cpu topology

cpu的拓扑结构的定义如下：
struct cpu_topology {
    int thread_id;
    int core_id;
    int cluster_id;
    cpumask_t thread_sibling;
    cpumask_t core_sibling;
};
可以看到cpu 拓扑结构相关的就是cluster/core/thread. 平时我们用lscpu看到就是这三个.
lscpu
Architecture:          aarch64
Byte Order:            Little Endian
CPU(s):                64
On-line CPU(s) list:   0-63
Thread(s) per core:    1
Core(s) per socket:    4
Socket(s):             16
NUMA node(s):          4
NUMA node0 CPU(s):     0-15
NUMA node1 CPU(s):     16-31
NUMA node2 CPU(s):     32-47
NUMA node3 CPU(s):     48-63
kernel_init_freeable->smp_prepare_cpus->init_cpu_topology 来从dts表中parse cluster/core/thread的值填到cpu_topology 结构体中
void __init init_cpu_topology(void)
{
    reset_cpu_topology();

    /*
     * Discard anything that was parsed if we hit an error so we
     * don't use partial information.
     */
    if (of_have_populated_dt() && parse_dt_topology())
        reset_cpu_topology();
}
init_cpu_topology 首先调用将cpu_topology 结构体清零
static void __init reset_cpu_topology(void)
{
    unsigned int cpu;

    for_each_possible_cpu(cpu) {
        struct cpu_topology *cpu_topo = &cpu_topology[cpu];

        cpu_topo->thread_id = -1;
        cpu_topo->core_id = 0;
        cpu_topo->cluster_id = -1;

        cpumask_clear(&cpu_topo->core_sibling);
        cpumask_set_cpu(cpu, &cpu_topo->core_sibling);
        cpumask_clear(&cpu_topo->thread_sibling);
        cpumask_set_cpu(cpu, &cpu_topo->thread_sibling);
    }
}
然后调用of_have_populated_dt（）判断当前是否有dts.判断的方法如下：
static inline bool of_have_populated_dt(void)
{
    return of_root != NULL;
}
从这个判断也可以看到当前4.9的kernel中的cpu topology 不支持ACPI传递.
of_have_populated_dt（）判断通过后就通过parse_dt_topology 来parse cluster/core/thread的值填到cpu_topology 结构体中。如果失败则调用reset_cpu_topology来清零
static int __init parse_dt_topology(void)
{
    struct device_node *cn, *map;
    int ret = 0;
    int cpu;

    cn = of_find_node_by_path("/cpus");
    if (!cn) {
        pr_err("No CPU information found in DT\n");
        return 0;
    }

    /*
     * When topology is provided cpu-map is essentially a root
     * cluster with restricted subnodes.
     */
    map = of_get_child_by_name(cn, "cpu-map");
    if (!map)
        goto out;

    ret = parse_cluster(map, 0);
    if (ret != 0)
        goto out_map;

    /*
     * Check that all cores are in the topology; the SMP code will
     * only mark cores described in the DT as possible.
     */
    for_each_possible_cpu(cpu)
        if (cpu_topology[cpu].cluster_id == -1)
            ret = -EINVAL;

out_map:
    of_node_put(map);
out:
    of_node_put(cn);
    return ret;
}
这个函数首先判断是否有/cpu这个节点，然后从cpu节点中找到cpu-map 这个子节点
然后调用parse_cluster来parse cluster
parse_cluster 先parse cluser再parse core
static int __init parse_core(struct device_node *core, int cluster_id,
                 int core_id)
{
    char name[10];
    bool leaf = true;
    int i = 0;
    int cpu;
    struct device_node *t;

    do {
        snprintf(name, sizeof(name), "thread%d", i);
        t = of_get_child_by_name(core, name);
        if (t) {
            leaf = false;
            cpu = get_cpu_for_node(t);
            if (cpu >= 0) {
                cpu_topology[cpu].cluster_id = cluster_id;
                cpu_topology[cpu].core_id = core_id;
                cpu_topology[cpu].thread_id = i;
            } else {
                pr_err("%s: Can't get CPU for thread\n",
                       t->full_name);
                of_node_put(t);
                return -EINVAL;
            }
            of_node_put(t);
        }
        i++;
    } while (t);

    cpu = get_cpu_for_node(core);
    if (cpu >= 0) {
        if (!leaf) {
            pr_err("%s: Core has both threads and CPU\n",
                   core->full_name);
            return -EINVAL;
        }

        cpu_topology[cpu].cluster_id = cluster_id;
        cpu_topology[cpu].core_id = core_id;
    } else if (leaf) {
        pr_err("%s: Can't get CPU for leaf core\n", core->full_name);
        return -EINVAL;
    }

    return 0;
}
最终在parse_core 函数中将dts中的到的信息填到cpu_topology 这个结构体中。