sched_ext: Add ops.sub_cid_sched_updated() to report the sched running on a cid

A parent sched that delegates cpus to sub-scheds has no way of telling how
much each delegatee is using them. A parent that sizes its delegations by
demand cannot measure it, and one that wants to hand a cid from one sub to
another cannot see which sub it would take the cid from.

Add ops.sub_cid_sched_updated(), invoked on a sched when what it sees
running on a cid changes: NONE when no task of its subtree runs there, SELF
for its own task, or a direct child's cgroup id. Changes inside a child's
subtree are not reported.

The op costs one pointer compare per context switch when the sched does not
change, a notification reaches only the scheds that see a change, and the
whole mechanism sits behind a static key that is on only while a loaded
sched implements the op. After a sched's tasks are gone, its disable closes
every rq session still pointing at it, so nothing refers to it once it is
freed.

The op is cid-form only like the other sub ops and runs with the rq lock
held on the context switch path.

Signed-off-by: Tejun Heo <tj@kernel.org>

0 files changed, 0 insertions, 0 deletions