Hello, well, after 2 weeks debugging I still cant find what is causing this problem : I have a 3d engine using XLib and OpenGL, but i got stranges slowdowns : my frame rate is at about 200, but approx once a second, the FPS drop to 10 to one or two frames and then come back to 200... I tested with my older engine, and it works fine sometimes, killing one specific application make the problem disapear... but it appears again later (even if i have not restarted the application) my CPU usage is at 5 % when not running the engine... I'm on a custom gentoo linux (Xorg 6.8.2 + blackbox, a minimal set of deamon) with ati drivers 8.14.13 (with 8.16.20, my system hang when I quit X), I saw the problem with kernel 2.6.12 and 2.6.11 any idea ? anyone ?

Post an example executable and see if it is just you and your hardware.

That might help narrow it down. Because then we could see how the hardware might be taxed at certain angles or whatever.

here it is : mawww.free.fr/mw.tar.bz2

mmmm need X11 OpenGL and libpng... i think everyone may have that

Seems to run at a pretty constant 170-200 FPS on my machine (Athlon 3000+, GeForceFX 5700. 512 MB RAM, Debian Testing).

One possible explanation might be that if you're using a busy loop, the kernel scheduler could decide that your program is a batch process instead of an interactive process, so that it gets scheduled out easily for a long time. This problem should go away if you sync to vertical retrace (provided that the driver supports IRQs properly) or artificially throttle your framerate so that you don't use 100% CPU.

cu,
Prefect

I tried your engine and experienced similar problems as you do Mawww. My machine is rather old so I got only 78fps but aprox. once a second fps seemed to drop to 58, not as bad problem as you had but clearly not normal.

800Mhz
Linux 2.6.10-cko3 i686 AMD Duron(tm) processor GNU/Linux
NVidia GF2 OpenGL version string: 1.5.3 NVIDIA 76.76