Digital Foundry Microsoft Xbox Scorpio Reveal [2017: 04-06, 04-11, 04-15, 04-16]

Here's what I get from the article.

In much the same way Polaris is just specific targeted changes to the previous GPU and VEGA is just specific targeted changes from Polaris, the Project Scorpio GPU is specific targeted changes to the XBO base GPU.

So in as much as Polaris and Vega define one path of GPU improvement and are thus different from the base GPU from which they started, so is the GPU Project Scorpio (obviously applies to PS4-P GPU as well) uses.

So for Project Scorpio they didn't want to start with a base of Polaris because it contained changes they did not want (IE - changed features they wanted to keep) or did not change certain aspects of the GPU as much as they wanted. They mentioned for example changes to various memory sizes, so I'd imagine things like Register space may have been increased which would alleviate some potential stalls common to GCN.

So while it isn't Polaris or Vega, it may still represent a quite significant change in architechture, if not in features, similar in scope if not in features to Polaris or Vega.

So going from the base feature set of the XBO GPU, they mention taking features of Polaris and Vega. And they mentioned other changes not contained in either Polaris or Vega.

Considering their focus on keeping the base features as similar to the base XBO as possible, I'd imagine that leaving out double rate FP16 was a conscious choice on their end. IE - they were already incorporating features from Vega, but opted not to include double rate FP16 as it didn't fit their design goals for the GPU for Project Scorpio. Or to put it another way, they thought the die space for double rate FP16 could be better used for something else that would be of more general benefit for titles currently in the market or entering the market. Not to mention that in focusing on improving how graphics are rendered for current titles, double rate FP16 wouldn't help with that.

Regards,
SB

 

For all we know that's just another DX12 feature and not an actual change to the hardware. MS has a recent track record of conflating the two and DF has a bad history of not even being able to parse information about how CB rendering works at all.

Frankly, I'd bet good money the vast majority of the customizations MS is counting are entirely related to the switch to GDDR5 and the removal of ESRAM. That being the case it's disingenuous to consider them anything like a competitive advantage when it's probable the result just makes the Scorpio APU work like the PS4 APU always has.

 

What evidence do we have that DF don't know how CB rendering works?

It's always exciting to bet good money on people with far more insight being liars.

Having basically no meaningful modifications would certainly be an interesting end result from having run tens of thousands of simulated runs through hardware variations and making several tens of unique modification requests to available IP.

 

Not only consoles, pcs as well

And the mantra for Ms.is to carry over the workflow from XBO to scorpio, and W10 pcs, all.of them DX12

 

The article's quote is pretty general:

The memory interface queues may have been sped up due the change to a wider GDDR5 interface, or if they're queues in the uncore they could have sped up due to everything else being clocked significantly higher as well. The prior consoles had a lot matching the GPU speed, which Scorpio did increase significantly. I think that might serve more to make CPU and GPU upclocks suffer less from diminishing returns, rather than standing out on its own.

Optimizing how memory translation operations happen is a fuzzy thing to interpret.
Some possibilities might be more capacity to cache translations between host and guest, or tweaks to the TLB or page table walker that reflect what Microsoft knows as the owner of the hypervisor and system memory arrangement.

In theory, the VM's overheads would have been reduced already, since Microsoft mentioned that it did a lot of work like this for the Xbox One and over time it's seemed like there have been enough examples where the Microsoft's CPU-bound performance managed to edge the PS4. Maybe there are specific functions that Microsoft wanted improved, but from the standpoint of how the Xbox One didn't clearly suffer in CPU terms versus its non-virtualized competition, it might not be as obvious because a lot of other work has been done to avoid the overhead.

I think changing the vector register file's capacity would be a notable change. It's something that has been constant even as other elements of the architecture have changed.

 

just wish that Scorpio is fully PC compatible, if it is I will get it day one, if not, dunno. Since my predictions aren't always right we shall wait and see.

