[Feat] enable hierarchical mc2 ops on A2 by default

[hwhaokun]

What this PR does / why we need it?

Previously, it was necessary to set the environment variables HCCL_INTRA_PCIE_ENABLE=1 and HCCL_INTRA_ROCE_ENABLE=0. This PR enables hierarchical MC2 operations on A2 by default.

Does this PR introduce any user-facing change?

How was this patch tested?

• vLLM version: v0.13.0
• vLLM main: vllm-project/vllm@7157596

[gemini-code-assist]

Code Review

This pull request correctly enables hierarchical MC2 operations on A2 devices by default, removing the need for specific environment variables. However, there is a potential issue in vllm_ascend/ops/fused_moe/token_dispatcher.py where the expert_scales parameter is now passed unconditionally. This could lead to incorrect behavior on non-A2 devices. I have provided comments and suggestions to make this parameter conditional, aligning it with the intended A2-specific change.

[gemini-code-assist]

The expert_scales parameter should not be added unconditionally, as it is specific to hierarchical communication which is being enabled for A2 devices. It should be moved into the conditional block for A2 devices. Please remove it from this general dictionary initialization.

        }

[gemini-code-assist]

To ensure hierarchical communication is correctly configured only for A2 devices, the expert_scales parameter should be added here, inside the conditional block, along with comm_alg.

        if get_ascend_device_type() == AscendDeviceType.A2:
            kwargs_mc2["comm_alg"] = "hierarchy"
            kwargs_mc2["expert_scales"] = topk_weights.to(torch.float32)

[github-actions]

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