Add CausalMask support with new flash attention api #604
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petercad
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applications/flash_attention_v2/collective/xe_fmha_fwd_mainloop.hpp
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Pull Request Overview
This PR adds support for causal masking in the flash attention implementation by introducing a new SubgroupLayoutQK template parameter and implementing the causal mask logic in the mainloop.
Key Changes:
- Added
SubgroupLayoutQKtemplate parameter to the collective mainloop and kernel interfaces - Implemented causal masking logic that applies
-INFINITYto attention scores beyond the causal boundary - Updated the example runner to conditionally instantiate causal or non-causal configurations based on user options
Reviewed Changes
Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.
| File | Description |
|---|---|
applications/flash_attention_v2/collective/xe_fmha_fwd_mainloop.hpp |
Implements causal mask logic and removes the static assertion that previously blocked causal mask usage |
applications/flash_attention_v2/kernel/xe_fhma_fwd_kernel.hpp |
Adds subgroup layout type alias and computes sequence coordinates for causal masking |
examples/06_bmg_flash_attention/xe_fmha_fwd_runner.hpp |
Adds SubgroupLayoutQK template parameter to mainloop type |
examples/06_bmg_flash_attention/06_xe_fmha_fwd.cpp |
Conditionally selects causal or non-causal kernel based on is_causal option |
applications/flash_attention_v2/collective/xe_fmha_fwd_mainloop.hpp
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Signed-off-by: Chen, Xi2 <[email protected]>
Signed-off-by: Chen, Xi2 <[email protected]>
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Signed-off-by: Chen, Xi2 <[email protected]>
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petercad
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Nov 10, 2025
petercad
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Nov 10, 2025
petercad
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Nov 10, 2025
Signed-off-by: Chen, Xi2 <[email protected]>
Signed-off-by: Chen, Xi2 <[email protected]>
tdeng5
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Nov 12, 2025
taozha2
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Nov 12, 2025
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