  The Linac Coherent Light Source (LCLS) is an X- ray free electron laser
(XFEL) facility enabling the study of the structure and dynamics of single
macromolecules. A major upgrade will bring the repetition rate of the X-ray
source from 120 to 1 million pulses per second. Exascale high performance
computing (HPC) capabilities will be required to process the corresponding data
rates. We present SpiniFEL, an application used for structure determination of
proteins from single-particle imaging (SPI) experiments. An emerging technique
for imaging individual proteins and other large molecular complexes by
outrunning radiation damage, SPI breaks free from the need for crystallization
(which is difficult for some proteins) and allows for imaging molecular
dynamics at near ambient conditions. SpiniFEL is being developed to run on
supercomputers in near real-time while an experiment is taking place, so that
the feedback about the data can guide the data collection strategy. We describe
here how we reformulated the mathematical framework for parallelizable
implementation and accelerated the most compute intensive parts of the
application. We also describe the use of Pygion, a Python interface for the
Legion task-based programming model and compare to our existing MPI+GPU
implementation.
