Large language models (LLMs) have achieved significant success across various domains. However, training these LLMs typically involves substantial memory and computational costs during both forward and backward propagation. While parameter-efficient fine-tuning (PEFT) considerably reduces the training memory associated with parameters, it does not address the significant computational costs and activation memory. In this paper, we propose Dropping Backward Propagation (DropBP), a novel approach designed to reduce computational costs and activation memory while maintaining accuracy. DropBP randomly drops layers during backward propagation, which is essentially equivalent to training shallow submodules generated by undropped layers and residual connections. Additionally, DropBP calculates the sensitivity of each layer to assign an appropriate drop rate, thereby stabilizing the training process. DropBP is not only applicable to full fine-tuning but can also be orthogonally integrated with all types of PEFT by dropping layers during backward propagation. Specifically, DropBP can reduce training time by 44% with comparable accuracy to the baseline, accelerate convergence to the same perplexity by 1.5$\times$, and enable training with a sequence length 6.2$\times$ larger on a single NVIDIA-A100 GPU.

Large language models (LLMs) have achieved significant success across various domains. However, training these LLMs typically involves substantial memory and computational costs during both forward and backward propagation. While parameter-efficient fine-tuning (PEFT) considerably reduces the training memory associated with parameters, it does not address the significant computational costs and activation memory. In this paper, we propose Dropping Backward Propagation (DropBP), a novel approach designed to reduce computational costs and activation memory while maintaining accuracy. DropBP randomly drops layers during backward propagation, which is essentially equivalent to training shallow submodules generated by undropped layers and residual connections.

Training deep neural networks typically involves substantial computational costs during both forward and backward propagation. The conventional layer dropping techniques drop certain layers during training for reducing the computations burden. However, dropping layers during forward propagation adversely affects the training process by degrading accuracy. In this paper, we propose Dropping Backward Propagation (DropBP), a novel approach designed to reduce computational costs while maintaining accuracy. DropBP randomly drops layers during the backward propagation, which does not deviate forward propagation. Moreover, DropBP calculates the sensitivity of each layer to assign appropriate drop rate, thereby stabilizing the training process. DropBP is designed to enhance the efficiency of the training process with backpropagation, thereby enabling the acceleration of both full fine-tuning and parameter-efficient fine-tuning using backpropagation. Specifically, utilizing DropBP in QLoRA reduces training time by 44%, increases the convergence speed to the identical loss level by 1.5$\times$, and enables training with a 6.2$\times$ larger sequence length on a single NVIDIA-A100 80GiB GPU in LLaMA2-70B. The code is available at https://github.com/WooSunghyeon/dropbp.