Depending on the application and the SLI configuration one or more of the SLI modes listed above may be more appropriate, while some may be undesirable, and some may only be a good choice with appropriate application-specific settings.
One of the most common modes is AFR. By default, when AFR mode is forcefully enabled for a given application using the NVIDA control panel, the driver has to allow all inter-GPU synchronization and communication required to handle inter-frame dependencies and guarantee the correctness of the results. This typically will lead to no SLI performance scaling. The NVIDIA driver supports application-specific SLI profiles that select the best mode for SLI performance scaling, and allow the driver to use heuristics to avoid certain forms of inter-GPU communication or CPU-GPU synchronization. By sending your application to NVIDIA we can create a profile for your application, which will obviate the need for some of the common changes suggested in this document to handle SLI configurations. In some cases, however, driver profiles may not be the most optimal solution, and application changes may be recommended. Once we have created a profile for an application, the profile is added to our next driver release, making it available to the end users as soon as they install the updated driver.
In the absence of an SLI profile, SLIAA is a good alternative to take advantage of multiple GPUs in SLI configurations, even if the application is CPU bound, since SLIAA doesn't require buffering more frames than in a single GPU configuration, or taking care of any major synchronization across GPUs. SLIAA also does not require any SLI-specific work from the application developer. However, when the application uses Direct3D 10 and later it does require that the application supports regular MSAA. When the application uses Direct3D 9, SLIAA can be used in any application that already has the ability to use the driver override for MSAA, which is available in some applications that don?t support MSAA directly.
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