sched_ext: Rename scx_bpf_consume() to scx_bpf_dsq_move_to_local()

In sched_ext API, a repeatedly reported pain point is the overuse of the
verb "dispatch" and confusion around "consume":

- ops.dispatch()
- scx_bpf_dispatch[_vtime]()
- scx_bpf_consume()
- scx_bpf_dispatch[_vtime]_from_dsq*()

This overloading of the term is historical. Originally, there were only
built-in DSQs and moving a task into a DSQ always dispatched it for
execution. Using the verb "dispatch" for the kfuncs to move tasks into these
DSQs made sense.

Later, user DSQs were added and scx_bpf_dispatch[_vtime]() updated to be
able to insert tasks into any DSQ. The only allowed DSQ to DSQ transfer was
from a non-local DSQ to a local DSQ and this operation was named "consume".
This was already confusing as a task could be dispatched to a user DSQ from
ops.enqueue() and then the DSQ would have to be consumed in ops.dispatch().
Later addition of scx_bpf_dispatch_from_dsq*() made the confusion even worse
as "dispatch" in this context meant moving a task to an arbitrary DSQ from a
user DSQ.

Clean up the API with the following renames:

1. scx_bpf_dispatch[_vtime]()		-> scx_bpf_dsq_insert[_vtime]()
2. scx_bpf_consume()			-> scx_bpf_dsq_move_to_local()
3. scx_bpf_dispatch[_vtime]_from_dsq*()	-> scx_bpf_dsq_move[_vtime]*()

This patch performs the second rename. Compatibility is maintained by:

- The previous kfunc names are still provided by the kernel so that old
  binaries can run. Kernel generates a warning when the old names are used.

- compat.bpf.h provides wrappers for the new names which automatically fall
  back to the old names when running on older kernels. They also trigger
  build error if old names are used for new builds.

The compat features will be dropped after v6.15.

v2: Comment and documentation updates.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Andrea Righi <arighi@nvidia.com>
Acked-by: Changwoo Min <changwoo@igalia.com>
Acked-by: Johannes Bechberger <me@mostlynerdless.de>
Acked-by: Giovanni Gherdovich <ggherdovich@suse.com>
Cc: Dan Schatzberg <dschatzberg@meta.com>
Cc: Ming Yang <yougmark94@gmail.com>

6 files changed, 20 insertions, 9 deletions

diff --git a/tools/sched_ext/include/scx/common.bpf.h b/tools/sched_ext/include/scx/common.bpf.h
index 16c7100c69e4..535377649a22 100644
--- a/tools/sched_ext/include/scx/common.bpf.h
+++ b/tools/sched_ext/include/scx/common.bpf.h
@@ -40,7 +40,7 @@ void scx_bpf_dsq_insert(struct task_struct *p, u64 dsq_id, u64 slice, u64 enq_fl
 void scx_bpf_dsq_insert_vtime(struct task_struct *p, u64 dsq_id, u64 slice, u64 vtime, u64 enq_flags) __ksym __weak;
 u32 scx_bpf_dispatch_nr_slots(void) __ksym;
 void scx_bpf_dispatch_cancel(void) __ksym;
-bool scx_bpf_consume(u64 dsq_id) __ksym;
+bool scx_bpf_dsq_move_to_local(u64 dsq_id) __ksym;
 void scx_bpf_dispatch_from_dsq_set_slice(struct bpf_iter_scx_dsq *it__iter, u64 slice) __ksym __weak;
 void scx_bpf_dispatch_from_dsq_set_vtime(struct bpf_iter_scx_dsq *it__iter, u64 vtime) __ksym __weak;
 bool scx_bpf_dispatch_from_dsq(struct bpf_iter_scx_dsq *it__iter, struct task_struct *p, u64 dsq_id, u64 enq_flags) __ksym __weak;
diff --git a/tools/sched_ext/include/scx/compat.bpf.h b/tools/sched_ext/include/scx/compat.bpf.h
index 183aa4c6f674..c00ed24a8721 100644
--- a/tools/sched_ext/include/scx/compat.bpf.h
+++ b/tools/sched_ext/include/scx/compat.bpf.h
@@ -43,6 +43,7 @@
  */
 void scx_bpf_dispatch___compat(struct task_struct *p, u64 dsq_id, u64 slice, u64 enq_flags) __ksym __weak;
 void scx_bpf_dispatch_vtime___compat(struct task_struct *p, u64 dsq_id, u64 slice, u64 vtime, u64 enq_flags) __ksym __weak;
+bool scx_bpf_consume___compat(u64 dsq_id) __ksym __weak;
 
 #define scx_bpf_dsq_insert(p, dsq_id, slice, enq_flags)				\
 	(bpf_ksym_exists(scx_bpf_dsq_insert) ?					\
@@ -54,12 +55,22 @@ void scx_bpf_dispatch_vtime___compat(struct task_struct *p, u64 dsq_id, u64 slic
 	 scx_bpf_dsq_insert_vtime((p), (dsq_id), (slice), (vtime), (enq_flags)) : \
 	 scx_bpf_dispatch_vtime___compat((p), (dsq_id), (slice), (vtime), (enq_flags)))
 
+#define scx_bpf_dsq_move_to_local(dsq_id)					\
+	(bpf_ksym_exists(scx_bpf_dsq_move_to_local) ?				\
+	 scx_bpf_dsq_move_to_local((dsq_id)) :					\
+	 scx_bpf_consume___compat((dsq_id)))
+
 #define scx_bpf_dispatch(p, dsq_id, slice, enq_flags)				\
 	_Static_assert(false, "scx_bpf_dispatch() renamed to scx_bpf_dsq_insert()")
 
