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Fast Communication: The Ring Bus

Larrabee: Intel's New GPU
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To manage cache coherence, communication between the different processors, and access to fixed units like the texture units, Intel has designed a fairly classic ring bus. This type of topology has become rather familiar recently, in the Cell processor and in certain AMD GPUs (X1800, X1900, etc.), for example, since it greatly simplifies the system of interconnections when the amount of data in the bus gets increases.

Intel has given Larrabee two 512-bit buses, one in each direction, to limit communication latency. However, that solution isn’t sufficient to avoid latency reaching problematic levels when the number of processors increases beyond a certain point, and so in Larrabee implementations using more than 16 cores, there are several, shorter ring buses (probably serving eight cores only).

We might point out in passing that Intel’s diagram of Larrabee is not quite exact. To avoid needless complication, Intel has put the memory controllers on either side of the chip, and all the texture units at the left. In practice, the texture units and memory controllers will be distributed around the periphery of the ring, rather then being all in the same place. Obviously, that’s to avoid problems with congestion with a configuration like the one shown in the diagram.

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  • 0 Hide
    thepinkpanther , March 23, 2009 6:35 AM
    very interesting, i know nvidia cant settle for being the second best. As always its good for the consumer.
  • 6 Hide
    IzzyCraft , March 23, 2009 6:49 AM
    Yes interesting, but intel already makes like 50% of every gpu i rather not see them take more market share and push nvidia and amd out although i doubt it unless they can make a real performer, which i have no doubt on paper they can but with drivers etc i doubt it.
  • 0 Hide
    Anonymous , March 23, 2009 6:50 AM
    I wonder if their aim is to compete to appeal to the gamer market to run high end games?
  • 0 Hide
    Alien_959 , March 23, 2009 8:12 AM
    Very interesting, finally some more information about Intel upcoming "GPU".
    But as I sad before here if the drivers aren't good, even the best hardware design is for nothing. I hope Intel invests more on to the software side of things and will be nice to have a third player.
  • 0 Hide
    crisisavatar , March 23, 2009 8:28 AM
    cool ill wait for windows 7 for my next build and hope to see some directx 11 and openGL3 support by then.
  • 0 Hide
    Stardude82 , March 23, 2009 8:32 AM
    Maybe there is more than a little commonality with the Atom CPUs: in-order execution, hyper threading, low power/small foot print.

    Does the duo-core NV330 have the same sort of ring architecture?
  • 2 Hide
    liemfukliang , March 23, 2009 10:27 AM
    Driver. If Intel made driver as bad as Intel Extreme than event if Intel can make faster and cheaper GPU it will be useless.
  • 3 Hide
    IzzyCraft , March 23, 2009 10:44 AM
    Hope for an Omega Drivers equivalent lol?
  • 1 Hide
    phantom93 , March 23, 2009 11:16 AM
    Damn, hoped there would be some pictures :( . Looks interesting, I didn't read the full article but I hope it is cheaper so some of my friends with reg desktps can join in some Orginal Hardcore PC Gaming XD.
  • 9 Hide
    Slobogob , March 23, 2009 11:51 AM
    I was quite suprised by the quality of this article and am quite eager to see the follow up.
  • 1 Hide
    JeanLuc , March 23, 2009 12:26 PM
    Well I am looking forward to Larrabee but I'll keep my optimisim under wraps until I start seeing some screenshots of Larabee in action playing real games i.e. not Intel demo's.

    I wonder just how compatible larrabee is going to be with older games?
  • 3 Hide
    tipoo , March 23, 2009 12:46 PM
    Great article! Keep ones like this coming!
  • -2 Hide
    tipoo , March 23, 2009 12:48 PM
    IzzyCraftHope for an Omega Drivers equivalent lol?



    That would be FANTASTIC! Maybe the same people who make the Omega drivers could make alternate Larrabee drivers? We all know Intel sucks balls at drivers.
  • 7 Hide
    armistitiu , March 23, 2009 12:49 PM
    So this is Intel's approach to a GPU... we put lots of simple x86 cores in it , add SMT and vector operations and hope that they would do the job of a GPU. IMHO Larrabee will be a complete failure as GPU but as an x86 CPU that is highly parallel this thing could screw AMD's FireStream and NVIDIA's CUDA (OPENCL too) beacause it's x86 and the programming is pretty popular for this kind of architecture.
  • 0 Hide
    wicko , March 23, 2009 1:18 PM
    IzzyCraftYes interesting, but intel already makes like 50% of every gpu i rather not see them take more market share and push nvidia and amd out although i doubt it unless they can make a real performer, which i have no doubt on paper they can but with drivers etc i doubt it.

    Yeah but that 50% includes all the integrated cards that no consumer even realizes they're buying most of the time.. but not in discrete cards. I'd like to see a bit more competition on the discrete side.
  • 2 Hide
    B-Unit , March 23, 2009 1:26 PM
    wtfnl"Simultaneous Multithreading (SMT). This technology has just made a comeback in Intel architectures with the Core i7, and is built into the Larrabee processors." just thought i'd point out that with the current amd vs intel fight..if intel takes away the x86 licence amd will take its multithreading and ht tech back leaving intel without a cpu and a useless gpu


    Umm, what makes you think that AMD pioneered multi-threading? And Intel doesnt use HyperTransport, so they cant take it away.
  • 1 Hide
    justaguy , March 23, 2009 2:02 PM
    Now we know what they're trying to do with it. There's still no indication if it will work or not.

    I really don't see the 1st gen. being successful-it's not like AMD and nVidia are goofing around waiting for Intel to join up and show them a real GPU. Although there's no numbers on this that I've seen, I'm thinking Larry's going to have a pretty big die size to fit all those mini-cores so it better perform, because it will cost a decent sum.
  • 8 Hide
    crockdaddy , March 23, 2009 2:09 PM
    I would mention ... "but will it play crysis" but I am not sure how funny that is anymore.
  • -4 Hide
    Pei-chen , March 23, 2009 2:12 PM
    Can't wait for Larrabee; hopefully a single Larrabee can have the performance of 295. Nvidia and ATI are slacking as they know they can price fixing and stop coming out with better GPU, just more cards with the same old GPU.
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