On the Three P's of Parallel Programming for Heterogeneous Computing: Performance, Productivity, and Portability

Abstract

ÐAs FPGAs and GPUs continue to make inroads into high-performance computing (HPC), the need for languages and frameworks that offer performance, productivity, and portability across heterogeneous platforms, such as FPGAs and GPUs, continues to grow. OpenCL and SYCL have emerged as frameworks that offer cross-platform functional portability between FPGAs and GPUs. While functional portability across a diverse set of platforms is an important feature of portable frameworks, achieving performance portability often requires vendor and platform-specific optimizations. Achieving performance portability, therefore, comes at the expense of productivity.This paper presents a quantification of the tradeoffs between performance, portability, and productivity of OpenCL and SYCL. It extends and complements our prior work on quantifying performance-productivity tradeoffs between Verilog and OpenCL for the FPGA. In addition to evaluating the performance-productivity tradeoffs between OpenCL and SYCL, this work quantifies the performance portability (PP) of OpenCL and SYCL as well as their code convergence (CC), i.e., a measure of productivity across different platforms (e.g., FPGA and GPU). Using two applications as case studies (i.e., edge detection using the Sobel filter, and graph link prediction using the Jaccard similarity index), we characterize the tradeoffs between performance, portability, and productivity. Our results show that OpenCL and SYCL offer complementary tradeoffs. While OpenCL delivers better performance portability than SYCL, SYCL offers better code convergence and a 1.6× improvement in source lines of code over OpenCL.