CODEWITHSUNDEEP
c++opencvparallel-processingdft
Stepan Yakovenko
Stepan Yakovenko

Reputation: 9206

Is cv::dft transform multithreaded?

I need to boost cv::dft perfomance in multithreaded environment. I've done a simple test on Windows 10 on Core-i5 Intel processor:

enter image description here

Here I see that CPU is not fully loaded (50% usage only). Individual threads are loaded equally and also far from 100%. Why is that and how can I fix it? Can DFT easily pluralized? Is it implemented in OpenCV library? Are there special build flags to enable it (which)?

UPDATE: Running this code on linux gives a bit different result, but also below 100% utilization:

enter image description here

Upvotes: 0

Views: 312

Answers (1)

Stepan Yakovenko
Stepan Yakovenko

Reputation: 9206

First of all, behavior of cv::dft depends on OpenCV build flags, for example if you set WITH_IPP, then it will use Intel Primitives to speedup computation. FFT is memory-bound, if you simply launch more threads, you most probably wouldn't significantly benefit from this parallelism, because threads will be waiting for each other to finish accessing memory, I've observed this both on Linux and Windows. To gain more performance you should use FFTW3 which has some sophisticated algorithm for multi-threaded mode (should be ./configure-d with special flag). I observed up to 7x speedup with 8 threads. But FFTW has only payed business-friendly license, imposing GNU license for your software. I have not found any other opensource components which can handle FFT parallelism in a smart way.

Upvotes: 1

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