[jandrewrogers]

The general pattern is a fixed set of resources that are consumed/retired at a fixed maximum rate, where the optimal design consistently gets as close to the maximum rate as possible without exceeding the resource limit. There are (at least) two other places in software where backpressure is used, both commonly found in the database world:

Storage I/O scheduling, which unlike the network case is often not interrupt-driven. As you approach the IOPS rate limit for the system due to high priority tasks, the rate of IOPS scheduled for low priority tasks like background write-back in databases is dynamically reduced to maintain headroom for high priority tasks. This is implemented as backpressure on low-priority tasks.

In query processing, a query as a user would understand it can materialize upwards of millions of sub-operations on the same server that can run concurrently given adequate system resources. The number of sub-operations that can be in-flight and retired per second is approximately fixed and shared across all concurrent user queries. For large queries, you incrementally materialize these sub-operations at a rate based on the instantaneous capacity of the system to handle new sub-operations. This is backpressure based on execution slot (and related memory) availability.

Writing software for barrel processors takes this to the extreme. The entire software design principle is to consistently generate fine-grained concurrent threads of execution at runtime that are close to the hardware concurrency limit globally (which is very high) but never exceeds it. Highly optimized code quickly gets pretty weird but it is basically all backpressure mechanics to maintain throughput.