[Beowulf] Moores Law is dying

Joe Landman landman at scalableinformatics.com
Tue Apr 14 17:11:53 EDT 2009


Jon Forrest wrote:
>> that compilers will never try to unroll code at that level, even when
>> enormous memory systems are commonplace?
> 
> Again, the enormous memory systems you mention consist mostly
> of enormous amounts of data, not text.
> 

... 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 ...

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.

[...]

>> and "the program" being run on a multitasking
>> operating system is the union of all "sub" programs being run on the
>> system, with or without shared libraries (sharing is expensive in
>> performance, remember -- we do it to save memory because it is a scarce
>> resource).
> 
> 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).



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Joseph Landman, Ph.D
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