ndzip-gpu: Efficient lossless Compression of Scientific Floating-Point Data on GPUs

Lossless data compression is a promising software approach for reducing the bandwidth requirements of scientific applications on accelerator clusters without introducing approximation errors. Suitable compressors must be able to effectively compact floating-point data while saturating the system interconnect to avoid introducing unnecessary latencies. We present ndzip-gpu, a novel, highly-efficient GPU parallelization scheme for the block compressor ndzip, which has recently set a new milestone in CPU floating-point compression speeds. Through the combination of intra-block parallelism and efficient memory access patterns, ndzip-gpu achieves high resource utilization in decorrelating multi-dimensional data via the Integer Lorenzo Transform. We further introduce a novel, efficient warp-cooperative primitive for vertical bit packing, providing a high-throughput data reduction and expansion step. Using a representative set of scientific data, we compare the performance of ndzip-gpu against five other, existing GPU compressors. While observing that effectiveness of any compressor strongly depends on characteristics of the dataset, we demonstrate that ndzip-gpu offers the best average compression ratio for the examined data. On Nvidia Turing, Volta and Ampere hardware, it achieves the highest single-precision throughput by a significant margin while maintaining a favorable trade-off between data reduction and throughput in the double-precision case.