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Subject[PATCH] sched/fair: fix unthrottle_cfs_rq for leaf_cfs_rq list
Date
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@zoho.com.cn>
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
---

This path applies on top of 20200507203612.GF19331@lorien.usersys.redhat.com
and fixes similar problem for unthrottle_cfs_rq()

kernel/sched/fair.c | 37 ++++++++++++++++++++++++++++---------
1 file changed, 28 insertions(+), 9 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index e2450c2e0747..4b73518aa25c 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4803,26 +4803,44 @@ 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);

+unthrottle_throttle:
/*
* The cfs_rq_throttled() breaks in the above iteration can result in
* incomplete leaf list maintenance, resulting in triggering the
@@ -4831,7 +4849,8 @@ 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
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