Linux SCHED_OTHER、SCHED_FIFO 和 SCHED_RR - 差异
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Linux SCHED_OTHER, SCHED_FIFO and SCHED_RR - differences
提问by eve
Can someone explain the differences between SCHED_OTHER, SCHED_FIFO and SCHED_RR?
有人可以解释 SCHED_OTHER、SCHED_FIFO 和 SCHED_RR 之间的区别吗？
Thanks
谢谢
采纳答案by Claudio
SCHED_FIFO and SCHED_RR are so called "real-time" policies. They implement the fixed-priority real-time scheduling specified by the POSIX standard. Tasks with these policies preempt every other task, which can thus easily go into starvation (if they don't release the CPU).
SCHED_FIFO 和 SCHED_RR 是所谓的“实时”策略。它们实现了 POSIX 标准规定的固定优先级实时调度。具有这些策略的任务会抢占其他所有任务，因此很容易陷入饥饿状态（如果它们不释放 CPU）。
The difference between SCHED_FIFO and SCHED_RR is that among tasks with the same priority, SCHED_RR performs a round-robin with a certain timeslice; SCHED_FIFO, instead, needs the task to explicitly yield the processor.
SCHED_FIFO 和 SCHED_RR 的区别在于，在优先级相同的任务中，SCHED_RR 以一定的时间片进行循环；相反，SCHED_FIFO 需要任务显式让出处理器。
SCHED_OTHER is the common round-robin time-sharing scheduling policy that schedules a task for a certain timeslice depending on the other tasks running in the system.
SCHED_OTHER 是常见的循环分时调度策略，它根据系统中运行的其他任务将任务调度到某个时间片。
Update: since Linux 3.14, there is an additional policy called SCHED_DEADLINE. This policy implements the Constant Bandwidth Server (CBS) algorithm on top of Earliest Deadline Firstqueues. Each task under this policy is assigned a deadline, and the earliest-deadline task is executed. The best resource describing this algorithm is Deadline scheduling in the Linux kernel.
更新：从 Linux 3.14 开始，还有一个名为SCHED_DEADLINE的附加策略。此策略在最早截止日期优先队列之上实施恒定带宽服务器 (CBS) 算法。此策略下的每个任务都分配了一个截止日期，并执行最早截止日期的任务。描述此算法的最佳资源是Linux 内核中的 Deadline 调度。
Update 2: since Linux 4.13, SCHED_DEADLINE has replaced CBS with the Greedy Reclamation of Unused Bandwidth (GRUB) algorithm.
更新 2：自 Linux 4.13 起，SCHED_DEADLINE 已用贪婪回收未使用带宽 (GRUB) 算法取代了 CBS 。
回答by Drioueche Mohammed
Here is the differences between SCHED_OTHER, SCHED_FIFO and SCHED_RR based on Linux Manual (http://man7.org/linux/man-pages/man7/sched.7.html)
以下是基于 Linux 手册 ( http://man7.org/linux/man-pages/man7/sched.7.html) 的SCHED_OTHER、SCHED_FIFO 和 SCHED_RR 之间的差异
SCHED_FIFO: First in-first out scheduling
SCHED_FIFO：先进先出调度
SCHED_FIFOcan be used only with static priorities higher than 0, which means that when a SCHED_FIFO threads becomes runnable, it will always immediately preempt any currently running SCHED_OTHER, SCHED_BATCH, or SCHED_IDLE thread. SCHED_FIFO is a simple scheduling algorithm without time slicing.
SCHED_FIFO只能用于高于 0 的静态优先级，这意味着当 SCHED_FIFO 线程变为可运行时，它将始终立即抢占任何当前正在运行的 SCHED_OTHER、SCHED_BATCH 或 SCHED_IDLE 线程。SCHED_FIFO 是一种简单的调度算法，没有时间分片。
SCHED_RR: Round-robin scheduling
SCHED_RR：循环调度
SCHED_RRis a simple enhancement of SCHED_FIFO. Everything described above for SCHED_FIFO also applies to SCHED_RR, except that each thread is allowed to run only for a maximum time quantum. If a SCHED_RR thread has been running for a time period equal to or longer than the time quantum, it will be put at the end of the list for its priority.
SCHED_RR是 SCHED_FIFO 的简单增强。上面针对 SCHED_FIFO 描述的所有内容也适用于 SCHED_RR，除了每个线程只允许运行最大时间量。如果 SCHED_RR 线程已运行的时间段等于或长于时间片，则它会因其优先级而被放在列表的末尾。
SCHED_OTHER: Default Linux time-sharing scheduling
SCHED_OTHER：Linux 默认分时调度
SCHED_OTHERcan be used at only static priority 0 (i.e., threads under real-time policies always have priority over SCHED_OTHER processes. SCHED_OTHER is the standard Linux time-sharing scheduler that is intended for all threads that do not require the special real-time mechanisms.
SCHED_OTHER只能用于静态优先级 0（即实时策略下的线程始终优先于 SCHED_OTHER 进程。SCHED_OTHER 是标准的 Linux 分时调度程序，适用于所有不需要特殊实时机制的线程.
