1 files changed, 34 insertions, 22 deletions

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 41293d5d9b75..597ce5b718d2 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -840,11 +840,33 @@ static s64 entity_lag(struct cfs_rq *cfs_rq, struct sched_entity *se, u64 avrunt
 	return clamp(vlag, -limit, limit);
 }
 
-static void update_entity_lag(struct cfs_rq *cfs_rq, struct sched_entity *se)
+/*
+ * Delayed dequeue aims to reduce the negative lag of a dequeued task. While
+ * updating the lag of an entity, check that negative lag didn't increase
+ * during the delayed dequeue period which would be unfair.
+ * Similarly, check that the entity didn't gain positive lag when DELAY_ZERO
+ * is set.
+ *
+ * Return true if the lag has been adjusted.
+ */
+static __always_inline
+bool update_entity_lag(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
+	s64 vlag = entity_lag(cfs_rq, se, avg_vruntime(cfs_rq));
+	bool ret;
+
 	WARN_ON_ONCE(!se->on_rq);
 
-	se->vlag = entity_lag(cfs_rq, se, avg_vruntime(cfs_rq));
+	if (se->sched_delayed) {
+		/* previous vlag < 0 otherwise se would not be delayed */
+		vlag = max(vlag, se->vlag);
+		if (sched_feat(DELAY_ZERO))
+			vlag = min(vlag, 0);
+	}
+	ret = (vlag == se->vlag);
+	se->vlag = vlag;
+
+	return ret;
 }
 
 /*
@@ -5564,13 +5586,6 @@ static void clear_delayed(struct sched_entity *se)
 	}
 }
 
-static inline void finish_delayed_dequeue_entity(struct sched_entity *se)
-{
-	clear_delayed(se);
-	if (sched_feat(DELAY_ZERO) && se->vlag > 0)
-		se->vlag = 0;
-}
-
 static bool
 dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
 {
@@ -5596,6 +5611,7 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
 		if (sched_feat(DELAY_DEQUEUE) && delay &&
 		    !entity_eligible(cfs_rq, se)) {
 			update_load_avg(cfs_rq, se, 0);
+			update_entity_lag(cfs_rq, se);
 			set_delayed(se);
 			return false;
 		}
@@ -5635,7 +5651,7 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
 	update_cfs_group(se);
 
 	if (flags & DEQUEUE_DELAYED)
-		finish_delayed_dequeue_entity(se);
+		clear_delayed(se);
 
 	if (cfs_rq->nr_queued == 0) {
 		update_idle_cfs_rq_clock_pelt(cfs_rq);
@@ -7084,18 +7100,14 @@ requeue_delayed_entity(struct sched_entity *se)
 	WARN_ON_ONCE(!se->sched_delayed);
 	WARN_ON_ONCE(!se->on_rq);
 
-	if (sched_feat(DELAY_ZERO)) {
-		update_entity_lag(cfs_rq, se);
-		if (se->vlag > 0) {
-			cfs_rq->nr_queued--;
-			if (se != cfs_rq->curr)
-				__dequeue_entity(cfs_rq, se);
-			se->vlag = 0;
-			place_entity(cfs_rq, se, 0);
-			if (se != cfs_rq->curr)
-				__enqueue_entity(cfs_rq, se);
-			cfs_rq->nr_queued++;
-		}
+	if (update_entity_lag(cfs_rq, se)) {
+		cfs_rq->nr_queued--;
+		if (se != cfs_rq->curr)
+			__dequeue_entity(cfs_rq, se);
+		place_entity(cfs_rq, se, 0);
+		if (se != cfs_rq->curr)
+			__enqueue_entity(cfs_rq, se);
+		cfs_rq->nr_queued++;
 	}
 
 	update_load_avg(cfs_rq, se, 0);