UpdateSubresource (Constant Buffer) + Draw pattern inhibits GPU parallelism

[ajmiles]

A common D3D11 pattern was to issue pairs of UpdateSubresource + Draw, where constant buffers were updated just-in-time before each draw.

This pattern, when translated to D3D12 is:

1. ResourceBarrier (old state -> COPY_DEST)
2. CopyBufferRegion
3. ResourceBarrier (COPY_DEST -> VERTEX_AND_CONSTANT_BUFFER)
4. Draw

That pattern means no draw overlaps with any other.

Some sort of 'rename' operation could occur, similar to the MAP_DISCARD behaviour from D3D11 to better allow GPU parallelism.