linux-kernel - [PATCH v2] sched/fair: fix unthrottle_cfs_rq for leaf_cfs

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Date:   Wed, 13 May 2020 14:34:22 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, linux-kernel@...r.kernel.org
Cc:     pauld@...hat.com, ouwen210@...mail.com, pkondeti@...eaurora.org,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: [PATCH v2] sched/fair: fix unthrottle_cfs_rq for leaf_cfs_rq list

Although not exactly identical, unthrottle_cfs_rq() and enqueue_task_fair()
are quite close and follow the same sequence for enqueuing an entity in the
cfs hierarchy. Modify unthrottle_cfs_rq() to use the same pattern as
enqueue_task_fair(). This fixes a problem already faced with the latter and
add an optimization in the last for_each_sched_entity loop.

Reported-by Tao Zhou <zohooouoto@...o.com.cn>
Reviewed-by: Phil Auld <pauld@...hat.com>
Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
---

v2 changes:
- Remove useless if statement

 kernel/sched/fair.c | 41 ++++++++++++++++++++++++++++++-----------
 1 file changed, 30 insertions(+), 11 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 4e12ba882663..a0c690d57430 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4816,26 +4816,44 @@ void unthrottle_cfs_rq(struct cfs_rq *cfs_rq)
 	idle_task_delta = cfs_rq->idle_h_nr_running;
 	for_each_sched_entity(se) {
 		if (se->on_rq)
-			enqueue = 0;
+			break;
+		cfs_rq = cfs_rq_of(se);
+		enqueue_entity(cfs_rq, se, ENQUEUE_WAKEUP);
 
+		cfs_rq->h_nr_running += task_delta;
+		cfs_rq->idle_h_nr_running += idle_task_delta;
+
+		/* end evaluation on encountering a throttled cfs_rq */
+		if (cfs_rq_throttled(cfs_rq))
+			goto unthrottle_throttle;
+	}
+
+	for_each_sched_entity(se) {
 		cfs_rq = cfs_rq_of(se);
-		if (enqueue) {
-			enqueue_entity(cfs_rq, se, ENQUEUE_WAKEUP);
-		} else {
-			update_load_avg(cfs_rq, se, 0);
-			se_update_runnable(se);
-		}
+
+		update_load_avg(cfs_rq, se, UPDATE_TG);
+		se_update_runnable(se);
 
 		cfs_rq->h_nr_running += task_delta;
 		cfs_rq->idle_h_nr_running += idle_task_delta;
 
+
+		/* end evaluation on encountering a throttled cfs_rq */
 		if (cfs_rq_throttled(cfs_rq))
-			break;
+			goto unthrottle_throttle;
+
+		/*
+		 * One parent has been throttled and cfs_rq removed from the
+		 * list. Add it back to not break the leaf list.
+		 */
+		if (throttled_hierarchy(cfs_rq))
+			list_add_leaf_cfs_rq(cfs_rq);
 	}
 
-	if (!se)
-		add_nr_running(rq, task_delta);
+	/* At this point se is NULL and we are at root level*/
+	add_nr_running(rq, task_delta);
 
+unthrottle_throttle:
 	/*
 	 * The cfs_rq_throttled() breaks in the above iteration can result in
 	 * incomplete leaf list maintenance, resulting in triggering the
@@ -4844,7 +4862,8 @@ void unthrottle_cfs_rq(struct cfs_rq *cfs_rq)
 	for_each_sched_entity(se) {
 		cfs_rq = cfs_rq_of(se);
 
-		list_add_leaf_cfs_rq(cfs_rq);
+		if (list_add_leaf_cfs_rq(cfs_rq))
+			break;
 	}
 
 	assert_list_leaf_cfs_rq(rq);
-- 
2.17.1