Understanding the Cell Microprocessor
by Anand Lal Shimpi on March 17, 2005 12:05 AM EST- Posted in
- CPUs
Final Words
Concluding anything about Cell requires a multifaceted look at the architecture and the platform as a whole.First from the perspective of the game industry, more specifically Playstation 3:
Cell’s architecture is similar to the next version of Microsoft’s Xbox and upcoming PC microprocessors in that it is heavily multithreaded. The next Xbox will execute between 3 and 6 threads simultaneously, while desktop PC microprocessors will execute between 2 - 4. The problem is that while Xbox 2/360/Next and the PC will be using multiple general purpose cores, Cell relies on more specialized hardware to achieve its peak performance. Cell’s SPEs being Altivec/VMX derived is a benefit, which should mean that the ISA is more familiar to developers working on any POWER based architecture, but the approach to development on Cell vs. development on the PC will literally be on opposite ends of the spectrum, with the new Xbox somewhere in between.
The problem here is that big game development houses often develop and optimize for the least common denominator when it comes to hardware, and offer ports with minor improvements to other platforms. Given Cell’s architecture, it hardly looks like a suitable “base” platform to develop for. We’d venture to say that a game developed for and ported from the PC or Xbox Next would be under-utilizing Cell’s performance potential unless significant code re-write time was spent.
Console-only development houses, especially those with close ties to Sony, may find themselves able to harness the power of Cell much more efficiently than developers who ascribe to the write-once, port-many process of cross-platform development. Given EA’s recent acquisition and licensing-spree, this is a very valid concern.
With Cell, Sony has effectively traded hardware complexity for programmer burden, but if anyone is willing to bear the burden of a complicated architecture, it is a game developer. The problem grows in complexity once you start factoring in porting to multiple platforms in a timely manner while still attempting to achieve maximum performance.
As a potential contender in the PC market, Cell has a very tall ladder to climb before even remotely appearing on the AMD/Intel radars. The biggest strength that the x86 market has is backwards compatibility, which is the main thing that has kept alternative ISAs out of the PC business. Regardless of how much hype is drummed up around Cell, the processor is not immune to the same laws of other contenders in the x86 market - a compatible ISA is a must. And as Intel’s Justin Rattner put it, “if there are good ideas in that architecture, PC architecture is very valuable and it will move to incorporate those ideas.”
Once again, what’s most intriguing is the similarity, at a high level, of Intel’s far future multi-core designs to Cell today. The main difference is that while Intel’s Cell-like designs will be built on 32nm or smaller processes, Cell is being introduced at 90nm - meaning that Intel is envisioning many more complex cores on a single die than Cell. Intel can make that kind of migration to a Cell-like design because their microprocessors already have a very large user base. IBM, Sony and Toshiba can’t however - Cell must achieve a very large user base initially in order to be competitive down the road. Unfortunately, seeing a future for Cell far outside of Playstation 3 and Sony/Toshiba CE devices is difficult at best.
The first thing you have to keep in mind is that Cell’s architecture is nothing revolutionary, it’s been done before. TI’s MVP 320C8X is a multi-processor DSP that sounds a lot like Cell: http://focus.ti.com/docs/military/catalog/general/general.jhtml?templateId=5603&path=templatedata/cm/milgeneral/data/dsp_320c80&familyId=44. So, while Cell is the best mass-market attempt at a design approach that has been tried before, it doesn’t have history on its side for success beyond a limited number of applications.
Regardless of what gaming platform you’re talking about, Cell’s ability to offer an array of cores to handle sophisticated physics and AI processing is the future. AGEIA’s announcement of the PhysX PPU (and the fact that it’s been given the “thumbs up” by Ubisoft and Epic Games) lends further credibility to Cell’s feasibility as a high performance gaming CPU.
The need for more realistic physics environments and AI in games is no illusion; the question is will Intel’s forthcoming dual and multi-core CPUs (with further optimized SIMD units) offer enough parallelism and performance for game developers, or will the PPU bring Cell-like architecture to the desktop PC well ahead of schedule? The answer to that question could very well shape the future of desktop PCs even more so than the advent of the GPU.
Facebook
Twitter
RSS
70 Comments
View All Comments
Poser - Thursday, March 17, 2005 - link
There were moments while reading this article that I expected there to be a "Test Yourself" quiz at the end of the chapter ... er, article. Which isn't to say that articles like this are too textbookish, it's to say that they're wonderfully educational. And very, very cool for being so.I'm half joking when I say this (but only half) -- a real "test" at the end of the article would be fun. I could see if I really understood what I read, and even get to compare my score to the rest of the, uhm, class.
drinkmorejava - Thursday, March 17, 2005 - link
very nice, how long did it take to write that thing?Eug - Thursday, March 17, 2005 - link
#42,That's an interesting page, cuz everyone on OS X already knows that Word is slow on the Mac. It brings us back to the original statement that some ported software may be problematic performance-wise.
