[Spec Decoding] Support MTP for dsv3.2

[Paiiiiiiiiiiiiii]

Motivation

Based on #11109
We have implemented MTP support for DS v3.2 and cuda graph in our in-house maintained version of sglang.
Since the community has completed the MTP modification, we are ready to contribute this feature back to the community.

python -m sglang.launch_server --model deepseek-ai/DeepSeek-V3.2-Exp --tp 8 --attention-backend nsa --nsa-prefill flashmla_prefill --nsa-decode flashmla_decode --speculative-algorithm EAGLE --speculative-num-steps 3 --speculative-eagle-topk 1 --speculative-num-draft-tokens 4 --cuda-graph-max-bs 32 --max-running-requests 32

Modifications

Todo

• Accuracy test

Accuracy Tests

python3 /gsm8k/bench_sglang.py --num-questions 200

Benchmarking and Profiling

Checklist

• Format your code according to the Format code with pre-commit.
• Add unit tests according to the Run and add unit tests.
• Update documentation according to Write documentations.
• Provide accuracy and speed benchmark results according to Test the accuracy and Benchmark the speed.

[gemini-code-assist]

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[Paiiiiiiiiiiiiii]

@Fridge003 here

[Fridge003]

Accuracy results:
#11596 (comment)

[Fridge003]

cc @hnyls2002 Can you also take a look?

[wwj-2017-1117]

--nsa-prefill flashmla_prefill

launch_server.py: error: argument --nsa-prefill-backend: invalid choice: 'flashmla_prefill' (choose from flashmla_sparse, flashmla_kv, fa3, tilelang, aiter)

[Fridge003]

@wwj-2017-1117 The server arguments name changed recently. Please use flashmla_sparse instead of flashmla_prefill
Ref: https://docs.sglang.ai/basic_usage/deepseek_v32.html

[llc-kc]

@Paiiiiiiiiiiiiii Can we use use MTP in PD? Should the MTP-related parameters be added to the prefill launch parameters, or only to the decode?
Thank you very much.

[Paiiiiiiiiiiiiii]

@Paiiiiiiiiiiiiii Can we use use MTP in PD? Should the MTP-related parameters be added to the prefill launch parameters, or only to the decode? Thank you very much.

Yes, it can be used in PD, you need to add MTP-related parameters to the P node like D.