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PS3 Cell Processor 'Broken'?
Posted by
Zonk
on Mon Jun 05, 2006 08:27 AM
from the it's-drinking dept.
from the it's-drinking dept.
D-Fly writes "Charlie Demerijian at the Inquirer got a look at some insider specs on the PS3, and says, Sony screwed up big time with the Cell processor; the memory read speed on the current Devkits is something like 3 orders of magnitude slower than the write speed; and is unlikely to improve much before the ship date. The slide from Sony pictured in the article is priceless: 'Local Memory Read Speed ~16Mbps, No this isn't a Typo.' Demerjian says when the PS3 comes out a full year after the XBox360, it's still going to be inferior: 'Someone screwed up so badly it looks like it will relegate the console to second place behind the 360.'" This is the Inquirer, so take with a grain of salt. Just the same, doesn't sound too good for Sony or IBM.
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PS2 Vs PS3 (Score:5, Informative)
If you really want to dig into the details of the Cell processor, check out Sony's resources [scei.co.jp]. You have to agree to a bunch of things to get to the pdfs but there's a lot of information [scei.co.jp] in them. Another place you can find information is IBM's resource site [ibm.com] which contains a lot of stuff including the programming handbook.
Inquirer, yes, but... (Score:5, Insightful)
Re:Inquirer, yes, but... (Score:5, Insightful)
By the way, I'm not discounting that it could be real - it's got me curious enough to look on the web for the last 10 mins for some documentation to back up the claims in the story.. I couldn't find anything though.
Anyone got any real documentation or anything to back up the claim?
Re:Inquirer, yes, but... (Score:5, Insightful)
The picture says that the read speed for the Cell from "Local Memory" is 16Mb a second. Assuming it is true (I've got no reason to doubt it), then it still doesn't matter.
The "Local Memory" is the RSX graphics memory. The Cell shouldn't need to read this. The PS3 would still work even if the Cell couldn't read this memory at all. This memory is where you store textures and other graphics data.
Re:Inquirer, yes, but... (Score:5, Informative)
The RSX can read the Cell's RAM at ridiculous speeds which is all that matters. The RSX can render out of main memory, so you shouldn't ever be using the Cell to read from the RSX's RAM at all. The Cell will probably be manipulating vector data for the RSX, but 256MB for all executable code and vector data is still more than enough. The 256MB attached to the RSX would have been used primarily for textures even if the Cell could read from it at reasonable speeds
main memories read speed is 25GB/s (Score:5, Insightful)
I assume the local memory is not going to be used much for 'reading' and only main memory is going to be used.
Re:main memories read speed is 25GB/s (Score:5, Informative)
So it is perfectly normal for texture memory to be nearly write-only. As long as writing to it is extremely fast (which it is in this case according to the PP slide), that isn't a problem.
Does it really matter? (Score:5, Funny)
Why ./ is bashing Sony so much? (Score:5, Insightful)
Re:Why ./ is bashing Sony so much? (Score:5, Funny)
DevStation? (Score:5, Funny)
DeviStation
Article completely misses the point (Score:5, Insightful)
That the read performance for the Cell from this memory is dreadful is no surprise. This is exactly the same architecture that has been traditionally used in PCs. Reading graphics memory from the main processor is usually really really slow.
This memory is where you store textures and other graphics data. The main processor will usually have little need to read from this memory. If it does, then, as apparently Sony says, you just get the RSX to write to main memory instead.
This is a non-story. People have dealt with this for PC games for a long time.
For goodness sake... (Score:5, Informative)
"Load and store operations (LS), 6 Clock cycles Latency". And that's the time it takes for the instruction to complete, not to be issued to memory.
(3.2Ghz / 6 cycles) * 16 bytes != 16MB/s
Personally, I'm gonna bet on IBM being right, seeing how they're the ones who made the bloody thing. I don't trust the inquirer anyway, but if those figures are true, the most likely answer is inefficiencies in their benchmarking programs, (Such as instruction starvation, a nasty side effect of using SPU's)
History Repeats Itself (Score:5, Insightful)
I think being too connected to the online debates about this stuff can make you lose sight of what the more average public thinks and bases their purchase decisions on. That's why the only real argument for the PS3's failure so far is the high price, not questions about performance or developer issues.
16MB/s = CPU reading GPU memory directly (Score:5, Informative)
Memory transfer bandwidth between each SPU and its SPU Local Memory is something more like 25GB/s (gigabyte per second); sustained actual bandwidth between all SPUs is greater than 100GB/s; peak theoretical is greater than 200GB/s (assuming all 8 SPUs present for simplicity).
