Xbox 360 Interview: Todd Holmdahl by Team Xbox

[Brimstone]

cores and three VMX vector units (one per core) while the PS3 has one CPU core, one vector unit, and seven SPEs. These differences found in both consoles’ architectures result in the Xbox 360 having more general purpose power than the PS3 while the PlayStation 3 has more floating-point performance (2 TFLOPs against 1 TFLOP of the Xbox 360 to be precise). Isn’t this a major advantage of the PS3 over the Xbox 360?

Todd Holmdahl: No. The PS3’s vaunted teraflop “advantage†is only an advantage on paper, because the PS3’s performance will be limited by its architecture. Real games are about 80% general purpose code and about 20% floating point code. Xbox 360 has three 3.2 GHz general purpose processors to Sony’s one, and it is these main cores, not special purpose SPEs, that are best suited for game code.

The PS3’s design requires high levels of floating point performance, because the PS3 GPU is unable to do automatic load balancing between pixels and vertices, so performance will drop off during vertex processing. The PS3’s design requires that the CPU take up the slack. On Xbox 360, we do not plan for the CPU to do any vertex processing at all, which leaves all of the processor’s power for game simulation code.

Floating point performance is much more relevant on the GPU, where Xbox 360 has more floating point performance than PS3. Not only does the Xbox 360 GPU have greater raw shader power than the PS3 GPU (240 GFLOPS versus estimated 228.8 GFLOPS on PS3), it will also use more of its power. The Xbox 360’s unified shader model will automatically optimize graphics for each game (vertex or pixel shading), without the developer having to write any extra code. Xbox 360 will also have embedded DRAM to avoid bandwidth bottlenecks and to give developers “free†anti-aliasing to eliminate jagged edges in every game.

Both systems have 512 MB of memory, but we gave developers the flexibility to decide how they use it, while Sony’s split memory architecture is more limited in its options. (We actually looked at the split memory architecture and decided not to use it because of those limitations).

Sony’s emphasis on certain areas of the PS3’s performance is a nice way to distract attention from the fact that they seem to have no response to Xbox Live. Only Xbox 360 has the hardware, software and services to enable the complete gaming and entertainment experience.

http://interviews.teamxbox.com/xbox/1190/Xbox-360-Interview-Todd-Holmdahl/p1/

 

[Acert93]

cores and three VMX vector units (one per core) while the PS3 has one CPU core, one vector unit, and seven SPEs. These differences found in both consoles’ architectures result in the Xbox 360 having more general purpose power than the PS3 while the PlayStation 3 has more floating-point performance (2 TFLOPs against 1 TFLOP of the Xbox 360 to be precise). Isn’t this a major advantage of the PS3 over the Xbox 360?

Actually for the CPUs it is 218GFLOPs (CELL) to 115GFLOPs (XeCPU). Both companies have been very bad about talking about 1 or 2TFLOPs of programmable preformance... it is becoming pretty clear they each have ~500GFLOPs of programmable fp power. This whole "target flops" is kind of silly... like the rest of the interview.

Todd Holmdahl: No. The PS3’s vaunted teraflop “advantage†is only an advantage on paper, because the PS3’s performance will be limited by its architecture. Real games are about 80% general purpose code and about 20% floating point code. Xbox 360 has three 3.2 GHz general purpose processors to Sony’s one, and it is these main cores, not special purpose SPEs, that are best suited for game code.

Maybe true. But SPEs are well suited for some MODERN game concepts that GPs have not been too ineffecient to do. Also, we will see many GP code become SPE friendly--neccessity is the mother of innovation.

The PS3’s design requires high levels of floating point performance, because the PS3 GPU is unable to do automatic load balancing between pixels and vertices, so performance will drop off during vertex processing. The PS3’s design requires that the CPU take up the slack.

Actually, VS in most PC games are in general under utlized. Using the CPU to take up slack is a perk NOT a neccessity! Flexibility anyone?

On Xbox 360, we do not plan for the CPU to do any vertex processing at all, which leaves all of the processor’s power for game simulation code.

$#%$# Yeah, explain the patents buddy. Arstechnica.com actually has a very good read on this. The entire L2 Loch where Xenos can read/write to CPU cache... yeah, just what I thought.

This type of stuff is annoying. The XeCPU is designed to do procedural synthesis by taking HOS models and tesselating them and feeding them directly to the GPU. Call it semantics (maybe he does not consider that vertex work?) but it seems pretty clear they are similar tasks. And while not every 360 game will use this feature I am guessing many will due to the savings on main memory and bandwidth and it will allow the GPU to focus more xel shading.

The Xbox 360’s unified shader model will automatically optimize graphics for each game (vertex or pixel shading), without the developer having to write any extra code. Xbox 360 will also have embedded DRAM to avoid bandwidth bottlenecks and to give developers “free†anti-aliasing to eliminate jagged edges in every game.

Welcome back to earth. I can agree with this... I guess it is his job to under play his competitors strengths and overplay his own.

Both systems have 512 MB of memory, but we gave developers the flexibility to decide how they use it, while Sony’s split memory architecture is more limited in its options. (We actually looked at the split memory architecture and decided not to use it because of those limitations).

Really?

The GPU has 256MB @ 22GB/s.
The CPU has 256MB @ 25GB/s.

And they can share read eachothers memory pools... I believe the GPU can write to all 512MB @ 37GB/s.

Not taking the eDRAM into consideration (which has significant savings... great feature) it would appear that any detriment caused by two pools is at least made up for with the extra bandwidth.

So I think he is barking up the wrong tree. If he was singing from the rooftops the praises of eDRAM and the benefit to AA and other framebuffer effects I would be right with him. That is a huge perk. But the 360 UMA *alone* is not necessarily better. It is the UMA+eDRAM that I think is what he should focus on.

