Active Resource Management for Declarative Data-Flow Processing

S-Net is a declarative asynchronous data-flow coordination language. Like many other high-level multi-core programming approaches, the S-Net runtime system makes use of light-weight task abstractions that are automatically mapped to a set of heavy-weight kernel threads for execution. The number of kernel threads is typically motivated by the number of cores in the hardware. We argue that such a fixed choice of kernel threads is suboptimal in two scenarios. Firstly, an application may temporarily expose less concurrency than the underlying hardware offers. In this case the cores waste energy. Secondly, the number of hardware cores effectively available to an application may dynamically change in multi-application and/or multi-user environments. This leads to an over-approximation of the available hardware by individual applications, costly time scheduling by the operating system and, as a consequence, to both waste of energy and loss of performance. We propose an active resource management layer for S-Net that effectively overcomes these issues.