Feasibility of Cell emulation

[Shifty Geezer]

If Sony moves away from Cell next gen, will any processor be able to emulate Cell effectively for BC? What are the architectural pitfalls that could prevent that? From some highlighted insights by T.B. about the intricacies like the MFC, I'm thinking a conventional multicore PPC, ARM or x86 won't be able to, but I'd rather hear from people who know about these things what they think!

 

[Cyan]

If Sony moves away from Cell next gen, will any processor be able to emulate Cell effectively for BC? What are the architectural pitfalls that could prevent that? From some highlighted insights by T.B. about the intricacies like the MFC, I'm thinking a conventional multicore PPC, ARM or x86 won't be able to, but I'd rather hear from people who know about these things what they think!

If you say a multicore PPC, ARM or x86 won't be able to do it, then there isn't much left it could run Cell legacy code. I think the reason why it's difficult to emulate the Cell is that it will be very hard to find a similar design in next gen consoles and processors in general. In all honesty, after reading developers posts and unless they are having serious issues with their user base asking for backwards compatibility, if I were Sony I would drop BC for good. or I would create a compatible processor, just adding Hyperthreading, something that developers are asking for when next generation starts.

 

[patsu]

There are business feasbility and technical feasibility. I assume you're talking about the second one Shifty ?

 

[archangelmorph]

Nothing currently available would likely be able to emulate the CELL with any reasonable performance...

Without SPEs you're going to have a very hard time getting the kind of throughput they can achieve on highly optimized, vectorized code, even on some of the fastest desktop CPUs

 

[Shifty Geezer]

There are business feasbility and technical feasibility. I assume you're talking about the second one Shifty ?

Yes. The design of Cell to me suggests it cannot be emulated in the next few iterations of processors. PPC would get closest as it could at least share the same ISA, and perhaps could feature ideas for the purposes of emulation, but that'd be an odd business to enter into for a single product requiring Cell BC.

 

[Arwin]

The Cell would have to be partly emulated by CPU, partly by GPU. Imho only a new processor designed to be compatible with Cell could emulate it.

But emulation is probably dead anyway. We'll just see re-releases instead.

 

[patsu]

Nothing currently available would likely be able to emulate the CELL with any reasonable performance...

Without SPEs you're going to have a very hard time getting the kind of throughput they can achieve on highly optimized, vectorized code, even on some of the fastest desktop CPUs

Why ? What are the specific trouble spots and use cases ?

 

[patsu]

The Cell would have to be partly emulated by CPU, partly by GPU. Imho only a new processor designed to be compatible with Cell could emulate it.

But emulation is probably dead anyway. We'll just see re-releases instead.

Emulation or backward compatibility. I wouldn't say they are dead. The PS2 -> PS3 transition may be an exception because Sony wanted people to buy more PS3 games given the big jump in investment.

If the transition is seamless to begin with, then minimal effort to upgrade old games (to run on the new console) may very well be welcomed for some. They can focus on the new game modes and assets rather than the engine code.

 

[TheChefO]

I'd think it would make more sense to build on the Cell rather than try to emulate it.

The design is paid for and is better able to scale than most other designs. Granted, SPU usage seems to be a pain, but if they design it right, SPU usage may not be necessary for most games.

A 4-8+ core PPE cell with 8(+) SPE's would still have BC enabling Sony to not trash the Digital content that consumers have purchased and not trash the investment developers have in Cell over the past 5 years.

The GPU/Ram will be the defining edge next gen. As long as it isn't a pain to get code working (devs should well know Cell by now) then they can get software on the shelves asap and have a viable launch lineup instead of trying to figure out how to take advantage of a new design.

Cheaper to produce and grow with and similar results on screen vs anything MS is likely to come up with.

 

[Grall]

But emulation is probably dead anyway. We'll just see re-releases instead.

