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[Bugfix] Avoid too small block m/n for FlexAttention kernel option (#27853)

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Signed-off-by: Isotr0py <mozf@mail2.sysu.edu.cn>
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Isotr0py 2025-10-31 19:33:12 +08:00 committed by GitHub
parent e5ef4dfc11
commit 3933f18a5e
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vllm/v1/attention/backends/flex_attention.py
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@ -896,6 +896,8 @@ def get_kernel_options(
return kernel_options
else:
preferred_block = 32 if query.dtype == torch.float32 else 64
block_lower_bound = 16
block_m_candidate = ensure_divisible(preferred_block, block_m)
block_n_candidate = ensure_divisible(preferred_block, block_n)
@ -910,6 +912,9 @@ def get_kernel_options(
max(1, block_n_candidate // 2), block_n
)
block_m_candidate = max(block_m_candidate, block_lower_bound)
block_n_candidate = max(block_n_candidate, block_lower_bound)
kernel_options["BLOCK_M"] = block_m_candidate
kernel_options["BLOCK_N"] = block_n_candidate