Ridge point (machine balance)
Beginner
The bend in the roofline chart. Jobs to its right can use all the chip’s math; jobs to its left are held back by memory.
Novice
Peak compute divided by memory bandwidth, in FLOPs per byte. It is the least arithmetic intensity a workload needs to reach the chip’s peak speed.
Expert
Peak FLOP/s ÷ peak byte/s, defined per memory level. It has drifted right as compute grew faster than bandwidth, so more kernels fall on the slope. Williams et al. read it as a measure of how hard a machine is to program to peak.
Explained in What the workload needs (Architectures).
See also: Roofline model, Arithmetic (operational) intensity.