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[Performance] Remove redundant clone() calls in cutlass_mla #24891

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Merged
merged 2 commits into from
Sep 15, 2025
Merged

[Performance] Remove redundant clone() calls in cutlass_mla #24891

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[Performance] Remove redundant clone() calls in cutlass_mla
alexm-redhat Sep 15, 2025
54e6cd5
avoid a redundant contiguous() call for the end of the sm100 cutlass …
alexm-redhat Sep 15, 2025
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16 changes: 8 additions & 8 deletions vllm/v1/attention/backends/mla/cutlass_mla.py
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Original file line number Diff line number Diff line change
Expand Up @@ -210,9 +210,14 @@ def _sm100_cutlass_mla_decode(
sm_scale,
num_kv_splits,
)
returned_lse = lse[:, :H].contiguous(
) if self.need_to_return_lse_for_decode else lse
return out[:, :H].contiguous(), returned_lse

if H < MAX_HEADS:
# Extract the subsets of the outputs
returned_lse = lse[:, :H].contiguous(
) if self.need_to_return_lse_for_decode else lse
out = out[:, :H]
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@mgoin mgoin Sep 15, 2025

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I understand putting this in a conditional, but why can we remove the contiguous for out if we can't for lse?

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@alexm-redhat alexm-redhat Sep 15, 2025

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Most likely lse as well, I was just on the safe side, since I don't know how to test it.


return out, returned_lse

def _sm100_forward_decode(
self,
Expand All @@ -228,11 +233,6 @@ def _sm100_forward_decode(
self._workspace.ensure_size(attn_metadata, self._num_kv_splits)

# Run MLA
# Clone q_nope and q_pe to make sure strides computation is correct.
# TODO: Check if we really need it
q_nope = q_nope.clone()
q_pe = q_pe.clone()

o, lse = self._sm100_cutlass_mla_decode(
q_nope,
q_pe,
Expand Down