[Flightgear-devel] Shader performance and multiple GPU?

[Torsten D. <To...@t3...>]

Hi,

as pointed out in other threads, I am currently assembling a machine with five 
nVidia cards. The machine and the cards are fast enough to render a steady 
60fps, synced to vblank. 
But this is only with shaders disabled. The moment, I enable shaders and 3d-
clouds, the frame rate drops to 20fps and sometimes even less. This does not 
happen when I limit the display to just one single GPU. One GPU with dual 
screen ("TwinView") runs at framerates beyond limits even with all shaders on 
and quality level to highest. The moment I add a second card to the setup, it 
slows down significantly.
I know that shaders are little program fragments running on the GPU itself. 
Now, what happens, if a shader effect spawns multiple GPU's, e.g. a cloud 
which is visible across the entire window? 

Cheers, Torsten