7 November 2006
Ferry

PS3’s Cell three times more powerful as the Xbox 360 processor?

This summer Sony created a training website for Canadian Wal Mart employees. The access codes got leaked when a store visitor saw a manager put up internal documents around the store.

After logging in, Sony marketing spin quotes can be found while employees read, learn & test their PS3 knowledge. Here’s the real gem:

“Welcome to your PS3 Retail Online Training. We trust that you will find the following information valuable and assist you in understanding and explaining PS3 Technology to your customers and staff. … The Cell Processor is essentially as powerful as 3 Xbox 360 CPU’s or 35 PlayStation® 2 CPU’s”

And you wonder why store clerks so seldom know what they are talking about? How in the world is “The Cell is actually 7 SPU’s (Synthetic Processing Units) each running at 3.2 GHZ” supposed to inform customers? Here’s a screenshot (click to enlarge) of one of the tests where employees can win prizes if they get all the answers right.


Oh and by the way, most developers say that the horsepower inside both the Xbox 360 and PS3 will be comparable a few years from now as it’s all about what they can get out of their processors to use in-game. That’s a good thing and also why Gears of War look prettier in graphical detail than any PS3 launch games shown so far.

A direct quote from Silicon Knights president Denis Dyack says: “The 360 and the PS3 are equal in power in my eyes,” Dyack says. “Maybe the PS3 has more processing power. The 360 has more available memory. It’s pretty much a net, net. The public perception of the PS3 was that it was much more powerful. To developers, they look even.“

10 November 2006 09:22
Jack

How is it that the fan boys take no notice of what professonal developers say?
The are roughly the same, its about the games…Who knows, maybe the Wii will be more fun than Halo 3, but lets see.

Enought of I know this and I know that. You don’t unless you develop Unreal or called EA.

10 November 2006 12:11
PS3 XBOX360 developer

Thanks guys, great read ROTFL ))

p.s: interestingly none of the well informed noticed, that the PS3 has easily twice the memory bandwidth…

10 November 2006 12:47
Marco

yeah but if everyone here remembers correctly. when the ps2 was about to come out, sony had stated that it would be able to do toy story graphics…..that was a lie lol so who noes what they say and what will actually be truth with the ps3

10 November 2006 17:22
James

I don’t know much in detail about SPU’s but must admit that the first gen round of PS3 games look better than the first gen 360 games (Remember Quake, Ridge Racer and PD Zero? – not all that for me graphically). Wether its because the 360 was rushed or the PS3’s more powerfull, I dont know. I have a 360 and for now I’m happy with it, (could do with more action adventure games though) but I wont be spending £500 on a PS3 come March in the UK. The real battle starts Xmas 07… When both consoles are at optimum pricing and developers get to grips with the hardware.

11 November 2006 20:49
Terrence B

go to the Link…it has already been proven…the 360 is more powerful than the PS3…IGN has said it and it is over..Both systems will be excellent IMO. It is just a matter of time before halo 3 comes out and to what it did to the ps2 back in the day.
go to the link
http://xbox360.ign.com/articles/617/617951p1.html

12 November 2006 04:57
James

Damn…

13 November 2006 15:17
xboxfanboi

Halo did nothing to the PS2 as far as I know it is still a viable system unlike that over sized black non backwards compatible piece of cr*p the x box. Sorry you wasted your money on a 360 I know it stings a little but face the facts. PS3 is a much better console. Trade it in before it’s too late.

26 November 2006 21:41
Joe

Yeah xbox is gonna say that tard they said it back in 2005. Ok and the 8 there is 8 one is set for redun. And it has one cpu i believe not 100% they havnt even told half the specs yet. But each can be used for many things because when u play a game your gpu has to do a total of maybe 5 diff tasks. Lighting, Shading, Texture, Res and Polys. Pretty much. Ok now they have a gpu which runs at 540mhz or somthing crazy. So that gets handeld now the spus help with those maybe 2 or three will do that and the rest can do any thing els one can do phys one can do enemy ai and maybe the other could do friendly ai. Idk how they will break them up in future but the ps3 has better tech it came out more then a year after the xbox. So give it up. And go to game spot to get your info.

