[Solved] High kwin CPU usage w/ desktop effects on (4.1)

[kjjjjshab]

I've noticed high CPU temps even with Dynamic CPU Freq set, so this weekend I set out to investigate... the offending process is kwin, and only when desktop effects are on... it jumps to 90%-ish every few seconds, which in turn keeps my AMD 3800 running at full 2400 instead of going down to 1000 as it should when everything else is idle. So my temps which should be at 35 are at 50+.

So, if I turn off desktop effects that "fixes" it, but of course that is not an option, so I started to turn on and off different effects thinking that one of them was causing the problem, but no one change seemed to help.

So I turned on Show FPS just to see how well it was performing, and then magic happened... the kwin jumps went down to 15% CPU which was enough to keep my freq at 1000 and drop my temps to where they should be... but, WHY? Why does reporting out the fps fix it? And of course, this isn't a permanent fix, since i hardly want the fps on my desktop at all times, but what the heck?

Anyone?

[kjjjjshab]

Sometime in my attempts to fix other issues, I must have turned on System Setting -> Desktop -> Advanced Options... Use VSync. With that unchecked, kwin performance once again is in the 3-6% levels that keep the CPU at 1000 and thus temps low.

No idea why the show fps had the same effect.

[schnook9]

awesome!! This totally worked for me.  No clue why it does what it does either, or how it got checked for that matter, but I'm back down to manageable CPU.

Thanks much!!

[kjjjjshab]

...
Thanks much!!

Great! I hate thinking I was just talking to myself in this thread! 

[dibl]

I must have turned on System Setting -> Desktop -> Advanced Options... Use VSync. With that unchecked, kwin performance once again is in the 3-6% levels that keep the CPU at 1000 and thus temps low.

Nope, I don't think you turned it on.  I just found it turned on by default.  When I unchecked it, Kwin resource usage as shown in top when from about 40% to about 7%.  Much better!   

[epswinde]

Yeah, I was having the same problem, hopefully this fixes it.

[tlue]

I had the same problem. Deacitvating VSync solved it. Thank you!

[Daxxi]

Sometime in my attempts to fix other issues, I must have turned on System Setting -> Desktop -> Advanced Options... Use VSync. With that unchecked, kwin performance once again is in the 3-6% levels that keep the CPU at 1000 and thus temps low.

I'm on Kubuntu Karmic with Nvidia drivers and the high kwin CPU% was frequently occurring.
It was noticeable by the mouse pointer moving erratically.

Bye, bye VSync !

Thank you for that fix, Google & kjjjjshab 

[Daxxi]

Back again at high CPU%, so VSync is not my fix 

Just checked "Disable Desktop Effects" [Apply] ... kwin% reduces immediately ... then uncheck [Apply] and kwin% stays low. 

It seems that the act of updating the settings is all that's needed to fix the blockage. 

I might experiment with a CRON job to do that at intervals, if possible.