Clearing Up Misconceptions about CUDA and Larrabee

[Rob Williams]

The non-gaming GPU games are heating up, and Intel is hot on NVIDIA's tail, but can you predict who will reign surpreme in two-years time?

Both Intel and NVIDIA have lots to say about their respective GPU architectures, as well as the competition's. Partly because of this, there are numerous misconceptions floating around about both Larrabee and CUDA, so we decided to see if we could put to rest a few of the most common ones.

You can read the full article here and discuss it here.

[Kougar]

Great article!

Hm, tough call. I can't pretend to truly know anything about the coding and compiling and who's code is more closely related to C, but Anand's article really does put Larrabee into a positive light in my opinion.

Whatever NVIDIA may say, their "shaders" are not fully programable and this does constrain performance tuning to an extent, and it makes for some large limitations. As NVIDIA themselves pointed out Intel uses software to manage threads, assign workloads, and generally uses their software driver to replace what NVIDIA and ATI have always done with pure hardware.

The biggest advantage to this, besides that it could be either a huge boon or a huge performance hit, is if I understand things correctly Intel can update their driver to change their "DX10" Larrabee into a "DX10.1" or "DX11" or "DX12" GPU. In effect all of this mess about which DX version is neccesary becomes moot. Even better, game developers can write their games to use whatever they want, since if the Larrabee driver can take the code and convert it out into something that runs on the hardware. So if I understood things right, Intel is significantly less constrained with their approach.

The proof will be in the pudding though, and Larrabee's advantages mean little if it can't deliver the performance to make them worthwhile. Thankfully Anandtech pointedly mentioned Intel's GPU driver team is busy working on those IGP drivers, while a new team is actually working on the Larrabee drivers. I think we all know Intel's poor track record with IGP drivers and missing/delayed integrated graphics features.

[Rob Williams]

I do think it's obvious that NVIDIA cards are not as programmable as Larrabee will be, especially given that Larrabee is essentially a CPU with multiple x86 cores designed for specific workloads. NVIDIA said otherwise, and I'm sure they'll claim that for a while. If I had the ability to go out and test, I'd do so. I think I need to get in contact with current CUDA developers, and pick their brains a little bit.

Originally Posted by Kougar

The biggest advantage to this, besides that it could be either a huge boon or a huge performance hit, is if I understand things correctly Intel can update their driver to change their "DX10" Larrabee into a "DX10.1" or "DX11" or "DX12" GPU.

Yes, exactly, they'd be able to do that without issue. Larrabee just needs to be fast enough to handle the increased work.

As for the GPU driver and the like, I agree. Intel has a completely different team working on Larrabee, so to assume that their driver will suffer the same humiliation as their IGP ones (which I can vouch for as being less-than-stellar) would be extremely foolish. Intel has the money, the manpower and some incredibly smart people working on Larrabee. It's not going to suffer due to a lackluster GPU driver, I'm sure of that much.

[Kougar]

Well Intel is great with hardware, but I won't rule it out just yet that they might have a few issues to iron out with drivers, especially since this is the first of a kind for them. And their last attempt with a discrete GPU didn't really work out so well. I will just have to see how the "new" Intel handles this one.

Their approach to the entire software/hardware design is simply brilliant though...

Another advantage would be multi-GPU scaling. Since it is all down via software the workload can be evenly distributed across all the available Larrabee cards or "multi-cores" with near perfect scaling. In effect Intel has the ability to skip the multi-GPU growing pains NVIDIA and ATI have had to work through the hard way...