Real-Time Scheduling and Analysis of OpenMP Task Systems with Tied Tasks

OpenMP is a promising framework for developing parallel real-time software on multi-cores. Although similar to the DAG task model, OpenMP task systems are significantly more difficult to analyze due to constraints posed by the OpenMP specification. An important feature in OpenMP is tied tasks, which must execute on the same thread during the whole life cycle. Although tied tasks enjoy benefits in simplicity and efficiency, it was considered to be not suitable to real-time systems due to its complex behavior. In this paper, we study the realtime scheduling and analysis of OpenMP task systems with tied tasks. First, we show that under the existing scheduling algorithms in OpenMP, tied tasks indeed may lead to extremely bad timing behaviors where the parallel workload is sequentially executed completely. To solve this problem, we proposed a new scheduling algorithm and developed two response time bounds for it, with different trade-off between simplicity and analysis precision. Experiments with both randomly generated OpenMP task systems and realistic OpenMP programs show that the response time bounds obtained by our approach for tied task systems are very close to that of untied tasks.