Some major design changes are afoot for AMD’s fusion platform and for future GPUs. AMD is calling is next GPU architecture GCN or “graphics next core.” At the first AMD developer conference, titled AFDS, AMD showcased some new features for it’s upcoming Llano GPUs. The major changes are as follows:
VLIW4 to SIMD – This change allows for better GPGPU performance. VLIW5 and VLIW4 were efficient for graphics calculations, but not for general purpose (varying) CPU computations. SIMD brings the best of both worlds. In fact, Nvidia has been using this for quite some time within their Fermi architecture.
Unified Memory – Both CPU and GPU can utilize the same address spaces. The GPU now has built in address translation hardware just for this specific design implementation.
Improved C++ GPGPU programming and debugging support – Previously developers had to utilize assembly and some C to achieve the desired implementation. Now programmers can take full advantage of a high level language with AMD GPUs.
Compute Units – Instead of the traditional steam processor, AMD will utilized its new SIMD architecute (which is comprised of multiple ALUs making up a 16 bit wide vector SIMD block). Each compute unit has 4 SIMD blocks with an L1 cache. Overall, each CU with have its own L1 cache and all CU’s will share a L2 cache (which all Nvidia and AMD GPU’s currently employ).
Partially Resident Textures (PRT) – As with John Carmack’s MegaTexture technology, textures can now be partially loaded in memory for quicker access. This allows for the use of larger textures to be more efficiently used on a much larger scale than previous implementations. The main differnece is of course that insead of being implemented via software (id tech 5) it will now be implemented via hardware.
Thus, AMD’s fusion GPU code named Llano, will bring some major changes to the table that will dramatically improve on-die GPU performance when calculating and handling general purpose computations. In terms of graphics improvements the main difference revealed thus far is in terms of textures and memory usage. More information will be established as time progresses. Whether or not some of these changes will go into affect for AMD’s upcoming Southern Island GPU’s (Radeon HD 7000 sereies) has yet to be seen.