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ycjuan / libffm

A Library for Field-aware Factorization Machines

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k_aligned & memory requirements

mpekalski opened this issue · comments

commented

  1. It would be useful to mention in the README that memory allocation depends on k_aligned, not just k. So changing k from 4 to 5 actually doubles memory requirements.

  2. Is there any particular reason why you align k to the power of 2?

commented

Perhaps you already know: memory needs to be aligned on 16 byte boundaries to efficiently use the SSE instructions. The authors implemented the W_f_j_k multidimensional array as a flat 1d one, so if you want all the latent vectors to be on a 16 byte boundary , you need the memory used by each vector to be a multiple of 16. For floats, which are usually 4 bytes long, that means k_aligned has to be a multiple of 4.

I don't see any obvious advantage of using k=2**x ...

commented

Yes, k_aligned need to be a multiple of 4 and this is because of the use of SSE instructions. We will consider to have some document about this. Thanks for feedback.