Optimization of Numerous Small Dense-Matrix–Vector Multiplications in H-Matrix Arithmetic on GPU

Dense-matrix–vector multiplication is one of the well-known important matrix calculations. This calculation is provided a general matrix–vector multiplication (GEMV) function in the basic linear algebra subprograms (BLAS) libraries for several computation hardware. Traditionally, studies focus one large dense-matrix (the length of each side of the dense matrix is long)–vector multiplication. However, some applications require acceleration of numerous small dense-matrix–vector multiplications. This feature is provided by batched BLAS libraries. This calculation is also needed to compute a hierarchical-matrix–vector multiplication. In this study, we implemented numerous small dense-matrix–vector multiplications on a Pascal GPU and evaluated the performance. Thus, we considered the impact of optimization parameters and succeeded in obtaining a better performance than previous works. The maximum differences from our previous work is 28.47% and from batched GEMV of MAGMA BLAS is upto 81.81%. Moreover, we considered the use of two optimization parameters in one GPU kernel; one parameter was applied to some matrices, whereas the second parameter was applied to other matrices. The amount of the improvement was limited (upto 5%), a performance improvement was achieved. Our result will serve as a good reference for users who need to use numerous small dense-matrix–vector multiplications on a GPU and want to optimize a matrix–vector multiplication by hand-tuning and auto-tuning.