And the generic comment on the Mac side about Premiere is, well... use Final Cut Pro. :) Here is a test that seems a bit more useful, since it tests Cinema4D and After Effects, two apps that people use on the Mac and both of which are reasonably well optimized:
http://digitalvideoediting.com/articles/viewarticl...
That's a good point about the memory scaling though. The IMC with AMD's chips is a definite advantage. I'm sure the G5 970MP dual-core won't get an IMC either.
Anyways, as far as this article is concerned, the G5 is kinda irrelevant. The interesting part for Apple in Cell is the PPE unit. It's also interesting that Anand says the original SPE was supposed to be VMX/Altivec. But the current SPE is not Altivec so it's less applicable for Apple, at least in the near term.
It would be interesting to know how fast a dual-core 3 GHz PPE would be in general laptop-type code, and how much power it would put out.
MDme - Thursday, March 17, 2005 - link
#39, 40, 41http://www.pcworld.com/news/article/0,aid,112749,p...
remember that the athlon 64 chips scale better at higher clock speeds due to the mem controller scaling as well.
Eug - Thursday, March 17, 2005 - link
Well, one example is Cinebench 2003:The dual G5 2.0 GHz is about the same speed as a dual 0pteron 246 2.0 GHz, with a score at around 500ish.
http://www.aceshardware.com/read.jsp?id=60000284
BTW, a dual G5 2.5 GHz scores 633.
suryad - Thursday, March 17, 2005 - link
Hmm that is interesting what you say Eug. I see your point do you have any links on straight comparos between an FX and a top of the line Mac? Or from personal experience folding and such...Eug - Thursday, March 17, 2005 - link
#38. It's a mistake to say an AMD FX 55 smokes a dual G5 2.5. For instance, if you like scientific dual-threaded stuff, the G5 does very well. However, the AMD FX 55 IS faster than a single G5 2.5. It's got a slight edge clock-for-clock, and it's clocked slightly higher too.The real problem is when you have stuff built for x86 ported over to PPC. It just isn't great on the Mac side performance-wise in that situation. And Macs aren't tweaked for gaming either. The AMD is going to smoke the Mac in Doom 3 of course.
I think with the performance advantage of the Opteron, I'd put a single G5 2.5 in the range of performance of a single Opteron 2.2-2.4 GHz, depending on the app. The real interesting part though will be the coming quarter, when the new G5s are released. They should get a significant clock speed bump (20%?) and information on dual-core G5s are already out there (like with AMD and their dual-core Athlons). They also get a cache boost. Right now they only have 512 KB, but are expected to get 1 MB L2.
suryad - Thursday, March 17, 2005 - link
Well scrotemaninov I am not disputing that the POWER architecture by IBM is brilliantly done. IBM is definitely one of those companies churning out brilliant and elegant technology always in the background.But my problem with the POWER technology is from what I understand very limitedly, is that the POWER processors in the Mac machines are a derivative of that architecture right? Why the heck are they so damn slow then?
I mean you can buy an AMD FX 55 based on the crappy legacy x86 arch and it smokes the dual 2.5 GHz Macs easily!! Is it cause of the OS? Because so far from what I have seen, if the Macs are any indication of the performance capabilities of the POWER architecture, the Cell will not be a big hit.
I did read though at www.aceshardware.com benchmark reviews of the POWER5 architecture with some insane number of cores if I recall correctly and the benchmarks were of the charts. They are definitely not what the Macs have installed in them...
scrotemaninov - Thursday, March 17, 2005 - link
#35: different approaches to solving the same problem.Intel came up with x86 a long time ago and it's complete rubbish but they maintain it for backwards compatibility (here's an argument for Open Source Software if ever there was one...). They have huge amounts of logic to effectively translate x86 into RISC instructions - look at the L1I Trace Cache in the P4 for example.
IBM aren't bound by the same constraints - their PowerPC ISA is really quite nice and so there's no where near the same amount of pain suffered trying to deal with the same problem. It does seem however, that IBM are almost at the point that Intel want to be in 10 years time...
Verdant - Thursday, March 17, 2005 - link
here is a question...it mentions (or alludes) in the article that having no cache means that knowing exactly when an instruction would be executed is possible, is the memory interface therefore a strict "real time system" ?