Static Scheduling of Moldable Streaming Tasks With Task Fusion for Parallel Systems With DVFS
Christoph Keßler, Sebastian Litzinger, Jörg Keller
Abstract
We consider the problem of statically scheduling a task graph of moldable streaming tasks (i.e., the actor network) to a multicore or many-core CPU with discrete dynamic voltage and frequency scaling (DVFS). We employ an integer linear programming (ILP) approach that combines allocating cores to tasks, mapping tasks to core subsets, selecting a DVFS level for each task, and considering all options for task fusion as provided by a cost model, given data throughput and latency requirements and targeting low energy consumption. We also propose a partly decoupled approach that applies greedy prefusion before running an ILP-based scheduler considering the other three subproblems together. We use microbenchmarking on an ARM big.LITTLE architecture to quantify the advantage of task fusion in the above setting, and evaluate the use of task fusion in terms of energy savings, latency improvement, and scheduling time for three real-world applications. We confirm the scheduling results by running the applications with and without task fusions on the ARM big.LITTLE. Results indicate that streaming applications can profit from task fusion, as we achieve a significant reduction of energy consumption in most cases, while scheduling time is only moderately increased.