[PATCH v3 3/5] sched: sync a se with prev cfs_rq when changing cgroup

[byungchul . park]

From: Byungchul Park <byungchul.park@xxxxxxx>

current code is wrong with cfs_rq's average load when changing a task's
cfs_rq to another. i tested with "echo pid > cgroup" and found that
e.g. cfs_rq->avg.load_avg became larger and larger whenever changing
cgroup to another again and again. we have to sync se's average load
with both *prev* cfs_rq and next cfs_rq when changing its cgroup.

Signed-off-by: Byungchul Park <byungchul.park@xxxxxxx>
---
 kernel/sched/fair.c |    8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 191d9be..1be042a 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8040,8 +8040,14 @@ static void task_move_group_fair(struct task_struct *p, int queued)
 	if (!queued && (!se->sum_exec_runtime || p->state == TASK_WAKING))
 		queued = 1;
 
+	cfs_rq = cfs_rq_of(se);
 	if (!queued)
-		se->vruntime -= cfs_rq_of(se)->min_vruntime;
+		se->vruntime -= cfs_rq->min_vruntime;
+
+#ifdef CONFIG_SMP
+	/* synchronize task with its prev cfs_rq */
+	detach_entity_load_avg(cfs_rq, se);
+#endif
 	set_task_rq(p, task_cpu(p));
 	se->depth = se->parent ? se->parent->depth + 1 : 0;
 	cfs_rq = cfs_rq_of(se);
-- 
1.7.9.5

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