I am using ubuntu 14.04 on my 4GPU rig (3x radeon 280x and 1 270)

when I silenarmy it stucks, so I had to add config option to use only 1 instance. Now its running fine and it makes total 67 sols. I do not know if that is good.
When I look at gpu utilisation on atitweak, O see utilization is low. why?

here is the output of atitweak:

tim@rig0:~$ .local/bin/atitweak -s
0. AMD Radeon R9 200 Series      (:0.0)
    engine clock 1070MHz, memory clock 1600MHz, core voltage 1.2VDC, performance level 3, utilization 75%
    fan speed 23% (994 RPM) (default)
    temperature 56 C
    powertune 0%
1. AMD Radeon R9 200 Series                           (:0.1)
    engine clock 1150MHz, memory clock 1500MHz, core voltage 1.175VDC, performance level 3, utilization 73%
    fan speed 20% (1070 RPM) (default)
    temperature 52 C
    powertune 0%
2. AMD Radeon (TM) R9 200 Series (:0.2)
    engine clock 975MHz, memory clock 1400MHz, core voltage 1.215VDC, performance level 3, utilization 79%
    fan speed 34% (1101 RPM) (default)
    temperature 54 C
    powertune 0%
3. AMD Radeon R9 200 Series                           (:0.3)
    engine clock 1150MHz, memory clock 1500MHz, core voltage 1.175VDC, performance level 3, utilization 72%
    fan speed 21% (1024 RPM) (default)
    temperature 54 C
    powertune 0%


any suggestions?