最近读openswitch的文档，看到下面一段话，说所有的CFM/BFD等协议，ARP修改相关的包都会经过slowpath/慢路径处理。
Performance
Open vSwitch has a concept of a “fast path” and a “slow path”; ideally all packets stay in the fast path. This distinction between slow path and fast path is the key to making sure that Open vSwitch performs as fast as possible. Some factors can force a flow or a packet to take the slow path. As one example, all CFM, BFD, LACP, STP, and LLDP processing takes place in the slow path, in the cases where Open vSwitch processes these protocols itself instead of delegating to controller-written flows. As a second example, any flow that modifies ARP fields is processed in the slow path. These are corner cases that are unlikely to cause performance problems in practice because these protocols send packets at a relatively slow rate, and users and controller authors do not normally need to be concerned about them.
突然想起了很多年以前，公司的产品是在ATCA v1版本的机架办卡上，性能不得不说和现在差很远。记得有一个问题是这样，机架里的一个switch板块会不定期出现CPU性能的问题。最后调查的结果是收到的ARP有点多，导致底层需要往上传递ARP，最终导致CPU性能问题。
和这里的慢路径一个道理，switch需要二层的ARP做ip/mac的mapping表，需要当前交换机做一些处理。需要消耗CPU。
经过云化之后，ATCA也慢慢被淘汰了。都换成了HP服务器。
