  In this paper, we present the details of our multi-node GPU-FFT library, as
well its scaling on Selene HPC system. Our library employs slab decomposition
for data division and MPI for communication among GPUs. We performed GPU-FFT on
$1024^3$, $2048^3$, and $4096^3$ grids using a maximum of 512 A100 GPUs. We
observed good scaling for $4096^3$ grid with 64 to 512 GPUs. We report that the
timings of multicore FFT of $1536^3$ grid with 196608 cores of Cray XC40 is
comparable to that of GPU-FFT of $2048^3$ grid with 128 GPUs. The efficiency of
GPU-FFT is due to the fast computation capabilities of A100 card and efficient
communication via NVlink.
