GPGPU

Would you like to buy a vowel? Pick "j", it's a good one. So what if it's not a vowel. My blog, my rules. Lately I had a major crash on all things "J". Which is why I moved to Japan.

It's part of my "Most expensive places in the world" tour, unlikely coming to a city near you. I lived in New York City, Oslo, London and now Tokyo. I'm going to write a book about all of that entitled "How to see the world while having no money whatsoever". It's really more of a pamphlet. I have one sentence so far "Find good friends" and the rest are just pictures of black (and they capture the very essence of it).

José Fonseca helped me immensely with the move to Japan, which was great. Japan is amazing, even though finding vegetarian food is almost like a puzzle game and trying to read Japanese makes me feel very violated. So if you live in Tokyo your prayers have been answered, I'm here for your pleasure. Depending on your definition of pleasure of course.

Short of that I've been working on this "graphics" thing. You might have heard of it. Apparently it's real popular in some circles. I've been asked about GPGPU a few times and since I'm here to answer all questions (usually in the most sarcastic way possible... don't judge me, bible says not to, I was born this way) I'm going to talk about GPGPU.

To do GPGPU there's ATI's CTM, NVIDIA's Cuda, Brooke and a number of others. One of the issues is that there is no standard API for doing GPGPU across GPU's from different vendors so people end up using e.g. OpenGL. So the question is whether Gallium3D could make such things as scatter reads accessible, without falling back to using vertex shaders or vertex shaders/fragment shaders combination to achieve them.

Core purpose of Gallium3D is to model the way graphics hardware actually works. So if the ability to do scatter reads is available in modern hardware then Gallium3D will have support for it in the API. Now having said that, it looks like scatter reads are usually done in a few steps, meaning that while some of the GPGPU specific api's expose it as one call, internally number of cycles passes as few instructions are actually being executed to satisfy the request. As such this functionality is obviously not the best to expose in a piece of code which models the way hardware works. That functionality one would implement on top of that api.
I do not have docs for the latest GPU's from ATI and AMD so I can't say what it is that they definitely support. If you have that info let me know. As I said the idea being that if we'll see hardware supporting something natively then it will be exposed in Gallium3D.

Also you wouldn't want to use Gallium3D as the GPGPU api. It is too low level for that and exposes vasts parts of the graphics pipeline. What you (or "I" with vast amount of convincing and promises of eternal love) would do is write a "state tracker". State trackers are pieces of code layered on top of Gallium3D which are used to do state handling for the public API of your choice. Any api layered like this will execute directly on the GPU. I'm not 100% certain whether this will cure all sickness and stop world hunger but it should do, what even viagra never could, for all GPGPU fanatics. The way this looks is a little like this:

This also shows an important aspect of Gallium3D - to accelerate any number of graphical API's or to create a GPU based non-graphics API, one doesn't need N number of drivers (with N being the number of API's), as we currently do. Gallium3D driver (that's singular!) is enough to accelerate 2D, 3D, GPGPU and my blog writing skills. What's even better is that of the aforementioned only the last one is wishful thinking.

So one would create some nice dedicated GPGPU api and put it on top of Gallium3D. Also since Gallium3D started using LLVM for shaders, with minimal effort it's perfectly possible to put any language on top of GPU.

And they lived happily ever after... "Who" did is a detail, since it's obvious they lived happily ever after thanks to Gallium3D.