Retraining Conditions: How Much to Retrain a Network After Pruning?

Abstract

Restoring the desired performance of a pruned model requires a fine-tuning step, which lets the network relearn using the training data, except that the parameters are initialised to the pruned parameters. This relearning procedure is a key component in deciding the time taken in building a hardware-friendly architecture. This paper analyses the fine-tuning or retraining step after pruning the network layer-wise and derives lower bounds for the number of epochs the network will take based on the amount of pruning done. Analyses on the propagation of errors through the layers while pruning layer-wise is also performed and a new parameter named ‘Net Deviation’ is proposed which can be used to estimate how good a pruning algorithm is. This parameter could be an alternative to ‘test accuracy’ that is normally used. Net Deviation can be calculated while pruning, using the same data that was used in the pruning procedure. Similar to the test accuracy degradation for different amounts of pruning, the net deviation curves help compare the pruning methods. As an example, a comparison between Random pruning, Weight magnitude based pruning and Clustered pruning is performed on LeNet-300-100 and LeNet-5 architectures using Net Deviation. Results indicate clustered pruning to be a better option than random approach, for higher compression.