Re: [boost] GSoC Ideas: Optimizing Boost libraries for multi-core machines

From: Jens Seidel (jensseidel_at_[hidden])
Date: 2008-04-02 15:46:46

On Wed, Apr 02, 2008 at 12:21:43PM -0500, Stephen Nuchia wrote:
> In my experience, there are very few instances where parallelism can be
> usefully concealed behind a library interface.  OpenMP has very high
> overhead and will help only for very long-running functions -- at least
> under Microsoft's compiler on x86 and x64 platforms.  Algorithms that
> are likely to be applied to very large datasets could have the OMP
> pragmas inserted optionally but they would need to be protected by
> #ifdef logic (or given distinct names) because otherwise the overhead

Does #ifdef around #pragma omp indeed work? At least
#define PARALLEL #pragma omp
and using PARALLEL does not work.

> will destroy programs that make more frequent calls on smaller datasets.
 
> I must also repeat the age-old, time-tested capital-T Truth about
> optimization: if you do something that is not suggested by and validated
> against careful analysis of realistic use cases you are wasting your
> time.  I strongly advise you to not start hacking without solid data.

The compression algorithms (zip, ...) (part of the streams library?)
would be a very good candidate. I once tested a parallel bzip2 algorithm
and it scales really well.

Jens