sched: Clean up idle task SMP logic

The idle post_schedule flag is just a vile waste of time, furthermore
it appears unneeded, move the idle_enter_fair() call into
pick_next_task_idle().

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: alex.shi@linaro.org
Cc: mingo@kernel.org
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/n/tip-aljykihtxJt3mkokxi0qZurb@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/sched/idle_task.c

@@ -19,11 +19,6 @@ static void pre_schedule_idle(struct rq *rq, struct task_struct *prev)
 	idle_exit_fair(rq);
 	rq_last_tick_reset(rq);
 }
-
-static void post_schedule_idle(struct rq *rq)
-{
-	idle_enter_fair(rq);
-}
 #endif /* CONFIG_SMP */
 /*
  * Idle tasks are unconditionally rescheduled:
@@ -41,8 +36,7 @@ pick_next_task_idle(struct rq *rq, struct task_struct *prev)
 
 	schedstat_inc(rq, sched_goidle);
 #ifdef CONFIG_SMP
-	/* Trigger the post schedule to do an idle_enter for CFS */
-	rq->post_schedule = 1;
+	idle_enter_fair(rq);
 #endif
 	return rq->idle;
 }
@@ -106,7 +100,6 @@ const struct sched_class idle_sched_class = {
 #ifdef CONFIG_SMP
 	.select_task_rq		= select_task_rq_idle,
 	.pre_schedule		= pre_schedule_idle,
-	.post_schedule		= post_schedule_idle,
 #endif
 
 	.set_curr_task          = set_curr_task_idle,