Re-releasing PS2 games, re-tooled to run on PS3 is feasible because PS2 was a relatively simple piece of kit. Cell is extremely high-performing, it's high-performing even today if just looking at the SPEs when running optimized code. I believe you'd need something like a Sandybridge-E to top Cell's floating point performance...

It's going to be a huge undertaking to re-write today's triple-A games for another system that isn't Cell compatible, it might very well be simpler for Sony to stick the currently available SPEs (six, unless the seventh has been unlocked by later firmwares) on whatever new CPU they decide to use, and then just re-compile the PPE code for the new chip.

 

[Arwin]

The PS2 wasn't that simple a piece of kit, and personally I have little trouble imagining a new generation console that is a much closer match with the PS3, PS2 or both than the difference between the PS2 and PS3.

I think precisely those things that are hard to do with anything but Cell now, will be a much more common feature/strength of upcoming designs.

 

[patsu]

I'd think it would make more sense to build on the Cell rather than try to emulate it.

The design is paid for and is better able to scale than most other designs. Granted, SPU usage seems to be a pain, but if they design it right, SPU usage may not be necessary for most games.

A 4-8+ core PPE cell with 8(+) SPE's would still have BC enabling Sony to not trash the Digital content that consumers have purchased and not trash the investment developers have in Cell over the past 5 years.

The GPU/Ram will be the defining edge next gen. As long as it isn't a pain to get code working (devs should well know Cell by now) then they can get software on the shelves asap and have a viable launch lineup instead of trying to figure out how to take advantage of a new design.

Cheaper to produce and grow with and similar results on screen vs anything MS is likely to come up with.

The pain is not generally associated with the SPUs. So far, the complains were more leveled at the limited split memory and GPU vertex limits. We even hear some developers marvel at the SPUs, although some others use the SPUs simply like a regular vector/math engine. ^_^

The PPU is noticeably weaker than the SPUs. I assume Sony will improve it more, and perhaps make the SPUs (or SPU-like entities) work with the GPU(s) more efficiently ?

OTOH, if the GPU (or GPUs) is powerful enough, the developers can also achieve similar results by running more iterations to approximate the result.

 

[Persistantthug]

The Cell would have to be partly emulated by CPU, partly by GPU. Imho only a new processor designed to be compatible with Cell could emulate it.

But emulation is probably dead anyway. We'll just see re-releases instead.

HD remasters/re releases were only made possible because there was no network that had to be carried over.

Obviously, That's not the case anymore.

Consumers have an invested interest in the network......developers have an invested interest in the network.....and even more important, Sony has billions of dollars worth of invested interest in the network.

Backwards Compatibility for the PS3 games is pretty much mandatory for the PS4.

 

[TheChefO]

HD remasters/re releases were only made possible because there was no network that had to be carried over.

Obviously, That's not the case anymore.

Consumers have an invested interest in the network......developers have an invested interest in the network.....and even more important, Sony has billions of dollars worth of invested interest in the network.

Backwards Compatibility for the PS3 games is pretty much mandatory for the PS4.

This.

I think however Sony gets it done, they need to maintain BC (along with MS) due to the investment in DC if they expect any semblance of loyalty into nextgen.


@Patsu: As long as the cpu can run native cell code without hassle, I think everyone involved will be happy. How they choose to grow from that point will be interesting to see, but if I were in their shoes, I'd minimize the headache/time-sink for developers to get code on the shelf, maintain BC, and let the GPU/Ram be the edge to compete nextgen.

Let's not forget, even if they did absolutely nothing to improve Cell nextgen, and all they did was improve the GPU, PS4 would still see improved CPU performance due to the fact devs could (finally) use cell for things other than helping the gpu.

If this gen has taught us anything I'd say it's that the CPU is of little importance in differentiating the console experience for consumers.

For Sony to invest heavily on the CPU is just money that isn't spent on the (programmable) GPU...

