Systolic Sparse Tensor Slices: FPGA Building Blocks for Sparse and Dense AI Acceleration

Abstract: FPGA architectures have recently been enhanced to meet the substantial computational demands of modern deep neural networks (DNNs). To this end, both FPGA vendors and academic researchers have proposed in-fabric blocks that perform efficient tensor computations. However, these blocks are primarily optimized for dense computation, while most DNNs exhibit sparsity. To address this limitation, we propose incorporating structured sparsity support into FPGA architectures. We architect 2D systolic in-fabric blocks, named systolic sparse tensor (SST) slices, that support multiple degrees of sparsity to efficiently accelerate a wide variety of DNNs. SSTs support dense operation, 2:4 (50%) and 1:4 (75%) sparsity, as well as a new 1:3 (66.7%) sparsity level to further increase flexibility. When demonstrating on general matrix multiplication (GEMM) accelerators, which are the heart of most current DNN accelerators, our sparse SST-based designs attain up to 5x higher FPGA frequency and 10.9x lower area, compared to traditional FPGAs. Moreover, evaluation of the proposed SSTs on state-of-the-art sparse ViT and CNN models exhibits up to 3.52x speedup with minimal area increase of up to 13.3%, compared to dense in-fabric acceleration.