聊聊Linux内核进程调度上篇

// 省略大部分字段，着重描述下运行队列中的一些字段
struct rq {
    // 每个CPU的运行队列的锁
    raw_spinlock_t lock;
    // 运行队列的进程数
    unsigned int nr_running;
    // 当前CPU上的负载
    struct load_weight load;
    // 进程切换的次数
    u64 nr_switches;
    // 公平调度器
    struct cfs_rq cfs;
    // 实时调度器
    struct rt_rq rt;
    // deadline调度器
    struct dl_rq dl;
    unsigned long nr_uninterruptible;
    // 正在运行的进程任务
    struct task_struct *curr;
    // 空闲的进程任务
    struct task_struct *idle;
    // 停止的进程任务
    struct task_struct *stop;
    unsigned long next_balance;
};

static void __sched notrace __schedule(bool preempt)
{
    next = pick_next_task(rq, prev, &rf);
}

// 选择一个优先级最高的进程执行
static inline struct task_struct *pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
{
    const struct sched_class *class;
    struct task_struct *p;

    if (likely((prev->sched_class == &idle_sched_class ||
                prev->sched_class == &fair_sched_class) &&
               rq->nr_running == rq->cfs.h_nr_running)) {
        p = fair_sched_class.pick_next_task(rq, prev, rf);
        if (unlikely(p == RETRY_TASK))
            goto again;
        if (unlikely(!p))
            p = idle_sched_class.pick_next_task(rq, prev, rf);
        return p;
    }

again:
    for_each_class(class) {
        p = class->pick_next_task(rq, prev, rf);
        if (p) {
            if (unlikely(p == RETRY_TASK))
                goto again;
            return p;
        }
    }
    BUG();
}