I have a problem while using the PARDISO in FORTRAN to solve a large sparse system. The processor of my computer is Intel i7-3770 CPU 3.40GHz. I tried to call the MKL_SET_NUM_THREADS() and the OMP_SET_NUM_THREADS() to set the number of threads will be used in the PARDISO solver. When the value is 1, the CPU usage is around 13%, which indicates only 1 threads is used. I then changed the number to 4, the CPU usage is around 50% which also is right according to the number of threads I have set. But the problem is when I change the number to values greater than 4, such as 8, the CPU usage keeps around 50%. So, the question is how can I increase the number of threads for the PARDISO solver such that the CPU usage can be increased further and the time to solve the equation system can be further decreased? Thanks for any help on this issue.