The Design Experiment: Could Intel Build a GPU?

Larrabee is fundamentally built out of existing Intel x86 core technology, which not only means that the chip design isn't foreign to Intel, but also has serious implications for the future of desktop microprocessors. Larrabee isn't however built on Intel's current bread and butter, the Core architecture, instead Intel turned to a much older architecture as the basis for Larrabee: the original Pentium.

The original Pentium was manufactured on a 0.80µm process, later shrinking to 0.60µm. The question Intel posed was this: could an updated version of the Pentium core, built on a modern day process and equipped with a very wide vector unit, make a solid foundation for a high-end GPU?

To first test the theory Intel took a standard Core 2 Duo, with a 4MB L2 cache at an undisclosed clock speed (somewhere in the 1.8 - 2.9GHz range I'd guess). Then, on the same manufacturing process, roughly the same die area and power consumption, Intel sought to find out how many of these modified Pentium cores it could fit. The number was 10.

So in the space of a dual-core Core 2 Duo, Intel could construct this hypothetical 10-core chip. Let's look at the stats:

  Intel Core 2 Duo Hypothetical Larrabee
# of CPU Cores 2 out of order 10 in-order
Instructions per Issue 4 per clock 2 per clock
VPU Lanes per Core 4-wide SSE 16-wide
L2 Cache Size 4MB 4MB
Single-Stream Throughput 4 per clock 2 per clock
Vector Throughput 8 per clock 160 per clock

 

Note that what we're comparing here are operation throughputs, not how fast it can actually execute anything, just how many operations it can retire per clock.

Running a single instruction stream (e.g. single threaded application), the Core 2 can process as many as four operations per clock, since it can issue 4-instructions per clock and it isn't execution unit constrained. The 10-core design however can only issue two instructions per clock and thus the peak execution rate for a single instruction stream is two operations per clock, half the throughput of the Core 2. That's fine however since you'll actually want to be running vector operations on this core and leave your single threaded tasks to your Core 2 CPU anyways, and here's where the proposed architecture spreads its wings.

With two cores, each with their ability to execute 4 concurrent SSE operations per clock, you've got a throughput of 8 ops per clock on Core 2. On the 10-core design? 160 ops per clock, an increase of 20x in roughly the same die area and power budget.

On paper this could actually work. If you had enough of these cores, you could get the vector throughput necessary to actually build a reasonable GPU. Of course there are issues like adapting the x86 instruction set for use in a GPU, getting all of the cores to communicate with one another and actually keeping all of these execution resources busy - but this design experiment showed that it was possible.

Thus Larrabee was born.

Index Not Quite a Pentium, Not Quite an Atom: The Larrabee Core
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  • iop3u2 - Monday, August 04, 2008 - link

    First of all it's called d3d not directx.

    Secondly you seem to imply that direct3d/opengl will cease to exist at some point if larrabee succeeds. I thinks you don't quite get what they are. They are APIs. Larrabee won't make programming APIless. Are you serious anand or what?
    Reply
  • The Preacher - Tuesday, August 05, 2008 - link

    It could make programming D3D/OpenGL-less for programs/PCs that exploit Larrabee. And if the share of such programs/PCs increases, the share of competing solutions logically decreases and might eventually vanish (although not anytime soon). Reply
  • iop3u2 - Tuesday, August 05, 2008 - link

    Just because you can for example write a c program without the c lib it doesn't mean that people follow that road. It's all about what programmers will choose to do.

    Also, even if they do vanish there will still be a need for an api. So there will either be a new api or they won't vanish. Both situations make no difference whatsoever to the fact that larrabee will always need api implementations.
    Reply
  • ZootyGray - Tuesday, August 05, 2008 - link

    right - and I will put hotels on boardwalk and park place :)

    I used to own an 815chipset - it was like version 14 or whatever so it didn't suk as bad as some of the earlier ones - but it did blow up - I think pixelated FarCry and Doom3 really killed it. But o sure, the software fixes and bubblegum patches made it good, for a while. I really do think I am going to wait for this just so I can watch the lineups of returns - or read the funny forums posts of sheep seeking help - baaaahaha :) The best part is that it doesn't exist - delay, postpone - kinda like the 64bit chip also. Maybe later, maybe. But the ads invade the livingroom.
    Make sure you keep yer getouttajailfree card - receipt.
    Ummm let's see: I think I will buy this one!

    Reality is that 4870x2 is on deck. Not 'rumour and sigh'. I just know there will be a 16page article on that - not!
    Reply
  • Pok3R - Monday, August 04, 2008 - link

    Larrabee means good news for consumers, and definitely bad news for nvidia. Maybe the worst in decades...with AMD and Ati having enough human resources now to face it, and Nvidia having nothing but bad policies and falling stocks despite good $elling numbers...

