A software toolkit developed at Berkeley Lab to better understand supercomputer performance is now being used to boost application performance for researchers running codes at NERSC and other supercomputing facilities. “Since its initial development, what is now known as the Empirical Roofline Toolkit (ERT) has benefitted from contributions by several Berkeley Lab staff. Along the way, HPC users who write scientific applications for manycore systems have been able to apply the toolkit to their applications and see how changing parameters of their code can improve performance.”