Adaptive OpenMP Runtime System for Embedded Multicores

Abstract

The recent OpenMP device constructs enable application writers to utilize the host CPUs along with other attached computational resources, in an intuitive and productive manner. These target-related directives offload portions of the program code (kernels) to any of the available computational devices; the kernels themselves can take advantage of the multiplicity of processing elements within the target device by employing OpenMP constructs. However, most co-processors or accelerators, especially embedded ones, have limited resources. This severely constrains the extend of OpenMP support that can be implemented within a device. A usual design decision is to support OpenMP partially, in effect hindering the full exploitation of the device capabilities through a high-level programming model. In this work, we present a novel solution to this problem for embedded multicores. We propose a compiler-assisted, adaptive runtime system organization, which generates application-specific support by implementing only the OpenMP functionality required each time. Full OpenMP support is available if needed. However, in the usual scenario where kernels do not require complex OpenMP functionalities, our method can lead to dramatically reduced executable sizes. Our proposal is demonstrated by a complete implementation on the popular Parallella board.