epoll是Linux内核为处理大批量文件描述符而作了改进的poll，是Linux下多路复用IO接口select/poll的增强版本，它能显著提高程序在大量并发连接中只有少量活跃的情况下的系统CPU利用率。另一点原因就是获取事件的时候，它无须遍历整个被侦听的描述符集，只要遍历那些被内核IO事件异步唤醒而加入Ready队列的描述符集合就行了。epoll除了提供select/poll那种IO事件的水平触发(Level Triggered)外，还提供了边缘触发(Edge Triggered)，这就使得用户空间程序有可能缓存IO状态，减少epoll_wait/epoll_pwait的调用，提高应用程序效率(Epoll is an improved poll for the Linux kernel to handle large batch file descr iptors, an enhanced version of the multiplexed IO interface select/poll under Linux, which can significantly improve the application rate of the system CPU in a large number of concurrent connections in a large number of concurrent connections. Another reason is that when an event is obtained, it does not need to traverse the entire set of listener descr iptors, just traversing the descr iptor sets that are added to the Ready queue asynchronously by the kernel IO event. In addition to providing the level trigger (Level Triggered) of the select/poll IO event (Level Triggered), epoll provides the edge trigger (Edge Triggered), which makes the user space program likely to cache the IO state, reduce the call of the epoll_wait/epoll_pwait, and improve the efficiency of the application)