1. 程序排程類初始化

建立程序時，程序排程類的初始化在函式sched_fork()中進行

(kernel/sched/core.c)

int sched_fork(unsigned long clone_flags, struct task_struct *p)
{
    unsigned long flags;
    int cpu = get_cpu();

    __sched_fork(clone_flags, p);
    /*
     * We mark the process as running here. This guarantees that
     * nobody will actually run
 
 it, and a signal or other external
     * event cannot wake it up and insert it on the runqueue either.
     */
    p->state = TASK_RUNNING;---------------------------------------程序執行狀態設定

    /*
     * Make sure we do not leak PI boosting priority to the child.
     */
    p->prio = current->normal_prio;--------------------------------程序初始優先順序
 


    /*
     * Revert to default priority/policy on fork if requested.
     */
    if (unlikely(p->sched_reset_on_fork)) {
        if (task_has_dl_policy(p) || task_has_rt_policy(p)) {
            p->policy = SCHED_NORMAL;
            p->static_prio = NICE_TO_PRIO(0);
            p->rt_priority = 0
 
;
        } else if (PRIO_TO_NICE(p->static_prio) < 0)
            p->static_prio = NICE_TO_PRIO(0);---------------------靜態優先順序

        p->prio = p->normal_prio = __normal_prio(p);
        set_load_weight(p);

        /*
         * We don't need the reset flag anymore after the fork. It has
         * fulfilled its duty:
         */
        p->sched_reset_on_fork = 0;
    }

    if (dl_prio(p->prio)) {
        put_cpu();
        return -EAGAIN;
    } else if (rt_prio(p->prio)) {
        p->sched_class = &rt_sched_class;--------------------\
    } else {                                                  \
        p->sched_class = &fair_sched_class;---------------------排程類設定
    }

    if (p->sched_class->task_fork)
        p->sched_class->task_fork(p);

    /*
     * The child is not yet in the pid-hash so no cgroup attach races,
     * and the cgroup is pinned to this child due to cgroup_fork()
     * is ran before sched_fork().
     *
     * Silence PROVE_RCU.
     */
    raw_spin_lock_irqsave(&p->pi_lock, flags);
    set_task_cpu(p, cpu);-------------------------------------設定程序到某CPU
    raw_spin_unlock_irqrestore(&p->pi_lock, flags);

#ifdef CONFIG_SCHED_INFO
    if (likely(sched_info_on()))
        memset(&p->sched_info, 0, sizeof(p->sched_info));
#endif
#if defined(CONFIG_SMP)
    p->on_cpu = 0;
#endif
    init_task_preempt_count(p);
#ifdef CONFIG_SMP
    plist_node_init(&p->pushable_tasks, MAX_PRIO);
    RB_CLEAR_NODE(&p->pushable_dl_tasks);
#endif

    put_cpu();
    return 0;
}

2. 執行佇列

系統的所有就緒佇列都在runqueues陣列中，陣列元素個數與cpu個數相關

DECLARE_PER_CPU_SHARED_ALIGNED(struct rq, runqueues);

核心中與佇列相關的一些巨集定義如下：

#define cpu_rq(cpu)     (&per_cpu(runqueues, (cpu)))
#define this_rq()       this_cpu_ptr(&runqueues)
#define task_rq(p)      cpu_rq(task_cpu(p))
#define cpu_curr(cpu)       (cpu_rq(cpu)->curr)
#define raw_rq()        raw_cpu_ptr(&runqueues)

執行佇列結構體如下：

struct rq {
    /* runqueue lock: */
    raw_spinlock_t lock;

    /*
     * nr_running and cpu_load should be in the same cacheline because
     * remote CPUs use both these fields when doing load calculation.
     */
    unsigned int nr_running;
#ifdef CONFIG_NUMA_BALANCING
    unsigned int nr_numa_running;
    unsigned int nr_preferred_running;
#endif
    #define CPU_LOAD_IDX_MAX 5
    unsigned long cpu_load[CPU_LOAD_IDX_MAX];
    unsigned long last_load_update_tick;
#ifdef CONFIG_NO_HZ_COMMON
    u64 nohz_stamp;
    unsigned long nohz_flags;
#endif
#ifdef CONFIG_NO_HZ_FULL
    unsigned long last_sched_tick;
#endif
    /* capture load from *all* tasks on this cpu: */
    struct load_weight load;
    unsigned long nr_load_updates;
    u64 nr_switches;

    struct cfs_rq cfs;
    struct rt_rq rt;
    struct dl_rq dl;

#ifdef CONFIG_FAIR_GROUP_SCHED
    /* list of leaf cfs_rq on this cpu: */
    struct list_head leaf_cfs_rq_list;
#endif /* CONFIG_FAIR_GROUP_SCHED */

    /*
     * This is part of a global counter where only the total sum
     * over all CPUs matters. A task can increase this counter on
     * one CPU and if it got migrated afterwards it may decrease
     * it on another CPU. Always updated under the runqueue lock:
     */
    unsigned long nr_uninterruptible;

    struct task_struct *curr, *idle, *stop;
    unsigned long next_balance;
    struct mm_struct *prev_mm;

    unsigned int clock_skip_update;
    u64 clock;
    u64 clock_task;

    atomic_t nr_iowait;

#ifdef CONFIG_SMP
    struct root_domain *rd;
    struct sched_domain *sd;

    unsigned long cpu_capacity;
    unsigned long cpu_capacity_orig;

    struct callback_head *balance_callback;

    unsigned char idle_balance;
    /* For active balancing */
    int active_balance;
    int push_cpu;
    struct cpu_stop_work active_balance_work;
    /* cpu of this runqueue: */
    int cpu;
    int online;

    struct list_head cfs_tasks;

    u64 rt_avg;
    u64 age_stamp;
    u64 idle_stamp;
    u64 avg_idle;

    /* This is used to determine avg_idle's max value */
    u64 max_idle_balance_cost;
#endif

#ifdef CONFIG_IRQ_TIME_ACCOUNTING
    u64 prev_irq_time;
#endif
#ifdef CONFIG_PARAVIRT
    u64 prev_steal_time;
#endif
#ifdef CONFIG_PARAVIRT_TIME_ACCOUNTING
    u64 prev_steal_time_rq;
#endif

    /* calc_load related fields */
    unsigned long calc_load_update;
    long calc_load_active;

#ifdef CONFIG_SCHED_HRTICK
#ifdef CONFIG_SMP
    int hrtick_csd_pending;
    struct call_single_data hrtick_csd;
#endif
    struct hrtimer hrtick_timer;
#endif

#ifdef CONFIG_SCHEDSTATS
    /* latency stats */
    struct sched_info rq_sched_info;
    unsigned long long rq_cpu_time;
    /* could above be rq->cfs_rq.exec_clock + rq->rt_rq.rt_runtime ? */

    /* sys_sched_yield() stats */
    unsigned int yld_count;

    /* schedule() stats */
    unsigned int sched_count;
    unsigned int sched_goidle;

    /* try_to_wake_up() stats */
    unsigned int ttwu_count;
    unsigned int ttwu_local;
#endif

#ifdef CONFIG_SMP
    struct llist_head wake_list;
#endif

#ifdef CONFIG_CPU_IDLE
    /* Must be inspected within a rcu lock section */
    struct cpuidle_state *idle_state;
#endif
};

3. 排程類

核心中的排程類有下面幾項：

• 空閒排程類：kernel/sehed/idle.c
• 公平排程類：kernel/sehed/fair.c
• 實時排程類：kernel/sehed/rt.c
• 最後期限排程類：kernel/sehed/deadline.c

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