[Bug]: Bugs in the new logprobs_mode

[YunruiZhang]

🐛 Describe the bug

The new logprobs_mode has many bugs. When set to logprobs_mode = 'processed_logprobs', it returns the same values as logprobs_mode = 'raw_logprobs'. Additionally, when set to 'processed_logits' or 'raw_logits', it does not produce any meaningful output the logprobs are all -inf except for rank = 1, which gives 0. I am using MODEL_ID = "Qwen/Qwen3-30B-A3B-Thinking-2507-FP8"

[Liu-congo]

if no one has been working on it, i'd like to try to fix it

[Liu-congo]

@YunruiZhang emm could you provide a detail reproduction script for the issue, i've test the logprobs_mode on qwen3-0.6B, it worked fine

[YunruiZhang]

Hi, I think my problem is that the vllm engine falls back to v0 when i am trying to use Qwen/Qwen3-30B-A3B-Thinking-2507-FP8. However when I force to use v1 engine it will give error "NotImplementedError: VLLM_USE_V1=1 is not supported with --kv-cache-dtype." it seems the fp8 kv cache is still not supported for Qwen3.

[Liu-congo]

sounds reasonable. but in issue #15191, it seems to have supported fp8 kvcache, i think there might be some further reason we haven't noticed