Fix XAttention reference code for better alignment with the original #32451
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l-bat
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| if ((k_block_idx == | ||
| (blocked_attention_scores_shape[2] - blocked_attention_scores_shape[1] + q_block_idx)) || | ||
| k_block_idx == 0) { | ||
| // We preserve first-in-row and diagonal blocks always, and include their score in the | ||
| // cumulative sum. The target for the rest of the blocks in row is to fill up the | ||
| // rest of the attention mass fraction so that with the diagonal and first blocks they | ||
| // comprise the `threshold` portion of the entire causal attention mass in this row | ||
| retval[head_idx].insert({q_block_idx, k_block_idx}); | ||
| cumsum += current_score; |
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@luo-cheng2021 can you confirm that the GPU uses the same logic?
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Confirmed, this keep same logic with GPU kernel, thanks.
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WeldonWangwang
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The original PR adding XAttention reference code was not completely aligned with the original code.
Fixed were:
thresholdportion of the total K-row block sum and always include diagonal/first-in-row blocks.Added more E2E tests that compare against the original code results, which are fixed in the test code as reference. Note that the original non-Triton code contained bugs, which had to be fixed in order to obtain correct references (see vshampor/x-attention@fdc5c34).