[B][SRU][PATCH 5/5] sched/fair: Fix unthrottle_cfs_rq() for leaf_cfs_rq list

[po-hsu.lin at canonical.com]

From: Vincent Guittot <vincent.guittot at linaro.org>

Buglink: https://bugs.launchpad.net/bugs/1931325

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.

Fixes: fe61468b2cb (sched/fair: Fix enqueue_task_fair warning)
Reported-by Tao Zhou <zohooouoto at zoho.com.cn>
Signed-off-by: Vincent Guittot <vincent.guittot at linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz at infradead.org>
Reviewed-by: Phil Auld <pauld at redhat.com>
Reviewed-by: Ben Segall <bsegall at google.com>
Link: https://lkml.kernel.org/r/20200513135528.4742-1-vincent.guittot@linaro.org

(backported from commit 39f23ce07b9355d05a64ae303ce20d1c4b92b957)
[PHLin: backported w/o changes for SCHED_IDLE tasks count tracking 43e9f7f231e40e]
[PHLin: backported w/o changes for runnable average signal 9f68395333ad7f]
Signed-off-by: Po-Hsu Lin <po-hsu.lin at canonical.com>
---
 kernel/sched/fair.c | 37 +++++++++++++++++++++++++++++--------
 1 file changed, 29 insertions(+), 8 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index b4d224f..737b454 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4673,7 +4673,6 @@ void unthrottle_cfs_rq(struct cfs_rq *cfs_rq)
 	struct rq *rq = rq_of(cfs_rq);
 	struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(cfs_rq->tg);
 	struct sched_entity *se;
-	int enqueue = 1;
 	long task_delta;
 
 	se = cfs_rq->tg->se[cpu_of(rq)];
@@ -4696,20 +4695,41 @@ void unthrottle_cfs_rq(struct cfs_rq *cfs_rq)
 	task_delta = cfs_rq->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;
+
+		/* 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);
+
+		update_load_avg(cfs_rq, se, UPDATE_TG);
+
 		cfs_rq->h_nr_running += 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
@@ -4718,7 +4738,8 @@ 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);
-- 
2.7.4