SLI AFR performance problem
I'm trying to use a simple perormance benchmark under SLI alternating frames mode (AFR). I'm running a Dell XPS 700 system with two 7900 GTX boards. I've got the SLI heads-up-display enabled, with page flipping enabled sync to vblank disabled.
My benchmark application renders a densely tesselated square with millions of triangles using VBO. I can 500-550 M tris/sec whether I run with or without SLI AFR (I wouldn't expect a speedup from SFR mode, since this has a vertex bottleneck). I am not doing any readback, glFinish, pbuffers, etc. I'm linking with FreeGLUT. I saw some mention in the GPU Programming Guide of making sure that the framebuffer doesn't need to keep the data after a swap buffers. I'm not sure how to check that in OpenGL/Linux. (If it is the same as allowing page flipping, then I guess it is covered, but I notice no performance decrease if I disallow page flipping.)
Any ideas what I'm doing wrong? BTW, the HUD shows the SLI logo as well as two white vertical lines towards the left side of the window. Do the lines show anything meaningful besides the fact that I'm in AFR mode?
I've attached the benchmark program to this post. For anyone under Linux and willing to run it, does it report different performance for you in SLI-AFR mode versus non-SLI mode?
Thanks for any insight.