Support CPU input for device QuantileDMatrix.
#8136
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trivialfis
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src/data/ellpack_page.cu
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| auto r_end = d_row_ptr[ridx + 1]; | ||
| size_t rsize = r_end - r_begin; | ||
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| if (ifeature >= rsize) { |
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Can't you set the null values here?
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Thanks for the suggestion. Let me try to merge the kernels.
src/data/iterative_dmatrix.h
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| * - The CPU format and the GPU format are different, the former uses a CSR + CSC for | ||
| * histogram index while the latter uses only Ellpack. This results into a design that | ||
| * we can obtain the GPU format from CPU but not the other way around since we can't | ||
| * recover the CSC from Ellpack. More concretely, if users want to construct a CPU |
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What is the problem with obtaining CSC from ellpack?
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How to get the feature index for each element from ellpack?
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It's encoded in the bin number, which are the values in Ellpack. If the dataset is sparse you would have to look this up with binary search I guess.
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Didn't think of that. Yup, we can recover the feature index by binary searching the cut values. Will update the comment and leave it for a different PR for copying data from GPU to CPU.
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Updated the note. Will work on the other direction of conversion.
- Copy `GHistIndexMatrix` to `Ellpack` when needed.
trivialfis
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GHistIndexMatrixtoEllpackwhen needed.