Scheduling

记一笔，没啥特别。

Unix 系统的分时调度中，nice值（通过 nice(1) 来控制）是管理员告诉调度器的一个参数，这个参数令内核在考虑就绪进程优先级时，根据其值适当增大或减少执行绪的动态优先级。很明显，如果采用抢占式调度，如果执行绪等待时间较长，或者由于某种原因获得了优先级奖励（例如I/O导致的等待），即使有更重要的任务需要执行，内核还是会将这个执行绪调度进来并进行执行；反之，如果执行绪使用的 CPU 很多（计算密集型任务，如压缩等等），即使这个执行绪进行的就是最重要的任务，它仍然可能被置入休眠状态。

An interesting conversation in FreeBSDChina’s core:

delphij -> yarshure: I need some help on qmail
yarshure -> delphij: alu is qmail guru
delphij (continue the conversation with alu and finally solved the problem)

This is a complex problem. A peer to peer system consists many self-determinating nodes is hard to control, and when it goes crazy, it will be easy to launch a distributed denial-of-service (DDoS) attack.

Here are some of my thoughts, well, they are not mature and some of them might be misleading, but I will write them here.