Real-time Deep Neural Network (DNN) inference with low-latency requirement has become increasingly important for numerous applications in both cloud computing (e.g., Apple's Siri) and edge computing (e.g., Google Waymo's driverless car). FPGA-based DNN accelerators have demonstrated both superior flexibility and performance; in addition, for real-time inference with low batch size, FPGA is expected to achieve further performance improvement. However, the performance gain from the single-FPGA design is obstructed by the limited on-chip resource. In this paper, we employ multiple FPGAs to cooperatively run DNNs with the objective of achieving super-linear speed-up against single-FPGA design. In implementing such systems, we found two barriers that hinder us from achieving the design goal: (1) the lack of a clear partition scheme for each DNN layer to fully exploit parallelism, and (2) the insufficient bandwidth between the off-chip memory and the accelerator due to the growing size of DNNs. To tackle these issues, we propose a general framework, "Super-LIP", which can support different kinds of DNNs. In this paper, we take Convolutional Neural Network (CNN) as a vehicle to illustrate Super-LIP. We first formulate an accurate system-level model to support the exploration of best partition schemes. Then, we develop a novel design methodology to effectively alleviate the heavy loads on memory bandwidth by moving traffic from memory bus to inter-FPGA links. We implement Super-LIP based on ZCU102 FPGA boards. Results demonstrate that Super-LIP with 2 FPGAs can achieve 3.48x speedup, compared to the state-of-the-art single-FPGA design. What is more, as the number of FPGAs scales up, the system latency can be further reduced while maintaining high energy efficiency.
The development of FPGA-based DNNs accelerator evolves in three stages. At the early stage @cite_4 @cite_30 @cite_19 @cite_5 @cite_21 @cite_33 , the whole FPGA is designed as one accelerator, and a controller iteratively moves data from off-chip DRAM to the accelerator to be executed. In the second stage, it is observed that the computation resource cannot be fully utilized with the one-size accelerator due to the varied computation and memory requirements in DNN layers. To overcome this shortage, multiple accelerators are integrated into one FPGA @cite_24 @cite_25 @cite_12 . However, the restrict resource on one board still limits the performance boosting of DNNs on FPGAs.
@cite_30 @cite_4 @cite_33 @cite_21 @cite_24 @cite_19 @cite_5 @cite_25 @cite_12
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Building a high-performance EPGA accelerator for Deep Neural Networks (DNNs) often requires RTL programming, hardware verification, and precise resource allocation, all of which can be time-consuming and challenging to perform even for seasoned FPGA developers. To bridge the gap between fast DNN construction in software (e.g., Caffe, TensorFlow) and slow hardware implementation, we propose DNNBuilder for building high-performance DNN hardware accelerators on FPGAs automatically. Novel techniques are developed to meet the throughput and latency requirements for both cloud- and edge-devices. A number of novel techniques including high-quality RTL neural network components, a fine-grained layer-based pipeline architecture, and a column-based cache scheme are developed to boost throughput, reduce latency, and save FPGA on-chip memory. To address the limited resource challenge, we design an automatic design space exploration tool to generate optimized parallelism guidelines by considering external memory access bandwidth, data reuse behaviors, FPGA resource availability, and DNN complexity. DNNBuilder is demonstrated on four DNNs (Alexnet, ZF, VGG16, and YOLO) on two FPGAs (XC7Z045 and KU115) corresponding to the edge- and cloud-computing, respectively. The fine-grained layer-based pipeline architecture and the column-based cache scheme contribute to 7.7x and 43x reduction of the latency and BRAM utilization compared to conventional designs. We achieve the best performance (up to 5.15x faster) and efficiency (up to 5.88x more efficient) compared to published FPGA-based classification-oriented DNN accelerators for both edge and cloud computing cases. We reach 4218 GOPS for running object detection DNN which is the highest throughput reported to the best of our knowledge. DNNBuilder can provide millisecond-scale real-time performance for processing HD video input and deliver higher efficiency (up to 4.35x) than the GPU-based solutions. Current-generation Deep Neural Networks (DNNs), such as AlexNet and VGG, rely heavily on dense floating-point matrix multiplication (GEMM), which maps well to GPUs (regular parallelism, high TFLOP s). Because of this, GPUs are widely used for accelerating DNNs. Current FPGAs offer superior energy efficiency (Ops Watt), but they do not offer the performance of today's GPUs on DNNs. In this paper, we look at upcoming FPGA technology advances, the rapid pace of innovation in DNN algorithms, and consider whether future high-performance FPGAs will outperform GPUs for next-generation DNNs. The upcoming Intel® 14-nm Stratix? 