Wii U GPU new info and more speculation

[timmah]

HoloDust said:

timmah said:

It could still theoretically be a custom chip based on the architecture of the E6760, it is certainly very, very customized, so we really don't know what part they used as the basis for the chip. My assumption from seeing performance in the NFS-MW video compared to other cards is, it CANNOT be a 160SP 6450, not a chance, and performance seems to be AT LEAST in the neighborhood of the stock 5550 up to 6570 range based on how it's running that game. As far as memory bandwidth, we've heard developers complain about the CPU (though that should be ok when properly utilized due to a short pipeline and OOOE), but there's been nothing but praise for the memory architecture so far, so maybe that's not a big deal. Not a single developer has said anything about Memory bandwidth issues. Every system Nintendo has built since GC has been very efficient and well balanced, so I assume they would continue that tradition.

Keep in mind, we have a part number for the memory, but don't know to what degree it's been customized, if at all. We don't know for certain what the memory clock rate is, and nobody has actually presented a benchmark to test real-world performance. How does the memory controller use EDRAM? Can the system use some type of predictive prefetch to EDRAM to accelerate real-world memory performance? We have a die shot of the GPU, but no solid answer as to what part it's based on. We also don't know wat the 30% of the GPU that is 'unknown' does - we are fairly certain it has a hardware tessellation unit, but what else did Nintendo bake into the chip? Did Nintendo & AMD create some crazy DX11 type fixed functions to give developers 'free' lighting or other 'free' effects? Maybe some kind of proprietary hardware texture compression is available to negate a potential RAM bottleneck? Some of that is a bit far fetched, but this is Nintendo we're talking about. We have no idea the details of the 'unknowns', and I would assume that 30% does something... I wish Nintendo would just release the damn specs!

As you  might remember, 5550 comes in 3 flavours (all with same core and mem clock, over 128bit bus) - GDDR5 (27VP rating), DDR3 (21.8VP) and DDR2 (16.5VP). As you may see, memory bandwith is bottleneck, and is sole purpose for difference in perfomance between 3 versions.

5550 DDR3 is more than enough to have NFS sort of visuals at 720p. Problem is, WiiU's suggested bandwith (DDR3/64 bit) matches the lowest version (DDR2/128bit), 12.8GB/s in both cases. Where I supose the problem lies is overcoming that bottleneck and pushing that (hypotetical) 5550 to behave more like it's DDR3 over 128bit bus.

But, what puzzels me most is, as you said, that nobody complained about memory subsystem, on the contrary, I think I remember some devs saying it's well balanced. Now, that 6450 is 64bit card, and those 64bits are actually well balanced for it...

I'm still thinking it's some 320SP config inside, IMHO 6570 would be overkill for such bottlenecked system, but, as I said, I really wish they actually went at least with it and 128bit bus (and of course, better CPU, but that comes from my WiiHD vs WiiU standpoint).

...But the 6450 can't do what we saw in that video.

Keep in mind, the developers do not indicate that there is any RAM bottleneck, quite the contrary in fact. This leads to one or more of the following possibilities: (a.) the bandwidth assumptions are wrong, (b.) the memory controller alleviates the 'bottleneck' by utilizing EDRAM and maybe some sort of predictive prefetch, (c.) there is some *really* good hardware texture compression that effectively eliminates any memory bottleneck. One or a combination of these possibilities would remove the 'bottlenecked system' argument... if games are coded properly. Early ports have never been an indication of a system's power, so I reserve judgement for at least a year. Speculation says RAM bottleneck, developers say the opposite, I believe the devs.