Little’s law
Beginner
A simple rule: how many things are waiting equals how fast they arrive times how long each one stays.
Novice
: the average number of items in a system equals the rate at which they arrive times the average time each one stays. Ten requests per microsecond, each taking half a microsecond, means five in progress on average.
Expert
Sizes queues and outstanding-request limits: to sustain bandwidth when each request takes latency , a requester must keep bytes in flight. That sets the number of miss-handling registers, DMA tags and interconnect buffers. It holds whatever the arrival pattern.