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# Liger Kernel: Efficient Triton Kernels for LLM Training


## Key Features

- **Ease of use:** Simply patch your Hugging Face model with one line of code, or compose your own model using our Liger Kernel modules.
- **Time and memory efficient:** In the same spirit as Flash-Attn, but for layers like **RMSNorm**, **RoPE**, **SwiGLU**, and **CrossEntropy**! Increases multi-GPU training throughput by 20% and reduces memory usage by 60% with **kernel fusion**, **in-place replacement**, and **chunking** techniques.
- **Exact:** Computation is exact—no approximations! Both forward and backward passes are implemented with rigorous unit tests and undergo convergence testing against training runs without Liger Kernel to ensure accuracy.
- **Lightweight:** Liger Kernel has minimal dependencies, requiring only Torch and Triton—no extra libraries needed! Say goodbye to dependency headaches!
- **Multi-GPU supported:** Compatible with multi-GPU setups (PyTorch FSDP, DeepSpeed, DDP, etc.).
- **Trainer Framework Integration**: [Axolotl](https://github.com/axolotl-ai-cloud/axolotl), [LLaMa-Factory](https://github.com/hiyouga/LLaMA-Factory), [SFTTrainer](https://github.com/huggingface/trl/releases/tag/v0.10.1), [Hugging Face Trainer](https://github.com/huggingface/transformers/pull/32860), [SWIFT](https://github.com/modelscope/ms-swift), [oumi](https://github.com/oumi-ai/oumi/tree/main)

## Installation

### Dependencies

- `torch >= 2.1.2`
- `triton >= 2.3.0`

### Optional Dependencies

- `transformers >= 4.x`: Required if you plan to use the transformers models patching APIs. The specific model you are working will dictate the minimum version of transformers.

> **Note:**
> Our kernels inherit the full spectrum of hardware compatibility offered by [Triton](https://github.com/triton-lang/triton).

To install from source:

```bash
git clone https://github.com/linkedin/Liger-Kernel.git
cd Liger-Kernel

# Install Default Dependencies
# Setup.py will detect whether you are using AMD or NVIDIA
pip install -e .

# Setup Development Dependencies
pip install -e ".[dev]"

# NOTE -> For AMD users only
pip3 install --pre torch torchvision torchaudio --index-url https://download.pytorch.org/whl/nightly/rocm6.3/
```


## Getting Started

There are a couple of ways to apply Liger kernels, depending on the level of customization required.

### 1. Use AutoLigerKernelForCausalLM

Using the `AutoLigerKernelForCausalLM` is the simplest approach, as you don't have to import a model-specific patching API. If the model type is supported, the modeling code will be automatically patched using the default settings.

```python
from liger_kernel.transformers import AutoLigerKernelForCausalLM

# This AutoModel wrapper class automatically monkey-patches the
# model with the optimized Liger kernels if the model is supported.
model = AutoLigerKernelForCausalLM.from_pretrained("path/to/some/model")
```

### 2. Apply Model-Specific Patching APIs

Using the [patching APIs](#patching), you can swap Hugging Face models with optimized Liger Kernels.

```python
import transformers
from liger_kernel.transformers import apply_liger_kernel_to_llama

# 1a. Adding this line automatically monkey-patches the model with the optimized Liger kernels
apply_liger_kernel_to_llama()

# 1b. You could alternatively specify exactly which kernels are applied
apply_liger_kernel_to_llama(
  rope=True,
  swiglu=True,
  cross_entropy=True,
  fused_linear_cross_entropy=False,
  rms_norm=False
)

# 2. Instantiate patched model
model = transformers.AutoModelForCausalLM("path/to/llama/model")
```

### 3. Compose Your Own Model

You can take individual [kernels](https://github.com/linkedin/Liger-Kernel?tab=readme-ov-file#model-kernels) to compose your models.

```python
from liger_kernel.transformers import LigerFusedLinearCrossEntropyLoss
import torch.nn as nn
import torch

model = nn.Linear(128, 256).cuda()

# fuses linear + cross entropy layers together and performs chunk-by-chunk computation to reduce memory
loss_fn = LigerFusedLinearCrossEntropyLoss()

input = torch.randn(4, 128, requires_grad=True, device="cuda")
target = torch.randint(256, (4, ), device="cuda")

loss = loss_fn(model.weight, input, target)
loss.backward()
```