DropBP: Accelerating Fine-Tuning of Large Language Models

This is the official repository for DropBP: Accelerating Fine-Tuning of Large Language Models accepted in Neurips2024.

Abstract

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. Furthermore, our DropBP enabled a throughput increase of 79% on a NVIDIA A100 GPU and 117% on an Intel Gaudi2 HPU. The code is available at [https://github.com/WooSunghyeon/dropbp](https://github.com/WooSunghyeon/dropbp).

Install

1. Install PyTorch before installing DropBP library.

2. Build

pip install -v -e .

Usage

1. Install DropBP layer to your model

• Note that you have to insert the flops of layers in DropBP layers
• For instance, in general transformer,
• FLOPs of attention layers: $8bsh^2+4bhs^2$
• FLOPs of mlp layers: $16bsh^2$
• It's okay to input the ratio of FLOPs for each layer, rather than exact

import torch
..
from dropbp.layer import DropBP

...
class Block(nn.Modoule): # transformer block
    def __init__(self, ..):
        self.norm_1 = ...
        self.attn = ...
        self.norm_2 = ...
        self.mlp = ...
        
        # Define DropBP layers
        # The FLOPs below is about general transformer block per batch*seq
        # with intermediate_size = 4*hidden_size
        attn_flops = 8*config.hidden_size**2 + 4*config.hidden_size*self.sequence_length 
        mlp_flops = 16*config.hidden_size**2
        self.dropbp_attn = DropBP(flops=attn_flops)
        self.dropbp_mlp = DropBP(flops=mlp_flops)
        ...
    def forward(self, x, ..):
        h = self.attn(self.norm_1(x), ...)
        x = self.dropbp_attn(h)+x   # instead of 'x = h+x'  
        h = self.mlp(self.norm_2(x))
        x = self.dropbp_mlp(h)+x    # instead of 'x = h+x'    
        return x

2. Integrate the DropBP API into your training code

import torch
from dropbp.handler import DropBPHandler

model = ... # user define model
optimizer = ... # user define optimizer

dropbp_handler = DropBPHandler(model) # define drop handler
dropbp_handler.set_initial_drop_rate(drop_rate) # set a drop rate

# training loop
for iter in ...
    dropbp_handler.dropbp_handler.set_dropped_layers()  # set the dropped layers for each iteration
    def backprop: # define backprop
        output = model(data)
        loss = loss_func(output, target)
        optimizer.zero_grad() # this line must be present
        loss.backward()

    if iter == int(max_iter * 0.1) # adjust drop rates at 10% of training process 
        dropbp_handler.sensitivity_based_drop_bp(backprop, drop_rate) # it automatically adjusts drop rates
    
    out = model(data)
    loss = loss_func(output,target)
    non_grad = dropbp_handler.detact_non_grad() # detect when all layers are dropped
    if not(non_grad): # exclude the above situation for avoiding error
        loss.backward()
    optimizer.step()
    ...

Applications

Our DropBP library can be very easily integrated with existing training code as:

Huggingface

Lit-GPT

optimum-habana