[PATCH 5/5] sched_ext: idle: Introduce node-aware idle cpu kfunc helpers

[Andrea Righi <arighi@nvidia.com>]

Add the following kfunc's to provide scx schedulers direct access to
per-node idle cpumasks information:

 int scx_bpf_cpu_to_node(s32 cpu)
 const struct cpumask *scx_bpf_get_idle_cpumask_node(int node)
 const struct cpumask *scx_bpf_get_idle_smtmask_node(int node)
 s32 scx_bpf_pick_idle_cpu_node(const cpumask_t *cpus_allowed,
				int node, u64 flags)

Signed-off-by: Andrea Righi <arighi@nvidia.com>
---
 kernel/sched/ext_idle.c                  | 121 +++++++++++++++++++++++
 tools/sched_ext/include/scx/common.bpf.h |   4 +
 tools/sched_ext/include/scx/compat.bpf.h |  19 ++++
 3 files changed, 144 insertions(+)

diff --git a/kernel/sched/ext_idle.c b/kernel/sched/ext_idle.c
index 0deef6987f76e..df8cd76c86fdd 100644
--- a/kernel/sched/ext_idle.c
+++ b/kernel/sched/ext_idle.c
@@ -680,6 +680,33 @@ void __scx_update_idle(struct rq *rq, bool idle, bool do_notify)
 /********************************************************************************
  * Helpers that can be called from the BPF scheduler.
  */
+
+static int validate_node(int node)
+{
+	if (!static_branch_likely(&scx_builtin_idle_per_node)) {
+		scx_ops_error("per-node idle tracking is disabled");
+		return -ENOTSUPP;
+	}
+
+	/* Return no entry for NUMA_NO_NODE (not a critical scx error) */
+	if (node == NUMA_NO_NODE)
+		return -ENOENT;
+
+	/* Make sure node is in a valid range */
+	if (node < 0 || node >= nr_node_ids) {
+		scx_ops_error("invalid node %d", node);
+		return -EINVAL;
+	}
+
+	/* Make sure the node is part of the set of possible nodes */
+	if (!node_possible(node)) {
+		scx_ops_error("unavailable node %d", node);
+		return -EINVAL;
+	}
+
+	return node;
+}
+
 __bpf_kfunc_start_defs();
 
 static bool check_builtin_idle_enabled(void)
@@ -691,6 +718,21 @@ static bool check_builtin_idle_enabled(void)
 	return false;
 }
 
+/**
+ * scx_bpf_cpu_to_node - Return the NUMA node the given @cpu belongs to
+ */
+__bpf_kfunc int scx_bpf_cpu_to_node(s32 cpu)
+{
+#ifdef CONFIG_NUMA
+	if (cpu < 0 || cpu >= nr_cpu_ids)
+		return -EINVAL;
+
+	return idle_cpu_to_node(cpu);
+#else
+	return 0;
+#endif
+}
+
 /**
  * scx_bpf_select_cpu_dfl - The default implementation of ops.select_cpu()
  * @p: task_struct to select a CPU for
@@ -723,6 +765,27 @@ __bpf_kfunc s32 scx_bpf_select_cpu_dfl(struct task_struct *p, s32 prev_cpu,
 	return prev_cpu;
 }
 
+/**
+ * scx_bpf_get_idle_cpumask_node - Get a referenced kptr to the
+ * idle-tracking per-CPU cpumask of a target NUMA node.
+ *
+ * Returns an empty cpumask if idle tracking is not enabled, if @node is
+ * not valid, or running on a UP kernel. In this case the actual error will
+ * be reported to the BPF scheduler via scx_ops_error().
+ */
+__bpf_kfunc const struct cpumask *scx_bpf_get_idle_cpumask_node(int node)
+{
+	node = validate_node(node);
+	if (node < 0)
+		return cpu_none_mask;
+
+#ifdef CONFIG_SMP
+	return idle_cpumask(node)->cpu;
+#else
+	return cpu_none_mask;
+#endif
+}
+
 /**
  * scx_bpf_get_idle_cpumask - Get a referenced kptr to the idle-tracking
  * per-CPU cpumask.
@@ -747,6 +810,31 @@ __bpf_kfunc const struct cpumask *scx_bpf_get_idle_cpumask(void)
 #endif
 }
 
