[julia-users] Why can't julia make the most of the system resource?

[博陈]

<https://lh3.googleusercontent.com/-9paHdkUPBA4/VnVWcUZqSxI/AAAAAAAAAA0/fPuVTg1k0UI/s1600/QQ%25E6%2588%25AA%25E5%259B%25BE20151219210640.png>
As can be seen, all the 8 cores of my pc is being used by the julia 
program, however, only 35% of the system resource is covered. My julia code 
mainly does the fft operates in a loop. I use fftw.set_num_threads(8) 
outside the loop.  In my opinion, the top command should exhibit nearly 
100% use of the system resource, but that's not true.