    The future, today, is definitely Intel vs AMD/Ati.
    Reply
  • initialised - Monday, August 04, 2008 - link

    a miniature render farm (you know like they use to make films like Hulk and WALL-E) on a chip. Lets hope AMD and nVidia can keep up. Reply
  • ZootyGray - Monday, August 04, 2008 - link

    Really? Guess again. There is NOT anything to keep up to.

    I do not accept that the grafx loser in the industry is going to simply become numero uno overnight.

    You really think that nvidia and ati have been sleeping for decades?

    Supporting the destruction of ntel's only competitors leaves us at the mercy of a group that's already been busted for monop and antitrst.

    Well written article? Of course, but I think it's like you are all fished in on many fronts. Nothing is really known except spin. This is beachfront property in the desert.

    There's nothing to watch except what we usually watch - released hardware benchmarks.

    I tell you AMD is going to be the cpu of choice in a few months when the truth about the bias in the benchies is revealed. And try - try real hard - to imagine ati+amd creating the ultimate cpu+gpu powerhouse. ntel needs this hype because I am not the only one with vision here. they are rich and scared, for now.

    but such talk seems to be frowned upon - so let's all cheer for the best grafx manufacturer - ntel = kkaakk! sorry to offend, so many of you just might be lost in the paid mob. so just watch and you will see for yourself- no need to believe me. I really know almost nothing - but I am free to see for myself. sorry to offend - I just can't cosign bs. but that's just me and a very few other posters here who have also been criticized. watch and see for yourself. watch...
    Reply
  • Mr Roboto - Monday, August 04, 2008 - link

    I'd have to agree with the skeptics here. While the article is well written and informative (What AnandTech articles aren't?) it's purely speculation that Intel can get all of the variables right. How does a company that hasn't made a competitive GPU since the days of the 486 suddenly jump to Nvidia and ATI GPU type levels on their first try, never mind surpassing them. It's absolutely absurd to think that these chips are going to replace GPU's in terms of performance. I believe Larrabee will kick the shit out of Intel's own IGP but then again that's not much of a feat.

    Again I have to agree with previous posters that Intel just isn't that innovative. Even as I speak their are many lawsuits pending against Intel, most of them having to do with accusations of stolen IP that were used to design the Core2Duo. Antitrust suits aside, it's clear that Intel is similar to MS in that they just bully, bribe or outright steal to get ahead then pay whatever fines are levied because in the end they can never fine them enough to not make it worthwhile for Intel or MS to break the law.

    The 65nm Core2Duo is amazing. The 45nm E8400 I just bought is even more so. However the more I think about Intel's past failures as well as how they operate as a company the more far fetched this whole thing becomes.

    IMO they should have tried to compete in the dedicated GPU market before trying something like this. From a purely marketing standpoint Intel and graphics just don't go together. To come in to a new field in which they are unproven (I would bet Intel executives believe that building IGP's have somehow given them experience) and make outrageous claims such as the GPU is dead and Intel will now be the leader, is absurd.
    Reply
  • JarredWalton - Tuesday, August 05, 2008 - link

    I think a lot of you are missing the point that we fully understand this is all on paper and what remains to be seen is how it actually pans out in practice. Without the necessary drivers to run DirectX and OpenGL at high performance, this will fail. How many times was that mentioned? At least two or three.

    Now, the other thing to consider is that in terms of complexity, a modern Core 2 core is far more complex to design than any of the GPUs out there. You have all sorts of general functions that need to be coded. A GPU core these days consists of a relatively simple core that you then repeat 4, 8, 16, 32, etc. times. Intel is doing exactly that with Larrabee. They went back to a simple x86 core and tacked on some serious vector processing power. Sounds a lot like NVIDIA's SP or ATI's SPU really.

    Fundamentally, they have what is necessary to make this work, and all that remains is to see if they can pull off the software side. That's a big IF, but then Intel is a big company. We have reached the point where GPUs and CPUs are merging - CUDA and GPGPU aim to do just that in some ways - so for Intel to start at the CPU side and move towards a GPU is no less valid an approach than NVIDIA/ATI starting at GPUs and moving towards general purpose CPUs.
    Reply
  • Midwayman - Monday, August 04, 2008 - link

    I not interested in the graphics so much. It may or may not compete with the the top end nvidia chips if released on time. What is more interesting is if this can easily be integrated as a general purpose cpu for non-graphics work? Imagine getting a benefit out of your gpu 100% of the time, not just when you're gaming. I know its possible to use more modern GPU's this way if you code specifically for them, but with its x86 architecture, it might be able to do it without having apps specifically coded for it.
    Reply

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