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Fix: Incorrect Tensor Size for NestedTensor QKV Transform #2450

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Fix: Incorrect Tensor Size for NestedTensor QKV Transform #2450

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f43b636
Update Attention.cpp
yucai-intel Dec 2, 2025
590ebe6
Merge branch 'main' into yucai/mha/nested/fix
yucai-intel Dec 4, 2025
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10 changes: 10 additions & 0 deletions src/ATen/native/transformers/Attention.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -38,6 +38,16 @@ std::tuple<Tensor, Tensor, Tensor> transform_bias_rescale_qkv_xpu(
auto T = qkv.is_nested() ? native::NestedTensor_get_max_size(
*native::get_nested_tensor_impl(qkv))[0]
: qkv.size(1);
if (qkv.is_nested()) {
// Don't mess with non-nested case for now since it's not set up to fiddle
// with mask size.

// Round T up to next multiple of 8 so as to be able to utilize Tensor
// cores. Otherwise, sometimes with padding, *no* row will have the maximum
// sequence length and so we'll have a non-divisible-by-8 dimension even if
// the model author chose a multiple of 8.
T = T + (8 - (T % 8)) % 8;
}
auto _3D = qkv_bias.size(0);
auto D = _3D / 3;
TORCH_CHECK(D % num_head == 0);
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