A knowledge-driven approach to multi-objective IoT task graph scheduling in fog-cloud computing

• We study IoT task graph scheduling in fog-cloud computing environment. • We present an automatic algorithm for knowledge exploration and acquisition. • We develop a genetic algorithm with two crossover and mutation operators. • We present and characterize features to construct a random forest classifier. • We develop a method to refine the knowledge with less importance in the solution. Despite the significant growth of Internet of Things (IoT), there are prominent limitations of this emerging technology, such as limited processing power and storage. Along with the expansion of IoT networks, the fog-cloud computing paradigm has been developed to optimize the provision of services to IoT users by offloading computations to the more powerful processing resources. In this paper, with the aim of optimizing multiple objectives of makespan, energy consumption, and cost, we develop a novel automatic three-module algorithm to schedule multiple task graphs offloaded from IoT devices to the fog-cloud environment. Our algorithm combines the Genetic Algorithm (GA) and the Random Forest (RF) classifier, which we call Hybrid GA-RF (HGARF). Each of the three modules has a responsibility and they are repeated sequentially to extract knowledge from the solution space in the form of IF-THEN rules. The first module is responsible for generating solutions for the training set using a GA. Here, we introduce a chromosome encoding method and a crossover operator to create diversity for multiple task graphs. By expressing a concept called bottleneck and two conditions, we also develop a mutation operator to identify and reduce the workload of certain processing centers. The second module aims at generating rules from the solutions of the training set, and to that end employs an RF classifier. Here, in addition to proposing features to construct decision trees, we develop a format for extracting and recording IF-THEN rules. The third module checks the quality of the generated rules and refines them by predicting the processing resources as well as removing less important rules from the rule set. Finally, the developed HGARF algorithm automatically determines its termination condition based on the quality of the provided solutions. Experimental results demonstrate that our method effectively improves the objective functions in large-size task graphs by up to 13.24 % compared to some state-of-the-art methods.