[radeonhd] Re: Updated R5xx 3D Programming Guide

[Jerome Glisse]

On Sat, 05 Apr 2008 15:58:45 +0200
Syren Baran <sbaran at gmx.de> wrote:

> 
> Shouldt we start with the first thing first?
> That would be the assembler, just turning the opcodes into binary form.
> Well, and some way to transfer the binary to the gpu.
> That shouldnt be much of a hassle (the command set is pretty limited,
> luckily).
> Still have some reading in those docs to do, but i think i could write a
> simple assembler.
> 
> Syren
> 

GPU are not a CPU, programming them is far more complexe than programming
CPU, you have to handle things that CPU do for you. For instance you have
setup how data are routed to GPU. Also GPU are not intended to run usual
program, ie program with if, swith, jump, and others alike instructions.
GPU could handle such instructions but your often limited in the depth you
can have (for instance no more than 16 nested for, if statement). I think
a good analogy is the cell processor where for OS they have a unit which
is just like a CPU while stream unit look like a GPU.

So any application which want to efficiently use a GPU need to be cut btw
the core application which would run on a "normal" CPU and a specific part
intended to run on GPU. This part need to be designed with GPU specificity
in mind. This why i don't think a compiler, at least in the sense you seems
to think about, is of any use with a GPU. I am confident that through gallium
we will be able to offer a sane api to enable application to properly use
horse power of GPU. Note that similar problematic exist with multi-cpu, you
can't really take advantage of multiple CPU only with a specific compiler,
your application have to designed for multi-CPU.

Cheers,
Jerome Glisse <glisse at freedesktop.org>