The NVIDIA FreeBSD driver contains support for NVIDIA SLI FrameRendering and NVIDIA Multi-GPU FrameRendering. Both of these technologies allow an OpenGL application to take advantage of multiple GPUs to improve visual performance.

The distinction between SLI and Multi-GPU is straightforward. SLI is used to leverage the processing power of GPUs across two or more graphics cards, while Multi-GPU is used to leverage the processing power of two GPUs colocated on the same graphics card. If you want to link together separate graphics cards, you should use the "SLI" X config option. Likewise, if you want to link together GPUs on the same graphics card, you should use the "MultiGPU" X config option. If you have two cards, each with two GPUs, and you wish to link them all together, you should use the "SLI" option.

Rendering Modes

In FreeBSD, with two GPUs SLI and Multi-GPU can both operate in one of three modes: Alternate Frame Rendering (AFR), Split Frame Rendering (SFR), and Antialiasing (AA). When AFR mode is active, one GPU draws the next frame while the other one works on the frame after that. In SFR mode, each frame is split horizontally into two pieces, with one GPU rendering each piece. The split line is adjusted to balance the load between the two GPUs. AA mode splits antialiasing work between the two GPUs. Both GPUs work on the same scene and the result is blended together to produce the final frame. This mode is useful for applications that spend most of their time processing with the CPU and cannot benefit from AFR.

With four GPUs, the same options are applicable. AFR mode cycles through all four GPUs, each GPU rendering a frame in turn. SFR mode splits the frame horizontally into four pieces. AA mode splits the work between the four GPUs, allowing antialiasing up to 64x. With four GPUs SLI can also operate in an additional mode, Alternate Frame Rendering of Antialiasing. (AFR of AA). With AFR of AA, pairs of GPUs render alternate frames, each GPU in a pair doing half of the antialiasing work. Note that these scenarios apply whether you have four separate cards or you have two cards, each with two GPUs.

With a Quadro Plex Visual Computing System (VCS), the same options as above are available, if your Quadro Plex VCS has two or four GPUs. In addition, there is a special SLI Mosaic Mode to extend a single X screen transparently across all of the available display outputs on the Quadro Plex VCS.

Enabling Multi-GPU

Multi-GPU is enabled by setting the "MultiGPU" option in the X configuration file; see Appendix B, X Config Options for details about the "MultiGPU" option.

The nvidia-xconfig utility can be used to set the "MultiGPU" option, rather than modifying the X configuration file by hand. For example:

    % nvidia-xconfig --multigpu=on

Enabling SLI

SLI is enabled by setting the "SLI" option in the X configuration file; see Appendix B, X Config Options for details about the SLI option.

The nvidia-xconfig utility can be used to set the SLI option, rather than modifying the X configuration file by hand. For example:

    % nvidia-xconfig --sli=on

Enabling SLI Mosaic Mode

The simplest way to configure Mosaic Mode using a grid of monitors is to use nvidia-settings (see Chapter 23, Using the nvidia-settings Utility). The steps to perform this configuration are as follows:

Hardware requirements

SLI functionality requires:

For the latest in supported SLI and Multi-GPU configurations, including SLI- and Multi-GPU capable GPUs and SLI-capable motherboards, see http://www.slizone.com.

Other Notes and Requirements

The following other requirements apply to SLI and Multi-GPU:

    % __GL_DOOM3=1 doom3

    #!/bin/sh
    # Needed to make symlinks/shortcuts work.
    # the binaries must run with correct working directory
    cd "/usr/local/games/doom3/"
    export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:.
    export __GL_DOOM3=1
    exec ./doom.x86 "$@"