【Linux 内核】CPU 分类与状态 ( CPU 处理器分类 | 根据物理属性分类 SMT、MC、SoC | Linux 内核中 CPU 分类 | Linux 内核源码中的 CPU 状态源码 )

一、CPU 处理器分类

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1、根据物理属性分类 ( SMT、MC、SoC )

根据 CPU 的物理属性 , 可以将 CPU 分为如下几类 :

• SMT : 全称 " Simultaneous Multithreading " , 同时多线程 , 又称为 " 超线程 " , 一个物理核心 , 可以有 $2$ 个执行线程 , 使用相同的 CPU 资源 , 共享 L1 Cache 缓存 ;
• MC : Multicore 多核 , 每个物理核心 独享一个 L1 Cache 缓存 ;
• SoC : System on Chip , 系统级芯片 ;

2、Linux 内核中 CPU 分类

Linux 内核中 , 对 CPU 处理器的分类 :

• CONFIG_SCHED_SMT : 对应 SMT 芯片 , " 超线程 " , 一个物理核心 , 可以有 $2$ 个执行线程 , 使用相同的 CPU 资源 , 共享 L1 Cache 缓存 ;
• CONFIG_SCHED_MC : 对应 MC 多核芯片 , 每个物理核心 独享一个 L1 Cache 缓存 ;
• DIE : 对应 SoC 芯片 ;

二、Linux 内核源码中的 CPU 状态源码

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Linux 内核中 , 通过 bitmap 管理 CPU 处理器 , 并且在 Linux 源码中的 linux-5.6.18\include\linux\cpumask.h 头文件源码中 , 定义了 CPU 的四种状态 :

• cpu_possible_mask : 表示系统中 可以执行的 CPU 核心个数 , 可执行指的是现在可以运行 以及 将来某个时间段可以运行 ;
• cpu_online_mask : 表示当前系统中 有多少个正在运行的 CPU 核心个数 ;
• cpu_present_mask : 表示当前系统中 有多少个具备 online 条件的 CPU 核心个数 , 不一定都处于 online 状态 ;
• cpu_active_mask : 表示当前系统中 有多少个活跃的 CPU 核心 ;

/*
 * The following particular system cpumasks and operations manage
 * possible, present, active and online cpus.
 *
 *     cpu_possible_mask- has bit 'cpu' set iff cpu is populatable
 *     cpu_present_mask - has bit 'cpu' set iff cpu is populated
 *     cpu_online_mask  - has bit 'cpu' set iff cpu available to scheduler
 *     cpu_active_mask  - has bit 'cpu' set iff cpu available to migration
 *
 *  If !CONFIG_HOTPLUG_CPU, present == possible, and active == online.
 *
 *  The cpu_possible_mask is fixed at boot time, as the set of CPU id's
 *  that it is possible might ever be plugged in at anytime during the
 *  life of that system boot.  The cpu_present_mask is dynamic(*),
 *  representing which CPUs are currently plugged in.  And
 *  cpu_online_mask is the dynamic subset of cpu_present_mask,
 *  indicating those CPUs available for scheduling.
 *
 *  If HOTPLUG is enabled, then cpu_possible_mask is forced to have
 *  all NR_CPUS bits set, otherwise it is just the set of CPUs that
 *  ACPI reports present at boot.
 *
 *  If HOTPLUG is enabled, then cpu_present_mask varies dynamically,
 *  depending on what ACPI reports as currently plugged in, otherwise
 *  cpu_present_mask is just a copy of cpu_possible_mask.
 *
 *  (*) Well, cpu_present_mask is dynamic in the hotplug case.  If not
 *      hotplug, it's a copy of cpu_possible_mask, hence fixed at boot.
 *
 * Subtleties:
 * 1) UP arch's (NR_CPUS == 1, CONFIG_SMP not defined) hardcode
 *    assumption that their single CPU is online.  The UP
 *    cpu_{online,possible,present}_masks are placebos.  Changing them
 *    will have no useful affect on the following num_*_cpus()
 *    and cpu_*() macros in the UP case.  This ugliness is a UP
 *    optimization - don't waste any instructions or memory references
 *    asking if you're online or how many CPUs there are if there is
 *    only one CPU.
 */

extern struct cpumask __cpu_possible_mask;
extern struct cpumask __cpu_online_mask;
extern struct cpumask __cpu_present_mask;
extern struct cpumask __cpu_active_mask;
#define cpu_possible_mask ((const struct cpumask *)&__cpu_possible_mask)
#define cpu_online_mask   ((const struct cpumask *)&__cpu_online_mask)
#define cpu_present_mask  ((const struct cpumask *)&__cpu_present_mask)
#define cpu_active_mask   ((const struct cpumask *)&__cpu_active_mask)