Comments on the paper by Huadong Xiao, Jing Sun, Xiaofeng Bian and Zhijun Dai, "GPU acceleration of the WSM6 cloud microphysics scheme in GRAPES model"

The authors of the paper (Xiaoa et al., 2013) presented a speedup of 140 for the WSM6 microphysics module running on a low-cost NVidia Geforce 605 with 48 CUDA cores. Unfortunately the presented speedup cannot be achieved using that hardware. In this communication, we comment on several implementation mistakes pertaining to that paper. Their actual speedup is only about 12 . A failure in their CUDA kernel launch also explains that the potential temperature differences between their CPU and GPU versions could be as large as 1.61.