From CPU to GPU in Two days: 3D elastic orthorhombic modeling with openAcc.

Wavefield modeling is necessary in modern seismic imaging applications such as reverse time migration and full-waveform inversion. When the medium has complex structures such as salt bodies or carbonate reservoirs finite-difference methods (FDM) for wavefield simulation (extrapolation) are typically used to handle those cases. FDM allows us to simulate a multitude of realistic wave phenomena, but in some cases it makes our applications computationally intensive. When large numbers of sources and receivers are considered, a large number of wavefield extrapolations in the process of inversion is executed. To accelerate the 3-D wavefield simulation in elastic orthorhombic anisotropic media we rely on GPU technology. With the OpenAcc PGI compiler we create a pool of automatically managed memory that is shared between the CPU and GPU, thus achieving data management with minimal code modifications. We collapse the tightly nested loops used for velocity and stress updates which allows us to improve the execution time of the whole code by about ten percent. We report a performance speedup as we compare to a 16 core dual socket Haswell server of 1.15X on a K80 GPU and 2.32X when using the Pascal Tesla P100 GPU.