Applying Models of Computation to OpenCL Pipes for FPGA Computing

Abstract

OpenCL pipes offer a powerful construct for synthesizing multi-kernel FPGA applications with inter-kernel communication dependencies. The communication discipline between the FPGA kernels is restricted to producer-consumer style patterns supported with on-chip FPGA FIFOs. While this provides few restrictions on the usage, the OpenCL compiler is unable to provide guarantees on buffering capacity or schedulability of the connected kernels. Without these guarantees, an OpenCL developer may over-provision hardware resources or assume pessimistic timing during scheduling. We propose imposing a communication discipline inspired from models of computation (e.g.Ptolemy) such as synchronous dataflow (SDF), and bulk synchronous (BSP). These models offer a restricted subset of communication patterns that enable implementation tradeoffs and deliver performance and resource guarantees. This is useful for OpenCL developers operating within the constraints of the FPGA device. We provide a preliminary analysis of our proposal and sketch programmer and compiler responsibilities that would be needed for integrating these features into the FPGA OpenCL environment.