My executable called 'LoadLibrary' that loades a dllthat areusing OpenMP and the behaviour is good
Now I do LoadLibray to a differnt dll that also use OpenMP and the performace are going up and down.
If I use only on LoadLibrary no matter which dll it will wor fine.
This sounds as both DLLs are starting there own OpenMP thread pool (for use within each respective DLL).
Try setting the KMP_BLOCK_TIME=0 (environment variable) or if your version of the OpenMP runtime library has a callable function to set the block time to 0 then try that.
Without the above, you will also experienct this problem running an application that uses OpenMP and which calls the DLL itself using a different OpenMP thread pool.