10 FPGAs will have thousands of hard floating-point units (DSPs) and on-chip RAMs (M20K memory blocks). They will also have high bandwidth memories (HBMs) and improved frequency (HyperFlex? core architecture). This combination of features brings FPGA raw floating point performance within striking distance of GPUs. Meanwhile, DNNs are quickly evolving. For example, recent innovations that exploit sparsity (e.g., pruning) and compact data types (e.g., 1-2 bit) result in major leaps in algorithmic efficiency. However, these innovations introduce irregular parallelism on custom data types, which are difficult for GPUs to handle but would be a great fit for FPGA's extreme customizability. This paper evaluates a selection of emerging DNN algorithms on two generations of Intel FPGAs (Arria'10, Stratix'10) against the latest highest performance Titan X Pascal GPU. We created a customizable DNN accelerator template for FPGAs and used it in our evaluations. First, we study various GEMM operations for next-generation DNNs. Our results show that Stratix 10 FPGA is 10 , 50 , and 5.4x better in performance (TOP sec) than Titan X Pascal GPU on GEMM operations for pruned, Int6, and binarized DNNs, respectively. Then, we present a detailed case study on accelerating Ternary ResNet which relies on sparse GEMM on 2-bit weights (i.e., weights constrained to 0,+1,-1) and full-precision neurons. The Ternary ResNet accuracy is within 1 of the full-precision ResNet which won the 2015 ImageNet competition. On Ternary-ResNet, the Stratix 10 FPGA can deliver 60 better performance over Titan X Pascal GPU, while being 2.3x better in performance watt. Our results indicate that FPGAs may become the platform of choice for accelerating next-generation DNNs. FPGA is a promising candidate for the acceleration of Deep Neural Networks (DNN) with improved latency and energy consumption compared to CPU and GPU-based implementations. DNNs use sequences of layers of regular computation that are well suited for HLS-based design for FPGA. However, optimizing large neural networks under resource constraints is still a key challenge. HLS must manage on-chip computation, buffering resources, and off-chip memory accesses to minimize the total latency. In this paper, we present a design framework for DNNs that uses highly configurable IPs for neural network layers together with a new design space exploration engine for Resource Allocation Management (REALM). We also carry out efficient memory subsystem design and fixed-point weight re-training to further improve our FPGA solution. We demonstrate our design framework on the Long-term Recurrent Convolution Network for video inputs. Our implementation on a Xilinx VC709 board achieves 3.1X speedup compared to an NVIDIA K80 and 4.75X speedup compared to an Intel Xeon with 17.5X lower energy per image. FPGA-based CNN accelerators have advantages in flexibility and power efficiency and so are being deployed by a number of cloud computing service providers, including Microsoft, Amazon, Tencent, and Alibaba. Given the increasing complexity of neural networks, however, it is becoming challenging to efficiently map CNNs to multi-FPGA platforms. In this work, we present a scalable framework, FPDeep, which helps engineers map a specific CNN's training logic to a multi-FPGA cluster or cloud and to build RTL implementations for the target network. With FPDeep, multi-FPGA accelerators work in a deeply-pipelined manner using a simple 1-D topology; this enables the accelerators to map directly onto many existing platforms, including Catapult, Catapult2, and almost any tightly-coupled FPGA cluster. FPDeep uses two mechanisms to facilitate high-performance and energy-efficiency. First, FPDeep provides a strategy to balance workload among FPGAs, leading to improved utilization. Second, training of CNNs is executed in a fine-grained inter- and intra-layer pipelined manner, minimizing the time that features need to remain available while waiting for back-propagation. This reduces the storage demand to where only on-chip memory is required for convolution layers. Experiments show that FPDeep has good scalability to a large number of FPGAs, with the limiting factor being the FPGA-to-FPGA bandwidth. Using six transceivers per FPGA, FPDeep shows linearity up to 60 FPGAs. We evaluate energy efficiency in GOPs J and find that FPDeep provides up to 3.4 times higher energy efficiency than the Tesla K80 GPU.