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Posted to issues@mxnet.apache.org by "mureva (via GitHub)" <gi...@apache.org> on 2023/05/01 14:32:25 UTC
[GitHub] [mxnet] mureva opened a new issue, #21195: gather_nd vs. take
mureva opened a new issue, #21195:
URL: https://github.com/apache/mxnet/issues/21195
I have an observation and I'm hoping someone can advise.
I have a scenario where I maintain a large table of vectors, so a basic (n,m) array of n vectors of size m. I then have some system that generates indices into this table, and I want to pull rows out of the table at those indices. (more background? A hash table version of NeRF is what we're making).
So, I have a set of indices, and I want to gather the rows out of the table to make use of elsewhere. There's two operators in mxnet that will do the job - `gather_nd` and `take`
I could have more than 100k, even 1000k indices:
- at 100k `take` will do a forward pass in less than 1 ms, but a backward pass will take about 45 ms. Meanwhile, `gather_nd` will do a forward pass in about 16 ms, and a backward pass in under 1 ms.
- At 1000k indices, `take` is 4 ms fwd, 400 ms bwd, gather is 170 ms fwd, 1ms bwd. .
So... obvious question... is there a way to get the best of both worlds here? The fast forward pass of `take`, the fast backward pass of `gather_nd`?
Is there a better operator for gathering rows from the table?
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[GitHub] [mxnet] mureva closed issue #21195: gather_nd vs. take
Posted by "mureva (via GitHub)" <gi...@apache.org>.
mureva closed issue #21195: gather_nd vs. take
URL: https://github.com/apache/mxnet/issues/21195
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[GitHub] [mxnet] mureva commented on issue #21195: gather_nd vs. take
Posted by "mureva (via GitHub)" <gi...@apache.org>.
mureva commented on issue #21195:
URL: https://github.com/apache/mxnet/issues/21195#issuecomment-1529792880
Had another look through the documentation, and though I hadn't thought of it that way, the other option is to use the embedding function. And woderfully, that appears to be the best of both worlds that I wanted,
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