vllm - 💡(How to fix) Fix [Question]HOW TO Enabling FlashAttention- 4 backend for NVIDIA PRO 6000 (Blackwell) with MiniMax-2.5-230B [1 participants]

Fix Plan

To use FlashAttention-4 (FA4) instead of falling back to FlashAttention-2 (FA2), you need to ensure your environment and model configuration support the newer backend.

Here are the steps to follow:

• Update your vllm configuration to explicitly use the FA4 backend.
• Verify that your NVIDIA drivers and CUDA versions are compatible with FA4.

Code Changes

You can specify the attention backend in your model configuration. For example:

import vllm

# Define your model with FA4 backend
model = vllm.MinimaxM2(
    num_layers=24,
    hidden_size=4096,
    num_heads=16,
    attention_backend='flash_attention_4',
)

Alternatively, you can set the VLLM_attention_backend environment variable:

export VLLM_attention_backend=flash_attention_4

Verification

After making these changes, verify that your model is using the FA4 backend by checking the logs or the model's configuration. You can also monitor your system's performance to ensure it's leveraging the improved memory efficiency and throughput of FA4.

Extra Tips

• Ensure your system meets the minimum requirements for FA4, including compatible NVIDIA drivers and sufficient VRAM.
• If you encounter issues, check the vllm documentation and GitHub issues for known problems and workarounds.