[PATCH 4/7] sched/rt: Add early exit on balance path

[Peter Zijlstra]

Add/make consistent an early exit on the balance_{rt,dl}() path. When there are
no pushable tasks, there is no point in taking the rq lock and all that jazz.

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
 kernel/sched/deadline.c |   10 +++-------
 kernel/sched/rt.c       |    3 +++
 2 files changed, 6 insertions(+), 7 deletions(-)

--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -3250,17 +3250,13 @@ static void pull_dl_task(struct rq *this
 				   src_rq->dl.earliest_dl.next))
 			continue;
 
+		if (!has_pushable_dl_tasks(src_rq))
+			continue;
+
 		/* Might drop this_rq->lock */
 		push_task = NULL;
 		double_lock_balance(this_rq, src_rq);
 
-		/*
-		 * If there are no more pullable tasks on the
-		 * rq, we're done with it.
-		 */
-		if (src_rq->dl.dl_nr_running <= 1)
-			goto skip;
-
 		p = pick_earliest_pushable_dl_task(src_rq, this_cpu);
 
 		/*
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -2303,6 +2303,9 @@ static void pull_rt_task(struct rq *this
 		    this_rq->rt.highest_prio.curr)
 			continue;
 
+		if (!has_pushable_tasks(src_rq))
+			continue;
+
 		/*
 		 * We can potentially drop this_rq's lock in
 		 * double_lock_balance, and another CPU could