Why is opencv not using all cores after upgrading to Mavericks? I'm running a CPU intensive command on Mavericks (Opencv_traincasscade).  Under Mountain Lion the process used to use all 8 cores all the way though.  However after upgrading it drops to 1 core after a short time.



Could this be app nap? Is there anything I can do to fix this?
Being able to use multiple-cores or threads is dependent on the process. This is not AppNap or OS X causing the change.

Your process, opencv_traincascade, may be resource constrained after a few moments and thus reduced to queuing up tasks as it waits for disk access or another limited resource.

In this case you may need to switch to a different build of OpenCV:


  Note that opencv_traincascade application can use TBB for multi-threading. To use it in multicore mode OpenCV must be built with TBB.



Cascade Classifier Training
How do I build OpenCV with TBB?


Installing OpenCV with TBB via brew:

brew install opencv --with-tbb