[PATCH 2/8] sched/topology: introduce sched_numa_find_next_cpu()

Yury Norov
2023-03-25T18:55:44Z

The function searches for the next CPU in a given cpumask according to
NUMA topology, so that it traverses cpus per-hop.

If the CPU is the last cpu in a given hop, sched_numa_find_next_cpu()
switches to the next hop, and picks the first CPU from there, excluding
those already traversed.

Signed-off-by: Yury Norov <yury.norov@gmail.com>
---
include/linux/topology.h | 7 +++++++
kernel/sched/topology.c | 39 +++++++++++++++++++++++++++++++++++++++
2 files changed, 46 insertions(+)

diff --git a/include/linux/topology.h b/include/linux/topology.h
index fea32377f7c7..4a63154fa036 100644
--- a/include/linux/topology.h
+++ b/include/linux/topology.h
@@ -247,6 +247,7 @@ static inline const struct cpumask *cpu_cpu_mask(int cpu)

#ifdef CONFIG_NUMA
int sched_numa_find_nth_cpu(const struct cpumask *cpus, int cpu, int node);
+int sched_numa_find_next_cpu(const struct cpumask *cpus, int cpu, int node, unsigned int *hop);
extern const struct cpumask *sched_numa_hop_mask(unsigned int node, unsigned int hops);
#else
static __always_inline int sched_numa_find_nth_cpu(const struct cpumask *cpus, int cpu, int node)
@@ -254,6 +255,12 @@ static __always_inline int sched_numa_find_nth_cpu(const struct cpumask *cpus, i
return cpumask_nth(cpu, cpus);
}

+static __always_inline
+int sched_numa_find_next_cpu(const struct cpumask *cpus, int cpu, int node, unsigned int *hop)
+{
+ return find_next_bit(cpumask_bits(cpus), small_cpumask_bits, cpu);
+}
+
static inline const struct cpumask *
sched_numa_hop_mask(unsigned int node, unsigned int hops)
{
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 051aaf65c749..1860d9487fe1 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -2130,6 +2130,45 @@ int sched_numa_find_nth_cpu(const struct cpumask *cpus, int cpu, int node)
}
EXPORT_SYMBOL_GPL(sched_numa_find_nth_cpu);

+/*
+ * sched_numa_find_next_cpu() - given the NUMA topology, find the next cpu
+ * cpumask: cpumask to find a cpu from
+ * cpu: current cpu
+ * node: local node
+ * hop: (in/out) indicates distance order of current CPU to a local node
+ *
+ * The function searches for next cpu at a given NUMA distance, indicated
+ * by hop, and if nothing found, tries to find CPUs at a greater distance,
+ * starting from the beginning.
+ *
+ * returns: cpu, or >= nr_cpu_ids when nothing found.
+ */
+int sched_numa_find_next_cpu(const struct cpumask *cpus, int cpu, int node, unsigned int *hop)
+{
+ unsigned long *cur, *prev;
+ struct cpumask ***masks;
+ unsigned int ret;
+
+ if (*hop >= sched_domains_numa_levels)
+ return nr_cpu_ids;
+
+ masks = rcu_dereference(sched_domains_numa_masks);
+ cur = cpumask_bits(masks[*hop][node]);
+ if (*hop == 0)
+ ret = find_next_and_bit(cpumask_bits(cpus), cur, nr_cpu_ids, cpu);
+ else {
+ prev = cpumask_bits(masks[*hop - 1][node]);
+ ret = find_next_and_andnot_bit(cpumask_bits(cpus), cur, prev, nr_cpu_ids, cpu);
+ }
+
+ if (ret < nr_cpu_ids)
+ return ret;
+
+ *hop += 1;
+ return sched_numa_find_next_cpu(cpus, 0, node, hop);
+}
+EXPORT_SYMBOL_GPL(sched_numa_find_next_cpu);
+
/**
* sched_numa_hop_mask() - Get the cpumask of CPUs at most @hops hops away from
* @node
--
2.34.1