The National Energy Research Scientific Computing (NERSC) Center is the primary computing facility for the United States Department of Energy, Office of Science. With over 5,000 users and over 600 different applications utilizing NERSC systems, it is critically important to examine the workload running on NERSCs large supercomputers in order to procure systems that perform well for a broad workload. In this paper we show the breakdown of the NERSC workload by science area, algorithm, memory, thread usage and more. We also describe the methods used to collect data from NERSCs Hopper (Cray XE6) system.

The newest NERSC supercomputer Cori is a Cray XC40 system consisting of 2,388 Intel Xeon Haswell nodes and 9,688 Intel Xeon-Phi “Knights Landing” (KNL) nodes. Compared to the Xeon-based clusters NERSC users are familiar with, optimal performance on Cori requires consideration of KNL mode settings; process, thread, and memory affinity; fine-grain parallelization; vectorization; and use of the high-bandwidth MCDRAM memory. This paper describes our efforts preparing NERSC users for KNL through the NERSC Exascale Science Application Program, Web documentation, and user training. We discuss how we configured the Cori system for usability and productivity, addressing programming concerns, batch system configurations, and default KNL cluster and memory modes. System usage data, job completion analysis, programming and running jobs issues, and a few successful user stories on KNL are presented.