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I've had quite a strange phenomenon with Xorg for some time now: After logging in to my laptop (specifics below) the cpu consumption of Xorg increases monotonically, even if the computer is idle and nobody sits in front of it. I measured the phenomenon over night+morning and got the following result:

up/min  cpu%
14      3.4
29      3.4
44      3.6
59      3.9
74      4.2
89      4.5
[snip]
734     17.8
749     18.1
764     18.5
779     18.8
794     19.1
809     19.4

It actually continues like this regardless whether somebody (=me) uses the computer or not. If you approximate this, it is about 0.025 %/min. Do you have any clue why this happens or how I could figure this out?

Some specs:

CPU: Atom with 1.6 GHz max
Distro: Ubuntu 10.04 LTS
GUI: Gnome 2.30.2
WM: xmonad 0.9.1
X.Org X Server 1.7.6
Linux Kernel: 2.6.32-33
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2 Answers

up vote 5 down vote accepted

This is a bug, either in an application that's running on your X server, or in the X server and triggered by an application you're running, or (most likely) in your display driver.

To pinpoint the culprint, start an X server that's not running any risky application. Log out, then switch to a text console by pressing Ctrl+Alt+F1. Log in, then run sudo service gdm stop and startx xterm -e top -- :0. If the CPU load increases, then your driver is the culprit; otherwise it could be either an application making repeated requests to the X server or a bug in the X server. If you can't see any application using up CPU time, the X server is likely to be the sole culprit.

Once you've done a little bit of investigation, report the bug to your distribution. (Search first to see if someone has already reported it.) For Ubuntu, look at How do I report a bug?. Include the line in the output of lspci for your video card.

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As starting xterm with startx seemed to cause some sort of trouble, I started it directly from gdm when logging in. This is a very nice idea, and I am experimenting with it. I'll report back if there is any success (it always takes some time to verify if the load increases or not). – bitmask Aug 1 '11 at 2:47
up vote 3 down vote

If the culprit is a client application, xrestop might come handy. Useful when the client leaks Xorg resources. It's a top-like application for Xorg resources.

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xrestop is certainly a nice tool, but does not seem to indicate the cpu usage, caused by that application (there does not seem to be a memory leak, only a computation leak .. so to speak). Could you elaborate how I can figure out the client application that causes trouble with xrestop? – bitmask Aug 1 '11 at 2:41
1  
If you can find some unexpected growth of the amount of resources used by a client over time, then you have a suspect (xrestop shows the pid of the process and/or X identifier). If nothing shows up, probably the issue is internal to the X server. – Stéphane Gimenez Aug 1 '11 at 10:26

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