how many cpus are supported by solver while using subroutine
 

I use Flow-3d 10.1 in Win7-64bit, not the MP version.
When I solve common problem, all cpus work well and it reaches 100% in the task manager.
But I find that only 2 cpus can be used if the model includes fortran subroutine by customization.
Is it true and how to improve it? Please help me! Thanks!