[RFC PATCH v3 05/13] MIPS: Initialize sbm topology on multi-node systems

[K Prateek Nayak]

For MIPS systems that support NUMA, configure the sparsebitmap (sbm)
topology.

The two systems that toggle NUMA - loongson64 and sgi-ip27, find the
number of nodes and the maximum threads present in an instance. The
data structures used to parse the topology are marked __initdata to
allow reclaim post init.

In both cases - loongson64 and sgi-ip27, loongson3_smp_setup() and
node_scan_cpus() sets node IDs for all possible CPUs ensuring
configure_sbm_topology() captures the full possible system.

arch_sbm_cpu_instance_id() returns the cpu_to_node() mapping to derive
the instance ID and group the CPUs sharing the node on the same sbm
instance (leaf).

Signed-off-by: K Prateek Nayak <kprateek.nayak@xxxxxxx>
---
Tested on QEMU with loongson3_defconfig from
https://gitlab.postmarketos.org/royka1/linux/-/blob/apollo-7.1.0-r3/arch/mips/configs/loongson3_defconfig?ref_type=tags

QEMU cmdline:

  qemu-system-mips64el \
  -M loongson3-virt,accel=tcg \
  -smp sockets=2,cores=4 \
  -cpu Loongson-3A1000 \
  -kernel vmlinux \
  -append "console=ttyS0 root=/dev/ram" \
  -nographic
---
 arch/mips/include/asm/topology.h |  6 +++++
 arch/mips/kernel/topology.c      | 43 ++++++++++++++++++++++++++++++++
 arch/mips/loongson64/smp.c       |  3 +++
 arch/mips/sgi-ip27/ip27-smp.c    |  3 +++
 4 files changed, 55 insertions(+)

diff --git a/arch/mips/include/asm/topology.h b/arch/mips/include/asm/topology.h
index 5158c802eb65..7a57cbd59819 100644
--- a/arch/mips/include/asm/topology.h
+++ b/arch/mips/include/asm/topology.h
@@ -21,4 +21,10 @@ extern struct cpumask __cpu_primary_thread_mask;
 #define cpu_primary_thread_mask ((const struct cpumask *)&__cpu_primary_thread_mask)
 #endif
 
+#ifdef CONFIG_NUMA
+extern void configure_sbm_topology(void);
+#else /* !CONFIG_NUMA */
+static void __maybe_unused configure_sbm_topology(void) { }
+#endif /* CONFIG_NUMA */
+
 #endif /* __ASM_TOPOLOGY_H */
diff --git a/arch/mips/kernel/topology.c b/arch/mips/kernel/topology.c
index 9429d85a4703..729a811e8b99 100644
--- a/arch/mips/kernel/topology.c
+++ b/arch/mips/kernel/topology.c
@@ -5,9 +5,52 @@
 #include <linux/node.h>
 #include <linux/nodemask.h>
 #include <linux/percpu.h>
+#include <linux/sbm.h>
 
 static DEFINE_PER_CPU(struct cpu, cpu_devices);
 
+#ifdef CONFIG_NUMA
+/* sbm setup data - only needed during init */
+static struct cpumask cpu_sbm_setup_map __initdata;
+static int __node_thread_count[NR_CPUS] __initdata;
+
+int arch_sbm_cpu_instance_id(int cpu)
+{
+	return cpu_to_node(cpu);
+}
+
+void __init configure_sbm_topology(void)
+{
+	int num_sbm_instances, max_threads_per_instance = 1;
+	int i;
+
+	for_each_possible_cpu(i) {
+		bool found = false;
+		int j;
+
+		for_each_cpu(j, &cpu_sbm_setup_map) {
+			if (cpu_to_node(i) == cpu_to_node(j)) {
+				found = true;
+				break;
+			}
+		}
+
+		if (!found) {
+			cpumask_set_cpu(i, &cpu_sbm_setup_map);
+			__node_thread_count[i] = 1;
+			continue;
+		}
+
+		__node_thread_count[j] += 1;
+		max_threads_per_instance = max(max_threads_per_instance,
+					       __node_thread_count[j]);
+	}
+
+	num_sbm_instances = cpumask_weight(&cpu_sbm_setup_map);
+	sbm_set_topology(num_sbm_instances, max_threads_per_instance);
+}
+#endif /* CONFIG_NUMA */
+
 static int __init topology_init(void)
 {
 	int i, ret;
diff --git a/arch/mips/loongson64/smp.c b/arch/mips/loongson64/smp.c
index e584299d0fde..22174ae2b574 100644
--- a/arch/mips/loongson64/smp.c
+++ b/arch/mips/loongson64/smp.c
@@ -17,6 +17,7 @@
 #include <asm/smp.h>
 #include <asm/time.h>
 #include <asm/tlbflush.h>
+#include <asm/topology.h>
 #include <asm/cacheflush.h>
 #include <loongson.h>
 #include <loongson_regs.h>
@@ -493,6 +494,8 @@ static void __init loongson3_smp_setup(void)
 	if (smp_group[0])
 		ipi_write_enable(0);
 
+	configure_sbm_topology();
+
 	cpu_set_core(&cpu_data[0],
 		     cpu_logical_map(0) % loongson_sysconf.cores_per_package);
 	cpu_data[0].package = cpu_logical_map(0) / loongson_sysconf.cores_per_package;
diff --git a/arch/mips/sgi-ip27/ip27-smp.c b/arch/mips/sgi-ip27/ip27-smp.c
index 62733e049570..244f8d987f13 100644
--- a/arch/mips/sgi-ip27/ip27-smp.c
+++ b/arch/mips/sgi-ip27/ip27-smp.c
@@ -15,6 +15,7 @@
 #include <asm/page.h>
 #include <asm/processor.h>
 #include <asm/ptrace.h>
+#include <asm/topology.h>
 #include <asm/sn/agent.h>
 #include <asm/sn/arch.h>
 #include <asm/sn/gda.h>
@@ -80,6 +81,8 @@ void cpu_node_probe(void)
 		highest = node_scan_cpus(nasid, highest);
 	}
 
+	configure_sbm_topology();
+
 	printk("Discovered %d cpus on %d nodes\n", highest + 1, num_online_nodes());
 }
 
-- 
2.34.1