Since this is a tuning guide, I would have liked to see a separation of 3 attributes:

* Service-time: The actual time taken by the thread/process once it begins processing a request.

* Latency: The time spent by the request waiting to get processed (ex: languishing in a queue on the client/server side). This is when the request was latent.

* Response time: A combination of Service-time + Latency as recorded by the server. From a client's POV, this would additionally include the overhead from the network media etc.

Most performance models seem to isolate these separately to get a deeper sense of where the bottlenecks are. When there's just a single queue for everything then it makes sense to make the service-time as short as possible. But if you have multiple workload-based queues then you can do more interesting things.