So his point on PS3's NUMA is kind of lost.

Sony’s emphasis on certain areas of the PS3’s performance is a nice way to distract attention from the fact that they seem to have no response to Xbox Live. Only Xbox 360 has the hardware, software and services to enable the complete gaming and entertainment experience.

Hardware. Software. Services.

I am at least glad MS has a holistic approach.

That said, ROTFLOL. I have a hard time believing Sony is focusing on performance because they do not have Live. They could make a Live service (they are on record as only being mildly interested in such--mainly for small 3rd parties--and instead leaving large developers to have control over online) but they choose not to.

Could it be MS is focusing on Live because it is an advantage they have and it takes the ol' eyes off the specs?

Not that 360 is BAD in the specs, but this is such a fan-boi PR release

 

[Bohdy]

Real games are about 80% general purpose code and about 20% floating point code.

I hear this a lot from the X360 design team and collaborators, but I wonder if they have ever considered that ratio would naturally change if there were more FP power available? Perhaps they choose not to...

 

[Farid]

In others news, the sky is blue.

There's nothing new in this interview, everything claimed in this article has already been discussed here, a few dozen times at least.

By now, thanks to the millions of articles and interviews about MS and Sony, we know the official PR stances of those two. No need to post each and every articles containing the same, and now really old, marketing-technical jargon mishmash.

And the problem with threads that discuss marketing-technical terms, other than they're a waiste of time and bandwidth, is that it turns this board, more and more, into Gamefaq-2...

 

[Acert93]

Real games are about 80% general purpose code and about 20% floating point code.

I hear this a lot from the X360 design team and collaborators, but I wonder if they have ever considered that ratio would naturally change if there were more FP power available? Perhaps they choose not to...

Oh they have... that is why the XeCPU has 115GFLOPs of floating point performance. Basically each core is ~2-3x as powerful as a comparable desktop PC x86 core at FP.

So they see the need... but they have decided it is more important to downplay their competitions advantage.

Call me idealistic, but I would be more happy hearing, "We believe we have a more powerful machine. In the past games have typically used 80% GP code, and while we will see that trend change some with procedural synthesis, accurate physics, and the like there is also a greater need for GP processing as well for AI and general game logic. We are confident we have found the middle ground while are competitor has gone 'All or Broke' on floating point performance. We wanted a design that was an evolutionary step for programmers as they move toward multithreaded code. Multithreading is going to be a challenge for all programmers so we wanted to make the transition as painless as possible. Requiring programmers to choose between two CPU code types and having to serialize code into 7 threads that must be fed continually to even begin to see full potential is a lot harder than 1 core type with 3 cores all sharing the same cache. With 6 HW threads programmers can just push their code into the que and let the processor do the heavy work" blah blah blah

Still a lot of SPIN there, but at least I could digest something like that--even if it still downplays your competitors merits.

I have a wild hunch that MS and Sony PR people saw our PR threads and they each have office pools seeing who can get into the thread quickest The more outlandish the better!

 

[Acert93]

And the problem with threads that discuss marketing-technical terms, other than they're a waiste of time and bandwidth, is that it turns this board, more and more, into Gamefaq-2...

As the console forum I think it is valid to examine their current tactics, including PR.

And if we wont debunk their junk who will? this probably should have been in the MS PR thread... that said, it was still interesting to read.

 

[passby]

Real games are about 80% general purpose code and about 20% floating point code.

Except that the 20% of floating point code occupies 80% of the application's runtime.

Sorry can't resist. I agree that this thread should sink away quickly.

 

[JasonLD]

Most of the points made in the article is discussed like thousand times before and nothing new...I think this belongs in MS PR thread.
Dang..can't wait for TGS so we can start comparing real games...tired of numbers game.

 

[Farid]

As the console forum I think it is valid to examine their current tactics, including PR.

And if we wont debunk their junk who will? this probably should have been in the MS PR thread... that said, it was still interesting to read.

Don't get me wrong Acert, I know that some people can discuss seriously, and intelligibly these kind of topics. That, I know.

But what I also know is that kind of threads with their mainstream PR, with their overexagerared marketing numbers, and their apples-to-oranges comparisons, are a perfect spot for the trolls that inhabit the forum these days...

Also, all the points raised in this interview have already been argued a few time already. And all those other threads died horrible deaths, sadly.

 

[Rockster]

I'm sooooo over the pissing matches. Neither one of these machines is going to overpower the other. Because with games, there are so many ways to skin the same cat, the kind knife hardly matters. I just wish everyone were equally cynical about both companies claims.

 

[Pozer]

I don't know whats worse. The fact we have to hear six months of MS PR spin or the fact we have six months of the same due from Sony. Quite alot of hot air considering we're gonna have another 5 years of multiconsole ports and the occasional true exclusive.

 

[Acert93]

As the console forum I think it is valid to examine their current tactics, including PR.

And if we wont debunk their junk who will? this probably should have been in the MS PR thread... that said, it was still interesting to read.

Don't get me wrong Acert, I know that some people can discuss seriously, and intelligibly these kind of topics. That, I know.

But what I also know is that kind of threads with their mainstream PR, with their overexagerared marketing numbers, and their apples-to-oranges comparisons, are a perfect spot for the trolls that inhabit the forum these days...

Also, all the points raised in this interview have already been argued a few time already. And all those other threads died horrible deaths, sadly.

You are right... I was trying to be anti-troll

And you are right these have been argued before. I think my rebutal was fair, so maybe JVD will close this thread and move the news piece to the MS PR thread?

 

[jvd]

This belongs in the ms pr thread