The growth rate in energy consumed by data centers in the United States has been declining in the past five years compared to its earlier accelerating pace. This reduced growth rate was achieved in large part due to energy efficiency improvements. Measuring, monitoring and managing usage has been key to making these improvements in energy efficiency. The metric Power Usage Effectiveness (PUE) has been effective in driving the energy efficiency of data centers, but it has limitations. PUE does not account for the power distribution and cooling losses inside the IT equipment, which is particularly problematic for HPC. Similarly, reporting performance and analyzing the amount of power used to run High Performance Linpack for a Top500 and/or Green500 submission has been successful in helping to drive improvements in supercomputing system energy efficiency. Power efficiency, (Megaflops per watt) shows average efficiency nearly tripling between 2007 and 2011. But just as PUE isn't perfect for the data center, so are there problems with the power/energy measurement methodologies, workloads and metrics for supercomputer systems. Work is actively being done on both of these topics. The ability to achieve the 20MW target for an Exascale system is challenging and will require shifts in architecture, technology and application usage models as well as tighter coupling between the data center infrastructure and the computer system. This paper will describe initiatives led by the Energy Efficient High Performance Computing Working Group that will help us hit our 20 MW target.
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