  Workloads in data processing clusters are often represented in the form of
DAG (Directed Acyclic Graph) jobs. Scheduling DAG jobs is challenging. Simple
heuristic scheduling algorithms are often adopted in practice in production
data centres. There is much room for scheduling performance optimisation for
cost saving. Recently, reinforcement learning approaches (like decima) have
been attempted to optimise DAG job scheduling and demonstrate clear performance
gain in comparison to traditional algorithms. However, reinforcement learning
(RL) approaches face their own problems in real-world deployment. In
particular, their black-box decision making processes and generalizability in
unseen workloads may add a non-trivial burden to the cluster administrators.
Moreover, adapting RL models on unseen workloads often requires significant
amount of training data, which leaves edge cases run in a sub-optimal mode. To
fill the gap, we propose a new method to distill a simple scheduling policy
based on observations of the behaviours of a complex deep learning model. The
simple model not only provides interpretability of scheduling decisions, but
also adaptive to edge cases easily through tuning. We show that our method
achieves high fidelity to the decisions made by deep learning models and
outperforms these models when additional heuristics are taken into account.
