Baker said that Mantle still abstracts the details of the shader cores themselves, so that it is not clear if it is running on a vector machine or a scalar machine. However, what isn't abstracted is the basic way a GPU operates, he said. The GPU is another processor, just like any other, that reads and writes memory. One thing that has happened is that GPUs are now general in terms of functionality. They can read memory anywhere. They can write memory anywhere."
Mantle puts the responsibility onto the developer. Some feel that is too much, but this really is not any different from managing multiple CPUs on a system, which Oxide have gotten good at. Oxide does not program multiple CPUs with an API, it just does it itself. Mantle gives us a similar capability for the GPU, he said. When asked about the performance in Star Swarm, Baker indicated that the performance will depend on how exploitative you are, and the specifics of the engine. In the case of Star Swarm, the team was limited in what they could do by driver overhead problems. There have been decisions made where the team traded GPU performance for CPU.
Baker said that the Direct3D performance for the game absolutely outstanding. We have spent a huge amount of time optimising around D3D, and are biased in D3D's favor. “Mantle, on the other hand, we've spent far less time with and currently have only pretty basic optimizations. But Mantle is such an elegant API that it still dwarfs our D3D performance," Baker said.
