[PATCH 2/2] sched_ext: Update demo schedulers and selftests to drop ops.cpu_acquire/release()

[Cheng-Yang Chou <yphbchou0911@gmail.com>]

ops.cpu_acquire() and ops.cpu_release() are deprecated in favor of
handling CPU preemption via the sched_switch tracepoint. Update scx_qmap
and the maximal selftest to use the new approach.

In scx_qmap, remove the cpu_release fallback and the
__COMPAT_scx_bpf_reenqueue_local_from_anywhere() compat guard from
qmap_sched_switch(), unconditionally handling preemption via the TP.

In the maximal selftest, replace the cpu_acquire and cpu_release stubs
with a minimal sched_switch TP program.

Signed-off-by: Cheng-Yang Chou <yphbchou0911@gmail.com>
---
 tools/sched_ext/scx_qmap.bpf.c                  | 15 ++-------------
 tools/testing/selftests/sched_ext/maximal.bpf.c | 15 ++++++---------
 2 files changed, 8 insertions(+), 22 deletions(-)

diff --git a/tools/sched_ext/scx_qmap.bpf.c b/tools/sched_ext/scx_qmap.bpf.c
index a4a1b84fe359..a11e27c8de77 100644
--- a/tools/sched_ext/scx_qmap.bpf.c
+++ b/tools/sched_ext/scx_qmap.bpf.c
@@ -11,8 +11,8 @@
  *
  * - BPF-side queueing using PIDs.
  * - Sleepable per-task storage allocation using ops.prep_enable().
- * - Using ops.cpu_release() to handle a higher priority scheduling class taking
- *   the CPU away.
+ * - Using the sched_switch tracepoint to handle a higher priority scheduling
+ *   class taking the CPU away.
  * - Core-sched support.
  *
  * This scheduler is primarily for demonstration and testing of sched_ext
@@ -562,9 +562,6 @@ SEC("tp_btf/sched_switch")
 int BPF_PROG(qmap_sched_switch, bool preempt, struct task_struct *prev,
 	     struct task_struct *next, unsigned long prev_state)
 {
-	if (!__COMPAT_scx_bpf_reenqueue_local_from_anywhere())
-		return 0;
-
 	/*
 	 * If @cpu is taken by a higher priority scheduling class, it is no
 	 * longer available for executing sched_ext tasks. As we don't want the
@@ -586,13 +583,6 @@ int BPF_PROG(qmap_sched_switch, bool preempt, struct task_struct *prev,
 	return 0;
 }
 
-void BPF_STRUCT_OPS(qmap_cpu_release, s32 cpu, struct scx_cpu_release_args *args)
-{
-	/* see qmap_sched_switch() to learn how to do this on newer kernels */
-	if (!__COMPAT_scx_bpf_reenqueue_local_from_anywhere())
-		scx_bpf_reenqueue_local();
-}
-
 s32 BPF_STRUCT_OPS(qmap_init_task, struct task_struct *p,
 		   struct scx_init_task_args *args)
 {
@@ -999,7 +989,6 @@ SCX_OPS_DEFINE(qmap_ops,
 	       .dispatch		= (void *)qmap_dispatch,
 	       .tick			= (void *)qmap_tick,
 	       .core_sched_before	= (void *)qmap_core_sched_before,
-	       .cpu_release		= (void *)qmap_cpu_release,
 	       .init_task		= (void *)qmap_init_task,
 	       .dump			= (void *)qmap_dump,
 	       .dump_cpu		= (void *)qmap_dump_cpu,
diff --git a/tools/testing/selftests/sched_ext/maximal.bpf.c b/tools/testing/selftests/sched_ext/maximal.bpf.c
index 01cf4f3da4e0..5858f64313e9 100644
--- a/tools/testing/selftests/sched_ext/maximal.bpf.c
+++ b/tools/testing/selftests/sched_ext/maximal.bpf.c
@@ -67,13 +67,12 @@ void BPF_STRUCT_OPS(maximal_set_cpumask, struct task_struct *p,
 void BPF_STRUCT_OPS(maximal_update_idle, s32 cpu, bool idle)
 {}
 
-void BPF_STRUCT_OPS(maximal_cpu_acquire, s32 cpu,
-		    struct scx_cpu_acquire_args *args)
-{}
-
-void BPF_STRUCT_OPS(maximal_cpu_release, s32 cpu,
-		    struct scx_cpu_release_args *args)
-{}
+SEC("tp_btf/sched_switch")
+int BPF_PROG(maximal_sched_switch, bool preempt, struct task_struct *prev,
+	     struct task_struct *next, unsigned long prev_state)
+{
+	return 0;
+}
 
 void BPF_STRUCT_OPS(maximal_cpu_online, s32 cpu)
 {}
@@ -150,8 +149,6 @@ struct sched_ext_ops maximal_ops = {
 	.set_weight		= (void *) maximal_set_weight,
 	.set_cpumask		= (void *) maximal_set_cpumask,
 	.update_idle		= (void *) maximal_update_idle,
-	.cpu_acquire		= (void *) maximal_cpu_acquire,
-	.cpu_release		= (void *) maximal_cpu_release,
 	.cpu_online		= (void *) maximal_cpu_online,
 	.cpu_offline		= (void *) maximal_cpu_offline,
 	.init_task		= (void *) maximal_init_task,
-- 
2.48.1