sched_ext: scx_qmap: Add proxy execution support

Add a -X option to opt scx_qmap into queueing mutex-blocked tasks for
proxy execution. Without the option, SCX_OPS_ENQ_BLOCKED remains clear
and mutex waiters block normally. With -X, blocked donors are passed to
qmap_enqueue() with SCX_ENQ_BLOCKED.

When scx_qmap receives a blocked donor, select a cid allowed by the task
and held by qmap, preferring its current cid. Dispatch the donor to that
cid's local DSQ with a fresh slice and SCX_ENQ_PREEMPT, adding
SCX_ENQ_IMMED when the cid is time-shared. This places the donor at the
head of an eligible DSQ and requests an immediate reschedule, allowing
the core proxy-exec path to run the mutex owner using the donor's
scheduling context as soon as the donor is selected.

Partition ownership can change concurrently with enqueue, so the
self-cid intersection can disappear between the initial check and cid
selection. Validate the selected cid before indexing per-cid state or
constructing a local DSQ id, and fall back to rescue placement if the
intersection has disappeared.

The blocked policy is intentionally unfair and can strongly prioritize
tasks using contended mutexes, but scx_qmap is a demo scheduler and such
aggressive behavior makes proxy-exec support easy to observe. Count all
blocked dispatch attempts in nr_enq_blocked and report their
per-interval delta.

Acked-by: John Stultz <jstultz@google.com>
Signed-off-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

0 files changed, 0 insertions, 0 deletions