Roofline: An Insightful Visual Performance Model for Multicore Architectures

Manufacturers will likely offer multiple products with differing numbers of cores to cover multiple price-performance points, since Moore's Law will permit the doubling of the number of cores per chip every two years. While diversity may be understandable in this time of uncertainty, it exacerbates the already difficult jobs of programmers, compiler writers, and even architects. Hence, an easy-to-understand model that offers performance guidelines would be especially valuable. This article proposes one such model called Roofline, demonstrating it on four diverse multicore computers using four key floating-point kernels. The proposed Roofline model ties together floating-point performance, operational intensity, and memory performance in a 2D graph. The Roofline sets an upper bound on performance of a kernel depending on the kernel's operational intensity. If people think of operational intensity as a column that hits the roof, either it hits the flat part of the roof, meaning performance is compute-bound, or it hits the slanted part of the roof, meaning performance is ultimately memory-bound.