一，调度类
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1.1 调度类结构体:struct sched_class
//kernel/sched/sched.hstruct sched_class { const struct sched_class *next; void (*enqueue_task) (struct rq *rq, struct task_struct *p, int flags); void (*dequeue_task) (struct rq *rq, struct task_struct *p, int flags); void (*yield_task) (struct rq *rq); bool (*yield_to_task)(struct rq *rq, struct task_struct *p, bool preempt); void (*check_preempt_curr)(struct rq *rq, struct task_struct *p, int flags); /* * It is the responsibility of the pick_next_task() method that will * return the next task to call put_prev_task() on the @prev task or * something equivalent. * * May return RETRY_TASK when it finds a higher prio class has runnable * tasks. */ struct task_struct * (*pick_next_task)(struct rq *rq, struct task_struct *prev, struct rq_flags *rf); void (*put_prev_task)(struct rq *rq, struct task_struct *p); #ifdef CONFIG_SMP int (*select_task_rq)(struct task_struct *p, int task_cpu, int sd_flag, int flags); void (*migrate_task_rq)(struct task_struct *p, int new_cpu); void (*task_woken)(struct rq *this_rq, struct task_struct *task); void (*set_cpus_allowed)(struct task_struct *p, const struct cpumask *newmask); void (*rq_online)(struct rq *rq); void (*rq_offline)(struct rq *rq);#endif void (*set_curr_task)(struct rq *rq); void (*task_tick)(struct rq *rq, struct task_struct *p, int queued); void (*task_fork)(struct task_struct *p); void (*task_dead)(struct task_struct *p); /* * The switched_from() call is allowed to drop rq->lock, therefore we * cannot assume the switched_from/switched_to pair is serliazed by * rq->lock. They are however serialized by p->pi_lock. */ void (*switched_from)(struct rq *this_rq, struct task_struct *task); void (*switched_to) (struct rq *this_rq, struct task_struct *task); void (*prio_changed) (struct rq *this_rq, struct task_struct *task, int oldprio); unsigned int (*get_rr_interval)(struct rq *rq, struct task_struct *task); void (*update_curr)(struct rq *rq); #define TASK_SET_GROUP 0#define TASK_MOVE_GROUP 1 #ifdef CONFIG_FAIR_GROUP_SCHED void (*task_change_group)(struct task_struct *p, int type);#endif};
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enqueue_task：向就绪队列添加一个新进程。在进程从睡眠状态变为可运行状态时，即发生该操作。
dequeue_task：将一个进程从就绪队列去除。在进程从可运行状态切换到不可运行状态时，就会发生该操作。
yield_task：在进程想要自愿放弃对处理器的控制权时，可以使用 sched_yield 系统调用。这导致内核调用 yield_task。
check_preempt_curr：用一个新唤醒的进程来抢占当前进程。例如在用 wake_up_new_task 唤醒信进程时，会调用该函数。
pick_next_task：用于选择下一个将要运行的进程。
set_curr_task：在进程的调度策略发生变化时，需要调用 set_curr_task。还有其他一些场合也调用该函数。
task_tick：在每次激活周期性调度器时，由周期性调度器调用。
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1.2 停机调度类：stop_sched_class
//kernel/sched/stop_task.c/* * Simple, special scheduling class for the per-CPU stop tasks: */const struct sched_class stop_sched_class = { .next = &dl_sched_class, .enqueue_task = enqueue_task_stop, .dequeue_task = dequeue_task_stop, .yield_task = yield_task_stop, .check_preempt_curr = check_preempt_curr_stop, .pick_next_task = pick_next_task_stop, .put_prev_task = put_prev_task_stop, #ifdef CONFIG_SMP .select_task_rq = select_task_rq_stop, .set_cpus_allowed = set_cpus_allowed_common,#endif .set_curr_task = set_curr_task_stop, .task_tick = task_tick_stop, .get_rr_interval = get_rr_interval_stop, .prio_changed = prio_changed_stop, .switched_to = switched_to_stop, .update_curr = update_curr_stop,};
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1.3 限期调度类：dl_sched_class
//kernel/sched/deadline.cconst struct sched_class dl_sched_class = { .next = &rt_sched_class, .enqueue_task = enqueue_task_dl, .dequeue_task = dequeue_task_dl, .yield_task = yield_task_dl, .check_preempt_curr = check_preempt_curr_dl, .pick_next_task = pick_next_task_dl, .put_prev_task = put_prev_task_dl, #ifdef CONFIG_SMP .select_task_rq = select_task_rq_dl, .migrate_task_rq = migrate_task_rq_dl, .set_cpus_allowed = set_cpus_allowed_dl, .rq_online = rq_online_dl, .rq_offline = rq_offline_dl, .task_woken = task_woken_dl,#endif .set_curr_task = set_curr_task_dl, .task_tick = task_tick_dl, .task_fork = task_fork_dl, .prio_changed = prio_changed_dl, .switched_from = switched_from_dl, .switched_to = switched_to_dl, .update_curr = update_curr_dl,};
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1.4 实时调度类：rt_sched_class
