Re: [Caml-list] SMP multithreading

[Gerd Stolpmann <info@gerd-stolpmann.de>]

Am Dienstag, den 16.11.2010, 22:35 +0200 schrieb Eray Ozkural:
> 
> 
> On Tue, Nov 16, 2010 at 7:04 PM, Gerd Stolpmann
> <info@gerd-stolpmann.de> wrote:
>         Am Montag, den 15.11.2010, 22:46 -0800 schrieb Edgar
>         Friendly: 
>              * As somebody mentioned "implicit parallelization": Don't
>         expect
>                anything from this. Even if a good compiler finds ways
>         to
>                parallelize 20% of the code (which would be a lot), the
>         runtime
>                effect would be marginal. 80% of the code is run at
>         normal speed
>                (hopefully) and dominates the runtime behavior. The
>         point is
>                that such compiler-driven code improvements are only
>         local
>                optimizations. For getting good parallelization results
>         you need
>                to restructure the design of the program - well, maybe
>                compiler2.0 can do this at some time, but this is not
>         in sight. 
> 
> I think you are underestimating parallelizing compilers. 

I was more citing Amdahl's law, and did not want to criticize any effort
in this area. It's more the usefulness for the majority of problems. How
useful is the best parallelizing compiler if only a small part of the
program _can_ actually benefit from it? Think about it. If you are not
working in an area where many subroutines can be sped up, you consider
this way of parallelizing as a waste of time. And this is still true for
the majority of problems. Also, for many problems that can be tackled,
the scalability is very limited.

Gerd 
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