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
Programming for Larrabee
The Larrabee programming model is what sets it apart from the competition. While competing GPU architectures have become increasingly programmable over the years, Larrabee starts from a position of being fully programmable. To the developer, it appears as exactly what it is - an arrangement of fully cache coherent x86 microprocessors. The first iteration of Larrabee will hide this fact from the OS through its graphics driver, but future versions of the chip could conceivably populate task manager just like your desktop x86 cores do today.
You have two options for harnessing the power of Larrabee: writing standard DirectX/OpenGL code, or writing directly to the hardware using Larrabee C/C++, which as it turns out is standard C (you can use compilers from MS, Intel, GCC, etc...). In a sense, this is no different than what NVIDIA offers with its GPUs - they will run DirectX/OpenGL code, or they can also run C-code thanks to CUDA. The difference here is that writing directly to Larrabee gives you some additional programming flexibility thanks to the GPU being an array of fully functional x86 GPUs. Programming for x86 architectures is a paradigm that the software community as a whole is used to, there's no learning curve, no new hardware limitations to worry about and no waiting on additional iterations of CUDA to enable new features. You treat Larrabee like you treat your host CPU.
Game developers aren't big on learning new tricks however, especially on an unproven, unreleased hardware platform such as Larrabee. Larrabee must run DirectX/OpenGL code out of the box, and to do this Intel has written its own Larrabee native software renderer to interface between DX/OGL and the Larrabee hardware.
In AMD/NVIDIA GPUs, DirectX/OpenGL instructions map to an internal GPU instruction set at runtime. With Larrabee Intel does this mapping in software, taking DX/OGL instructions, mapping them to its software renderer, and then running its software renderer on the Larrabee hardware.
This intermediate stage should incur a performance penalty, as writing directly to Larrabee is always going to be faster. However Intel has apparently produced a highly optimized software renderer for Larrabee, once that's efficient enough so that any performance penalty introduced by the intermediate stage is made up for by the reduction of memory bandwidth enabled by the software renderer (we'll get to how this is possible in a moment).
Developers can also use a hybrid approach to Larrabee development. Larrabee can run standard DX/OGL code but if there are features developers want to implement that aren't enabled in the current DirectX version, they can simply write those features that they want in Larrabee C/C++.
Without hardware it's difficult to tell exactly how well Larrabee will run DirectX/OpenGL code, but Intel knows it must succeed on running current games very well in order to make this GPU a success.
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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?