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
Shading Tiles with Larrabee (With Extra Goodies)
We've looked at the way we get from triangles to tiles a bit. Intel shared a bit of a deeper look at how they are organizing their software render on the back end (from the tiles to the screen).
First, full tiles are fetched into cache. Reaching back to understanding how threads are organized, we can have four simulatneous threads running, and keeping all four of these threads working on parts of the same data set will help keep from thrashing the cache. Intel has indicated that the organization of software rendering threads durring back end processing will be as illustrated in the following diagram.
We see that there are 4 thread with one acting as a fragment setup thread which takes all the geometry in the tile and creating fragments from it for further processing. There are then three work threads that take ready fragments (or more like groups of 4 to 16 fragments each -- just a guess for now), check to see if they are visible, shade the fragment (load textures and run associated shader programs), perform any antialiasing and handle blend operations. Remember that this is all just software. It doesn't have to happen this way, but this is the direction Intel had indicated they have taken for their software renderer and for implementing DirectX and OpenGL.
By the time Larrabee arrives as a product, I certainly hope that we'll get a deeper look at what's really going on under the hood and how everything is organized. I suppose the holy grail would be if Intel decides to release it's software renderer source code to the general public, but even if we don't get that we'll try to get information on all the different types of threads, fibers and strands that are spawned to handle all the different steps in the rendering pipeline.
Beyond just taking traditionally fixed function features and running them in software, Intel can do a few cool things that are difficult with current hardware. In order to get layered transparency to work right, game developers need to sort objects and polygons as best then can from back to front (rendendering the furthest object to the screen first). If this isn't done, we can get some funky artifacts that don't look right. Since all this is software, Intel can do a few cool things to help developers out: where there is transparency, they can maintain an list of fragments at that screen position with z info attached rather than just blending or discarding data immediately. This way, when the blend is performed, it can be done properly no matter what order the geometry was rendered in.
Additionally, Irregular Z-buffers (which can allow for the creation of screen resolution shadow maps to avoid artifacts) and other complex data structures that can't easily or efficiently be implemented on traditional GPU hardware can be implemented on Larrabee without a second thought. Some of this stuff Intel can do on the back end to improve quality and performance in all applications, but some of it really won't make a difference until developers start to embrace the new architecture. And it's not just doing new things -- there are probably plenty of devs out there who would love to entirely skip the step of sorting their polygons when dealing with layered transparency.
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Shinei - Monday, August 4, 2008 - link
Some competition might do nVidia good--if Larrabee manages to outperform nvidia, you know nvidia will go berserk and release another hammer like the NV40 after R3x0 spanked them for a year.Maybe we'll start seeing those price/performance gains we've been spoiled with until ATI/AMD decided to stop being competitive.
Overall, this can only mean good things, even if Larrabee itself ultimately fails.
Griswold - Monday, August 4, 2008 - link
Wake-up call dumbo. AMD just started to mop the floor with nvidias products as far as price/performance goes.watersb - Monday, August 4, 2008 - link
great article!You compare the Larrabee to a Core 2 duo - for SIMD instructions, you multiplied by a (hypothetical) 10 cores to show Larrabee at 160 SIMD instructions per clock (IPC). But you show non-vector IPC as 2.
For a 10-core Larrabee, shouldn't that be x10 as well? For 20 scalar IPC
Adamv1 - Monday, August 4, 2008 - link
I know Intel has been working on Ray Tracing and I'm really curious how this is going to fit into the picture.From what i remember Ray Tracing is a highly parallel and scales quite well with more cores and they were talking about introducing it on 8 core processors, it seems to me this would be a great platform to try it on.
SuperGee - Thursday, August 7, 2008 - link
How it fit's.GPU from ATI and nV are called HArdware renderers. Stil a lot of fixed funtion. Rops TMU blender rasterizer etc. And unified shader are on the evolution to get more general purpouse. But they aren't fully GP.
This larrabee a exotic X86 massive multi core. Will act as just like a Multicore CPU. But optimised for GPU task and deployed as GPU.
So iNTel use a Software renderer and wil first emulate DirectX/OpenGL on it with its drivers.
Like nv ATI is more HAL with as backup HEL
Where Larrabee is pure HEL. But it's parralel power wil boost Software method as it is just like a large bunch of X86 cores.
HEL wil runs fast, as if it was 'HAL' with LArrabee. Because the software computing power for such task are avaible with it.
What this means is that as a GFX engine developer you got full freedom if you going to use larrabee directly.
Like they say first with a DirectX/openGL driver. Later with also a CPU driver where it can be easy target directly. thus like GPGPU task. but larrabee could pop up as extra cores in windows.
This means, because whatever you do is like a software solution.
You can make a software rendere on Ratracing method, but also a Voxel engine could be done to. But this software rendere will be accelerated bij the larrabee massive multicore CPU with could do GPU stuf also very good. But will boost any software renderer. Offcourse it must be full optimised for larrabee to get the most out of it. using those vector units and X86 larrabee extention.
Novalogic could use this to, for there Voxel game engine back in the day's of PIII.
It could accelerate any software renderer wich depend heavily on parralel computing.
icrf - Monday, August 4, 2008 - link
Since I don't play many games anymore, that aspect of Larrabee doesn't interest me any more than making economies of scale so I can buy one cheap. I'm very interested in seeing how well something like POV-Ray or an H.264 encoder can be implemented, and what kind of speed increase it'd see. Sure, these things could be implemented on current GPUs through Cuda/CTM, but that's such an different kind of task, it's not at all quick or easy. If it's significantly simpler, we'd actually see software sooner that supports it.cyberserf - Monday, August 4, 2008 - link
one word: MATROXGuuts - Monday, August 4, 2008 - link
You're going to have to use more than one word, sorry... I have no idea what in this article has anything to do with Matrox.phaxmohdem - Monday, August 4, 2008 - link
What you mean you DON'T have a Parhelia card in your PC? WTF is wrong with you?TonyB - Monday, August 4, 2008 - link
but can it play crysis?!