[Bugfix] [DeepSeek-V3.2] fix sparse_attn_indexer weights padding

[kebe7jun]

Purpose

This PR #29287 does not include #32175, so, it will cause batch_size_next_n == batch_size * next_n

cc @ganyi1996ppo

Test Plan

# Prefill
vllm serve /gpfs/rd/models/DeepSeek-V3.2 -tp=2 -dp 4 --trust-remote-code --enable-expert-parallel --all2all-backend=deepep_high_throughput --gpu_memory_utilization=0.9 --max-model-len 102400 --tokenizer-mode=deepseek_v32  --enable-eplb --eplb-config '{"window_size":"32","step_interval":"32","num_redundant_experts":"8", "async": "True"}'                 --kv-transfer-config '{"kv_connector":"NixlConnector","kv_role":"kv_both"}' --num-gpu-blocks-override 2000 --speculative-config.method=mtp --speculative-config.num_speculative_tokens=1

# Decode
vllm serve /gpfs/rd/models/DeepSeek-V3.2 -tp=2 --trust-remote-code --enable-expert-parallel --all2all-backend=deepep_low_latency --gpu_memory_utilization=0.9 --max-model-len 102400 --tokenizer-mode=deepseek_v32  --enable-eplb       --kv-transfer-config '{"kv_connector":"NixlConnector","kv_role":"kv_both"}' -dp 4 --speculative-config.method=mtp --speculative-config.num_speculative_tokens=1 --num-gpu-blocks-override 2000

# Router
python /gpfs/rd/kebe/vllm/tests/v1/kv_connector/nixl_integration/toy_proxy_server.py --prefiller-hosts <PREFILLER_IP> --decoder-host <DECODER_IP> --prefiller-ports 8000 --decoder-ports 8000 --port 8001

and run bench:

vllm bench serve --port 8001 --random-input-len 4096 --random-output-len 200 --num-prompts 500 --max-concurrency 128 --seed $RANDOM  --model /gpfs/rd/models/DeepSeek-V3.2

Test Result

vllm bench ok.

---

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[gemini-code-assist]

Code Review

This pull request correctly addresses a bug in the sparse_attn_indexer by ensuring the weights tensor is padded consistently with the q_fp8 tensor during the decode phase. The changes in vllm/model_executor/layers/sparse_attn_indexer.py properly handle both cases where padding is required and not required, preventing potential shape mismatches and incorrect behavior. The fix appears correct and complete.

[kebe7jun]

@LucasWilkinson PTAL.

[LucasWilkinson]

@kebe7jun thanks for the contribution! https://github.com/vllm-project/vllm/pull/34552/changes#r2855124116 is actually close to landing which should eliminate the need for padding, will hold off to see if we can land that in a couple days

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @kebe7jun.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork