[Info-vax] Intel previews new Itanium "Poulson" processor

[John Wallace]

On Feb 24, 8:34 pm, JF Mezei <jfmezei.spam... at vaxination.ca> wrote:
> Rich Jordan wrote:
> >http://tinyurl.com/6ch9wj5   (hothardware.com)
>
> What does "Intel previews Poulson" actually mean ?
>
> Are they just releasing general specs and they have yet to implement all
> of that ?
>
> Or have they already built sample chips that seem to work ?
>
> In other words, are we talking months or years before this makes it into
>  customers' machines ?
>
> Also, just so I understand correctly. If they have 12 instead of 6
> execution units, is it correct to state that a program compiled for
> Tukwila, will still use only 6 units on Poulson, leaving the remaining 6
> iddle ?

"a program compiled for Tukwila, will still use only 6 units on
Poulson, leaving the remaining 6 iddle ?"

That was the general EPIC principle. The compiler must see the
parallelizable stuff in a given block of code and construct bundles of
instructions accordingly. If the execution environment widens, a
recompile with the matching new compiler will be needed to make use of
the VVLIW capabilities (previously IA64 was a Very Long Instruction
Word, now it's a VVLIW). Some reports are quoting Intel as saying that
users should not have to recompile to take advantage of the 12-
instruction issue, which is a rather strange thing to say about
different generations of EPIC machines and compilers.

Subject to confirmation or correction by someone who really knows
about EPIC and compilers, obviously.

Far more details on superscalar vs EPIC than I can recite can still be
found in the Alpha vs IA64 whitepaper which can still be found at:
http://www.cs.trinity.edu/~mlewis/CSCI3294-F01/Papers/alpha_ia64.pdf

On a slightly different tack, IA64 implementations have been, and
still are, basically big fat on-chip caches with a weird processor (or
several weird processors) attached. In the case of Poulson, the
advertised performance is delivered by implementing some 50MB of
cache, mostly L3 (obviously), and if you see a picture of the chip
you'll see the cache takes up about the same space as the processing
(unlike say a modern AMD64 chip with rather less cache).

Depending on whose reports you believe, the old old story (never
backed up by much real evidence that I saw) about "improved RAS with
Itanium" is back again with Poulson too. If anyone out there now has
any hard evidence of Poulson's RAS features not available in modern
AMD64 implementations and their Intel x86-64 clones, Intel's IA64
people (and me) would be delighted for you to share it. On the other
hand I'd also be interested in anyone from Intel saying "it's just the
same as Xeon really". They can't have it both ways.