[Kernel] Remove unused N/B constexpr params from pack/unpack seq kernels#48813
[Kernel] Remove unused N/B constexpr params from pack/unpack seq kernels#48813aryan331277 wants to merge 1 commit into
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Related to vllm-project#48650. _pack_seq_kernel's N and _unpack_seq_triton_kernel's B were declared as tl.constexpr but never referenced in either kernel body. Since constexpr values are baked into Triton's JIT cache key, these unused params caused pure cache-key pollution , unnecessary recompiles triggered by token/request count changes that don't actually affect the compiled kernel. Removed both unused params from the kernel signatures and their call sites. No logic change. Verified via manual pack/unpack round-trip tests (fp32, varying batch sizes and sequence lengths) on a T4 GPU, all passed. Note: tests/kernels/attention/test_pack_unpack_triton.py requires fp8e4m3 support (compute capability 8.9+) and fails identically on unmodified main when run on a T4 (compute capability 7.5), confirmed via git stash before testing. Not a regression from this change, environment limitation only. Happy for a reviewer with fp8-capable hardware to confirm. Signed-off-by: Aryan Karmore <bt24csd009@iiitn.ac.in>
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Related to #48650. _pack_seq_kernel's N and _unpack_seq_triton_kernel's B were declared as tl.constexpr but never referenced in either kernel body. Since constexpr values are baked into Triton's JIT cache key, these unused params caused pure cache-key pollution , unnecessary recompiles triggered by token/request count changes that don't actually affect the compiled kernel.
Purpose
_pack_seq_kernel'sNand_unpack_seq_triton_kernel'sBare declared astl.constexprbut never referenced in either kernel body. Since constexpr values are baked into Triton's JIT cache key, these unused params cause pure cache-key pollution — unnecessary recompiles triggered by token/request count changes that don't actually affect the compiled kernel. One of several instances flagged in #48650.Removed both unused params from the kernel signatures and their call sites. No logic change.
Related to #48650.
Test Plan
tests/kernels/attention/test_pack_unpack_triton.py— attempted, but requires fp8e4m3 support (compute capability 8.9+). Confirmed viagit stashthat it fails identically on unmodifiedmainon a T4 (compute capability 7.5), so this is an environment limitation, not something introduced by this change.Test Result
Manual round-trip tests (fp32, lengths
[4,4,4],[1,7,3],[10,1,1,1,1],[50,60,70],[1],[100,100,100,100]) — all passed, exact match against input.test_pack_unpack_triton.pycould not be run to completion locally due to the fp8 hardware requirement above. Happy for a reviewer with fp8-capable hardware to confirm the full suite passes — the change itself only removes unused constexpr params and doesn't touch any fp8-specific logic.