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[Kernel] [CPU] refactor cpu_attn.py:_run_sdpa_forward for better memory access #24701

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Merged
merged 1 commit into from
Sep 12, 2025
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[Kernel] [CPU] refactor cpu_attn.py:_run_sdpa_forward for better memory access #24701

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8 changes: 4 additions & 4 deletions vllm/v1/attention/backends/cpu_attn.py
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Original file line number Diff line number Diff line change
Expand Up @@ -641,10 +641,6 @@ def _run_sdpa_forward(
attn_metadata: TorchSDPAMetadata,
attn_type: str = AttentionType.DECODER,
) -> None:
if self.num_kv_heads != self.num_heads:
key = key.repeat_interleave(self.num_queries_per_kv, dim=1)
value = value.repeat_interleave(self.num_queries_per_kv, dim=1)

attn_masks = attn_metadata.get_attn_bias(attn_type)
if attn_masks is None:
if self.alibi_slopes is not None:
Expand All @@ -665,6 +661,10 @@ def _run_sdpa_forward(
key = key.movedim(0, key.dim() - 2)
value = value.movedim(0, value.dim() - 2)

if self.num_kv_heads != self.num_heads:
key = key.repeat_interleave(self.num_queries_per_kv, dim=-3)
value = value.repeat_interleave(self.num_queries_per_kv, dim=-3)

causal_attn = (attn_type == AttentionType.DECODER)

seq_lens_q, seq_lens_kv = attn_metadata.get_seq_lens(attn_type)
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