$K$-nearest neighbor search is one of the fundamental tasks in various applications and the hierarchical navigable small world (HNSW) has recently drawn attention in large-scale cloud services, as it easily scales up the database while offering fast search. On the other hand, a computational storage device (CSD) that combines programmable logic and storage modules on a single board becomes popular to address the data bandwidth bottleneck of modern computing systems. In this paper, we propose a computational storage platform that can accelerate a large-scale graph-based nearest neighbor search algorithm based on SmartSSD CSD. To this end, we modify the algorithm more amenable on the hardware and implement two types of accelerators using HLS- and RTL-based methodology with various optimization methods. In addition, we scale up the proposed platform to have 4 SmartSSDs and apply graph parallelism to boost the system performance further. As a result, the proposed computational storage platform achieves 75.59 query per second throughput for the SIFT1B dataset at 258.66W power dissipation, which is 12.83x and 17.91x faster and 10.43x and 24.33x more energy efficient than the conventional CPU-based and GPU-based server platform, respectively. With multi-terabyte storage and custom acceleration capability, we believe that the proposed computational storage platform is a promising solution for cost-sensitive cloud datacenters.

Image-text retrieval (ITR) that identifies the relevant images for a given text query, or vice versa, is the fundamental task in emerging vision-and-language machine learning applications. Recently, the cross-modal approach that extracts image and text features in separate reasoning pipelines but performs the similarity search on the same embedding representation is proposed for the real-time ITR system. However, the similarity search that finds the most relevant data in huge data embeddings for a given query becomes the bottleneck of the ITR system.In this paper, we propose a dual-mode similarity search accelerator that can solve the computational hurdle for online image-to-text and text-to-image retrieval service. We propose an embedding compression scheme that removes the sparsity in the text embeddings, further eliminating the time-consuming masking operations in the later processing pipeline. Combining with the data quantization from 32-bit floating-point to 8- bit integer, we reduce the target dataset size by 95.1% with less than 0.1% accuracy loss for 1024-dimensional embedding features. In addition, we propose a streamlined similarity search data flow for both query types, which minimizes the required memory bandwidth with maximal data reuse. The query and data embeddings are guaranteed to be fetched only once from the external memory with the optimized data flow. Based on the proposed data representation and flow, we design a scalable similarity search accelerator that includes multiple ITR kernels. Each ITR kernel has modular design, composed of a separate memory access module and a computing module. The computing module supports pipelined operations of the four similarity search tasks: dot product calculation, data reordering, partial score aggregation, and ranking. We double the number of processing operations in the computing module with the DSP packing technique. Finally, we implement the proposed accelerator with six ITR kernels on the Xilinx Alveo U280 FPGA card. It shows 2.98 tera operations per second (TOPS) performance at 186 MHz, achieving 526/144 and 1163/306 queries per second (QPS) performance for image-to-text and text-to-image retrieval on MS-COCO 1K/5K benchmark. It is up to 359.0 × and 13.9 × faster and 503.6 × and 68.7 × more energy-efficient than the baseline and optimized GPU implementation on Nvidia Titan RTX, respectively.

K-nearest neighbor algorithm that searches the K closest samples in a high dimensional feature space is one of the most fundamental tasks in machine learning and image retrieval applications. Computational storage device that combines computing unit and storage module on a single board becomes popular to address the data bandwidth bottleneck of the conventional computing system. In this paper, we propose a nearest neighbor search acceleration platform based on computational storage device, which can process a large-scale image dataset efficiently in terms of speed, energy, and cost. We believe that the proposed acceleration platform is promising to be deployed in cloud datacenters for data-intensive applications.