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Forums - Sony - Mark Cerny Explains The PS4's GPU - Can Perform Asynchronous Complex Processes

globalisateur on 30 June 2013
Hynad said:
ethomaz said:

slowmo said:

Contrary to Ethomaz's belief that this will be a big benefit now, this is in actual fact, a feature that will be great in the long run for optimization rather than short term while developers are still working to understand the architecture.  I don't buy his comment on lifting it above PC GPU's because as you say the stronger CPU in most gaming PC's means they dont need the help from the GPU (as the lack of use of Nvidias tech as proven).

This is nothing to do with gimping the CPU though and is a very clever tweak to add flexibility at a low cost that could be of great benefit in the hands of the right developers.

I agree with you... I just disagree that the Jaguar is that bad... I think devs can use the CPU for a lot of tasks.

Rember the PS4 CPU is a 8-core Jaguar running at 1.6Ghz.

The actual clock of the PS4 CPU hasn't yet been confirmed, as far as I know.

Here's the official spec sheet:




There was a rumor that Sony wanted to boost the CPU clock to 2ghz.


Due to efficiency and ease to code, it's better to clock the CPU twice the speed of the GPU, hence we would have 1.6GHz CPU  and 800MHz GPU.

But as they annouced 1.84TFLOPS for the GPU it implied a GPU with a 800MHz final frequency and by simple deduction a CPU of 1.6Ghz.

If they overclocked the CPU to 2 GHz it would complicate the work of the developers and raise the heat produced by the CPU not in a linear way. But a lot much more heat for the PS4 to dissipate.

So it is very improbable that they decided to overclock the CPU.



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drkohler on 30 June 2013
globalisateur said:

If they overclocked the CPU to 2 GHz it would complicate the work of the developers

Huh? The chip designers have to take care of that. Developers wouldn't care the least, they'd just have a faster cpu...



Machiavellian on 30 June 2013
ethomaz said:

Machiavellian said:

Ok, thanks for clearing that up.  That should mean that the GPU can perform both graphics and Compute functions at the same time, how does this effect processing.  In other words, will graphics take a hit if you are using the compute units at the same time or vice versa.  I know in the past this was a problem for AMD chips.

No hit at all.

GNC can do that too in a limited way... in GCN you have 2 schedules (ACE) so if they are full you can't send more asynchronous (Compute or Graphics) process to GPU... so you need to wait the tasks finish to send more taks to GPU.

I don't how many tasks a ACE can schedule to CPU at the same time but I will use 1:1 to make easy the example... so each ACE can schedule 1 task in GPU per time.

2 ACE = 2 tasks... so you can run 2 different traks in the GPU at the same time.
8 ACE = 8 tasks... so you can run 8 different tasks in the GPU at the same time.

Eg.

I have 4 different tasks to execute in a GPU with 18CUs (I'm using CUs to make more easy the example):

1. Graphic render (needs 10CUs)
2. Decompression (needs 1 CU)
3. Physics Simulation (needs 4 CUs)
4. Collision Detection (needs 2CUs)

So in GNC you can schedule only 2 tasks at the same time, so you will execute:

1. Graphic render (needs 10CUs)
2. Decompression (needs 1 CU)

You will have 7 CUs free but that can't be used... so you need to wait the task 1 or 2 to finish to start the 3.

But in PS4 GPU you have 8 tasks at the same time, so you will execute everyting at the same time:

1. Graphic render (needs 10CUs)
2. Decompression (needs 1 CU)
3. Physics Simulation (needs 4 CUs)
4. Collision Detection (needs 2CUs)

You will have 1 CUs free yet... so if you have another tasks that needs 1CU you can use it because you are only using 4 ACEs and have another 4 free.

What that means? More efficience... you can use all the resource of the GPU at the same time without need to wait the GPU tasks finish.

NOTE. All the numbers are created and just used to try to explain with examples... the ACE can schecule more than 1 task per unit... and there are more than 1 task for graphic render too.

The point is... with 8 ACEs you can use the idle units of GPU to do others things in parallel... you can put more tasks in parallel into GPU... if at same time you are using only 50% of the units in GPU with 2 ACEs then with 8 ACEs you can the other 50%.

Efficiency is the work.

That's another feature that put the console GPU over the PC GPU for now... you can use more and better the power of the GPU... in console you can extract more from the GPU with less idle time.

Hmmm, this should mean that developers who cut their teeth with the Cell should be able to leverage that same tech when building PS4 games. This is just my assumption.  Hopfully this will mean a much better output from games being developed by internal teams like ND who have excellent experience with such parallel development.  I wonder what is the average speed of a compute unit in relation to a cell unit.



Machiavellian on 30 June 2013
drkohler said:
globalisateur said:

If they overclocked the CPU to 2 GHz it would complicate the work of the developers

Huh? The chip designers have to take care of that. Developers wouldn't care the least, they'd just have a faster cpu...

Overclocking the CPU above the GPU in a APU design does not sound like a win win situation.  Either way, its not like Sony really need to do it.  The machine has plenty of horsepower and it gains them nothing to introduce an element that could make developers games unstable or their hardware.



ethomaz on 30 June 2013

Machiavellian said:

Hmmm, this should mean that developers who cut their teeth with the Cell should be able to leverage that same tech when building PS4 games. This is just my assumption.  Hopfully this will mean a much better output from games being developed by internal teams like ND who have excellent experience with such parallel development.  I wonder what is the average speed of a compute unit in relation to a cell unit.

I expect to see that too... well eveything that I wrote here is theoretical and now we need to wait and see if the devs can put that in pratical through games



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ethomaz on 30 June 2013

Machiavellian said:

Overclocking the CPU above the GPU in a APU design does not sound like a win win situation.  Either way, its not like Sony really need to do it.  The machine has plenty of horsepower and it gains them nothing to introduce an element that could make developers games unstable or their hardware.

I checked months ago the AMD's APU and there are nothing hiting to 2:1 clock CPU:GPU... in fact I can't found a direct ratio between them... each APU have one clock for GPU and other for CPU using different ratios.

Eg. Jaguar APUs.

 You can see more here: http://en.wikipedia.org/wiki/List_of_AMD_Accelerated_Processing_Unit_microprocessors (there are APU with 2.4Ghz in CPU and 400, 500 and 600Mhz in GPU).



zuvuyeay on 01 July 2013

good vid,got a real history form cerny,pretty cool life

sounds like sony are going as cheap and easy/friendly as they can to me tech wise but of course i'm not very smart



                                                                                                                                        Above & Beyond

   

Michelasso on 01 July 2013

I must just say congratulations to all the guys explaining this thing in the various posts. This stuff is amazing.



Porcupine_I on 01 July 2013

"So the concept is that as game developers learn to use these techniques later on in the console life cycle, we will see richer and even more interactive worlds.”

And that is all i wanted to hear.



“It appeared that there had even been demonstrations to thank Big Brother for raising the chocolate ration to twenty grams a week. And only yesterday, he reflected, it had been announced that the ration was to be reduced to twenty grams a week. Was it possible that they could swallow that, after only twenty-four hours? Yes, they swallowed it.”

- George Orwell, ‘1984’

Scoobes on 01 July 2013

Sounds good. So a slight improvement on the current GCN architecture that should open up the possibilities for devs later on in the gen.

I imagine that most devs don't have people that are versed in using the GPU for these types of tasks so I suppose the question remains as to which devs will be able to make use of the tech. As far as I'm aware, people with this sort of expertise is still fairly rare.




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