Increasing Flexibility of Cloud FPGA Virtualization

FPGA virtualization enables multiple tenants to share programmable hardware resources for application accelerations in cloud. However, such technique is still of limited usage in commercial FPGA cloud platforms, which mainly lies in: 1) absence of direct programming interfaces of the virtualized FPGA accelerators (vFPGAs) in tenants' virtual machines (VMs), 2) a fixed VM-vFPGA data movement scheme that is inadaptive to a wide range of data sizes among different applications, and 3) performance degradation due to unregulated inter-vFPGA competitions for limited shareable external resources (e.g., off-chip DRAM bandwidth). To tackle all the above issues, we propose a flexible FPGA virtualization framework and prototype an open cloud platform with ARM SoC-equipped FPGAs. Under such framework, tenants are allowed to directly initiate FPGA partial reconfiguration in isolated VMs via a direct I/O-like vFPGA device driver with as low as 20ms overhead. A hybrid data movement approach that leverages both memory-mapped I/O and DMA is also introduced in our framework to adaptively guarantee moderate VM-vFPGA bandwidth towards various data sizes. Moreover, a lightweight priority-based hardware scheduler is elaborated to monitor and dynamically allocate off-chip DRAM bandwidth among vFPGAs. Based on our preliminary infrastructure-level evaluation results, the proposed framework and the open prototyping are of significant interests to researchers looking forward to conducting further explorations in FPGA virtualization.