sched_ext: Remove scx_ops_allow_queued_wakeup static_key

scx_ops_allow_queued_wakeup is used to encode SCX_OPS_ALLOW_QUEUED_WAKEUP
into a static_key. The test is gated behind scx_enabled(), and, even when
sched_ext is enabled, is unlikely for the static_key usage to make any
meaningful difference. It is made to use a static_key mostly because there
was no reason not to. However, global static_keys can't work with the
planned hierarchical multiple scheduler support. Remove the static_key and
instead test SCX_OPS_ALLOW_QUEUED_WAKEUP directly.

In repeated hackbench runs before and after static_keys removal on an AMD
Ryzen 3900X, I couldn't tell any measurable performance difference.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Changwoo Min <changwoo@igalia.com>
Acked-by: Andrea Righi <arighi@nvidia.com>

1 files changed, 7 insertions, 5 deletions

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 1adf5c299cce..f0ed0cec4c98 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -928,8 +928,6 @@ DEFINE_STATIC_KEY_FALSE(__scx_switched_all);
 static struct sched_ext_ops scx_ops;
 static bool scx_warned_zero_slice;
 
-DEFINE_STATIC_KEY_FALSE(scx_ops_allow_queued_wakeup);
-
 static struct static_key_false scx_has_op[SCX_OPI_END] =
 	{ [0 ... SCX_OPI_END-1] = STATIC_KEY_FALSE_INIT };
 
@@ -4414,6 +4412,13 @@ bool task_should_scx(int policy)
 	return policy == SCHED_EXT;
 }
 
+bool scx_allow_ttwu_queue(const struct task_struct *p)
+{
+	return !scx_enabled() ||
+		(scx_ops.flags & SCX_OPS_ALLOW_QUEUED_WAKEUP) ||
+		p->sched_class != &ext_sched_class;
+}
+
 /**
  * scx_softlockup - sched_ext softlockup handler
  * @dur_s: number of seconds of CPU stuck due to soft lockup
@@ -4728,7 +4733,6 @@ static void scx_disable_workfn(struct kthread_work *work)
 	static_branch_disable(&__scx_enabled);
 	for (i = SCX_OPI_BEGIN; i < SCX_OPI_END; i++)
 		static_branch_disable(&scx_has_op[i]);
-	static_branch_disable(&scx_ops_allow_queued_wakeup);
 	scx_idle_disable();
 	synchronize_rcu();
 
@@ -5367,8 +5371,6 @@ static int scx_enable(struct sched_ext_ops *ops, struct bpf_link *link)
 		if (((void (**)(void))ops)[i])
 			static_branch_enable(&scx_has_op[i]);
 
-	if (ops->flags & SCX_OPS_ALLOW_QUEUED_WAKEUP)
-		static_branch_enable(&scx_ops_allow_queued_wakeup);
 	if (scx_ops.cpu_acquire || scx_ops.cpu_release)
 		scx_ops.flags |= SCX_OPS_HAS_CPU_PREEMPT;