Re: Why warning on configure --enable-openmp ?

[Alois Schloegl]

On 05/04/11 15:41, John W. Eaton wrote:
> On  3-May-2011, address@hidden wrote:
>
> | I'm trying to use OpenMP within some mex-files, When configuring octave
> | with openmp enabled,
> |    ./configure --enable-openmp
> | one gets the following warning:
> |
> | configure: WARNING: You used the EXPERIMENTAL --enable-openmp option.
> | configure: WARNING: Are you sure that is what you want to do?
> | configure: WARNING:
> | configure: WARNING: This option enables experimental SMP multithreding
> | configure: WARNING: code that has had very little testing. There is no
> | configure: WARNING: certainity that the results returned by Octave with
> | configure: WARNING: this option enabled will be correct.
> |
> | However, there is no single
> |         #pragma omp
> | within the whole source code of octave - OpenMP is obviously not used by
> | the core of Octave. Therefore, I'm wondering what this warning is about?
> | Should this warn about the possibility that some library might give wrong
> | results? What is the problem the warning tries to warn about ?
>
> The --enable-openmp configure option just checks for a compiler flag
> and libraries.  I don't think anything else was ever done with it.
> Unless someone wants to take on the task of making this actually do
> something useful, then maybe it should just be removed?
>
> jwe


Yes, I think this warning should be removed. It is detrimental to the 
use of openmp with in Octave. At first I was afraid of using openmp - 
because of this. And it took me some time to investigate further.

I'm using openmp within some core functions of the NaN-toolbox 
(sumkskipn_mex and covm_mex), and it shows competitive results of Octave 
against the proprietary alternative. Actually, I see that Octave is up 
to 15% faster (in CPU time as well as real time) than ML. That's a 
result, I do not see without openmp. And as far as I can see, there are 
no detrimental effects. Therefore, I suggest to go even a step further 
and --enable-openmp in the default configuration.


Alois