cfs_rq, struct sched_entity *curr,
 	schedstat_set(curr->exec_max, max((u64)delta_exec, curr->exec_max));
 
 	curr->sum_exec_runtime += delta_exec;
-	cfs_rq->exec_clock += delta_exec;
+	schedstat_add(cfs_rq, exec_clock, delta_exec);
 	delta_exec_weighted = delta_exec;
 	if (unlikely(curr->load.weight != NICE_0_LOAD)) {
 		delta_exec_weighted = calc_delta_fair(delta_exec_weighted,