Towards a GPU accelerated selective sparsity multilayer perceptron algorithm using K-Nearest Neighbors search.

The use of artificial neural networks and deep learning is common in several areas of knowledge. In many situations, it is necessary to use neural networks with many neurons. For example, the Extreme Classification problems can use neural networks that process more than 500,000 classes and inputs with more than 100,000 dimensions, which can make the training process unfeasible due to the high computational cost required. To overcome this limitation, several techniques were proposed in past works, such as the SLIDE algorithm, whose implementation is based on the construction of hash tables and on CPU parallelism. This work proposes the SLIDE-GPU, which replaces the use of hash tables by algorithms that use GPU to search for approximate neighbors, or approximate nearest neighbors (ANN) search. In addition, SLIDE-GPU also proposes the use of GPU to accelerate the activation step of neural networks. Among the experiments carried out, it was possible to notice a training process acceleration of up to 268% in execution time considering the inference accuracy, although currently maintaining the backpropagation phase with CPU processing. This suggests that further acceleration can be obtained in future work, by using massive parallelism in the entire process. The ANN-based technique provides better inference accuracy at each epoch, which helps producing the global acceleration, besides using the GPU in the neuron activation step. The GPU neuron activation acceleration reached a 28.09 times shorter execution time compared to the CPU implementation on this step alone.