GPU backslash performance much slower than CPU

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Meme Young
Meme Young 2020-12-27
编辑： Matt J 2022-5-26
I am doing numerical power flow caclulation by modifying the functions of matpower, an open source toolbox. By modifying its function newtonpf.m, GPU computation can be implemented. However, I found that GPU performance is much much slower than CPU. When calculating the built-in case3012wp of matpower, the matrix in newtonpf.m will be :
A: 5725 * 5725 sparse double, b: 5725 * 1 double.
The process of A \ b in the 1st iteration of newtonpf() will generally take around 0.01 sec on my i7-10750H + RTX 2070super MSI-GL65.
But if A and b are changed into GPU arrays, the process of A \ b will take the following time if A is the following types:
full double, 0.8 sec
sparse double, 4 sec
full single, 0.1 sec
(sparse single is not supported)
So why is the diference in performance? I thought GPU could do things much faster than CPU.
Files are attached as follows. Atest is sparse and Agpu is a sparse gpu array. All are doubles.
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kant
kant 2022-5-26
I also have this problem for my matlab code? Has the problem been solved？
Matt J
Matt J 2022-5-26
编辑：Matt J 2022-5-26
@kant It has been concluded that this is expected behavior, but see below.

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回答（1 个）

Matt J
Matt J 2020-12-27
This thread looks relevant. It appears that sparse mldivide on the GPU is not expected to be faster.
https://www.mathworks.com/matlabcentral/answers/500526-solution-of-large-sparse-matrix-systems-using-gpu-mldivide
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Meme Young
Meme Young 2020-12-30
What do you mean sparse solver algorithm Mr Knight? like pcg()? I have tried it is not as efficient as this way: reordering using amd(), LU decomp, and two backslashes based on the decomp, especially when coping with the type of sparse matrix that I uploaded
Joss Knight
Joss Knight 2021-1-10
编辑：Joss Knight 2021-1-10
Yes, PCG, GMRES, CGS, LSQR, QMR, TFQMR, BICG, BICGSTAB. Try them all, play with tolerance, iterations and preconditioning - something is likely to work. I'm not an expert in this field but this is what the sparse community tend to do.

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