Energy saving strategies for parallel applications with point-to-point communication phases

• We present a runtime procedure to detect communication phases.
• We propose novel frequency scaling strategies to save energy.
• We explore the opportunity of energy saving in quantum chemistry software GAMESS.
• Different process binding strategies are proposed for GAMESS.

Although high-performance computing traditionally focuses on the efficient execution of large-scale applications, both energy and power have become critical concerns when approaching exascale. Drastic increases in the power consumption of supercomputers affect significantly their operating costs and failure rates. In modern microprocessor architectures, equipped with dynamic voltage and frequency scaling (DVFS) and CPU clock modulation (throttling), the power consumption may be controlled in software. Additionally, network interconnect, such as Infiniband, may be exploited to maximize energy savings while the application performance loss and frequency switching overheads must be carefully balanced. This paper advocates for a runtime assessment of such overheads by means of characterizing point-to-point communications into phases followed by analyzing the time gaps between the communication calls. Certain communication and architectural parameters are taken into consideration in the three proposed frequency scaling strategies, which differ with respect to their treatment of the time gaps. The experimental results are presented for NAS parallel benchmark problems as well as for the realistic parallel electronic structure calculations performed by the widely used quantum chemistry package GAMESS. For the latter, three different process-to-core mappings were studied as to their energy savings under the proposed frequency scaling strategies and under the existing state-of-the-art techniques. Close to the maximum energy savings were obtained with a low performance loss of 2% on the given platform.