Question about leading dimension handling for quantization scales in cuBLASLt matmul

[Haoyan-Ma]

I have a question regarding how to handle leading dimensions for quantization scales in cuBLASLtMatmul when the input matrices are not tightly packed.

Suppose the leading dimensions of matrices A and B are larger than their logical sizes (M, N, K), i.e., they are strided / padded layouts rather than contiguous M×K or K×N.

For quantized matmul using:

A_scale = CUBLASLT_MATMUL_MATRIX_SCALE_VEC128_32F

B_scale = CUBLASLT_MATMUL_MATRIX_SCALE_BLK128x128_32F

How should the leading dimensions of the corresponding scale tensors be handled?

Specifically:

1.Are scale tensors always expected to be contiguous in memory?

2.Or do scale tensors also support their own leading dimensions / strides similar to matrices A and B?

3.If A or B has padding due to larger leading dimensions, should the scales reflect the padded layout or only the logical tile layout?

I couldn’t find clear documentation on how scale tensor strides relate to matrix strides, so any clarification would be appreciated.

[rsdubtso]

Hi @Haoyan-Ma. Thanks for the question and apologies for a delayed response.

1. Currently — yes, the scales are expected to be contiguous in memory.

2. No, there is no support for leading dimension.

3. Not completely sure if I understood the question. Scaling factor dimensions are computed based on M, N and K matmul arguments and do not take leading dimensions of A and B into account.

Let me k know if you have any additional questions.

[Haoyan-Ma]

Thank you for the clarification and no worries about the delay.