开发自定义压缩算法：kvpress插件开发全流程教程-开发者社区

开发自定义压缩算法：kvpress插件开发全流程教程

【免费下载链接】kvpressLLM KV cache compression made easy项目地址: https://gitcode.com/gh_mirrors/kv/kvpress

在大型语言模型（LLM）的应用中，KV缓存压缩是提升性能的关键技术。kvpress作为一款强大的LLM KV缓存压缩框架，允许开发者轻松实现和集成自定义压缩算法。本教程将带你从零开始构建一个kvpress插件，掌握核心开发流程和最佳实践。

为什么选择kvpress开发压缩插件？

kvpress提供了灵活的插件架构，让开发者能够专注于压缩算法的核心逻辑，而无需处理复杂的缓存管理和模型集成细节。其主要优势包括：

简化开发流程：统一的接口设计和钩子机制，降低压缩算法的实现难度
广泛的模型支持：兼容Llama、Mistral、Phi3、Qwen等主流LLM架构
灵活的组合方式：支持多个压缩算法的组合使用，实现更高效的压缩策略
完善的测试框架：提供全面的测试工具，确保压缩算法的可靠性和性能

图：kvpress插件架构示意图，展示了压缩算法如何与LLM模型集成

开发环境准备

开始开发前，请确保你的环境满足以下要求：

克隆项目仓库：

git clone https://gitcode.com/gh_mirrors/kv/kvpress cd kvpress

安装依赖：
```
pip install -e .[dev]
```
开发工具：
- Python 3.8+
- PyTorch 2.0+
- 代码编辑器（推荐VS Code或PyCharm）

核心概念：BasePress基类解析

所有kvpress压缩插件都需要继承BasePress基类，该类定义了压缩算法与框架交互的标准接口。关键方法包括：

compress()：实现核心压缩逻辑，必须在子类中重写
forward_hook()：处理模型前向传播时的缓存压缩时机
__call__()：上下文管理器，负责注册和移除钩子

# kvpress/presses/base_press.py class BasePress: """ Base class for all KV cache compression methods. This class provides the foundation for implementing various key-value cache compression techniques. Subclasses must implement the `compress` method to define their specific compression logic. """ def compress( self, module: nn.Module, hidden_states: torch.Tensor, keys: torch.Tensor, values: torch.Tensor, attentions: torch.Tensor, kwargs: dict, ) -> tuple[torch.Tensor, torch.Tensor]: """ The core logic of the compression method. Parameters ---------- module : nn.Module The transformer attention layer where compression is applied. hidden_states : torch.Tensor Hidden states of the current layer with shape (batch_size, seq_len, hidden_dim). keys : torch.Tensor Key tensors from the KV cache with shape (batch_size, num_kv_heads, seq_len, head_dim). values : torch.Tensor Value tensors from the KV cache with shape (batch_size, num_kv_heads, seq_len, head_dim). attentions : torch.Tensor Attention weights from the layer with shape (batch_size, num_heads, seq_len, seq_len). kwargs : dict Additional keyword arguments from the forward pass. Returns ------- tuple[torch.Tensor, torch.Tensor] Compressed keys and values tensors with reduced sequence length. """ raise NotImplementedError("compress method must be implemented in subclass")

