CPU-FPGA Heterogeneous Platforms Research Articles

L-FNNG: Accelerating Large-Scale KNN Graph Construction on CPU-FPGA Heterogeneous Platform

Due to the high complexity of constructing exact k -nearest neighbor graphs, approximate construction has become a popular research topic. The NN-Descent algorithm is one of the representative in-memory algorithms. To effectively handle large datasets, existing state-of-the-art solutions combine the divide-and-conquer approach and the NN-Descent algorithm, where large datasets are divided into multiple partitions, and a subgraph is constructed for each partition before all the subgraphs are merged, reducing the memory pressure significantly. However, such solutions fail to address inefficiencies in large-scale k -nearest neighbor graph construction. In this paper, we propose L-FNNG, a novel solution for accelerating large-scale k -nearest neighbor graph construction on CPU-FPGA heterogeneous platform. The CPU is responsible for dividing data and determining the order of partition processing, while the FPGA executes all construction tasks to utilize the acceleration capability fully. To accelerate the execution of construction tasks, we design an efficient FPGA accelerator, which includes the Block-based Scheduling (BS) and Useless Computation Aborting (UCA) techniques to address the problems of memory access and computation in the NN-Descent algorithm. We also propose an efficient scheduling strategy that includes a KD-tree-based data partitioning method and a hierarchical processing method to address scheduling inefficiency. We evaluate L-FNNG on a Xilinx Alveo U280 board hosted by a 64-core Xeon server. On multiple large-scale datasets, L-FNNG achieves, on average, 2.3 × construction speedup over the state-of-the-art GPU-based solution.

PH-CF: A Phased Hybrid Algorithm for Accelerating Subgraph Matching Based on CPU-FPGA Heterogeneous Platform

Nowadays, more and more data are represented and stored by a graph structure, and subgraph matching is a fundamental problem in a variety of scientific machine learning and industrial applications, such as remote sensing image registration, industrial inspection, etc. Due to the NP-hard problem of subgraph matching, the explosive growth of graph data, the disadvantages of high energy consumption, and the high overhead of CPU and GPU platforms, computing subgraph matching is becoming more and more challenging. To alleviate this problem, we propose a phased hybrid algorithm to accelerate the enumeration task of subgraph matching, called <monospace xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">PH-CF</monospace> , based on the CPU-FPGA heterogeneous platform. This approach can make full use of the pipeline and data flow mechanism, low power consumption, and configurable characteristics of FPGA. First, the matching order of query vertices automatically selects GQL or RI methods according to the sparsity of the data (query) graph. Second, a candidate vertex auxiliary data structure set partitioning method is designed to effectively realize the load balance of multiple computing units at the FPGA and CPU host sides. Third, FPGA's pipeline and data flow mechanism is used to accelerate the enumeration phase of subgraph matching. Experimental results on real-world and synthetic datasets show that the performance of the <monospace xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">PH-CF</monospace> outperforms the state-of-the-arts. <monospace xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">PH-CF</monospace> can obtain the average performance improvement of up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$16.07\times$</tex-math></inline-formula> , <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$38.61\times$</tex-math></inline-formula> , and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$11.46\times$</tex-math></inline-formula> over CFL, CECI, and DP-iso, respectively. Moreover, our approach has good stability and robustness on various datasets.

PPOAccel: A High-Throughput Acceleration Framework for Proximal Policy Optimization

Reinforcement Learning (RL) is a major branch of AI that enables agents to learn optimal decision making via interaction with the environment. Proximal Policy Optimization (PPO) is the state-of-the-art policy optimization based RL algorithm which achieves superior overall performance on various benchmarks. A PPO agent iteratively optimizes its policy - a function which chooses optimal actions approximated by a DNN, with each iteration consisting of two computationally intensive phases: Sample Generation - where agents inference on its policy and interact with the environment to collect data, and Model Update - where the policy is trained using the collected data. In this paper, we develop the first high-throughput PPO accelerator on CPU-FPGA heterogeneous platform. Our unified systolic-array based design accelerates both the inference and the training of the deep neural network used in a RL algorithm, and is generalizable to various MLP and CNN models across a wide range of RL applications. We develop novel optimizations to simultaneously reduce data access and computation latencies, specifically: (a) optimal data flow mapping to systolic array, (b) novel memory-blocked data layout to enable streaming stall-free data access in both forward and backward propagations, and, (c) a systolic array compute sharing technique to mitigate load imbalance in the training of two networks. We evaluate our design on widely used robotics and gaming benchmarks, achieving 1.4×–26× and 1.3×–2.7× improvements in throughput, respectively, when compared with state-of-the-art CPU/CPU-GPU implementations.

Aggressive Pipelining of Irregular Applications on Reconfigurable Hardware

CPU-FPGA heterogeneous platforms offer a promising solution for high-performance and energy-efficient computing systems by providing specialized accelerators with post-silicon reconfigurability. To unleash the power of FPGA, however, the programmability gap has to be filled so that applications specified in high-level programming languages can be efficiently mapped and scheduled on FPGA. The above problem is even more challenging for irregular applications, in which the execution dependency can only be determined at run time. Thus over-serialized accelerators are generated from existing works that rely on compile time analysis to schedule the computation. In this work, we propose a comprehensive software-hardware co-design framework, which captures parallelism in irregular applications and aggressively schedules pipelined execution on reconfigurable platform. Based on an inherently parallel abstraction packaging parallelism for runtime schedule, our framework significantly differs from existing works that tend to schedule executions at compile time. An irregular application is formulated as a set of tasks with their dependencies specified as rules describing the conditions under which a subset of tasks can be executed concurrently. Then datapaths on FPGA will be generated by transforming applications in the formulation into task pipelines orchestrated by evaluating rules at runtime, which could exploit fine-grained pipeline parallelism as handcrafted accelerators do. An evaluation shows that this framework is able to produce datapath with its quality close to handcrafted designs. Experiments show that generated accelerators are dramatically more efficient than those created by current high-level synthesis tools. Meanwhile, accelerators generated for a set of irregular applications attain 0.5x~1.9x performance compared to equivalent software implementations we selected on a server-grade 10-core processor, with the memory subsystem remaining as the bottleneck.