Interaction cost: for when event counts just don´t add up

Most performance analysis tasks boil down to finding bottlenecks. In the context of this article, a bottleneck is any event (for example, branch mispredict, window stall, or arithmetic-logic unit (ALU) operation) that limits performance. Bottleneck analysis is critical to an architect´s work, whether the goal is tuning processors for energy efficiency, improving the effectiveness of optimizations, or designing a more balanced processor. Interaction cost helps to improve processor performance and decrease power consumption by identifying when designers can choose among a set of optimizations and when it´s necessary to perform them all