sched_ext: idle: Introduce node-aware idle cpu kfunc helpers

Introduce a new kfunc to retrieve the node associated to a CPU:

 int scx_bpf_cpu_node(s32 cpu)

Add the following kfuncs to provide BPF schedulers direct access to
per-node idle cpumasks information:

 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)
 s32 scx_bpf_pick_any_cpu_node(const cpumask_t *cpus_allowed,
 			       int node, u64 flags)

Moreover, trigger an scx error when any of the non-node aware idle CPU
kfuncs are used when SCX_OPS_BUILTIN_IDLE_PER_NODE is enabled.

Cc: Yury Norov [NVIDIA] <yury.norov@gmail.com>
Signed-off-by: Andrea Righi <arighi@nvidia.com>
Reviewed-by: Yury Norov [NVIDIA] <yury.norov@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 182 insertions, 0 deletions

diff --git a/kernel/sched/ext_idle.c b/kernel/sched/ext_idle.c
index 8dacccc82ed6..759a06774b5b 100644
--- a/kernel/sched/ext_idle.c
+++ b/kernel/sched/ext_idle.c
@@ -728,6 +728,33 @@ void scx_idle_disable(void)
 /********************************************************************************
  * 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 -EOPNOTSUPP;
+	}
+
+	/* 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)
@@ -740,6 +767,23 @@ static bool check_builtin_idle_enabled(void)
 }
 
 /**
+ * scx_bpf_cpu_node - Return the NUMA node the given @cpu belongs to, or
+ *		      trigger an error if @cpu is invalid
+ * @cpu: target CPU
+ */
+__bpf_kfunc int scx_bpf_cpu_node(s32 cpu)
+{
+#ifdef CONFIG_NUMA
+	if (!ops_cpu_valid(cpu, NULL))
+		return NUMA_NO_NODE;
+
+	return 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
  * @prev_cpu: CPU @p was on previously
@@ -772,6 +816,28 @@ prev_cpu:
 }
 
 /**
+ * scx_bpf_get_idle_cpumask_node - Get a referenced kptr to the
+ * idle-tracking per-CPU cpumask of a target NUMA node.
+ * @node: 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.
  *
@@ -796,6 +862,32 @@ __bpf_kfunc const struct cpumask *scx_bpf_get_idle_cpumask(void)
 }
 
 /**
+ * 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.
+ * @node: 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_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
  * core is free.
@@ -860,6 +952,35 @@ __bpf_kfunc bool scx_bpf_test_and_clear_cpu_idle(s32 cpu)
 }
 
 /**
+ * scx_bpf_pick_idle_cpu_node - Pick and claim an idle cpu from @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
  * @flags: %SCX_PICK_IDLE_CPU_* flags
@@ -877,10 +998,18 @@ __bpf_kfunc bool scx_bpf_test_and_clear_cpu_idle(s32 cpu)
  *
  * Unavailable if ops.update_idle() is implemented and
  * %SCX_OPS_KEEP_BUILTIN_IDLE is not set.
+ *
+ * Always returns an error if %SCX_OPS_BUILTIN_IDLE_PER_NODE is set, use
+ * scx_bpf_pick_idle_cpu_node() instead.
  */
 __bpf_kfunc s32 scx_bpf_pick_idle_cpu(const struct cpumask *cpus_allowed,
 				      u64 flags)
 {
+	if (static_branch_maybe(CONFIG_NUMA, &scx_builtin_idle_per_node)) {
+		scx_ops_error("per-node idle tracking is enabled");
+		return -EBUSY;
+	}
+
 	if (!check_builtin_idle_enabled())
 		return -EBUSY;
 
@@ -888,6 +1017,46 @@ __bpf_kfunc s32 scx_bpf_pick_idle_cpu(const struct cpumask *cpus_allowed,
 }
 
 /**
+ * scx_bpf_pick_any_cpu_node - Pick and claim an idle cpu if available
+ *			       or pick any CPU from @node
+ * @cpus_allowed: Allowed cpumask
+ * @node: target NUMA node
+ * @flags: %SCX_PICK_IDLE_CPU_* flags
+ *
+ * Pick and claim an idle cpu in @cpus_allowed. If none is available, pick any
+ * CPU in @cpus_allowed. Guaranteed to succeed and returns the picked idle cpu
+ * number if @cpus_allowed is not empty. -%EBUSY is returned if @cpus_allowed is
+ * empty.
+ *
+ * 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).
+ *
+ * If ops.update_idle() is implemented and %SCX_OPS_KEEP_BUILTIN_IDLE is not
+ * set, this function can't tell which CPUs are idle and will always pick any
+ * CPU.
+ */
+__bpf_kfunc s32 scx_bpf_pick_any_cpu_node(const struct cpumask *cpus_allowed,
+					  int node, u64 flags)
+{
+	s32 cpu;
+
+	node = validate_node(node);
+	if (node < 0)
+		return node;
+
+	cpu = scx_pick_idle_cpu(cpus_allowed, node, flags);
+	if (cpu >= 0)
+		return cpu;
+
+	cpu = cpumask_any_distribute(cpus_allowed);
+	if (cpu < nr_cpu_ids)
+		return cpu;
+	else
+		return -EBUSY;
+}
+
+/**
  * scx_bpf_pick_any_cpu - Pick and claim an idle cpu if available or pick any CPU
  * @cpus_allowed: Allowed cpumask
  * @flags: %SCX_PICK_IDLE_CPU_* flags
@@ -900,12 +1069,20 @@ __bpf_kfunc s32 scx_bpf_pick_idle_cpu(const struct cpumask *cpus_allowed,
  * If ops.update_idle() is implemented and %SCX_OPS_KEEP_BUILTIN_IDLE is not
  * set, this function can't tell which CPUs are idle and will always pick any
  * CPU.
+ *
+ * Always returns an error if %SCX_OPS_BUILTIN_IDLE_PER_NODE is set, use
+ * scx_bpf_pick_any_cpu_node() instead.
  */
 __bpf_kfunc s32 scx_bpf_pick_any_cpu(const struct cpumask *cpus_allowed,
 				     u64 flags)
 {
 	s32 cpu;
 
+	if (static_branch_maybe(CONFIG_NUMA, &scx_builtin_idle_per_node)) {
+		scx_ops_error("per-node idle tracking is enabled");
+		return -EBUSY;
+	}
+
 	if (static_branch_likely(&scx_builtin_idle_enabled)) {
 		cpu = scx_pick_idle_cpu(cpus_allowed, NUMA_NO_NODE, flags);
 		if (cpu >= 0)
@@ -922,11 +1099,16 @@ __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_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_node, KF_RCU)
 BTF_ID_FLAGS(func, scx_bpf_pick_any_cpu, KF_RCU)
 BTF_KFUNCS_END(scx_kfunc_ids_idle)