Checking for Best Practices

Before you begin to use OpenGL Driver Monitor as an analysis tool, it’s a good idea to check your code to see if you are following the most recent best practices for using OpenGL. See:

• The “Improving Performance” chapter in OpenGL Programming Guide for Mac for a discussion of best practices

• OpenGL Profiler User Guide. You’ll find advice on functions that you need to make sure you use correctly, if you use them at all.

Checking Data Transfer Rates

To check data transfer rates, monitor the following:

• VRAM usage. See whether VRAM usage is at capacity by looking at Current Video Memory in Use (vramUsedBytes) or Current Free Video Memory (vramFreeBytes). If it is at capacity, investigate whether the system is low on VRAM or whether VRAM usage is unusually high for an application running on the system.

• Swap rate. A variety of parameters, such as Buffer Swaps (bufferSwapCount), let you investigate the cause of unusually high swap rates. Check to see whether the swapped data is dynamic or static. If the data os static, make sure you are using caches, vertex buffer objects, or some other technique that’s optimized for static data. Use swaps only for dynamic data, and only when the data changes.

• The time spent by the CPU waiting for the GPU. Look at CPU Wait for GPU (hardwareWaitTime). If the CPU spends a lot of time simply waiting, check to see whether you are calling glFlush or glFinish inappropriately. There are only a few cases where you actually need to use these calls, and these cases are rare. For more information, see the “Improving Performance” chapter in OpenGL Programming Guide for Mac.

Checking for Suboptimal Surface and Texture Paging

You need to make sure that your application is not paging texture and surface data unnecessarily. When it does page, you should use the accelerated graphics port (AGP pathway, which is also known as DMA transfer). Non-AGP transfers slow performance. You can check for less optimal paging by looking at these parameters:

• Surface Page Off Data (Non-AGP) (surfacePageOffBytes)

• Surface Page On Data (Non-AGP) (surfacePageInBytes)

• Texture Page Off Data (Non-AGP) (texturePageOutBytes)

• Texture Page Off Data (Non-AGP) (texturePageInBytes)

Non-AGP transfer is acceptable only if you must reorder data or align it. If possible, use this type of data transfer at initialization time and not during a rendering loop.

If your application has a lot of paging activity, whether it’s AGP or non-AGP, consider using framebuffer objects.