Linux 民意调查与 epoll 洞察力
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poll vs. epoll insight
提问by Cartesius00
Are there some simple rules of thumb when to use pollvs. epollin a low-latency environment? epollshould have higher overhead if only few of file-descriptors is monitored. Please, give some insight, answers "check it yourself" put elsewhere.
在低延迟环境中何时使用pollvs.是否有一些简单的经验法则epoll？epoll如果只监视很少的文件描述符，则应该有更高的开销。请给出一些见解，答案“自己检查”放在其他地方。
采纳答案by R.. GitHub STOP HELPING ICE
Always use pollunless all of the following are satisfied:
poll除非满足以下所有条件，否则始终使用：
- You can ensure you're on a (Linux) system that has
epollor you provide a fallback for systems that don't. - You have a hugenumber of file descriptors active (at least 1000-10000).
- The set of file descriptors you're working with is stable over a long time period (adding/removing file descriptors from the
epolllist is just as expensive as apolloperation, since it requires entering/leaving kernelspace).
- 您可以确保您使用的 (Linux) 系统具有
epoll或为没有的系统提供后备。 - 您有大量的文件描述符处于活动状态（至少 1000-10000）。
- 您正在使用的文件描述符集在很长一段时间内是稳定的（从
epoll列表中添加/删除文件描述符与poll操作一样昂贵，因为它需要进入/离开内核空间）。
回答by Fred Foo
epoll(7)summarizes it succinctly: epoll"scales well to large numbers of watched file descriptors." However, pollis a POSIX standard interface, so use that when portability is required.
epoll(7)简洁地总结它：epoll“可以很好地扩展到大量监视的文件描述符。” 但是，poll是 POSIX 标准接口，因此在需要可移植性时使用它。
回答by plaes
First of all, poll(2)is only level-triggered, but epoll(4)can be used as either edge- or level-triggered interface.
首先，poll(2)它只是电平触发，但epoll(4)可以用作边缘或电平触发接口。
Now complexity: pollcomplexity regarding number of watched descriptors (fds) is O(n) as it scans all the fds every time when a 'ready' event occurs, epollis basically O(1) as it doesn't do the linear scan over all the watched descriptors.
现在的复杂性：poll关于观察描述符 (fds) 数量的复杂性是 O(n)，因为它每次发生“就绪”事件时都会扫描所有 fds，epoll基本上是 O(1)，因为它不进行所有线性扫描监视的描述符。
In terms of portability - as epollis Linux-specific I would suggest checking out libevand libeventlibraries.
Also, check out Dan Kegel's excellent writeup: "The C10K problem".
在可移植性方面 - 与epollLinux 特定的一样，我建议查看libev和libevent库。另外，请查看 Dan Kegel 的优秀文章：“ C10K 问题”。
