STEEL-RT: combining single task–single executor model and expanded scheduling to ease heterogeneity exploitation

The ever-increasing complexity in terms of heterogeneity and available parallelism of modern architectures, together with the growing software ecosystem in terms of application libraries and runtime systems are posing a new challenge in terms of programmability on top of the already difficult task of extracting high parallel performance. With the goal of simplifying the programmability at the extreme, we first present the single task–single executor (STSE) model, in which the execution entry point consists solely on a single task assigned to an abstract execution context or executor, representing the whole system platform. As a second contribution, we introduce the expanded scheduling operations that endow executors with additional runtime task scheduling capabilities, and explain how executors can be composed to express and exploit different architectural features at run time under the framework of a single/multiple–task/executor taxonomy. As a result, we introduce STEEL, a novel programming model built on these concepts and STEEL-RT, a coupled high-performance runtime implementation for it. We illustrate the potential of STEEL by means of runtime experiments on a modern heterogeneous architecture, showing that complex and efficient heterogeneous executions are accessible from a STSE approach.