If you had access to the full version of the presentation (part of the full Sony PS3 SDK and technotes), you'd realise that that slide is part of a presentation about the RSX (the PS3's GPU). As such, when it refers to "Local Memory", it means RSX's Local Memory (eg graphics memory, video memory, VRAM or whatever you call it in fanboy/ps3/360-is-teh-suck websites). To be understood outside that context, the columns would be better labelled "Main System Memory" and "GPU Local Memory".
The Inquirer article seems to suggest that this figure of 16MB/s (megabyte per second, by the way, what the fuck is it with journalists swapping bits for bytes? why don't they get their shift/capslock keys fixed?) is some kind of show stopper. No it isn't. It simply means that the Cell processor has 16MB/s bandwidth when reading directly from memory-mapped GPU address space. So what? Unless you're planning on calling memcpy() or some shit to bring your data back then it doesn't really matter.
On RSX-initiated transfers you have 20GB/s bandwidth to do the same transfer (from RSX local to main system memory). Cell read bandwidth of GPU memory might as well have 0MB/s (ie no connection at all) and it wouldn't matter a bit.
Yay! (Score:5, Interesting)
Everyone close to me in the industry said I was crazy and that this would all smooth out and Sony would easily retain its market share if not grow more. I wasn't buying it and stuck to my guns, I'm pretty happy about my decision almost daily since day 1 of E3 this year.
I was against UMD from the beginning, yet everyone claimed that the sales were stellar. Looks like they weren't and they are proprietary, expensive, unwieldy little discs that no one wants to deal with. The "cell" processor was without a dobt my turning point, I have ZERO faith in it or the architecture and it will not become this ubiquitous omnipresent processor as so many claim, even IBM has major problems with it and designing compilers and dev software for their own product. Control schemes have been radically changed from initial proposals, and too quickly to be properly tested... that is a bomb yet to go off. System price and dev costs that are just too high for our current economic situation as well as for widespread adoption. There are more issues, but top it all off with a new unproven media that is also expensive and offers no real consumer advantages and you have the high risk of a catastrophic failure that could hurt Sony and IBM even more than they are already hurting.
The best that can happen is that companies finally lose the DRM/proprietary/Closed nature of their consumer electronics. Stop treating customers as criminals and start to offer them affordable and accessible entertainment that is convenient. I'd actually prefer consoles to standardize and become built into consumer electronics so that developers and consumers can really get to work on a stable and long lasting platform. Imagine the possibilities. There is a lot to be said for standards.
Re:Go Sony, go! (Score:5, Funny)
Re:Go Sony, go! (Score:5, Funny)
Re:Go Sony, go! (Score:5, Informative)
Re:Go Sony, go! (Score:5, Interesting)
And it turned out to be one fo the most successful consoles ever.
Re:Go Sony, go! (Score:5, Funny)
Not trying to flamebait here, but what is one of the OS's that will be running on PS3? Hint, it starts with L and ends with X.
Re:Go Sony, go! (Score:5, Informative)
IMO it's reasonable to have asynchronous communication with the graphics subsystem. The only stupid thing going on is calling graphics cards memory "Local Memory". It suggests that the X-Box got it right by having one big chunk of memory that is read by both the CPU and GPU even if most developers will make the same basic split anyway.
Re:Go Sony, go! (Score:5, Informative)
Presumably in the (unlikely?) event you did need the output from the RSX graphics chip for manipulation by the Cell processor gubbins, you could get it to render to main memory, let the processor do the appropriate data-diddling, then have the RSX read it back again?
The 'local memory' is presumably the RSX's private play area, and thus the RSX gets maximum-stupendous-speed priority, and the Cell gets occasional access at weekends. Which is a bonus, and not even necessary...
Re:Go Sony, go! (Score:5, Informative)
In the slide, the "Local Memory" refers to the RSX local memory, not the SPU local memory. The article says that the next slide is Sony telling devs to use the RSX to do the transfer instead, which only makes sense if it is talking about the RSX memory.
Your conclusion is right though, as this also is memory that the Cell doesn't need to read from.
Re:D-Fly, you piece of shit: Mbps != MB/s (Score:5, Informative)
1) The poster had no clue
2) Zonk (and for that matter, the whole
3) This mistake happens _constantly_ on
4) Anyone with even a basic understanding of computers wouldn't make this mistake
Just more proof that "IT" != computer science