Evaluation of FFT for GPU Cluster Using Tightly Coupled Accelerators Architecture

Inter-node communications between accelerators in heterogeneous clusters require extra latency because of the time required to transfer data copies between the host and accelerator. Such communication latencies inhibit the optimal performance of affected applications. To address this problem, we proposed the Tightly Coupled Accelerators (TCA) architecture and designed an interconnection router chip named PEACH2. Accelerators in the TCA architecture communicate directly via the PCIe protocol, which is the current fundamental interface for all the accelerators and the host CPU, to eliminate protocol and data copy overheads. In this paper, we apply the TCA architecture to the Fast Fourier Transform (FFT) program, which is commonly used in scientific computations. First, we implemented all-to-all communication to TCA. The all-to-all communication was then applied to FFTE, which is one of the implementations of FFT. Based on the evaluation results using the HA-PACS/TCA system, we achieved the speedup of 2.7 with TCA in comparison with that with MPI using 16 nodes on the medium size.