I've recently encountered a rather nasty problem. X.org tends to use an extraordinary amount of my available CPU-clock cycles for no apparant reason.

When I first login to KDE, X.org uses around 1-2 % of my dual-core CPU. Everything works fine and is responsive. It's only a matter of time before it uses up to 20 % of the CPU, which is by far the biggest rescource hog by that time - usually about an hour or two after I logged in. The nearest "competitors" are plasma-desktop and kwin but neither usually use more than 1-2 % each.

When x.org start using that much of the cpu, everything is slow to respond up to the point that you start wondering if the system as a whole has frozen. Just bringing a window to the front can literally take 10-20 seconds!

I first thought it may have been my plasma and/or kwin configuration that wasn't optimal or even corrupt, but I've started those from scratch with no noticeable difference. And the settings now are quite modest too. Not many kwin-effects (essentially just taskbar-thumbnails, cover-flow alt-tab, magic lamp, highlight window, dialog parent, dim inactive, and present windows). Plasma is quite modest too. Just one workspace, and just one activity too. I use two panels, and only lancelot, quick-access (3 of that one), digital clock, eyes, trashcan, icon, logout, quicklaunch, smoothtasks, playwolf, system load viewer, yaWP, systray, pictureframe, and device-manager.

I don't think it's one of the plasmoids though, because I got the same behavior with even fewer plasmoids.

If I log out and in again (no reboot) everything is back to normal. I'm no expert at how x.org works, so what I wonder: how do I trouble-shoot this?

Generally, X.org doesn't "just" use up lots of CPU by itself - it's usually caused by some program that want to repaint way too often.

Considering that for me Plasma takes up no CPU, my best bet is that one of the applets in your "modest" list is misbehaving. My suggestion would be to log out of KDE, back up whichever configuration files Plasma uses to store its configuration, and see if the problem persists (I'm 95% certain it won't). It could be something completely innocent-looking.

Alec wrote:Considering that for me Plasma takes up no CPU, my best bet is that one of the applets in your "modest" list is misbehaving. My suggestion would be to log out of KDE, back up whichever configuration files Plasma uses to store its configuration, and see if the problem persists (I'm 95% certain it won't). It could be something completely innocent-looking.

Actually, that's what I thought as well at first. But considering that I've never had any problems with these plasmoids before it seemed like a stretch. I'm going to try with an even more back-to-the-basics approach just to make sure, but since I've been running these plasmoids for what seems like an eternity (relatively speaking) with none of this until a few days ago it seems far-fetched.

And yes, plasma usually doesn't take any CPU to speak of here either. It was at about 1 % when I checked when x.org was hogging the cpu but usually it's waaay down on the process list.

Hm, I wonder if it could be some remnant of an earlier nvidia-driver that's making x.org "confused"? Yes, that seems very far-fetched too but that's the only difference in hardware that should make a difference. I used to use a nvidia-card, but now it's Intel-graphics (and yes, x.org has been reconfigured to use Intel instead of nvidia).

Just out of curiosity and for the sake of comparison: how much cpu does x.org take for you?

I'll continue investigating this

If I'm not doing anything, it's usually at 1%.

My processor is a 1.7 GHz Core2Duo (usually running at 800 MHz), and I've got an nVidia GeForce Go 7300 card.


Since you mention that you switched the graphics card recently, have you tried disabling compositing to see if that alleviates the problem?

Can you possibly trace ( by starting to kill applications when X.org CPU usage reaches a moderate point ) which applications are at fault? If it is Plasma, then start removing applets until the problem goes away.

Alec wrote:If I'm not doing anything, it's usually at 1%.

Okay, so your values sound like mine are when everything's going as it should.

And yes, I've tried turning composite off but with no difference.

bcooksley wrote:Can you possibly trace ( by starting to kill applications when X.org CPU usage reaches a moderate point ) which applications are at fault? If it is Plasma, then start removing applets until the problem goes away.

I'm in the process of doing that actually, but so far with no success. It might even be a plasmoid, even though I don't understand why one should suddenly start misbehaving. Still, considering that the plasmoids running have been the only common denominator when x.org starts to spike I've managed to see. Nothing else can be running and still x.org start going up.

Kryten2X4B wrote:I'm in the process of doing that actually, but so far with no success. It might even be a plasmoid, even though I don't understand why one should suddenly start misbehaving. Still, considering that the plasmoids running have been the only common denominator when x.org starts to spike I've managed to see. Nothing else can be running and still x.org start going up.

Okay, scratch that. I've managed to find the culprit. Or rather culprits. It wasn't x.org at all, and not plasma on its own either. Plasma is involved, but not only plasma.

It's plasma's systray that's causing this together with iconifying Kontact into the systray. If Kontact's never iconified, this doesn't happen. But as soon as it has been iconified once in any given session, x.org starts eating cpu-cycles. It doesn't help if I after that quit Kontact completely either.

Since it's not x.org's fault (at least not directly) and thus not Linux/BSD specific, could someone move this to a better sub-forum?

Hi,

I would like to know if there has been any progress on this issue.
I also suffer this problem, and it seems to be linked to KDE, as I cannot see it in awesome. I have to do more tests with other DMs, and try to remove programs from the systray.
What happens is that after some time X increses to 25%, then 100% of one core (I have an i7 Lynnfield CPU on a P55 platform). Since only one core is maxed, the system is not unresponsive, but this still consumes a lot of CPU time.
I detect the bug in KDE 4.5 rc2.
Is there a bug report already filled for this issue?

Thanks.

I will respond to myself: there is a bug report that seems to match this issue: https://bugs.kde.org/show_bug.cgi?id=220047
I confirmed the bug for KDE 4.5rc2, please vote for this bug if you are affected by it too