3.7.5.1. CFS调度器概述
3.7.5.1.1. cfs调度器类fair_sched_class
CFS完全公平调度器的调度类叫 fair_sched_class ,其定义在kernel/sched/fair.c中,它是我们熟知的struct sched_class调度器类型
/*
* All the scheduling class methods:
*/
const struct sched_class fair_sched_class = {
.next = &idle_sched_class, //下个优先级的调度类,所有的调度类通过next链接在一个链表中
.enqueue_task = enqueue_task_fair, //向就绪队列中添加一个进程,它将调度实体(进程)放入红黑树中,并对nr_running变量加1
.dequeue_task = dequeue_task_fair, //将一个进程从就绪队列中删除
.yield_task = yield_task_fair, //在进程想要资源放弃对处理器的控制权时,可使用sched_yield系统调用
.yield_to_task = yield_to_task_fair,
.check_preempt_curr = check_preempt_wakeup, //该函数将检查当前运行的任务是否被抢占,在实际抢占正在运行的任务之前,cfs调度器将执行公平性测试,这将驱动唤醒式抢占
.pick_next_task = pick_next_task_fair, //选择接下来要运行的最合适的进程
.put_prev_task = put_prev_task_fair, //用另外一个进程替代当前运行的进程
.set_next_task = set_next_task_fair, //当任务修改其调度类或修改其任务组时,将调用这个函数
#ifdef CONFIG_SMP
.balance = balance_fair,
.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
.task_tick = task_tick_fair, //在每次激活周期调度器时,由周期性调度器调用,该函数通常调用自time tick函数,它可能引起进程切换,这将驱动运行时抢占
.task_fork = task_fork_fair, //内核调度程序为调度模块提供了管理新任务启动的机会，用于建立fork系统调用和调度器之间的关联,每次新进程建立后，则用new_task通知调度器,cfs使用
//它进行组调度，而用于实时任务的调度模块则不会使用这个函数
.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
#ifdef CONFIG_UCLAMP_TASK
.uclamp_enabled = 1,
#endif
};
3.7.5.1.2. cfs就绪队列
就绪队列时全局调度器许多操作的起点，但是进程并不是由就绪队列直接管理的,调度管理是各个调度器的职责，因此在各个就绪队列中潜入了特定调度类的子就绪队列( cfs的顶级调度队列struct cfs_rq,实时调度类的就绪队列struct rt_rq和deadline调度类的就绪队列struct dl_rq)
//cfs调度的运行队列，每个CPU的rq会包含一个cfs_rq，而每个组调度的sched_entity也会有自己的一个cfs_rq队列
/* CFS-related fields in a runqueue */
struct cfs_rq {
struct load_weight load; //cfs运行
unsigned long runnable_weight;//cfs运行队列中所有进程的总负载
unsigned int nr_running; //cfs_rq中调度实体的数量
unsigned int h_nr_running; /* SCHED_{NORMAL,BATCH,IDLE} */ //只对进程组有效
unsigned int idle_h_nr_running; /* SCHED_IDLE */
u64 exec_clock;
//当前cfs队列上最小运行时间，单调递增
//两种情况下更新该值
//1.更新当前运行任务的累计运行时间时
//2.当任务从队列删除去,如任务睡眠或者退出,这时候会查看剩下的任务的vruntime是否大于min_vruntime，如果是则更新该值
u64 min_vruntime;
#ifndef CONFIG_64BIT
u64 min_vruntime_copy;
#endif
struct rb_root_cached tasks_timeline; //该红黑树的root
/*
* 'curr' points to currently running entity on this cfs_rq.
* It is set to NULL otherwise (i.e when none are currently running).
*/
struct sched_entity *curr; //当前正在运行的sched_entity(对于组虽然他不会在cpu上运行,但是当它的下层有一个task在cpu上运行,那么它所在的cfs_rq就把它当作是该cfs_rq上当前正在运行的sched_entity)
struct sched_entity *next; //表示有些进程急需运行,即使不遵从cfs调度也必须运行它，调度时会检查是否next需要调度,有就调度next
struct sched_entity *last;
struct sched_entity *skip;
#ifdef CONFIG_SCHED_DEBUG
unsigned int nr_spread_over;
#endif
#ifdef CONFIG_SMP
/*
* CFS load tracking
*/
struct sched_avg avg;
#ifndef CONFIG_64BIT
u64 load_last_update_time_copy;
#endif
struct {
raw_spinlock_t lock ____cacheline_aligned;
int nr;
unsigned long load_avg;
unsigned long util_avg;
unsigned long runnable_sum;
} removed;
#ifdef CONFIG_FAIR_GROUP_SCHED
unsigned long tg_load_avg_contrib;
long propagate;
long prop_runnable_sum;
/*
* h_load = weight * f(tg)
*
* Where f(tg) is the recursive weight fraction assigned to
* this group.
*/
unsigned long h_load;
u64 last_h_load_update;
struct sched_entity *h_load_next;
#endif /* CONFIG_FAIR_GROUP_SCHED */
#endif /* CONFIG_SMP */
#ifdef CONFIG_FAIR_GROUP_SCHED
struct rq *rq; /* CPU runqueue to which this cfs_rq is attached */
/*
* leaf cfs_rqs are those that hold tasks (lowest schedulable entity in
* a hierarchy). Non-leaf lrqs hold other higher schedulable entities
* (like users, containers etc.)
*
* leaf_cfs_rq_list ties together list of leaf cfs_rq's in a CPU.
* This list is used during load balance.
*/
int on_list;
struct list_head leaf_cfs_rq_list;
struct task_group *tg; /* group that "owns" this runqueue */
#ifdef CONFIG_CFS_BANDWIDTH
int runtime_enabled;
s64 runtime_remaining;
u64 throttled_clock;
u64 throttled_clock_task;
u64 throttled_clock_task_time;
int throttled;
int throttle_count;
struct list_head throttled_list;
#endif /* CONFIG_CFS_BANDWIDTH */
#endif /* CONFIG_FAIR_GROUP_SCHED */
};