[PATCH 5/7] sched_ext: idle: Introduce SCX_OPS_BUILTIN_IDLE_PER_NODE
From: Andrea Righi
Date: Wed Feb 12 2025 - 11:53:09 EST
Add the new scheduler flag SCX_OPS_BUILTIN_IDLE_PER_NODE, which allows
BPF schedulers to select between using a global flat idle cpumask or
multiple per-node cpumasks.
This only introduces the flag and the mechanism to enable/disable this
feature without affecting any scheduling behavior.
Cc: Yury Norov <yury.norov@xxxxxxxxx>
Signed-off-by: Andrea Righi <arighi@xxxxxxxxxx>
---
kernel/sched/ext.c | 21 ++++++++++++++++++--
kernel/sched/ext_idle.c | 29 +++++++++++++++++++++-------
kernel/sched/ext_idle.h | 4 ++--
tools/sched_ext/include/scx/compat.h | 3 +++
4 files changed, 46 insertions(+), 11 deletions(-)
diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index c47e7e2024a94..c3e154f0e8188 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -138,6 +138,12 @@ enum scx_ops_flags {
*/
SCX_OPS_ENQ_MIGRATION_DISABLED = 1LLU << 4,
+ /*
+ * If set, enable per-node idle cpumasks. If clear, use a single global
+ * flat idle cpumask.
+ */
+ SCX_OPS_BUILTIN_IDLE_PER_NODE = 1LLU << 5,
+
/*
* CPU cgroup support flags
*/
@@ -148,6 +154,7 @@ enum scx_ops_flags {
SCX_OPS_ENQ_EXITING |
SCX_OPS_ENQ_MIGRATION_DISABLED |
SCX_OPS_SWITCH_PARTIAL |
+ SCX_OPS_BUILTIN_IDLE_PER_NODE |
SCX_OPS_HAS_CGROUP_WEIGHT,
};
@@ -3409,7 +3416,7 @@ static void handle_hotplug(struct rq *rq, bool online)
atomic_long_inc(&scx_hotplug_seq);
if (scx_enabled())
- scx_idle_update_selcpu_topology();
+ scx_idle_update_selcpu_topology(&scx_ops);
if (online && SCX_HAS_OP(cpu_online))
SCX_CALL_OP(SCX_KF_UNLOCKED, cpu_online, cpu);
@@ -5184,6 +5191,16 @@ static int validate_ops(const struct sched_ext_ops *ops)
return -EINVAL;
}
+ /*
+ * SCX_OPS_BUILTIN_IDLE_PER_NODE requires built-in CPU idle
+ * selection policy to be enabled.
+ */
+ if ((ops->flags & SCX_OPS_BUILTIN_IDLE_PER_NODE) &&
+ (ops->update_idle && !(ops->flags & SCX_OPS_KEEP_BUILTIN_IDLE))) {
+ scx_ops_error("SCX_OPS_BUILTIN_IDLE_PER_NODE requires CPU idle selection enabled");
+ return -EINVAL;
+ }
+
return 0;
}
@@ -5308,7 +5325,7 @@ static int scx_ops_enable(struct sched_ext_ops *ops, struct bpf_link *link)
static_branch_enable_cpuslocked(&scx_has_op[i]);
check_hotplug_seq(ops);
- scx_idle_update_selcpu_topology();
+ scx_idle_update_selcpu_topology(ops);
cpus_read_unlock();
diff --git a/kernel/sched/ext_idle.c b/kernel/sched/ext_idle.c
index ed1804506585b..59b9e95238e97 100644
--- a/kernel/sched/ext_idle.c
+++ b/kernel/sched/ext_idle.c
@@ -14,6 +14,9 @@
/* Enable/disable built-in idle CPU selection policy */
static DEFINE_STATIC_KEY_FALSE(scx_builtin_idle_enabled);
+/* Enable/disable per-node idle cpumasks */
+static DEFINE_STATIC_KEY_FALSE(scx_builtin_idle_per_node);
+
#ifdef CONFIG_SMP
#ifdef CONFIG_CPUMASK_OFFSTACK
#define CL_ALIGNED_IF_ONSTACK
@@ -204,7 +207,7 @@ static bool llc_numa_mismatch(void)
* CPU belongs to a single LLC domain, and that each LLC domain is entirely
* contained within a single NUMA node.
