[PATCH 10/10] sched_ext: idle: Introduce NUMA aware idle cpu kfunc helpers

Andrea Righi
2024-12-20T15:42:00Z

Add the following kfunc's to provide scx 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)
int scx_bpf_cpu_to_node(s32 cpu)

Signed-off-by: Andrea Righi <arighi@nvidia.com>
---
kernel/sched/ext_idle.c | 163 ++++++++++++++++++++---
tools/sched_ext/include/scx/common.bpf.h | 4 +
tools/sched_ext/include/scx/compat.bpf.h | 19 +++
3 files changed, 170 insertions(+), 16 deletions(-)

diff --git a/kernel/sched/ext_idle.c b/kernel/sched/ext_idle.c
index b36e93da1b75..0f8ccc1e290e 100644
--- a/kernel/sched/ext_idle.c
+++ b/kernel/sched/ext_idle.c
@@ -28,6 +28,60 @@ static bool check_builtin_idle_enabled(void)
return false;
}

+static bool check_builtin_idle_per_node_enabled(void)
+{
+ if (static_branch_likely(&scx_builtin_idle_per_node))
+ return true;
+
+ scx_ops_error("per-node idle tracking is disabled");
+ return false;
+}
+
+/*
+ * Validate and resolve a NUMA node.
+ *
+ * Return the resolved node ID on success or a negative value otherwise.
+ */
+static int validate_node(int node)
+{
+ if (!check_builtin_idle_per_node_enabled())
+ return -EINVAL;
+
+ /* If no node is specified, use the current one */
+ if (node == NUMA_NO_NODE)
+ return numa_node_id();
+
+ /* Make sure node is in a valid range */
+ if (node < 0 || node >= nr_node_ids) {
+ scx_ops_error("invalid node %d", node);
+ return -ENOENT;
+ }
+
+ /* 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;
+}
+
+/*
+ * Return the node id associated to a target idle CPU (used to determine
+ * the proper idle cpumask).
+ */
+static int idle_cpu_to_node(int cpu)
+{
+ int node;
+
+ if (static_branch_maybe(CONFIG_NUMA, &scx_builtin_idle_per_node))
+ node = cpu_to_node(cpu);
+ else
+ node = NUMA_FLAT_NODE;
+
+ return node;
+}
+
#ifdef CONFIG_SMP
struct idle_cpumask {
cpumask_var_t cpu;
@@ -83,22 +137,6 @@ static void idle_masks_init(void)

static DEFINE_STATIC_KEY_FALSE(scx_selcpu_topo_llc);

-/*
- * Return the node id associated to a target idle CPU (used to determine
- * the proper idle cpumask).
- */
-static int idle_cpu_to_node(int cpu)
-{
- int node;
-
- if (static_branch_maybe(CONFIG_NUMA, &scx_builtin_idle_per_node))
- node = cpu_to_node(cpu);
- else
- node = NUMA_FLAT_NODE;
-
- return node;
-}
-
static bool test_and_clear_cpu_idle(int cpu)
{
int node = idle_cpu_to_node(cpu);
@@ -613,6 +651,17 @@ static void reset_idle_masks(void) {}
*/
__bpf_kfunc_start_defs();

+/**
+ * scx_bpf_cpu_to_node - Return the NUMA node the given @cpu belongs to
+ */
+__bpf_kfunc int scx_bpf_cpu_to_node(s32 cpu)
+{
+ if (cpu < 0 || cpu >= nr_cpu_ids)
+ return -EINVAL;
+
+ return idle_cpu_to_node(cpu);
+}
+
/**
* scx_bpf_select_cpu_dfl - The default implementation of ops.select_cpu()
* @p: task_struct to select a CPU for
@@ -645,6 +694,28 @@ __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.
+ *
+ * NUMA_NO_NODE is interpreted as the current node.
+ *
+ * Returns an empty cpumask if idle tracking is not enabled, if @node is not
+ * valid, or running on a UP kernel.
+ */
+__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 get_idle_cpumask(node);
+#else
+ return cpu_none_mask;
+#endif
+}
+
/**
* scx_bpf_get_idle_cpumask - Get a referenced kptr to the idle-tracking
* per-CPU cpumask.
@@ -664,6 +735,32 @@ __bpf_kfunc const struct cpumask *scx_bpf_get_idle_cpumask(void)
return get_idle_cpumask(NUMA_FLAT_NODE);
}

+/**
+ * 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.
+ *
+ * NUMA_NO_NODE is interpreted as the current node.
+ *
+ * Returns an empty cpumask if idle tracking is not enabled, if @node is not
+ * valid, or running on a UP kernel.
+ */
+__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 get_idle_smtmask(node);
+ else
+ return get_idle_cpumask(node);
+#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
@@ -722,6 +819,36 @@ __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_CPU_* flags
+ *
+ * Pick and claim an idle cpu in @cpus_allowed from the NUMA node @node.
+ * Returns the picked idle cpu number on success. -%EBUSY if no matching cpu
+ * was found.
+ *
+ * If @node is NUMA_NO_NODE, the search is restricted to the current NUMA
+ * node. Otherwise, the search starts from @node and proceeds to other
+ * online NUMA nodes in order of increasing distance (unless
+ * SCX_PICK_IDLE_NODE is specified, in which case the search is limited to
+ * the target @node).
+ *
+ * Unavailable if ops.update_idle() is implemented and
+ * %SCX_OPS_KEEP_BUILTIN_IDLE is not set or if %SCX_OPS_KEEP_BUILTIN_IDLE 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
@@ -785,11 +912,15 @@ __bpf_kfunc s32 scx_bpf_pick_any_cpu(const struct cpumask *cpus_allowed,
__bpf_kfunc_end_defs();

BTF_KFUNCS_START(scx_kfunc_ids_select_cpu)
+BTF_ID_FLAGS(func, scx_bpf_cpu_to_node)
BTF_ID_FLAGS(func, scx_bpf_select_cpu_dfl, KF_RCU)
+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_select_cpu)
diff --git a/tools/sched_ext/include/scx/common.bpf.h b/tools/sched_ext/include/scx/common.bpf.h
index 858ba1f438f6..fe0433f7c4d9 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 d56520100a26..dfc329d5a91e 100644
--- a/tools/sched_ext/include/scx/compat.bpf.h
+++ b/tools/sched_ext/include/scx/compat.bpf.h
@@ -125,6 +125,25 @@ bool scx_bpf_dispatch_vtime_from_dsq___compat(struct bpf_iter_scx_dsq *it__iter,
false; \
})

+#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().
--
2.47.1