动手开发：构建你的第一个压缩插件

下面我们将创建一个简单但实用的压缩插件——基于Key Norm的压缩算法，该算法通过计算键的范数来决定保留哪些键值对。

步骤1：创建插件文件

在kvpress/presses/目录下创建新文件mynorm_press.py：

touch kvpress/presses/mynorm_press.py

步骤2：实现压缩算法

编辑mynorm_press.py文件，实现基于Key Norm的压缩逻辑：

import torch from torch import nn from typing import Tuple from kvpress.presses.base_press import BasePress class MyNormPress(BasePress): """ KV cache compression based on key norm values. This press keeps the keys with the highest norm values, discarding those with lower norms. """ def __init__(self, compression_ratio: float = 0.5): """ Initialize the MyNormPress. Parameters ---------- compression_ratio : float The ratio of sequence length to keep after compression (0 < compression_ratio <= 1). For example, 0.5 means keeping 50% of the original sequence length. """ if not (0 < compression_ratio <= 1): raise ValueError(f"compression_ratio must be in (0, 1], got {compression_ratio}") self.compression_ratio = compression_ratio def compress( self, module: nn.Module, hidden_states: torch.Tensor, keys: torch.Tensor, values: torch.Tensor, attentions: torch.Tensor, kwargs: dict, ) -> Tuple[torch.Tensor, torch.Tensor]: # Calculate the norm of each key key_norms = keys.norm(dim=-1) # Shape: (batch_size, num_kv_heads, seq_len) # Determine how many tokens to keep batch_size, num_heads, seq_len = key_norms.shape keep_count = int(seq_len * self.compression_ratio) keep_count = max(keep_count, 1) # Ensure at least one token is kept # Get indices of the top keep_count keys for each batch and head _, top_indices = torch.topk(key_norms, keep_count, dim=-1, sorted=True) # Expand indices to match the dimensions of keys and values # (batch_size, num_heads, keep_count) -> (batch_size, num_heads, keep_count, 1) top_indices = top_indices.unsqueeze(-1) # Gather the top keys and values using the indices # keys shape: (batch_size, num_heads, seq_len, head_dim) compressed_keys = torch.gather(keys, dim=2, index=top_indices.expand(-1, -1, -1, keys.shape[-1])) compressed_values = torch.gather(values, dim=2, index=top_indices.expand(-1, -1, -1, values.shape[-1])) return compressed_keys, compressed_values

步骤3：注册插件

为了让kvpress框架识别你的新插件，需要在kvpress/presses/__init__.py中添加导出：

# 在文件末尾添加 from .mynorm_press import MyNormPress

测试你的压缩插件

良好的测试是确保压缩算法可靠性的关键。kvpress提供了完善的测试框架，让你可以轻松验证插件功能。

创建测试文件

在tests/presses/目录下创建测试文件test_mynorm_press.py：

import torch from transformers import DynamicCache from kvpress import MyNormPress from tests.fixtures import unit_test_model # noqa: F401 def test_mynorm_press_basic(unit_test_model): # noqa: F811 """Test basic functionality of MyNormPress""" # Create press with 50% compression ratio press = MyNormPress(compression_ratio=0.5) # Apply the press to the model with press(unit_test_model): # Create dummy input input_ids = torch.randint(0, 1024, (1, 256), device=unit_test_model.device) # Run model with empty cache cache = DynamicCache() outputs = unit_test_model(input_ids, past_key_values=cache) # Check that cache has been compressed seq_length = cache.get_seq_length() assert seq_length == 128, f"Expected compressed sequence length 128, got {seq_length}" def test_mynorm_press_different_ratios(unit_test_model): # noqa: F811 """Test MyNormPress with different compression ratios""" for ratio in [0.1, 0.3, 0.7, 0.9]: press = MyNormPress(compression_ratio=ratio) with press(unit_test_model): input_ids = torch.randint(0, 1024, (1, 256), device=unit_test_model.device) cache = DynamicCache() unit_test_model(input_ids, past_key_values=cache) expected_length = int(256 * ratio) assert cache.get_seq_length() == expected_length, \ f"For ratio {ratio}, expected {expected_length}, got {cache.get_seq_length()}"

运行测试

使用pytest运行你的测试：

pytest tests/presses/test_mynorm_press.py -v

高级技巧：插件组合与优化

kvpress支持将多个压缩插件组合使用，创造更强大的压缩策略。例如，你可以将分块压缩与你的自定义压缩算法结合：

from kvpress import ChunkPress, MyNormPress # Create a composed press that applies MyNormPress to 64-token chunks chunk_press = ChunkPress( press=MyNormPress(compression_ratio=0.5), chunk_length=64 ) # Apply the composed press to the model with chunk_press(model): # Run generation with combined compression outputs = model.generate(input_ids, max_new_tokens=100)

常见的优化方向包括：