*/
-void scx_idle_update_selcpu_topology(void)
+void scx_idle_update_selcpu_topology(struct sched_ext_ops *ops)
{
bool enable_llc = false, enable_numa = false;
unsigned int nr_cpus;
@@ -237,13 +240,19 @@ void scx_idle_update_selcpu_topology(void)
* If all CPUs belong to the same NUMA node and the same LLC domain,
* enabling both NUMA and LLC optimizations is unnecessary, as checking
* for an idle CPU in the same domain twice is redundant.
+ *
+ * If SCX_OPS_BUILTIN_IDLE_PER_NODE is enabled ignore the NUMA
+ * optimization, as we would naturally select idle CPUs within
+ * specific NUMA nodes querying the corresponding per-node cpumask.
*/
- nr_cpus = numa_weight(cpu);
- if (nr_cpus > 0) {
- if (nr_cpus < num_online_cpus() && llc_numa_mismatch())
- enable_numa = true;
- pr_debug("sched_ext: NUMA=%*pb weight=%u\n",
- cpumask_pr_args(numa_span(cpu)), numa_weight(cpu));
+ if (!(ops->flags & SCX_OPS_BUILTIN_IDLE_PER_NODE)) {
+ nr_cpus = numa_weight(cpu);
+ if (nr_cpus > 0) {
+ if (nr_cpus < num_online_cpus() && llc_numa_mismatch())
+ enable_numa = true;
+ pr_debug("sched_ext: NUMA=%*pb weight=%u\n",
+ cpumask_pr_args(numa_span(cpu)), numa_weight(cpu));
+ }
}
rcu_read_unlock();
@@ -530,6 +539,11 @@ void scx_idle_enable(struct sched_ext_ops *ops)
}
static_branch_enable(&scx_builtin_idle_enabled);
+ if (ops->flags & SCX_OPS_BUILTIN_IDLE_PER_NODE)
+ static_branch_enable(&scx_builtin_idle_per_node);
+ else
+ static_branch_disable(&scx_builtin_idle_per_node);
+
#ifdef CONFIG_SMP
/*
* Consider all online cpus idle. Should converge to the actual state
@@ -543,6 +557,7 @@ void scx_idle_enable(struct sched_ext_ops *ops)
void scx_idle_disable(void)
{
static_branch_disable(&scx_builtin_idle_enabled);
+ static_branch_disable(&scx_builtin_idle_per_node);
}
/********************************************************************************
diff --git a/kernel/sched/ext_idle.h b/kernel/sched/ext_idle.h
index bbac0fd9a5ddd..339b6ec9c4cb7 100644
--- a/kernel/sched/ext_idle.h
+++ b/kernel/sched/ext_idle.h
@@ -13,12 +13,12 @@
struct sched_ext_ops;
#ifdef CONFIG_SMP
-void scx_idle_update_selcpu_topology(void);
+void scx_idle_update_selcpu_topology(struct sched_ext_ops *ops);
void scx_idle_init_masks(void);
bool scx_idle_test_and_clear_cpu(int cpu);
s32 scx_pick_idle_cpu(const struct cpumask *cpus_allowed, u64 flags);
#else /* !CONFIG_SMP */
-static inline void scx_idle_update_selcpu_topology(void) {}
+static inline void scx_idle_update_selcpu_topology(struct sched_ext_ops *ops) {}
static inline void scx_idle_init_masks(void) {}
static inline bool scx_idle_test_and_clear_cpu(int cpu) { return false; }
static inline s32 scx_pick_idle_cpu(const struct cpumask *cpus_allowed, u64 flags)
diff --git a/tools/sched_ext/include/scx/compat.h b/tools/sched_ext/include/scx/compat.h
index b50280e2ba2ba..d63cf40be8eee 100644
--- a/tools/sched_ext/include/scx/compat.h
+++ b/tools/sched_ext/include/scx/compat.h
@@ -109,6 +109,9 @@ static inline bool __COMPAT_struct_has_field(const char *type, const char *field
#define SCX_OPS_SWITCH_PARTIAL \
__COMPAT_ENUM_OR_ZERO("scx_ops_flags", "SCX_OPS_SWITCH_PARTIAL")
+#define SCX_OPS_BUILTIN_IDLE_PER_NODE \
+ __COMPAT_ENUM_OR_ZERO("scx_ops_flags", "SCX_OPS_BUILTIN_IDLE_PER_NODE")
+
static inline long scx_hotplug_seq(void)
{
int fd;
--
2.48.1