+/**
+ * scx_bpf_get_idle_smtmask_node - Get a referenced kptr to the
+ * idle-tracking, per-physical-core cpumask of a target NUMA node. Can be
+ * used to determine if an entire physical core is free.
+ *
+ * Returns an empty cpumask if idle tracking is not enabled, if @node is
+ * not valid, or running on a UP kernel. In this case the actual error will
+ * be reported to the BPF scheduler via scx_ops_error().
+ */
+__bpf_kfunc const struct cpumask *scx_bpf_get_idle_smtmask_node(int node)
+{
+	node = validate_node(node);
+	if (node < 0)
+		return cpu_none_mask;
+
+#ifdef CONFIG_SMP
+	if (sched_smt_active())
+		return idle_cpumask(node)->smt;
+	else
+		return idle_cpumask(node)->cpu;
+#else
+	return cpu_none_mask;
+#endif
+}
+
 /**
  * scx_bpf_get_idle_smtmask - Get a referenced kptr to the idle-tracking,
  * per-physical-core cpumask. Can be used to determine if an entire physical
@@ -811,6 +899,35 @@ __bpf_kfunc bool scx_bpf_test_and_clear_cpu_idle(s32 cpu)
 		return false;
 }
 
+/**
+ * scx_bpf_pick_idle_cpu_node - Pick and claim an idle cpu from a NUMA node
+ * @cpus_allowed: Allowed cpumask
+ * @node: target NUMA node
+ * @flags: %SCX_PICK_IDLE_* flags
+ *
+ * Pick and claim an idle cpu in @cpus_allowed from the NUMA node @node.
+ *
+ * Returns the picked idle cpu number on success, or -%EBUSY if no matching
+ * cpu was found.
+ *
+ * The search starts from @node and proceeds to other online NUMA nodes in
+ * order of increasing distance (unless SCX_PICK_IDLE_IN_NODE is specified,
+ * in which case the search is limited to the target @node).
+ *
+ * Always returns an error if ops.update_idle() is implemented and
+ * %SCX_OPS_KEEP_BUILTIN_IDLE is not set, or if
+ * %SCX_OPS_BUILTIN_IDLE_PER_NODE is not set.
+ */
+__bpf_kfunc s32 scx_bpf_pick_idle_cpu_node(const struct cpumask *cpus_allowed,
+					   int node, u64 flags)
+{
+	node = validate_node(node);
+	if (node < 0)
+		return node;
+
+	return scx_pick_idle_cpu(cpus_allowed, node, flags);
+}
+
 /**
  * scx_bpf_pick_idle_cpu - Pick and claim an idle cpu
  * @cpus_allowed: Allowed cpumask
@@ -874,10 +991,14 @@ __bpf_kfunc s32 scx_bpf_pick_any_cpu(const struct cpumask *cpus_allowed,
 __bpf_kfunc_end_defs();
 
