/** TODO:** Migration compensation and resist like credit2 to better use cache;* Lock Holder Problem, using yield?* Self switch problem: VCPUs of the same domain may preempt each other;*/
//任务:
//对补偿和抗拒部分进行移植，类似credit2高效利用缓存
//锁的持有者问题，使用yield吗?
//自开关的问题：同一个域的可能会互相抢占VCPU;/** Design:** This scheduler follows the Preemptive Global Earliest Deadline First (EDF)* theory in real-time field.* At any scheduling point, the VCPU with earlier deadline has higher priority.* The scheduler always picks highest priority VCPU to run on a feasible PCPU.* A PCPU is feasible if the VCPU can run on this PCPU and (the PCPU is idle or* has a lower-priority VCPU running on it.)*
//设计思路
//该调度器遵循全局抢占最早时限优先(EDF)理论,用于实时调度领域
//在每次调度中，那些有更早期限的任务将会有更高的优先级
//调度器总是选择一个更高优先级的VCPU运行在可运行的物理CPU上。
//一个可运行的pcpu指的是一个VCPU可以运行在该pcpu上，(包括pcpu处于空闲或有低优先级任务)* Each VCPU has a dedicated period and budget.* The deadline of a VCPU is at the end of each period;* A VCPU has its budget replenished at the beginning of each period;* While scheduled, a VCPU burns its budget.* The VCPU needs to finish its budget before its deadline in each period;* The VCPU discards its unused budget at the end of each period.* If a VCPU runs out of budget in a period, it has to wait until next period.*
//每一个VCPU都有专属的期限和预算
//一个VCPU的期限是每个周期的结束时间
//一个VCPU拥有的预算在每个周期的开始补充
//若调度，一个VCPU消耗他的预算
//一个VCPU必须在每一个周期内完成他的预算
//一个VCPU在每个周期丢掉未用完的预算
//如果在一个周期内VCPU用光了预算，就得等待下一个周期* Each VCPU is implemented as a deferable server.* When a VCPU has a task running on it, its budget is continuously burned;* When a VCPU has no task but with budget left, its budget is preserved.** Queue scheme:* A global runqueue and a global depletedqueue for each CPU pool.* The runqueue holds all runnable VCPUs with budget, sorted by deadline;* The depletedqueue holds all VCPUs without budget, unsorted;** Note: cpumask and cpupool is supported.*///每一个VCPU以可延期的服务实现
//当一个VCPU运行任务时，预算被持续的消耗
//当一个VCPU没有任务但是有剩余的预算，该预算被保留//队列方案
//为每一个cpu池设置一个全局的运行队列和全局的耗尽队列
//运行队列保存所有的可运行的VCPU和预算，以期限排序
//耗尽队列以非排序的方式保存所有预算用完的VCPU/** Locking:* A global system lock is used to protect the RunQ and DepletedQ.* The global lock is referenced by schedule_data.schedule_lock* from all physical cpus.** The lock is already grabbed when calling wake/sleep/schedule/ functions* in schedule.c** The functions involes RunQ and needs to grab locks are:*    vcpu_insert, vcpu_remove, context_saved, __runq_insert*///全局的锁用于保护runq和depletedq
//全局的锁由所有物理CPU在schedule_data.schedule_lock引用
//schedule.c中每次唤醒/睡眠/调度函数运行时，已经上锁了
//包含runq的函数，需要上锁的有VCPU的插入移除、运行队列插入、上下文保存