From ef010fa294b8bbfa08178313b2b818ca6c292f15 Mon Sep 17 00:00:00 2001
From: Peter Zijlstra <peterz@infradead.org>
Date: Sat, 6 May 2017 16:11:34 +0200
Subject: [PATCH] sched/fair: More accurate reweight_entity()

References: bnc#1066110 Scheduler utilisation tracking
Patch-mainline: v4.15-rc1
Git-commit: 840c5abca499a858619954dbcffc82110bb6e076

When a (group) entity changes it's weight we should instantly change
its load_avg and propagate that change into the sums it is part of.
Because we use these values to predict future behaviour and are not
interested in its historical value.

Without this change, the change in load would need to propagate
through the average, by which time it could again have changed etc..
always chasing itself.

With this change, the cfs_rq load_avg sum will more accurately reflect
the current runnable and expected return of blocked load.

Reported-by: Paul Turner <pjt@google.com>
[josef: compile fix !SMP || !FAIR_GROUP]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Mel Gorman <mgorman@suse.de>
---
 kernel/sched/fair.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index fbd651918cc4..837efd4bc9f8 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2899,12 +2899,22 @@ static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
 		if (cfs_rq->curr == se)
 			update_curr(cfs_rq);
 		account_entity_dequeue(cfs_rq, se);
+		dequeue_runnable_load_avg(cfs_rq, se);
 	}
+	dequeue_load_avg(cfs_rq, se);
 
 	update_load_set(&se->load, weight);
 
-	if (se->on_rq)
+#ifdef CONFIG_SMP
+	se->avg.load_avg = div_u64(se_weight(se) * se->avg.load_sum,
+				   LOAD_AVG_MAX - 1024 + se->avg.period_contrib);
+#endif
+
+	enqueue_load_avg(cfs_rq, se);
+	if (se->on_rq) {
 		account_entity_enqueue(cfs_rq, se);
+		enqueue_runnable_load_avg(cfs_rq, se);
+	}
 }
 
 static inline int throttled_hierarchy(struct cfs_rq *cfs_rq);