 

[Elan Tedronai]

What kind of question is this? There's nothing out there that can emulate the cell to the point of consumer satisfactin. Nothing at all.

If sony plans to make the ps4 backwards compatible then they will have to use the cell one way or another

 

[Shifty Geezer]

What kind of question is this?

A futile and pointless one. As a technical question asked in the technical forum, I had hoped for someone with processor savvy to talk about the issues facing Cell emulation, and what would be needed to get it working. But contributors could only regurgitate the non-technical "Is BC important" discussion already had, to be topped off with brainless contributions like your own founded on no technical savvy whatsoever. So I give up.

 

[AlexV]

I think it holds merit, so with all due apologies to Shifty I'll reopen this one. Also, in order to rile thing up, I suggest that people do a slightly better work at documenting themselves...moving beyond "omagad it's deep magicTM" would be good. CELL is old, cute but not exactly cutting edge, it doesn't have an awesome memory pipe, it doesn't have hardware caching, the ISA is not exactly from another galaxy, IPC is pretty gimpy. As long as the emulator writers are actually aware about prefetching to cater to the DMA work (albeit modern prefetchers should do a reasonably good job anyways), you'd probably end up doing the bulk of work from L2.

A reasonably modern core like NHLM or SB is considerably ahead of CELL in terms of execution prowess, and now it's working from a cache that's quite fast. You also have HT to help fill in some bubbles. More importantly, people have done work behind the scenes on this and it's reasonable, to say the least. So please, less rehashing of memes like: "we tweaked CELL so hard it's over 9000 now, if we had an updated version that ran at Graham's Number GHz and had Moser's Number SPEWs it would crack the very fabric of the universe".

 

[Shifty Geezer]

It's more the intricacies that make it look hard to me, based on the talk between Vitaly, T.B, and Sebbbi in a couple of Cell threads. The MFC is more sohpisticated than we thought. Well, I guess another core could be used to do its workload prefetching data to the cache.

TBH I know diddly squat about low-level CPU emulation! If it can be 'proven' that another architecture in a configuration suitable for a console (not a 16 core server CPU!) can perform BC duties admirably, that'd be one less of only a few reasons to stick with Cell, and if one of the architectures is better suited (ARM vs. x86) then that'd be a high probability choice for PS4.

 

[Love_In_Rio]

Bluegene/Q maybe?. There are rumours of it being modified in the Marenostrum supercomputer of Barcelona to be used in PS4.

 

[Dominik D]

It's more the intricacies that make it look hard to me, based on the talk between Vitaly, T.B, and Sebbbi in a couple of Cell threads. The MFC is more sohpisticated than we thought. Well, I guess another core could be used to do its workload prefetching data to the cache.

TBH I know diddly squat about low-level CPU emulation! If it can be 'proven' that another architecture in a configuration suitable for a console (not a 16 core server CPU!) can perform BC duties admirably, that'd be one less of only a few reasons to stick with Cell, and if one of the architectures is better suited (ARM vs. x86) then that'd be a high probability choice for PS4.

I think one has to answer one question first: do you want emulation, or simulation? There's a problem of not having simulation if you want to replicate behavior including stalls, race conditions, etc. So for example if you want to emulate/simulate Commodore 64, you need certain things to be timed in a specific way so you can outsmart the "hardware" and put sprites on the border. But if you don't care about it and you only aim for the sunny day scenarios, I think you could get away with emulation on PPC, where you patch your code for the new architecture (e.g. substitute missing ops with existing ones, rewrite jumps,...) and you get PS3 (or some other CELL) binaries running if you emulate enough hardware. The thing is: with heavily multithreaded code running on, say, PS3 you're going to hit all sorts of conditions that weren't there on CELL. Performance will be different and unpredictable, but if you have enough horsepower, you should be OK. This is pretty much what MS did with 360 back compat and that's why some games did not work (corner cases with horrible performance characteristics and code too performant and HW-dependent to run in emu on 360).