SLI in AFR mode is completely killing performance in our application. We determined this is when doing RTT operations. We’ve tried a simplified rendering now and seen framerates go from ~200 in SFR to 6-8 in AFR with a single 4096^2 16bit shadow map (lower resolutions perform better but still horribly). Without rendering the shadow map, AFR behaves as expected. The same system also behaves as expected with a number of Direct3D applications that support SLI.
The shadow maps are cleared and rerendered every frame (via FBO), the viewport is set to the entire map and scissoring is disabled. The map is not bound before it is updated or by the time SwapBuffers is called. I even tried removing the attachment from the FBO. No luck.
So, what’s the deal? I don’t see how else I could convince the driver that the other GPU does not require a copy of the texture’s current contents. Numerous searches on the net found nothing and I’m following what little documentation there is from nvidia to the letter.