29 November 2006 20:19
Kevin

Now the 360’s GPU is one impressive piece of work and I’ll say from the get go it’s much more advanced than the PS3’s GPU so I’m not sure where to begin, but I’ll start with what Microsoft said about it. Microsoft said Xenos was clocked at 500MHZ and that it had 48-way parallel floating-point dynamically-scheduled shader pipelines (48 unified shader units or pipelines) along with a polygon performance of 500 Million triangles a second.

Before going any further I’ll clarify this 500 Million Triangles a second claim. Can the 360’s GPU actually achieve this? Yes it can, BUT there would be no pixels or color at all. It’s the triangle setup rate for the GPU and it isn’t surprising it has such a higher triangle setup rate due to it having 48 shaders units capable of performing vertex operations whereas all other released GPUs can only dedicate 8 shader units to vertex operations. The PS3 GPU’s triangle setup rate at 550MHZ is 275 million a second and if its 500MHZ will have 250 million a second. This is just the setup rate do NOT expect to see games with such an excessive number of polygons because it wont happen.

Microsoft also says it can also achieve a pixel-fillrate of 16Gigasamples per second. This GPU here inside the Xbox 360 is literally an early ATI R600, which when released by ATI for the pc will be a Directx 10 GPU. Xenos in a lot of areas manages to meet many of the requirements that would qualify it as a Directx 10 GPU, but falls short of the requirements in others. What I found interesting was Microsoft said the 360’s GPU could perform 48 billion shader operations per second back in 2005. However Bob Feldstein, VP of engineering for ATI, made it very clear that the 360’s GPU can perform 2 of those shaders per cycle so the 360’s GPU is actually capable of 96 billion shader operations per second.

To quote ATI on the 360’s GPU they say.
“On chip, the shaders are organized in three SIMD engines with 16 processors per unit, for a total of 48 shaders. Each of these shaders is comprised of four ALUs that can execute a single operation per cycle, so that each shader unit can execute four floating-point ops per cycle.”
# 48 shader units * 4 ops per cycle = 192 shader ops per clock
# Xenos is clocked at 500MHZ *192 shader ops per clock = 96 billion shader ops per second.

(Did anyone notice that each shader unit on the 360’s GPU doesn’t perform as many ops per pipe as the rsx? The 360 GPU makes up for it by having superior architecture, having many more pipes which operate more efficiently and along with more bandwidth.)

Did Microsoft just make a mistake or did they purposely misrepresent their GPU to lead Sony on? The 360’s GPU is revolutionary in the sense that it’s the first GPU to use a Unified Shader architecture. According to developers this is as big a change as when the vertex shader was first introduced and even then the inclusion of the vertex shader was merely an add-on not a major change like this. The 360’s GPU also has a daughter die right there on the chip containing 10MB of EDRAM. This EDRAM has a framebuffer bandwidth of 256GB/s which is more than 5 times what the RSX or any GPU for the pc has for its framebuffer (even higher than G80’s framebuffer).

Thanks to the efficiency of the 360 GPU’s unified shader architecture and this 10MB of EDRAM the GPU is able to achieve 4XFSAA at no performance cost. ATI and Microsoft’s goal was to eliminate memory bandwidth as a bottleneck and they seem to have succeeded. If there are any pc gamers out there they notice that when they turn on things such as AA or HDR the performance goes down that’s because those features eat bandwidth hence the efficiency of the GPU’s operation decreases as they are turned on. With the 360 HDR+4XAA simultaneously are like nothing to the GPU with proper use of the EDRAM. The EDRAM contains a 3D logic unit which has 192 Floating Point Unit processors inside. The logic unit will be able to exchange data with the 10MB of RAM at 2 Terabits a second. Things such as antialiasing, computing z depths or occlusion culling can happen on the EDRAM without impacting the GPU’s workload.

Xenos writes to this EDRAM for its framebuffer and it’s connected to it via a 32GB/sec connection (this number is extremely close to the theoretical because the EDRAM is right there on the 360 GPU’s daughter die.) Don’t forget the EDRAM has a bandwidth of 256GB/s and its only by dividing this 256GB/s by the initial 32GB/s that we get from the connection of Xenos to the EDRAM we find out that Xenos is capable of multiplying its effective bandwidth to the frame buffer by a factor of 8 when processing pixels that make use of the EDRAM, which includes HDR or AA and other things. This leads to a maximum of 32*8=256GB/s which, to say the least, is a very effective way of dealing with bandwidth intensive tasks.

