How to select to use OpenMP or Intel TBB?

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1

Hello there. I have compiled OpenCV 3.4.16 with “WITH_TBB” and “WITH_OPENMP” flags enabled by using CMake 3.22.0. The TBB version I used was tbb2019_20191006. Then I built libraries for Release and Debug by using Visual Studio 2019 Community Edition. When I check
build information using cv::getBuildInformation( ) I don’t see any information about TBB, it only says OpenMP.

cv::getBuildInformation( ) results

Screenshot_3

Do I need to make separate builds for OpenMP and Intel TBB? If I don’t need to build them as separate builds, how do I activate/select to use OpenMP or Intel TBB in my OpenCV code?

2

i have meet the same question, how to activate/select to use OpenMP or Intel TBB in my OpenCV code, have you solve this problem?

3

There was a Stackoverflow post from 2015.

TLDR: You should build OpenCV with the parallel framework you want/intend to use.

But since this was a 7-year-old post, I don’t know if the same thing still applies or not.

4

thanks for reply, opencv did choose the parallel framework by the following order:

/* IMPORTANT: always use the same order of defines
   1. HAVE_TBB         - 3rdparty library, should be explicitly enabled
   2. HAVE_CSTRIPES    - 3rdparty library, should be explicitly enabled
   3. HAVE_OPENMP      - integrated to compiler, should be explicitly enabled
   4. HAVE_GCD         - system wide, used automatically        (APPLE only)
   5. HAVE_CONCURRENCY - part of runtime, used automatically    (Windows only - MSVS 10, MSVS 11)
*/

and i also find that we can explicit select by this api setParallelForBackend .
BTW, do you know which parallel framework is faster on windows with cpu?

1 Like
5

Well, I’ve never done a benchmark but I think we might consider that the TBB would yield better optimization for Intel CPUs than OpenMP.

6

thanks, i try to build opencv with tbb, i set -DWITH_TBB=ON, i also download TBB, how ca i tell opencv where to find tbb?is there some other cmake option to set?

7

You need to provide directories for TBB ( directories of include, lib, etc.), there is an option about that at CMake.

8

thanks a lot, i successfully compile opencv with tbb,however in my test, TBB is 1.5 or 2.0 slower than CONCURRENCY, is it reasonable?

9

What do you mean by “Concurrency”?

10

probably that, is my guess.

11

here:

/* IMPORTANT: always use the same order of defines
   1. HAVE_TBB         - 3rdparty library, should be explicitly enabled
   2. HAVE_CSTRIPES    - 3rdparty library, should be explicitly enabled
   3. HAVE_OPENMP      - integrated to compiler, should be explicitly enabled
   4. HAVE_GCD         - system wide, used automatically        (APPLE only)
   5. HAVE_CONCURRENCY - part of runtime, used automatically    (Windows only - MSVS 10, MSVS 11)
*/