Hok: Higher-Order GPU kernels in Elixir

GPUs (Graphics Processing Units) are usually programmed using low-level languages like CUDA or OpenCL. Although these languages allow the implementation of very optimized software, they are difficult to program due to their low-level nature, where programmers have to mix coordination code, i.e., how tasks are created and distributed, with the actual computation code. In this paper we present Hok, an extension to the Elixir functional language that allows the implementation of higher-order GPU kernels, granting programmers the ability to clearly separate coordination from computation. The Hok system provides a DSL (Domain-Specific Language) for writing low-level GPU kernels that can be parameterized with the computation code. Hok allows device functions, including anonymous functions, to be created and referenced in the host code so that they can configure a kernel before it is launched.We demonstrate that Hok can be used to implement high-level abstractions such as algorithmic skeletons and array comprehensions. We also present experiments that demonstrate the usability of the current implementation of Hok, and show that high speedups can be obtained in comparison to pure Elixir, specially in computationally intensive programs with large inputs.