 #define scx_bpf_dispatch_vtime(p, dsq_id, slice, vtime, enq_flags)		\
 	_Static_assert(false, "scx_bpf_dispatch_vtime() renamed to scx_bpf_dsq_insert_vtime()")
 
+#define scx_bpf_consume(dsq_id) ({						\
+	_Static_assert(false, "scx_bpf_consume() renamed to scx_bpf_dsq_move_to_local()"); \
+	false;									\
+})
+
 /*
  * Define sched_ext_ops. This may be expanded to define multiple variants for
  * backward compatibility. See compat.h::SCX_OPS_LOAD/ATTACH().
diff --git a/tools/sched_ext/scx_central.bpf.c b/tools/sched_ext/scx_central.bpf.c
index 153d9656c75f..e6fad6211f6c 100644
--- a/tools/sched_ext/scx_central.bpf.c
+++ b/tools/sched_ext/scx_central.bpf.c
@@ -219,13 +219,13 @@ void BPF_STRUCT_OPS(central_dispatch, s32 cpu, struct task_struct *prev)
 		}
 
 		/* look for a task to run on the central CPU */
-		if (scx_bpf_consume(FALLBACK_DSQ_ID))
+		if (scx_bpf_dsq_move_to_local(FALLBACK_DSQ_ID))
 			return;
 		dispatch_to_cpu(central_cpu);
 	} else {
 		bool *gimme;
 
-		if (scx_bpf_consume(FALLBACK_DSQ_ID))
+		if (scx_bpf_dsq_move_to_local(FALLBACK_DSQ_ID))
 			return;
 
 		gimme = ARRAY_ELEM_PTR(cpu_gimme_task, cpu, nr_cpu_ids);
diff --git a/tools/sched_ext/scx_flatcg.bpf.c b/tools/sched_ext/scx_flatcg.bpf.c
index 4dcb6c747b46..4e3afcd260bf 100644
--- a/tools/sched_ext/scx_flatcg.bpf.c
+++ b/tools/sched_ext/scx_flatcg.bpf.c
@@ -665,7 +665,7 @@ static bool try_pick_next_cgroup(u64 *cgidp)
 		goto out_free;
 	}
 
-	if (!scx_bpf_consume(cgid)) {
+	if (!scx_bpf_dsq_move_to_local(cgid)) {
 		bpf_cgroup_release(cgrp);
 		stat_inc(FCG_STAT_PNC_EMPTY);
 		goto out_stash;
@@ -745,7 +745,7 @@ void BPF_STRUCT_OPS(fcg_dispatch, s32 cpu, struct task_struct *prev)
 		goto pick_next_cgroup;
 
 	if (vtime_before(now, cpuc->cur_at + cgrp_slice_ns)) {
-		if (scx_bpf_consume(cpuc->cur_cgid)) {
+		if (scx_bpf_dsq_move_to_local(cpuc->cur_cgid)) {
 			stat_inc(FCG_STAT_CNS_KEEP);
 			return;
 		}
@@ -785,7 +785,7 @@ void BPF_STRUCT_OPS(fcg_dispatch, s32 cpu, struct task_struct *prev)
 pick_next_cgroup:
 	cpuc->cur_at = now;
 
-	if (scx_bpf_consume(FALLBACK_DSQ)) {
+	if (scx_bpf_dsq_move_to_local(FALLBACK_DSQ)) {
 		cpuc->cur_cgid = 0;
 		return;
 	}
diff --git a/tools/sched_ext/scx_qmap.bpf.c b/tools/sched_ext/scx_qmap.bpf.c
index 65c52cc4fffb..08f121252c56 100644
--- a/tools/sched_ext/scx_qmap.bpf.c
+++ b/tools/sched_ext/scx_qmap.bpf.c
@@ -374,7 +374,7 @@ void BPF_STRUCT_OPS(qmap_dispatch, s32 cpu, struct task_struct *prev)
 	if (dispatch_highpri(false))
 		return;
 
-	if (!nr_highpri_queued && scx_bpf_consume(SHARED_DSQ))
+	if (!nr_highpri_queued && scx_bpf_dsq_move_to_local(SHARED_DSQ))
 		return;
 
 	if (dsp_inf_loop_after && nr_dispatched > dsp_inf_loop_after) {
@@ -439,7 +439,7 @@ void BPF_STRUCT_OPS(qmap_dispatch, s32 cpu, struct task_struct *prev)
 			if (!batch || !scx_bpf_dispatch_nr_slots()) {
 				if (dispatch_highpri(false))
 					return;
-				scx_bpf_consume(SHARED_DSQ);
+				scx_bpf_dsq_move_to_local(SHARED_DSQ);
 				return;
 			}
 			if (!cpuc->dsp_cnt)
diff --git a/tools/sched_ext/scx_simple.bpf.c b/tools/sched_ext/scx_simple.bpf.c
index ce86a4a690b5..31f915b286c6 100644
--- a/tools/sched_ext/scx_simple.bpf.c
+++ b/tools/sched_ext/scx_simple.bpf.c
@@ -94,7 +94,7 @@ void BPF_STRUCT_OPS(simple_enqueue, struct task_struct *p, u64 enq_flags)
 
 void BPF_STRUCT_OPS(simple_dispatch, s32 cpu, struct task_struct *prev)
 {
-	scx_bpf_consume(SHARED_DSQ);
+	scx_bpf_dsq_move_to_local(SHARED_DSQ);
 }
 
 void BPF_STRUCT_OPS(simple_running, struct task_struct *p)