Re: Help clear up a misconception about SMP systems

Steven N. Hirsch (shirsch@adelphia.net)
Fri, 9 Oct 1998 21:16:45 -0400 (EDT)


On Fri, 9 Oct 1998, Alex Buell wrote:

> Hi guys,
>
> Can you help clear up a misconception about SMP that I have at the
> moment?
>
> When two or more processors come into play, what is the increase rate of
> processing over a single processor? Is does it works out as 100% increase
> over that of a single processor or is it limited by other factors such as
> caching, disk i/o or whatever?
>
> I'm guessing it's a 100% increase.

In a perfect world that's what would happen. In reality, the speedup
curve flattens with larger n. In one of the more interesting courses of
my recent CS studies, we spent a semester analyzing this numerically for a
bunch of different architectures.

The high point was getting remote access to a CM-5 supercomputer (1024
Sparc CPU's IIRC) for benchmarking simultaneous linear equation solutions
in Fortran-90. Toto, I don't think we're in Kansas anymore...

But, yes, communication latencies prevent anything like linear scaling.

Steve

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