On Thu Dec 11, 2025 at 8:45 PM EST, Tejun Heo wrote:

Factor out local_dsq_post_enq() which performs post-enqueue handling for local DSQs - triggering resched_curr() if SCX_ENQ_PREEMPT is specified or if the current CPU is idle. No functional change.

This will be used by the next patch to fix move_local_task_to_local_dsq().

Cc: stable@vger.kernel.org # v6.12+ Reviewed-by: Andrea Righi arighi@nvidia.com Signed-off-by: Tejun Heo tj@kernel.org

---

Reviewed-by: Emil Tsalapatis emil@etsalapatis.com

kernel/sched/ext.c | 34 +++++++++++++++++++--------------- 1 file changed, 19 insertions(+), 15 deletions(-)

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c index c4465ccefea4..c78efa99406f 100644 --- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -982,6 +982,22 @@ static void refill_task_slice_dfl(struct scx_sched *sch, struct task_struct *p) __scx_add_event(sch, SCX_EV_REFILL_SLICE_DFL, 1); } +static void local_dsq_post_enq(struct scx_dispatch_q *dsq, struct task_struct *p,

• 	       u64 enq_flags)
  

+{

• struct rq *rq = container_of(dsq, struct rq, scx.local_dsq);
• bool preempt = false;
• if ((enq_flags & SCX_ENQ_PREEMPT) && p != rq->curr &&

•    rq->curr->sched_class == &ext_sched_class) {
  

• rq->curr->scx.slice = 0;
  

• preempt = true;
  

• }
• if (preempt || sched_class_above(&ext_sched_class, rq->curr->sched_class))

• resched_curr(rq);
  

+}

static void dispatch_enqueue(struct scx_sched *sch, struct scx_dispatch_q *dsq, struct task_struct *p, u64 enq_flags) { @@ -1093,22 +1109,10 @@ static void dispatch_enqueue(struct scx_sched *sch, struct scx_dispatch_q *dsq, if (enq_flags & SCX_ENQ_CLEAR_OPSS) atomic_long_set_release(&p->scx.ops_state, SCX_OPSS_NONE);

• if (is_local) {

• struct rq *rq = container_of(dsq, struct rq, scx.local_dsq);
  

• bool preempt = false;
  

• if ((enq_flags & SCX_ENQ_PREEMPT) && p != rq->curr &&
  

•     rq->curr->sched_class == &ext_sched_class) {
  

• 	rq->curr->scx.slice = 0;
  

• 	preempt = true;
  

• }
  

• if (preempt || sched_class_above(&ext_sched_class,
  

• 				 rq->curr->sched_class))
  

• 	resched_curr(rq);
  

• } else {

• if (is_local)

• local_dsq_post_enq(dsq, p, enq_flags);
  

• else raw_spin_unlock(&dsq->lock);

• }

} static void task_unlink_from_dsq(struct task_struct *p,

On Thu Dec 11, 2025 at 8:45 PM EST, Tejun Heo wrote:

move_local_task_to_local_dsq() is used when moving a task from a non-local DSQ to a local DSQ on the same CPU. It directly manipulates the local DSQ without going through dispatch_enqueue() and was missing the post-enqueue handling that triggers preemption when SCX_ENQ_PREEMPT is set or the idle task is running.

The function is used by move_task_between_dsqs() which backs scx_bpf_dsq_move() and may be called while the CPU is busy.

Add local_dsq_post_enq() call to move_local_task_to_local_dsq(). As the dispatch path doesn't need post-enqueue handling, add SCX_RQ_IN_BALANCE early exit to keep consume_dispatch_q() behavior unchanged and avoid triggering unnecessary resched when scx_bpf_dsq_move() is used from the dispatch path.

Fixes: 4c30f5ce4f7a ("sched_ext: Implement scx_bpf_dispatch[_vtime]_from_dsq()") Cc: stable@vger.kernel.org # v6.12+ Reviewed-by: Andrea Righi arighi@nvidia.com Signed-off-by: Tejun Heo tj@kernel.org

Reviewed-by: Emil Tsalapatis emil@etsalapatis.com

---

kernel/sched/ext.c | 10 ++++++++++ 1 file changed, 10 insertions(+)

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c index c78efa99406f..695503a2f7d1 100644 --- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -988,6 +988,14 @@ static void local_dsq_post_enq(struct scx_dispatch_q *dsq, struct task_struct *p struct rq *rq = container_of(dsq, struct rq, scx.local_dsq); bool preempt = false;

• /*

• * If @rq is in balance, the CPU is already vacant and looking for the
  

• * next task to run. No need to preempt or trigger resched after moving
  

• * @p into its local DSQ.
  

• */
  

• if (rq->scx.flags & SCX_RQ_IN_BALANCE)

• return;
  

• if ((enq_flags & SCX_ENQ_PREEMPT) && p != rq->curr && rq->curr->sched_class == &ext_sched_class) { rq->curr->scx.slice = 0;

@@ -1636,6 +1644,8 @@ static void move_local_task_to_local_dsq(struct task_struct *p, u64 enq_flags, dsq_mod_nr(dst_dsq, 1); p->scx.dsq = dst_dsq;

• local_dsq_post_enq(dst_dsq, p, enq_flags);

} /**