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CPU: AMD Phenom II X4 955 Ubuntu 11.10 amd64

I launch some application that use only one core and when I look at cpu-load graphic in gnome-system-monitor I found that all of my four CPU's loaded not symmetrically: most of all (by time) loaded CPU2, then CPU1, then CPU3 and CPU4 was loaded for 10sec only. CPU2 was loaded at 100% for 3minutes without rest. When no application that uses a lot of CPU runing I also have CPU4 loaded lower than others. Ubuntu try to kill my PC or it's should be like this?

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You need to provide more information. You don't say what version of Ubuntu you are using. You don't say what applications are running. A normal Ubuntu system consists of lots of running processes. And even if a program is single threaded and doesn't use multiple processes, it can still be moved between processors. It's perfectly legal for "some application" to do heavy work. –  Jo-Erlend Schinstad Jan 22 '12 at 5:29
    
problem that CPU4 loaded lower than other CPU's, I don't sure that it is normal –  avi9526 Jan 22 '12 at 5:53
    
Perhaps you can explain why you expect symmetric CPU usage. –  mikewhatever Jan 22 '12 at 6:01
    
hmm, i just think that CPU's have the same topology and non-symmetric load can overheat one part of the chip, or not? –  avi9526 Jan 22 '12 at 8:50
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2 Answers

up vote 4 down vote accepted

Many programs are - unfortunately - not multi-processing capable and run in a single thread/on a single processor. Some use threads, which can be executed on another processor core than the "main" program.

If you have a program that uses a single thread only, it only needs one processor and it does not make sense to move it around the other CPUs, because that takes time.

However, you can be sure that the mapping of processes to cores is fine the way it is. See http://en.wikipedia.org/wiki/Scheduling_(computing)#Linux for some information.

And no, processor cores do not overheat if only one is used over some time.

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I am experiencing similar odd behaviour with a quad-core processor. I only wanted to reply because I think I can maybe help clarify.

The problem is not that certain programs use only 1 core, I would understand that, however it's that certain programs are using all the cores asymmetrically.. So in other words at any given time only 1 of the 4 cores is at 100% while the others drop to 10 - 30. It operates like this for a few seconds and then switches cores.

I've taken a screen-shot of this behaviour while using DeVeDe 3.21.0 (ffmpeg 0.8.4 is the backend, I think. -version says it was built with gcc 4.6.3) to better illustrate it:

http://i49.tinypic.com/fblqj9.png

Using Ubuntu 12.04.1 LTS, also here's uname output:

3.2.0-33-generic-pae #52-Ubuntu SMP i686 athlon i386 GNU/Linux

Hope this helps clarify the problem.

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