ShapeShifter: a morphable microprocessor for low power

A composite core contains large and small heterogeneous microengines. The most important property of composite cores is their ability to select the most proper microengine for running applications to save power without sacrificing too much performance. To achieve this, a composite core tries to predict the performance of the passive microengine by collecting various processor statistics from the active microengine at runtime. In the method proposed in the literature, the microengine, which is more ideal for running the rest of the application, is determined by a migrationdecision circuitry that is bound to collected statistics and complex functions, which are run in a sequential manner. In this study, we propose the ShapeShifter architecture that holds a single out-of-order core to switch its mode of instruction execution between out-of-order and in-order modes. With a simple mode-change decision circuitry, which is bound to only two processor statistics, we can save more than 25% power, more than 21% on energy-delay product, and more than 16% on energy-delay-square product on the average, by only sacrificing less than 5% of performance.