On Sat, 2004-08-07 at 06:24, Florian Schmidt wrote: > > do you know how, in the case of volountary preemption and threaded irq > handlers, the irq's used by X11 are handled? i removed the nvidia module > from my kernelvand rebooted to have it untainted, but of course the X11 > nv module does neither report to /proc/interrupts nor /proc/irq. SInce > it is on another bus [agp] i suppose this is no problem but i always > wondered about the interplay of the kernel an X. It looks to me like an > area which might still have some surprises.. > I believe that video cards use interrupts for 3d engine completion - you tell the card to render such and such, rotate 30 degrees, zoom, and you get an interrupt when it's done and ready for the next command. There are certainly some surprises in this area. If 2D acceleration is enabled on my onboard Via CLE266 video, the 2D engine will cause interrupts from the PCI slot to be disabled for long periods. I am not sure yet if this a bug or a feature. I recommend disabling all hardware video acceleration when tuning a system for low latency (set Option "NoAccel" and commend out the "dri" line). This will prevent X from interacting directly with your hardware - it is complicated enough when only the kernel can access hardware. Then, once you get that working, re-enable 2D acceleration, then DRI/3D acceleration, if these do not cause problems. This will make it much easier to get the problematic video drivers fixed. Lee
