index_select is normally used as part of a sparse operation. While PyTorch supports a generic index_select for an arbitrary-dimension index selection, its performance for a special case like the dim 0 index selection is suboptimal. For this reason, we implement a specialized index_select for dim 0. In some cases, we have observed 1.4x performance gain from FBGEMM’s index_select compared to the one from PyTorch (using uniform index distribution).
More about the implementation of influential instances can be found on our GitHub page and tutorials.