I have 2 questions:
I want the OpenCV to use vectorization whenever possible. How can i do that? (I don't have IPP).
If I enable TBB option in OpenCV build, are resulting programs will try to create multiple threads by default? Is there a way to control it (sometimes the program must run in single thread, and sometimes it can use more)?
There are multiple ways to use vectorization/parallelization in OpenCV.
However, they only activate code that was written for TBB/SSE, etc. It will not parallelize generic code.
There are multiple flags to control vectorization, which you can set/unset in CMake:
WITH_TBB (Off by deafault) - activates multithread processingCV_ENABLE_IPP (Off by default) - activates IPP library. Because many OpenCV functions are already optimized with SSE, the gains of IPP are low now. It used to be a big boost in the old times, when OpenCV code was only C-based.CV_SSE2 (On by default) - similar in functionaliry and results with IPP, just that it's opensource. Many building blocks in OpenCV are optimized manually with SSE.CV_ENABLE_UNROLLED (?? default) - Experimental feature, that activates some 4- or 8- unroll loops. It theoretically helps compiler optimize the code, and improves memory access. However, the coverage of this feature in code is still very limited.If enabled, TBB will start by default a number of threads equal to the number of processor cores in your PC. You can view/set the number of threads with the following functions:
setNumThreads is used to control the number of threads. But I have to check if it works for TBB...
Thank you for the answer. It raised another question. I thought that setNumThreads designed for use with TBB. Where else it can be used and why do you have any doubts about using it with TBB?
Simply because it was broken once, and I'm not sure that it was fixed. But 95% that it works now.
Asked: 2012-07-24 02:46:32 -0600
Seen: 6,960 times
Last updated: Jul 24 '12
