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# Kernels（自定义内核）

自定义内核针对矩阵乘法、注意力计算和归一化等特定算子进行优化，使其运行更快。将多个算子融合到单个内核中可以减少对 GPU 显存的读写次数，降低内存带宽使用，同时消除逐算子的启动开销。

## Hub 内核

[Hub](https://huggingface.co/kernels-community) 上托管了社区内核，你可以通过 [`KernelConfig`] 加载它们。将配置传入 [`~AutoModelForCausalLM.from_pretrained`] 的 `kernel_config` 参数即可。内核加载后，会在训练过程中自动激活。有关所有可用选项，请参阅[加载内核](./kernel_doc/loading_kernels#kernelconfig)指南。

```py
from transformers import AutoModelForCausalLM, KernelConfig

kernel_config = KernelConfig(
    kernel_mapping={
        "RMSNorm": "kernels-community/rmsnorm",
    }
)
model = AutoModelForCausalLM.from_pretrained(
    "Qwen/Qwen3-0.6B",
    use_kernels=True,
    kernel_config=kernel_config,
)
```

## Liger

[Liger Kernel](https://github.com/linkedin/Liger-Kernel) 将 RMSNorm、RoPE、SwiGLU、CrossEntropy 和 FusedLinearCrossEntropy 等层融合为单个 Triton 内核。它与 FlashAttention、FSDP 和 DeepSpeed 兼容，能够提升多 GPU 训练的吞吐量，同时降低显存占用，让更大的词汇量、批次大小和上下文长度变得更加可行。

```bash
pip install liger-kernel
```

在 [`TrainingArguments`] 中设置 `use_liger_kernel=True`，即可用 Liger 内核替换对应的模型层。

> [!TIP]
> 请参阅 [patching](https://github.com/linkedin/Liger-Kernel#patching) 页面获取支持的模型完整列表。

```py
from transformers import TrainingArguments

training_args = TrainingArguments(
    ...,
    use_liger_kernel=True
)
```

要控制哪些层被替换，可以通过 `liger_kernel_config` 字典来指定。可选参数因模型而异，包括：`rope`、`swiglu`、`cross_entropy`、`fused_linear_cross_entropy`、`rms_norm` 等。

```py
from transformers import TrainingArguments

training_args = TrainingArguments(
    ...,
    use_liger_kernel=True,
    liger_kernel_config={
        "rope": True,
        "cross_entropy": True,
        "rms_norm": False,
        "swiglu": True,
    }
)
```

## 下一步

- 参阅[注意力后端](./attention_interface)指南，了解 FlashAttention 等降低显存占用的内核详情。
- 参阅 [torch.compile](./torch_compile) 指南，了解如何编译整个训练步骤的前向和反向传播。