Digital Foundry face to face with PS4 chief architect Mark Cerny.
Digital Foundry: The whole concept of stepping into the shoes of Ken Kutaragi as chief architect of the next PlayStation... How did that feel? It's a huge responsibility.
Mark Cerny: Well, Ken is a genius, so it was not possible to duplicate his approach. We had to find a different way of making console hardware.
Digital Foundry: You talked in your keynote about a team, sitting in a room - a plain room - basically designing the future of video games. Was there an existing team starting to architect PlayStation 4 when you made your pitch? Did you integrate with that team? Did you bring in your own people?
Mark Cerny: In 2007 we started to do a post-mortem on PlayStation 3 to figure out what worked and what didn't and PlayStation 4 didn't really get kicked off until 2008. So at the time that I had my epiphany - that I had the right skillset for the job - there wasn't much active development.
Digital Foundry: So you could shape the hardware in the direction you wanted? Or was there an existing department?
Mark Cerny: I'm outside of Sony, so I work with whatever organisation that Sony has. I made my pitch just as they were starting to get going.
Digital Foundry: From your keynote this morning, one of the key things I took away that while there's a lot of doom and gloom surrounding the 'death of the console', there was absolutely nothing about that in your speech. It was fresh, optimistic, packed with new ideas. How do you think PlayStation 4 addresses the current state of gaming?
Mark Cerny: I think that right now is the best time in the history of gaming to be a gamer. And if you look at it in terms of percentage, you conclude immediately that consoles are small. But that's a consequence of so many more people playing games than have ever played games before. So thanks to tablets and thanks to smartphones, we have this huge audience that now enjoys games. As for what's bringing them to console, that heavy content I was talking about is what consoles are designed for - Skyrim and Assassin's Creed - and I think on top of that we're now going to have the richness of the smaller, nimbler indie titles that are coming in.
Digital Foundry: You were talking about the move to x86 as a viable console architecture. Microsoft tried it on the original Xbox with variable results, and it was pretty much dismissed after that. Can you talk more in-depth about the result of your research?
Mark Cerny: What I was looking at on my holiday was just the instruction set of the CPUs and it really seemed to me that things had been changing recently and maybe we were on the verge of a transformation in the x86 architecture and how it would be used. That didn't mean that we would use an x86 architecture - all that happened as a result of that was that I wondered if we could add it to our list of options. Then, when our hardware project kicked off for real in 2008, I and the ICE team and a number of other technology people within Sony did a very detailed analysis of x86 and how code would work on that versus other processors.
So we looked at the kinds of things we'd been doing on SPUs, we looked at general purpose code. We looked at writing in assembly for that platform versus others. We looked at compiled code and did about 15 different presentations showing off various aspects of the x86 architecture, and our first big meeting on PlayStation 4 was with the first-party teams. We spent most of the day going through our learnings on x86 and we'd come to the conclusion that it was useful in a console but we had to ask them if they thought it could be useful in a console.
Digital Foundry: I guess from there we move to AMD as the partner of choice for creating PlayStation 4. Was it the research and products along the lines of the APUs that most excited you?
Mark Cerny: You know, this probably doesn't quite answer your question, but there are so many issues involved in working with a vendor. The business relationship is also very important. The timelines are very important, because you might be working with the brightest people in the business but if their product doesn't come out in the specific year that you need it, you can't work with them. There were a tremendous number of considerations and the choice of AMD came out of that.
Digital Foundry: You've talked about what we might perhaps call an "alt-PS4" [design] with 1TB of bandwidth. Was that an initial study, or did you go anywhere with it?
Mark Cerny: I just chose that story because that's the clearest way I could find in showing our new philosophy. By the PS3 era of thinking, we would definitely have gone with that design. But with the new way of thinking, we wanted to be sure that accessibility was there. We went with this combination of year-one accessibility and then a very interesting feature-set which... there's a Gamasutra article where I went through the major points... for year three or year four. The accessibility's had a big pay-off. There are 140 titles in development for PlayStation 4 right now and we have the strongest launch line-up in the history of Sony Computer Entertainment.
