  Over the past five years, graphics processing units (GPUs) have had a
transformational effect on numerical lattice quantum chromodynamics (LQCD)
calculations in nuclear and particle physics. While GPUs have been applied with
great success to the post-Monte Carlo "analysis" phase which accounts for a
substantial fraction of the workload in a typical LQCD calculation, the initial
Monte Carlo "gauge field generation" phase requires capability-level
supercomputing, corresponding to O(100) GPUs or more. Such strong scaling has
not been previously achieved. In this contribution, we demonstrate that using a
multi-dimensional parallelization strategy and a domain-decomposed
preconditioner allows us to scale into this regime. We present results for two
popular discretizations of the Dirac operator, Wilson-clover and improved
staggered, employing up to 256 GPUs on the Edge cluster at Lawrence Livermore
National Laboratory.