//kernel/sched/rt.cconst struct sched_class rt_sched_class = { .next = &fair_sched_class, .enqueue_task = enqueue_task_rt, .dequeue_task = dequeue_task_rt, .yield_task = yield_task_rt, .check_preempt_curr = check_preempt_curr_rt, .pick_next_task = pick_next_task_rt, .put_prev_task = put_prev_task_rt, #ifdef CONFIG_SMP .select_task_rq = select_task_rq_rt, .set_cpus_allowed = set_cpus_allowed_common, .rq_online = rq_online_rt, .rq_offline = rq_offline_rt, .task_woken = task_woken_rt, .switched_from = switched_from_rt,#endif .set_curr_task = set_curr_task_rt, .task_tick = task_tick_rt, .get_rr_interval = get_rr_interval_rt, .prio_changed = prio_changed_rt, .switched_to = switched_to_rt, .update_curr = update_curr_rt,};
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1.5 公平调度类：fair_sched_class
//kernel/sched/fair.c/* * All the scheduling class methods: */const struct sched_class fair_sched_class = { .next = &idle_sched_class, .enqueue_task = enqueue_task_fair, .dequeue_task = dequeue_task_fair, .yield_task = yield_task_fair, .yield_to_task = yield_to_task_fair, .check_preempt_curr = check_preempt_wakeup, .pick_next_task = pick_next_task_fair, .put_prev_task = put_prev_task_fair, #ifdef CONFIG_SMP .select_task_rq = select_task_rq_fair, .migrate_task_rq = migrate_task_rq_fair, .rq_online = rq_online_fair, .rq_offline = rq_offline_fair, .task_dead = task_dead_fair, .set_cpus_allowed = set_cpus_allowed_common,#endif .set_curr_task = set_curr_task_fair, .task_tick = task_tick_fair, .task_fork = task_fork_fair, .prio_changed = prio_changed_fair, .switched_from = switched_from_fair, .switched_to = switched_to_fair, .get_rr_interval = get_rr_interval_fair, .update_curr = update_curr_fair, #ifdef CONFIG_FAIR_GROUP_SCHED .task_change_group = task_change_group_fair,#endif};
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1.6 空闲调度类：idle_sched_class、
//kernel/sched/idle.c/* * Simple, special scheduling class for the per-CPU idle tasks: */const struct sched_class idle_sched_class = { /* .next is NULL */ /* no enqueue/yield_task for idle tasks */ /* dequeue is not valid, we print a debug message there: */ .dequeue_task = dequeue_task_idle, .check_preempt_curr = check_preempt_curr_idle, .pick_next_task = pick_next_task_idle, .put_prev_task = put_prev_task_idle, #ifdef CONFIG_SMP .select_task_rq = select_task_rq_idle, .set_cpus_allowed = set_cpus_allowed_common,#endif .set_curr_task = set_curr_task_idle, .task_tick = task_tick_idle, .get_rr_interval = get_rr_interval_idle, .prio_changed = prio_changed_idle, .switched_to = switched_to_idle, .update_curr = update_curr_idle,};
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二，调度的实体 struct sched_entity
2.1 简介
调度器并不直接操作进程，而是处理可调度实体。一个实体由 sched_entity 的一个实例表示。
在进程注册到就绪队列时，嵌入的 sched_entity 实例的 on_rq 成员设置为 1，否则为 0。
2.2 结构体代码
//include/linux/sched.hstruct sched_entity { /* For load-balancing: */ struct load_weight load; unsigned long runnable_weight; struct rb_node run_node; struct list_head group_node; unsigned int on_rq; u64 exec_start; u64 sum_exec_runtime; u64 vruntime; u64 prev_sum_exec_runtime; u64 nr_migrations; struct sched_statistics statistics; #ifdef CONFIG_FAIR_GROUP_SCHED int depth; struct sched_entity *parent; /* rq on which this entity is (to be) queued: */ struct cfs_rq *cfs_rq; /* rq "owned" by this entity/group: */ struct cfs_rq *my_q;#endif #ifdef CONFIG_SMP /* * Per entity load average tracking. * * Put into separate cache line so it does not * collide with read-mostly values above. */ struct sched_avg avg;#endif};
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2.3 进程描述符 task_struct 里调度相关的成员
//include/linux/sched.hstruct task_struct { ...... int prio; int static_prio; int normal_prio; unsigned int rt_priority; const struct sched_class *sched_class; struct sched_entity se; struct sched_rt_entity rt; ...... unsigned int policy; int nr_cpus_allowed; cpumask_t cpus_allowed; ......};
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三，调度器
3.1 基础知识
调度程序依靠几个函数来完成调度工作，其中最重要的函数是：
scheduler_tick()：维持当前最新的 time_slice 计数器。
try_to_wake_up()：唤醒睡眠进程。
schedule()：选择要被执行的新进程。
load_balance()：维持多处理器系统中运行队列的平衡。
3.2 pick_next_task()
pick_next_task()会以优先级为顺序，从高到低，依次检查每一个调度类，并且从最高优先级的调度类中，选择最高优先级的进程。
每一个调度类都实现了 pick_next_task()函数，它会返回指向下一个可运行进程的指针，或者没有时返回 NULL。
3.3 上下文切换 / context_switch()
3.3.1 switch_mm()
该函数负责把虚拟内存从上一个进程映射切换到新进程中。
3.3.2 switch_to()
该函数负责从上一个进程的处理器状态切换到新进程的处理器状态。这包括保存、恢复栈信息和寄存器信息，还有其他任何与体系结构相关的状态信息，都必须以每个进程为对象进行管理和保存。
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