Linux kernel BUSY_POLL 机制

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原创最新推荐文章于 2026-10-12 16:24:58 发布 2.7k 阅读 AI 写同款· GEO 优化 ›

Linux select/poll/epoll 实现原理剖析 select(2)，poll(2) 以轮询的方式检查 fd 集合，轮询一遍没有就绪事件发生就会将自己挂起，等待监视的文件将自己唤醒（超时和信号都可以唤醒）。而 epoll(7) 是设备就绪时，调用回调函数，把就绪 fd 放入就绪链表中，并唤醒在 epoll_wait(2) 中进入睡眠的进程。虽然都要睡眠和交替，但是 select(2) 和 poll(2) 在“醒着”的时候要遍历整个 fd 集合，而 epoll(7) 在“醒着”的时候只要判断一下就绪链表是否为空就行了，这节省了大量的 CPU 时间。阅读详情

https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/performance_tuning_guide/sect-red_hat_enterprise_linux-performance_tuning_guide-networking-configuration_tools

Configuring Busy Polling

Busy polling helps reduce latency in the network receive path by allowing socket layer code to poll the receive queue of a network device, and disabling network interrupts. This removes delays caused by the interrupt and the resultant context switch. However, it also increases CPU utilization. Busy polling also prevents the CPU from sleeping, which can incur additional power consumption.

Busy polling is disabled by default. To enable busy polling on specific sockets, do the following.

Set sysctl.net.core.busy_poll to a value other than 0. This parameter controls the number of microseconds to wait for packets on the device queue for socket poll and selects. Red Hat recommends a value of 50.
Add the SO_BUSY_POLL socket option to the socket.

To enable busy polling globally, you must also set sysctl.net.core.busy_read to a value other than 0. This parameter controls the number of microseconds to wait for packets on the device queue for socket reads. It also sets the default value of the SO_BUSY_POLL option. Red Hat recommends a value of 50 for a small number of sockets, and a value of 100 for large numbers of sockets. For extremely large numbers of sockets (more than several hundred), use epoll instead.

Busy polling behavior is supported by the following drivers. These drivers are also supported on Red Hat Enterprise Linux 7.