Roofline

Roofline refers to the upper edge or silhouette formed by the roof and upper walls of a building as seen in elevation. In architecture, the roofline helps define the building’s visual profile, proportion, and massing, and can influence how a structure relates to its surrounding landscape. Terms such as eave line, cornice, ridge line, and skyline are often used when describing or modifying the roofline. The concept is important in design, planning, and heritage contexts, where the line contributes to character, scale, and weather protection.

In computing, the Roofline Model is a performance analysis tool used to characterize the theoretical upper bound on a computer’s performance for a given workload. It visualizes attainable floating-point performance (FLOP/s) as a function of arithmetic intensity (FLOPs per byte). The model consists of two ceilings: a horizontal line at the processor’s peak compute rate and a sloped line defined by the peak memory bandwidth. The envelope formed by these ceilings represents the maximum achievable performance, and an actual kernel’s performance sits below this roof. If a kernel lies under the memory-bandwidth line, it is memory-bound; if it hits the horizontal ceiling, it is compute-bound. The model helps identify optimization targets, such as increasing data reuse to raise arithmetic intensity or improving memory bandwidth and compute efficiency.

The Roofline Model is widely used in high-performance computing to guide code optimization and hardware-software co-design, while the architectural roofline remains a distinct, non-technical term describing a building’s silhouette.