 

While what you suggest is possible, I think you are really underestimating the gains achievable with proper simulation. There are number of techniques to analyze and optimize in this situation, but I personally prefer a forest of trees approach for this kind of situation as, to me, it provides greater visibility to options that provide unexpected and /or outsized gains. They could have easily found 60 places where making adjustments yielded strong ROI.

 

Well, it's a feature on pc, so it's not like scorpio wouldn't be the only place it was available. Nvidia and AMD both support it, Nvidia earlier. I would guess there are other reasons why they chose not to implement a newer CU that includes double-rate fp16.

 

AFAIK, double rate FP16 is only enabled for CUDA on NVidia hardware in Windows and not for general game usage through either Vulkan or DirectX.

Regards,
SB

 

What about with SM 6.0?

The hardware is out there. Microsoft should be fully aware of that working with Nvidia, AMD on Directx.

I'm very curious to see what kind of performance improvements AMD's rapid-packed math will bring, but for ps4 pro to match scorpio in alu performance it would have to bring a 50% performance improvement, on average, which is asking a lot. The Frostbite GDC slides talk about fp16 bringing a 30% performance improvement to their checkerboard resolve shader, but checkboard resolve plus temporal AA is only 1.15ms of their frame time. How much performance improvement does fp16 bring to the rest of their shaders? Is 30% an upper limit case or an average?

Again, I think there must have been other factors in determining which features they decided to add. Hard to know what it would be. We just know they had as a performance target, and they chose clock speed as the way to get there.

 

There's nothing that prevents its use in Vulkan or DirectX. Just NVidia have chosen not to expose the feature outside of CUDA. It remains to be seen whether AMD exposing it in Vega will prompt NVidia to change their stance on it.

I don't believe they even expose it in OpenGL or OpenCL either (but I could be wrong). They could easily expose the feature via extensions in Vulkan, OGL, and OCL if they wanted.

Actually this seems to imply that FP16 rate on 1080 is only 1/64 rate (probably artificially limited?).

https://devtalk.nvidia.com/default/...scal-geforce-gtx-1080-gtx-1070-amp-gtx-1060/6

Basically they view it as a professional and not a consumer facing feature.

Regards,
SB

 

So Scorpio wont support all/any SM6.0 requirements?

 

Isn't that an argument for not embracing any new technology?

Flags are not the same as requirments. It's more likely SM6.0 can take advantage of RPM but that support in hardware is not required.

 

What I don't get about this simulation approach to improve their design is that shouldn't this be AMD's job during the design stages of their APUs and GPUs? It's as if MS would be the "only" one who has an idea how games use their hardware in the first place to localise critical areas and improve on them.

 

It may become common optimization in the PC space if NVIDIA ports it to their next mainstream GPU from GP100 and Tegra X1 now that AMD touts it as one of the biggest changes in Vega.

http://www.anandtech.com/show/11002/the-amd-vega-gpu-architecture-teaser/2

Things like normal maps won't require 32bit precision, it can accelerate pixel shader performance significantly. The other Vega feature present in the PS4 Pro is Intelligent Workgroup Distributor. Does the Scorpio GPU have any Vega features?

 

As soon as I read the article, I knew what the staple internet warcry would be from here on out.....

 

I think it would be unreasonable for AMD to be expected to profile and design their APU based on wider system architecture features like ESRAM, VMs, differing memory types, custom APIs (GNM, GNMX), CPU/GPU OS/hypervisor reservations that will also impact performance. AMD could do this but surely this is something that better sits with Microsoft and Sony who are also talking directly with their developers.

 

MMU load with MS specific hypervisor structure is understandable but ESRAM is not issue with Scorpio and as this is about Scorpio design seriously improved through simulators. I'm sure you don't talk here about bus width and their GDDR5 clocks. Tuning to specific memory setup should be part of AMD's 1x1 of GPU designs.

Scorpio is an APU based of AMD Jaguar and GPU assets. That they may need some adjustments for their specific GPU setup makes sense but for the general designs? That should be AMD's responsibility because it affects their own PC products.

 

What data point is this? If you're referring to the DF Forza Apex analysis it makes no such conclusion.