Topic: Lair Dev: PS3's Cell is 'Limitless' (Read 185 times)

m_hael · « **Reply #15 on:** April 17, 2007, 02:00:00 PM »

QUOTE(ConteZero76 @ Apr 17 2007, 11:01 AM)

Let's ask michael if he has access to these informations (right now, not then) and if there's still that limitation...
Right ?

and yes... I have access to this information right now.

m_hael · « **Reply #16 on:** April 17, 2007, 02:18:00 PM »

QUOTE(ConteZero76 @ Apr 17 2007, 11:37 AM)

... disagreed ... again

Yet again, where the information about 1.5 SPU come from ?

difficult does not mean impossible, standard thread switching is definitely possible and in use fully when the 6th spu's avaiable to developers for games is concerned.

Linux running on ps3 has access to 6spu's fully because it is NOT running the full ps3 kernel, only parts of it and thus does not need the extra 50% of an spu; games require it. Linux is further limited by a hypervisor, games are not.

QUOTE(ConteZero76 @ Apr 17 2007, 12:15 PM)

Good.
Proof ?

proof would require disclosure of materials currently under NDA.

you should also know that you are person #208083729 in the line of people that doubted me... the other 208083728 now either believe, or trust in other people who DO believe, enough to not argue.

m_hael · « **Reply #17 on:** April 17, 2007, 02:31:00 PM »

I can't be bother to argue with you... go ahead and proclaim your victory...

epsilon72 · « **Reply #18 on:** April 17, 2007, 02:36:00 PM »

@ users trying to argue with m_hael....

Mage · « **Reply #19 on:** April 21, 2007, 03:14:00 PM »

QUOTE(ConteZero76 @ Apr 18 2007, 05:29 AM)

SPU aren't made for multitasking, you've got to use cooperative multitasking (i.e. the SPU has to switch himself from one task to another using some sort of embedded OS) or via a "brute" switch.
About the rest Linux uses PS3 like every other application, only RSX is half shut down, nothing that should bother the OS.
As for the rest I still doesn't see what's the reason to use two SPU (if you could be kind enough to explain me).

And you should believe me, I'm Claus, Santa Claus.

Actually the SPU can easily be forced to do a context switch, and it takes around 20 microseconds according to this interview with a senior IBM programmer. As 20 microseconds isn't much time, it is possible that Sony does use a second SPU at times.
Also, the PPU can easily control context switches on the SPU, via the MMIO registers. This is public knowledge in the IBM docs.

Even if the SPU is running in isolation mode you can replace the currently running context, assuming the ppu task is in the same LPAR as the SPU.

QUOTE

dW: Looking at the multitasking model -- which has the pre-emptive scheduling -- when it comes to a context change, what's the order of magnitude versus some of the effects like cache misses?

Chow: The context switch for the whole SPE takes about 20 microseconds. The majority of the latency of the context switch save and restore is because you have to swap out the whole local store and then replace that with the new context. It is very expensive compared to the native PowerPC® threads. For the PPE core, you don't have to save and restore the whole execution memory image of the PowerPC task. To context switch an SPE program properly, a lot of activities need to happen.We have to wait for the outstanding DMAs to complete, copy out of all of the entries in the DMA queues, copy out of all the local store and register content... By the way, it is a huge register file. Then you have to bring in the previous context and other context to be swapped back in. It takes a relative long time to complete. That's the reason we usually favor the "run to completion" model.

http://www-128.ibm.c...ary/pa-expert8/

Mr Invader · « **Reply #20 on:** April 21, 2007, 08:40:00 PM »

m_hael...

You say that the SPU's are quick and good at processing along with the GPU(or something like that), and the fact that they are underutilized is why the current PS3 games don't look as good as their 360 counterparts. You also say that eventually PS3 titles will look better than 360 titles.

I can't argue with that, I'd say your right.

But exactly HOW much better will they look, could you give us a comparison or something?

And how does the architecture of the PS3 put it at a disadvantage compared to the 360? I've always heard until now that the 360 would be a better gaming device, in what ways is it better than the PS3?

m_hael · « **Reply #21 on:** April 21, 2007, 09:42:00 PM »

I can't give you a comparisen as such simply because any program is limited only by its designers. What I can provide is some perspective on latent power.

both machines are inherently at the mercy of their respective designs.