Digital Foundry: Is there a sense of homogenisation in terms of what is a games machine now? There's x86 architecture, there's a GPU. Were there any concerns that it would be difficult to make PlayStation 4 stand out?
Mark Cerny: Consoles hit above their weight when you look at the price/performance. There's a few reasons for that. One is that the software layer in-between the game creators and the hardware is much thinner than it is on PC. Another reason is that because the hardware doesn't change, you can focus in just on that one particular architecture and learn a lot about it and then the games over the years... You'll see the benefits in terms of the graphics and the quality of the world simulation and the like. On top of that we did significant customisation of the GPU to make sure that there was that extra target for people to go after in 2016/2017. Put that all together, I think the future's looking very bright for PlayStation 4.
Digital Foundry: There's a cluster of CPU cores [in PS4]. Their purpose in the PC market - I think there are dual and quad configurations - is for tablets. There are two of those [in PS4]. Then you have what I can only describe as a massive GPU...
Mark Cerny: I call it a super-charged PC architecture. And that's because we have gone in and altered it in a number of ways to make it better for gaming. So we have unified memory which certainly makes creating a game easier - that was the number one feature requested by the games companies. Because of that you don't have to worry about splitting your programmatical assets from your graphical assets because they are never in the ratios that the hardware designers chose for the memory. And then for the GPU we went in and made sure if would work better for asynchronous fine-grain compute because I believe that in the GPU, we'll get in a couple of years into the hardware cycle and it'll be used for a lot more than graphics.
Now when I say that many people say, "but we want the best possible graphics". It turns out that they're not incompatible. If you look at how the GPU and its various sub-components are utilised throughout the frame, there are many portions throughout the frame - for example during the rendering of opaque shadowmaps - that the bulk of the GPU is unused. And so if you're doing compute for collision detection, physics or ray-casting for audio during those times you're not really affecting the graphics. You're utilising portions of the GPU that at that instant are otherwise under-utilised. And if you look through the frame you can see that depending on what phase it is, what portion is really available to use for compute.
Digital Foundry: I think the thing that excites me most about the PS4 is that it's a fixed hardware design, developers can get the most visually from it but they don't need to just concentrate GPU power on, say, slightly higher quality shadowmaps. They've got GPU compute sitting there that can be doing new things, exciting things. Is this something we'll be seeing further on down the line? Is this something you're pathfinding with Knack?
Mark Cerny: Knack is a small title. Knack will not be leading the way in terms of utilisation. We'll be looking much more towards teams that have done that in the past like Ubisoft with Assassin's Creed and Watch_Dogs, Naughty Dog with their next titles or Sony Santa Monica with theirs. I think Killzone is going to be doing that. All we are doing ultimately is setting it up so that developers can take it any way that they want go. So if increased visual fidelity is what is most interesting to that team, that is what they can focus on. We just wanted to be sure that they could also dig in on GPGPU [general purpose computing on GPU] as well.
Digital Foundry: You've got eight CPU cores in PlayStation 4 and in your presentation you said that the choice was between four or eight. Did you investigate four cores? AMD obviously has hardware that satisfies that need. Is it simply down to performance per watt?
Mark Cerny: Well, it is true that performance per watt is quite good for Jaguar - that has been helping us out in general. I guess we knew that our design space would accommodate either four or eight so we proceeded accordingly.
Digital Foundry: So Jaguar was the best fit?
Mark Cerny: To be honest, when we asked people, we heard absolutely every answer you could think of. One developer even told me their technology could accommodate a thousand cores! But for us it was very important to find out what the mainstream would be, what the overwhelming majority of the games industry would need.
Digital Foundry: Going back to GPU compute for a moment, I wouldn't call it a rumour - it was more than that. There was a recommendation - a suggestion? - for 14 cores [GPU compute units] allocated to visuals and four to GPU compute...
Mark Cerny: That is bad leaks and not any sort form of formal evangelisation. The point is the hardware is intentionally not 100 per cent round. It has a little bit more ALU in it than if you were thinking strictly about graphics. As a result of that you have an opportunity, almost like an incentivisation, to use that ALU for GPGPU.
