Comparison of Single-ISA Heterogeneous versus Wide Dynamic Range Processors for Mobile Applications

Mobile computing devices demand processors to offer a wide range of performance/power trade-offs so that they can provide much needed high performance or low power consumption depending on a given operating requirement. While dynamic voltage/frequency scaling (DVFS) has been the most powerful technique to provide such trade-offs, few processor vendors have the capability to provide a sufficient DVFS range requiring joint optimization of devices and circuits. Facing such a challenge, two promising approaches are proposed: scaling the amount of processor resources such as on-chip memory and execution units, i.e., dynamic resource scaling (DRS) and switching between big out-of-order (OoO) and little in-order cores in a single-ISA heterogeneous processor such as ARM's big. LITTLE. In this paper, we compare a single-ISA heterogeneous processor with a wide dynamic range (WDR) processor augmented with DRS in terms of (1) device-, circuit-, architecture-level implications, (2) design challenges, (3) area, (4) performance, and (5) energy efficiency. We evaluate a big. LITTLE processor (as a representative of single-ISA heterogeneous processor) based on Cortex-A15/A7 and a WDR processor based on Cortex-A15 running various mobile and SPEC2006 benchmarks. Our experiments demonstrate that the WDR processor combined with DRS can deliver energy efficiency close to the single-ISA heterogeneous processor, depending on the power overhead of circuit implementation to provide the wide DVFS range.