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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DerekWilson - Monday, August 4, 2008 - link
this is a pretty good observation ...but no matter how much potential it has, performance in games is going to be the thing that actually makes or breaks it. it's of no use to anyone if no one buys it. and no one is going to buy it because of potential -- it's all about whether or not they can deliver on game performance.
Griswold - Monday, August 4, 2008 - link
Well, it seems you dont get it either.helms - Monday, August 4, 2008 - link
I decided to check out the development of this game I heard about ages ago that seemed pretty unique not only the game but the game engine for it. Going to the website it seems Intel acquired them at the end of February.http://www.projectoffset.com/news.php">http://www.projectoffset.com/news.php
http://www.projectoffset.com/technology.php">http://www.projectoffset.com/technology.php
I wonder how significant this is.
iwodo - Monday, August 4, 2008 - link
I forgot to ask, how will the Software Render works out on Mac? Since all Direct X code are run to Software renderer doesn't that fundamentally mean most of the current Windows based games could be run on Mac with little work?MamiyaOtaru - Monday, August 4, 2008 - link
Not really. Larrabee will be translating directx to its software renderer. But unless Microsoft ports the directX API to OSX, there will be nothing for Larrabee to translate.Aethelwolf - Monday, August 4, 2008 - link
I wonder if game devs can write their games in directx then have the software renderer convert it into larrabee's ISA on windows platform, capturing the binary somehow. Distribute the directx on windows and the software ISA for mac. No need for two separate code paths.iwodo - Monday, August 4, 2008 - link
If anyone can just point out the assumption anand make are false? Then it would be great, because what he is saying is simply too good to be true.One point to mention the 4Mb Cache takes up nearly 50% of the die size. So if intel could rely more on bandwidth and saving on cache they could put in a few more core.
And am i the only one who think 2010 is far away from Introduction. I think 2009 summer seems like a much better time. Then they will have another 6 - 8 months before they move on to 32nm with higher clock speed.
And for the Game developers, with the cash intel have, 10 Million for every high profile studio like Blizzard, 50 Million to EA to optimize for Intel. It would only cost them 100 million of pocket money.
ZootyGray - Monday, August 4, 2008 - link
I was thinking of all the p90's I threw away - could have made a cpu sandwich, with a lil peanut software butter, and had this tower of babel thing sticking out the side of the case with a fan on top, called lazarus, or something - such an opportunity to utilize all that old tek - such imagery.griswold u r funny :)
Griswold - Monday, August 4, 2008 - link
You definitely are confused. Time for a nap.paydirt - Monday, August 4, 2008 - link
STFU Griswald. It's not helpful for you to grade every comment. Grade the article if you like... Anandtech, is it possible to add an ignore user function for the comments?