[xubuntu-users] CPU usage

[Tim]

I am trying to work out why three piece of software are giving me 
different results. My PC has a Intel i3 4 core processor and I am 
running Xubuntu 12.10

I normally have GKrellm running on my desktop which list the 4 cores 
separately and from time to time I will see cpu usage jumping around 
more than usual while the PC is sat there not being used but with google 
chrome, thunderbird and firefox open (with several tabs in use), normal 
with these program open all 4 cores will be sat at between 0 and 2%. 
When it goes mad 2 cores will be around 12% and two cores bouncing 
between 12% to 60%.

If I open task manager (part of the xfce goodies pack) the list of 
running task will show very little cpu usage maybe chrome using 1 or 2 % 
briefly (I have show all processes ticked in preferences), but the cpu 
graph at the top of the screen will show something about 20% being used. 
Now if I run htop it will show Chrome (which was the last time it 
happened) with a very high cpu usage around 70%.

I am not to concerned as to what is causing the CPU usage, my PC runs 
24\7 so I just close either Firefox or Chrome down as they are the 
normal culprits but why am I getting three different results from 3 
different programs and which one should I trust??