sched_ext: Add reject DSQ for cap-rejected dispatches

When a sub-scheduler dispatches a task to a CPU it lacks the required
capability on, the task must be rejected rather than allowed to run.

Add the machinery for that. Each rq gets a reject DSQ, a kernel-internal
holding queue that is never run and that the BPF scheduler cannot reach. An
insert that must be refused is diverted there instead of the local DSQ, and
a deferred requeue then hands the parked tasks back to the BPF scheduler to
re-decide. A cap revoke extends this to already-queued tasks. When the
revoke reaches the cpu's effective caps, the cpu scans its local DSQ and
reenqueues the tasks that no longer qualify.

A migration-disabled task must run on its cpu, so a capless one is admitted
anyway and counted in the new SCX_EV_SUB_FORCED_ADMIT event.

This is preparation for the actual sub-sched cap enforcement. The divert is
wired but inert here.

v2: Admit offline-rq and migration_pending inserts to local, not reject. (sashiko AI)

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

0 files changed, 0 insertions, 0 deletions