Digital Foundry: I seem to recall you might have talked about a toolchain where code could be compiled either for CPU or GPU. Is that right or have I got that completely wrong?
Mark Cerny: That's completely wrong! Such a toolchain does exist. It's AMD's HSA [Heterogeneous System Architecture]. That's very exciting but our current strategies are about exposing the low-level aspects of the GPU to a higher-level language. We think that's where the greatest benefit is in year one.
Digital Foundry: Is there dedicated audio processing hardware within the PlayStation 4? What can it do?
Mark Cerny: There's dedicated audio hardware. The principal thing that it does is that it compresses and decompresses audio streams, various formats. So some of that is for the games - you'll have many, many audio streams in MP3 or another format and the hardware will take care of that for you. Or, on the system side for example, audio chat - the compression and decompression of that.
Digital Foundry: More advanced surround - is this also something you'd be using GPU compute for?
Mark Cerny: So the GPU is a natural place to do a number of different types of audio processing. It really does come down though to the amount of parallelisation that is natural to perform for that algorithm, and that does vary greatly depending on what you are doing specifically in your audio processing. I think that as you go forward we will see a hybrid approach in a couple of years where certain aspects of the audio are being done on GPU.
Digital Foundry: Referring to your presentation you were talking about audio ray-casting... As I understand the idea, you're simulating what happens to soundwaves when they hit a particular material...
Mark Cerny: We'll cast rays to see if you can shoot something. You really need to know that so you know what to do with the reticule. It'll be a different colour if you can shoot an enemy or not shoot an enemy. For audio, [it's] whether you can hear a source or not. We'll be casting a couple of hundred rays. It's actually quite time-consuming to do those calculations and it turns out to be a pretty natural fit for the GPU. You can take your couple of hundred rays, have them processed in bundles of 64 on the GPU and then the game designers get to make up new and more creative ways to use that ray-casting.
Digital Foundry: If we can go on to GDDR5 and the PlayStation Meeting in New York... 8GB, it surprised everyone. Was it really that late in the day that the decision was made to bump up the memory? You said earlier that you weren't in the meeting where the developers were demanding it, how crucial was it?
Mark Cerny: That was really a case where our developer-driven process worked. So we received feedback, we listened to the feedback, we altered the hardware as a result. As far as how late it was in the process, actually what you're seeing there is just the developers were very, very good about keeping information confidential. As near as I can tell that all came from one rogue hacker, who wasn't even disclosed by us, how managed to hack into a developer and extract both the Microsoft and Sony documentation.
Digital Foundry: Developers tell us that they love the GDDR5, they love the bandwidth but there are questions on latency. How do you cope with that in your set-up? It's not something that developers have much experience with in terms of interfacing with a CPU.
Mark Cerny: Latency in GDDR5 isn't particularly higher than the latency in DDR3. On the GPU side... Of course, GPUs are designed to be extraordinarily latency tolerant so I can't imagine that being much of a factor.
Digital Foundry: I'd like to talk quickly about digital delivery. I love this concept of being able to play a game while it downloads in the background. Do you have a target in mind for the kind of bandwidth that's required to sustain a seamless experience?
Mark Cerny: Interestingly, the target bandwidth required depends on the length of the game. The longer the game is, the less bandwidth you'll need to be loading in the later stages of the game. There's another factor there as well. Are you playing continuously as a download or do you play for a few hours and then put the system on standby for the rest of the evening where it can continue to download and then resume the next day?
Digital Foundry: Some of the most exciting features, such as video-sharing [of gameplay]... Again, will those adapt to upstream bandwidth available to users? Before I went fibre, I had 800kbps upload - that's terrible. Is there a danger that some features will be of a lower quality or simply won't work for some people?
Mark Cerny: Certainly the broadband infrastructure - not just for the user, but for the country - is relevant when you are designing systems. I guess our focus has been primarily on coming up with the over-arching concept that will be compelling to users.
Digital Foundry: Final question. Two years from now, are you going to pitch to develop PlayStation 5?
Mark Cerny: [Laughs] Can you just put "Mark laughs" in there?
http://www.eurogamer.net/articles/digitalfoundry-face-to-face-with-mark-cerny