In order for this to be possible developers would need to setup their rendering engine to take advantage of both the EDRAM and the available onboard 3D logic. If anyone is confused why the 32GB/s is being multiplied by 8 its because once data travels over the 32GB/s bus it is able to be processed 8 times by the EDRAM logic to the EDRAM memory at a rate of 256GB/s so for every 32GB/s you send over 256GB/s gets processed. This results in RSX being at a bandwidth disadvantage in comparison to Xenos. Needless to say the 360 not only has an overabundance of video memory bandwidth, but it also has amazing memory saving features. For example to get 720P with 4XFSAA on traditional architecture would require 28MB worth of memory. On the 360 only 16MB is required. There are also features in the 360’s Direct3D API where developers are able to fit 2 128×128 textures into the same space required for one, for example. So even with all the memory and all the memory bandwidth, they are still very mindful of how it’s used.

29 November 2006 20:21
Kevin

#

How is one CPU better than another?

GFLOPS is something that gets thrown around a lot, but it should be clear that the peak theoretical GFLOP numbers for both these CPUs are:
# 115GFLOPS Theoretical Peak Performance for 360 CPU
# 218GFLOPS Theoretical Peak Performance for PS3 CPU.

These CPU theories will not be achieved in real world performance. What IBM did when testing for theoretical peaks on both CPUs can’t really be considered as representative of how the processors would actually perform in real world situations, because of the type of testing done is too controlled. It’s a much too perfect of an environment and game development is going to involve an unforgiving environment that doesn’t cater so well to the perfect environment the CPUs were tested under.

The GFLOP numbers for the PS3 were calculated based on 8 running SPE, so the fact that the PS3 uses only 6 SPE for game applications lowers the peak theoretical even further, as majority of the floating point work on the PS3’s CPU is done via the SPE. Each SPE has a peak theoretical of 25.6GFLOPS. So the total peak theoretical performance for all 6 SPE would be 153.6GFLOPS, but why is that number also not achievable?

In IBM’s controlled testing environment, their optimized code on 8 SPE only yielded a performance number of 155.5GFLOPS. If it took 8 SPE to achieve that, no way 6 will be able to and that testing was done in a fashion that didn’t model all the complexities of DMA and the memory system. Using a 1Kx1K matrix and 8 SPE they were able to achieve 73.4GFLOPS, but the PS3 uses 6 SPE for games and these tests were done in controlled environments. So going on this information, even 73.4GFLOPS is seemingly out of reach, showing us that Sony didn’t necessarily lie about the cell’s performance as they made clear the 218GFLOPS was “theoretical.” But just like Microsoft they definitely wanted you to misinterpret these numbers into believing they were achievable.

Even while taking all of this into consideration, the CPUs can’t reach those crazy performance numbers; the PS3’s cell still comfortably comes out on top in terms of overall floating point capability, but it should be known that the available power on the PS3’s cell will be significantly more difficult to harness than the available power on the 360’s CPU.

It’s also worth mentioning that even the PS2 CPU had more than twice the GFLOPS of the original Xbox’s CPU, but it didn’t necessarily lead it to being the performance winner. This time around, while the cell has the GFLOPS advantage, its advantage isn’t quite as big as the PS2 CPU had on the Xbox. This teaches us that there is more than one meter of real world performance.

The PS3’s cell processor has 1 Power PC core similar to that of the 3 Power PC cores sustaining the 360’s 3 core design (without the vmx-128 enhancements available on each of the 360’s cores) and 7 SPE (synergistic processing element). The 8th is disabled to improve yields. One of the SPE is used to run the PS3’s operating system while the other 6 are available for games. The reason the PS3’s CPU will be significantly more difficult to program for is because the CPU is asymmetric, unlike the 360’s CPU. Because of the PS3 CPU only having 1 PPE compared to the 360’s 3, all game control, scripting, AI and other branch intensive code will need to be crammed into two threads which share a very narrow execution core and no instruction window. The cell’s SPE will be unable to help out here as they are not as robust; hence, not fit for accelerating things such as AI, as it’s fairly branch intensive and the SPE lacks branch prediction capability entirely.

