MODES: model-based optimization on distributed embedded systems

Abstract

The predictive performance of a machine learning model highly depends on the corresponding hyper-parameter setting. Hence, hyper-parameter tuning is often indispensable. Normally such tuning requires the dedicated machine learning model to be trained and evaluated on centralized data to obtain a performance estimate. However, in a distributed machine learning scenario, it is not always possible to collect all the data from all nodes due to privacy concerns or storage limitations. Moreover, if data has to be transferred through low bandwidth connections it reduces the time available for tuning. Model-Based Optimization (MBO) is one state-of-the-art method for tuning hyper-parameters but the application on distributed machine learning models or federated learning lacks research. This work proposes a framework textit{MODES} that allows to deploy MBO on resource-constrained distributed embedded systems. Each node trains an individual model based on its local data. The goal is to optimize the combined prediction accuracy. The presented framework offers two optimization modes: (1) textit{MODES}-B considers the whole ensemble as a single black box and optimizes the hyper-parameters of each individual model jointly, and (2) textit{MODES}-I considers all models as clones of the same black box which allows it to efficiently parallelize the optimization in a distributed setting. We evaluate textit{MODES} by conducting experiments on the optimization for the hyper-parameters of a random forest and a multi-layer perceptron. The experimental results demonstrate that, with an improvement in terms of mean accuracy (textit{MODES}-B), run-time efficiency (textit{MODES}-I), and statistical stability for both modes, textit{MODES} outperforms the baseline, i.e., carry out tuning with MBO on each node individually with its local sub-data set.