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Re: [f-cpu] x86-64 long article

hi !

nico wrote:


On Fri, 24 Jan 2003 22:00:56 +0100 (CET)
devik <devik@cdi.cz> wrote:
:) If you want more than 8 fcpu in a single machine use multicore
chip ! :)

Hmm .. Their Opteron or NUMA in general is good because
of independent memory access.
With multicore and limited pin count what to do ?
Share the L2/ L3 caches. It's a whole new way of doing optimising
(tight multithreading) but it could work nice.

Alright, but then, when the core needs to communicate, all the pins' bandwidth will be saturated.
Look at the Opteron's 1000 pins and ask yourself how much this will cost ....
It's the OLD problem of a system's "cut" and the non linear ratio between the gate count
and the pin count .... this is my major problem.
I believe that this will put a limit to 4 FC0s on a single chip.
Looking at other numers, i think that half of the die's surface will contain L2 and L3 and it's
good, despite the high fabrication cost. But adding too many cores will suffocate the whole chip.
On top of that, a lot of software will need major rewrites to include finer multithreading.

Furthermore, even if we run at only 100MHz on an old technology, this will be an incredible
success for freedom, for the "alternate computing" world and for us in general. Extreme
performance will come naturally later, we only have to make one core work and others
will want to join. So let's concentrate on the critical things, as we will be able
to play with top technology later :-)

bon week-end,

devik

YG

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