sched_ext: idle: Introduce scx_bpf_nr_node_ids()

Similarly to scx_bpf_nr_cpu_ids(), introduce a new kfunc
scx_bpf_nr_node_ids() to expose the maximum number of NUMA nodes in the
system.

BPF schedulers can use this information together with the new node-aware
kfuncs, for example to create per-node DSQs, validate node IDs, etc.

Signed-off-by: Andrea Righi <[email protected]>
Signed-off-by: Tejun Heo <[email protected]>

Author: arighi

kernel/sched/ext.c

@@ -7113,6 +7113,16 @@ __bpf_kfunc void scx_bpf_cpuperf_set(s32 cpu, u32 perf)
 	}
 }
 
+/**
+ * scx_bpf_nr_node_ids - Return the number of possible node IDs
+ *
+ * All valid node IDs in the system are smaller than the returned value.
+ */
+__bpf_kfunc u32 scx_bpf_nr_node_ids(void)
+{
+	return nr_node_ids;
+}
+
 /**
  * scx_bpf_nr_cpu_ids - Return the number of possible CPU IDs
  *
@@ -7325,6 +7335,7 @@ BTF_ID_FLAGS(func, scx_bpf_dump_bstr, KF_TRUSTED_ARGS)
 BTF_ID_FLAGS(func, scx_bpf_cpuperf_cap)
 BTF_ID_FLAGS(func, scx_bpf_cpuperf_cur)
 BTF_ID_FLAGS(func, scx_bpf_cpuperf_set)
+BTF_ID_FLAGS(func, scx_bpf_nr_node_ids)
 BTF_ID_FLAGS(func, scx_bpf_nr_cpu_ids)
 BTF_ID_FLAGS(func, scx_bpf_get_possible_cpumask, KF_ACQUIRE)
 BTF_ID_FLAGS(func, scx_bpf_get_online_cpumask, KF_ACQUIRE)

tools/sched_ext/include/scx/common.bpf.h

@@ -70,6 +70,7 @@ void scx_bpf_dump_bstr(char *fmt, unsigned long long *data, u32 data_len) __ksym
 u32 scx_bpf_cpuperf_cap(s32 cpu) __ksym __weak;
 u32 scx_bpf_cpuperf_cur(s32 cpu) __ksym __weak;
 void scx_bpf_cpuperf_set(s32 cpu, u32 perf) __ksym __weak;
+u32 scx_bpf_nr_node_ids(void) __ksym __weak;
 u32 scx_bpf_nr_cpu_ids(void) __ksym __weak;
 int scx_bpf_cpu_node(s32 cpu) __ksym __weak;
 const struct cpumask *scx_bpf_get_possible_cpumask(void) __ksym __weak;

tools/sched_ext/include/scx/compat.bpf.h

@@ -189,6 +189,10 @@ static inline bool __COMPAT_is_enq_cpu_selected(u64 enq_flags)
  *
  * Preserve the following __COMPAT_scx_*_node macros until v6.17.
  */
+#define __COMPAT_scx_bpf_nr_node_ids()						\
+	(bpf_ksym_exists(scx_bpf_nr_node_ids) ?					\
+	 scx_bpf_nr_node_ids() : 1U)
+
 #define __COMPAT_scx_bpf_cpu_node(cpu)						\
 	(bpf_ksym_exists(scx_bpf_cpu_node) ?					\
 	 scx_bpf_cpu_node(cpu) : 0)