sched/fair: Cleanup fair_server

The throttle interaction made my brain hurt, make it consistently
about 0 transitions of h_nr_running.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

kernel/sched/fair.c

@@ -5849,10 +5849,10 @@ static bool throttle_cfs_rq(struct cfs_rq *cfs_rq)
 	/* At this point se is NULL and we are at root level*/
 	sub_nr_running(rq, task_delta);
 
-done:
 	/* Stop the fair server if throttling resulted in no runnable tasks */
 	if (rq_h_nr_running && !rq->cfs.h_nr_running)
 		dl_server_stop(&rq->fair_server);
+done:
 	/*
 	 * Note: distribution will already see us throttled via the
 	 * throttled-list.  rq->lock protects completion.
@@ -5940,16 +5940,16 @@ void unthrottle_cfs_rq(struct cfs_rq *cfs_rq)
 			goto unthrottle_throttle;
 	}
 
+	/* Start the fair server if un-throttling resulted in new runnable tasks */
+	if (!rq_h_nr_running && rq->cfs.h_nr_running)
+		dl_server_start(&rq->fair_server);
+
 	/* At this point se is NULL and we are at root level*/
 	add_nr_running(rq, task_delta);
 
 unthrottle_throttle:
 	assert_list_leaf_cfs_rq(rq);
 
-	/* Start the fair server if un-throttling resulted in new runnable tasks */
-	if (!rq_h_nr_running && rq->cfs.h_nr_running)
-		dl_server_start(&rq->fair_server);
-
 	/* Determine whether we need to wake up potentially idle CPU: */
 	if (rq->curr == rq->idle && rq->cfs.nr_running)
 		resched_curr(rq);
@@ -6771,6 +6771,7 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
 	struct sched_entity *se = &p->se;
 	int idle_h_nr_running = task_has_idle_policy(p);
 	int task_new = !(flags & ENQUEUE_WAKEUP);
+	int rq_h_nr_running = rq->cfs.h_nr_running;
 
 	/*
 	 * The code below (indirectly) updates schedutil which looks at
@@ -6780,13 +6781,6 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
 	 */
 	util_est_enqueue(&rq->cfs, p);
 
-	if (!throttled_hierarchy(task_cfs_rq(p)) && !rq->cfs.h_nr_running) {
-		/* Account for idle runtime */
-		if (!rq->nr_running)
-			dl_server_update_idle_time(rq, rq->curr);
-		dl_server_start(&rq->fair_server);
-	}
-
 	/*
 	 * If in_iowait is set, the code below may not trigger any cpufreq
 	 * utilization updates, so do it here explicitly with the IOWAIT flag
@@ -6832,6 +6826,13 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
 			goto enqueue_throttle;
 	}
 
+	if (!rq_h_nr_running && rq->cfs.h_nr_running) {
+		/* Account for idle runtime */
+		if (!rq->nr_running)
+			dl_server_update_idle_time(rq, rq->curr);
+		dl_server_start(&rq->fair_server);
+	}
+
 	/* At this point se is NULL and we are at root level*/
 	add_nr_running(rq, 1);
 
@@ -6872,6 +6873,7 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags)
 	int task_sleep = flags & DEQUEUE_SLEEP;
 	int idle_h_nr_running = task_has_idle_policy(p);
 	bool was_sched_idle = sched_idle_rq(rq);
+	int rq_h_nr_running = rq->cfs.h_nr_running;
 
 	util_est_dequeue(&rq->cfs, p);
 
@@ -6926,14 +6928,14 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags)
 	/* At this point se is NULL and we are at root level*/
 	sub_nr_running(rq, 1);
 
+	if (rq_h_nr_running && !rq->cfs.h_nr_running)
+		dl_server_stop(&rq->fair_server);
+
 	/* balance early to pull high priority tasks */
 	if (unlikely(!was_sched_idle && sched_idle_rq(rq)))
 		rq->next_balance = jiffies;
 
 dequeue_throttle:
-	if (!throttled_hierarchy(task_cfs_rq(p)) && !rq->cfs.h_nr_running)
-		dl_server_stop(&rq->fair_server);
-
 	util_est_update(&rq->cfs, p, task_sleep);
 	hrtick_update(rq);
 }