[Linux-ia64] Itanium gets supercomputing software

Greg Lindahl lindahl at keyresearch.com
Wed Apr 16 17:13:17 EDT 2003


On Tue, Apr 15, 2003 at 10:08:20AM -0500, Richard Walsh wrote:

>  I do think EPIC is valuable on several scores.  First, it frees real 
>  estate on the chip by reducing/eliminatin out-of-order execution hardware 
>  allowing for larger caches (3 MB on chip today) and future additional 
>  functional unit parallelism or additional cores on the same chip.

Nope. You can look up the size of the EPIC core; it's not small. It
only can have 3 MB on chip cache today because it's the largest
possible chip you can build. That cache is much larger than the
processor core.

>  Second, it allows generated code to be tuned to the width (number
>  of simultaneous instructions alowed) of the processor.

Good compilers have instruction scheduling which do this on other
chips. While it's easier to understand what's going on when the
parallelism is explicit, you'll find that scientific codes get a
pretty amazing number of instructions per cycle on quite a few cpus
and compilers.

The promise of EPIC was that it would be eaiser to do this. You'll
have to talk to some compiler people to find out if they think it was
easier. The ones I know hate EPIC was a passion.

-- greg

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