I have installed Ubuntu GNOME in BIOS mode on my MacBook (BIOS mode so that the proprietary NVIDIA drivers work. I need them for gaming.).

For some reason, a lot of CPU is being used while not really doing anything. It swings between 20-30% on both cores, usually. But when I look at the list of processes and sort by CPU usage, I do not see anything special. No processes intensively doing anything.

How can I fix this?

EDIT: Output of top command.

jop@jop-MacBook:~$ top

top - 17:08:02 up 41 min,  2 users,  load average: 0,51, 0,69, 0,95
Tasks: 202 total,   2 running, 200 sleeping,   0 stopped,   0 zombie
%Cpu(s): 11,9 us,  5,8 sy,  0,0 ni, 80,3 id,  0,5 wa,  0,0 hi,  1,5 si,  0,0 st
KiB Mem:   7908316 total,  2919940 used,  4988376 free,   153248 buffers
KiB Swap:  3906244 total,        0 used,  3906244 free,  1326544 cached

  PID USER      PR  NI  VIRT  RES  SHR S  %CPU %MEM    TIME+  COMMAND           
 3785 root      20   0  195m  82m  26m S  22,9  1,1   2:43.77 Xorg              
 4429 jop       20   0 1543m 150m  60m S   7,3  1,9   1:26.26 compiz            
 4198 jop       20   0  633m  21m  11m S   1,7  0,3   0:04.96 unity-panel-ser   
 7425 jop       20   0  564m  18m  12m S   1,7  0,2   0:00.84 gnome-terminal    
 7019 jop       20   0  806m  89m  46m S   1,0  1,2   0:10.01 chrome            
 7323 jop       20   0  966m  93m  23m S   1,0  1,2   0:06.85 chrome            
 6742 root      20   0     0    0    0 S   0,7  0,0   0:00.43 kworker/0:3       
    3 root      20   0     0    0    0 S   0,3  0,0   0:06.01 ksoftirqd/0       
 7008 root      20   0     0    0    0 S   0,3  0,0   0:00.27 kworker/1:3       
 7302 jop       20   0  972m  96m  28m S   0,3  1,2   0:06.32 chrome            
 7310 jop       20   0  382m  63m  39m S   0,3  0,8   0:00.34 chrome            
 7498 jop       20   0 24840 1600 1120 R   0,3  0,0   0:00.22 top               
    1 root      20   0 27176 2944 1412 S   0,0  0,0   0:01.58 init              
    2 root      20   0     0    0    0 S   0,0  0,0   0:00.00 kthreadd          
    5 root       0 -20     0    0    0 S   0,0  0,0   0:00.00 kworker/0:0H      
    6 root      20   0     0    0    0 S   0,0  0,0   0:00.00 kworker/u4:0      
    7 root      rt   0     0    0    0 S   0,0  0,0   0:02.04 migration/0       

Even when xorg isn't so busy like when I copied, CPU usage is higher then what the processes use.