FPGAs are increasingly prevalent in cloud deployments, serving as Smart NICs
or network-attached accelerators. Despite their potential, developing
distributed FPGA-accelerated applications remains cumbersome due to the lack of
appropriate infrastructure and communication abstractions. To facilitate the
development of distributed applications with FPGAs, in this paper we propose
ACCL+, an open-source versatile FPGA-based collective communication library.
Portable across different platforms and supporting UDP, TCP, as well as RDMA,
ACCL+ empowers FPGA applications to initiate direct FPGA-to-FPGA collective
communication. Additionally, it can serve as a collective offload engine for
CPU applications, freeing the CPU from networking tasks. It is user-extensible,
allowing new collectives to be implemented and deployed without having to
re-synthesize the FPGA circuit. We evaluated ACCL+ on an FPGA cluster with 100
Gb/s networking, comparing its performance against software MPI over RDMA. The
results demonstrate ACCL+'s significant advantages for FPGA-based distributed
applications and highly competitive performance for CPU applications. We
showcase ACCL+'s dual role with two use cases: seamlessly integrating as a
collective offload engine to distribute CPU-based vector-matrix multiplication,
and serving as a crucial and efficient component in designing fully FPGA-based
distributed deep-learning recommendation inference.

为了方便开发分布式 FPGA 应用，本文提出了一种开源的多功能基于 FPGA 的集体通信库 ACCL+，可以作为 CPU 应用的集体卸载引擎，同时通过两个应用案例展示其在分布式深度学习推荐推理中的关键作用和高效性能。