[Beowulf] Moores Law is dying

Jon Forrest jlforrest at berkeley.edu
Tue Apr 14 18:09:40 EDT 2009


Joe Landman wrote:

> Imagine you are a processor, and you have written to a location in ram. 
>  So now your cache line is dirty, and waiting in queue to be flushed 
> out.  In your parallel program, along comes someone else who really, 
> really wants to read that cache line.  Ok, so this forces you to a) 
> flush it now, b) mark that line as clean.  Then the next CPU gets that 
> cache line, does it's write, and whammo, some other CPU wants to do the 
> same thing to it as you did.

But this wouldn't happen in the scenarios you describe
because text is read-only. There would be no updaters or writers
or any kind of contention. The text pages would have to get filled
at image activation time, and maybe later if text section page
faults occur. But, these activities would be done by the OS once
per page.

> I know you might postulate that 32 bit text is effectively the CS 
> equivalent of "C" in physics ... you may approach it asymptotically, but 
> never actually get there ... but unlike in physics, there isn't really 
> an underlying reason why you might not get there.

The underlying reason in this case is complexity.

Jon


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