[PATCH v2] sched/deadline: Skip meaningless bw updates in dl_task_offline_migration

[Shang XiaoJing]

Skip meaningless bw updates on root domain if task still stay in same rd
while calling dl_task_offline_migration.

Signed-off-by: Shang XiaoJing <shangxiaojing@xxxxxxxxxx>
---
changes in v2:
- fix subject and comment message
---
 kernel/sched/deadline.c | 28 +++++++++++++++-------------
 1 file changed, 15 insertions(+), 13 deletions(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 8e14dc21d829..9660e166c8ec 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -714,20 +714,22 @@ static struct rq *dl_task_offline_migration(struct rq *rq, struct task_struct *p
 		add_rq_bw(&p->dl, &later_rq->dl);
 	}
 
-	/*
-	 * And we finally need to fixup root_domain(s) bandwidth accounting,
-	 * since p is still hanging out in the old (now moved to default) root
-	 * domain.
-	 */
-	dl_b = &rq->rd->dl_bw;
-	raw_spin_lock(&dl_b->lock);
-	__dl_sub(dl_b, p->dl.dl_bw, cpumask_weight(rq->rd->span));
-	raw_spin_unlock(&dl_b->lock);
+	if (&rq->rd != &later_rq->rd) {
+		/*
+		 * And we finally need to fixup root_domain(s) bandwidth accounting,
+		 * since p is still hanging out in the old (now moved to default) root
+		 * domain.
+		 */
+		dl_b = &rq->rd->dl_bw;
+		raw_spin_lock(&dl_b->lock);
+		__dl_sub(dl_b, p->dl.dl_bw, cpumask_weight(rq->rd->span));
+		raw_spin_unlock(&dl_b->lock);
 
-	dl_b = &later_rq->rd->dl_bw;
-	raw_spin_lock(&dl_b->lock);
-	__dl_add(dl_b, p->dl.dl_bw, cpumask_weight(later_rq->rd->span));
-	raw_spin_unlock(&dl_b->lock);
+		dl_b = &later_rq->rd->dl_bw;
+		raw_spin_lock(&dl_b->lock);
+		__dl_add(dl_b, p->dl.dl_bw, cpumask_weight(later_rq->rd->span));
+		raw_spin_unlock(&dl_b->lock);
+	}
 
 	set_task_cpu(p, later_rq->cpu);
 	double_unlock_balance(later_rq, rq);
-- 
2.17.1