"Cool" Load Balancing for High Performance Computing Data Centers

As we move to exascale machines, both peak power demand and total energy consumption have become prominent challenges. A significant portion of that power and energy consumption is devoted to cooling, which we strive to minimize in this work. We propose a scheme based on a combination of limiting processor temperatures using dynamic voltage and frequency scaling (DVFS) and frequency-aware load balancing that reduces cooling energy consumption and prevents hot spot formation. Our approach is particularly designed for parallel applications, which are typically tightly coupled, and tries to minimize the timing penalty associated with temperature control. This paper describes results from experiments using five different CHARM++ and MPI applications with a range of power and utilization profiles. They were run on a 32-node (128-core) cluster with a dedicated air conditioning unit. The scheme is assessed based on three metrics: the ability to control processors' temperature and hence avoid hot spots, minimization of timing penalty, and cooling energy savings. Our results show cooling energy savings of up to 63 percent, with a timing penalty of only 2-23 percent.