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Intel lifts wraps on next-generation Larrabee: should NVIDIA and ATI be worried?

by Tarinder Sandhu on 4 August 2008, 07:58

Tags: Intel (NASDAQ:INTC)

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It's all about running it on those cores, baby

Software-driven power

Let's think about this for a second. Intel is using a complete x86 CPU architecture, albeit with necessary bolt-ons such as the 16-wide ALU unit, to run graphics. What that really means is that rendering takes place in software. Yup, you've read that right: Larrabee uses massive parallel power to software-run code.

So, after input data has been provided, vertex shading; geometry shading; primitive setup; rasterisation; pixel shading; and blending - the step-by-step building blocks of a modern GPU - are all done in software in Larrabee, rather than, in the main, shading, as it is on current NVIDIA or ATI cards.

Intel reckons that this makes Larrabee fully programmable and far more suited to future workloads, but such an approach comes at the inevitable cost of having developers natively code for Larrabee using a C/C++ API. The 'problem' is somewhat mitigated by the fact that coding shouldn't be too different than writing for x86, which, after all, is what Larrabee is based upon.

Being software-based has other intrinsic advantages too, such as driver-updating for newer APIs when they become available. Kind of like adding microcode for your CPU.

DirectX and OpenGL will be supported, of course, and the traditional rendering pipeline can be run through software, but it's not how Larrabee talks best.

Bin it

No matter how good a VPU-orientated architecture is internally, having lots and lots of usable memory bandwidth is, and always will be, important. We don't know the speed of interface-width of real-word Larrabee, but Sieler did divulge that the architecture uses what Intel terms a binning approach, which saves bandwidth compared to the immediate mode currently employed by GPUs.



Binning is analogous to the tiling approach used by older GPUs, made popular by PowerVR. Sieler explained that a scene is broken down into tiles, say a 128x128 tile for 32-bit depth and colour. The primitives for this tile are then calculated and stored in 'bins' in the external memory. Once required, the bins are emptied and the screen drawn, saving on unnecessary rendering by simply not drawing what you won't see.

Scaling

It's absolutely imperative that Larrabee's performance scales as core counts increase, and Intel is adamant that this is the case, by trotting out the graphic below.



Through several optimisations, including breaking down certain games' engines large vertex buffers - FEAR, for example - into manageable chunks, Intel reckons that there's a near-linear increase in performance as more and more cores are added to the mix.

How is this possible, you might ask? The reasoning, we suppose, lies with the software-driven approach of the rendering - you don't need to add in a commensurate number of ROPs and texture units: the cores (and dedicated logic) do it all.

What we don't know

Intel remains tight-lipped on just how many cores various iterations of Larrabee will ship with. We don't know exactly when it will come to market. How will software-based rendering actually pan out from an efficiency point of view? What about speeds, memory sizes, caches, power requirements? 

What will NVIDIA and ATI have in response? What we do know is that Larrabee is as real as a hangover, but who will be suffering it next year: NVIDIA, ATI, or Intel?

 


HEXUS Forums :: 7 Comments

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should NVIDIA and ATI be worried?
No, but TimeLogic should be.
If this approach takes off, then NVIDIA ought to be worried as they can have no direct response. AMD already have a similar base in the pipeline, but NV currently have neither the license or the partner to reply.

It's going to be a case of 2 heavy-weights having a tug-o-war contest in order to determine which approach wins out by the looks of it.

The real winner here (and looking longer term) is the budget builders.

Have to say, it's nice to see some innovation again. We've got an interesting few year coming up.
with intel basing it on a modified old architechture, does this mean that it could be cheap to reproduce?
Biscuit
with intel basing it on a modified old architechture, does this mean that it could be cheap to reproduce?
If you have a license for x86, maybe. Guess what nVidia don't have.
Techncially speaking, both AMD and nVidia do a ‘software’ approch also. The drivers compile OpenGL and DX calls into a binary language their GPUs understand. Whether the x86 approch pays off for Intel remains to be seen, either way this is looking to be the best solution for a ‘fused’ CPU and GPU unit in the long term.