sched_ext: Deliver cgroup ops to each task_group's sched

With sub-schedulers claiming cgroup subtrees, cgroup ops must be delivered
to each task_group's sched rather than always to root. Add tg->scx.sched to
track which sched initialized the task_group. It is set and cleared together
with SCX_TG_INITED.

Deliver the ops accordingly:

- ops.cgroup_exit() goes to the sched whose ops.cgroup_init() it pairs with.

- ops.cgroup_prep_move/move/cancel_move() go to the task's sched, and only
  for moves that don't re-home the task. A re-homing move is reported
  through the ops.exit_task/init_task() pair instead. The cgroups passed to
  the move ops can be outside the sched's inited set as the cpu controller
  can be coarser than the sub-scheduler topology.

- Knobs of a cgroup belong to the parent, so ops.set_weight/idle/bandwidth()
  go to the parent task_group's sched.

All task_groups currently resolve to the root sched, so no behavior changes
until sub-schedulers start claiming cgroups.

While at it, scx_cgroup_init() is restructured so both paths share the
recording.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/linux/sched/ext.h b/include/linux/sched/ext.h
index cce42b21f5f5..a6db5d300f30 100644
--- a/include/linux/sched/ext.h
+++ b/include/linux/sched/ext.h
@@ -298,6 +298,8 @@ static inline bool scx_rcu_cpu_stall(const struct cpumask *stalled_mask) { retur
 
 struct scx_task_group {
 #ifdef CONFIG_EXT_GROUP_SCHED
+	struct scx_sched	*sched;
+
 	u32			flags;		/* SCX_TG_* */
 	u32			weight;
 	u64			bw_period_us;