42 lines
2.3 KiB
Markdown
42 lines
2.3 KiB
Markdown
|
# Global Multi-Level KV Cache
|
||
|
|
|
||
|
|
## Background
|
||
|
|
In the decoding phase of large language models (LLMs), frequent access to historical KV cache due to autoregressive generation creates a bottleneck in memory bandwidth. As model sizes and context windows expand (e.g., 128K Tokens consuming over 40GB of memory), the pressure on single-device memory increases dramatically. Existing solutions (such as vLLM) exhibit significant limitations in long-context scenarios: prefill time surges, severe memory bandwidth contention during decoding, and the need for excessive resource reservation to meet SLO requirements (TTFT < 2s, TBT < 100ms). This often results in GPU utilization below 40% and difficulties in leveraging cross-server resources. To address this, we propose a distributed global multi-level KV cache management system, adopting a memory-compute integrated architecture to break through single-machine resource constraints.
|
||
|
|
|
||
|
|
## Feature Introduction
|
||
|
|
The xLLM Global KV Cache feature is primarily implemented through the following three modules:
|
||
|
|
- **etcd**: For cluster service registration, load information synchronization, and global cache state management.
|
||
|
|
- **xLLM Service**: For scheduling requests and managing all compute instances.
|
||
|
|
- **xLLM**: The compute instances handling requests.
|
||
|
|
|
||
|
|
The overall architecture is shown in the diagram below:
|
||
|
|
|
||
|
|
|
||
|
|
## Usage Example
|
||
|
|
|
||
|
|
### Preparation
|
||
|
|
|
||
|
|
#### Install Dependencies
|
||
|
|
- **xLLM**: Refer to [Quick Start](../getting_started/quick_start.md)
|
||
|
|
- **xLLM Service**: Refer to [PD disaggregation](../getting_started/disagg_pd.md)
|
||
|
|
|
||
|
|
### Usage Instructions
|
||
|
|
|
||
|
|
1. **etcd Startup Configuration:**
|
||
|
|
```bash
|
||
|
|
./etcd --listen-peer-urls=http://0.0.0.0:10999 --listen-client-urls=http://0.0.0.0:10998
|
||
|
|
```
|
||
|
|
|
||
|
|
2. **xLLM Service Startup Configuration:**
|
||
|
|
```bash
|
||
|
|
./xllm_master_serving --etcd_addr="127.0.0.1:10998" --http_server_port 28888 --rpc_server_port 28889 --tokenizer_path=/path/to/tokenizer_config_dir/
|
||
|
|
```
|
||
|
|
|
||
|
|
3. **xLLM Startup Configuration:**
|
||
|
|
Add the following gflag parameters when starting xLLM:
|
||
|
|
```bash
|
||
|
|
--enable_service_routing=true
|
||
|
|
--enable_cache_upload=true
|
||
|
|
# PD separation currently does not support Global KVCache Management
|
||
|
|
--enable_disagg_pd=false
|
||
|
|
```
|