TCP request and response workload tuning

TCP request and response workloads are workloads that involve a two-way exchange of information.

Examples of request and response workloads are Remote Procedure Call (RPC) types of applications or client/server applications, like web browser requests to a web server, NFS file systems (that use TCP for the transport protocol), or a database's lock management protocol. Such request are often small messages and larger responses, but might also be large requests and a small response.

The primary metric of interest in these workloads is the round-trip latency of the network. Many of these requests or responses use small messages, so the network bandwidth is not a major consideration.

Hardware has a major impact on latency. For example, the type of network, the type and performance of any network switches or routers, the speed of the processors used in each node of the network, the adapter and bus latencies all impact the round-trip time.

Tuning options to provide minimum latency (best response) typically cause higher CPU overhead as the system sends more packets, gets more interrupts, etc. in order to minimize latency and response time. These are classic performance trade-offs.

Primary tunables for request and response applications are the following:

• tcp_nodelay or tcp_nagle_limit
• tcp_nodelayack
• Adapter interrupt coalescing settings