I’m sure people remember from the section detailing how the 360 and PS3’s processors are less robust compared to processors we use on our desktop computers and the consequences of being in order execution. Well the PS3’s SPE are further stripped down than even the Power PC Cores and, as a result, isn’t as capable of handling as many different types of code like the 1 Power PC Core available on the PS3’s cell or the 3 Power PC Cores available on the 360’s CPU. The problem with being asymmetric is when you program for the Power PC Core on the PS3 CPU, the method of programming you used to get the most out of that Power PC core is no longer effective when breaking off tasks for the SPE to work on. Going from the PPE to the SPE on the PS3 requires a different compiler and a different set of tools.

When you come to the realization that the key to making up for the CPU is in-order execution is the rather complicated parallel programming, you realize that the CPU being asymmetric and having just a single PPE makes something that was already extremely difficult even more difficult. So a developer’s job is harder when you factor in that the PS3 has a 512KB L2 cache which is half the size of the 360 CPU’s 1MB L2 cache… that single PPE the PS3 CPU has isn’t receiving much help with branches in the cache department.

Microsoft made a better decision from the perspective of the developer; it’s still difficult, but much easier compared to working with the Cell architecture. The 360’s CPU isn’t asymmetric like the PS3’s cell and has 3 PPE as opposed to 1, but all 3 are robust enough to help handle the type of code only the PS3’s single PPE is capable of handling. When Microsoft says they have three times the general purpose processing power this is what they mean. Based on the simple fact that the 360 has 3 Power PC cores to the PS3’s 1, more processing power can be dedicated to helping with things such as game control AI, scripting and other types of branch intensive code.

From the perspective of a developer the 360’s CPU’s biggest advantage is that all 3 of the 360’s cores are identical, all run from the same memory pool and they’re synchronized, in addition to being cache coherent. You can just create an extra thread right in your program and have it do some work. This allows the developer to create very nice structures so if you know how to get the best possible performance out of one core you know how to get the best possible performance out of all 3 because they operate in perfect synch.

Each core on the 360’s processor is capable of performing 2 threads each (Think of it as similar to hyper threading), so the 360’s CPU is capable of handling 6 simultaneous running threads at once. This brings me to a very important advantage for the PS3’s Cell CPU, its concurrency. While the 360 CPU may be able to handle 6 processor threads simultaneously it still only has 3 physical CPU cores so every 2 threads must share processing power on a single core. Whereas with the PS3, it has 1 PPE and 6 SPE for games, which are like extra physical processors). If each of the PS3’s 6 SPE used for games are working on a specific task such as collision, cloth physics, animation, water surface simulation or particles, they wouldn’t need to worry about processing power being taken away from another part of the game because the SPE don’t share processing power.

The only cause for concern would be the 512KB L2 cache being shared by 7 simultaneous running SPE and a PPE, but that’s what developers are for; they work around things like this. In practice, this should allow PS3 games to potentially have more things going on at once than 360 games. Ignoring the difficulties of programming for the PS3 CPU, it should be known that the PS3’s CPU is very good when it comes to vertex-related operations because the PS3’s CPU handles graphics code better than the 360’s CPU. It is also possible that through good parallelism of physics code on the SPE that physics code could also run better on the PS3 CPU due to the concurrency advantage.

The 360 CPU however, due to its 3 symmetric General Purpose Cores, is not only much easier to program for than the cell, but having 3 PPE capable of handling things such as AI also means the 360’s CPU will be the better of the 2 CPUs when it comes to AI code. Either way we can look forward to great things from both CPUs in the future.

Before I end off, I’d like to point out a game that in my opinion, from a technical standpoint, is one the most brilliant uses of the PS3’s CPU. All things considered, such as in-order execution and the other complications of the architecture, Heavenly Sword is quite the standout in nearly every regard: incredible combat animations, awesome group enemy AI, and great physics. At the very least this is what I gathered from seeing videos of the E3 demo; it’s a reminder that regardless of the challenges, there are developers that are up to the challenge and its only going to get better with time.