Intel's Larrabee Architecture Disclosure: A Calculated First Move
by Anand Lal Shimpi & Derek Wilson on August 4, 2008 12:00 AM EST- Posted in
- GPUs
Putting it all Together - Return of the Ring Bus
Intel is keeping two important details of Larrabee very quiet: the details of the instruction set and the configuration of the finished product. Remember that Larrabee won't ship until sometime in 2009 or 2010, the first chips aren't even back from the fab yet, so not wanting to discuss how many cores Intel will be able to fit on a single Larrabee GPU makes sense.
The final product will be some assembly of a multiple of 8 Larrabee cores, we originally expected to see something in the 24-to-32 core range but that largely depends on targeted die size as we'll soon explain:
Intel's own block diagrams indicated two memory controller partitions, but it's unclear whether or not we should read into this. AMD and NVIDIA both use 64-bit memory controllers and simply group multiples of them on a single chip. Given that Intel's Larrabee will be more memory bandwidth efficient than what AMD and NVIDIA have put out, it's quite possible that Larrabee could have a 128-bit memory interface, although we do believe that'd be a very conservative move (we'd expect a 256-bit interface). Coupled with GDDR5 (which should be both cheaper and highy available by the Larrabee timeframe) however, anything is possible.
All of the cores are connected via a bi-directional ring bus (512-bits in each direction), presumably running at core speed. Given that Larrabee is expected to run at 2GHz+, this is going to be one very high-bandwidth bus. This is half the bit-width of AMD's R600/RV670 ring bus, but the higher speed should more than make up the difference.
AMD recently abandoned their ring bus memory architecture citing a savings in die area and a lack of need for such a robust solution as the reason. A ring bus, as memory busses go, is fairly straight forward and less complex than other options. The disadvantage is that it is a lot of wires and it delivers high bandwidth to all the clients on the bus whether they need it or not. Of course, if all your memory clients need or can easily use high bandwidth then that's a win for the ring bus.
Intel may have a better use for going with the ring bus than AMD: cache coherency and inter-core communication. Partitioning the L2 and using the ring bus to maintain coherency and facilitate communication could make good use of this massive amount of data moving power. While Cell also allows for internal communication, Intel's solution of providing direct access to low latency, coherent L1 and L2 partitions while enabling massive bandwidth behind the L2 cache could result in a much faster and easier to program architecture when data sharing is required.
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erikespo - Monday, August 4, 2008 - link
http://en.wikipedia.org/wiki/Square_%28geometry%29">http://en.wikipedia.org/wiki/Square_%28geometry%29helpful page to take you back to first grade
and excuse my decimal point.. it is 204.49mm total per core or 14.3mm^2
erikespo - Monday, August 4, 2008 - link
Explain.lets use smaller numbers for you 2mm^2 is 2mm by 2 mm or 4 total mm
double that and it is 4mm^2 or 4 mm by 4 mm or 16mm total..
we are talking about area or 2 dimensions not 1 dimension.
Same math applies to the article
MamiyaOtaru - Monday, August 4, 2008 - link
No, you're way off. 2mm² is TWO square millimeters. (a rectangle 1x2 for example). Double that would be 4mm², which could either be 1x4 or 2x2.NUMBERmm² doesn't mean NUMBERxNUMBER mm, it means exactly what it says: NUMBER mm².
Using your smaller numbers: 2mm² is not "4 total mm"; it is TWO mm². Saying it is 4 total mm doesn't even make sense. You _can't_ measure area in millimeters. You measure it in square millimeters, and there are two of them (_2_mm²).
Here's an mspaint visual (if links work: http://img105.imageshack.us/my.php?image=squaremma...">http://img105.imageshack.us/my.php?image=squaremma...
You're so sure you're right on this, it's really depressing :(
darkequitus - Monday, August 4, 2008 - link
I did not appriciate the writer creaming over every digital page they wrote. especially when Larrabee's performance is mainl at the moment based on INtel hype and nothing real.ZootyGray - Monday, August 4, 2008 - link
THANK YOU.Somebody finally said it.
The others prefer Eutopian illusion - aka the curse aka ntel antitrust. ntel has no grafx and the fools in the public buy "inside' and nvid and ati aren't exactly friends of the curse.
welcome to the matrix. wakey wakey
ZootyGray - Monday, August 4, 2008 - link
and a 16 pager on maybe might could be should be = wannabe "employ-boy"- payday ? hooyeh. This is so disappointing for me. Credibility sags to a new low.
strikeback03 - Tuesday, August 5, 2008 - link
Someone whose two posts contain about 10 complete words and no complete thoughts says Anandtech's credibility has sagged to a new low?ZootyGray - Tuesday, August 5, 2008 - link
haha yeh - lots of room for thinking.or - if no thinkeez - ya gots der 16 pg inundation (that's a big word like marmalade) all based on nothing-is-real - you like that kind of brainwash? we don't know anything; but here's the tekspex?
btw - did u get it? the matrix idea? watch the movie. cos here it is. pardon my loaded cryptic literacy.
thx
if you don't get it - well, that's what they want - a world of sleeping mob. never mind, that's just my concern.
The Preacher - Monday, August 4, 2008 - link
I don't really care about how good it will be executing some software renderer but I feel it is going to kick ass in scientific calculations. Matrix operations, FFT/convolution, tremendous bandwidth, double precission... I may write C++/x86 assembly code directly for it and I may put this into a rack of servers and use it through MPI. Give me a compiler with vector intrinsic functions for it and my dreams just came true! :)elerick - Monday, August 4, 2008 - link
I have been a daily reader of another hardware review site for years. I ready nearly every articles that headlines and find many of them quite lacking. Today I got wind of your review for the Larabee. It was very well written and produced an amazing amount of tech knowledge not really commonly reviewed. I'm glad to have found you this site, and I never create an account but today I felt obligated to. Great work.PS: any news on that AMD / Fusion? or is that just them being intimidated by Intel's Larrabee?