By-passing the out-of-order execution pipeline to increase energy-efficiency

Out-of-order execution significantly increases the performance of superscalar processors. The out-of-order execution mechanism is, however, energy-inefficient, which inhibits scaling superscalar processors to high issue widths and large instruction windows. In this paper, we build on the observation that between 19% and 36% of the instructions are immediately ready for execution, even before entering the issue queue. Yet, these instructions proceed to the energy-consuming steps of instruction wake-up and select and they needlessly occupy space in the issue queue. To save energy, we propose for these instructions to by-pass the out-of-order execution core. Instead, we execute them on an energy-efficient single-issue in-order by-pass pipeline. The by-pass pipeline executes a significant fraction of all instructions, allowing performance-energy trade-offs with respect to the issue width of the out-of-order pipeline and to the issue queue size. By making these trade-offs, we show energy r...

• Type: Conference
• Year: 2007
• Where: CF
• Authors: Hans Vandierendonck, Philippe Manet, Thibault Delavallee, Igor Loiselle, Jean-Didier Legat
• Keywords: Applied Computing, CF 2007, Issue Queue, Out-of-order Execution, Superscalar Processors