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The Homa Network Protocol

network protocol [LWN subscriber-only content] Most networking applications are still based on TCP, which was designed for efficient and reliable transport of streams of data across a distributed Internet. Data-center applications, instead, are often dominated by large number of small messages between many locally connected hosts.

The design of Homa is intended to remove that overhead while taking advantage of what current data-center networking hardware can do, with a focus on minimizing the latency between a request and its response. There is a limit on how many bytes of this "unscheduled" request data can be sent in this manner, which is determined by the round-trip time of the network; it should be just high enough to keep the request-transmission pipeline full until an initial response can be received from the server side. There is also a fair amount of thought that has gone into letting systems overcommit their resources by issuing more grants than they can immediately handle; the purpose here is to keep the pipelines full even if some senders do not transmit as quickly as expected.

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