Replace the __SCX_CAP_DUMMY placeholder with SCX_CAP_ENQ_IMMED, which gates
inserting IMMED tasks onto a cid's local DSQ. An IMMED enqueue is guaranteed
to either get its task running on the cpu at once or hand it back to the
scheduler, so IMMED work can never pile up on the cpu's queue and a cpu can
be shared across sub-scheds through IMMED access without any of them
swamping it.
That makes ENQ_IMMED the natural baseline, the minimal cap to make any use
of a cpu. SCX_CAP_BASE aliases it so gates on basic cpu access can state the
intention instead of naming ENQ_IMMED.
Enforcement covers inserts and queued tasks. An insert without the cap is
diverted to the reject DSQ, and queued tasks are reenqueued when the cap is
lost. scx_bpf_sub_dispatch() skips a child that lacks the cap on the cpu, as
its inserts would only be rejected. Vacating the running task on cap loss
lands in a later patch.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
147d1885f3