sched_ext: s/SCX_RQ_BALANCING/SCX_RQ_IN_BALANCE/ and add SCX_RQ_IN_WAKEUP

SCX_RQ_BALANCING is used to mark that the rq is currently in balance().
Rename it to SCX_RQ_IN_BALANCE and add SCX_RQ_IN_WAKEUP which marks whether
the rq is currently enqueueing for a wakeup. This will be used to implement
direct dispatching to local DSQ of another CPU.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: David Vernet <void@manifault.com>

kernel/sched/ext.c

@@ -1827,6 +1827,9 @@ static void enqueue_task_scx(struct rq *rq, struct task_struct *p, int enq_flags
 {
 	int sticky_cpu = p->scx.sticky_cpu;
 
+	if (enq_flags & ENQUEUE_WAKEUP)
+		rq->scx.flags |= SCX_RQ_IN_WAKEUP;
+
 	enq_flags |= rq->scx.extra_enq_flags;
 
 	if (sticky_cpu >= 0)
@@ -1843,7 +1846,7 @@ static void enqueue_task_scx(struct rq *rq, struct task_struct *p, int enq_flags
 
 	if (p->scx.flags & SCX_TASK_QUEUED) {
 		WARN_ON_ONCE(!task_runnable(p));
-		return;
+		goto out;
 	}
 
 	set_task_runnable(rq, p);
@@ -1858,6 +1861,8 @@ static void enqueue_task_scx(struct rq *rq, struct task_struct *p, int enq_flags
 		touch_core_sched(rq, p);
 
 	do_enqueue_task(rq, p, enq_flags, sticky_cpu);
+out:
+	rq->scx.flags &= ~SCX_RQ_IN_WAKEUP;
 }
 
 static void ops_dequeue(struct task_struct *p, u64 deq_flags)
@@ -2420,7 +2425,7 @@ static int balance_one(struct rq *rq, struct task_struct *prev, bool local)
 	bool has_tasks = false;
 
 	lockdep_assert_rq_held(rq);
-	rq->scx.flags |= SCX_RQ_BALANCING;
+	rq->scx.flags |= SCX_RQ_IN_BALANCE;
 
 	if (static_branch_unlikely(&scx_ops_cpu_preempt) &&
 	    unlikely(rq->scx.cpu_released)) {
@@ -2514,7 +2519,7 @@ static int balance_one(struct rq *rq, struct task_struct *prev, bool local)
 has_tasks:
 	has_tasks = true;
 out:
-	rq->scx.flags &= ~SCX_RQ_BALANCING;
+	rq->scx.flags &= ~SCX_RQ_IN_BALANCE;
 	return has_tasks;
 }
 
@@ -5063,7 +5068,7 @@ static bool can_skip_idle_kick(struct rq *rq)
 	 * The race window is small and we don't and can't guarantee that @rq is
 	 * only kicked while idle anyway. Skip only when sure.
 	 */
-	return !is_idle_task(rq->curr) && !(rq->scx.flags & SCX_RQ_BALANCING);
+	return !is_idle_task(rq->curr) && !(rq->scx.flags & SCX_RQ_IN_BALANCE);
 }
 
 static bool kick_one_cpu(s32 cpu, struct rq *this_rq, unsigned long *pseqs)

kernel/sched/sched.h

@@ -737,8 +737,10 @@ enum scx_rq_flags {
 	 * only while the BPF scheduler considers the CPU to be online.
 	 */
 	SCX_RQ_ONLINE		= 1 << 0,
-	SCX_RQ_BALANCING	= 1 << 1,
-	SCX_RQ_CAN_STOP_TICK	= 1 << 2,
+	SCX_RQ_CAN_STOP_TICK	= 1 << 1,
+
+	SCX_RQ_IN_WAKEUP	= 1 << 16,
+	SCX_RQ_IN_BALANCE	= 1 << 17,
 };
 
 struct scx_rq {