Abstract
In this paper we describe the Denovo code system. Denovo solves the
six-dimensional, steady-state, linear Boltzmann transport equation, of
central importance to nuclear technology applications such as reactor core
analysis (neutronics), radiation shielding, nuclear forensics and radiation
detection. The code features multiple spatial differencing schemes,
state-of-the-art linear solvers, the Koch-Baker-Alcouffe (KBA)
parallel-wavefront sweep algorithm for inverting the transport operator, a
new multilevel energy decomposition method scaling to hundreds of thousands
of processing cores, and a modern, novel code architecture that supports
straightforward integration of new features. In this paper we discuss the
performance of Denovo on the 10--20 petaflop ORNL GPU-based system, Titan.
We describe algorithms and techniques used to exploit the capabilities of
Titan's heterogeneous compute node architecture and the challenges of
obtaining good parallel performance for this sparse hyperbolic PDE solver
containing inherently sequential computations. Numerical results
demonstrating Denovo performance on early Titan hardware are presented.
