sched_ext: Rename scx_bpf_dispatch[_vtime]() to scx_bpf_dsq_insert[_vtime]()

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 first set of renames. 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: 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>

2 files changed, 28 insertions, 2 deletions

diff --git a/tools/sched_ext/include/scx/common.bpf.h b/tools/sched_ext/include/scx/common.bpf.h
index 248ab790d143..16c7100c69e4 100644
--- a/tools/sched_ext/include/scx/common.bpf.h
+++ b/tools/sched_ext/include/scx/common.bpf.h
@@ -36,8 +36,8 @@ static inline void ___vmlinux_h_sanity_check___(void)
 
 s32 scx_bpf_create_dsq(u64 dsq_id, s32 node) __ksym;
 s32 scx_bpf_select_cpu_dfl(struct task_struct *p, s32 prev_cpu, u64 wake_flags, bool *is_idle) __ksym;
-void scx_bpf_dispatch(struct task_struct *p, u64 dsq_id, u64 slice, u64 enq_flags) __ksym;
-void scx_bpf_dispatch_vtime(struct task_struct *p, u64 dsq_id, u64 slice, u64 vtime, u64 enq_flags) __ksym;
+void scx_bpf_dsq_insert(struct task_struct *p, u64 dsq_id, u64 slice, u64 enq_flags) __ksym __weak;
+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;
diff --git a/tools/sched_ext/include/scx/compat.bpf.h b/tools/sched_ext/include/scx/compat.bpf.h
index e5afe9efd3f3..183aa4c6f674 100644
--- a/tools/sched_ext/include/scx/compat.bpf.h
+++ b/tools/sched_ext/include/scx/compat.bpf.h
@@ -35,6 +35,32 @@
 	 scx_bpf_dispatch_vtime_from_dsq((it), (p), (dsq_id), (enq_flags)) : false)
 
 /*
+ * v6.13: The verb `dispatch` was too overloaded and confusing. kfuncs are
+ * renamed to unload the verb.
+ *
+ * Build error is triggered if old names are used. New binaries work with both
+ * new and old names. The compat macros will be removed on v6.15 release.
+ */
+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;
+
+#define scx_bpf_dsq_insert(p, dsq_id, slice, enq_flags)				\
+	(bpf_ksym_exists(scx_bpf_dsq_insert) ?					\
+	 scx_bpf_dsq_insert((p), (dsq_id), (slice), (enq_flags)) :		\
+	 scx_bpf_dispatch___compat((p), (dsq_id), (slice), (enq_flags)))
+
+#define scx_bpf_dsq_insert_vtime(p, dsq_id, slice, vtime, enq_flags)		\
+	(bpf_ksym_exists(scx_bpf_dsq_insert_vtime) ?				\
+	 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_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 sched_ext_ops. This may be expanded to define multiple variants for
  * backward compatibility. See compat.h::SCX_OPS_LOAD/ATTACH().
  */