360 relies heavily upon a unified memory architecture which provides a lot of versatility when it comes to writing code quickly for it. Sadly this very architecture also represents its biggest bottleneck; the 1MB shared L2 cache. Each and every operation done by any of the 6 HW threads will access the cache thus the cache is effectively reduced to 170kb/thread. As systems become more and more thread centric this limit will rear its head and slow the machine down.

That said the GPU on the 360 is also unified at its core with 48ALU's to be assigned to either Pixel or Vertex shading at will. This is a massive advantage that results in porting from 360->ps3 being fairly difficult.

On the Ps3 the GPU (RSX) does not possess a good vertex pipeline, the system as a whole relies upon the SPU's. The SPU's rely upon the DMA unit to get data & code to and from main memory. The DMA unit is extremely fast... so fast that it has yet to be a bottleneck. Because the SPU's operate independant of main memory access and without any cache interference they are extremely useful. SPU programs can act entirely asynchronously and thus the PPU need never synchronise with operations (if designed well). The power of SPU's has yet to be realised even in games considered to be "stressing" the systems... the information I've seen shows SPU's, even for advanced games, utilised under 10% of the time.

So...

each have their bottlenecks BUT... as 360 HW thread utilisation increases the speed of each thread will decrease due to cache misses... ps3 does not have this issue, as SPU utilisation increases the DMA unit may become stressed but it will not become a bottleneck for all but Pixel level operations nor will the increased utilisation affect the main threads running on PPU.

in short, 360 will plateau soon, ps3 will not.

Mr Invader · « **Reply #22 on:** April 23, 2007, 07:57:00 PM »

QUOTE(m_hael @ Apr 21 2007, 10:49 PM)

in short, 360 will plateau soon, ps3 will not.

Soon? Like a year? Two to three years?

How much further does the 360 have to go before it plateaus?

dvsone · « **Reply #23 on:** April 24, 2007, 12:16:00 AM »

QUOTE(m_hael @ Apr 17 2007, 01:51 AM)

Because the SPU's are so versatile I would predict that within a few generations of games we'll start seeing graphics more advanced on ps3 than we will on 360.

m_hael says it going to be a few generations before he believes we'll start seeing more advanced graphics on the PS3. So I can't understand why he would say that when he expects the 360 graphics to plateau soon. Maybe he could explain.

m_hael · « **Reply #24 on:** April 24, 2007, 03:56:00 AM »

my last post said nothing about graphics, it only talked about CPU.

as far as timeline... difficult to say... as I said at the very begining the whole thing is in the hands of the programmers involved.

m_hael · « **Reply #25 on:** April 24, 2007, 11:34:00 AM »

local memory = graphics memory, local to the GPU... why would anything but the GPU read from it?

mlmadmax · « **Reply #26 on:** April 24, 2007, 02:14:00 PM »

What this all means to me, is that the PS3 can be kick ass but that all depends on programming. From what I have gathered taking advantage of this limitless architecture is very hard to do right now. Since it is so hard to program for wouldn't this cause production costs to skyrocket and could this be one of the reasons why it is taking so long for anything to come to market?

What I am trying to say is will any of this translate to great games anytime soon. That is what is important to me. Right now not only to games look and play better on my 360 I get to play these great looking games now.

Also it sounds like a lot of the advantages of the PS3 are on the cpu side of things. Doesn't this benefit things like physics and popups and not textures and frame rate?

In short will the PS3's benefits in hardware engineering actually show thru in a game i can walk into a store and buy anytime soon or will it be a case of to little to late?

Lamens terms would help

m_hael · « **Reply #27 on:** April 24, 2007, 05:53:00 PM »

backtrack a little to read my post on how the PS3's SPU's will help out hte GPU.

The ps3 offers people like me a significant benefit over simpler systems; a challenge with significant rewards.

as for timescale... difficult to say as I'm not privvy to every companies codebase... I do however have many many friends in the industry and discuss these things widely on a daily basis.

my guess would be by xmas '07 you'll start to see a leveling with xmas '08 being the turning point.

hamwbone · « **Reply #28 on:** April 24, 2007, 06:28:00 PM »

*here comes the redneck*

none of this matters if my controller doesnt rumble!

m_hael · « **Reply #29 on:** April 24, 2007, 06:58:00 PM »

I saw that you'd posted and simply KNEW it would be something faceious....

Author Topic: Lair Dev: PS3's Cell is 'Limitless' (Read 185 times)