sched/fair: Move update_nohz_stats() to the CONFIG_NO_HZ_COMMON block to...

sched/fair: Move update_nohz_stats() to the CONFIG_NO_HZ_COMMON block to simplify the code & fix an unused function warning

When !CONFIG_NO_HZ_COMMON we get this new GCC warning:

   kernel/sched/fair.c:8398:13: warning: ‘update_nohz_stats’ defined but not used [-Wunused-function]

Move update_nohz_stats() to an already existing CONFIG_NO_HZ_COMMON #ifdef
block.

Beyond fixing the GCC warning, this also simplifies the update_nohz_stats() function.

[ mingo: Rewrote the changelog. ]

Fixes: 0826530d ("sched/fair: Remove update of blocked load from newidle_balance")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lore.kernel.org/r/20210329144029.29200-1-yuehaibing@huawei.com

kernel/sched/fair.c

@@ -8430,28 +8430,6 @@ group_type group_classify(unsigned int imbalance_pct,
 	return group_has_spare;
 }
 
-static bool update_nohz_stats(struct rq *rq)
-{
-#ifdef CONFIG_NO_HZ_COMMON
-	unsigned int cpu = rq->cpu;
-
-	if (!rq->has_blocked_load)
-		return false;
-
-	if (!cpumask_test_cpu(cpu, nohz.idle_cpus_mask))
-		return false;
-
-	if (!time_after(jiffies, READ_ONCE(rq->last_blocked_load_update_tick)))
-		return true;
-
-	update_blocked_averages(cpu);
-
-	return rq->has_blocked_load;
-#else
-	return false;
-#endif
-}
-
 /**
  * update_sg_lb_stats - Update sched_group's statistics for load balancing.
  * @env: The load balancing environment.
@@ -10406,6 +10384,24 @@ void nohz_balance_enter_idle(int cpu)
 	WRITE_ONCE(nohz.has_blocked, 1);
 }
 
+static bool update_nohz_stats(struct rq *rq)
+{
+	unsigned int cpu = rq->cpu;
+
+	if (!rq->has_blocked_load)
+		return false;
+
+	if (!cpumask_test_cpu(cpu, nohz.idle_cpus_mask))
+		return false;
+
+	if (!time_after(jiffies, READ_ONCE(rq->last_blocked_load_update_tick)))
+		return true;
+
+	update_blocked_averages(cpu);
+
+	return rq->has_blocked_load;
+}
+
 /*
  * Internal function that runs load balance for all idle cpus. The load balance
  * can be a simple update of blocked load or a complete load balance with