[Feature]: Add head_dim=256 support to fmha_v3_fwd kernels
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- Dominant language
- Python
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Description
Suggestion Description
Current fmha v3 kernel only supports head_dim=128 or 192. We have observed significant performance gains when using the v3 compared to v2 kernel. But models like Qwen3-Next with head_dim=256 are not able to benefit from the perf improvement.
Operating System
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GPU
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ROCm Component
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First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by locating the fmha_v3_fwd kernels and reviewing how head_dim=128 and 192 are currently handled. The work is complete when head_dim=256 is supported by the v3 forward kernels and its correctness and performance can be verified against the existing v2 and v3 paths.
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Assessment
- Domain
- machine-learning, performance
- Issue type
- Feature
- Difficulty
- 5/5
- Estimated time
- Over a week
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 30/100