DirectX 12: The future of it within the console gaming space (specifically the XB1)

As far I've understood it, pretty much all games these days use compute shaders (for post-processing if nothing else) and for most games, which use Direct3D, the choice for compute-API is DirectCompute.
This might be changing now that more and more games are being planned for multiplatform (SteamOS/Linux) even on PC

 

Not sure to post here or ESRAM thread, but Gaming Bolt has an article today where Brad Wardell makes some incendiary claims that the new DX12 SDK will solve the X1's resolution woes due to allowing control of ESRAM. And interestingly, supposedly there would be some kind of auto ESRAM "easy button"?

http://gamingbolt.com/dx12-should-r...ssue-on-the-xbox-one-esram-to-receive-new-api

Read more at http://gamingbolt.com/dx12-should-r...-esram-to-receive-new-api#RX3TjaUvjuAcHGEJ.99

 

I guess the key point here is how much further would the xbox have to stretch to obtain 1080p.
A lot of people just use TFLOPs as a way to measuring performance, but I feel from a technical perspective, that is not really capturing the entire picture.

I've often wondered how AAA developers truly budget what they can and cannot fit in a game at the start of a project.

And so, after much deliberation, I believe they do it like this any of you guys are free to correct me.

They look at the resolution and amount of shaders involved as a target and that will ultimately determine the amount of floating point operations that the game will consume. We will say X amount - or they reverse engineer a target from their target hardware or something. But they should have an idea of how heavy their code should be.

Because you are a console developer I guess, say targeting PS4 for example. you know you have a peak 1.84 TFLOP. No problem
That means, every second PS4 is capable of 1.84 Terra floating ops. Okay. So for 60fps, you need 16.6 ms.
So that means it can only do
0.030666666666666 TFLOPs in a 16.6ms frame.
or 30.7 billion flops per frame.

Your game needs to be less than 30.7 billion flops per frame, or it is theoretically impossible to do.
Now interestingly, once that frame counter begins, every clock cycle that is unused or used, the number of flops go away. For reference on PS4 there are 1.84 Million FLOP per millisecond.
So game developers must be budgeting how much time could they have possibly idle when your GPU is doing nothing due to cache misses, waiting to read and write memory, waiting for instructions, changing states, waiting for sync points.. etc

So games will likely be targeting much less than 30.7 billion in this case, they need to factor in latency and stuff. So eventually they come to a budget.
Now this is why I believe when Naughty Dog said hey we can run UC4 at 1080p/60 it's because the GPU code must be less than 30.7 billion flops to make it happen. But they were having troubles with the loss cycles, since once the frame ticker starts, you're losing FLOPs whether you are using them or not. So it runs at 30fps instead. And that gives them access to 61.4 billion flops, how many are wasted, and how many are actually doing work is beyond me. There are only two ways ND will be able to hit this target, they either use less FLOPS to do the same task (optimization) or they find a way to use more FLOPS and have less idle time (saturation).

Same thing applies to Xbox One.
22 Billion flops per frame @ 60 frames per second. Now if the budget of the game is less than 22 Billion flops per frame @ 1080p, it could theoretically fit in XBox's budget. But once again you're going to have to have that uphill climb. Will directX12 up the efficiency so much that there is very little wasted FLOPs? Shrug.

If so, then, yea I guess it can do it, but it's still up to the ability of the developers and the budget of the game.

 

My only comment is that the tflop output for both systems is theoretical and I am sure the actual output can vary depending on what exactly you are using the system for.

 

Peak, not theoretical. You'd have to use them all and not have waste, but you're right, I'm not sure how this would translate to GPGPU calculations.

 

This video from pcper shows an initial review of DirectX 12 performance (draw calls per second). Seems to be pretty substantial increase over DirectX 11 depending on the hardware. At the end (7:06 mark) they show the results from an AMD APU...this is probably the closest thing we could have to compare to an Xbox One. It basically gets 8X the draw call performance. Not sure how to read into that.

 

DX12 – Multi-Threading Shadow Map Rendering Performance Boost, Can Be Applied to Existing Engines

http://www.dsogaming.com/news/dx12-...nce-boost-can-be-applied-to-existing-engines/

 

Additionally, PC World has performed a few tests as well, and they say that the leap is insane.

http://www.pcworld.com/article/2900814/tested-directx-12s-potential-performance-leap-is-insane.html

 

I've always read in interviews that dx are shitty, but never imagined so much...

