I am trying to perform ph.x calculations on lead-halide perovskite primitive cell with `8 8 8` k points in scf calculation and `6 6 6` q -point grid. The calculation is computationally expensive and taking a long time.

I want to parallelize the calculation using `start_q`, `last_q`, `start_irr` and `last_irr`. How can i assign values to these parameters? Is there any rule of a thumb to assign the values?