[Perf] flashinfer gdn decode kernel intergration

[ZJY0516]

Purpose

Do not review it

Test Plan

Test Result

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• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan, such as providing test command.
• The test results, such as pasting the results comparison before and after, or e2e results
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[gemini-code-assist]

Code Review

This pull request introduces performance optimizations for the Qwen3-Next model by integrating FlashInfer kernels for Gated Delta Net (GDN) decode and Multi-Token Processing (MTP). The changes are well-structured, adding new optimized code paths while retaining the existing implementations as fallbacks. This ensures correctness and compatibility on hardware that does not support the new kernels. The logic for selecting the appropriate kernel based on hardware capabilities and input shapes appears to be correct. The state management for speculative decoding with the new MTP kernel is also handled properly. Overall, the changes are a solid performance enhancement, and I have no high or critical severity concerns.

[JaheimLee]

Hi, does this support full cuda graph? PIECEWISE mode is slow.

[ZJY0516]

Hi, does this support full cuda graph? PIECEWISE mode is slow.

decode should support full cuda graph

[ZJY0516]

wait for flashinfer-ai/flashinfer#2619

wait for flashinfer-ai/flashinfer#2727

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @ZJY0516.

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