Changing CPU Frequency in CoMD Proxy Application Offloaded to Intel Xeon Phi Co-processors.

Obtaining exascale performance is a challenge. Although the technology of today features hardware with very high levels of concurrency, exascale performance is primarily limited by energy consumption. This limitation has lead to the use of GPUs and specialized hardware such as many integrated core (MIC) co-processors and FPGAs for computation acceleration. The Intel Xeon Phi co-processor, built upon the MIC architecture, features many low frequency, energy efficient cores. Applications, even those which do not saturate the large vector processing unit in each core, may benefit from the energy-efficient hardware and software of the Xeon Phi. This work explores the energy savings of applications which have not been optimized for the co-processor. Dynamic voltage and frequency scaling (DVFS) is often used to reduce energy consumption during portions of the execution where performance is least likely to be affected. This work investigates the impact on energy and performance when DVFS is applied to the CPU during MIC-offloaded sections (i.e., code segments to be processed on the co-processor). Experiments, conducted on the molecular dynamics proxy application CoMD, show that as much as 14% energy may be saved if two Xeon Phi's are used. When DVFS is applied to the host CPU frequency, energy savings of as high as 9% are obtained in addition to the 8% saved from reducing link-cell count.