 

So, what's the general consensus around here these days? Is dx12 going to turn the xb1 into a ps4 beating monster, or is dx12 only for PC with xb1 getting small gains?

Personally, the more info that comes out, I'm going with the former...though to be sure if the former is the case, MS have been unnecessarily quiet on the subject.

To take a couple of headline items. Massively increased draw call rates due to parallel submission and 50% reduction in frame rendering time due to using async rendering of shadowmaps. Just these two examples alone would result in huge gains.

What is going on?

 

Neither is true. As stated a few pages back, these benchmarks are specifically designed to show drawcall improvements. I'm surprised so many publications are suggesting that the proportional increase across games will be consistent. They won't. Not unless there's a game that uses drawcalls to this excess and can't bundle them.

 

DX12 will benefit PC games most. The Bone may get some small improvements here and there, but likely nothing most people would notice on screen.

 

I think that's a slight misconception.
Xbox One supports to date DX11 with XBO extensions for esram and some bundle features. It also supports a low level version of DX11 which they refer to as fast semantics. The equivalents on PS4 are GNMX and GNM. While we don't have the splits on how many developers use the high level APi vs the low level one, it's pretty safe to assume the high Level one is used in a lot of studios.

There are many people that think just because consoles have low level APIs it means that all developers are capable of using them or that all engines have them employed.

Ryse Son of Rome is considered widely as Xbox Ones best looking game, and it is entirely built on DX11. Fast semantics didn't even become available until March of 2014.

That pretty much goes for all launch games on Xbox. BF4 is such a game as well and I don't necessarily know if they migrated BF4 Hardline to a fast semantics engine.

So if a developer moves their engine like Crytek3 from DX11 to DX12 will mean that they are now moving to a low overhead API, closer to metal code, and a multithreaded renderer which they had none of before.

Having said that though, it wouldn't surprise me to see a lot of games released using DX11.3 and not DX12 as the years go on.

 

This absolutely is not going to happen. The PS4 already has it's own low level API which it likely even more efficient (since it's specific to the PS4 architecture) then DX12.

This would only be in the most corner of cases, you're never going to double overall frames per second using async compute. The highest estimates I've gheard so far for peak improvements is in the 30% range, with 15-18% being more normal. That, and the PS4 already has access to async compute through it's own API.

 

@iroboto
Why is it "safe" to assume most XBO devs are using the high level API? For any multiplatform title, the XBO version is starting from a significant hardware deficit. I'd think these devs would jump on any performance improvement option available to them. Likewise, I'd think MS would make any and all such performance improvement options available to all devs ASAP, rather than waiting for DX12's official release.

 

Both platforms I mean. Let's look at the number of games that started well before as DX11 engines
BF4
UE4
CryEngine
What Ubisoft uses
Likely whatever EA uses for its sports games.

We've read interviews about "the crew" where they were leveraging GNMX. So that really starts to draw some parts of the landscape. If AAA developers aren't all fully aligned in using low level then it does say a lot about the goals of the company.
1st wave games might have had too hard of a deadline, too much to learn, tools immature, and learning the new hardware. Having to deal with a low level API may have been too much. If the code works why re-write it all just for Xbox One? Who cares that it performs worse, it's MS fault that they didn't put in beefy enough hardware. If you are already learning a new API Like GNM(X) do you really want to invest into learning fast semantics?

I only see console exclusives getting that treatment. Or highly talented companies going that route where resources are plentiful.

But next couple of waves we will likely see more developers head to the lower level.
For developers that haven't left DX11: DX12 is a good reason to upgrade as it benefits PC, mobile and Xbox One.

 

I agree, clearly the tests are synthetic purely to demonstrate one facet, however there are documented (sort of...) examples where the xb1 has been bottlenecked by its single threadred draw call submission. That bottleneck is no more with dx12. Surely that's going to have an impact?

 

Regarding shadowmaps, I'm wondering if this would benefit Forward+/Clustered Forward solutions more than Deferred Shading renderers.

hm...

 

Now here I have to disgaree. From what I gather the performance gains from dx12 have little to do with getting close to the metal, but everything to do with utilising multiple CPU cores to submit work to the GPU. Dx12 is paradigm shift in the approach rather than getting even closer to the metal.

Having said that, the last time I got close to metal was on the amiga's blitter in about 1986...so I could be misunderstanding the situation...

 

That's not something exclusive to the "creators of DirectX".

Regardless, PS4 has superior GPU specs.