[Beowulf] Moores Law is dying

Jon Forrest jlforrest at berkeley.edu
Tue Apr 14 14:41:46 PDT 2009

Joe Landman wrote:

> ... so I see you have never used an interprocedural analysis (-ipa) 
> switch :)
> Allows you do do things like, I dunno, inline one whole routine inside 
> another ...

I've never used this but from your description I don't
see how it leads to larger text sizes at runtime. After all, if you have
routine A which is 10 bytes, and routine B which is 20 bytes,
it would seem that they collectively take 30 bytes no matter
if they stand alone or one inside the other. I might not
be understanding this right, though.

> Usually leads to much larger program text sizes.
> This said, I have seen very large programs from RISC days hitting well 
> more than 1 GB of text.  I haven't played with any recently though.

Let's say this is about right. Do you see such programs getting
even larger in the future?

>> Why is sharing expensive in performance? It might take a little
>> overhead to setup and manage, but why is having multiple virtual
>> addresses map to the same physical memory expensive?
> Contention.  Memory hot spots.  Been there, done that.  We are about to 
> do this all over again (collectively).

Naively I would think that text memory hot spots would be a good
thing, because then all the benefits of caching would kick in.
There would be no cache coherence overhead since text is read-only.
Why is this a bad thing?

Jon Forrest
Research Computing Support
College of Chemistry
173 Tan Hall
University of California Berkeley
Berkeley, CA
jlforrest at berkeley.edu

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