Re: [Help-gsl] OpenMP and GSL ?

[Maxime Boissonneault]

Hello,
I realize that my answer never reached the list, so here it is once again.

Jochen Küpper a écrit :
> Hi Maxime,
>
> > I would like to know if there is any plan in adding OpenMP support to 
> > GSL ?
>
> I had looked into this myself before with limited success.
> Most importantly, however, I just didn't find time to get serious 
> about it...
>
> > OpenMP is the easiest way of parallelizing any code and require 
> > almost no work. I have myself modified the Runge-Kutta-Felhberg (4,5) 
> > algorithm to take profit of my Core 2 Duo CPU. In the attached file, 
> > I simply added a couple of #pragma that tells the compiler to split 
> > the loop in many threads. If these pragma are not understood, it does 
> > not break the compilation. If they are, you can get a speedup that is 
> > close to the number of CPUs you have in many cases.
>
> What speed-up (in wall time) are you really seeing from these 
> modifications?
> How complex/expensive is your function evaluation?
I've done some tests a long time ago. From what I remember, my function 
was taking 75% of the running time, and the integration with RKF45 was 
taking about 25%. With the OpenMP version of the RKF45 that I attached 
to my first email, I obtained a gain of about 10% in running time with 2 
CPUs. This means that RKF45 was running almost twice as fast with 2 
cpus. I emphasize that this change was _really_ easy to make.
> > I don't know if you guys use unit testing to test GSL, but if you do, 
> > adding OpenMP support could be very easy (since I believe that 
> > whatever change you make to a code must be tested against unit tests).
>
> Greetings,
> Jochen