[RFC PATCH v3 07/10] sched/fair: Prepare task_change_group_fair() for per-task throttling

[Valentin Schneider <vschneid@redhat.com>]

Later commits will change CFS bandwidth control throttling from a
per-cfs_rq basis to a per-task basis. This means special care needs to be
taken around any transition a task can have into and out of a cfs_rq.

To ease reviewing, the transitions are patched with dummy-helpers that are
implemented later on.

Add helpers to task_change_group_fair() to cover CPU cgroup
migration. If changing to a throttled taskgroup/cfs_rq, the task needs to
be throttled. Conversely, if the task is already throttled but changing to
a taskgroup/cfs_rq that still has some runtime, the task must be unthrottled.

Signed-off-by: Valentin Schneider <vschneid@redhat.com>
---
 kernel/sched/fair.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index acac0829c71f3..ec4cf7308a586 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -12935,6 +12935,14 @@ static void task_change_group_fair(struct task_struct *p)
 #endif
 	set_task_rq(p, task_cpu(p));
 	attach_task_cfs_rq(p);
+
+	if (!cfs_bandwidth_used())
+		return;
+
+	if (task_needs_throttling(p))
+		task_throttle_setup(p);
+	else
+		task_throttle_cancel(p);
 }
 
 void free_fair_sched_group(struct task_group *tg)
-- 
2.43.0