How to improve QuartusII compile time

I made several test,

going from one cpu to 2 cpu (in the qaurtus option)

on a dual core processor (e6600) only speed up by 10 %,

because Qaurtus only uses both core at the beginning and at the end of the fitter.

And aside that, sometime Quartus runs forever when 2 cpu's are used (probably a sync problem between the multithread sw code).