  Power is an often-cited reason for moving to advanced architectures on the
path to Exascale computing. This is due to the practical concern of delivering
enough power to successfully site and operate these machines, as well as
concerns over energy usage while running large simulations. Since accurate
power measurements can be difficult to obtain, processor thermal design power
(TDP) is a possible surrogate due to its simplicity and availability. However,
TDP is not indicative of typical power usage while running simulations. Using
commodity and advance technology systems at Lawrence Livermore National
Laboratory (LLNL) and Sandia National Laboratory, we performed a series of
experiments to measure power and energy usage in running simulation codes.
These experiments indicate that large scale LLNL simulation codes are
significantly more efficient than a simple processor TDP model might suggest.
