CFS makes the desktop unresponsive and barely usable

[exabyte]

So, a few days ago I decided to move to 2.6.24, mainly because of the the new scheduler (I was using 2.6.22 before this). Since then, I'm experiencing a performance problem. While I'm not sure that it's related to CFS, because there are other kernel changes between 22 and 24, CFS is the main suspect.

My system is not new, Athlon XP 2100+, I don't feel this problem on my laptop, which has a significantly faster CPU. The problem is that when the CPU is loaded, for example I'm compiling something, the system becomes unresponsive, lagged and slow (currently the letters I'm writing are appearing on the screen up to a second after I press the keys).

The situation before the kernel upgrade: If I was doing something resource intensive, it did disturb my work, but it goes like this... If portage is compiling something with nice 1, and at the same time distccd is compliing something with nice 5, I don't feel any impact on the responsiveness. While the processes are running slower and Flash videos are skipping, desktop responsiveness was perfectly OK. Of course, if some of the compilers did try to allocate too much memory or portage began a disk-intensive task, everything lagged, but that's not related to this problem. (Well, and of course, Firefox is always lagged, but it doesn't count.)

The situation after the kernel upgrade: I had to move my portage nice level to 7 and my distccd nice level to 10. Even now, with only portage running, everything is slow. I had ro register two forums (this one and the Ubuntu forum) during the emerge -DuN world I'm currently performing, and the fact that I had to confirm my registration via email made me want to kill the admins -- switching between my Firefox and Thunderbird window has never been slower, I see them redrawing slowly, left clicking on the activation link I see the menu slowly appearing and pasting it isn't faster either. And quite ironic, when portage begins a disk-intensive task, everything becomes more responsive, because the CPU becomes less loaded.


A few notes:
1. KDE/Qt applications continue to work fine, only applications using the slow toolkit (GTK+) and switching between windows feel slower. Also, rendering fonts in Qt apps is slow, too. (Konsole printing out the portage output.)
2. Everything is fine when portage is regenerating ld.so.cache. It's slow when it's checking the package checksums or running gcc.
3. I did experience the same before the upgrade, under heavy load. Also I've experience the same in Firefox (not other applications), if I forgot to close/reopen it often, as one should. The difference is that now it is that way always when there is a load.
4. Some other possibly related to the problem kernel options: CONFIG_PREEMPT_VOLUNTARY=y, CONFIG_NO_HZ=y, CONFIG_HZ_1000=y (I don't believe this one has any effect on anything with NO_HZ).
5. When I'm typing, the letters appear in the right order (usually under a heavy load they bgine apeparnig lie ktihs, which is still the case).
6. Neither music, nor video is skipping under load, even the situation is slightly improved with the new kernel, because it had the tendency to skip under certain conditions - with the new kernel it doesn't.

Anyone share a similar experence on the forum? Any ideas what I can do to improve the situation? Thank you for your reply in advance.

[rlittle]

You should search more. Take a look at https://forums.gentoo.org/viewtopic-t-657398-highlight-.html

They found that disabling CFS helped them out.
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[Paapaa]

[exabyte]

Thank you. That improved the situation a lot.
I also switched to CONFIG_PREEMPT with CONFIG_PREEMPT_BKL on, which also improved responsiveness.

[rlittle]

Sorry, it was late and I hallucinated that CFS was the same as fair group CPU scheduler. /shakes head/
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