Performance issue with using EBO

Mali-400 has relatively light vertex processing capability versus it's fragment processing; it can have multiple fragment processing cores (there are four in the Galaxy S2), but only ever has a single vertex processing core. Things to check:

• How many vertices per frame are you trying to render?
• How many primitives per frame are you trying to render?
• How good are your index buffers? Are you getting good reusue of vertices across a connected mesh, or are you processing duplicate vertices at the same location?
• How good is your attribute buffer packing? Does it contain unused attributes which cause cache pollution unnecessarily?
• Are your index buffers contiguous, and without holes?

This final point is a critical one to get right; Mali will shade all vertices between the min and max index value in the index buffer. For example, if your index buffer says [0, 1, 49] then you will end up shading 50 vertices, and only actually use three. Removing holes avoids redundant vertex computation.

One common issue related to this with landscapes is a dynamic  level of detail scheme in which only a single "full detail" master mesh is used, and lower level of details simply sparsely index into that master mesh. Because Mali will shade all of the index values between min and max you generally end up with redundant vertex processing. To avoid this create specific VBO regions for the vertex data each level of detail, and switch to the unique index ranges for each. E.g. it should look something like this:

General optimizations to consider:

• Reducing mesh complexity, using dynamic LOD schemes to select lower detail meshes for more distant models.
• Reducing vertex shader complexity, so the vertex processor has to do less work per vertex.

HTH,

Pete

Mali-400 has relatively light vertex processing capability versus it's fragment processing; it can have multiple fragment processing cores (there are four in the Galaxy S2), but only ever has a single vertex processing core. Things to check:

• How many vertices per frame are you trying to render?
• How many primitives per frame are you trying to render?
• How good are your index buffers? Are you getting good reusue of vertices across a connected mesh, or are you processing duplicate vertices at the same location?
• How good is your attribute buffer packing? Does it contain unused attributes which cause cache pollution unnecessarily?
• Are your index buffers contiguous, and without holes?

This final point is a critical one to get right; Mali will shade all vertices between the min and max index value in the index buffer. For example, if your index buffer says [0, 1, 49] then you will end up shading 50 vertices, and only actually use three. Removing holes avoids redundant vertex computation.

One common issue related to this with landscapes is a dynamic  level of detail scheme in which only a single "full detail" master mesh is used, and lower level of details simply sparsely index into that master mesh. Because Mali will shade all of the index values between min and max you generally end up with redundant vertex processing. To avoid this create specific VBO regions for the vertex data each level of detail, and switch to the unique index ranges for each. E.g. it should look something like this:

General optimizations to consider:

• Reducing mesh complexity, using dynamic LOD schemes to select lower detail meshes for more distant models.
• Reducing vertex shader complexity, so the vertex processor has to do less work per vertex.

HTH,

Pete

Mali Performance 6: Efficiently Updating Dynamic Resources

The blog mostly talks about textures, but exactly the same issues apply to all buffer-based resources.

Cheers,
Pete