Nicolas Boulay wrote:
Yep. Why nobody like the idea to keep every thing simple with 4 scalar
core ?
The control and routing hardware for doing vectors is simpler than
doing four scalars at the same time.
No because you need to access easly each vector member.
So only difference, is to manage many core instead of one. But todays Ati and
Nvidia use at maximum 48 shader. So we will have to manage many core in
parrallel.
No, you have misunderstood how the nVidia and ATI GPUs are
designed.
Each of those 48 shader units has a four-way vector ALU.
The management problem is dividing up each vertex of a
triangle, or each fragment within a scan line, to be
assigned to a different shader unit. Each of the shader
units is executing it's own program. It's the same kind
of multiprocessing problem as dividing up, say, SETI or
similar parallel problems across many CPUs.
What we are discussing is how to execute the instructions
WITHIN a single shader unit.
The argument for vectors is that, with todays GPUs, the
majority of the instructions are four-way vector ops to
begin with. It's not like regular C/C++/Java code where
the compiler has to try and identify vector-like sequences.
In shader code, every vector value and vector operation is
explicitly declared/written in the source code, so it's
easy for the assembler/compiler to generate vector ops.
This also makes it easy to translate shaders into SSE or
AltiVec code sequences on conventional CPUs, which is
how various pure software pixel shader implementations
get their performance.
--
Hugh Fisher
DCS, ANU
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