 BTF_KFUNCS_START(scx_kfunc_ids_idle)
+BTF_ID_FLAGS(func, scx_bpf_cpu_to_node)
+BTF_ID_FLAGS(func, scx_bpf_get_idle_cpumask_node, KF_ACQUIRE)
 BTF_ID_FLAGS(func, scx_bpf_get_idle_cpumask, KF_ACQUIRE)
+BTF_ID_FLAGS(func, scx_bpf_get_idle_smtmask_node, KF_ACQUIRE)
 BTF_ID_FLAGS(func, scx_bpf_get_idle_smtmask, KF_ACQUIRE)
 BTF_ID_FLAGS(func, scx_bpf_put_idle_cpumask, KF_RELEASE)
 BTF_ID_FLAGS(func, scx_bpf_test_and_clear_cpu_idle)
+BTF_ID_FLAGS(func, scx_bpf_pick_idle_cpu_node, KF_RCU)
 BTF_ID_FLAGS(func, scx_bpf_pick_idle_cpu, KF_RCU)
 BTF_ID_FLAGS(func, scx_bpf_pick_any_cpu, KF_RCU)
 BTF_KFUNCS_END(scx_kfunc_ids_idle)
diff --git a/tools/sched_ext/include/scx/common.bpf.h b/tools/sched_ext/include/scx/common.bpf.h
index 7055400030241..7dd8ba2964553 100644
--- a/tools/sched_ext/include/scx/common.bpf.h
+++ b/tools/sched_ext/include/scx/common.bpf.h
@@ -63,13 +63,17 @@ 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_cpu_ids(void) __ksym __weak;
+int scx_bpf_cpu_to_node(s32 cpu) __ksym __weak;
 const struct cpumask *scx_bpf_get_possible_cpumask(void) __ksym __weak;
 const struct cpumask *scx_bpf_get_online_cpumask(void) __ksym __weak;
 void scx_bpf_put_cpumask(const struct cpumask *cpumask) __ksym __weak;
+const struct cpumask *scx_bpf_get_idle_cpumask_node(int node) __ksym __weak;
 const struct cpumask *scx_bpf_get_idle_cpumask(void) __ksym;
+const struct cpumask *scx_bpf_get_idle_smtmask_node(int node) __ksym __weak;
 const struct cpumask *scx_bpf_get_idle_smtmask(void) __ksym;
 void scx_bpf_put_idle_cpumask(const struct cpumask *cpumask) __ksym;
 bool scx_bpf_test_and_clear_cpu_idle(s32 cpu) __ksym;
+s32 scx_bpf_pick_idle_cpu_node(const cpumask_t *cpus_allowed, int node, u64 flags) __ksym __weak;
 s32 scx_bpf_pick_idle_cpu(const cpumask_t *cpus_allowed, u64 flags) __ksym;
 s32 scx_bpf_pick_any_cpu(const cpumask_t *cpus_allowed, u64 flags) __ksym;
 bool scx_bpf_task_running(const struct task_struct *p) __ksym;
diff --git a/tools/sched_ext/include/scx/compat.bpf.h b/tools/sched_ext/include/scx/compat.bpf.h
index 50e1499ae0935..caa1a80f9a60c 100644
--- a/tools/sched_ext/include/scx/compat.bpf.h
+++ b/tools/sched_ext/include/scx/compat.bpf.h
@@ -130,6 +130,25 @@ bool scx_bpf_dispatch_vtime_from_dsq___compat(struct bpf_iter_scx_dsq *it__iter,
 	 scx_bpf_now() :							\
 	 bpf_ktime_get_ns())
 
+#define __COMPAT_scx_bpf_cpu_to_node(cpu)					\
+	(bpf_ksym_exists(scx_bpf_cpu_to_node) ?					\
+	 scx_bpf_cpu_to_node(cpu) : 0)
+
+#define __COMPAT_scx_bpf_get_idle_cpumask_node(node)				\
+	(bpf_ksym_exists(scx_bpf_get_idle_cpumask_node) ?			\
+	 scx_bpf_get_idle_cpumask_node(node) :					\
+	 scx_bpf_get_idle_cpumask())						\
+
+#define __COMPAT_scx_bpf_get_idle_smtmask_node(node)				\
+	(bpf_ksym_exists(scx_bpf_get_idle_smtmask_node) ?			\
+	 scx_bpf_get_idle_smtmask_node(node) :					\
+	 scx_bpf_get_idle_smtmask())
+
+#define __COMPAT_scx_bpf_pick_idle_cpu_node(cpus_allowed, node, flags)		\
+	(bpf_ksym_exists(scx_bpf_pick_idle_cpu_node) ?				\
+	 scx_bpf_pick_idle_cpu_node(cpus_allowed, node, flags) :		\
+	 scx_bpf_pick_idle_cpu(cpus_allowed, flags))
+
 /*
  * Define sched_ext_ops. This may be expanded to define multiple variants for
  * backward compatibility. See compat.h::SCX_OPS_LOAD/ATTACH().
-- 
2.48.1