sched_ext: Fix processs_ddsp_deferred_locals() by unifying DTL_INVALID handling

With the preceding update, the only return value which makes meaningful
difference is DTL_INVALID, for which one caller, finish_dispatch(), falls
back to the global DSQ and the other, process_ddsp_deferred_locals(),
doesn't do anything.

It should always fallback to the global DSQ. Move the global DSQ fallback
into dispatch_to_local_dsq() and remove the return value.

v2: Patch title and description updated to reflect the behavior fix for
    process_ddsp_deferred_locals().

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: David Vernet <void@manifault.com>

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index fdb0986d8c76479689ef07461cbd03dbe0f7915b..3980f81fec5e872829495dfd7cfb6dc4cb57cabd 100644 (file)
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -2370,12 +2370,6 @@ retry:
        return false;
 }
 
-enum dispatch_to_local_dsq_ret {
-       DTL_DISPATCHED,         /* successfully dispatched */
-       DTL_LOST,               /* lost race to dequeue */
-       DTL_INVALID,            /* invalid local dsq_id */
-};
-
 /**
  * dispatch_to_local_dsq - Dispatch a task to a local dsq
  * @rq: current rq which is locked
@@ -2390,9 +2384,8 @@ enum dispatch_to_local_dsq_ret {
  * The caller must have exclusive ownership of @p (e.g. through
  * %SCX_OPSS_DISPATCHING).
  */
-static enum dispatch_to_local_dsq_ret
-dispatch_to_local_dsq(struct rq *rq, struct scx_dispatch_q *dst_dsq,
-                     struct task_struct *p, u64 enq_flags)
+static void dispatch_to_local_dsq(struct rq *rq, struct scx_dispatch_q *dst_dsq,
+                                 struct task_struct *p, u64 enq_flags)
 {
        struct rq *src_rq = task_rq(p);
        struct rq *dst_rq = container_of(dst_dsq, struct rq, scx.local_dsq);
@@ -2405,13 +2398,11 @@ dispatch_to_local_dsq(struct rq *rq, struct scx_dispatch_q *dst_dsq,
         */
        if (rq == src_rq && rq == dst_rq) {
                dispatch_enqueue(dst_dsq, p, enq_flags | SCX_ENQ_CLEAR_OPSS);
-               return DTL_DISPATCHED;
+               return;
        }
 
 #ifdef CONFIG_SMP
        if (likely(task_can_run_on_remote_rq(p, dst_rq, true))) {
-               bool dsp;
-
                /*
                 * @p is on a possibly remote @src_rq which we need to lock to
                 * move the task. If dequeue is in progress, it'd be locking
@@ -2436,10 +2427,8 @@ dispatch_to_local_dsq(struct rq *rq, struct scx_dispatch_q *dst_dsq,
                }
 
                /* task_rq couldn't have changed if we're still the holding cpu */
-               dsp = p->scx.holding_cpu == raw_smp_processor_id() &&
-                       !WARN_ON_ONCE(src_rq != task_rq(p));
-
-               if (likely(dsp)) {
+               if (likely(p->scx.holding_cpu == raw_smp_processor_id()) &&
+                   !WARN_ON_ONCE(src_rq != task_rq(p))) {
                        /*
                         * If @p is staying on the same rq, there's no need to
                         * go through the full deactivate/activate cycle.
@@ -2467,11 +2456,11 @@ dispatch_to_local_dsq(struct rq *rq, struct scx_dispatch_q *dst_dsq,
                        raw_spin_rq_lock(rq);
                }
 
-               return dsp ? DTL_DISPATCHED : DTL_LOST;
+               return;
        }
 #endif /* CONFIG_SMP */
 
-       return DTL_INVALID;
+       dispatch_enqueue(&scx_dsq_global, p, enq_flags | SCX_ENQ_CLEAR_OPSS);
 }
 
 /**
@@ -2548,20 +2537,10 @@ retry:
 
        dsq = find_dsq_for_dispatch(this_rq(), dsq_id, p);
 
-       if (dsq->id == SCX_DSQ_LOCAL) {
-               switch (dispatch_to_local_dsq(rq, dsq, p, enq_flags)) {
-               case DTL_DISPATCHED:
-                       break;
-               case DTL_LOST:
-                       break;
-               case DTL_INVALID:
-                       dispatch_enqueue(&scx_dsq_global, p,
-                                        enq_flags | SCX_ENQ_CLEAR_OPSS);
-                       break;
-               }
-       } else {
+       if (dsq->id == SCX_DSQ_LOCAL)
+               dispatch_to_local_dsq(rq, dsq, p, enq_flags);
+       else
                dispatch_enqueue(dsq, p, enq_flags | SCX_ENQ_CLEAR_OPSS);
-       }
 }
 
 static void flush_dispatch_buf(struct rq *rq)