Transitioning Users from the Franklin XT4 System to the Hopper XE6 System

The Hopper XE6 system, NERSC’s first peta-flop system with over 153,000 cores has increased the computing hours available to the Department of Energy’s Office of Science users by more than a factor of 4. As NERSC users transition from the Franklin XT4 system with 4 cores per node to the Hopper XE6 system with 24 cores per node, they have had to adapt to a lower amount of memory per core and onnode I/O performance which does not scale up linearly with the number of cores per node. This paper will discuss Hopper’s usage during the “early user period” and examine the practical implications of running on a system with 24 cores per node, exploring advanced aprun and memory affinity options for typical NERSC applications as well as strategies to improve I/O performance.