Quantifying Overheads in Charm++ and HPX using Task Bench

Abstract: Asynchronous Many-Task (AMT) runtime systems take advantage of multi-core architectures with light-weight threads, asynchronous executions, and smart scheduling. In this paper, we present the comparison of the AMT systems Charm++ and HPX with the main stream MPI, OpenMP, and MPI+OpenMP libraries using the Task Bench benchmarks. Charm++ is a parallel programming language based on C++, supporting stackless tasks as well as light-weight threads asynchronously along with an adaptive runtime system. HPX is a C++ library for concurrency and parallelism, exposing C++ standards conforming API. First, we analyze the commonalities, differences, and advantageous scenarios of Charm++ and HPX in detail. Further, to investigate the potential overheads introduced by the tasking systems of Charm++ and HPX, we utilize an existing parameterized benchmark, Task Bench, wherein 15 different programming systems were implemented, e.g., MPI, OpenMP, MPI + OpenMP, and extend Task Bench by adding HPX implementations. We quantify the overheads of Charm++, HPX, and the main stream libraries in different scenarios where a single task and multi-task are assigned to each core, respectively. We also investigate each system's scalability and the ability to hide the communication latency.