[mdlug] Parallella: A Supercomputer For Everyone by Adapteva — Kickstarter

[Michael Mol]

On Fri, Oct 12, 2012 at 4:01 PM, Garry Stahl <tesral at wowway.com> wrote:
> On 10/12/2012 01:54 AM, Aaron Kulkis wrote:
>
>>> If you're paying attention to the things necessary to squeeze every
>>> last {int|fl}op of performance from a given modern CPU, you'll find
>>> that you need to keep several different variants of your code handy to
>>> account for difference in execution speed or stall behavior for
>>> individual instructions across different brands of CPUs--even
>>> different models within the same brand!
>
>
> Amgia programers did exactly that.  Programs like ImageFX would have
> executables for 68k 020 030 and 040 processors depending on what you had in
> your Amiga you picked the right one to install.  Installers would ask you
> what your hardware setup was.

So, three images, written and tuned in assembly. Sounds like a lot of
work went into it.

That matrix would be far, far more complex today:

(Some of these questions become irrelevant if more recent technologies
are available; the earlier tech could be assumed present, or could be
presumed obsolete.)
Is floating point available in hardware?
Is mmx available?
Is 3dnow! available?
Is sse available? (obviated if a later version is available, or if
64-bit is available)
Is sse2 available?
Is sse3 available?
Is sse4 available?
Is sse4.1 available?
Is avx available?
Is avx2 available?
Is the machine 32-bit or 64-bit?

And that's before you get into questions of individual CPU expense
(we're talking about high-efficiency, count-every-cycle code, right?)
for each instruction, where the CPU expense will differ from brand to
brand, model to model or even stepping to stepping!

Also, remember what I said about earlier technologies being assumed
present if later technologies are present? With Intel (the brand, not
necessarily the architecture) processors, features appear and
disappear depending on the target market.

That's a *ton* of variance to pay attention to.

-- 
:wq