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

[Aaron Kulkis]

Michael Mol wrote:
> 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.
>

GCC compiler can custom-tune for all of that.