Many datacenter operators have deployed FPGAs as hardware accelerators because their reconfigurability allows them to be repurposed as the application mix changes. Directly attaching the FPGA to the network further reduces latency, improves cost-performance, and reduces energy use relative to mediating network communications with CPUs. However, building accelerated applications or services for direct-attached FPGAs is challenging, especially with the complex I/O and multi-accelerator capacity of modern FPGAs. To address this, we propose Apiary, a microkernel operating system for direct-attached FPGA accelerators. The key idea in Apiary is to raise the level of abstraction for accelerated application code, with security, virtualization, threaded execution, and interprocess communication provided by the hardware OS layer.

Direct-attached accelerators, where application accelerators are directly connected to the datacenter network via a hardware network stack, offer substantial benefits in terms of reduced latency, CPU overhead, and energy use. However, a key challenge is that modern datacenter network stacks are complex, with interleaved protocol layers, network management functions, and virtualization support. To operators, network feature agility, diagnostics, and manageability are often considered just as important as raw performance. By contrast, existing hardware network stacks only support basic protocols and are often difficult to extend since they use fixed processing pipelines. We propose Beehive, a new, open-source FPGA network stack for direct-attached accelerators designed to enable flexible and adaptive construction of complex network functionality in hardware. Application and network protocol elements are modularized as tiles over a network-on-chip substrate. Elements can be added or scaled up/down to match workload characteristics with minimal effort or changes to other elements. Flexible diagnostics and control are integral, with tooling to ensure deadlock safety. Our implementation interoperates with standard Linux TCP and UDP clients, with a 4x improvement in end-to-end RPC tail latency for Linux UDP clients versus a CPU-attached accelerator. Beehive is available at https://github:com/beehive-fpga/beehive

FPGAs are increasingly used to accelerate modern applications, and cloud providers offer FPGA platforms on-demand with a variety of FPGAs, I/O peripherals, and memory options. FPGA vendors expose I/O with low-level interfaces that limit application portability. Current approaches to abstracting these interfaces trade level of abstraction against performance.